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Buddhima Indraratna - One of the best experts on this subject based on the ideXlab platform.

  • Radial consolidation characteristics of soft undisturbed clay based on large specimens
    Elsevier, 2018
    Co-Authors: Pankaj Baral, Cholachat Rujikiatkamjorn, Buddhima Indraratna, Richard Kelly
    Abstract:

    In recent years, reconstituted small samples have often been used to assess the performance of radial consolidation due to prefabricated vertical drains (PVDs), but the permeability and compressibility of samples of undisturbed soil often differ from those of the remoulded ones. The problem seems more complex in marine environment due to the presence of random coarse particles including gravels, shells and natural partings. Performing small-scale laboratory experiment with reconstituted samples, especially in marine environment, cannot predict the exact soil behaviour in the field. This paper describes an experimental programme that measures radial consolidation using a conventional Rowe cell and a large-scale consolidometer, where the samples of undisturbed soil obtained from a site along the Pacific Highway (north of Sydney) were compared using measured settlements and excess pore pressures. Moreover, this paper highlights the implications of the Smear effect and sample size influence, which are imperative in translating the laboratory testing practices to actual real-life behaviour. The effect of vacuum pressure on the coefficient of radial consolidation of a large-scale undisturbed test specimen is also discussed. The paper demonstrates that the extent of Smear Zone in the field can be very similar to the large-scale laboratory consolidation test using a scaled-down drain and mandrel, but considerably different from the data obtained for small laboratory specimens. Keywords: Consolidation, Soft soil, Vertical drain, Undisturbed cla

  • Characterization of Smear Zone caused by mandrel action
    IFCEE 2015, 2015
    Co-Authors: Buddhima Indraratna, Cholachat Rujikiatkmajorn, Made Ardana
    Abstract:

    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.

  • conceptual model describing Smear Zone caused by mandrel action
    Geotechnique, 2013
    Co-Authors: Cholachat Rujikiatkamjorn, Buddhima Indraratna, Made Ardana, Serge Leroueil
    Abstract:

    In this study the characteristics and extent of the Smear Zone are investigated using a large, undisturbed sample. The aim of using such a sample is to capture the realistic characteristics of the Smear Zone in relation to the in situ soil structure during the installation of prefabricated vertical drains (PVDs) using a mandrel. The extent of the Smear Zone for Bulli clay (New South Wales, Australia) is determined on the basis of normalised permeability (kh/khu) and the reduction in the water content upon consolidation. The permeability and compressibility of the soil are investigated to determine the extent to which the soil surrounding the PVD has become disturbed. In laboratory testing, the soil consolidation behaviour due to a PVD is studied using a large-scale consolidometer apparatus. The numerical results have shown that the writers' solutions give excellent agreement with laboratory observations.

  • radial consolidation modelling incorporating the effect of a Smear Zone for a multilayer soil with downdrag caused by mandrel action
    Canadian Geotechnical Journal, 2010
    Co-Authors: Cholachat Rujikiatkamjorn, Buddhima Indraratna
    Abstract:

    A system of prefabricated vertical drains with surcharge preloading is an effective method for promoting radial drainage and accelerated soil consolidation. A piecewise technique is employed to ana...

  • design procedure for vertical drains considering a linear variation of lateral permeability within the Smear Zone
    Canadian Geotechnical Journal, 2009
    Co-Authors: Cholachat Rujikiatkamjorn, Buddhima Indraratna
    Abstract:

    A system of vertical drains with surcharge preloading is an effective method for promoting radial drainage and accelerated soil consolidation. This study presents a procedure for the design of vert...

Dennis T. Bergado - One of the best experts on this subject based on the ideXlab platform.

  • prefabricated vertical drain pvd and deep cement mixing dcm stiffened dcm sdcm techniques for soft ground improvement
    IOP Conference Series: Earth and Environmental Science, 2018
    Co-Authors: Dennis T. Bergado, P V Long, Salisa Chaiyaput, Aramugam Balasubramaniam
    Abstract:

