C. Zwanenburg
info
Please Note
<p>This page displays the records of the person named above and is not linked to a unique person identifier. This record may need to be merged to a profile.</p>
13 records found
1
The Development of Creep in Peat over Time
A Validation of the Isotach Framework
Multiple long-term constant rate of strain (CRS) tests were performed on Zegveld peat from the Netherlands. The aim of performing these tests is to check the validity of the Isotach Framework. Different isotachs can be visualized by changing the applied displacement rate during CRS testing. The trajectories of these isotachs are determined to conclude on both the level of parallelism as well as the mutual distance between different isotachs. The results show a high degree of parallelism. The mutual distance between the different isotachs remains largely unchanged. Transient behaviour is observed around a change in strain rate.
The obtained results show a decent decent of parallelism within the studied strain rat ereegime. The mutual distance between the different isotachs remains largely unchanged within this strain rate regime. However, the results show that the trajectory of the isotachs corresponding to the lowest strain rate seem to diverge from those at higher strain rates. In practice, diverging isotachs result in stress-dependency of creep. Furthermore, it is concluded that the mutual distance between different isotachs increases with a decrease in strain rate. Additional CRS tests underline this observation. This increase in distance with lower strain rates in practice results in non-constant creep behaviour on logarithmic time scale, giving rise to tertiary creep. The observations made are important since field strain rates are shown to be a few orders of magnitude lower than those applied in conventional CRS tests.
The performed CRS tests showed transient behaviour around a change in strain rate. The time needed for the soil to fully adjust to the new strain rate increases with decreasing strain rate. This could give rise to invalid parameter determination since the soil’s state has not yet moved to the isotach corresponding to the new strain rate. The obtained results of the step-changed CRS tests are simulated using the NEN-Bjerrum Isotach model, the abc-isotach model, the Soft Soil Creep model and the MIT Elasto-Viscoplastic model of Yuan and Whittle. Overall, a satisfactory fit is found between the models and the actual CRS test data. The MIT Y&W EVP model and the Soft Soil Creep model are capable of accurately simulating the observed transient behaviour around a change in strain rate.
...
The obtained results show a decent decent of parallelism within the studied strain rat ereegime. The mutual distance between the different isotachs remains largely unchanged within this strain rate regime. However, the results show that the trajectory of the isotachs corresponding to the lowest strain rate seem to diverge from those at higher strain rates. In practice, diverging isotachs result in stress-dependency of creep. Furthermore, it is concluded that the mutual distance between different isotachs increases with a decrease in strain rate. Additional CRS tests underline this observation. This increase in distance with lower strain rates in practice results in non-constant creep behaviour on logarithmic time scale, giving rise to tertiary creep. The observations made are important since field strain rates are shown to be a few orders of magnitude lower than those applied in conventional CRS tests.
The performed CRS tests showed transient behaviour around a change in strain rate. The time needed for the soil to fully adjust to the new strain rate increases with decreasing strain rate. This could give rise to invalid parameter determination since the soil’s state has not yet moved to the isotach corresponding to the new strain rate. The obtained results of the step-changed CRS tests are simulated using the NEN-Bjerrum Isotach model, the abc-isotach model, the Soft Soil Creep model and the MIT Elasto-Viscoplastic model of Yuan and Whittle. Overall, a satisfactory fit is found between the models and the actual CRS test data. The MIT Y&W EVP model and the Soft Soil Creep model are capable of accurately simulating the observed transient behaviour around a change in strain rate.
...
Multiple long-term constant rate of strain (CRS) tests were performed on Zegveld peat from the Netherlands. The aim of performing these tests is to check the validity of the Isotach Framework. Different isotachs can be visualized by changing the applied displacement rate during CRS testing. The trajectories of these isotachs are determined to conclude on both the level of parallelism as well as the mutual distance between different isotachs. The results show a high degree of parallelism. The mutual distance between the different isotachs remains largely unchanged. Transient behaviour is observed around a change in strain rate.
The obtained results show a decent decent of parallelism within the studied strain rat ereegime. The mutual distance between the different isotachs remains largely unchanged within this strain rate regime. However, the results show that the trajectory of the isotachs corresponding to the lowest strain rate seem to diverge from those at higher strain rates. In practice, diverging isotachs result in stress-dependency of creep. Furthermore, it is concluded that the mutual distance between different isotachs increases with a decrease in strain rate. Additional CRS tests underline this observation. This increase in distance with lower strain rates in practice results in non-constant creep behaviour on logarithmic time scale, giving rise to tertiary creep. The observations made are important since field strain rates are shown to be a few orders of magnitude lower than those applied in conventional CRS tests.
The performed CRS tests showed transient behaviour around a change in strain rate. The time needed for the soil to fully adjust to the new strain rate increases with decreasing strain rate. This could give rise to invalid parameter determination since the soil’s state has not yet moved to the isotach corresponding to the new strain rate. The obtained results of the step-changed CRS tests are simulated using the NEN-Bjerrum Isotach model, the abc-isotach model, the Soft Soil Creep model and the MIT Elasto-Viscoplastic model of Yuan and Whittle. Overall, a satisfactory fit is found between the models and the actual CRS test data. The MIT Y&W EVP model and the Soft Soil Creep model are capable of accurately simulating the observed transient behaviour around a change in strain rate.
The obtained results show a decent decent of parallelism within the studied strain rat ereegime. The mutual distance between the different isotachs remains largely unchanged within this strain rate regime. However, the results show that the trajectory of the isotachs corresponding to the lowest strain rate seem to diverge from those at higher strain rates. In practice, diverging isotachs result in stress-dependency of creep. Furthermore, it is concluded that the mutual distance between different isotachs increases with a decrease in strain rate. Additional CRS tests underline this observation. This increase in distance with lower strain rates in practice results in non-constant creep behaviour on logarithmic time scale, giving rise to tertiary creep. The observations made are important since field strain rates are shown to be a few orders of magnitude lower than those applied in conventional CRS tests.
The performed CRS tests showed transient behaviour around a change in strain rate. The time needed for the soil to fully adjust to the new strain rate increases with decreasing strain rate. This could give rise to invalid parameter determination since the soil’s state has not yet moved to the isotach corresponding to the new strain rate. The obtained results of the step-changed CRS tests are simulated using the NEN-Bjerrum Isotach model, the abc-isotach model, the Soft Soil Creep model and the MIT Elasto-Viscoplastic model of Yuan and Whittle. Overall, a satisfactory fit is found between the models and the actual CRS test data. The MIT Y&W EVP model and the Soft Soil Creep model are capable of accurately simulating the observed transient behaviour around a change in strain rate.
Verification of two numerical implementations of small-strain stiffness within the HSsmall model
Assessing their impact on overshooting behaviour to improve the accuracy of deformation predictions in geotechnical analyses
Master thesis
(2025)
-
E.R. Eman, R.B.J. Brinkgreve, E. Kementzetzidis, C. Zwanenburg, R. Azeiteiro, I. del Brocco
The current Hardening Soil small-strain (HSsmall) model, developed by Benz (2007), is capable of capturing the behaviour of a wide range of soil types, including their small-strain response. However, under specific conditions, the model exhibits overshooting, which is the overestimation of the material’s elastic stiffness upon the closure of a small unloading-reloading (UL-RL) cycle interrupting monotonic loading, rather than recovering the stiffness corresponding to the onset of the cycle, as observed in real soil behaviour. Overshooting leads to underestimated deformations and consequently non-conservative results.
To address this issue, PLAXIS (part of Seequent, the Bentley Subsurface company) proposed two formulations: the Continuous Brick (CB) formulation, which replaces the small-strain component of the HSsmall model, and a Memory-Surface-Based (MSB) formulation, which extends it. Both have been implemented in the source code of the existing HSsmall constitutive model. However, their implementations had not yet been verified in the literature, nor had an assessment of overshooting, the motivation behind their development, been conducted.
This research aims to close that gap and to determine which of the two formulations provides the most suitable approach. Implementing the best-performing formulation into the HSsmall model results in a new more robust state-of-the-art model.
Accordingly, the following research question is posed:
‘To what extent do the Continuous Brick formulation, as a new formulation for small-strain stiffness, and the Memory-Surface-based formulation, as an extension to the existing small-strain stiffness formulation within the Hardening Soil small-strain model, reduce the overshooting observed in the current formulation?’
This question is addressed through a structured test plan consisting of two main components: (i) single stress point simulations to verify whether the formulations behave as expected at the most fundamental level, and (ii) a boundary value problem to evaluate their performance under more numerically demanding conditions representative of practical applications in the pre-failure range, where small strain stiffness strongly influences the magnitude of deformations.
It was found that both formulations reduce overshooting to a negligible level. However, their effectiveness decreases in simulations involving nested cycles, as both formulations exhibit the limitation of retaining the memory of only a single UL-RL cycle. Although both formulations perform well, the MSB formulation proves to be the most suitable approach: it is easier to interpret, appears more robust, retains the small-strain component of the original HSsmall model, and yields a response consistent with the HSsmall model under monotonic loading.
Extending the HSsmall model with the MSB formulation leads to more accurate deformation estimations in geotechnical problems especially within the pre-failure range, as deformations will no longer be underestimated, without introducing additional model parameters. Moreover, adopting this formulation will not have major consequences for the end user, since its behaviour is consistent with that of the HSsmall model, except that overshooting no longer occurs.
...
To address this issue, PLAXIS (part of Seequent, the Bentley Subsurface company) proposed two formulations: the Continuous Brick (CB) formulation, which replaces the small-strain component of the HSsmall model, and a Memory-Surface-Based (MSB) formulation, which extends it. Both have been implemented in the source code of the existing HSsmall constitutive model. However, their implementations had not yet been verified in the literature, nor had an assessment of overshooting, the motivation behind their development, been conducted.
This research aims to close that gap and to determine which of the two formulations provides the most suitable approach. Implementing the best-performing formulation into the HSsmall model results in a new more robust state-of-the-art model.
Accordingly, the following research question is posed:
‘To what extent do the Continuous Brick formulation, as a new formulation for small-strain stiffness, and the Memory-Surface-based formulation, as an extension to the existing small-strain stiffness formulation within the Hardening Soil small-strain model, reduce the overshooting observed in the current formulation?’
