This paper aims at presenting a numerical study of the behaviour of Tunis soft soil improved by v... more This paper aims at presenting a numerical study of the behaviour of Tunis soft soil improved by vacuum consolidation combined with geodrains. An experimental investigation was carried out on reconstituted samples of Tunis soft soil (TSS) initially extracted from the centre of Tunis city at 35 m of depth. Three consolidation tests were carried out in a cell of 126mm inner diameter and 290-mm height, the first one included a consolidation test by preload stress (q = 100 kPa). In the second test, vacuum consolidation tests (p v =100 kPa) were performed. The third test comprised a vacuum consolidation test combined with the preload (p v =50 kPa and q = 50 kPa). Simulation of those tests by the finite-element PLAXIS-2D code was implemented in axisymmetric conditions. Soft soil model was used to describe the behavior of Tunis soft soil (TSS). During this simulation, a parametric study was performed by varying the horizontal permeability k h of TSS. Then, by comparing the numerical results to the recorded data in laboratory, it has been verified that the numerical predicted settlements are higher than those measured during the performed laboratory tests. Further, numerical results confirmed that when the coefficient k h increases, the consolidation is complete in a shorter time. This work highlighted the usefulness of combining the vacuum pressure and geodrains improvement techniques to improve the behaviour of Tunis soft soil.
The present paper studies the use of stone columns as a means of mitigating liquefaction potentia... more The present paper studies the use of stone columns as a means of mitigating liquefaction potential. A numerical model using the 2D finite difference code FLAC is developed and validated with published experimental results from literature to simulate the shaking table test. The liquefaction potential of silty sand layer that was improved with stone columns was evaluated in terms of the maximum pore water pressure ratio \( r_{u} \) which is usually defined as the ratio of pore water pressure to the initial vertical effective stress in the soil. Soil liquefaction potential has often been defined when \( r_{u} \) reaches 1.0. Numerical analyses showed that the liquefaction potential decreased after stone columns reinforcement. Parametric analyses were performed to investigate the effect of the excitation frequency and amplitude and the effect of stone columns installation process on liquefaction potential.
As a ground improvement technique, the new method composed by a cylindrical cavity expansion (CCE... more As a ground improvement technique, the new method composed by a cylindrical cavity expansion (CCE) combined with vertical drains (VD) greatly accelerates the consolidation of soft soil. In fact, the cylindrical cavity applies a radial displacement in the soil. Excess pore pressures will be consequently generated and the consolidation process will occur at the vicinity of the cavity wall. The dissipation of excess pore pressures can be enhanced in presence of VD installed at a radial distance rd from the center of the cylindrical cavity. Because of CCE installations in soft soil, surrounding soil properties are altered in such a manner that horizontal permeability of the soil in the smear zone reduces. The purpose of the present paper is to investigate the subsequent consolidation around CCE using the Finite Difference Method (FDM) by taking into account the CCE installation disturbance. Parametric analysis aimed to investigate the effect of the extent of the disturbed zone, the soil...
Studying the stability of slopes is of great interest since it is associated to various geotechni... more Studying the stability of slopes is of great interest since it is associated to various geotechnical applications, e.g., access embankments and landslide mitigation. This paper describes the research conducted to determine the failure load applied at the top of excavations in sandy soils during the construction of deep digs without the use of retaining systems. An experimental program was performed to measure the failure load of ten laboratory-compacted sand slope models that were constructed using different slope angle values and different locations for the applied loading, which consisted of an imposed uniform rate of vertical displacement at the top of the slope. Then, a three-dimensional (3D) numerical model of the laboratory tests was developed to simulate the observed behavior during the experiments by the Plaxis 3D code. The Mohr–Coulomb (MC) and hardening soil (HS) models were used to describe the behavior of the compacted sand. The results showed that the 3D numerical simul...
