In March 2016, an addendum to the Dutch design guideline for micropiles, CUR 236, was published. This addendum elaborated on the ‘axial stiffness of micropiles’. The softening behaviour was here first mentioned as an aspect relevant for the axial stiffness of the micropiles. Due to the slender geometry of the micropiles, this further translates into axial capacity. Up to this moment very little research was done into this phenomenon and to be conservative a ‘best guess’ of 50% of the peak shear stress was made. The goal of this thesis is to have a more profound understanding about this (strain) softening behaviour, leading to the main research question: “How does strain softening manifest for micropiles under tensile loading?”. This strain softening behaviour can be further subdivided into the mobilisation from peak to residual shear stress and the reduction of the residual shear stress relative to the peak. Furthermore, the installation effects play a big role in the bearing capacity. Also, some thought is given to the large scale measurements of the behaviour. Three different paths are chosen to research the strain softening behaviour. Numerical modelling, small scale tests on sand and large scale pile tests are performed. In case of the numerical modelling, the large scale situation is simulated in the numerical software Plaxis, using an axisymmetric model and the hypoplastic constitutive model. Direct shear tests are assumed to represent a small part of the micropile, simulating the local softening behaviour. Numerous tests are performed varying relative density and top pressure to assess the local strain softening behaviour. Last, a method is developed to quantify the occurring ratio between peak and residual shear stress in-situ, extending on the current prescribed testing procedure (CUR 236, 2011). The only constitutive model available that describes the critical state soil behaviour for sand is the hypoplastic sand model. However, the combination of the tensile loading, softening implementation into the hypoplastic sand model in Plaxis and the deformations, induce considerable inaccuracies and physically impossible behaviour. This rejects further elaboration with this approach. The direct shear tests are performed on only sand, based on the results of Uesugi & Kishida (1987), assuming a rough surface. In summary, a clear dependency on relative density and average confining pressure is observed. Varying from a reduction of approximately 30% for samples with the maximum possible density to 0% for a sand with a medium dense packing. Furthermore, the displacements necessary to mobilise from peak to residual shear stress show a uniform trend, independent of relative density or pressure. Quantitatively, the displacement ranges between 2 and 3 mm. In the large scale tests, due to unexpected, structural failure, the majority of the test results, unfortunately, were unusable. The pile test that did produce workable results, behaved as expected. It could be deduced that the used methodology works. The use of the hypoplastic constitutive model in Plaxis, does not give the expected results. It can thus be concluded that a fully coupled stress – strain analysis of the problem is unfortunately impossible. Concluding on the direct shear tests performed, the implementation in the CUR 236 addendum is too simplistic. In terms of ratio between peak and residual shear stress, a dependency based on relative density and average confining pressure should be included. In terms of displacement, the found displacement is larger. It should however be noted that the direct shear tests are only a simplification, approximating the actual situation. The performed large scale tests do show results in line with expectations and could be used in the future to assess the softening behaviour in-situ.

Throughout the years the requirements of sheet pile walls have changed. Therefore reassessment of these structure's reliability is of importance. In this thesis, Bayesian updating is used for the reliability updating task. Updating processes require measurements of the structure under known conditions. Although for practical and economical reasons failure measurements of structures are seldomely available. Therefore the research focusses on whether it is possible to update a sheet pile wall's reliability using service domain measurements instead. Parameter updating methods generally return the statistically most likely parameter values for producing the observations. Using a theoretical sheet pile wall case, it is tested if the Bayesian updating method is able to effectively return the true soil parameter values as the most likely parameter set. The results show that the Bayesian updating method is very capable of approaching the used observations with the updated model response. Also the updated values of the most influential parameters show evolution in the direction of their true values. But the method does have difficulties with returning the true soil parameter values, even when applied to a theoretical case and with the use of elaborate observation configurations. Recommendations are given on further research concerning the use of the Bayesian updating method, the different influences on its performance and method application limitations.

