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Buddhima Indraratna - One of the best experts on this subject based on the ideXlab platform.
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Analytical model for vacuum consolidation incorporating soil disturbance caused by mandrel-driven Drains
Canadian Geotechnical Journal, 2017Co-Authors: Darshana Perera, Buddhima Indraratna, Cholachat Rujikiatkamjorn, Serge Leroueil, Richard KellyAbstract:When vacuum preloading is applied with vertical Drains, the rate of consolidation can be increased, and the stability of an embankment is enhanced due to the inward lateral movement. The aim of this study is to develop an analytical solution for vacuum preloading that accurately captures the more realistic variations in compressibility and permeability in actual ground conditions as a result of Drain Installation. The soil samples were obtained from various locations after Drain Installation to determine the characteristics of soil surrounding the vertical Drain in terms of compressibility and permeability. The main differences between the proposed and conventional models are described by considering the stress history and preloading pressure. The effect of pre-consolidation pressure and the magnitude of applied preloading are examined through the dissipation of average excess pore pressure and associated settlement. The analysis of a selected case history employing the writers’ solution indicates improve...
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Characterization of smear zone caused by mandrel action
IFCEE 2015, 2015Co-Authors: Buddhima Indraratna, Cholachat Rujikiatkmajorn, Made ArdanaAbstract:In this study the smear zone due to vertical Drain Installation is studied using a large, in-situ sample to capture the realistic characteristics of the smear zone in relation to the in-situ soil structure. The smear zone extent for Bulli clay (New South Wales, Australia) is quantified on the basis of normalised permeability and the reduction in the water content prior to consolidation. The permeability and compressibility of the soil are used to determine the extent to which the soil surrounding the PVD had become disturbed. In laboratory testing, the soil consolidation behaviour due to a prefabricated vertical Drain (PVD) is studied using a large scale consolidometer apparatus.
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Soil disturbance analysis due to vertical Drain Installation
Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 2015Co-Authors: Buddhima Indraratna, Darshana Perera, Cholachat Rujikiatkamjorn, Richard KellyAbstract:The Installation of Drains creates a disturbed region known as a smear zone where the change in the clay structure affects the horizontal permeability and compressibility. The parameters required to characterise the smear effect are the extent of the smear zone and the ratio of the horizontal coefficient of permeability in the undisturbed zone and in the smear zone. Only limited studies have been carried out on different aspects of soil disturbance due to driving vertical Drains and its effects on the subsequent consolidation. In this paper the disturbed zone around a rectangular mandrel was characterised using soil samples obtained from the soft clay layer at various locations beneath an embankment built at Ballina, Australia, where vertical Drains were installed. By determining the change in the coefficient of permeability, the water content and volume compressibility across the smear zone, the effects of soil disturbance on consolidation due to the Installation of Drains can be quantified using the ava...
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Briefing: Effect of Drain Installation patterns on rate of consolidation
Proceedings of the Institution of Civil Engineers - Ground Improvement, 2015Co-Authors: Cholachat Rujikiatkamjorn, Buddhima IndraratnaAbstract:Prefabricated vertical Drains (PVDs) are employed to accelerate consolidation by decreasing the Drainage path length. In the present study, using analytical solutions, an attempt was made to evaluate and quantify the effectiveness of two non-conventional PVD Installation patterns, involving a parallel Drain wall compared with a circular Drain ring pattern, in contrast to conventional PVD Installation (square or triangular patterns). The governing equations are based on the equal strain theory including the smear effect, and they provide a relative comparison between the two newly proposed Installation patterns and the conventional square PVD grid, in terms of both the consolidation time and the equivalent Drain spacing. The comparisons between the new and conventional Installation patterns are made based on a single Drain analysis and the density of PVDs per unit area.