Recent Advances in Geo-Environmental Engineering, Geomechanics and Geotechnics, and Geohazards, 2018
Landslide hazard is often seen in the boundary of loess platforms in northwest China. There are m... more Landslide hazard is often seen in the boundary of loess platforms in northwest China. There are more than 60 loess landslides recorded in Jingyang platform in the past five decades. Two types of the loess landslide, which are flowslide and slide, have been categorized. In this study, a statistical analysis to characterize the loess landslides was conducted. Additionally, a series of constant shear drained (CSD) triaxial tests were undertaken to reveal the triggering mechanism of the loess landslides. The irrigation-water infiltration and sequence and rule of loess landslide play a crucial role in triggering the loess landslides. These results provide the insights into the countermeasures recommended to resist the loess landslide hazard, thereby reduce the potential of loess landslide in the future.
The purpose of this paper is to experimentally investigate the consolidation of the reconstituted... more The purpose of this paper is to experimentally investigate the consolidation of the reconstituted Tunis soft soil ‘TSS’ improved by Prefabricated Vertical Drains PVD. After geotechnical characterization, a consolidation test with vertical loading is performed on a mutli-drains cell, i.e. cell with soil improved by three drains installed in triangular pattern. The PVD used in this study is the Mebradrain 88 (Mb88) type which is commonly used in previous soil improvement projects in Tunisia. The test is conducted through a specific laboratory test apparatus “consolidometer”. The settlements of soft soil specimen were measured during the consolidation test. Soil samples were extracted from different positions to measure water content ω variation after consolidation test. Results show that a significant water content reduction is observed after consolidation tests (approximately 64%) mainly at the vicinity of the PVD. Finally, the assessment of consolidation settlement was investigated ...
The purpose of this paper is to investigate the acceleration of consolidation through a new metho... more The purpose of this paper is to investigate the acceleration of consolidation through a new method composed by a cylindrical cavity expansion (CCE) combined with vertical drains (VD). In fact, the cylindrical cavity applies a radial displacement in the soil. Excess pore pressures will be consequently generated and the consolidation process will occur at the vicinity of the cavity wall. The dissipation of excess pore pressures can be enhanced in presence of VD installed at a radial distance r d from the center of the cylindrical cavity. During cavity expansion, the variation of excess pore pressures and incremental stresses are analyzed. The subsequent consolidation around the CCE in the presence of VD is solved using the Finite Difference Method (FDM) with taking into account the effect of the CCE installation. This effect is described by a decrease in horizontal permeability within a disturbed zone. Obtained results show that the proposed system of consolidation i.e., composed by a CCE combined with VD, greatly accelerates the consolidation of soil. Furthermore, the effects of the extent of the disturbed zone and the soil permeability reduction have a significant influence on the consolidation of the soil. The application of the proposed method to the case of "Tunis Rades La Goulette Bridge" is presented and discussed.
Soil Testing, Soil Stability and Ground Improvement, 2017
The pressuremeter test is an in situ controlled load-deformation test that is performed on the wa... more The pressuremeter test is an in situ controlled load-deformation test that is performed on the wall of a borehole using a radially expanded cylindrical probe. From the test readings (volume variation based on controlled pressure), a plane deformation stress-strain curve can be obtained for the soil. Since the initial prototype, the pressuremeter has consistently been improved in its design, and the latest version of the pressuremeter, which is called the "auto-controlled Pressuremeter" has been developed to address the issues of repeatability and accumulation of approximations in a test. This apparatus is fully automatic and autonomous, and manages all steps of the test as instructed by the operator. The auto-controlled Pressuremeter simplifies the work procedure for the operator, reinforces the reliability of the results, and reduces the time of set up. The present paper describes the auto-controlled pressuremeter, and compares it with the manual pressuremeter. The first part of the paper compares the deficiencies of the manual and auto-controlled Pressuremeter. In the second part, test results of the two types of pressuremeter that have been performed in similar conditions are presented and commented.
