In this paper, the geotechnical aspects of soft clay improvement using prefabricated vertical dra... more In this paper, the geotechnical aspects of soft clay improvement using prefabricated vertical drains (PVDs) with special reference to embankments will be demonstrated. The Cavity Expansion Theory is employed to predict the smear zone caused by the installation of mandrel driven vertical drains. Analytical and Numerical analyses adopting the equivalent plane strain solution are conducted to predict the excess pore pressures, lateral and vertical displacements. The advantages and limitations of vacuum application through vertical drains avoiding the need for high surcharge embankments are discussed using the proposed solutions. A few selected case histories are discussed and analyzed, including the site of the 2nd Bangkok International Airport, the coastal stretch of Muar Clay Plains in Malaysia and the Sunshine embankment, Australia. The predictions are compared with the available field data, verifying that the equivalent plane strain model can be used confidently with acceptable accuracy. Cyclic loading of PVDs is also examined in the laboratory in a manner appropriate for railway environments. It is shown that short PVDs can dissipate excess pore pressure as fast as they are built up under repeated loading conditions. Some selected on-ground experience of the first Author through the Ministry of Science and National Science Foundation during post-tsunami reconstruction efforts is described with specific reference to appropriate ground improvement requirements.
This study describes the performance of a full-scaleembankment raised on a soft marine clay, stab... more This study describes the performance of a full-scaleembankment raised on a soft marine clay, stabilized with vertical band drains in Malaysia. The finite element code CRISP, which is based on critical-state soil mechanics, has been employed to investigate the performance of the embankment and the underlying soft clay. Predictions of the excess pore pressures and both vertical and lateral displacements are made and compared with field observations. The limited use of closed-form solutions for the prediction of settlements at the line of symmetry of the embankment is also discussed. The effectiveness of the prefabricated drains has been evaluated according to the rate of excess-pore-pressure dissipation at the soil-drain interface. The numerical approach is based on a coupled consolidation analysis rather than on a conventional, purely undrained analysis. The numerical analysis reveals that for efficient vertical drains, the influence of smear and well resistance can be ignored. While the assumption of perfect drains may be acceptable in the long term, the short-term settlements are governed by the drain efficiency.
Journal of geotechnical and geoenvironmental …, 2002
The objective of this paper is to propose an explicit solution for the critical hydraulic gradien... more The objective of this paper is to propose an explicit solution for the critical hydraulic gradient required to move a base particle within a pore channel. The particle is assumed to displace when the applied hydrodynamic forces exceed this critical hydraulic gradient. The current ...
This paper describes the results of a series of large-scale triaxial tests conducted on greywacke... more This paper describes the results of a series of large-scale triaxial tests conducted on greywacke rockfill, used in dam construction in Southern Thailand. The tests are conducted at low to moderate confining stresses to relate their findings to the stability of rockfill dams Considering the current test results in conjunction with previous laboratory data, revised failure criteria for rockfill are proposed in non-dimensional form. For both low and high confining stresses, lower and upper bounds of strength envelopes have been established, based on a wide array of granular materials. The influence of the confining stress on the shear strength of rockfill is studied in depth, and the implications of a non-linear envelope at low normal stress levels on the stability of rockfill dams are discussed. Although two parallel rock-fill gradations for specimens compacted to similar porosities are considered, the exact role of particle size effect on hsear strenght is not examined in detail, as the difference in maximum particle sizes tested in this study is not sufficiently large.
In this chapter, a two-demensional plane strain solution is adopted for the embankment analysis, ... more In this chapter, a two-demensional plane strain solution is adopted for the embankment analysis, which includes the effects of smear zone caused by mandrel driven vertical drains. The equivalent (transformed) permeability coefficients are incorporated in finite element codes, employing modified Cam-clay theory. Selected numerical studies have been carried out to study the effect of embankment slope, construction rate, and drain spac- ing on the failure of the soft clay foundation. Finally, the observed and predicted performances of well-instrumented full-scale trial embankments built on soft Malaysian marine clay have been discussed in detail. The predicted results agree with the field measurements.
