Kousik Deb

Effect of Clogging on Rate of Consolidation of Stone Column–Improved Ground by Considering Particle Migration

AbstractInstallation of stone columns is one of the most popular ground improvement techniques used to improve the strength of soft soil. Owing to the presence of more pores in the stone column, it acts as a drainage path for seepage of water from the soil during consolidation. Thus, in addition to increasing the soil’s strength, the stone column also increases the rate of consolidation of the soil. The water present in the pores of the soil is not pure, and some fine particles released from the soil are also present. During the seepage, these fines present in the fluid also move along with it. Depending upon the amount of concentration of fines present in the seepage water, the clogging of the stone column takes place which reduces the permeability of the stone column. Thus, the rate of consolidation of the ground improved by the stone column also decreases because of the clogging. In the present study, a mathematical model for the consolidation rate of soil improved with stone columns has been developed...

Estimation of Design Parameters for Braced Excavation: Numerical Study

This paper discusses the development of a numerical model for a braced excavation to estimate the various design parameters that significantly influence the excavations behavior. The results of the numerical model were compared with those of a reported case study of a braced excavation in sand, and close agreement between the results was observed. The developed model is used for parametric study to show theinfluenceofdifferentdesignparameters,suchasstrutstiffness,wallthickness,strutarrangementandtheembeddeddepthofthewallonstrut force, maximum moment developed in the wall, maximum lateral displacement of the wall, and maximum vertical displacement of ground surface.Itwasfoundthat,amongallthecombinationsstudied,aparticulartypeofstrutarrangementforaparticularratioofembeddeddepthand excavation depth produces the best possible result. A design guideline is also presented based on the results of this numerical study. DOI: 10.1061/(ASCE)GM.1943-5622.0000207.

3D Finite-Element Dynamic Analysis of Rigid Pavement Using Infinite Elements

A solution algorithm based on three-dimensional (3D) finite-element analysis is presented to study the dynamic response of concrete pavements subjected to moving loads. The pavement is discretized by 20-node isoparametric brick elements. The supporting soil medium is idealized by the elastic continuum model. Kelvin elements are attached to the transmitting boundary separating the near field and far field of the infinite soil medium in the vertical and longitudinal directions. Three-dimensional, 16-node infinite elements are attached to the transmitting boundary in the longitudinal direction to simulate the infinite soil medium in vehicle traverse direction. The moving vehicle is modeled by a mass supported by a linear spring and dashpot assembly simulating the vehicle suspension system. The vehicle-pavement interaction force is modeled with a Dirac-delta function. The dynamic equilibrium equation is solved by applying the Newmark-Beta integration scheme. The effects of vehicle-pavement interaction, pavement thickness, and soil parameters on the dynamic response of pavement are investigated by conducting a parametric study. It has been observed that the dynamic interaction between the moving load and the pavement has a significant effect on pavement response.

Parameter Estimation for a System of Beams Resting on Stone Column–Reinforced Soft Soil

AbstractThe paper pertains to the development of a methodology for the identification of optimal design parameters for a system of beams resting on a stone column–improved soft soil. The simulation optimization–based methodology combines a finite difference–based simulation model and an evolutionary multiobjective optimization model. Two different formulations subjected to stress constraints have been incorporated within the methodology; i.e., (1) minimization of settlement at the center of the beam and minimization of the maximum bending moment and (2) minimization of settlement at the center of the beam and minimization of the maximum shear force. Critical evaluation of an illustrative system shows that stiffness of the stone columns or modular ratio and flexural rigidity of the beam are the most important parameters for optimal design. The obtained results also show the potential applicability of the proposed simulation optimization–based methodology.

Effect of Fines on Behavior of Braced Excavation in Sand: Experimental and Numerical Study

AbstractIn this paper, the effect of fine content in the retained sandy soil on the behavior of braced excavation has been studied using experimental and numerical models in terms of four design factors: strut force, bending moment developed in the wall, lateral deflection of the wall, and vertical displacement of the ground surface. In the experiments, the fine content of the soil has been estimated as 0, 5, and 10% (by weight). However, the numerical study has been conducted for different fine contents varying from 0 to 50% (by weight). The parametric study with 20 m depth of retaining wall; position of struts at 2, 7, 12, and 17 m below ground level; wall thickness and embedment depth as 6 and 80% of depth of excavation; and stiffness of support members as 5×105kN/m/m confirms that the values of the four design factors (strut force, wall moment, lateral wall defection, ground deflection, and net earth pressure acting on the wall) increase with the increase in fine content in the retained soil. It is al...