The purpose of this paper is to investigate the acceleration of consolidation through a new metho... more The purpose of this paper is to investigate the acceleration of consolidation through a new method composed by a cylindrical cavity expansion (CCE) combined with vertical drains (VD). In fact, the cylindrical cavity applies a radial displacement in the soil. Excess pore pressures will be consequently generated and the consolidation process will occur at the vicinity of the cavity wall. The dissipation of excess pore pressures can be enhanced in presence of VD installed at a radial distance r d from the center of the cylindrical cavity. During cavity expansion, the variation of excess pore pressures and incremental stresses are analyzed. The subsequent consolidation around the CCE in the presence of VD is solved using the Finite Difference Method (FDM) with taking into account the effect of the CCE installation. This effect is described by a decrease in horizontal permeability within a disturbed zone. Obtained results show that the proposed system of consolidation i.e., composed by a CCE combined with VD, greatly accelerates the consolidation of soil. Furthermore, the effects of the extent of the disturbed zone and the soil permeability reduction have a significant influence on the consolidation of the soil. The application of the proposed method to the case of "Tunis Rades La Goulette Bridge" is presented and discussed.
An experimental investigation was carried out on the reconstituted Tunis soft soil that was extra... more An experimental investigation was carried out on the reconstituted Tunis soft soil that was extracted from the center of Tunis City at 35 m depth. A specific laboratory test apparatus was designed and manufactured to perform three consolidation series of tests by applying a negative pressure, a preload or a vacuum pressure combined with preload. Excess pore pressure and settlement were measured during the consolidation process. Experimental results showed that for the same magnitude of preload and the vacuum pressure of 4 kPa, 8 kPa and 16 kPa and 30 kPa, the settlement caused by the vacuum pressure is lower than that generated by the preload. While the settlement generated by preloads of 60 kPa and 100 kPa are slightly smaller than those caused by the vacuum consolidation of 60 kPa and 100 kPa. Recorded excess pore pressure around the geodrain dissipated more quickly compared to excess pore pressure close to cell border. The normalized excess pore pressure for preload decreases when the applied preload increases and then increases quasi-linearly with the increase of horizontal distance between transducers to geodrain. While, the normalized excess pore pressure for vacuum pressure increases with the increase of the applied negative pressure and decreases with the increase of horizontal distance between transducers and the geodrain.
This paper presents an experimental study carried out on undisturbed cored samples of Tunis soft ... more This paper presents an experimental study carried out on undisturbed cored samples of Tunis soft soil extracted at 17.25 m depth at the lagoon of Sejoumi. Three series of oedometer tests were performed: the first one was a standard test on Tunis soft soil, the second one was performed on the same soil improved by a prefabricated vertical drain Mebradrain 88 (Mb88) type during which vertical drainage was prevented. The third series comprised similar tests to those of series two, during which horizontal and vertical drainage were allowed. The assessment of Carillo's theory was studied by quantifying the effect of radial and vertical consolidation from the observed global degree of consolidation of improved Tunis soft soil specimens by geodrains. The rate in decrease of coefficients cr and kr was greater than that recorded for coefficients cv and kr, respectively. Using the Carillo's theory, a lower degree of consolidation which starts from 10 % is obtained; however, when using simple approximate methods by considering recorded measures from series 3, higher degrees of consolidation starting from 70 % were obtained.
AbstractDuring many earthquakes, soil liquefaction causes dramatic damage. The use of a granular ... more AbstractDuring many earthquakes, soil liquefaction causes dramatic damage. The use of a granular column is a ground-improvement technique used to mitigate soil liquefaction. The present paper studies the performance of reinforcement with granular columns as a method for mitigation of potential risk of liquefaction during cyclic loading. The generation and dissipation of excess pore pressure are analyzed by considering the granular-column installation effect. This effect is described by a decrease in horizontal permeability within a disturbed zone around the column, which is described by constant, linear, and parabolic variations. The evolution of excess pore pressure is studied as a function of the disturbed zone in terms of reduced horizontal permeability. Obtained results show that a granular-column installation has a significant influence on the mitigation of liquefaction.
The ultimate bearing capacity of an isolated stone column is studied. The soil surrounding the co... more The ultimate bearing capacity of an isolated stone column is studied. The soil surrounding the column is modeled by a constitutive law of plastic potential with variable flow. This recent model permits the calculation of the limit pressure of an expanded cylindrical cavity from which ...
