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T.G. Wegman
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In 2017 new guidelines concerning macro stability calculations were implemented by the Dutch Ministry of Infrastructure and Environment. These guidelines are formulated in “Wettelijk Beoordelingsinstrumentarium” (WBI). The largest difference with the previous version of the guidelines concerns the material model that is prescribed to determine shear strength parameters. In triaxial tests shear strength parameters are to be determined at ultimate state (25% axial strain), which is assumed to be a good representation of critical state. Critical state is a concept from Critical State Soil Mechanics (CSSM) and assumed to be a good representation of the state reached after large deformations induced by macro instability. Another fundamental assumption in the WBI is the use of the SHANSEP method. This method encompasses a laboratory procedure and a normalisation method. CSSM was originally defined and elaborated under isotropic stress conditions while in engineering practice anisotropic conditions are mostly used.
The goal of this thesis is to investigate the undrained soil behaviour of organic clay in triaxial tests following the SHANSEP procedure and compare the results to the CSSM framework. In order to do so a series of eight K0-consolidated triaxial tests is executed using silty organic Oostvaarders plassen clay, which is assumed to be representative for a typical Dutch soil. A large range of over consolidation ratios is applied (1-20). Both compression and extension tests are executed. The triaxial tests are complemented by two K0-CRS tests and an isotropic compression test to determine relevant soil properties. The results are compared to the CSSM. The qualitative soil behaviour is analysed as well as the actual predicted undrained shear strength Su. Parameter relationships as described by CSSM are tried to be established from the data. The undrained shear strength is predicted by using numerical and analytical formulations of the Modified Cam Clay model, which is the most basic implementation
of CSSM. From the data a clear failure line could be determined in p'-q space. In the triaxial compression tests failure at ultimate state gave very consistent result, a failure line could precisely be determined. In extension failure at peak strength showed the most consistent results. Ultimate state could not be reached under representative stresses because the formation of large shear bands and necking during shearing. A unique p'-q-e relation was much harder to establish. The general trend as described by the CSSM was clearly visible but the uncertainty was rather large. Several factors contributed to the uncertainty. Among which the void ratio determination method that was used to determine the void ratio after the triaxial test, which is prone to errors. The MCC model was not able to model the stress path correctly and p'_0 at failure was not correctly predicted resulting in incorrect Su prediction. The MCC model overestimated Su in compression tests. In extension, however, Su is well predicted by the MCC model. The SHANSEP method turned out to be a very convenient way to normalise the undrained shear strength of the triaxial tests, both in compression and extension. Only at very large OCR Su/σ'_v0 is slightly overestimated. ...
The goal of this thesis is to investigate the undrained soil behaviour of organic clay in triaxial tests following the SHANSEP procedure and compare the results to the CSSM framework. In order to do so a series of eight K0-consolidated triaxial tests is executed using silty organic Oostvaarders plassen clay, which is assumed to be representative for a typical Dutch soil. A large range of over consolidation ratios is applied (1-20). Both compression and extension tests are executed. The triaxial tests are complemented by two K0-CRS tests and an isotropic compression test to determine relevant soil properties. The results are compared to the CSSM. The qualitative soil behaviour is analysed as well as the actual predicted undrained shear strength Su. Parameter relationships as described by CSSM are tried to be established from the data. The undrained shear strength is predicted by using numerical and analytical formulations of the Modified Cam Clay model, which is the most basic implementation
of CSSM. From the data a clear failure line could be determined in p'-q space. In the triaxial compression tests failure at ultimate state gave very consistent result, a failure line could precisely be determined. In extension failure at peak strength showed the most consistent results. Ultimate state could not be reached under representative stresses because the formation of large shear bands and necking during shearing. A unique p'-q-e relation was much harder to establish. The general trend as described by the CSSM was clearly visible but the uncertainty was rather large. Several factors contributed to the uncertainty. Among which the void ratio determination method that was used to determine the void ratio after the triaxial test, which is prone to errors. The MCC model was not able to model the stress path correctly and p'_0 at failure was not correctly predicted resulting in incorrect Su prediction. The MCC model overestimated Su in compression tests. In extension, however, Su is well predicted by the MCC model. The SHANSEP method turned out to be a very convenient way to normalise the undrained shear strength of the triaxial tests, both in compression and extension. Only at very large OCR Su/σ'_v0 is slightly overestimated. ...
In 2017 new guidelines concerning macro stability calculations were implemented by the Dutch Ministry of Infrastructure and Environment. These guidelines are formulated in “Wettelijk Beoordelingsinstrumentarium” (WBI). The largest difference with the previous version of the guidelines concerns the material model that is prescribed to determine shear strength parameters. In triaxial tests shear strength parameters are to be determined at ultimate state (25% axial strain), which is assumed to be a good representation of critical state. Critical state is a concept from Critical State Soil Mechanics (CSSM) and assumed to be a good representation of the state reached after large deformations induced by macro instability. Another fundamental assumption in the WBI is the use of the SHANSEP method. This method encompasses a laboratory procedure and a normalisation method. CSSM was originally defined and elaborated under isotropic stress conditions while in engineering practice anisotropic conditions are mostly used.