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Mathematical Modeling and Field Evaluation of Embankment Stabilized with Vertical Drains Incorporating Vacuum Preloading
2004Co-Authors: Buddhima Indraratna, Cholachat RujikiatkamjornAbstract:This study presents the analytical modeling of vertical Drains incorporating vacuum preloading in both axisymmetric and plane strain conditions. The effectiveness of vacuum pressure (i.e. both constant vacuum pressure and varied vacuum pressure) applied along the Drain is considered. A multiDrain plane strain model is employed to analyse an embankment at the site of Second Bangkok International Airport (SBIA) stabilised with prefabricated vertical Drains. At this site, a significantly reduced height of sand surcharge was applied by reducing the pore pressures through vacuum preloading. The results of FEM analysis confirm the efficiency of vacuum preloading in comparison with the conventional method of surcharge alone. INTRODUCTION In this study, analytical solutions for a single Drain incorporating vacuum preloading in both axisymmetric and plane strain conditions are introduced. In order to compare the efficiency of vacuum preloading, various possible distribution patterns of vacuum pressure via the vertical Drain system are discussed. Finally, the equivalent plane strain model in conjunction with the modified Cam-Clay theory is applied to 2 embankments at the Second Bangkok International Airport (SBIA). In recent years, prefabricated band Drains have been used widely for soft ground improvement. Radial Drainage accelerates soft soil consolidation. Baron (1948) and Hansbo (1981) introduced the unit cell theory for axisymmetric and plane strain conditions. Subsequently, the unit cell theory was extended by including a smear zone, which occurs when surrounding soil is remoulded during the vertical Drain Installation (Hird et al., 1992). Due to the increasing popularity of plane strain finite element analysis, Indraratna and Redana (1997) extended the equivalent unit cell theory to convert the axisymmetric parameters such as permeability into equivalent plane strain parameters. As a result, the plane strain finite element analyses have been used extensively to predict the behaviour of embankments improved by prefabricated vertical Drains (e.g. Indraratna and Redana, 2000). ANALYTICAL SOLUTIONS FOR VERTICAL Drain INCORPORATING VACUUM PRELOADING AND SMEAR EFFECTS In this section, the analytical solutions of unit cell for axisymmetric and plane strain conditions are revised from the original theory developed by Hird et al. (1992) and Indraratna and Redana (1997). Figures 1a and 1b illustrate the unit cell adopted for the axisymmetric and plane strain conditions, respectively. The efficiency of vacuum preloading is taken into account by dividing the distribution pattern of vacuum pressure into 4 distinct categories (Fig. 2): In order to increase the rate of consolidation, Kjellman (1952) introduced the concept of vacuum preloading to improve the soil strength. Recently, the system of vertical Drains enhanced by incorporating vacuum preloading has been applied in land reclamation projects (Shang et al., 1998, Chu, et al., 2000). Mohamedelhassan and Shang (2002) discussed the application of vacuum pressure and its benefits, but without any prefabricated vertical Drains (PVD). The benefits of this method include accelerating consolidation by increasing the hydraulic gradient and reducing the height of the embankment to achieve the same degree of consolidation. Case A: Vacuum pressure is constant along the Drain and across the soil element. Case B: Vacuum pressure is constant along the Drain while it varies linearly to zero across the soil element. This represents a large Drain spacing but relatively short Drain lengths. Paper No. 2.05 Page 1 Case C: Vacuum pressure varies linearly along the Drain while remaining constant across the soil element. This represents close Drain spacing and relatively long PVDs. Case D: ( )( ) ( ) ( ) ( )( ) ( ) , 0 , 0 ( , ) , , v ax w v ps w u r z p R r l z l R r u x z p B x l z l B b = − − − = − − − (1d) Case D: Vacuum pressure varies linearly along the Drain and across the soil element. This represents large Drain spacing and lengthy Drains. where, = vacuum pressure at radius and depth , = applied vacuum pressure at the top of the Drain, = radius of Drain well, l = length of Drain, u = vacuum pressure at distance , ( , ) v ax u r z r z 0 p w r ) x z , ( , v ps x and depth , and b = width of Drain well. Subscripts and z w ax ps denotes axisymmetric and plane strain condition, respectively. Smear boundary bw bs B rw rs R (a) Axisymmetric (b) Plane strain SOLUTIONS FOR AXISYMMETRIC CONDITION Fig. 1. The unit cell adopted for analytical solution In this section, for fully saturated soil, the solution for vertical Drain incorporating vacuum preloading and smear effects based on