The production and injection of fluids from and in reservoirs leads to changes in the in-situ stress in the subsurface. This can cause reservoir compaction, subsidence, fault reactivation and / or seismicity. As these effects may greatly influence society it is of importance to find accurate methods to describe them so they can be predicted or even better, mitigated. This thesis discusses a new analytical approach to calculate stress in the subsurface which incorporates the effects of differential compaction on the initiation of fault reactivation. This new approach is named Differential Compaction Loading (DCL) and the reason for its development is due to discrepancies observed between calculations using the Mohr-Coulomb failure criterion, also known as Poro-elastic Loading (PEL), and field observations. Geomechanical modelling was performed to assess fault failure sensitivity to a range of geometrical aspects as well as reservoir and fault properties. From this analysis, focusing on the reactivation pressure at which failure first occurs, an empirical sense of sensitivity was established. It was found that for the examined variations in the geometry the fault dip angle resulted in the largest spread in reactivation pressure. For the examined reservoir and fault properties, the friction angle was found to have the largest sensitivity. With these results it was possible to improve the estimates of essential parameters within the analytical approach, yielding a better fit between analytical and modelled solutions. These solutions lie closer to field observations. Hence, the new method of DCL shows a great improvement in calculation of stresses in the subsurface, compared to the method of PEL. This calibrated analytical approach allows for a quick assessment of the fault stability within a reservoir. Additionally, through the results from the geomechanical model new insights were obtained into the way stresses change and behave when a reservoir is depleted. The rotation of the principal stresses for each level of depletion was quantified and a new definition of the critical fault angle, the dip angle which will fail first, was derived. This links the depletion pressure and related rotation angle directly to a value of the new critical fault angle when DCL is present. Ultimately, these new insights into fault failure behaviour of boundary faults could be a useful tool in the step towards prediction and mitigation of production or injection related seismicity.

The design and reassessment of quays is subject to uncertainties. Examples of these uncertainties are the soil parameters, soil behavior and the current state of the structural parts. Especially in the reassessment of existing structures it is hard to prove a quay to be safe. In this thesis Bayesian updating is used as a method to reduce this uncertainty. Bayesian updating is a technique to probabilistically update the model prediction based on measurement data. One of the solutions to obtaining this data is test loading a quay wall. How to perform a test load and possible other solutions to obtaining the measurement data are not part of this research. The research focusses on how to use the data one obtains from a test loading. The effectiveness of test loading is reviewed by performing Bayesian updates with several fictitious measurement cases. Both Blum and a finite element model are updated based on fictitious strain and displacement measurements. The results show that Bayesian updating successfully reduces the standard deviations in all model predictions. This has a significant impact on the calculated reliability indices. The key benefit of performing a Bayesian update is that a statistically most likely combination of stochastic input parameters is determined. The thesis gives recommendations towards an application of Bayesian updating in practice and as fictitious measurement cases are used, an overall strategy is given for obtaining the required measurement data in practice.

As the construction of sub-aerial and submarine geotechnical structures increase in amount, rate and size, so do their associated risks. Often, with use constitutive models, finite element analyses (FEAs) are performed in order to identify and mitigate these risks. NorSand, which is a consti- tutive model based on critical state soil mechanics for particulate materials (e.g., sand), is one of the first models to integrate the state parameter ψ into its constitutive framework to model dense and loose sands material with the same parameter set. Importantly, it is able to identify the liquefaction potential as it can simulate softening behaviour due to pore pressure increase of loose soils in undrained conditions. Since NorSand has recently been implement into PLAXIS, a geotechnical analysis software capable of performing FEAs, it must be verified, validated and applied with the software, which is done in this report. First, stress-path and parametric analyses were conducted at single stress points. The stress- path analyses show how the state variables evolve for different triaxial conditions. Systematically changing the input parameters to extremes found in literature helped determine their influence on the evolution of stresses and strains. The resulting figures can be used to help future calibrations to experimental lab test data. The PLAXIS implemented NorSand (PLAXIS NorSand) was verified by comparing it with an implementation written in Visual Basic for Applications (VBA NorSand) by the authors of the model Jefferies and Been. Verification in this context means determining if PLAXIS NorSand is able to produce outputs as intended by the authors. Various testing conditions, both triaxial and direct simple shear, showed overlap and agreement between the outputs of both