The goal of this thesis is to investigate the undrained soil behaviour of organic clay in triaxial tests following the SHANSEP procedure and compare the results to the CSSM framework. In order to do so a series of eight K0-consolidated triaxial tests is executed using silty organic Oostvaarders plassen clay, which is assumed to be representative for a typical Dutch soil. A large range of over consolidation ratios is applied (1-20). Both compression and extension tests are executed. The triaxial tests are complemented by two K0-CRS tests and an isotropic compression test to determine relevant soil properties. The results are compared to the CSSM. The qualitative soil behaviour is analysed as well as the actual predicted undrained shear strength Su. Parameter relationships as described by CSSM are tried to be established from the data. The undrained shear strength is predicted by using numerical and analytical formulations of the Modified Cam Clay model, which is the most basic implementation
of CSSM. From the data a clear failure line could be determined in p'-q space. In the triaxial compression tests failure at ultimate state gave very consistent result, a failure line could precisely be determined. In extension failure at peak strength showed the most consistent results. Ultimate state could not be reached under representative stresses because the formation of large shear bands and necking during shearing. A unique p'-q-e relation was much harder to establish. The general trend as described by the CSSM was clearly visible but the uncertainty was rather large. Several factors contributed to the uncertainty. Among which the void ratio determination method that was used to determine the void ratio after the triaxial test, which is prone to errors. The MCC model was not able to model the stress path correctly and p'_0 at failure was not correctly predicted resulting in incorrect Su prediction. The MCC model overestimated Su in compression tests. In extension, however, Su is well predicted by the MCC model. The SHANSEP method turned out to be a very convenient way to normalise the undrained shear strength of the triaxial tests, both in compression and extension. Only at very large OCR Su/σ'_v0 is slightly overestimated.
The goal of this thesis is to investigate the undrained soil behaviour of organic clay in triaxial tests following the SHANSEP procedure and compare the results to the CSSM framework. In order to do so a series of eight K0-consolidated triaxial tests is executed using silty organic Oostvaarders plassen clay, which is assumed to be representative for a typical Dutch soil. A large range of over consolidation ratios is applied (1-20). Both compression and extension tests are executed. The triaxial tests are complemented by two K0-CRS tests and an isotropic compression test to determine relevant soil properties. The results are compared to the CSSM. The qualitative soil behaviour is analysed as well as the actual predicted undrained shear strength Su. Parameter relationships as described by CSSM are tried to be established from the data. The undrained shear strength is predicted by using numerical and analytical formulations of the Modified Cam Clay model, which is the most basic implementation
of CSSM. From the data a clear failure line could be determined in p'-q space. In the triaxial compression tests failure at ultimate state gave very consistent result, a failure line could precisely be determined. In extension failure at peak strength showed the most consistent results. Ultimate state could not be reached under representative stresses because the formation of large shear bands and necking during shearing. A unique p'-q-e relation was much harder to establish. The general trend as described by the CSSM was clearly visible but the uncertainty was rather large. Several factors contributed to the uncertainty. Among which the void ratio determination method that was used to determine the void ratio after the triaxial test, which is prone to errors. The MCC model was not able to model the stress path correctly and p'_0 at failure was not correctly predicted resulting in incorrect Su prediction. The MCC model overestimated Su in compression tests. In extension, however, Su is well predicted by the MCC model. The SHANSEP method turned out to be a very convenient way to normalise the undrained shear strength of the triaxial tests, both in compression and extension. Only at very large OCR Su/σ'_v0 is slightly overestimated.