This chapter starts with an introduction of a revised analytical model of radial drainage with va... more This chapter starts with an introduction of a revised analytical model of radial drainage with vacuum preloading in both axisymmetric and plane strain conditions. Observed from large-scale radial drainage consolidation tests, the influence of vacuum pressure distribu- tion along the drain length is examined through the dissipation of average excess pore pressure and associated settlement. The details of an appropriate conversion procedure by transforming permeability and vacuum pressure between axisymmetric and equivalent plane strain conditions are described through analytical and numerical schemes. The effects of the magnitude and distribution of vacuum pressure on soft clay consolidation are investigated on the basis of average excess pore pressure, consolidation settlement, and time analyses. The writers describe a multi-drain plane strain finite element method analy- sis based on permeability conversion, which is employed to study the behavior of embank- ments stabilized at the site of the Second Bangkok International Airport with vacuum-assisted prefabricated vertical drains. In the field, a constant suction head is not always stable because of the occurrence of air leaks; therefore the magnitude of applied vacuum pressure was adjusted accordingly. The theoretical (numerical) predictions are compared with measured field data such as settlements, excess pore pressures, and lateral movements. The case history analysis employing the writers’ model indicates improved accuracy of the predictions in relation to the field observations. The data indicate that the efficiency of the prefabricated vertical drains depends on the magnitude and distribution of vacuum pressure as well as on the extent of air leak protection provided in practice. In this lecture the interpretations of fully instrumented tests embankments and their role in the development of appropriate ground improvement techniques for highways, motorways and airfields on soft clay deposits is illustrated through well documented case studies in Bangkok, Thailand and Muar Flat Site in Kuala Lumpur. For the Bangkok Plain and with sand backfills the perform- ance of embankments with different schemes of vertical drains was evaluated over a period of 25 years. Aspects such as recharging ef- fects due to the drains, inadequate measures in maintaining vacuum during vacuum applications and possible hydraulic connections with large diameter drains are discussed. For the Muar test embankments, the role of fill strength in residual soil embankment and the field deformation analysis in separating consolidation settlement from immediate settlement and creep settlements is presented. Novel interpretations of settlement from pore pressure dissipations, secondary settlement from field measurements and decay of lateral de- formation rate with time were also made.
A new elastoplastic stressstrain constitutive model is developed for granular coarse aggregates ... more A new elastoplastic stressstrain constitutive model is developed for granular coarse aggregates incorporating the degradation of particles during triaxial shearing. Coarse granular aggregates are subjected to breakage during excessive stress changes. Most of the available constitutive models do not consider the degradation of particles during shearing. In the current model, a plastic flow rule has been developed incorporating the energy consumption due to particle breakage during shear deformation. A non-associated flow and a kinematic type yield locus have been adopted in the model. A general formulation for the rate of particle breakage during shearing has been developed and incorporated in the plastic flow rule. The effects of particle breakage on the plastic distortional and volumetric deformations are incorporated in the current model. The stressstrain formulations are developed within the general critical state framework. The model can accurately predict the stressstrain an...
A system of vertical drains combined with vacuum preloading is an effective method to accelerate ... more A system of vertical drains combined with vacuum preloading is an effective method to accelerate soil consolidation by promoting radial flow. This study presents the analytical modeling of vertical drains incorporating vacuum preloading in both axisymmetric and plane strain conditions. The effectiveness of the applied vacuum pressure along the drain length is considered. The exact solutions applied on the basis of the unit cell theory are supported by finite element analysis using ABAQUS software. Subsequently, the details of an appropriate matching procedure by transforming permeability and vacuum pressure between axisymmetric and equivalent plane strain conditions are described through analytical and numerical schemes. The effects of the magnitude and distribution of vacuum pressure on soft clay consolidation are examined through average excess pore pressure, consolidation settlement, and time analyses. Lastly, the practical implications of this study are discussed.Key words: cons...