implementations, verifying PLAXIS NorSand. Then, the model was compared to, albeit not in a traditional sense, an ’analytical solution’, which is the relationship between the mobilized friction ratio Mi and state parameter ψ in its simplest form. The mobilized friction ratio and stress ratio at peak strength of PLAXIS NorSand and the ’analytical solution’ were compared. The values between both showed less than 3% difference, further verifying PLAXIS NorSand. The constitutive model was then validated - i.e., established that PLAXIS NorSand is able to approximate soil behaviour as intended. First, by using the soil parameter set that had been derived from lab tests of Erksak sand as a baseline, the input parameters were varied until PLAXIS NorSand was calibrated to individual triaxial tests as best as possible. Then, triaxial tests of Erksak, Nerlerk and Ticino sand were approximated with PLAXIS NorSand without changing the soil parameters determined from lab test data. PLAXIS NorSand is able to follow lab test data decently well with one parameter set. And if one decides to take the time and calibrate individual lab tests, and deviate from soil parameters determined from a set of lab tests, they can be matched even better. Additionally, it showed a consistent need for activation of the softening flag (S = 1) in order to appropriately model loose soils in undrained conditions. Furthermore, NorSand exhibits indefinite hardening in dense soils during undrained loading, which can be avoided by employing a ’cavitation cut-off’. The last part of this report tested PLAXIS NorSand by applying it in FEAs of a simplified submerged landslide, which was subjected to 20 centimeters of displacement at the crest through a rigid slab in undrained conditions. First, the difference in slope behaviour due to change in soil density within NorSand was determined: dense soil resulted in the slope to be able to bear the full 20 centimeter displacement, whereas increasing the void ratio (i.e., increasing the positive value for the state parameter) gave the effect of even quicker slope collapse and a lower bearing capacity. In other words, when using NorSand, the looser soil the further the failure surface moves up and the quicker the structure fails to maintain equilibrium. Lastly, NorSand was compared to Modified Cam-Clay and Mohr-Coulomb to highlight the differences in their ability to model static liquefaction, while being triggered by unrealistic loading conditions. Even though none of the FEAs showed actual liquefaction, since it is accompanied with the fluidization and loss of structure, they still gave in indication of the liquefaction potential. NorSand, contrary to the other constitutive models, showed the expected high sensitivity to forced displacement resulting in clear shear bands resembling Prandtl-type failure mechanism and early onset soil body collapse.

Quay structures play an important role in society. How much load these structures can withstand however is not certain. This MSc thesis contains insight into the load capacity of the old Amazonehaven and the current SIF quay structures. Both are quay structures which use a combined sheet pile wall, a reinforced concrete relieving platform, M.V.-piles, and two rows of bearing piles. The objective of this MSc thesis was to determine the load capacity of the structures, the models should therefore be as close to the actual conditions as possible. For that reason no safety and/or material factors have been applied throughout this MSc thesis. The approach is shown below. A literature study was performed to gain insight into the areas of interest that needed to be studied. This theory in combination with a review of the structures led to the critical cross sections of the respective structures. These cross sections were then modelled with conventional design methods (Blum and D-Sheet Piling). The Blum method determined the individual contributions of several aspects (loads, water, soil) to the horizontal stress distribution along the combined sheet pile wall and calculated the reaction forces using a set of boundary conditions. Within D-Sheet Piling the relieving platform was modelled by removing it, the loads that acted on it, and the soil that rested on it. The last method that was applied was a FEM software (Plaxis 2D). The FEM models were validated in three steps: First, by comparing their results to that of the conventional methods, it was found that the results of the conventional methods were within ca. 30% of the FEM results. Second, by comparing the results to actual field data, here the results showed both deviation and similarities, these deviations could however be explained. Lastly, by critically assessing the models to ensure that certain aspects were incorporated into the models correctly, this resulted in uncertainty about drained or undrained soil conditions for the thicker clay layers. The main function of both quay structures was the storage of certain goods, for that reason the only aspect that was not constant in the test loading set up was the magnitude of the primary surcharge. Both geotechnical and structural failure were taken into consideration for the quay structures. The results of the FEM models showed that neither of the structures had failed at their design loading conditions. For the Amazonehaven it was found that the magnitude of the primary surcharge at the first failure of the model was relatively close to that of the design loading conditions, it was incited by the exceedance of the geotechnical bearing capacity of the M.V.-piles. The first failure of the SIF model occurred at a surcharge that was more than 4 times the magnitude of the design loading conditions, it was incited by the exceedance of the normal stress capacity of the M.V.-piles.

