Copyright (c) 2009 All rights reserved. http://works.bepress.com/crujikiatkamjorn Recent documents in Dr. C. Rujikiatkamjorn en-us Sun, 31 May 2009 04:39:28 PDT 3600 http://works.bepress.com/crujikiatkamjorn/36 http://works.bepress.com/crujikiatkamjorn/36 Thu, 29 Jan 2009 21:08:01 PST : In the analysis of axisymmetric problems, it is often imperative that aspects of geometry, material properties and loading characteristics are either maintained as constants or represented by continuous functions in the circumferential direction. In the case of radial consolidation beneath a circular embankment by vertical drains (i.e. circular oil tanks or silos), the discrete system of vertical drains can be substituted by continuous concentric rings of equivalent drain walls. An equivalent value for the coefficient of permeability of the soil is obtained by matching the degree of consolidation of a unit cell model. A rigorous solution to the continuity equation of radial drainage towards cylindrical drain walls is presented and verified by comparing its results with existing unit cell model. The proposed model is then adopted to analyse the consolidation process by vertical drains at the Skå-Edeby circular test embankment (Area II). The calculated values of settlement, lateral displacement and excess pore water pressure indicate good agreement with the field measurements. B. Indraratna http://works.bepress.com/crujikiatkamjorn/35 http://works.bepress.com/crujikiatkamjorn/35 Thu, 29 Jan 2009 21:07:54 PST This paper presents a three-dimensional (3D) and two-dimensional (2D) numerical analysis of a case study of a combined vacuum and surcharge preloading project for a storage yard at Tianjin Port, China. At this site, a vacuum pressure of 80 kPa and a fill surcharge of 50 kPa was applied on top of the 20m thick soft soil layer through prefabricated vertical drains (PVD) to achieve the desired settlements and to avoid embankment instability. In 3D analysis, the actual shape of PVDs and their installation pattern with the in-situ soil parameters were simulated. In contrast, the validity of 2D-plane strain analysis using equivalent permeability and transformed unit cell geometry was examined. In both cases, the vacuum pressure along the drain length was assumed to be constant as substantiated by the field observations. The finite element code, ABAQUS, using the modified Cam-clay model was used in the numerical analysis. The predictions of settlement, pore water pressure and lateral displacement were compared with the available field data, and an acceptable agreement was achieved for both 2D and 3D numerical analyses. It is found that both 3D and equivalent 2D analyses give similar consolidation responses at the vertical cross section where the lateral strain along the longitudinal axis is zero. The influence of vacuum may extend more than 10m from the embankment toe, where the lateral movement should be monitored carefully during the consolidation period to avoid any damage to adjacent structures. C. Rujikiatkamjorn http://works.bepress.com/crujikiatkamjorn/34 http://works.bepress.com/crujikiatkamjorn/34 Wed, 28 May 2008 12:15:30 PDT In this study, numerical modeling of a multi-drain system is employed to determine the optimum penetration depth of prefabricated vertical drains (PVDs) and the vacuum pressure that provides the maximum consolidation settlement and less lateral displacements. The plane strain analysis using an equivalent permeability with transformed unit cell geometry was considered for varying drain length and vacuum load. The effects of the vertical drain length and vacuum pressure on soft clay consolidation were examined through time for 90% degree of consolidation, associated settlement and lateral displacement. B. Indraratna http://works.bepress.com/crujikiatkamjorn/33 http://works.bepress.com/crujikiatkamjorn/33 Wed, 28 May 2008 12:15:26 PDT A system of vertical drains with surcharge load to accelerate consolidation by shortening the drainage path is one of the most popular methods of soft ground improvement. The conventional radial consolidation theory (including smear and well resistance) have been commonly employed to predict the behaviour of vertical drains in soft clay. Its mathematical formulation is based on the small strain theory, and for a given stress range, a constant volume compressibility (mv) and a constant coefficient of lateral permeability (kh) are assumed. However, the value of mv varies along the consolidation curve over a wide range of applied pressure (Dp). In the same manner, kh also changes with the void ratio (e). In this paper, the writers have replaced mv with the compressibility indices (Cc and Cr), which define the slopes of the e-logs' relationship. Moreover, the variation of horizontal permeability coefficient (kh) with void ratio (e) during consolidation is represented by the e-logkh relationship that has a slope of Ck. In contrast to the conventional analysis , the current study highlights the influence of the Cc/Ck (or Cr/Ck) ratio and the preloading increment ratio (Dp/si) on the consolidation process. The analytical predictions are compared with the experimental results using a large scale consolidation chamber, and these predictions show good agreement with the measured data. Finally, an embankment case history taken from Muar Plains, Malaysia is analysed based on the current solution, and compared with field measurements. B. Indraratna http://works.bepress.com/crujikiatkamjorn/32 http://works.bepress.com/crujikiatkamjorn/32 Wed, 28 May 2008 12:15:22 PDT 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. B. Indraratna http://works.bepress.com/crujikiatkamjorn/31 http://works.bepress.com/crujikiatkamjorn/31 Wed, 28 May 2008 12:15:17 PDT The purpose of this paper is to investigate the effectiveness of Prefabricated Vertical Drains (PVDs) in dissipating the excess pore water pressures induced by cyclic loading in soft clays. Cyclic triaxial testing on soft clay samples with vertical drains has been carried out using a large scale cyclic triaxial apparatus designed and built at the University of Wollongong. The samples used were 300 mm in diameter and 600 mm in height. The samples were anisotropically consolidated under ko condition to simulate the in-situ stress history of the field. Stress-controlled cycles were then applied to the soil samples with different loading frequencies. The excess pore water pressures were measured by several transducers located at different positions along the radius and height