Hansbo’s solution (1981) is illustrated. The corresponding expressions for the average excess pore pressure, u , at any time factor, Th, ax are given by: CL Drain interface Soil element -p0 -p0 CL -p0 -p0 Case A: Case A Case B ( ) { } ( ) 1 0, 1 , 0, 1 1 exp 8 ax h ax ax ax u p T p σ σ μ = + − − σ (2a) C L -p0(l-z)/l Soil element -p0 C L -p0(l-z)/l -p0 Case B: ( ) { } ( ) 1 0, 1 , 0, 1 1 ( ) exp 8 ( ) ax h ax ax ax u p G n T p G n σ σ σ = + − − μ (2b) Case C: Drain interface ( ) { } ( ) 1 0, 1 , 0, 1 1 2 exp 8 2 ax h ax ax ax u p T p σ σ σ = + − − μ (2c) Case C Case D Fig. 2. The distribution patterns of vacuum pressure in the horizontal and vertical directions Case D: ( ) { } ( ) 1 0, 1 , 0, 1 1 ( ) 2 exp 8 ( ) 2 ax h ax ax ax u p G n T p G n σ σ σ = + − − μ (2d) Based on the above distributions (Fig. 2), the equations for vacuum pressure at a given point in a unit cell can be given by: where, Case A: ( ) ( ) ( ) ( ) ( )( ) ( ) { } ( ) ( ) ( ) ( ) 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 1 3 4 4 1 1 1 4 1 ax ax h,ax h ,ax s w w
Cholachat Rujikiatkamjorn - One of the best experts on this subject based on the ideXlab platform.
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Analytical model for vacuum consolidation incorporating soil disturbance caused by mandrel-driven Drains
Canadian Geotechnical Journal, 2017Co-Authors: Darshana Perera, Buddhima Indraratna, Cholachat Rujikiatkamjorn, Serge Leroueil, Richard KellyAbstract:When vacuum preloading is applied with vertical Drains, the rate of consolidation can be increased, and the stability of an embankment is enhanced due to the inward lateral movement. The aim of this study is to develop an analytical solution for vacuum preloading that accurately captures the more realistic variations in compressibility and permeability in actual ground conditions as a result of Drain Installation. The soil samples were obtained from various locations after Drain Installation to determine the characteristics of soil surrounding the vertical Drain in terms of compressibility and permeability. The main differences between the proposed and conventional models are described by considering the stress history and preloading pressure. The effect of pre-consolidation pressure and the magnitude of applied preloading are examined through the dissipation of average excess pore pressure and associated settlement. The analysis of a selected case history employing the writers’ solution indicates improve...
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Soil disturbance analysis due to vertical Drain Installation
Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 2015Co-Authors: Buddhima Indraratna, Darshana Perera, Cholachat Rujikiatkamjorn, Richard KellyAbstract:The Installation of Drains creates a disturbed region known as a smear zone where the change in the clay structure affects the horizontal permeability and compressibility. The parameters required to characterise the smear effect are the extent of the smear zone and the ratio of the horizontal coefficient of permeability in the undisturbed zone and in the smear zone. Only limited studies have been carried out on different aspects of soil disturbance due to driving vertical Drains and its effects on the subsequent consolidation. In this paper the disturbed zone around a rectangular mandrel was characterised using soil samples obtained from the soft clay layer at various locations beneath an embankment built at Ballina, Australia, where vertical Drains were installed. By determining the change in the coefficient of permeability, the water content and volume compressibility across the smear zone, the effects of soil disturbance on consolidation due to the Installation of Drains can be quantified using the ava...
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Briefing: Effect of Drain Installation patterns on rate of consolidation
Proceedings of the Institution of Civil Engineers - Ground Improvement, 2015Co-Authors: Cholachat Rujikiatkamjorn, Buddhima IndraratnaAbstract:Prefabricated vertical Drains (PVDs) are employed to accelerate consolidation by decreasing the Drainage path length. In the present study, using analytical solutions, an attempt was made to evaluate and quantify the effectiveness of two non-conventional PVD Installation patterns, involving a parallel Drain wall compared with a circular Drain ring pattern, in contrast to conventional PVD Installation (square or triangular patterns). The governing equations are based on the equal strain theory including the smear effect, and they provide a relative comparison between the two newly proposed Installation patterns and the conventional square PVD grid, in terms of both the consolidation time and the equivalent Drain spacing. The comparisons between the new and conventional Installation patterns are made based on a single Drain analysis and the density of PVDs per unit area.