In this study, the assessment of the KIJK dike follows the new guidelines given by POV-M 2018 using PLAXIS. The macrostability assessment and design of the dike is examined for two cases. In the first case the dike is assessed based on the in-situ conditions (Green dike) whereas in the second case a cantilever sheet pile wall is used in the design (Blue dike) to strengthen the dike. Prior to the analysis the interpretation of the available laboratory data that were executed according to the new protocol (WBI 2017) and the parameter determination of the necessary input parameters of the considered constitutive models (SHANSEP NGI-ADP, Hardening Soil, Soft Soil models) is established. The undrained shear strength (su) of the SHANSEP NGI-ADP model is based on the SHANSEP concept and the normalised su (S (NC, OC)) and the strength increase exponent (m) parameters are needed. For the HS and the SS models the effective strength parameters φ and c are required. The FoS is determined with the use of the strength reduction method. Moreover, the CSSM framework is coupled with the SHANSEP (Stress History and Normalized Soil Engineering Properties) concept enabling the incorporation of the effect of stress history and the stress path characterizing the undrained shear strength in the design. The CSSM framework is applied in the design by determining the strength parameters of clays from an axial strain level equal to 25% under triaxial compression whereas for peats at 40% shear strain level under direct simple shearing conditions. In this study the strength parameters were additionally determined from the service conditions strain levels which are the 2% and 5% strain levels for clays and peats, respectively. The necessary strength parameters for the constitutive models are determined in the considered strain levels exposing their influence for both clays and peats. Moreover, the study includes the examination of the constitutive models at a single element level conducted in the Soil Test facility available in PLAXIS. When it comes to the design analysis, it was found that the SHANSEP NGI-ADP model fits properly the su determined from a cone penetration test. The HS and SS models based on the effective strength parameters may result in an undrained shear strength profile which deviates from the su that the soils exhibits in the field. The study points out that both the strain level dependency of the strength parameters and the selection of the constitutive model at critical loading influence the results in terms of the developed failure plane and the FoS, especially in the case of Green dikes. The study also elaborates the response of the models in regard to the design requirements for the calculation of displacements and the structural forces. Finally, this study answers the knowledge gap regarding how the strain level influences the strength of the examined soils and how this should be translated in the design along with the explanation on the effects of the selected constitutive model on the results.

Numerical modelling of pile foundations can be done in several ways. In commercial finite element packages two main options are available; using volume elements with interface elements between the pile and soil domains and the embedded beam approach. The embedded beam element was first proposed by Sadek and Shahrour (2004) and considers a beam element that can cross a solid element at any arbitrary location with any arbitrary inclination. This has several advantages to the volume pile method, such as the need for fewer elements and the mesh uncoupling of the pile and soil, which make this method much more efficient and leads to a significant reduction in calculation time. However, the embedded beam element also deals with a number of limitations and drawbacks. This research focuses on overcoming the mesh sensitivity, which is caused by the stress singularity that is introduced in the soil by the beam element. Also, the inability to take into account the pile surface will be resolved, aiming to improve the lateral pile-soil interaction. The idea of Turello et al. (2016) of an embedded beam element with explicit interaction surface is extended and generalised leading to a new embedded beam formulation. In the proposed model the beam displacements at the interaction surface are obtained by a mapping scheme that takes into account Timoshenko beam theory and which is generalised to model inclined piles as well. A constitutive equation that describes the relation between the interface stresses and relative displacements between the pile and soil is defined along the shaft and at the foot of the pile. Along the shaft of the pile a shear stress limit is defined based on the Mohr-Coulomb failure criterion in order to incorporate plasticity in lateral direction. Furthermore, a more practical and efficient assembly procedure is proposed. Validation of the proposed method proofs that the proposed model leads to a significant mesh sensitivity reduction in case of axially loaded models compared to the existing implementation. The overall response of laterally loaded piles is improved considerably as well. However, the proposed method is still unable to capture lateral interface behaviour in order to model soil slippage around the pile. Furthermore, it is recommended to formulate a generally applicable foot interface stiffness and to optimise the code in order to reduce the computation time. The description of the interaction surface opens up many new possibilities for future research, such as modelling the true cross-section shape.