of the soil specimen. The results of the excess pore water pressures and settlements are presented. The advantages of soft subsoil stabilized with PVDs under high frequency cyclic loading conditions are investigated and discussed together with the results of a numerical analysis using PLAXIS finite element code. A. Attya http://works.bepress.com/crujikiatkamjorn/30 http://works.bepress.com/crujikiatkamjorn/30 Wed, 28 May 2008 12:15:14 PDT The behaviour of saturated soft clays subjected to cyclic Loading is of considerable importance in the design of railway subgrades. Soft clays can be extensively found in many coastal regions of Australia up to significant depths, including the coastal belt and the central part of NSW. These soft clay deposits are characterized by very tow bearing capacity and excessive settlement. The increase in generated excess pore pressures due to heavy freight trains significantly reduces the bearing capacity and causes serious damage to the rail infrastructure such as clay pumping underneath tracks and excessive subsidence. The use of prefabricated vertical drains (PVDs) is one of the popular methods for soft ground improvement. In this paper, the behaviour of soft clay subjected to cyclic toads is investigated using large-scale triaxial tests. Cyclic triaxial tests on rebounded soft clay samples with vertical drains have been carried out using a large-scale triaxial apparatus designed and built at the University of Wollongong. The improvement gained by drained compression using PVDS is presented and discussed in terms of the pore pressure ratio. An attempt is also made to modes such behaviour numerically in CRISP finite element code. A. Attya http://works.bepress.com/crujikiatkamjorn/29 http://works.bepress.com/crujikiatkamjorn/29 Wed, 28 May 2008 12:15:10 PDT In this paper, an analytical solution based on actual radial soil permeability and compressibility is proposed considering the impact of parabolic variation of permeability in smear zone. The use of the spectral method for multilayered soil consolidation is introduced and verified. The Cavity Expansion Theory is employed to predict the extent of soil disturbance (smear zone) caused by the installation of mandrel driven vertical drains. The smear zone prediction is then compared to the data obtained from large-scale radial consolidation tests. Furthermore, the advantages and limitations of vacuum application through vertical drains are discussed using the proposed solutions. The applied vacuum pressure generates negative pore water pressure, resulting in an increase in effective stress within the soil, which leads to accelerated consolidation. Vacuum pressure is modelled as a distributed negative pressure (suction) along the drain length and across the soil surface. Analytical and numerical analyses incorporating the Authors' equivalent plane strain solution are conducted to predict the excess pore pressures, lateral and vertical displacements. Application of the theoretical models for a selected case history is discussed and analysed, at the site of the 2nd Bangkok International Airport. The predictions are compared with the available field data, showing that an equivalent plane strain model can be used confidently to predict the performance with acceptable accuracy through rigorous mathematical modelling and numerical analysis. The research findings verify that the role of smear, drain unsaturation, and vacuum distribution can significantly affect the soil consolidation, hence, these aspects need to be modelled appropriately to obtain reliable predictions. B. Indraratna http://works.bepress.com/crujikiatkamjorn/28 http://works.bepress.com/crujikiatkamjorn/28 Wed, 28 May 2008 12:15:06 PDT A system of vertical drains combined with vacuum preloading is an effective method for promoting radial flow to accelerate soil consolidation. This study presents the analytical modeling of a consolidation of vertical drains incorporating vacuum preloading considering both vertical and horizontal drainage. The effects of a number of dimensionless parameters involving the drain length, soil permeability and vacuum pressure are examined through average excess pore pressure, degree of consolidation, associated settlement and time factor analyses. An analysis of selected case histories compliments the use of the proposed solutions. Design charts are also presented for practical use. C. Rujikiatkamjorn http://works.bepress.com/crujikiatkamjorn/27 http://works.bepress.com/crujikiatkamjorn/27 Wed, 28 May 2008 12:15:03 PDT In this paper, the analytical solution for radial consolidation of soft soils is proposed considering the impacts of the variation of volume compressibility and permeability. The Cavity Expansion Theory is employed to predict the smear zone caused by the installation of mandrel driven vertical drains in soft clay. The smear zone prediction is then compared to the data obtained from the large-scale radial consolidation tests. Furthermore, the advantages and limitations of vacuum application through vertical drains in the absence of high surcharge embankments are discussed using the proposed solutions. The applied vacuum pressure generates negative pore water pressure, resulting in an increase in the effective stress, which leads to accelerated consolidation. Analytical and Numerical analysis incorporating the equivalent plane strain solution are conducted to predict the excess pore pressures, lateral and vertical displacements. The equivalent plane strain solution can be used as a predictive tool with acceptable accuracy due to the significant progress that has been made in the past few years through rigorous mathematical modelling and numerical analysis developed by the primary author and co-workers (Indraratna et al., 1992 - 2005). Several case histories are discussed and analysed, including the site of the 2nd Bangkok International Airport. The predictions are compared with the available field data, confirming that the equivalent plane strain model can be used confidently to predict the performance with acceptable accuracy. Difficulties in assuring good performance can also be analysed and interpreted through mathematical modelling, thereby enabling due caution in the design and construction stages. The research findings verify that the role of smear, drain unsaturation, and vacuum distribution can significantly affect soil consolidation, hence, these aspects need to be modelled appropriately in any numerical analysis to obtain reliable predictions. B. Indraratna