Copyright (c) 2009 All rights reserved. http://works.bepress.com/bindraratna Recent documents in Professor B. Indraratna en-us Sun, 31 May 2009 03:49:59 PDT 3600 http://works.bepress.com/bindraratna/80 http://works.bepress.com/bindraratna/80 Mon, 02 Feb 2009 14:25:40 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/bindraratna/79 http://works.bepress.com/bindraratna/79 Mon, 02 Feb 2009 14:25:39 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/bindraratna/78 http://works.bepress.com/bindraratna/78 Wed, 28 May 2008 11:48:44 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/bindraratna/77 http://works.bepress.com/bindraratna/77 Wed, 28 May 2008 11:48:40 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/bindraratna/76 http://works.bepress.com/bindraratna/76 Wed, 28 May 2008 11:48:36 PDT A permeable reactive barrier is being designed to remediate leachate from acid sulphate soils. The current research relates to testing of alkaline materials for use in the barrier, with an emphasis on waste materials. Thirteen alkaline materials including recycled concrete, limestone, calcite-bearing zeolitic breccia, blast furnace slag, lime and fly ash were tested. The batch tests involved several phases, such as leaching in deionised water to characterise the soluble components of the materials and the pH that each material could achieve. Another phase involved testing with acidic water (pH 3) to determine the acid leachable components of the materials and the pH after neutralisation. The pH achieved by each reactive material was controlled by the reaction kinetics of the dominant alkaline mineral. The concretes, fly ash, and air-cooled blast furnace slag (ACBFS) all achieved a pH that is consistent with the dissolution of lime (pH 11 to 12). The limestone and zeolitic breccias all achieved a pH consistent with the dissolution of calcite (pH ~7.4). Based on the results of the batch tests, a short-list of materials was selected that included a recycled concrete, ACBFS, three zeolitic breccias and limestone. The short-listed materials were examined for exhaustion of neutralising ability by repeatedly replacing the acidic water and monitoring the resultant pH. The precipitates that formed during this process were analysed to characterise the chemical reactions that occurred during the tests. Based on the results, the recycled concrete was selected for testing in columns that will simulate flow conditions through the barrier. A. N. Golab http://works.bepress.com/bindraratna/75 http://works.bepress.com/bindraratna/75 Wed, 28 May 2008 11:48:32 PDT The accurate flow measurement of each individual phase is important in unsaturated flow through rock joints, where both air and water phases flow together. An increase in the quantity of one fluid phase decreases the relative permeability of the other phase. The relative permeability is important in numerical models to analyze the risk of ground-water inundation and uncontrollable gas flows in underground excavations in jointed rock. A new apparatus, the High Pressure Two-Phase Triaxial Apparatus (HPTPTA), has been designed for examining the strength and coefficient of permeability characteristics of fractured and intact rocks under two-phase flows. In single-phase triaxial equipment, the rock specimen is subjected to a single fluid flow (either water, oil, or gas) through the fractures. In the HPTPTA, two fluids (e.g., water 1 air, water 1 oil, and oil 1 air) can be forced to flow through the specimen, and the flow rates of the fluids can be measured independently. The scope of tests that can be carried out in this apparatus is wide, including the evaluation of (1) stress-strain behavior subject to internal fluid flow; (2) relative permeability of each fluid phase under different degrees of saturation; and (3) the associated volume change of the specimen. In this paper, the design concepts of the HPTPTA and the results based on the testing of fractured rock specimens are discussed. The laboratory results are compared to a simplified mathematical model developed by the writers. Based on the laboratory results, it is shown that the well-known Darcy's law can be modified for estimating the two-phase flow rates using the relative permeability concept. B. Indraratna http://works.bepress.com/bindraratna/74 http://works.bepress.com/bindraratna/74 Wed, 28 May 2008 11:48:27 PDT Infill materials found in natural rock joints may cause a reduction in joint shear strength, influencing rock mass stability. This paper reports a study aimed at developing a semi-empirical methodology for predicting the shear strength of infilled joints, taking into account joint surface characteristics and the properties of the joint and infill materials. A new model for predicting the shear strength of infilled joints is presented, on the basis of a series of tests carried out on two types of model joint surface having asperity angles of 9.5° and 18.5°, with graphite and bentonite used as infill materials. All tests were carried out in a large-scale shear apparatus under constant normal stiffness (CNS) conditions. The results indicate that at low infill thickness to asperity height ratio ( t/a ), the combined effect of the basic friction angle (f b ) and the joint asperity angle ( i ) is pronounced, but it diminishes with increasing t/a ratio so that the shear strength converges towards that of the infill alone. Summation of two algebraic functions ( A and B ) that represent the joint and infill characteristics correctly models the decay of normalised shear strength with increasing t/a ratio. The new model successfully describes the observed shear strengths of the graphite and clay (bentonite) filled model joints. Abstract Les matériaux de remplissage trouvés dans les joints rocheux naturels peuvent causer une diminution de la résistance au cisaillement du joint, influençant la stabilité de la masse rocheuse. Cet exposé rend compte d'une étude destinée à développer une méthodologie semiempirique pour prédire la résistance au cisaillement de joint remplis, prenant en compte les caractéristiques de surface du joint et les propriétés du joint et des matériaux de remplissage. Nous présentons un nouveau modèle pour prédire la résistance au cisaillement de joints remplis, en nous basant sur une série de tests effectués sur deux types de surfaces de joint B. Indraratna http://works.bepress.com/bindraratna/73 http://works.bepress.com/bindraratna/73 Wed, 28 May 2008 11:48:23 PDT The use of native vegetation in the coastal regions of Australia has become increasingly popular for stabilising railway corridors built over expansive clays and compressive soft soils. The tree roots provide three stabilising functions: (a) they reinforce the soil; (b) they dissipate excess pore pressures; and (c) they establish sufficient matric suction to increase the shear strength. The matric suction generated within the tree root zone propagates radially into the soil matrix, as a function of the moisture content change. Considering soil conditions, the type of vegetation and atmospheric conditions, a mathematical model for the rate of root water uptake is developed. A conical shape is considered to represent the geometry of the tree root zone. Based on this model for the rate of root water uptake, the pore water pressure distribution and the movement of the ground adjacent to the tree are numerically analysed. Field measurements taken from the previously published literature are compared with the authors' numerical predictions. It is found that, given the approximation of the assumed model parameters, the agreement between the predicted results and field data is still promising. The study indicates that native vegetation improves the shear strength of the soil by increasing the matric suction, and also curtails soil movements. B. Indraratna http://works.bepress.com/bindraratna/72 http://works.bepress.com/bindraratna/72 Wed, 28 May 2008 11:48:19 PDT See the paper B. Indraratna http://works.bepress.com/bindraratna/71 http://works.bepress.com/bindraratna/71 Wed, 28 May 2008 11:48:16 PDT A vertical drain radial consolidation equation based on a parabolic reduction in permeability toward the drain is presented. The proposed equation, based on Hansbo's equal strain theory, is compared with settlement data from a laboratory test in a large scale consolidometer. R. Walker