Student report
(2018)
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Irene Benito Lazaro, Fransje van Oorschot, Rubayat Sobhan, Bart Veenings, Tiemen Wegman,
In Bangladesh, groundwater from shallow aquifers is used for communal drinking water supply on a large scale. This water is often polluted by naturally occurring arsenic, causing the largest scale poisoning through drinking water in the world (D. v. Halem, S. Bakker, G. Amy, & J. Van Dijk, 2009). In this report, a highly arsenic affected area in Bangladesh has been investigated. The main objective of this research is to obtain more insight in the three aspects of the DELTAP project: geology, water quality monitoring and safe water supply. It is aimed to analyse the relation between arsenic contamination and the local geology, to monitor the drinking water quality using mobile applications and to design and construct a water treatment unit. An important aspect of this research is to develop a monitoring and maintenance protocol in order to ensure safe water supply in the future. In the study area, 150 households have been selected and the water quality has been tested. The water quality has been assessed by measuring four chemical parameters and five physical parameters, using simple strip tests and mobile water quality applications. The results of the strip tests have been compared to the results of ICP-MS analysis in order to check the performance of the tests and the mobile apps. The arsenic and iron strip tests showed good performance. However, the manganese and
mmonium strip tests did not perform well. Furthermore, no relations between the presence of arsenic and other chemicals have been found. It can be concluded that simple strip tests in combination with mobile applications are a promising tool for water quality monitoring, applying the Mobile Crowd Participation strategy. Since arsenic in groundwater has a geological origin, the relation between arsenic concentration in the groundwater and geology should be understood distinctly. In order to get a better understanding of this relationship, multiple tools and theories have been investigated and tested. Firstly, a geo information system has been used to map arsenic concentrations that have been obtained from the performed water quality tests. Based on the spatial analysis of the arsenic concentrations, three drillings have been performed: one drilling in a high, medium and low arsenic contaminated area. By use of the SASMIT tool, a link between sediment colour and arsenic contamination has been observed. Furthermore, geomorphological data and satellite images have been used to identify geological features in landscape which could also be linked to arsenic levels. The sediment colour found in drillings is in good accordance with the arsenic levels found in groundwater and thus, proves to be a useful tool to predict arsenic concentrations in the fieldwork area. However, the geological features in the research area are hard to identify and link to the measured arsenic concentrations. A water treatment unit has been designed and constructed in order to provide safe water to 5 to 10 households. Based on the iron and arsenic concentrations from the ICP-MS results and on practical considerations, a suitable location for the water treatment unit has been selected. The ratio of these parameters is important to remove arsenic from the groundwater efficiently. The water treatment unit is based on oxidation of arsenic along with iron and subsequent filtration with a rapid sand filter. Both chemical and biotic oxidation of arsenic and iron are ensured by setting up a biofilm carrier column before the rapid sand and anthracite filter unit. Finally, a parallel resin column has been installed to remove the residual arsenic. The water quality throughout the system varied substantially during the timeline of the project. The produced safe water at the end of the fieldwork did not meet the drinking water standards set by the WHO. Nevertheless, several recommendations have been provided and, in the future, more intensive backwash of the water treatment unit might be the key to produce and distribute safe water. Overall, a deeper knowledge on arsenic contamination and their effects have been achieved, and the improvement of the Bangladeshis live quality has been attempted.
...
In Bangladesh, groundwater from shallow aquifers is used for communal drinking water supply on a large scale. This water is often polluted by naturally occurring arsenic, causing the largest scale poisoning through drinking water in the world (D. v. Halem, S. Bakker, G. Amy, & J. Van Dijk, 2009). In this report, a highly arsenic affected area in Bangladesh has been investigated. The main objective of this research is to obtain more insight in the three aspects of the DELTAP project: geology, water quality monitoring and safe water supply. It is aimed to analyse the relation between arsenic contamination and the local geology, to monitor the drinking water quality using mobile applications and to design and construct a water treatment unit. An important aspect of this research is to develop a monitoring and maintenance protocol in order to ensure safe water supply in the future. In the study area, 150 households have been selected and the water quality has been tested. The water quality has been assessed by measuring four chemical parameters and five physical parameters, using simple strip tests and mobile water quality applications. The results of the strip tests have been compared to the results of ICP-MS analysis in order to check the performance of the tests and the mobile apps. The arsenic and iron strip tests showed good performance. However, the manganese and
mmonium strip tests did not perform well. Furthermore, no relations between the presence of arsenic and other chemicals have been found. It can be concluded that simple strip tests in combination with mobile applications are a promising tool for water quality monitoring, applying the Mobile Crowd Participation strategy. Since arsenic in groundwater has a geological origin, the relation between arsenic concentration in the groundwater and geology should be understood distinctly. In order to get a better understanding of this relationship, multiple tools and theories have been investigated and tested. Firstly, a geo information system has been used to map arsenic concentrations that have been obtained from the performed water quality tests. Based on the spatial analysis of the arsenic concentrations, three drillings have been performed: one drilling in a high, medium and low arsenic contaminated area. By use of the SASMIT tool, a link between sediment colour and arsenic contamination has been observed. Furthermore, geomorphological data and satellite images have been used to identify geological features in landscape which could also be linked to arsenic levels. The sediment colour found in drillings is in good accordance with the arsenic levels found in groundwater and thus, proves to be a useful tool to predict arsenic concentrations in the fieldwork area. However, the geological features in the research area are hard to identify and link to the measured arsenic concentrations. A water treatment unit has been designed and constructed in order to provide safe water to 5 to 10 households. Based on the iron and arsenic concentrations from the ICP-MS results and on practical considerations, a suitable location for the water treatment unit has been selected. The ratio of these parameters is important to remove arsenic from the groundwater efficiently. The water treatment unit is based on oxidation of arsenic along with iron and subsequent filtration with a rapid sand filter. Both chemical and biotic oxidation of arsenic and iron are ensured by setting up a biofilm carrier column before the rapid sand and anthracite filter unit. Finally, a parallel resin column has been installed to remove the residual arsenic. The water quality throughout the system varied substantially during the timeline of the project. The produced safe water at the end of the fieldwork did not meet the drinking water standards set by the WHO. Nevertheless, several recommendations have been provided and, in the future, more intensive backwash of the water treatment unit might be the key to produce and distribute safe water. Overall, a deeper knowledge on arsenic contamination and their effects have been achieved, and the improvement of the Bangladeshis live quality has been attempted.