An experimental investigation has been conducted to study the mechanical properties of remolded T... more An experimental investigation has been conducted to study the mechanical properties of remolded Tunis soft soil reinforced by a group of sand columns. The tested soft soil, extracted from the city center of Tunis at a depth of 15 m, has poor mechanical properties, and its moisturesensitivity is very important. Specimens were initially slurry mixed at 1.5 times their liquid limit. They were then remolded at an initial K 0 consolidation path up to a vertical stress of 140 kPa. The holes, initially made in the specimens, were afterwards filled with standard sand which simulated the reinforcing column material. All the reinforced soil specimens were then subjected to consolidated undrained triaxial shear tests with measured excess pore-pressure (CU þu). Three confining pressures of 100, 200, and 300 kPa were applied during the consolidation phase. In addition to the unreinforced control specimen, three different types of reinforced specimens were used, namely, reinforced specimens with a single column, three columns, and four columns. All the reinforced specimens had the same area replacement ratio. The test results have shown that the number of reinforcing columns has a significant effect on the mechanical characteristics of the reinforced soft soil.
Theoretical and experimental studies have shown that stone columns can be used for accelerating t... more Theoretical and experimental studies have shown that stone columns can be used for accelerating the consolidation rate of soft soils by providing a drainage path, reducing foundation settlements, improving the bearing capacity of the soil, and limiting the risk of liquefaction due to seismic activity. This paper studies the influence of the main controlling parameters in the design of stone columns through a series of laboratory experiments. The effects of (a) the drainage conditions, (b) the grain size of the stone column material, (c) the confining pressure of the soil, and (d) the rate of deformation are investigated. Triaxial compression tests are performed on composite soil specimens of soft kaolin clay, reconstituted from a slurry with a central compacted reinforcement column. Two cases of reinforcement material are studied: sand and gravel. The behaviour of the reinforced soil compared with that of the unreinforced soil under the same loading and drainage conditions is analys...
This paper aims at presenting a numerical study of the behaviour of Tunis soft soil improved by v... more This paper aims at presenting a numerical study of the behaviour of Tunis soft soil improved by vacuum consolidation combined with geodrains. An experimental investigation was carried out on reconstituted samples of Tunis soft soil (TSS) initially extracted from the centre of Tunis city at 35 m of depth. Three consolidation tests were carried out in a cell of 126mm inner diameter and 290-mm height, the first one included a consolidation test by preload stress (q = 100 kPa). In the second test, vacuum consolidation tests (p v =100 kPa) were performed. The third test comprised a vacuum consolidation test combined with the preload (p v =50 kPa and q = 50 kPa). Simulation of those tests by the finite-element PLAXIS-2D code was implemented in axisymmetric conditions. Soft soil model was used to describe the behavior of Tunis soft soil (TSS). During this simulation, a parametric study was performed by varying the horizontal permeability k h of TSS. Then, by comparing the numerical results to the recorded data in laboratory, it has been verified that the numerical predicted settlements are higher than those measured during the performed laboratory tests. Further, numerical results confirmed that when the coefficient k h increases, the consolidation is complete in a shorter time. This work highlighted the usefulness of combining the vacuum pressure and geodrains improvement techniques to improve the behaviour of Tunis soft soil.
The present paper studies the use of stone columns as a means of mitigating liquefaction potentia... more The present paper studies the use of stone columns as a means of mitigating liquefaction potential. A numerical model using the 2D finite difference code FLAC is developed and validated with published experimental results from literature to simulate the shaking table test. The liquefaction potential of silty sand layer that was improved with stone columns was evaluated in terms of the maximum pore water pressure ratio \( r_{u} \) which is usually defined as the ratio of pore water pressure to the initial vertical effective stress in the soil. Soil liquefaction potential has often been defined when \( r_{u} \) reaches 1.0. Numerical analyses showed that the liquefaction potential decreased after stone columns reinforcement. Parametric analyses were performed to investigate the effect of the excitation frequency and amplitude and the effect of stone columns installation process on liquefaction potential.