This question is addressed through a structured test plan consisting of two main components: (i) single stress point simulations to verify whether the formulations behave as expected at the most fundamental level, and (ii) a boundary value problem to evaluate their performance under more numerically demanding conditions representative of practical applications in the pre-failure range, where small strain stiffness strongly influences the magnitude of deformations.
It was found that both formulations reduce overshooting to a negligible level. However, their effectiveness decreases in simulations involving nested cycles, as both formulations exhibit the limitation of retaining the memory of only a single UL-RL cycle. Although both formulations perform well, the MSB formulation proves to be the most suitable approach: it is easier to interpret, appears more robust, retains the small-strain component of the original HSsmall model, and yields a response consistent with the HSsmall model under monotonic loading.
Extending the HSsmall model with the MSB formulation leads to more accurate deformation estimations in geotechnical problems especially within the pre-failure range, as deformations will no longer be underestimated, without introducing additional model parameters. Moreover, adopting this formulation will not have major consequences for the end user, since its behaviour is consistent with that of the HSsmall model, except that overshooting no longer occurs.
...
The current Hardening Soil small-strain (HSsmall) model, developed by Benz (2007), is capable of capturing the behaviour of a wide range of soil types, including their small-strain response. However, under specific conditions, the model exhibits overshooting, which is the overestimation of the material’s elastic stiffness upon the closure of a small unloading-reloading (UL-RL) cycle interrupting monotonic loading, rather than recovering the stiffness corresponding to the onset of the cycle, as observed in real soil behaviour. Overshooting leads to underestimated deformations and consequently non-conservative results.
To address this issue, PLAXIS (part of Seequent, the Bentley Subsurface company) proposed two formulations: the Continuous Brick (CB) formulation, which replaces the small-strain component of the HSsmall model, and a Memory-Surface-Based (MSB) formulation, which extends it. Both have been implemented in the source code of the existing HSsmall constitutive model. However, their implementations had not yet been verified in the literature, nor had an assessment of overshooting, the motivation behind their development, been conducted.
This research aims to close that gap and to determine which of the two formulations provides the most suitable approach. Implementing the best-performing formulation into the HSsmall model results in a new more robust state-of-the-art model.
Accordingly, the following research question is posed:
‘To what extent do the Continuous Brick formulation, as a new formulation for small-strain stiffness, and the Memory-Surface-based formulation, as an extension to the existing small-strain stiffness formulation within the Hardening Soil small-strain model, reduce the overshooting observed in the current formulation?’
This question is addressed through a structured test plan consisting of two main components: (i) single stress point simulations to verify whether the formulations behave as expected at the most fundamental level, and (ii) a boundary value problem to evaluate their performance under more numerically demanding conditions representative of practical applications in the pre-failure range, where small strain stiffness strongly influences the magnitude of deformations.
It was found that both formulations reduce overshooting to a negligible level. However, their effectiveness decreases in simulations involving nested cycles, as both formulations exhibit the limitation of retaining the memory of only a single UL-RL cycle. Although both formulations perform well, the MSB formulation proves to be the most suitable approach: it is easier to interpret, appears more robust, retains the small-strain component of the original HSsmall model, and yields a response consistent with the HSsmall model under monotonic loading.
Extending the HSsmall model with the MSB formulation leads to more accurate deformation estimations in geotechnical problems especially within the pre-failure range, as deformations will no longer be underestimated, without introducing additional model parameters. Moreover, adopting this formulation will not have major consequences for the end user, since its behaviour is consistent with that of the HSsmall model, except that overshooting no longer occurs.
To address this issue, PLAXIS (part of Seequent, the Bentley Subsurface company) proposed two formulations: the Continuous Brick (CB) formulation, which replaces the small-strain component of the HSsmall model, and a Memory-Surface-Based (MSB) formulation, which extends it. Both have been implemented in the source code of the existing HSsmall constitutive model. However, their implementations had not yet been verified in the literature, nor had an assessment of overshooting, the motivation behind their development, been conducted.
This research aims to close that gap and to determine which of the two formulations provides the most suitable approach. Implementing the best-performing formulation into the HSsmall model results in a new more robust state-of-the-art model.
Accordingly, the following research question is posed:
‘To what extent do the Continuous Brick formulation, as a new formulation for small-strain stiffness, and the Memory-Surface-based formulation, as an extension to the existing small-strain stiffness formulation within the Hardening Soil small-strain model, reduce the overshooting observed in the current formulation?’
This question is addressed through a structured test plan consisting of two main components: (i) single stress point simulations to verify whether the formulations behave as expected at the most fundamental level, and (ii) a boundary value problem to evaluate their performance under more numerically demanding conditions representative of practical applications in the pre-failure range, where small strain stiffness strongly influences the magnitude of deformations.
It was found that both formulations reduce overshooting to a negligible level. However, their effectiveness decreases in simulations involving nested cycles, as both formulations exhibit the limitation of retaining the memory of only a single UL-RL cycle. Although both formulations perform well, the MSB formulation proves to be the most suitable approach: it is easier to interpret, appears more robust, retains the small-strain component of the original HSsmall model, and yields a response consistent with the HSsmall model under monotonic loading.
Extending the HSsmall model with the MSB formulation leads to more accurate deformation estimations in geotechnical problems especially within the pre-failure range, as deformations will no longer be underestimated, without introducing additional model parameters. Moreover, adopting this formulation will not have major consequences for the end user, since its behaviour is consistent with that of the HSsmall model, except that overshooting no longer occurs.
Strength development of soft soils
Prediction and verification of undrained shear strength for loaded soft soils
The study delves into the crucial role of undrained shear strength in the stability of civil engineering projects involving soft soils. It explores the enhancement of this strength through (pre)loading in conjunction with Prefabricated Vertical Drains (PVDs). The Stress History and Normalized Soil Engineering Properties (SHANSEP) framework is employed to forecast changes in strength across various phases - before, during, and after loading. Validation is conducted using Cone Penetration Tests with pore pressure measurements (CPTu), and the Nkt strength factor is employed to correlate CPTu data with undrained shear strength.
The research combines laboratory experiments and field data to predict undrained shear strength via SHANSEP, which is subsequently validated through CPTu measurements and monitoring. Two distinct datasets are examined in the study. The first dataset involves dike projects at 'de Markermeerdijken' in the Netherlands, where PVD-assisted surcharges of 5 meters are implemented. SHANSEP is utilized to predict strength levels before surcharge, post-surcharge removal (after >90% consolidation), and post-removal phases. These predictions are cross-validated using CPTu data and laboratory tests. The second dataset focuses on a reclamation project involving Marine Soft Clay strength in the Philippines. Strength correlations with CPTu tests during consolidation are established, and comparisons are made with data from piezometers and SHANSEP predictions.
The analysis uncovers that SHANSEP's precision is contingent on several factors:
1. The uncertainty surrounding Pre Overburden pressure (POP), leading to inaccuracies in initial strength predictions.
2. The effectiveness of preloading being compromised by limited load area relative to depth.
3. Submergence of the surcharge beneath the phreatic surface, resulting in diminished preload and gained strength.
4. Incorporating creep into predictions necessitates a reduction in SHANSEP's S factor.
5. Accurate predictions rely on high-quality laboratory tests.
SHANSEP demonstrates its ability to effectively forecast undrained shear strength in soft soils, with its predicted surcharge strength increments aligning with CPTu values. However, challenges are identified in predicting and verifying strength during consolidation due to the dominating influence of excess pore pressure.
The study's key findings recommend the inclusion of adjustments for preload submersion, consideration of load distribution, and the evaluation of partially drained CPTu data using parameters such as Bq and qt to enhance the verification of SHANSEP-predicted strengths. The study emphasizes caution against relying solely on CPTu or piezometer data for ensuring reliability and accuracy. ...
The research combines laboratory experiments and field data to predict undrained shear strength via SHANSEP, which is subsequently validated through CPTu measurements and monitoring. Two distinct datasets are examined in the study. The first dataset involves dike projects at 'de Markermeerdijken' in the Netherlands, where PVD-assisted surcharges of 5 meters are implemented. SHANSEP is utilized to predict strength levels before surcharge, post-surcharge removal (after >90% consolidation), and post-removal phases. These predictions are cross-validated using CPTu data and laboratory tests. The second dataset focuses on a reclamation project involving Marine Soft Clay strength in the Philippines. Strength correlations with CPTu tests during consolidation are established, and comparisons are made with data from piezometers and SHANSEP predictions.
The analysis uncovers that SHANSEP's precision is contingent on several factors:
1. The uncertainty surrounding Pre Overburden pressure (POP), leading to inaccuracies in initial strength predictions.
2. The effectiveness of preloading being compromised by limited load area relative to depth.
3. Submergence of the surcharge beneath the phreatic surface, resulting in diminished preload and gained strength.
4. Incorporating creep into predictions necessitates a reduction in SHANSEP's S factor.
5. Accurate predictions rely on high-quality laboratory tests.
SHANSEP demonstrates its ability to effectively forecast undrained shear strength in soft soils, with its predicted surcharge strength increments aligning with CPTu values. However, challenges are identified in predicting and verifying strength during consolidation due to the dominating influence of excess pore pressure.
The study's key findings recommend the inclusion of adjustments for preload submersion, consideration of load distribution, and the evaluation of partially drained CPTu data using parameters such as Bq and qt to enhance the verification of SHANSEP-predicted strengths. The study emphasizes caution against relying solely on CPTu or piezometer data for ensuring reliability and accuracy. ...
The study delves into the crucial role of undrained shear strength in the stability of civil engineering projects involving soft soils. It explores the enhancement of this strength through (pre)loading in conjunction with Prefabricated Vertical Drains (PVDs). The Stress History and Normalized Soil Engineering Properties (SHANSEP) framework is employed to forecast changes in strength across various phases - before, during, and after loading. Validation is conducted using Cone Penetration Tests with pore pressure measurements (CPTu), and the Nkt strength factor is employed to correlate CPTu data with undrained shear strength.
The research combines laboratory experiments and field data to predict undrained shear strength via SHANSEP, which is subsequently validated through CPTu measurements and monitoring. Two distinct datasets are examined in the study. The first dataset involves dike projects at 'de Markermeerdijken' in the Netherlands, where PVD-assisted surcharges of 5 meters are implemented. SHANSEP is utilized to predict strength levels before surcharge, post-surcharge removal (after >90% consolidation), and post-removal phases. These predictions are cross-validated using CPTu data and laboratory tests. The second dataset focuses on a reclamation project involving Marine Soft Clay strength in the Philippines. Strength correlations with CPTu tests during consolidation are established, and comparisons are made with data from piezometers and SHANSEP predictions.