Displacement control is of utmost importance in deep excavation design and is usually based on numerical modelling, e.g. Finite Element Method (FEM). Numerical methods tend to be more conservative when analysing soil behaviour during deep excavation, whereas for practical and economic reasons this is not favoured. The inverse analysis allows for the identification of the soil parameter set that can provide the measurements observed in the monitoring when it is applied in the model. When performed in a probabilistic concept, it reduces parameter uncertainty and enables the stochastic prediction of future soil behaviour. In this thesis, capabilities and limitations of difference advanced constitutive models are investigated. The Generalized Hardening Soil Small strain model (GHS) presents a positive aspect in modelling soil behaviour during deep excavation with its various stress/strain dependency settings. Because of the uncertainties originating from the size of the domain and limitations of site investigation, the soil parameters can only be shown as probability distributions. In order to make that distribution more accurate, comparative selection of several inverse analysis optimization algorithms is performed. Thereafter, choice of the relevant parameters is done based on the conducted sensitivity analysis and engineering judgement. Having the most competitive optimization approach selected, remote scripting with Python is used to utilise Finite Element (FE) modelling in the 2D Plaxis software. The input parameters are iteratively updated with response observation (diaphragm wall deflections) using the Ensemble Kalman filter optimisation algorithm based on a chosen excavation stage. The re-calibrated parameters are checked with the data, which was used to create synthetic measurements made using the same FE, to perform reliability assessment of the developed Python-based algorithm and investigate its capabilities and limitations. The further development of the presented optimisation method is expected to increase certainty in setting alarm thresholds in the applications of the Observational Method.

Currently, the settlements of high-rise buildings are calculated based on two methods. The single pile settlements (s1), are generated due to mobilised shaft friction and pile tip resistance. These settlements are determined with analytical methods (i.e. NEN 9997-1, 2017). Settlements related to pile group behaviour in soil layers below pile tip level (s2) are calculated with the equivalent raft approach i.e. Tomlinson (1977). However, an essential aspect for differential settlement calculations is the redistribution of loads by soil-structure interaction mechanisms, which are not currently incorporated in the calculation approach. A missing factor for a soil-structure interaction calculation is the lack of soil- displacement installation effects in the numerical methods for single pile behaviour. Therefore, this research is focussed on the implementation of a soil displacement single pile behaviour in PLAXIS 3D and thereby towards integration of the structural and geotechnical design in one calculation method for appropriate soil subgrade reactions and load redistribution. In this research numerical methods are used in combination with the embedded beam approach applied in PLAXIS 3D. To approximate the NEN9997 load-displacement behaviour of soil displacement single piles, the behaviour of the embedded beam in combination with the multi-linear shaft friction is fitted in PLAXIS 3D. The fit is conducted by increasing the stiffness of a soil volume below pile tip level. Which does account for the residual stresses after pile installation. The solution of this fit consists of two parts: improvements on behalf of the new embedded beam formulation after Smulders (2018) and a soil stiffness fit below pile tip level. Regarding the new embedded beam formulation, improvements have been determined on mesh-dependency and a stiffer load-displacement response. The fit method performs well in combination with the embedded beams while approaching the load-displacement response of soil-displacement piles according to NEN9997. However, the ultimate bearing capacity of the embedded pile should still be calculated with D-Foundations (analytical method based on NEN9997). In the pile group calculation, the behaviour of single piles is extrapolated to all piles in the PLAXIS 3D model. A plate element is modelled on top of the pile heads to achieve a redistribution of loads due to the overlying superstructure. In this way, the single pile behaviour and bending stiffness of the superstructure is implemented in the PLAXIS 3D model, and the soil-structure interaction calculation is possible. However, group effects due to the soil displacement installation method are only partly covered in this approach. The reduction or increase in skin resistance in pile groups is not covered since, the predefined maximum skin friction capacity is manually inserted as an input parameter and it is not an outcome of the PLAXIS 3D calculation. Afterwards, the proposed framework is applied to a practical case study including measurement data of a high-rise project in Amsterdam. The proposed framework turned out to capture soil-structure interaction properly by taking into account a part of the superstructure bending stiffness and single pile behaviour. Compared to current calculation approaches, complex soil behaviour is captured in redistribution of the loads. However, the calculated settlements are still deviating from the measurement data. A probable explanation for the discrepancy is the shift in applied load over time in PLAXIS 3D relative to the real construction process. In conclusion, an improvement in terms of modelling soil-structure interaction has been achieved by incorporating single pile behaviour and superstructure bending stiffness in PLAXIS 3D. Therefore, the possibilities of linking the structural design to the geotechnical design in an early stage of the design process will be feasible. Combining the designs in an early stage, the structural dimensions of columns and beams are calculated with appropriate soil subgrade reactions and load redistributions by the soil. However, it is recommended to apply more investigation on the behaviour of soil- displacement pile (groups) in combination with embedded beams because, group effects are still not completely incorporated.