As a ground improvement technique, the new method composed by a cylindrical cavity expansion (CCE... more As a ground improvement technique, the new method composed by a cylindrical cavity expansion (CCE) combined with vertical drains (VD) greatly accelerates the consolidation of soft soil. In fact, the cylindrical cavity applies a radial displacement in the soil. Excess pore pressures will be consequently generated and the consolidation process will occur at the vicinity of the cavity wall. The dissipation of excess pore pressures can be enhanced in presence of VD installed at a radial distance rd from the center of the cylindrical cavity. Because of CCE installations in soft soil, surrounding soil properties are altered in such a manner that horizontal permeability of the soil in the smear zone reduces. The purpose of the present paper is to investigate the subsequent consolidation around CCE using the Finite Difference Method (FDM) by taking into account the CCE installation disturbance. Parametric analysis aimed to investigate the effect of the extent of the disturbed zone, the soil...
Studying the stability of slopes is of great interest since it is associated to various geotechni... more Studying the stability of slopes is of great interest since it is associated to various geotechnical applications, e.g., access embankments and landslide mitigation. This paper describes the research conducted to determine the failure load applied at the top of excavations in sandy soils during the construction of deep digs without the use of retaining systems. An experimental program was performed to measure the failure load of ten laboratory-compacted sand slope models that were constructed using different slope angle values and different locations for the applied loading, which consisted of an imposed uniform rate of vertical displacement at the top of the slope. Then, a three-dimensional (3D) numerical model of the laboratory tests was developed to simulate the observed behavior during the experiments by the Plaxis 3D code. The Mohr–Coulomb (MC) and hardening soil (HS) models were used to describe the behavior of the compacted sand. The results showed that the 3D numerical simul...
Recent Advances in Geo-Environmental Engineering, Geomechanics and Geotechnics, and Geohazards, 2018
Landslide hazard is often seen in the boundary of loess platforms in northwest China. There are m... more Landslide hazard is often seen in the boundary of loess platforms in northwest China. There are more than 60 loess landslides recorded in Jingyang platform in the past five decades. Two types of the loess landslide, which are flowslide and slide, have been categorized. In this study, a statistical analysis to characterize the loess landslides was conducted. Additionally, a series of constant shear drained (CSD) triaxial tests were undertaken to reveal the triggering mechanism of the loess landslides. The irrigation-water infiltration and sequence and rule of loess landslide play a crucial role in triggering the loess landslides. These results provide the insights into the countermeasures recommended to resist the loess landslide hazard, thereby reduce the potential of loess landslide in the future.
The purpose of this paper is to experimentally investigate the consolidation of the reconstituted... more The purpose of this paper is to experimentally investigate the consolidation of the reconstituted Tunis soft soil ‘TSS’ improved by Prefabricated Vertical Drains PVD. After geotechnical characterization, a consolidation test with vertical loading is performed on a mutli-drains cell, i.e. cell with soil improved by three drains installed in triangular pattern. The PVD used in this study is the Mebradrain 88 (Mb88) type which is commonly used in previous soil improvement projects in Tunisia. The test is conducted through a specific laboratory test apparatus “consolidometer”. The settlements of soft soil specimen were measured during the consolidation test. Soil samples were extracted from different positions to measure water content ω variation after consolidation test. Results show that a significant water content reduction is observed after consolidation tests (approximately 64%) mainly at the vicinity of the PVD. Finally, the assessment of consolidation settlement was investigated ...