    Soft ground improvement techniques have become most practical and popular methods to increase soil strength, soil stiffness and reduce soil compressibility including the soft Bangkok clay. This paper focuses on comparative performances of prefabricated vertical drain (PVD) using surcharge, vacuum and heat preloading as well as the cement-admixed clay of Deep Cement Mixing (DCM) and Stiffened DCM (SDCM) methods. The Vacuum-PVD can increase the horizontal coefficient of consolidation, Ch, resulting in faster rate of settlement at the same magnitudes of settlement compared to Conventional PVD. Several field methods of applying vacuum preloading are also compared. Moreover, the Thermal PVD and Thermal Vacuum PVD can increase further the coefficient of horizontal consolidation, Ch, with the associated reduction of kh/ks values by reducing the drainage retardation effects in the Smear Zone around the PVD which resulted in faster rates of consolidation and higher magnitudes of settlements. Furthermore, the equivalent Smear effect due to non-uniform consolidation is also discussed in addition to the Smear due to the mechanical installation of PVDs. In addition, a new kind of reinforced deep mixing method, namely Stiffened Deep Cement Mixing (SDCM) pile is introduced to improve the flexural resistance, improve the field quality control, and prevent unexpected failures of the Deep Cement Mixing (DCM) pile. The SDCM pile consists of DCM pile reinforced with the insertion of precast reinforced concrete (RC) core. The full scale test embankment on soft clay improved by SDCM and DCM piles was also analysed. Numerical simulations using the 3D PLAXIS Foundation finite element software have been done to understand the behavior of SDCM and DCM piles. The simulation results indicated that the surface settlements decreased with increasing lengths of the RC cores, and, at lesser extent, increasing sectional areas of the RC cores in the SDCM piles. In addition, the lateral movements decreased by increasing the lengths (longer than 4 m) and, the sectional areas of the RC cores in the SDCM piles. The results of the numerical simulations closely agreed with the observed data and successfully verified the parameters affecting the performances and behavior of both SDCM and DCM piles.

  • comparison on the performance of prefabricated vertical drain pvd preloading combined with and without vacuum and heat
    Lowland technology international : the official journal of the International Association of Lowland Technology, 2011
    Co-Authors: J Saowapakpiboon, Dennis T. Bergado, S Artidteang
    Abstract:

    This paper focus on performance of prefabricated vertical drain (PVD) preloading combined with and without vacuum and heat to accelerate the consolidation of soft Bangkok clay. The laboratory tests were conducted using reconstituted specimens in large scale consolidometers combined with and without vacuum and heat. The flow parameters were back calculated in terms of the horizontal coefficient of consolidation (Ch) and the ratio between the horizontal permeability in undisturbed Zone (kh) to the horizontal permeability in Smear Zone (ks) or (kh/ks) based on Hansbo (1979) method. The back-calculation analysis results show that the combination of vacuum pressure and heat can increase the horizontal coefficient of consolidation, Ch of 126.42% and decrease of kh/ks of 63.33%. Furthermore, vacuum can increase higher rate of consolidation temperature can decrease viscosity of pore water by reducing the drainage retardation effects in the Smear Zone around the PVD which resulted in faster rate of consolidation and higher magnitude of settlement.

  • assessing the performance of prefabricated vertical drain with vacuum and heat preloading
    Geosynthetics International, 2009
    Co-Authors: J Saowapakpiboon, Y M Thann, Dennis T. Bergado, P Voottipruex
    Abstract:

    ABSTRACT: This paper presents the effects of vacuum and heat preloading of a prefabricated vertical drains (PVD) that are used to accelerate consolidation of soft Bangkok clay. Laboratory model tests were conducted in small-scale consolidometers with undisturbed and reconstituted specimens of untreated (PVD), vacuum-treated (vacuum-PVD) and temperature treated (thermo-PVD) materials. The flow parameters were back-calculated using the Hansbo (Ground Engineering, 12, No. 5, 16–25, 1979) method in terms of the horizontal coefficient of consolidation (Ch) and the ratio of the horizontal hydraulic conductivity in the undisturbed Zone (Kh) to the horizontal hydraulic conductivity in the Smear Zone (Ks) or (Kh/Ks). From the results of the laboratory tests, the increased hydraulic conductivity of the Smear Zone of undisturbed specimens using vacuum-PVD and thermo-PVD resulted in a decrease in Kh/Ks of about 11 and 12%, and an increase in Ch of 2 and 13%, respectively. On the other hand, the increased hydraulic co...

  • innovative thermal technique for enhancing the performance of prefabricated vertical drain during the preloading process
    Geotextiles and Geomembranes, 2006
    Co-Authors: H M Abuelnaga, Dennis T. Bergado, S Chaiprakaikeow
    Abstract:

    Abstract This paper examines the effect of raising the temperature of soft Bangkok clay, up to 90 °C, on the performance of the prefabricated vertical drain (PVD) during the preloading process. The effect of temperature on the engineering behavior of soft Bangkok clay was first investigated using a modified triaxial test apparatus and flexible wall permeameter which can handle temperatures up to 100 °C. The results of the triaxial tests on clay specimens demonstrate that raising the soil temperature increases its shear strength, under drained heating condition, as well as its hydraulic conductivity. In addition, large oedometer tests were performed to investigate the performance of PVD at elevated temperatures. The response of the soil sample with PVD for the thermal consolidation path which involved increasing the soil temperature at constant vertical effective stress condition and the thermo-mechanical path which involved increasing simultaneously both the soil temperature and the vertical effective stress were investigated. The consequent results indicated that the thermo-mechanical path shows promising results regarding the consolidation rate. For both reconstituted and undisturbed specimens, higher consolidation rate was observed for the soil specimen with PVD loaded under elevated temperature. This behavior can be attributed to the increase in the soil hydraulic conductivity as the soil temperature increases. Therefore, raising the soil temperature during the preloading period can enhance the performance of the PVD, particularly, by reducing the drainage retardation effects due to the Smear Zone around PVD.