New plane-strain lateral consolidation equations are formulated that neglect the well resistance ... more New plane-strain lateral consolidation equations are formulated that neglect the well resistance of vertical drains but are applicable for both Darcian and non-Darcian flow. The results of consolidation analyses using conventional Darcian (linear) flow and the new solution based on non-Darcian (exponential) flow are compared. A good match has been obtained between equivalent plane-strain and axisymmetric solutions. The advantage of the equivalent plane-strain procedure is that it not only matches the average degree of radial (axisymmetric) consolidation but also yields a more realistic excess pore pressure distribution in the lateral direction than the Darcian flow condition. The relevant parameters are illustrated graphically for convenience. Good agreement was obtained between the prediction of the new equivalent plane-strain solution and field data from a test area in Ska-Edeby, Sweden.Key words: plane strain, consolidation, soft clay, vertical drains.
Behaviour of soils in the vadose zone is closely linked to water balance between ground and atmos... more Behaviour of soils in the vadose zone is closely linked to water balance between ground and atmosphere. It seems that transpiration is the most uncertain and difficult to evaluate of all the terms in the soil water balance. The key variable to estimate the transpiration rate is the rate of root water uptake, which depends on the hydrological, geological and meteorological conditions. A mathematical model for the rate of root water uptake incorporating the root growth rate, ground conditions, type of vegetation and climatic parameters, has been developed. A conical shape is considered to represent the geometry of the tree root zone. Using this proposed model, the distribution of moisture and the matric suction profile adjacent to the tree are numerically analysed. Field measurements taken from literature published previously are compared with the authors’ numerical model. The predicted results obtained from the numerical analysis, compared favourably with the field measurements, justifying the assumptions upon which the model was developed. The analysis also indicates that soil suction and settlement increase over the time, with the effect being more significant in the first stages of transpiration.
This paper describes the observed and the predicted performance of a full-scale trial embankment ... more This paper describes the observed and the predicted performance of a full-scale trial embankment built to failure on a soft Malaysian marine clay. Predictions of the subsoil deformation, the critical height of fill and the corre¬ sponding slip surface are made and subsequently compared to the field measure¬ ments. It is of importance to realize that all the predictions were made prior to the actual failure of the embankment. The comparison with measurements was possible only after the International Symposium on Trial Embankments on Malaysian Ma¬ rine Clays, was held in Kuala Lumpur, Malaysia, in November 1989, during which the field data were made available to the invited predictors (including the second writer) by the Malaysian Highway Authority. Finite-element codes based on the modified Cam-clay theory (CRISP) and hyperbolic stress-strain model (ISBILD) were utilized to investigate the behavior of the embankment and the foundation soil until failure. The type of numerical modeling includes purely undrained, fully drained. and a coupled consolidation analysis. The finite-element solutions are subsequently compared with the conventional stability analysis.
Expansion of the rail network in congested coastal Australia compels track construction on soft c... more Expansion of the rail network in congested coastal Australia compels track construction on soft clayey subgrade, including fine-grained estuarine soils. In such low-lying areas, where the water table is close to the ground surface, the saturated soft subgrade is often subjected to pumping (mud slurry) under the application of cyclic wheel loads, thereby causing fouling of the overlying ballast. This technical note presents the results of a series of large-scale, drained, cyclic, triaxial tests conducted on clay-fouled ballast. The impact of fouling on the stress-strain behaviour, resilient modulus and degradation of ballast is discussed.
In this paper, the geotechnical aspects of soft clay improvement using prefabricated vertical dra... more In this paper, the geotechnical aspects of soft clay improvement using prefabricated vertical drains (PVDs) with special reference to embankments will be demonstrated. The Cavity Expansion Theory is employed to predict the smear zone caused by the installation of mandrel driven vertical drains. Analytical and Numerical analyses adopting the equivalent plane strain solution are conducted to predict the excess pore pressures, lateral and vertical displacements. The advantages and limitations of vacuum application through vertical drains avoiding the need for high surcharge embankments are discussed using the proposed solutions. A few selected case histories are discussed and analyzed, including the site of the 2nd Bangkok International Airport, the coastal stretch of Muar Clay Plains in Malaysia and the Sunshine embankment, Australia. The predictions are compared with the available field data, verifying that the equivalent plane strain model can be used confidently with acceptable accuracy. Cyclic loading of PVDs is also examined in the laboratory in a manner appropriate for railway environments. It is shown that short PVDs can dissipate excess pore pressure as fast as they are built up under repeated loading conditions. Some selected on-ground experience of the first Author through the Ministry of Science and National Science Foundation during post-tsunami reconstruction efforts is described with specific reference to appropriate ground improvement requirements.