The analysis uncovers that SHANSEP's precision is contingent on several factors:
1. The uncertainty surrounding Pre Overburden pressure (POP), leading to inaccuracies in initial strength predictions.
2. The effectiveness of preloading being compromised by limited load area relative to depth.
3. Submergence of the surcharge beneath the phreatic surface, resulting in diminished preload and gained strength.
4. Incorporating creep into predictions necessitates a reduction in SHANSEP's S factor.
5. Accurate predictions rely on high-quality laboratory tests.
SHANSEP demonstrates its ability to effectively forecast undrained shear strength in soft soils, with its predicted surcharge strength increments aligning with CPTu values. However, challenges are identified in predicting and verifying strength during consolidation due to the dominating influence of excess pore pressure.
The study's key findings recommend the inclusion of adjustments for preload submersion, consideration of load distribution, and the evaluation of partially drained CPTu data using parameters such as Bq and qt to enhance the verification of SHANSEP-predicted strengths. The study emphasizes caution against relying solely on CPTu or piezometer data for ensuring reliability and accuracy.
The research combines laboratory experiments and field data to predict undrained shear strength via SHANSEP, which is subsequently validated through CPTu measurements and monitoring. Two distinct datasets are examined in the study. The first dataset involves dike projects at 'de Markermeerdijken' in the Netherlands, where PVD-assisted surcharges of 5 meters are implemented. SHANSEP is utilized to predict strength levels before surcharge, post-surcharge removal (after >90% consolidation), and post-removal phases. These predictions are cross-validated using CPTu data and laboratory tests. The second dataset focuses on a reclamation project involving Marine Soft Clay strength in the Philippines. Strength correlations with CPTu tests during consolidation are established, and comparisons are made with data from piezometers and SHANSEP predictions.
The analysis uncovers that SHANSEP's precision is contingent on several factors:
1. The uncertainty surrounding Pre Overburden pressure (POP), leading to inaccuracies in initial strength predictions.
2. The effectiveness of preloading being compromised by limited load area relative to depth.
3. Submergence of the surcharge beneath the phreatic surface, resulting in diminished preload and gained strength.
4. Incorporating creep into predictions necessitates a reduction in SHANSEP's S factor.
5. Accurate predictions rely on high-quality laboratory tests.
SHANSEP demonstrates its ability to effectively forecast undrained shear strength in soft soils, with its predicted surcharge strength increments aligning with CPTu values. However, challenges are identified in predicting and verifying strength during consolidation due to the dominating influence of excess pore pressure.
The study's key findings recommend the inclusion of adjustments for preload submersion, consideration of load distribution, and the evaluation of partially drained CPTu data using parameters such as Bq and qt to enhance the verification of SHANSEP-predicted strengths. The study emphasizes caution against relying solely on CPTu or piezometer data for ensuring reliability and accuracy.
Stability assessment for dikes and dike reinforcement requires insight in soil strength behaviour. The required parameters for this assessment are typically obtained from conventional laboratory tests. These conventional tests are not performed under conditions found in the field. For example, a dike section resembles to plane strain conditions. Limited research is available for laboratory test under plane strain conditions, especially for organic clays. The plane strain biaxial apparatus presented by Allersma (1993) is used to perform tests on organic clay. The apparatus has not been used for several decades and it is described how the machine is refurbished. Preliminary tests and further improvements lead to familiarization with the apparatus. After this stage, laboratory tests on organic clay are performed and presented. The soil sample is loaded, leading to stress and pore pressure measurement. The measurements from laboratory tests are presented in chronological order. Several test set ups, most notably varying in their method to control the drainage conditions and to measure the pore pressure, are used. Assessment of the standard of these results in terms of accuracy, reliability and reproductivity is given. A notable challenge arising in the tests, is the uncontrolled drainage boundaries at the boundary between soil sample and soil sample enclosure: the biaxial cell. Conclusions are drawn from individual tests and consequentially improvements are made on the test set up. The test is re-created and numerically analysed in finite element programmes PLAXIS2D and PLAXIS3D. The numerical analysis and laboratory are compared and help to understand and predict the stress conditions found during tests in the laboratory. Remaining challenges are discussed on technical specifications and laboratory test set up. Concluded is that tests with this biaxial apparatus do not lead to results of a sufficiently high standard for further soil testing.
...
Stability assessment for dikes and dike reinforcement requires insight in soil strength behaviour. The required parameters for this assessment are typically obtained from conventional laboratory tests. These conventional tests are not performed under conditions found in the field. For example, a dike section resembles to plane strain conditions. Limited research is available for laboratory test under plane strain conditions, especially for organic clays. The plane strain biaxial apparatus presented by Allersma (1993) is used to perform tests on organic clay. The apparatus has not been used for several decades and it is described how the machine is refurbished. Preliminary tests and further improvements lead to familiarization with the apparatus. After this stage, laboratory tests on organic clay are performed and presented. The soil sample is loaded, leading to stress and pore pressure measurement. The measurements from laboratory tests are presented in chronological order. Several test set ups, most notably varying in their method to control the drainage conditions and to measure the pore pressure, are used. Assessment of the standard of these results in terms of accuracy, reliability and reproductivity is given. A notable challenge arising in the tests, is the uncontrolled drainage boundaries at the boundary between soil sample and soil sample enclosure: the biaxial cell. Conclusions are drawn from individual tests and consequentially improvements are made on the test set up. The test is re-created and numerically analysed in finite element programmes PLAXIS2D and PLAXIS3D. The numerical analysis and laboratory are compared and help to understand and predict the stress conditions found during tests in the laboratory. Remaining challenges are discussed on technical specifications and laboratory test set up. Concluded is that tests with this biaxial apparatus do not lead to results of a sufficiently high standard for further soil testing.
Master thesis
(2023)
-
T.J.J. Krielaart, C. Zwanenburg, R.B.J. Brinkgreve, W. van den Bos, S.H. Alkema
Crane hardstands serve as crucial platforms for supporting heavy lifting equipment and ensuring operational efficiency. However, crane hardstands are not infinitely stiff and will deform upon loading. Uneven loading during wind turbine installation will result in differential deformation of the crane hardstand, causing the crane to tilt. A small tilt of 0.3°, which is equivalent to around 30-60mm differential settlement depending on the crane, will create safety hazards, causing construction to be discontinued. As a result accurate deformation predictions are required to design a sufficient crane hardstand.
This research is conducted to investigate the influence factors of the deformation of a crane hardstand, evaluate the current prediction method and to improve the accuracy of future deformation predictions, so the hardstands can be designed more efficiently.
The research begins with a literature study on the above surface influences on the magnitude of the load and the corresponding soil behaviour of the soil profile beneath the hardstand. Furthermore the current prediction method is analyzed to dictate shortcomings. The expected influences found in the literature study are examined with full scale monitoring and testing cases. Finally, a sensitivity analysis is performed on the current prediction model to specify the parameters with the biggest influence on deformation for different variants. These parameters are then assessed on how a more accurate determination might influence the predicted deformations.
The numerical simulations are carried out using advanced finite element analysis software Plaxis, specifically the HS(small strain) model. This model enables the investigation of various factors affecting hardstand deformation, such as varying soil stiffness, load distribution, and foundation characteristics.
The biggest shortcoming of the current prediction method is found to be the exclusion of time dependent behavior. And the most influential soil parameters of the HS(small strain) model after the addition of a consolidation phase to the model are found to be the stiffness and permeability parameters. The deformation prediction is done for the entire range of uncertainty of these parameters (5-, 25-, 50-, 75-, 95- percentiles) to quantify prediction accuracy improvements were these parameters determined witch precise. For both peat and clean clay the permeability coefficient is found to, when determined more accurately, have a 50% chance to result in a predicted deformation reduction of between 40 to 60 %, while a more accurate prediction of the stiffness parameters Eoed E50 Eur has a 50% chance to result in a predicted deformation reduction of between 65 to 75%
The findings of the research can be used by engineers to test the effectiveness of their own hardstand deformation prediction method and provide advise on the benefits extra soil investigation might lead to.
Keywords: Crane hardstands, deformation analysis, differential settlement, cyclic loading, Hardening soil small strain, FEM-modeling, sensitivity analyses. ...
This research is conducted to investigate the influence factors of the deformation of a crane hardstand, evaluate the current prediction method and to improve the accuracy of future deformation predictions, so the hardstands can be designed more efficiently.
The research begins with a literature study on the above surface influences on the magnitude of the load and the corresponding soil behaviour of the soil profile beneath the hardstand. Furthermore the current prediction method is analyzed to dictate shortcomings. The expected influences found in the literature study are examined with full scale monitoring and testing cases. Finally, a sensitivity analysis is performed on the current prediction model to specify the parameters with the biggest influence on deformation for different variants. These parameters are then assessed on how a more accurate determination might influence the predicted deformations.
The numerical simulations are carried out using advanced finite element analysis software Plaxis, specifically the HS(small strain) model. This model enables the investigation of various factors affecting hardstand deformation, such as varying soil stiffness, load distribution, and foundation characteristics.
The biggest shortcoming of the current prediction method is found to be the exclusion of time dependent behavior. And the most influential soil parameters of the HS(small strain) model after the addition of a consolidation phase to the model are found to be the stiffness and permeability parameters. The deformation prediction is done for the entire range of uncertainty of these parameters (5-, 25-, 50-, 75-, 95- percentiles) to quantify prediction accuracy improvements were these parameters determined witch precise. For both peat and clean clay the permeability coefficient is found to, when determined more accurately, have a 50% chance to result in a predicted deformation reduction of between 40 to 60 %, while a more accurate prediction of the stiffness parameters Eoed E50 Eur has a 50% chance to result in a predicted deformation reduction of between 65 to 75%
The findings of the research can be used by engineers to test the effectiveness of their own hardstand deformation prediction method and provide advise on the benefits extra soil investigation might lead to.
Keywords: Crane hardstands, deformation analysis, differential settlement, cyclic loading, Hardening soil small strain, FEM-modeling, sensitivity analyses. ...