Aramugam Balasubramaniam - One of the best experts on this subject based on the ideXlab platform.

  • prefabricated vertical drain pvd and deep cement mixing dcm stiffened dcm sdcm techniques for soft ground improvement
    IOP Conference Series: Earth and Environmental Science, 2018
    Co-Authors: Dennis T. Bergado, P V Long, Salisa Chaiyaput, Aramugam Balasubramaniam
    Abstract:

    Soft ground improvement techniques have become most practical and popular methods to increase soil strength, soil stiffness and reduce soil compressibility including the soft Bangkok clay. This paper focuses on comparative performances of prefabricated vertical drain (PVD) using surcharge, vacuum and heat preloading as well as the cement-admixed clay of Deep Cement Mixing (DCM) and Stiffened DCM (SDCM) methods. The Vacuum-PVD can increase the horizontal coefficient of consolidation, Ch, resulting in faster rate of settlement at the same magnitudes of settlement compared to Conventional PVD. Several field methods of applying vacuum preloading are also compared. Moreover, the Thermal PVD and Thermal Vacuum PVD can increase further the coefficient of horizontal consolidation, Ch, with the associated reduction of kh/ks values by reducing the drainage retardation effects in the Smear Zone around the PVD which resulted in faster rates of consolidation and higher magnitudes of settlements. Furthermore, the equivalent Smear effect due to non-uniform consolidation is also discussed in addition to the Smear due to the mechanical installation of PVDs. In addition, a new kind of reinforced deep mixing method, namely Stiffened Deep Cement Mixing (SDCM) pile is introduced to improve the flexural resistance, improve the field quality control, and prevent unexpected failures of the Deep Cement Mixing (DCM) pile. The SDCM pile consists of DCM pile reinforced with the insertion of precast reinforced concrete (RC) core. The full scale test embankment on soft clay improved by SDCM and DCM piles was also analysed. Numerical simulations using the 3D PLAXIS Foundation finite element software have been done to understand the behavior of SDCM and DCM piles. The simulation results indicated that the surface settlements decreased with increasing lengths of the RC cores, and, at lesser extent, increasing sectional areas of the RC cores in the SDCM piles. In addition, the lateral movements decreased by increasing the lengths (longer than 4 m) and, the sectional areas of the RC cores in the SDCM piles. The results of the numerical simulations closely agreed with the observed data and successfully verified the parameters affecting the performances and behavior of both SDCM and DCM piles.

Hadi Khabbaz - One of the best experts on this subject based on the ideXlab platform.

  • assessment of the elastic viscoplastic behavior of soft soils improved with vertical drains capturing reduced shear strength of a disturbed Zone
    International Journal of Geomechanics, 2016
    Co-Authors: Babak Azari, Behzad Fatahi, Hadi Khabbaz
    Abstract:

    AbstractSoil disturbance induced by the installation of vertical drains reduces the horizontal soil permeability and shear strength in the disturbed Zone. Thus, the soil disturbance contributes to the reduced overconsolidation ratio (OCR) of the soil in the vicinity of drains, influencing soil deformation. Although a significant amount of research has been conducted on the effect of permeability variations in the Smear Zone, the influence of the reduced shear strength in the Smear Zone on the ground behavior has not been investigated. In this study, a numerical solution adopting an elastic-viscoplastic model with nonlinear creep function in combination with the consolidation equations has been developed. Moreover, the effects of shear strength variation in the disturbed Zone on the time-dependent behavior of soft soil deposits improved with vertical drains and preloading have been studied. The applied elastic-viscoplastic model is based on the framework of the modified Cam-clay model, capturing soil creep...

  • Trial Embankment Analysis to Predict Smear Zone Characteristics Induced by Prefabricated Vertical Drain Installation
    Geotechnical and Geological Engineering, 2014
    Co-Authors: Ali Parsa-pajouh, Philippe Vincent, Behzad Fatahi, Hadi Khabbaz
    Abstract:

    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.

  • Analyzing consolidation data to predict Smear Zone characteristics induced by vertical drain installation for soft soil improvement
    Geomechanics and Engineering, 2014
    Co-Authors: Ali Parsa-pajouh, Philippe Vincent, Behzad Fatahi, Hadi Khabbaz
    Abstract:

    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.