The purpose of this paper is to investigate the acceleration of consolidation through a new metho... more The purpose of this paper is to investigate the acceleration of consolidation through a new method composed by a cylindrical cavity expansion (CCE) combined with vertical drains (VD). In fact, the cylindrical cavity applies a radial displacement in the soil. Excess pore pressures will be consequently generated and the consolidation process will occur at the vicinity of the cavity wall. The dissipation of excess pore pressures can be enhanced in presence of VD installed at a radial distance r d from the center of the cylindrical cavity. During cavity expansion, the variation of excess pore pressures and incremental stresses are analyzed. The subsequent consolidation around the CCE in the presence of VD is solved using the Finite Difference Method (FDM) with taking into account the effect of the CCE installation. This effect is described by a decrease in horizontal permeability within a disturbed zone. Obtained results show that the proposed system of consolidation i.e., composed by a CCE combined with VD, greatly accelerates the consolidation of soil. Furthermore, the effects of the extent of the disturbed zone and the soil permeability reduction have a significant influence on the consolidation of the soil. The application of the proposed method to the case of "Tunis Rades La Goulette Bridge" is presented and discussed.
Soil Testing, Soil Stability and Ground Improvement, 2017
The pressuremeter test is an in situ controlled load-deformation test that is performed on the wa... more The pressuremeter test is an in situ controlled load-deformation test that is performed on the wall of a borehole using a radially expanded cylindrical probe. From the test readings (volume variation based on controlled pressure), a plane deformation stress-strain curve can be obtained for the soil. Since the initial prototype, the pressuremeter has consistently been improved in its design, and the latest version of the pressuremeter, which is called the "auto-controlled Pressuremeter" has been developed to address the issues of repeatability and accumulation of approximations in a test. This apparatus is fully automatic and autonomous, and manages all steps of the test as instructed by the operator. The auto-controlled Pressuremeter simplifies the work procedure for the operator, reinforces the reliability of the results, and reduces the time of set up. The present paper describes the auto-controlled pressuremeter, and compares it with the manual pressuremeter. The first part of the paper compares the deficiencies of the manual and auto-controlled Pressuremeter. In the second part, test results of the two types of pressuremeter that have been performed in similar conditions are presented and commented.
The purpose of this paper is to investigate the acceleration of consolidation through a new metho... more The purpose of this paper is to investigate the acceleration of consolidation through a new method composed by a cylindrical cavity expansion (CCE) combined with vertical drains (VD). In fact, the cylindrical cavity applies a radial displacement in the soil. Excess pore pressures will be consequently generated and the consolidation process will occur at the vicinity of the cavity wall. The dissipation of excess pore pressures can be enhanced in presence of VD installed at a radial distance r d from the center of the cylindrical cavity. During cavity expansion, the variation of excess pore pressures and incremental stresses are analyzed. The subsequent consolidation around the CCE in the presence of VD is solved using the Finite Difference Method (FDM) with taking into account the effect of the CCE installation. This effect is described by a decrease in horizontal permeability within a disturbed zone. Obtained results show that the proposed system of consolidation i.e., composed by a CCE combined with VD, greatly accelerates the consolidation of soil. Furthermore, the effects of the extent of the disturbed zone and the soil permeability reduction have a significant influence on the consolidation of the soil. The application of the proposed method to the case of "Tunis Rades La Goulette Bridge" is presented and discussed.
An experimental investigation was carried out on the reconstituted Tunis soft soil that was extra... more An experimental investigation was carried out on the reconstituted Tunis soft soil that was extracted from the center of Tunis City at 35 m depth. A specific laboratory test apparatus was designed and manufactured to perform three consolidation series of tests by applying a negative pressure, a preload or a vacuum pressure combined with preload. Excess pore pressure and settlement were measured during the consolidation process. Experimental results showed that for the same magnitude of preload and the vacuum pressure of 4 kPa, 8 kPa and 16 kPa and 30 kPa, the settlement caused by the vacuum pressure is lower than that generated by the preload. While the settlement generated by preloads of 60 kPa and 100 kPa are slightly smaller than those caused by the vacuum consolidation of 60 kPa and 100 kPa. Recorded excess pore pressure around the geodrain dissipated more quickly compared to excess pore pressure close to cell border. The normalized excess pore pressure for preload decreases when the applied preload increases and then increases quasi-linearly with the increase of horizontal distance between transducers to geodrain. While, the normalized excess pore pressure for vacuum pressure increases with the increase of the applied negative pressure and decreases with the increase of horizontal distance between transducers and the geodrain.