Crane hardstands serve as crucial platforms for supporting heavy lifting equipment and ensuring operational efficiency. However, crane hardstands are not infinitely stiff and will deform upon loading. Uneven loading during wind turbine installation will result in differential deformation of the crane hardstand, causing the crane to tilt. A small tilt of 0.3°, which is equivalent to around 30-60mm differential settlement depending on the crane, will create safety hazards, causing construction to be discontinued. As a result accurate deformation predictions are required to design a sufficient crane hardstand.
This research is conducted to investigate the influence factors of the deformation of a crane hardstand, evaluate the current prediction method and to improve the accuracy of future deformation predictions, so the hardstands can be designed more efficiently.
The research begins with a literature study on the above surface influences on the magnitude of the load and the corresponding soil behaviour of the soil profile beneath the hardstand. Furthermore the current prediction method is analyzed to dictate shortcomings. The expected influences found in the literature study are examined with full scale monitoring and testing cases. Finally, a sensitivity analysis is performed on the current prediction model to specify the parameters with the biggest influence on deformation for different variants. These parameters are then assessed on how a more accurate determination might influence the predicted deformations.
The numerical simulations are carried out using advanced finite element analysis software Plaxis, specifically the HS(small strain) model. This model enables the investigation of various factors affecting hardstand deformation, such as varying soil stiffness, load distribution, and foundation characteristics.
The biggest shortcoming of the current prediction method is found to be the exclusion of time dependent behavior. And the most influential soil parameters of the HS(small strain) model after the addition of a consolidation phase to the model are found to be the stiffness and permeability parameters. The deformation prediction is done for the entire range of uncertainty of these parameters (5-, 25-, 50-, 75-, 95- percentiles) to quantify prediction accuracy improvements were these parameters determined witch precise. For both peat and clean clay the permeability coefficient is found to, when determined more accurately, have a 50% chance to result in a predicted deformation reduction of between 40 to 60 %, while a more accurate prediction of the stiffness parameters Eoed E50 Eur has a 50% chance to result in a predicted deformation reduction of between 65 to 75%
The findings of the research can be used by engineers to test the effectiveness of their own hardstand deformation prediction method and provide advise on the benefits extra soil investigation might lead to.
Keywords: Crane hardstands, deformation analysis, differential settlement, cyclic loading, Hardening soil small strain, FEM-modeling, sensitivity analyses.
This research is conducted to investigate the influence factors of the deformation of a crane hardstand, evaluate the current prediction method and to improve the accuracy of future deformation predictions, so the hardstands can be designed more efficiently.
The research begins with a literature study on the above surface influences on the magnitude of the load and the corresponding soil behaviour of the soil profile beneath the hardstand. Furthermore the current prediction method is analyzed to dictate shortcomings. The expected influences found in the literature study are examined with full scale monitoring and testing cases. Finally, a sensitivity analysis is performed on the current prediction model to specify the parameters with the biggest influence on deformation for different variants. These parameters are then assessed on how a more accurate determination might influence the predicted deformations.
The numerical simulations are carried out using advanced finite element analysis software Plaxis, specifically the HS(small strain) model. This model enables the investigation of various factors affecting hardstand deformation, such as varying soil stiffness, load distribution, and foundation characteristics.
The biggest shortcoming of the current prediction method is found to be the exclusion of time dependent behavior. And the most influential soil parameters of the HS(small strain) model after the addition of a consolidation phase to the model are found to be the stiffness and permeability parameters. The deformation prediction is done for the entire range of uncertainty of these parameters (5-, 25-, 50-, 75-, 95- percentiles) to quantify prediction accuracy improvements were these parameters determined witch precise. For both peat and clean clay the permeability coefficient is found to, when determined more accurately, have a 50% chance to result in a predicted deformation reduction of between 40 to 60 %, while a more accurate prediction of the stiffness parameters Eoed E50 Eur has a 50% chance to result in a predicted deformation reduction of between 65 to 75%
The findings of the research can be used by engineers to test the effectiveness of their own hardstand deformation prediction method and provide advise on the benefits extra soil investigation might lead to.
Keywords: Crane hardstands, deformation analysis, differential settlement, cyclic loading, Hardening soil small strain, FEM-modeling, sensitivity analyses.
Long-term settlement is unavoidable but by good prediction accompanied risks can be reduced. Nowadays linear isotach models belong to the state of the art but result in very small strain rates when small load increments or unloading is applied. For that reason this study has focused on the validation of those predictions using InSAR. Different causes of settlement have been studied and it was found that fluctuations in groundwater do not affect the final settlement. Another influencing factor is the presence of organic matter and its degradation. This reduction of organic matter is caused by many factors and is yet too complicated to quantify and include in predicting models. In spite of the idea that predicted strain rates by linear isotach models are too small, InSAR results show that the measured displacement rates were actually smaller than predicted some years after construction for road segments of the A2 and that a new proposed model could be used to match these displacement rates better. The C+S model by Vergote et al. (2021) is an isotach model which uses non-linear isotachs which would reduce the strain rates faster than linear isotach models and viscoplastic swell is included which also reduces the total strain rate. Results on incremental loading tests show that this model captures the behaviour in unloading stages better than the linear isotach models but for conventional incremental loading tests the two models do not differ much. For field scale embankment scenarios the results show that the C+S model with non-linear isotachs and viscoplastic swell included will predict a longer swell period with more swell, lower total strain rates after the swell period with a faster decay and in the and less residual settlement.
...
Long-term settlement is unavoidable but by good prediction accompanied risks can be reduced. Nowadays linear isotach models belong to the state of the art but result in very small strain rates when small load increments or unloading is applied. For that reason this study has focused on the validation of those predictions using InSAR. Different causes of settlement have been studied and it was found that fluctuations in groundwater do not affect the final settlement. Another influencing factor is the presence of organic matter and its degradation. This reduction of organic matter is caused by many factors and is yet too complicated to quantify and include in predicting models. In spite of the idea that predicted strain rates by linear isotach models are too small, InSAR results show that the measured displacement rates were actually smaller than predicted some years after construction for road segments of the A2 and that a new proposed model could be used to match these displacement rates better. The C+S model by Vergote et al. (2021) is an isotach model which uses non-linear isotachs which would reduce the strain rates faster than linear isotach models and viscoplastic swell is included which also reduces the total strain rate. Results on incremental loading tests show that this model captures the behaviour in unloading stages better than the linear isotach models but for conventional incremental loading tests the two models do not differ much. For field scale embankment scenarios the results show that the C+S model with non-linear isotachs and viscoplastic swell included will predict a longer swell period with more swell, lower total strain rates after the swell period with a faster decay and in the and less residual settlement.
New solutions for future flooding problems are becoming more important than ever before. Emergency measures against failure of flood defenses may play an important role in flood risk management and is therefore currently being investigated. One of these measures is the BresDefender, which is a submersible floating pontoon that can be placed on the outer slope of a weakened dike section to prevent or delay failure. The application of the BresDefender can be divided into two scenarios: (1) to stop breach formation and (2) to limit water infiltration into the dike. The latter application scenario is expected to influence the development of the phreatic surface inside the dike, which affects dike safety. This study focuses on this scenario by assessing the effect of this seal on the development of the phreatic surface.
A numerical modelling approach is developed to describe this effect using the finite element method program PLAXIS, with add-on module PlaxFlow, to describe transient groundwater flow problems. This numerical modelling process starts off with the development of a model for a laboratory scale dike. In a previous study at the WaterLab, the phreatic surface level of the dike was measured over time for different degrees of sealing using a steel plate. These measurements are used to calibrate the numerical model, where the connection between seal and dike slope is described with a transmissive interface layer. It is concluded that this interface layer approximates the effect of the seal on the phreatic surface adequately.
The next step is to extent the numerical model to a larger scale dike consisting of heterogeneous soils. This model represents the dike located in the Flood Proof Holland test facility, which consists of a permeable core covered by a low-permeability layer. By modelling this transition from simple to complex, influences of permeability, heterogeneity, and damage of the cover on the phreatic surface are identified.
The effect of a seal on the phreatic surface is also studied using physical model tests of the dike at Flood Proof Holland. The position of the phreatic surface is measured by pressure sensors in standpipes, which are spread over the crest and inner slope of the dike. Different scenarios for the seal are examined: stiff plate, flexible textile, and no emergency measure (reference case). For every scenario, experiments are carried out with and without a damaged location in the outer slope of the dike, which lead to a total of six test cases.
The results of the physical model tests show multiple effects of the seal on the phreatic surface. First, the seal shows a delaying effect on the position of the phreatic surface, which implies that the seal delays the rise of the phreatic surface over time. The time until the phreatic surface reached a steady-state over the entire dike was increased with around 15% for plate cases and around 25% for textile cases when compared to the corresponding reference cases. Second, no decreasing effect on the phreatic surface can be observed, which means that the phreatic surface level in its steady-state condition is not affected by the placement of a seal on the outer slope. Third, the delaying effect is larger for a seal that consists of a flexible textile rather than a stiff plate. The connection between seal and dike cover is proved to be important since leakages underneath the seal influence its performance, especially when the dike is locally damaged.
Last, the textile seal has a three-dimensional effect on the development of the phreatic surface. A certain area of influence can be identified where the phreatic surface is affected. The effect of the phreatic surface is seen to be stronger for locations near the textile and this effect diminishes over time. For the textile case on a damaged dike, an initial decrease of the phreatic level is observed directly behind the textile ranging up to 30 cm.
Overall, the effect of a seal on the development of the phreatic surface is concluded to be relatively small. The effect is only of a time-varying nature and, in three dimensions, the effect diminishes for larger distances. The application of a textile in terms of dike safety shows only a marginal improvement, which occurs only in a limited time period. ...
A numerical modelling approach is developed to describe this effect using the finite element method program PLAXIS, with add-on module PlaxFlow, to describe transient groundwater flow problems. This numerical modelling process starts off with the development of a model for a laboratory scale dike. In a previous study at the WaterLab, the phreatic surface level of the dike was measured over time for different degrees of sealing using a steel plate. These measurements are used to calibrate the numerical model, where the connection between seal and dike slope is described with a transmissive interface layer. It is concluded that this interface layer approximates the effect of the seal on the phreatic surface adequately.
The next step is to extent the numerical model to a larger scale dike consisting of heterogeneous soils. This model represents the dike located in the Flood Proof Holland test facility, which consists of a permeable core covered by a low-permeability layer. By modelling this transition from simple to complex, influences of permeability, heterogeneity, and damage of the cover on the phreatic surface are identified.