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Mathematical Modeling and Field Evaluation of Embankment Stabilized with Vertical Drains Incorporating Vacuum Preloading
2004Co-Authors: Buddhima Indraratna, Cholachat RujikiatkamjornAbstract:This study presents the analytical modeling of vertical Drains incorporating vacuum preloading in both axisymmetric and plane strain conditions. The effectiveness of vacuum pressure (i.e. both constant vacuum pressure and varied vacuum pressure) applied along the Drain is considered. A multiDrain plane strain model is employed to analyse an embankment at the site of Second Bangkok International Airport (SBIA) stabilised with prefabricated vertical Drains. At this site, a significantly reduced height of sand surcharge was applied by reducing the pore pressures through vacuum preloading. The results of FEM analysis confirm the efficiency of vacuum preloading in comparison with the conventional method of surcharge alone. INTRODUCTION In this study, analytical solutions for a single Drain incorporating vacuum preloading in both axisymmetric and plane strain conditions are introduced. In order to compare the efficiency of vacuum preloading, various possible distribution patterns of vacuum pressure via the vertical Drain system are discussed. Finally, the equivalent plane strain model in conjunction with the modified Cam-Clay theory is applied to 2 embankments at the Second Bangkok International Airport (SBIA). In recent years, prefabricated band Drains have been used widely for soft ground improvement. Radial Drainage accelerates soft soil consolidation. Baron (1948) and Hansbo (1981) introduced the unit cell theory for axisymmetric and plane strain conditions. Subsequently, the unit cell theory was extended by including a smear zone, which occurs when surrounding soil is remoulded during the vertical Drain Installation (Hird et al., 1992). Due to the increasing popularity of plane strain finite element analysis, Indraratna and Redana (1997) extended the equivalent unit cell theory to convert the axisymmetric parameters such as permeability into equivalent plane strain parameters. As a result, the plane strain finite element analyses have been used extensively to predict the behaviour of embankments improved by prefabricated vertical Drains (e.g. Indraratna and Redana, 2000). ANALYTICAL SOLUTIONS FOR VERTICAL Drain INCORPORATING VACUUM PRELOADING AND SMEAR EFFECTS In this section, the analytical solutions of unit cell for axisymmetric and plane strain conditions are revised from the original theory developed by Hird et al. (1992) and Indraratna and Redana (1997). Figures 1a and 1b illustrate the unit cell adopted for the axisymmetric and plane strain conditions, respectively. The efficiency of vacuum preloading is taken into account by dividing the distribution pattern of vacuum pressure into 4 distinct categories (Fig. 2): In order to increase the rate of consolidation, Kjellman (1952) introduced the concept of vacuum preloading to improve the soil strength. Recently, the system of vertical Drains enhanced by incorporating vacuum preloading has been applied in land reclamation projects (Shang et al., 1998, Chu, et al., 2000). Mohamedelhassan and Shang (2002) discussed the application of vacuum pressure and its benefits, but without any prefabricated vertical Drains (PVD). The benefits of this method include accelerating consolidation by increasing the hydraulic gradient and reducing the height of the embankment to achieve the same degree of consolidation. Case A: Vacuum pressure is constant along the Drain and across the soil element. Case B: Vacuum pressure is constant along the Drain while it varies linearly to zero across the soil element. This represents a large Drain spacing but relatively short Drain lengths. Paper No. 2.05 Page 1 Case C: Vacuum pressure varies linearly along the Drain while remaining constant across the soil element. This represents close Drain spacing and relatively long PVDs. Case D: ( )( ) ( ) ( ) ( )( ) ( ) , 0 , 0 ( , ) , , v ax w v ps w u r z p R r l z l R r u x z p B x l z l B