Tailings dam failures are one of the most destructive phenomena in terms of the number of victims and the environmental impact generated. Over the years, different causes have been identified, with flow liquefaction being a prominent factor to consider when assessing the stability of tailings deposits. Due to the complex nature of these events, numerical models are considered an important alternative for the analysis and design phases of tailings dams. These models require the application of appropriate advanced soil constitutive models to reproduce the relevant features of the soil behaviour and, thus, obtain results that are a valid representation of the observations in reality. In this work, the capabilities and limitations of the Clay And Sand Model (CASM), originally proposed by Yu (1995, 1998) and NorSand model (Jefferies, 1993) are assessed using the finite element software PLAXIS in the analysis of flow liquefaction. The criteria considered in the assessment consist of the accuracy of the models to predict the response of the soil under different monotonic loading conditions, the efficiency of the models for their application and the consistency of results obtained from boundary value problems compared with reality. Both CASM and NorSand are models developed within the critical state soil mechanics framework and use the concept of the state parameter (Been and Jefferies, 1985). However, they present differences in their formulations and assumptions. The performance of the model is explored in this study at three different levels: the material point level, simple boundary value problem level and complex boundary value problem. Different laboratory tests are simulated for the material point level, analysing a single stress point. For the boundary value problems, the construction of an embankment and the well-known Tar Island Dyke flow liquefaction event are simulated. Before applying the models, the implementation of CASM into PLAXIS is widely verified, and additional verification exercises for the NorSand implementation are also presented. Parametric analyses are performed to have a better insight into the effect of the parameters in the response of the models. Moreover, CASM and NorSand calibrated for the same tailings materials are used for the simulations. Given that most of the model parameters can be estimated through very well established procedures using experimental data, in principle, the calibration of both models is relatively straightforward if the required experimental data is available and when the data is limited, correlations can be used to estimate the parameters of CASM assuming normally consolidated conditions, which is the state at which tailings are often found. The results of the thesis, at the material point level, show that CASM presents limitations to quantitatively predicting the response of dense materials. This is associated with the formulation and assumptions of the model. In the analysis of the boundary value problems, lower strengths and higher stiffness in terms of stress-strain response are obtained with CASM compared with NorSand. Despite these differences, the results of this thesis demonstrate that both CASM and NorSand can successfully reproduce flow liquefaction at the different study levels.

This thesis investigates the behavior of single and group micro piles under axial tensile loading. Micro piles are small diameter piles consist of grout and steel rebar and they are capable of absorbing tensile loads. By constructing a group of piles the bearing capacity of each pile within a group is less compared to the single pile. The reason is due to the existence of group effect in the pile group which influences the bearing capacity. During the production of the piles for Amsterdam car parking project, load tests are performed to check whether the piles behave according as expected which can be considered as acceptance tests. However in this test, only individual piles are tested and not a pile group. CUR 236 design procedure states that the bearing capacity of a pile in a pile group is less than the bearing capacity of that pile when it is loaded not in a group. To take this effect into account for the acceptance test, an additional load is added to the test load. It turned out at the Amsterdam car parking project that piles failed the acceptance tests due to this additional load which is required to apply according to CUR 236 design guide. However this procedure is questionable because the pile is loaded into a much higher level than it will actually experience during its lifetime. Therefore an evaluation of the standards and the influence of group effects on micro pile behavior is needed. The initial plan of approach was to investigate the standards of other countries and compare them to Dutch standards to find the eventual existing gap and propose an improvement method which did not succeed. The reason was that the standards of other countries were all written in their national language and therefore it was not possible to study them. Seeking for the research on tension pile group behavior did not help so much because many researchers believe that including a realistic group effect in the design is not an easy task and there was no clear conclusion on micro pile group influence. The direction of approach is then changed towards the numerical modelling and based on it the influence of group effects on micro pile behavior is presented. First a single micro pile is modelled with Finite Element Method in Plaxis. The single pile is finally modelled in plane strain by using Embedded Beam Row element. Model parameters and properties are defined based on Amsterdam case study. The load-displacement behavior of the single pile model was comparable with the one from Amsterdam field failure test and is therefore validated based on field failure test data. After development of single pile model, the model for pile groups is made. This group model is made to represent the practical situation in a building pit for Amsterdam case study. Three models for the pile group have been made which differ in pile spacing and the impact of this parameter on the capacity per micro pile is investigated. The different used pile spacings are 5D, 10D and 15D which are equal to 1 meter, 2 meters and 3 meters. Also for each pile spacing, the dominant failure mechanism is determined. According to the results it was concluded that for 5D and 10D pile spacing, the failure mechanism is based on soil plug pull-out while for 15D, it is according to slip failure. By validation of the pile group model, an improvement for the space between the piles within a pile group can be proposed as 10D where the soil plug pull-out is dominant failure mechanism. It is recommended to validate the pile group model based on full-scale failure test on pile groups or by small-scale test using Geo-centrifuge models. Also by monitoring, a real data base of the group behavior can be obtained. Comparing the monitoring data to the design values based on CUR 236 could give an idea how well the design guide is formulated.