The effect of a seal on the phreatic surface is also studied using physical model tests of the dike at Flood Proof Holland. The position of the phreatic surface is measured by pressure sensors in standpipes, which are spread over the crest and inner slope of the dike. Different scenarios for the seal are examined: stiff plate, flexible textile, and no emergency measure (reference case). For every scenario, experiments are carried out with and without a damaged location in the outer slope of the dike, which lead to a total of six test cases.
The results of the physical model tests show multiple effects of the seal on the phreatic surface. First, the seal shows a delaying effect on the position of the phreatic surface, which implies that the seal delays the rise of the phreatic surface over time. The time until the phreatic surface reached a steady-state over the entire dike was increased with around 15% for plate cases and around 25% for textile cases when compared to the corresponding reference cases. Second, no decreasing effect on the phreatic surface can be observed, which means that the phreatic surface level in its steady-state condition is not affected by the placement of a seal on the outer slope. Third, the delaying effect is larger for a seal that consists of a flexible textile rather than a stiff plate. The connection between seal and dike cover is proved to be important since leakages underneath the seal influence its performance, especially when the dike is locally damaged.
Last, the textile seal has a three-dimensional effect on the development of the phreatic surface. A certain area of influence can be identified where the phreatic surface is affected. The effect of the phreatic surface is seen to be stronger for locations near the textile and this effect diminishes over time. For the textile case on a damaged dike, an initial decrease of the phreatic level is observed directly behind the textile ranging up to 30 cm.
Overall, the effect of a seal on the development of the phreatic surface is concluded to be relatively small. The effect is only of a time-varying nature and, in three dimensions, the effect diminishes for larger distances. The application of a textile in terms of dike safety shows only a marginal improvement, which occurs only in a limited time period. ...
New solutions for future flooding problems are becoming more important than ever before. Emergency measures against failure of flood defenses may play an important role in flood risk management and is therefore currently being investigated. One of these measures is the BresDefender, which is a submersible floating pontoon that can be placed on the outer slope of a weakened dike section to prevent or delay failure. The application of the BresDefender can be divided into two scenarios: (1) to stop breach formation and (2) to limit water infiltration into the dike. The latter application scenario is expected to influence the development of the phreatic surface inside the dike, which affects dike safety. This study focuses on this scenario by assessing the effect of this seal on the development of the phreatic surface.
A numerical modelling approach is developed to describe this effect using the finite element method program PLAXIS, with add-on module PlaxFlow, to describe transient groundwater flow problems. This numerical modelling process starts off with the development of a model for a laboratory scale dike. In a previous study at the WaterLab, the phreatic surface level of the dike was measured over time for different degrees of sealing using a steel plate. These measurements are used to calibrate the numerical model, where the connection between seal and dike slope is described with a transmissive interface layer. It is concluded that this interface layer approximates the effect of the seal on the phreatic surface adequately.
The next step is to extent the numerical model to a larger scale dike consisting of heterogeneous soils. This model represents the dike located in the Flood Proof Holland test facility, which consists of a permeable core covered by a low-permeability layer. By modelling this transition from simple to complex, influences of permeability, heterogeneity, and damage of the cover on the phreatic surface are identified.
The effect of a seal on the phreatic surface is also studied using physical model tests of the dike at Flood Proof Holland. The position of the phreatic surface is measured by pressure sensors in standpipes, which are spread over the crest and inner slope of the dike. Different scenarios for the seal are examined: stiff plate, flexible textile, and no emergency measure (reference case). For every scenario, experiments are carried out with and without a damaged location in the outer slope of the dike, which lead to a total of six test cases.
The results of the physical model tests show multiple effects of the seal on the phreatic surface. First, the seal shows a delaying effect on the position of the phreatic surface, which implies that the seal delays the rise of the phreatic surface over time. The time until the phreatic surface reached a steady-state over the entire dike was increased with around 15% for plate cases and around 25% for textile cases when compared to the corresponding reference cases. Second, no decreasing effect on the phreatic surface can be observed, which means that the phreatic surface level in its steady-state condition is not affected by the placement of a seal on the outer slope. Third, the delaying effect is larger for a seal that consists of a flexible textile rather than a stiff plate. The connection between seal and dike cover is proved to be important since leakages underneath the seal influence its performance, especially when the dike is locally damaged.
Last, the textile seal has a three-dimensional effect on the development of the phreatic surface. A certain area of influence can be identified where the phreatic surface is affected. The effect of the phreatic surface is seen to be stronger for locations near the textile and this effect diminishes over time. For the textile case on a damaged dike, an initial decrease of the phreatic level is observed directly behind the textile ranging up to 30 cm.
Overall, the effect of a seal on the development of the phreatic surface is concluded to be relatively small. The effect is only of a time-varying nature and, in three dimensions, the effect diminishes for larger distances. The application of a textile in terms of dike safety shows only a marginal improvement, which occurs only in a limited time period.
A numerical modelling approach is developed to describe this effect using the finite element method program PLAXIS, with add-on module PlaxFlow, to describe transient groundwater flow problems. This numerical modelling process starts off with the development of a model for a laboratory scale dike. In a previous study at the WaterLab, the phreatic surface level of the dike was measured over time for different degrees of sealing using a steel plate. These measurements are used to calibrate the numerical model, where the connection between seal and dike slope is described with a transmissive interface layer. It is concluded that this interface layer approximates the effect of the seal on the phreatic surface adequately.
The next step is to extent the numerical model to a larger scale dike consisting of heterogeneous soils. This model represents the dike located in the Flood Proof Holland test facility, which consists of a permeable core covered by a low-permeability layer. By modelling this transition from simple to complex, influences of permeability, heterogeneity, and damage of the cover on the phreatic surface are identified.
The effect of a seal on the phreatic surface is also studied using physical model tests of the dike at Flood Proof Holland. The position of the phreatic surface is measured by pressure sensors in standpipes, which are spread over the crest and inner slope of the dike. Different scenarios for the seal are examined: stiff plate, flexible textile, and no emergency measure (reference case). For every scenario, experiments are carried out with and without a damaged location in the outer slope of the dike, which lead to a total of six test cases.
The results of the physical model tests show multiple effects of the seal on the phreatic surface. First, the seal shows a delaying effect on the position of the phreatic surface, which implies that the seal delays the rise of the phreatic surface over time. The time until the phreatic surface reached a steady-state over the entire dike was increased with around 15% for plate cases and around 25% for textile cases when compared to the corresponding reference cases. Second, no decreasing effect on the phreatic surface can be observed, which means that the phreatic surface level in its steady-state condition is not affected by the placement of a seal on the outer slope. Third, the delaying effect is larger for a seal that consists of a flexible textile rather than a stiff plate. The connection between seal and dike cover is proved to be important since leakages underneath the seal influence its performance, especially when the dike is locally damaged.
Last, the textile seal has a three-dimensional effect on the development of the phreatic surface. A certain area of influence can be identified where the phreatic surface is affected. The effect of the phreatic surface is seen to be stronger for locations near the textile and this effect diminishes over time. For the textile case on a damaged dike, an initial decrease of the phreatic level is observed directly behind the textile ranging up to 30 cm.
Overall, the effect of a seal on the development of the phreatic surface is concluded to be relatively small. The effect is only of a time-varying nature and, in three dimensions, the effect diminishes for larger distances. The application of a textile in terms of dike safety shows only a marginal improvement, which occurs only in a limited time period.
Vibratory installation of piles and casings can be extremely economical, therefore the contractors prefer pile driving. When compared to impact pile driving, vibratory pile driving generates less noise but this installation method is still fraught with uncertainties (Rausche 2003). Environmental effects (such as ground vibrations) have negative impacts which could lead to damage and failure under special circumstances.
The vibrations from the pile driving generate excess pore pressures and cause settles leading to failure in slopes. As part of the optimisation of mooring places for inland shipping and small coasters in Calandkanaal, the port of Rotterdam authority had a number of mooring places modified in the second half of 2016. A point of attention was the lack of analysis and a testing framework as there were uncertainties in excess pore pressure generation, an exposed area in the slope and slope stability. Based on these uncertainties, the work presented in this report tries to bridge this gap by answering
the following research question:
How can the existing knowledge on pile driving by means of vibratory installation be efficiently integrated into a 3D model which can practically estimate the factor of safety of the slope during vibratory installations?
To answer the main research question, a few sub-questions were formed, which are as follows:
• How can the vibratory parameters be integrated to model the slope stability?
• What is the thickness of the highly degraded zone around the pile due to vibratory pile driving?
• What are the limitations of the study?
The proposed work uses the vibratory pile driving data to generate excess pore pressure data using an empirical pore pressure model given by Green & Mitchell (2004) referred here as the GMP pore pressure model. Along with the pore pressures by using an empirical attenuation relation, the extent of the liquefied zone was determined giving an idea about the area of the slope affected by pile driving.
For slope stability, PLAXIS 3D is used along with its flow module. PLAXIS 3D gives an idea of the expected displacements in the geometry (slope) and the factor of safety. In a way to incorporate vibration effects, only the pore pressure are used as load inputs because of the difficulty of inducing
pile driving vibrations in a static calculation.
To add pore pressures into the geometry, a well was used with the infiltration function for the amount of time the pile was driven in the actual project. The volume input for the well infiltration is calculated in the same way as it was done in the actual project shown in the work of de Nijs (2019). PLAXIS 2D and D-geo stability software packages are also used in an attempt to make comparisons with the PLAXIS 3D model and validate the whole analysis. ...
The vibrations from the pile driving generate excess pore pressures and cause settles leading to failure in slopes. As part of the optimisation of mooring places for inland shipping and small coasters in Calandkanaal, the port of Rotterdam authority had a number of mooring places modified in the second half of 2016. A point of attention was the lack of analysis and a testing framework as there were uncertainties in excess pore pressure generation, an exposed area in the slope and slope stability. Based on these uncertainties, the work presented in this report tries to bridge this gap by answering
the following research question:
How can the existing knowledge on pile driving by means of vibratory installation be efficiently integrated into a 3D model which can practically estimate the factor of safety of the slope during vibratory installations?
To answer the main research question, a few sub-questions were formed, which are as follows:
• How can the vibratory parameters be integrated to model the slope stability?
• What is the thickness of the highly degraded zone around the pile due to vibratory pile driving?
• What are the limitations of the study?