This study describes the performance of a full-scaleembankment raised on a soft marine clay, stab... more This study describes the performance of a full-scaleembankment raised on a soft marine clay, stabilized with vertical band drains in Malaysia. The finite element code CRISP, which is based on critical-state soil mechanics, has been employed to investigate the performance of the embankment and the underlying soft clay. Predictions of the excess pore pressures and both vertical and lateral displacements are made and compared with field observations. The limited use of closed-form solutions for the prediction of settlements at the line of symmetry of the embankment is also discussed. The effectiveness of the prefabricated drains has been evaluated according to the rate of excess-pore-pressure dissipation at the soil-drain interface. The numerical approach is based on a coupled consolidation analysis rather than on a conventional, purely undrained analysis. The numerical analysis reveals that for efficient vertical drains, the influence of smear and well resistance can be ignored. While the assumption of perfect drains may be acceptable in the long term, the short-term settlements are governed by the drain efficiency.
Journal of geotechnical and geoenvironmental …, 2002
The objective of this paper is to propose an explicit solution for the critical hydraulic gradien... more The objective of this paper is to propose an explicit solution for the critical hydraulic gradient required to move a base particle within a pore channel. The particle is assumed to displace when the applied hydrodynamic forces exceed this critical hydraulic gradient. The current ...
This paper describes the results of a series of large-scale triaxial tests conducted on greywacke... more This paper describes the results of a series of large-scale triaxial tests conducted on greywacke rockfill, used in dam construction in Southern Thailand. The tests are conducted at low to moderate confining stresses to relate their findings to the stability of rockfill dams Considering the current test results in conjunction with previous laboratory data, revised failure criteria for rockfill are proposed in non-dimensional form. For both low and high confining stresses, lower and upper bounds of strength envelopes have been established, based on a wide array of granular materials. The influence of the confining stress on the shear strength of rockfill is studied in depth, and the implications of a non-linear envelope at low normal stress levels on the stability of rockfill dams are discussed. Although two parallel rock-fill gradations for specimens compacted to similar porosities are considered, the exact role of particle size effect on hsear strenght is not examined in detail, as the difference in maximum particle sizes tested in this study is not sufficiently large.
In this chapter, a two-demensional plane strain solution is adopted for the embankment analysis, ... more In this chapter, a two-demensional plane strain solution is adopted for the embankment analysis, which includes the effects of smear zone caused by mandrel driven vertical drains. The equivalent (transformed) permeability coefficients are incorporated in finite element codes, employing modified Cam-clay theory. Selected numerical studies have been carried out to study the effect of embankment slope, construction rate, and drain spac- ing on the failure of the soft clay foundation. Finally, the observed and predicted performances of well-instrumented full-scale trial embankments built on soft Malaysian marine clay have been discussed in detail. The predicted results agree with the field measurements.