  • numerical back analysis of Smear Zone properties for vertical drain assisted preloading in soft soils
    2011
    Co-Authors: Ali Parsapajouh, Behzad Fatahi, Hadi Khabbaz
    Abstract:

    : Installation of prefabricated vertical drains (PVDs) using a mandrel causes disturbance of the clay surrounding the drain, resulting in a Smear Zone of reduced permeability, which adversely affects consolidation process. There are two important parameters to characterize the Smear effects, namely, the Smear Zone diameter and the permeability ratio. In this study, FLAC finites difference software has been employed to investigate the effects of Smear Zone characteristics on required time for preloading. The results of a fully instrumented trial embankment in Sunshine Motorway, Queensland, have been used to verify the model, and parametric studies have been conducted on the predicted ground settlement and pore water pressure. According to the results, changes in Smear Zone parameters can significantly affect the consolidation period. It is observed that the characteristics of Smear Zone namely size and permeability have a substantial impact on the preloading design to achieve a certain soil strength and stiffness satisfying both bearing capacity and settlement design criteria.

  • uncertainties of Smear Zone characteristics in the design of preloading with prefabricated vertical drains
    2010
    Co-Authors: Parsa A Pajouh, Behzad Fatahi, Behnam Fatahi, H Khabbaz, Ali Parsa Pajouh, Hadi Khabbaz
    Abstract:

    Soft Soil, Prefabricated Vertical Drain, Preloading, Smear Zone, Permeability, Ground Improvement

I Wayan Redana - One of the best experts on this subject based on the ideXlab platform.

  • plane strain modeling of Smear effects associated with vertical drains
    Journal of Geotechnical and Geoenvironmental Engineering, 1999
    Co-Authors: Buddhima Indraratna, I Wayan Redana
    Abstract:

    The present study provides a methodology to include the Smear effect of vertical drains in a two-dimensional (2D) plane-strain finite-element model, employing the modified Cam-clay theory. The analysis is conducted by converting the radius of the Smear Zone and its permeability (axisymmetric) into equivalent plane strain parameters. The introduction of Smear effects improves the accuracy of the numerical model that is tested for a Malaysian soft clay, in this study.

  • development of the Smear Zone around vertical band drains
    Proceedings of the Institution of Civil Engineers - Ground Improvement, 1998
    Co-Authors: Buddhima Indraratna, I Wayan Redana
    Abstract:

    This study describes the effect of Smear on the settlements of soft clay foundations which have been improved by installation of vertical drains. The Smear Zone propagation around a band-shaped dra...

  • LABORATORY DETERMINATION OF Smear Zone DUE TO VERTICAL DRAIN INSTALLATION. TECHNICAL NOTE
    Journal of Geotechnical and Geoenvironmental Engineering, 1998
    Co-Authors: Buddhima Indraratna, I Wayan Redana
    Abstract:

    This paper is concerned with a laboratory study to investigate the effect of Smear due to vertical drain installation. The extent of the Smear Zone around a vertical drain was studied utilizing a large-scale consolidometer apparatus. The test results reveal that a significant reduction in the horizontal permeability takes place toward the central drain, whereas the vertical permeability remains relatively unchanged. The radius of the Smear Zone was estimated to be a factor of four to five times the radius of the central drain (mandrel), and the measured ratio of horizontal to vertical permeability approached unity at the drain-soil interface. The laboratory measured settlements are subsequently compared with the predictions based on the theory of Hansbo and the finite element method. It is of relevance to note that the inclusion of the correct variation of permeability ratios of the Smear Zone in the plane strain finite element analysis improves the accuracy of settlement predictions.

  • Laboratory Determination of Smear Zone due to Vertical Drain Installation
    Journal of Geotechnical and Geoenvironmental Engineering, 1998
    Co-Authors: Buddhima Indraratna, I Wayan Redana
    Abstract:

    This paper is mainly concerned with a laboratory study to investigate the effect of Smear due to vertical drain installation. The extent of the Smear Zone around a vertical drain was studied utilizing a large-scale consolidometer apparatus. The test results reveal that a significant reduction in the horizontal permeability takes place toward the central drain, whereas the vertical permeability remains relatively unchanged. The radius of the Smear Zone was estimated to be a factor of four to five times the radius of the central drain (mandrel), and the measured ratio of horizontal to vertical permeability approached unity at the drain-soil interface. The laboratory measured settlements are subsequently compared with the predictions based on the theory of Hansbo and the finite element method. It is of relevance to note that the inclusion of the correct variation of permeability ratios of the Smear Zone in the plane strain finite element analysis improves the accuracy of settlement predictions.