The proposed work uses the vibratory pile driving data to generate excess pore pressure data using an empirical pore pressure model given by Green & Mitchell (2004) referred here as the GMP pore pressure model. Along with the pore pressures by using an empirical attenuation relation, the extent of the liquefied zone was determined giving an idea about the area of the slope affected by pile driving.
For slope stability, PLAXIS 3D is used along with its flow module. PLAXIS 3D gives an idea of the expected displacements in the geometry (slope) and the factor of safety. In a way to incorporate vibration effects, only the pore pressure are used as load inputs because of the difficulty of inducing
pile driving vibrations in a static calculation.
To add pore pressures into the geometry, a well was used with the infiltration function for the amount of time the pile was driven in the actual project. The volume input for the well infiltration is calculated in the same way as it was done in the actual project shown in the work of de Nijs (2019). PLAXIS 2D and D-geo stability software packages are also used in an attempt to make comparisons with the PLAXIS 3D model and validate the whole analysis. ...
Vibratory installation of piles and casings can be extremely economical, therefore the contractors prefer pile driving. When compared to impact pile driving, vibratory pile driving generates less noise but this installation method is still fraught with uncertainties (Rausche 2003). Environmental effects (such as ground vibrations) have negative impacts which could lead to damage and failure under special circumstances.
The vibrations from the pile driving generate excess pore pressures and cause settles leading to failure in slopes. As part of the optimisation of mooring places for inland shipping and small coasters in Calandkanaal, the port of Rotterdam authority had a number of mooring places modified in the second half of 2016. A point of attention was the lack of analysis and a testing framework as there were uncertainties in excess pore pressure generation, an exposed area in the slope and slope stability. Based on these uncertainties, the work presented in this report tries to bridge this gap by answering
the following research question:
How can the existing knowledge on pile driving by means of vibratory installation be efficiently integrated into a 3D model which can practically estimate the factor of safety of the slope during vibratory installations?
To answer the main research question, a few sub-questions were formed, which are as follows:
• How can the vibratory parameters be integrated to model the slope stability?
• What is the thickness of the highly degraded zone around the pile due to vibratory pile driving?
• What are the limitations of the study?
The proposed work uses the vibratory pile driving data to generate excess pore pressure data using an empirical pore pressure model given by Green & Mitchell (2004) referred here as the GMP pore pressure model. Along with the pore pressures by using an empirical attenuation relation, the extent of the liquefied zone was determined giving an idea about the area of the slope affected by pile driving.
For slope stability, PLAXIS 3D is used along with its flow module. PLAXIS 3D gives an idea of the expected displacements in the geometry (slope) and the factor of safety. In a way to incorporate vibration effects, only the pore pressure are used as load inputs because of the difficulty of inducing
pile driving vibrations in a static calculation.
To add pore pressures into the geometry, a well was used with the infiltration function for the amount of time the pile was driven in the actual project. The volume input for the well infiltration is calculated in the same way as it was done in the actual project shown in the work of de Nijs (2019). PLAXIS 2D and D-geo stability software packages are also used in an attempt to make comparisons with the PLAXIS 3D model and validate the whole analysis.
The vibrations from the pile driving generate excess pore pressures and cause settles leading to failure in slopes. As part of the optimisation of mooring places for inland shipping and small coasters in Calandkanaal, the port of Rotterdam authority had a number of mooring places modified in the second half of 2016. A point of attention was the lack of analysis and a testing framework as there were uncertainties in excess pore pressure generation, an exposed area in the slope and slope stability. Based on these uncertainties, the work presented in this report tries to bridge this gap by answering
the following research question:
How can the existing knowledge on pile driving by means of vibratory installation be efficiently integrated into a 3D model which can practically estimate the factor of safety of the slope during vibratory installations?
To answer the main research question, a few sub-questions were formed, which are as follows:
• How can the vibratory parameters be integrated to model the slope stability?
• What is the thickness of the highly degraded zone around the pile due to vibratory pile driving?
• What are the limitations of the study?
The proposed work uses the vibratory pile driving data to generate excess pore pressure data using an empirical pore pressure model given by Green & Mitchell (2004) referred here as the GMP pore pressure model. Along with the pore pressures by using an empirical attenuation relation, the extent of the liquefied zone was determined giving an idea about the area of the slope affected by pile driving.
For slope stability, PLAXIS 3D is used along with its flow module. PLAXIS 3D gives an idea of the expected displacements in the geometry (slope) and the factor of safety. In a way to incorporate vibration effects, only the pore pressure are used as load inputs because of the difficulty of inducing
pile driving vibrations in a static calculation.
To add pore pressures into the geometry, a well was used with the infiltration function for the amount of time the pile was driven in the actual project. The volume input for the well infiltration is calculated in the same way as it was done in the actual project shown in the work of de Nijs (2019). PLAXIS 2D and D-geo stability software packages are also used in an attempt to make comparisons with the PLAXIS 3D model and validate the whole analysis.
Master thesis
(2022)
-
A. Oderwald Blázquez, C. Zwanenburg, K.H.A.A. Wolf, A.P. van den Eijnden, Kees Jan van der Made
For certain geotechnical structures, such as dikes and levees, the design quality is heavily reliant on the sampling quality. In addition, the extent of consequences on geotechnical design of using parameters from samples with a certain degree of disturbance in laboratory tests is unclear. While the available literature has been mainly focussed on disturbance experienced by clay samples, the same empirical findings are not always applicable to organic soils such as peat and organic clay. The global objective of this thesis was to gain an understanding of sampling disturbance in organic soils using both established and non-destructive experimental methods. In order to achieve this, the traditional Dutch Ackerman sampling technique was compared to that of a recently developed sampler, the Deltares Large Diameter Sampler (DLDS). Non-destructive methods and 1D consolidation parameters were used to quantify disturbance in organic soil samples.
The results from existing databases showed that organic clay has a clear linear trend between w and RR and peat showed no definitive correlation, although the peat sampled by the DLDS had significantly higher water contents than the peats from the Ackerman sampler. Moreover, 37% of organic clay and peat Ackerman samples had an ∆e/e0 below 7%. Meanwhile, all the DLDS results from the Deltares laboratory had an ∆e/e0 of less than 4%. The use of this parameter is still questionable for peats, as the higher e0 found in DLDS peats is the cause for low disturbance measurements. However, the ∆e/e0 index may be used in conjunction with other destructive and non-destructive disturbance parameters. Furthermore, the trend showed it becomes increasingly difficult to produce high quality samples with increasing in-situ vertical stress.
Using differences in shear wave velocity as a non-destructive disturbance determination technique, it was concluded that the increased shear wave velocity in Ackerman samples relative to the DLDS samples, although slight, was due to densification of the outermost volume of the sample being compressed by the sampling procedure. This effect was further observed in the other non-destructive method use in this investigation, CT scanning. Analysis of micro-CT scans showed that all specimens had higher greyvalue intensities at the perimeter than at the centre of the sample, however the observed effect was 7.4 times higher with the Ackerman specimens than with the DLDS specimens.
The main recommendation is to continue research on the effectiveness of using non-destructive methods to quantify sample disturbance in peats. For the sampling industry, it is advised to increase the diameter of the Ackerman sampling tubes to between 70 and 120 mm when sampling in peat. In addition, in light of the lesser disturbance caused by the DLDS, it is advised to deploy it in shallow peats instead of the Ackerman sampler with the current inner diameter of 67 mm. Furthermore, it is recommended to deploy both types of samplers side-by-side in sampling projects in order to diminish the effect of site-specific variables. ...
The results from existing databases showed that organic clay has a clear linear trend between w and RR and peat showed no definitive correlation, although the peat sampled by the DLDS had significantly higher water contents than the peats from the Ackerman sampler. Moreover, 37% of organic clay and peat Ackerman samples had an ∆e/e0 below 7%. Meanwhile, all the DLDS results from the Deltares laboratory had an ∆e/e0 of less than 4%. The use of this parameter is still questionable for peats, as the higher e0 found in DLDS peats is the cause for low disturbance measurements. However, the ∆e/e0 index may be used in conjunction with other destructive and non-destructive disturbance parameters. Furthermore, the trend showed it becomes increasingly difficult to produce high quality samples with increasing in-situ vertical stress.
Using differences in shear wave velocity as a non-destructive disturbance determination technique, it was concluded that the increased shear wave velocity in Ackerman samples relative to the DLDS samples, although slight, was due to densification of the outermost volume of the sample being compressed by the sampling procedure. This effect was further observed in the other non-destructive method use in this investigation, CT scanning. Analysis of micro-CT scans showed that all specimens had higher greyvalue intensities at the perimeter than at the centre of the sample, however the observed effect was 7.4 times higher with the Ackerman specimens than with the DLDS specimens.
The main recommendation is to continue research on the effectiveness of using non-destructive methods to quantify sample disturbance in peats. For the sampling industry, it is advised to increase the diameter of the Ackerman sampling tubes to between 70 and 120 mm when sampling in peat. In addition, in light of the lesser disturbance caused by the DLDS, it is advised to deploy it in shallow peats instead of the Ackerman sampler with the current inner diameter of 67 mm. Furthermore, it is recommended to deploy both types of samplers side-by-side in sampling projects in order to diminish the effect of site-specific variables. ...
For certain geotechnical structures, such as dikes and levees, the design quality is heavily reliant on the sampling quality. In addition, the extent of consequences on geotechnical design of using parameters from samples with a certain degree of disturbance in laboratory tests is unclear. While the available literature has been mainly focussed on disturbance experienced by clay samples, the same empirical findings are not always applicable to organic soils such as peat and organic clay. The global objective of this thesis was to gain an understanding of sampling disturbance in organic soils using both established and non-destructive experimental methods. In order to achieve this, the traditional Dutch Ackerman sampling technique was compared to that of a recently developed sampler, the Deltares Large Diameter Sampler (DLDS). Non-destructive methods and 1D consolidation parameters were used to quantify disturbance in organic soil samples.
The results from existing databases showed that organic clay has a clear linear trend between w and RR and peat showed no definitive correlation, although the peat sampled by the DLDS had significantly higher water contents than the peats from the Ackerman sampler. Moreover, 37% of organic clay and peat Ackerman samples had an ∆e/e0 below 7%. Meanwhile, all the DLDS results from the Deltares laboratory had an ∆e/e0 of less than 4%. The use of this parameter is still questionable for peats, as the higher e0 found in DLDS peats is the cause for low disturbance measurements. However, the ∆e/e0 index may be used in conjunction with other destructive and non-destructive disturbance parameters. Furthermore, the trend showed it becomes increasingly difficult to produce high quality samples with increasing in-situ vertical stress.