The Netherlands is prone to flooding as more than a quarter of the country lies under sea level. To combat flooding and ensure that the country remains dry structures such are levees and dikes have been installed. However, older water retaining structures are more than ever failing the stringent safety standard assessments. These older conventional reinforcement measures, including berm constructions, are not only costly but require an expanse of ground to ensure performability. Backward erosion piping is an internal erosion mechanism during which shallow pipes are formed in the direction opposite to the flow underneath water-retain structures as a result of the gradual removal of low cohesive material by the action of water. This mechanism is an important failure mechanism in both levees and dams where a cohesive layer covers a sand layer. Although failure resulting from backward erosion piping is not common, several levee failures in the United States, China and the Netherlands have been attributed to this mechanism. There are mitigation measures known to stop the backward erosion mechanism. One such measure is the placement of a seepage wall, to create a physical barrier directly in the flow path trying to reach the lowest region of the hydraulic head. A review of the literature showed that current design rules only consider groundwater flow calculations when determining the likelihood of hydraulic heave, one of the failure modes within the backward erosion process. Hydraulic heave in the backward erosion piping context is closely linked to the quicksand condition, essentially stating that once the effective stress is zero, the sand particles become suspended, liquifying a solid layer. The absence of an assessment of the effective stresses during the design process in conjunction with hydraulic heave has contributed to the main research question addressed by this thesis; How does a restricted exit for groundwater flow affect hydraulic heave compared to Terzaghi’s free exit situation?.

The current plan of bottom to top bottom sublevel stoping for the Kearney gold vein at the Cavanacaw mine, Omagh, Northern Ireland may not be the most effective in terms of stability. The Kearney ore body is a narrow vein gold deposit, which has been previously exploited through an open pit and is currently being developed as an underground operation using sublevel stoping (modified Avoca mining method). Stability within the mine is one of the key factors to be considered when it comes to hard rock mining. It should be considered equally as important from a safety and economic point of view. The extraction sequence plays an important role when considering the stability of a designed mine. This thesis aims to establish if the current planned sequence of extraction of bottom to top sublevel stoping is the most effective in terms of overall rock stability, or whether an alternative plan would be better? In the context of this thesis, the modified Avoca mining method is a form of sublevel stoping where material is extracted (stoped) between two drives (blind tunnels) and then backfilled. The project addressed, a conceptual study, field testing and laboratory testing in order to yield the information required to build several numerical models. The numerical modelling was carried out on several different stoping orders which met the constraints set out by Galantas, using the Hoek-Brown model within Plaxis2D. The analysis was conducted on the total displacements, phase displacements, predicted failure points and safety factors. The analysis of the different models showed that an alter- native stoping method of middle to top bottom to middle sublevel stoping peformed better in terms of stability. This improvement in stability was shown by an increase in the minimum safety factor from 3.20 to 3.50, over the current plan. There is further evidence in the reduction of the total number of predicted failure point by 25%.