This paper presents an experimental study carried out on undisturbed cored samples of Tunis soft ... more This paper presents an experimental study carried out on undisturbed cored samples of Tunis soft soil extracted at 17.25 m depth at the lagoon of Sejoumi. Three series of oedometer tests were performed: the first one was a standard test on Tunis soft soil, the second one was performed on the same soil improved by a prefabricated vertical drain Mebradrain 88 (Mb88) type during which vertical drainage was prevented. The third series comprised similar tests to those of series two, during which horizontal and vertical drainage were allowed. The assessment of Carillo's theory was studied by quantifying the effect of radial and vertical consolidation from the observed global degree of consolidation of improved Tunis soft soil specimens by geodrains. The rate in decrease of coefficients cr and kr was greater than that recorded for coefficients cv and kr, respectively. Using the Carillo's theory, a lower degree of consolidation which starts from 10 % is obtained; however, when using simple approximate methods by considering recorded measures from series 3, higher degrees of consolidation starting from 70 % were obtained.
AbstractDuring many earthquakes, soil liquefaction causes dramatic damage. The use of a granular ... more AbstractDuring many earthquakes, soil liquefaction causes dramatic damage. The use of a granular column is a ground-improvement technique used to mitigate soil liquefaction. The present paper studies the performance of reinforcement with granular columns as a method for mitigation of potential risk of liquefaction during cyclic loading. The generation and dissipation of excess pore pressure are analyzed by considering the granular-column installation effect. This effect is described by a decrease in horizontal permeability within a disturbed zone around the column, which is described by constant, linear, and parabolic variations. The evolution of excess pore pressure is studied as a function of the disturbed zone in terms of reduced horizontal permeability. Obtained results show that a granular-column installation has a significant influence on the mitigation of liquefaction.
The ultimate bearing capacity of an isolated stone column is studied. The soil surrounding the co... more The ultimate bearing capacity of an isolated stone column is studied. The soil surrounding the column is modeled by a constitutive law of plastic potential with variable flow. This recent model permits the calculation of the limit pressure of an expanded cylindrical cavity from which ...
An experimental investigation has been conducted to study the mechanical properties of remolded T... more An experimental investigation has been conducted to study the mechanical properties of remolded Tunis soft soil reinforced by a group of sand columns. The tested soft soil, extracted from the city center of Tunis at a depth of 15 m, has poor mechanical properties, and its moisturesensitivity is very important. Specimens were initially slurry mixed at 1.5 times their liquid limit. They were then remolded at an initial K 0 consolidation path up to a vertical stress of 140 kPa. The holes, initially made in the specimens, were afterwards filled with standard sand which simulated the reinforcing column material. All the reinforced soil specimens were then subjected to consolidated undrained triaxial shear tests with measured excess pore-pressure (CU þu). Three confining pressures of 100, 200, and 300 kPa were applied during the consolidation phase. In addition to the unreinforced control specimen, three different types of reinforced specimens were used, namely, reinforced specimens with a single column, three columns, and four columns. All the reinforced specimens had the same area replacement ratio. The test results have shown that the number of reinforcing columns has a significant effect on the mechanical characteristics of the reinforced soft soil.
Theoretical and experimental studies have shown that stone columns can be used for accelerating t... more Theoretical and experimental studies have shown that stone columns can be used for accelerating the consolidation rate of soft soils by providing a drainage path, reducing foundation settlements, improving the bearing capacity of the soil, and limiting the risk of liquefaction due to seismic activity. This paper studies the influence of the main controlling parameters in the design of stone columns through a series of laboratory experiments. The effects of (a) the drainage conditions, (b) the grain size of the stone column material, (c) the confining pressure of the soil, and (d) the rate of deformation are investigated. Triaxial compression tests are performed on composite soil specimens of soft kaolin clay, reconstituted from a slurry with a central compacted reinforcement column. Two cases of reinforcement material are studied: sand and gravel. The behaviour of the reinforced soil compared with that of the unreinforced soil under the same loading and drainage conditions is analys...
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