Using differences in shear wave velocity as a non-destructive disturbance determination technique, it was concluded that the increased shear wave velocity in Ackerman samples relative to the DLDS samples, although slight, was due to densification of the outermost volume of the sample being compressed by the sampling procedure. This effect was further observed in the other non-destructive method use in this investigation, CT scanning. Analysis of micro-CT scans showed that all specimens had higher greyvalue intensities at the perimeter than at the centre of the sample, however the observed effect was 7.4 times higher with the Ackerman specimens than with the DLDS specimens.
The main recommendation is to continue research on the effectiveness of using non-destructive methods to quantify sample disturbance in peats. For the sampling industry, it is advised to increase the diameter of the Ackerman sampling tubes to between 70 and 120 mm when sampling in peat. In addition, in light of the lesser disturbance caused by the DLDS, it is advised to deploy it in shallow peats instead of the Ackerman sampler with the current inner diameter of 67 mm. Furthermore, it is recommended to deploy both types of samplers side-by-side in sampling projects in order to diminish the effect of site-specific variables.
The results from existing databases showed that organic clay has a clear linear trend between w and RR and peat showed no definitive correlation, although the peat sampled by the DLDS had significantly higher water contents than the peats from the Ackerman sampler. Moreover, 37% of organic clay and peat Ackerman samples had an ∆e/e0 below 7%. Meanwhile, all the DLDS results from the Deltares laboratory had an ∆e/e0 of less than 4%. The use of this parameter is still questionable for peats, as the higher e0 found in DLDS peats is the cause for low disturbance measurements. However, the ∆e/e0 index may be used in conjunction with other destructive and non-destructive disturbance parameters. Furthermore, the trend showed it becomes increasingly difficult to produce high quality samples with increasing in-situ vertical stress.
Using differences in shear wave velocity as a non-destructive disturbance determination technique, it was concluded that the increased shear wave velocity in Ackerman samples relative to the DLDS samples, although slight, was due to densification of the outermost volume of the sample being compressed by the sampling procedure. This effect was further observed in the other non-destructive method use in this investigation, CT scanning. Analysis of micro-CT scans showed that all specimens had higher greyvalue intensities at the perimeter than at the centre of the sample, however the observed effect was 7.4 times higher with the Ackerman specimens than with the DLDS specimens.
The main recommendation is to continue research on the effectiveness of using non-destructive methods to quantify sample disturbance in peats. For the sampling industry, it is advised to increase the diameter of the Ackerman sampling tubes to between 70 and 120 mm when sampling in peat. In addition, in light of the lesser disturbance caused by the DLDS, it is advised to deploy it in shallow peats instead of the Ackerman sampler with the current inner diameter of 67 mm. Furthermore, it is recommended to deploy both types of samplers side-by-side in sampling projects in order to diminish the effect of site-specific variables.
A New Approach for Slope Stability Analysis
Combining the limit equilibrium method and finite element method
A new approach is proposed which uses concepts of both the limit equilibrium method (LEM) and finite element method (FEM) to analyse slope stability. The main limitation of the LEM is that it can give an incorrect display of the initial stresses. The FEM is able to overcome this limitation, however, it uses the shear strength reduction method (SSRM) to determine the safety factor. This SSRM has its limitations as well. It’s a mathematical approach to obtain the factor of safety, without using the strength definitions given by advanced soil models. The proposed method is able to overcome the limitations of both LEM and FEM. It uses a genetic algorithm to search for the most critical slip surface and the safety factor is defined as the as the ratio of the total maximum available shear strength along the slip surface to the total mobilised shear stress. Multiple case studies are performed in this research and the genetic algorithm is able to find a reasonable critical slip surface and safety factor in every example. The proposed method has proven to give reliable results compared to other analysis methods: LEM, FEM and other optimisation methods proposed in literature.
...
A new approach is proposed which uses concepts of both the limit equilibrium method (LEM) and finite element method (FEM) to analyse slope stability. The main limitation of the LEM is that it can give an incorrect display of the initial stresses. The FEM is able to overcome this limitation, however, it uses the shear strength reduction method (SSRM) to determine the safety factor. This SSRM has its limitations as well. It’s a mathematical approach to obtain the factor of safety, without using the strength definitions given by advanced soil models. The proposed method is able to overcome the limitations of both LEM and FEM. It uses a genetic algorithm to search for the most critical slip surface and the safety factor is defined as the as the ratio of the total maximum available shear strength along the slip surface to the total mobilised shear stress. Multiple case studies are performed in this research and the genetic algorithm is able to find a reasonable critical slip surface and safety factor in every example. The proposed method has proven to give reliable results compared to other analysis methods: LEM, FEM and other optimisation methods proposed in literature.
Master thesis
(2021)
-
N.S. Walrave, A.A.M. Dieudonné, C. Zwanenburg, R. Spruit, R.C. Lanzafame, M.G. van der Krogt, Rimmer Koopmans, Inge van Gelder
In the Netherlands the design condition for a dike is surmised to occur during winter where it is assumed that the dike is fully saturated. Preliminary results by Van Duinen (2020) indicate that suction remains present, albeit ever decreasing, during the winter. This means that it would be possible for a dike to dry out during the summer period such that it becomes unsaturated, and that any effects may not have fully disappeared during a normative event.
This problem is two-fold, as (i) the strength of an unsaturated soil is higher compared to a saturated soil, and (ii) it is unknown how the strength associated with the initially unsaturated zone can be modelled in a macro-stability calculation as it varies temporally. This report investigates the strength of the initially unsaturated zone in clay river dikes in the Eastern part of the Netherlands and it explores the opportunities which the better understanding of the strength may present for the factor of safety in a macro-stability calculation
The feasibility and applicability of the SSCC as formulated by Lu and Likos (2006) for conventional geotechnical laboratory tests is investigated. A literature review bundles international knowledge on unsaturated soil behavior which is relevant in the context of dike design. Silty clay samples from the dike trajectory of Ravenstein-Lith were investigated using the SSCC. It can be successfully applied to K0-CAU triaxial test when determining strength parameters using strain-compatibility. Compared to its conventional variant, the saturation stage must be skipped. Samples are air-dried under laboratory conditions to a prescribed volumetric water content which can then be linked to an amount of suction using the SWCC and a comparison can be made with the closed form of the SSCC (Lu et al., 2010).
The SSCC cannot be applied to DSS tests successfully. In DSS tests both slip and a diagonal failure plane was observed. This research was able to pinpoint at which shear strain slip would occur, and hence when tests are valid. DS tests were used to confirm the validity of DSS tests using CCSM.
A case study performed on a representative cross-section found a positive effect on the factor of safety due the additional strength related to the initially unsaturated zone. The FoS increased by at least 1.7% in the most conservative case and at least 5.0% in a scenario supported by field measurements. The current limited number of field measurements restricts a more precise determination. It is advised to perform more of these such that the initially unsaturated zone in a clay river dike can be modelled effectively and reliably with a high degree of certainty.
To conclude, with the application of the SSCC concept, the additional strength produced by considering the initially unsaturated zone in clay river dikes in the Netherlands leads to an opportunity where the dike can be designed more efficiently by reducing conservatism. Thus, taking the initially unsaturated zone in a dike into account can be considered as a valuable contribution to the toolbox of Dutch geotechnical engineers.
...
This problem is two-fold, as (i) the strength of an unsaturated soil is higher compared to a saturated soil, and (ii) it is unknown how the strength associated with the initially unsaturated zone can be modelled in a macro-stability calculation as it varies temporally. This report investigates the strength of the initially unsaturated zone in clay river dikes in the Eastern part of the Netherlands and it explores the opportunities which the better understanding of the strength may present for the factor of safety in a macro-stability calculation
The feasibility and applicability of the SSCC as formulated by Lu and Likos (2006) for conventional geotechnical laboratory tests is investigated. A literature review bundles international knowledge on unsaturated soil behavior which is relevant in the context of dike design. Silty clay samples from the dike trajectory of Ravenstein-Lith were investigated using the SSCC. It can be successfully applied to K0-CAU triaxial test when determining strength parameters using strain-compatibility. Compared to its conventional variant, the saturation stage must be skipped. Samples are air-dried under laboratory conditions to a prescribed volumetric water content which can then be linked to an amount of suction using the SWCC and a comparison can be made with the closed form of the SSCC (Lu et al., 2010).
The SSCC cannot be applied to DSS tests successfully. In DSS tests both slip and a diagonal failure plane was observed. This research was able to pinpoint at which shear strain slip would occur, and hence when tests are valid. DS tests were used to confirm the validity of DSS tests using CCSM.
A case study performed on a representative cross-section found a positive effect on the factor of safety due the additional strength related to the initially unsaturated zone. The FoS increased by at least 1.7% in the most conservative case and at least 5.0% in a scenario supported by field measurements. The current limited number of field measurements restricts a more precise determination. It is advised to perform more of these such that the initially unsaturated zone in a clay river dike can be modelled effectively and reliably with a high degree of certainty.
To conclude, with the application of the SSCC concept, the additional strength produced by considering the initially unsaturated zone in clay river dikes in the Netherlands leads to an opportunity where the dike can be designed more efficiently by reducing conservatism. Thus, taking the initially unsaturated zone in a dike into account can be considered as a valuable contribution to the toolbox of Dutch geotechnical engineers.
...
In the Netherlands the design condition for a dike is surmised to occur during winter where it is assumed that the dike is fully saturated. Preliminary results by Van Duinen (2020) indicate that suction remains present, albeit ever decreasing, during the winter. This means that it would be possible for a dike to dry out during the summer period such that it becomes unsaturated, and that any effects may not have fully disappeared during a normative event.
This problem is two-fold, as (i) the strength of an unsaturated soil is higher compared to a saturated soil, and (ii) it is unknown how the strength associated with the initially unsaturated zone can be modelled in a macro-stability calculation as it varies temporally. This report investigates the strength of the initially unsaturated zone in clay river dikes in the Eastern part of the Netherlands and it explores the opportunities which the better understanding of the strength may present for the factor of safety in a macro-stability calculation
The feasibility and applicability of the SSCC as formulated by Lu and Likos (2006) for conventional geotechnical laboratory tests is investigated. A literature review bundles international knowledge on unsaturated soil behavior which is relevant in the context of dike design. Silty clay samples from the dike trajectory of Ravenstein-Lith were investigated using the SSCC. It can be successfully applied to K0-CAU triaxial test when determining strength parameters using strain-compatibility. Compared to its conventional variant, the saturation stage must be skipped. Samples are air-dried under laboratory conditions to a prescribed volumetric water content which can then be linked to an amount of suction using the SWCC and a comparison can be made with the closed form of the SSCC (Lu et al., 2010).