The Netherlands is inherently challenged by water, as a large part of the country lies below sea level and several major rivers in North-western Europe cross the country. The most prevalent form of protection from coastal and river floods in the Netherlands includes approximately 22,000 km of earthen dikes, of which 3800 km are primary flood defenses (i.e., the first line of defense against high water). Subsidence, sea level rise, and the increase of rain intensity and river discharge due to climate change further challenge existing flood defenses to maintain required levels of safety. To do so, the top elevation of existing earthen dikes is often incrementally raised over time. However, raising a dike requires an extension of its base, which is frequently restricted by the presence of existing buildings and other spatial constraints. These dikes can be reinforced by alternative means such as a sheet pile wall. Another specific challenge regarding dike reinforcement in the Netherlands includes the presence of soft subsoil conditions at many dikes. These soft soils often consist of organic clays and peats. Such soils have a low stiffness and continue to deform over time; their strength is not well understood and often underestimated. Furthermore, organic soils are often not properly identified from Cone Penetration Tests (CPTs) using common interpretation methods, while CPT is the main testing method in the Netherlands. This research focuses on improving two aspects of the global stability assessment of dikes in the Netherlands: the modeling challenges of organic soil and dike reinforcement using sheet piles. Chapter 2 of this dissertation addresses the empirical relations for organic soils. The CPT-based correlation to derive the soil unit weight (Lengkeek et al. 2018) is validated and improved. Furthermore, new CPT-based correlations for organic soils are obtained by relating the soil state parameters to the cone resistance and the unique soil type properties to the friction ratio. An adjustment to Robertson (2010) CPT-based classification is proposed. In the improved SBT classification, organic soils (SBT=2) are redefined and subdivided into peat, organic clay, and mineral clay with organic matter. In chapter 3 the new Critical Stress Ratio (CSR) model is presented, which classifies as ‘Simplified Critical State Soil Mechanics’. The CSR model can be seen as a theoretical version of the SHANSEP equation, providing a link between effective stress parameters, obtained from common laboratory tests, and the undrained shear strength. The model can be implemented in LEM for ultimate limit state stability analysis. The CSR model provides the state dependent undrained shear strength for each stress point. The CSR model does not require to determine the exact yield contour as in a constitutive FEM model, this is taken into account by a variable spacing ratio, called the ‘Critical Stress Ratio’. This parameter of the CSR model can be regarded as the over-consolidation ratio at which no net excess pore pressures occurs, a parameter which can be fitted based on a few CAUC tests. Furthermore, the CSR model contains methods to obtain other model parameters for existing constitutive models used in the finite element method, such as the Poisson’s ratio which determines the horizontal and isotropic stress in unloading. Chapter 4 presents the set-up, results, and evaluation of the full-scale failure test. (In Dutch: ‘Eemdijk damwandproef’), initiated by the Dutch Flood Protection Programme. The Eemdijk full-scale failure tests involves separate tests on (1) sheet pile panels, (2) on a ground dike, as well as a combined test (3) on a ground dike with sheet pile reinforcement. The Eemdijk full-scale failure tests provides valuable insights through a detailed analysis of the deformations of dikes leading up to and beyond failure. Furthermore, the soil investigation is re-examined and parameters are determined for multiple constitutive models applied in FEM back-analyses. Finally, both the CPT-based methods, the CSR model and the SHANSEP-NGI-ADP model are validated at the Eemdijk test site. The back-analysis of the pull-over tests (PO-test) confirmed that the cross-section class 2 sheet piles (AZ26) reached the full plastic bending moment capacity and the cross-section class 3 sheet piles (AZ13-700 and GU8N) reached at least the elastic bending moment capacity. Furthermore, from the analysis of the SAAF measurements it is concluded that the stiffness of only the side sheet piles of panels should be reduced due to edge effects. The ground dike test (GD-test) and sheet pile reinforced dike test (SPD-test) allowed for a unique comparison and provided insight in the critical deformation rate prior to progressive failure. This criterion is useful in the assessment of unstable slopes. The GD-test illustrates the importance of high density of soil investigations and the importance of high quality CPTs (ISO class 1) and proper CPT based classification. The sheet pile reinforced dike test (SDP-test) shows that a continuous sheet pile, with sufficient length and embedment, makes an important contribution to the robustness of the dike after failure. Even after structural failure due to a plastic hinge, all sheet piles remained intact and interlocked. The failed sheet piles functioned as a weir and ultimately prevented breaching. Based on a careful examination of the Triaxial (CAUC) test it is recommended to use the 15% axial strain value as a basis for the ultimate value and to apply additional criteria to prevent unrealistic high or low values for the undrained shear strength, and to re-examine the applied geometrical corrections. Based on the performed variation analysis it is recommended to use average stiffness parameters in a SLS or ULS dike design analysis, when performed with advanced constitutive models in FEM. The alternative approaches to dike assessment presented in this research are expected to result in a more economic and better understood dike design and assessment based on improved field data interpretation (chapter 2,) undrained shear strength and modeling procedures (chapter 3) and takeaways from the full-scale tests and back analyses (chapter 4).@en