b = − − − = − − − (1d) Case D: Vacuum pressure varies linearly along the Drain and across the soil element. This represents large Drain spacing and lengthy Drains. where, = vacuum pressure at radius and depth , = applied vacuum pressure at the top of the Drain, = radius of Drain well, l = length of Drain, u = vacuum pressure at distance , ( , ) v ax u r z r z 0 p w r ) x z , ( , v ps x and depth , and b = width of Drain well. Subscripts and z w ax ps denotes axisymmetric and plane strain condition, respectively. Smear boundary bw bs B rw rs R (a) Axisymmetric (b) Plane strain SOLUTIONS FOR AXISYMMETRIC CONDITION Fig. 1. The unit cell adopted for analytical solution In this section, for fully saturated soil, the solution for vertical Drain incorporating vacuum preloading and smear effects based on Hansbo’s solution (1981) is illustrated. The corresponding expressions for the average excess pore pressure, u , at any time factor, Th, ax are given by: CL Drain interface Soil element -p0 -p0 CL -p0 -p0 Case A: Case A Case B ( ) { } ( ) 1 0, 1 , 0, 1 1 exp 8 ax h ax ax ax u p T p σ σ μ = + − − σ (2a) C L -p0(l-z)/l Soil element -p0 C L -p0(l-z)/l -p0 Case B: ( ) { } ( ) 1 0, 1 , 0, 1 1 ( ) exp 8 ( ) ax h ax ax ax u p G n T p G n σ σ σ = + − − μ (2b) Case C: Drain interface ( ) { } ( ) 1 0, 1 , 0, 1 1 2 exp 8 2 ax h ax ax ax u p T p σ σ σ = + − − μ (2c) Case C Case D Fig. 2. The distribution patterns of vacuum pressure in the horizontal and vertical directions Case D: ( ) { } ( ) 1 0, 1 , 0, 1 1 ( ) 2 exp 8 ( ) 2 ax h ax ax ax u p G n T p G n σ σ σ = + − − μ (2d) Based on the above distributions (Fig. 2), the equations for vacuum pressure at a given point in a unit cell can be given by: where, Case A: ( ) ( ) ( ) ( ) ( )( ) ( ) { } ( ) ( ) ( ) ( ) 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 1 3 4 4 1 1 1 4 1 ax ax h,ax h ,ax s w w
Ken Inouye - One of the best experts on this subject based on the ideXlab platform.
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FIELD EVALUATION OF THE LONG-TERM PERFORMANCE OF GEOCOMPOSITE SHEET DrainS
Geotextiles and Geomembranes, 2001Co-Authors: Jim Mckean, Ken InouyeAbstract:Abstract The long-term performance of geocomposite sheet Drains has been monitored at three sites by measuring the effect of the Drains on local groundwater hydrology during peak groundwater events. The study is on-going with the maximum record being 14 years at one location. One Drain was placed 2.4 m deep in a vertical trench in soil that varies from clay and clayey gravel to silty sand. Over a three-year period, this Drain has flowed as much as 100 l/min. Even during such extreme groundwater events, there has been essentially no rise in the water table just down gradient from the Drain. The peak hydraulic gradient toward this Drain consistently reaches 0.66–0.73 during major rainstorms and returns to a “base level” of 0.45–0.50 within 10 days after a storm peak. At a second site, a Drain was installed 8 m deep in a silty sand soil behind a retaining wall. This geocomposite has flowed up to 15 l/min with no rise in the water table in the retaining wall fill. Performance of the Drain has been consistently excellent over a 14-year period. Limited data suggest that the Drain discharge is proportional to about 13 times the average hydraulic gradient toward the Drain. At a third site, a Drain was installed to a maximum depth of 2.4 m in a vertical trench in a silty sand soil. Performance of this Drain is marginal because trench wall collapse during Drain Installation caused an uneven Drain slope toward the outlet. This is a common issue where trench Drains are installed at sites with a constantly high water table. The problem could be greatly mitigated by a geocomposite design in which vertical sections of the Drain are completely independent units that could be quickly dropped into a trench immediately behind the excavator. Despite the construction problems, this Drain is partially dewatering the road prism just down gradient from the geocomposite.
Richard Kelly - One of the best experts on this subject based on the ideXlab platform.