The SSCC cannot be applied to DSS tests successfully. In DSS tests both slip and a diagonal failure plane was observed. This research was able to pinpoint at which shear strain slip would occur, and hence when tests are valid. DS tests were used to confirm the validity of DSS tests using CCSM.
A case study performed on a representative cross-section found a positive effect on the factor of safety due the additional strength related to the initially unsaturated zone. The FoS increased by at least 1.7% in the most conservative case and at least 5.0% in a scenario supported by field measurements. The current limited number of field measurements restricts a more precise determination. It is advised to perform more of these such that the initially unsaturated zone in a clay river dike can be modelled effectively and reliably with a high degree of certainty.
To conclude, with the application of the SSCC concept, the additional strength produced by considering the initially unsaturated zone in clay river dikes in the Netherlands leads to an opportunity where the dike can be designed more efficiently by reducing conservatism. Thus, taking the initially unsaturated zone in a dike into account can be considered as a valuable contribution to the toolbox of Dutch geotechnical engineers.
This problem is two-fold, as (i) the strength of an unsaturated soil is higher compared to a saturated soil, and (ii) it is unknown how the strength associated with the initially unsaturated zone can be modelled in a macro-stability calculation as it varies temporally. This report investigates the strength of the initially unsaturated zone in clay river dikes in the Eastern part of the Netherlands and it explores the opportunities which the better understanding of the strength may present for the factor of safety in a macro-stability calculation
The feasibility and applicability of the SSCC as formulated by Lu and Likos (2006) for conventional geotechnical laboratory tests is investigated. A literature review bundles international knowledge on unsaturated soil behavior which is relevant in the context of dike design. Silty clay samples from the dike trajectory of Ravenstein-Lith were investigated using the SSCC. It can be successfully applied to K0-CAU triaxial test when determining strength parameters using strain-compatibility. Compared to its conventional variant, the saturation stage must be skipped. Samples are air-dried under laboratory conditions to a prescribed volumetric water content which can then be linked to an amount of suction using the SWCC and a comparison can be made with the closed form of the SSCC (Lu et al., 2010).
The SSCC cannot be applied to DSS tests successfully. In DSS tests both slip and a diagonal failure plane was observed. This research was able to pinpoint at which shear strain slip would occur, and hence when tests are valid. DS tests were used to confirm the validity of DSS tests using CCSM.
A case study performed on a representative cross-section found a positive effect on the factor of safety due the additional strength related to the initially unsaturated zone. The FoS increased by at least 1.7% in the most conservative case and at least 5.0% in a scenario supported by field measurements. The current limited number of field measurements restricts a more precise determination. It is advised to perform more of these such that the initially unsaturated zone in a clay river dike can be modelled effectively and reliably with a high degree of certainty.
To conclude, with the application of the SSCC concept, the additional strength produced by considering the initially unsaturated zone in clay river dikes in the Netherlands leads to an opportunity where the dike can be designed more efficiently by reducing conservatism. Thus, taking the initially unsaturated zone in a dike into account can be considered as a valuable contribution to the toolbox of Dutch geotechnical engineers.
This study aims for a software tool that predict secondary settlements in soft layers on which secondary dikes are founded based on cone penetration test data. In the literature study five equations have been found that relate cone resistance and friction ratio to volumetric weight and over consolidation ratio. With the volumetric weight and over consolidation ratio the NEN-Bjerrum settlement parameters can be determined and with that the strain for a layer. After this study the focus lies on developing a software tool and the resulting output. In the end it seems, qualitatively, that the results are not useful in engineering practise because the resulting settlements are unexpectedly large.
...
This study aims for a software tool that predict secondary settlements in soft layers on which secondary dikes are founded based on cone penetration test data. In the literature study five equations have been found that relate cone resistance and friction ratio to volumetric weight and over consolidation ratio. With the volumetric weight and over consolidation ratio the NEN-Bjerrum settlement parameters can be determined and with that the strain for a layer. After this study the focus lies on developing a software tool and the resulting output. In the end it seems, qualitatively, that the results are not useful in engineering practise because the resulting settlements are unexpectedly large.
Influence of the initial soil stress state on the cone factor
Reducing the uncertainties in the design of dikes on peat and clay
The uncertainties in undrained macro-stability analysis of dikes lead to overdimensioned and inefficient designs. The undrained shear strength (su¬), which describes the strength of clay and peat layers, is important information for the macro-stability analysis of a dike. The cone factor (Nc) gives a linear correlation between undrained shear strength (su¬) of the soil and the cone resistance (qc) from a cone penetration test (CPT)¬. In practice the uncertainty on this correlation, given by the variation coefficient, is high, especially it overestimates the su for high values of qc. As a result, a large reduction factor (RF) is taken into account between the expected value of su and the characteristic value of su used in calculations.
In literature the cone factor (Nc) is assumed to depend on the soil stiffness, the cone roughness and the initial soil stress state (∆). Including the initial soil stress state, or more specifically the horizontal soil stresses (σ’h0), in the cone factor determination can lead to a reduction of the variation coefficient. Based on literature and a numerical analysis it is found that including the initial soil stress state in the determination of Nc can lead to a difference of 10% in cone factor. However, the difference is less than 10% for most measures due to the relatively similar stress conditions over a large part of the cross section of a dike. In addition, a theoretical application of the initial soil stress state (Δ) shows that the overestimation of su for high values of qc cannot be solved by including it as found in literature.
A case study on the Hollandse IJsseldijk project has been conducted to back up the theoretical approach with experimental measurements. As a conclusion it is found that the variation coefficient is reduced slightly taking into account the initial horizontal soil stresses, resulting in a decrease of the reduction factor (RF) of 2-3%. Taking this small improvement and remaining unknowns in the calculation into account, it is concluded that including a measure of the in-situ soil stress state (Δ) in the determination of the cone factor (Nc) does not result in a significant reduction of the present uncertainties in dike assessment with existing approaches. ...
In literature the cone factor (Nc) is assumed to depend on the soil stiffness, the cone roughness and the initial soil stress state (∆). Including the initial soil stress state, or more specifically the horizontal soil stresses (σ’h0), in the cone factor determination can lead to a reduction of the variation coefficient. Based on literature and a numerical analysis it is found that including the initial soil stress state in the determination of Nc can lead to a difference of 10% in cone factor. However, the difference is less than 10% for most measures due to the relatively similar stress conditions over a large part of the cross section of a dike. In addition, a theoretical application of the initial soil stress state (Δ) shows that the overestimation of su for high values of qc cannot be solved by including it as found in literature.
A case study on the Hollandse IJsseldijk project has been conducted to back up the theoretical approach with experimental measurements. As a conclusion it is found that the variation coefficient is reduced slightly taking into account the initial horizontal soil stresses, resulting in a decrease of the reduction factor (RF) of 2-3%. Taking this small improvement and remaining unknowns in the calculation into account, it is concluded that including a measure of the in-situ soil stress state (Δ) in the determination of the cone factor (Nc) does not result in a significant reduction of the present uncertainties in dike assessment with existing approaches. ...
The uncertainties in undrained macro-stability analysis of dikes lead to overdimensioned and inefficient designs. The undrained shear strength (su¬), which describes the strength of clay and peat layers, is important information for the macro-stability analysis of a dike. The cone factor (Nc) gives a linear correlation between undrained shear strength (su¬) of the soil and the cone resistance (qc) from a cone penetration test (CPT)¬. In practice the uncertainty on this correlation, given by the variation coefficient, is high, especially it overestimates the su for high values of qc. As a result, a large reduction factor (RF) is taken into account between the expected value of su and the characteristic value of su used in calculations.
In literature the cone factor (Nc) is assumed to depend on the soil stiffness, the cone roughness and the initial soil stress state (∆). Including the initial soil stress state, or more specifically the horizontal soil stresses (σ’h0), in the cone factor determination can lead to a reduction of the variation coefficient. Based on literature and a numerical analysis it is found that including the initial soil stress state in the determination of Nc can lead to a difference of 10% in cone factor. However, the difference is less than 10% for most measures due to the relatively similar stress conditions over a large part of the cross section of a dike. In addition, a theoretical application of the initial soil stress state (Δ) shows that the overestimation of su for high values of qc cannot be solved by including it as found in literature.
A case study on the Hollandse IJsseldijk project has been conducted to back up the theoretical approach with experimental measurements. As a conclusion it is found that the variation coefficient is reduced slightly taking into account the initial horizontal soil stresses, resulting in a decrease of the reduction factor (RF) of 2-3%. Taking this small improvement and remaining unknowns in the calculation into account, it is concluded that including a measure of the in-situ soil stress state (Δ) in the determination of the cone factor (Nc) does not result in a significant reduction of the present uncertainties in dike assessment with existing approaches.
In literature the cone factor (Nc) is assumed to depend on the soil stiffness, the cone roughness and the initial soil stress state (∆). Including the initial soil stress state, or more specifically the horizontal soil stresses (σ’h0), in the cone factor determination can lead to a reduction of the variation coefficient. Based on literature and a numerical analysis it is found that including the initial soil stress state in the determination of Nc can lead to a difference of 10% in cone factor. However, the difference is less than 10% for most measures due to the relatively similar stress conditions over a large part of the cross section of a dike. In addition, a theoretical application of the initial soil stress state (Δ) shows that the overestimation of su for high values of qc cannot be solved by including it as found in literature.
A case study on the Hollandse IJsseldijk project has been conducted to back up the theoretical approach with experimental measurements. As a conclusion it is found that the variation coefficient is reduced slightly taking into account the initial horizontal soil stresses, resulting in a decrease of the reduction factor (RF) of 2-3%. Taking this small improvement and remaining unknowns in the calculation into account, it is concluded that including a measure of the in-situ soil stress state (Δ) in the determination of the cone factor (Nc) does not result in a significant reduction of the present uncertainties in dike assessment with existing approaches.