This chapter starts with an introduction of a revised analytical model of radial drainage with va... more This chapter starts with an introduction of a revised analytical model of radial drainage with vacuum preloading in both axisymmetric and plane strain conditions. Observed from large-scale radial drainage consolidation tests, the influence of vacuum pressure distribu- tion along the drain length is examined through the dissipation of average excess pore pressure and associated settlement. The details of an appropriate conversion procedure by transforming permeability and vacuum pressure between axisymmetric and equivalent plane strain conditions are described through analytical and numerical schemes. The effects of the magnitude and distribution of vacuum pressure on soft clay consolidation are investigated on the basis of average excess pore pressure, consolidation settlement, and time analyses. The writers describe a multi-drain plane strain finite element method analy- sis based on permeability conversion, which is employed to study the behavior of embank- ments stabilized at the site of the Second Bangkok International Airport with vacuum-assisted prefabricated vertical drains. In the field, a constant suction head is not always stable because of the occurrence of air leaks; therefore the magnitude of applied vacuum pressure was adjusted accordingly. The theoretical (numerical) predictions are compared with measured field data such as settlements, excess pore pressures, and lateral movements. The case history analysis employing the writers’ model indicates improved accuracy of the predictions in relation to the field observations. The data indicate that the efficiency of the prefabricated vertical drains depends on the magnitude and distribution of vacuum pressure as well as on the extent of air leak protection provided in practice. In this lecture the interpretations of fully instrumented tests embankments and their role in the development of appropriate ground improvement techniques for highways, motorways and airfields on soft clay deposits is illustrated through well documented case studies in Bangkok, Thailand and Muar Flat Site in Kuala Lumpur. For the Bangkok Plain and with sand backfills the perform- ance of embankments with different schemes of vertical drains was evaluated over a period of 25 years. Aspects such as recharging ef- fects due to the drains, inadequate measures in maintaining vacuum during vacuum applications and possible hydraulic connections with large diameter drains are discussed. For the Muar test embankments, the role of fill strength in residual soil embankment and the field deformation analysis in separating consolidation settlement from immediate settlement and creep settlements is presented. Novel interpretations of settlement from pore pressure dissipations, secondary settlement from field measurements and decay of lateral de- formation rate with time were also made.
A new elastoplastic stressstrain constitutive model is developed for granular coarse aggregates ... more A new elastoplastic stressstrain constitutive model is developed for granular coarse aggregates incorporating the degradation of particles during triaxial shearing. Coarse granular aggregates are subjected to breakage during excessive stress changes. Most of the available constitutive models do not consider the degradation of particles during shearing. In the current model, a plastic flow rule has been developed incorporating the energy consumption due to particle breakage during shear deformation. A non-associated flow and a kinematic type yield locus have been adopted in the model. A general formulation for the rate of particle breakage during shearing has been developed and incorporated in the plastic flow rule. The effects of particle breakage on the plastic distortional and volumetric deformations are incorporated in the current model. The stressstrain formulations are developed within the general critical state framework. The model can accurately predict the stressstrain an...
A system of vertical drains combined with vacuum preloading is an effective method to accelerate ... more A system of vertical drains combined with vacuum preloading is an effective method to accelerate soil consolidation by promoting radial flow. This study presents the analytical modeling of vertical drains incorporating vacuum preloading in both axisymmetric and plane strain conditions. The effectiveness of the applied vacuum pressure along the drain length is considered. The exact solutions applied on the basis of the unit cell theory are supported by finite element analysis using ABAQUS software. Subsequently, the details of an appropriate matching procedure by transforming permeability and vacuum pressure between axisymmetric and equivalent plane strain conditions are described through analytical and numerical schemes. The effects of the magnitude and distribution of vacuum pressure on soft clay consolidation are examined through average excess pore pressure, consolidation settlement, and time analyses. Lastly, the practical implications of this study are discussed.Key words: cons...
New plane-strain lateral consolidation equations are formulated that neglect the well resistance ... more New plane-strain lateral consolidation equations are formulated that neglect the well resistance of vertical drains but are applicable for both Darcian and non-Darcian flow. The results of consolidation analyses using conventional Darcian (linear) flow and the new solution based on non-Darcian (exponential) flow are compared. A good match has been obtained between equivalent plane-strain and axisymmetric solutions. The advantage of the equivalent plane-strain procedure is that it not only matches the average degree of radial (axisymmetric) consolidation but also yields a more realistic excess pore pressure distribution in the lateral direction than the Darcian flow condition. The relevant parameters are illustrated graphically for convenience. Good agreement was obtained between the prediction of the new equivalent plane-strain solution and field data from a test area in Ska-Edeby, Sweden.Key words: plane strain, consolidation, soft clay, vertical drains.