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Analytical model for vacuum consolidation incorporating soil disturbance caused by mandrel-driven Drains
Canadian Geotechnical Journal, 2017Co-Authors: Darshana Perera, Buddhima Indraratna, Cholachat Rujikiatkamjorn, Serge Leroueil, Richard KellyAbstract:When vacuum preloading is applied with vertical Drains, the rate of consolidation can be increased, and the stability of an embankment is enhanced due to the inward lateral movement. The aim of this study is to develop an analytical solution for vacuum preloading that accurately captures the more realistic variations in compressibility and permeability in actual ground conditions as a result of Drain Installation. The soil samples were obtained from various locations after Drain Installation to determine the characteristics of soil surrounding the vertical Drain in terms of compressibility and permeability. The main differences between the proposed and conventional models are described by considering the stress history and preloading pressure. The effect of pre-consolidation pressure and the magnitude of applied preloading are examined through the dissipation of average excess pore pressure and associated settlement. The analysis of a selected case history employing the writers’ solution indicates improve...
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Soil disturbance analysis due to vertical Drain Installation
Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 2015Co-Authors: Buddhima Indraratna, Darshana Perera, Cholachat Rujikiatkamjorn, Richard KellyAbstract:The Installation of Drains creates a disturbed region known as a smear zone where the change in the clay structure affects the horizontal permeability and compressibility. The parameters required to characterise the smear effect are the extent of the smear zone and the ratio of the horizontal coefficient of permeability in the undisturbed zone and in the smear zone. Only limited studies have been carried out on different aspects of soil disturbance due to driving vertical Drains and its effects on the subsequent consolidation. In this paper the disturbed zone around a rectangular mandrel was characterised using soil samples obtained from the soft clay layer at various locations beneath an embankment built at Ballina, Australia, where vertical Drains were installed. By determining the change in the coefficient of permeability, the water content and volume compressibility across the smear zone, the effects of soil disturbance on consolidation due to the Installation of Drains can be quantified using the ava...
Hadi Khabbaz - One of the best experts on this subject based on the ideXlab platform.
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Trial Embankment Analysis to Predict Smear Zone Characteristics Induced by Prefabricated Vertical Drain Installation
Geotechnical and Geological Engineering, 2014Co-Authors: Ali Parsa-pajouh, Philippe Vincent, Behzad Fatahi, Hadi KhabbazAbstract:In this study, FLAC finite difference software has been adopted to simulate the performance of the ground improved using prefabricated vertical Drains assisted preloading, considering smear zone characteristics. The numerical code has been applied to predict smear zone properties employing a back calculation procedure using the results of several case studies. The construction of a trial embankment is proposed as a reliable method to predict the smear zone characteristics. The proposed back calculation method is applied to estimate the minimum required degree of consolidation and consequently the minimum required preloading time, resulting in a reliable estimation of the smear zone permeability and extent. Three preloading case studies considering both conventional preloading and vacuum assisted preloading have been simulated to verify the numerical code and to conduct the parametric study using the back calculation procedure. According to the results, the properties of the smear zone can be back-calculated reliably, when at least 33 % degree of consolidation due to trial embankment construction is achieved.
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Analyzing consolidation data to predict smear zone characteristics induced by vertical Drain Installation for soft soil improvement
Geomechanics and Engineering, 2014Co-Authors: Ali Parsa-pajouh, Philippe Vincent, Behzad Fatahi, Hadi KhabbazAbstract:In this paper, the effects of variability of smear zone characteristics induced by Installation of prefabricated vertical Drains on the preloading design are investigated employing analytical and numerical approaches. Conventional radial consolidation theory has been adopted to conduct analytical parametric studies considering variations of smear zone permeability and extent. FLAC 2D finite difference software has been employed to conduct the numerical simulations. The finite difference analyses have been verified using three case studies including two embankments and a large-scale laboratory consolidometer with a central geosynthetic vertical Drain. A comprehensive numerical parametric study is conducted to investigate the influence of smear zone permeability and extent on the model predictions. Furthermore, the construction of the trial embankment is recommended as a reliable solution to estimate accurate smear zone properties and minimise the post construction settlement. A back-calculation procedure is employed to determine the minimum required waiting time after construction of the trial embankment to predict the smear zone characteristics precisely. Results of this study indicate that the accurate smear zone permeability and extent can be back-calculated when 30% degree of consolidation is obtained after construction of the trial embankment.