Behaviour of soils in the vadose zone is closely linked to water balance between ground and atmos... more Behaviour of soils in the vadose zone is closely linked to water balance between ground and atmosphere. It seems that transpiration is the most uncertain and difficult to evaluate of all the terms in the soil water balance. The key variable to estimate the transpiration rate is the rate of root water uptake, which depends on the hydrological, geological and meteorological conditions. A mathematical model for the rate of root water uptake incorporating the root growth rate, ground conditions, type of vegetation and climatic parameters, has been developed. A conical shape is considered to represent the geometry of the tree root zone. Using this proposed model, the distribution of moisture and the matric suction profile adjacent to the tree are numerically analysed. Field measurements taken from literature published previously are compared with the authors’ numerical model. The predicted results obtained from the numerical analysis, compared favourably with the field measurements, justifying the assumptions upon which the model was developed. The analysis also indicates that soil suction and settlement increase over the time, with the effect being more significant in the first stages of transpiration.
This paper describes the observed and the predicted performance of a full-scale trial embankment ... more This paper describes the observed and the predicted performance of a full-scale trial embankment built to failure on a soft Malaysian marine clay. Predictions of the subsoil deformation, the critical height of fill and the corre¬ sponding slip surface are made and subsequently compared to the field measure¬ ments. It is of importance to realize that all the predictions were made prior to the actual failure of the embankment. The comparison with measurements was possible only after the International Symposium on Trial Embankments on Malaysian Ma¬ rine Clays, was held in Kuala Lumpur, Malaysia, in November 1989, during which the field data were made available to the invited predictors (including the second writer) by the Malaysian Highway Authority. Finite-element codes based on the modified Cam-clay theory (CRISP) and hyperbolic stress-strain model (ISBILD) were utilized to investigate the behavior of the embankment and the foundation soil until failure. The type of numerical modeling includes purely undrained, fully drained. and a coupled consolidation analysis. The finite-element solutions are subsequently compared with the conventional stability analysis.
Expansion of the rail network in congested coastal Australia compels track construction on soft c... more Expansion of the rail network in congested coastal Australia compels track construction on soft clayey subgrade, including fine-grained estuarine soils. In such low-lying areas, where the water table is close to the ground surface, the saturated soft subgrade is often subjected to pumping (mud slurry) under the application of cyclic wheel loads, thereby causing fouling of the overlying ballast. This technical note presents the results of a series of large-scale, drained, cyclic, triaxial tests conducted on clay-fouled ballast. The impact of fouling on the stress-strain behaviour, resilient modulus and degradation of ballast is discussed.
Uploads
Papers by Buddhima Indraratna
In this lecture the interpretations of fully instrumented tests embankments and their role in the development of appropriate ground improvement techniques for highways, motorways and airfields on soft clay deposits is illustrated through well documented case studies in Bangkok, Thailand and Muar Flat Site in Kuala Lumpur. For the Bangkok Plain and with sand backfills the perform- ance of embankments with different schemes of vertical drains was evaluated over a period of 25 years. Aspects such as recharging ef- fects due to the drains, inadequate measures in maintaining vacuum during vacuum applications and possible hydraulic connections with large diameter drains are discussed. For the Muar test embankments, the role of fill strength in residual soil embankment and the field deformation analysis in separating consolidation settlement from immediate settlement and creep settlements is presented. Novel interpretations of settlement from pore pressure dissipations, secondary settlement from field measurements and decay of lateral de- formation rate with time were also made.
In this lecture the interpretations of fully instrumented tests embankments and their role in the development of appropriate ground improvement techniques for highways, motorways and airfields on soft clay deposits is illustrated through well documented case studies in Bangkok, Thailand and Muar Flat Site in Kuala Lumpur. For the Bangkok Plain and with sand backfills the perform- ance of embankments with different schemes of vertical drains was evaluated over a period of 25 years. Aspects such as recharging ef- fects due to the drains, inadequate measures in maintaining vacuum during vacuum applications and possible hydraulic connections with large diameter drains are discussed. For the Muar test embankments, the role of fill strength in residual soil embankment and the field deformation analysis in separating consolidation settlement from immediate settlement and creep settlements is presented. Novel interpretations of settlement from pore pressure dissipations, secondary settlement from field measurements and decay of lateral de- formation rate with time were also made.