Finite element analysis of rigid pavement on a nonlinear two parameter foundation model

Abstract A numerical iterative procedure based on finite element method has been presented for analyzing the dynamic response of pavement to moving load resting on a nonlinear subgrade. The pavement is descretized by finite and infinite beam elements. The foundation is modeled by Pasternaks two parameter soil medium. The nonlinear stress-strain relationship in the soil is considered. The dynamic vehicle-pavement interaction (VPI) effects are incorporated in the analysis. The effect of the material nonlinearity of the supporting soil medium on the pavement response is investigated by conducting a parametric study.

Effects of fines on compaction characteristics of poorly graded sands

Abstract For preliminary design and assessment, various researchers have correlated the compaction characteristics with different soil properties. In this study, an effort is made to correlate the compaction characteristics of poorly graded sand with the percentage of fines present in it. Plastic and non plastic fines are added to poorly graded sands in varying quantities and the changes in maximum dry unit weight and optimum moisture content are studied. It has been found from the studies that the addition of fines up to a certain amount increases the maximum dry unit weight of poorly graded sands and the amount of increase depends on the uniformity coefficient value of the sand.

Dynamic Pavement-Vehicle Interaction of Rigid Pavement Resting on Two-Parameter Soil Medium

An improved solution algorithm based on Finite Element Method is adopted to analyze rigid pavements under moving vehicular or aircraft loads. Analysis is based on the classical theory of thick plates resting on two-parameter elastic soil medium. The pavement is discretized by four node thick plate elements that account for the transverse shear deformation and bending. The underlying soil medium is modeled by Pasternak shear layer and linear elastic spring and dashpot systems. The dynamic interaction between the moving load and the pavement is considered by modeling the vehicle by spring-dashpot unit. The pavement-vehicle interaction force is modeled with Dirac-delta function. It has been observed that the dynamic interaction between the moving load and the pavement has significant effect on pavement response.

Distribution of Stress on Stone Column-Reinforced Soft Soil under Cylindrical Storage Tank

Structures with circular foundation (chimney, silo, oil tank) constructed on compressible soft soil, often have to opt for ground improvement like stone columns before construction. In this paper, the stress distribution on stone column-reinforced ground under cylindrical storage tank has been presented. Actual foundation soil reinforced with stone column is assumed as composite ground of soil and hollow cylindrical stone rings keeping the area ratio constant to carry the analysis in axi-symmetric condition. The soft soil, stone columns and granular fill are idealized using mechanical elements. The floor slab of the storage tank is assumed to be flexible enough to satisfy the theory of thin plate. Governing differential equations are derived to determine the vertical settlement and solved with finite difference technique. Contact stress at ground level is calculated from vertical settlement. It is observed that soft soil experiences heavy settlement and contact stress when the tank is full despite of low spacing to diameter ratio (S/dc = 3) and reasonable modular ratio (Ec/Es = 20). It is also observed that stress acting on edge stone column is lower as compared to the stress acting on center stone column even under uniformly loaded condition.

Effect of vehicle–pavement interaction on dynamic response of rigid pavements

In the present paper, dynamic response of rigid pavements subjected to moving vehicular loads is presented using an analytical procedure based on the finite element method. The vehicle–pavement interaction effects are taken into account while developing the solution algorithm. The concrete pavement is discretized by finite and infinite beam elements. Infinite elements are helpful in appropriate modeling of end conditions. The main purpose of the development of infinite elements is to model the unbounded domain. The underlying soil medium is modeled by Pasternak model which assumes the existence of shear interaction between the spring elements. The moving vehicle is represented by a mass supported by a spring-dashpot system. The vehicle -pavement interaction force is modeled with Dirac-delta function. Dynamic equilibrium equation is solved with Newmark-Beta integration scheme. It has been observed that the dynamic interaction between the moving load and the pavement has significant effect on pavement response. Parametric study is carried out to investigate the effect of vehicle–pavement interaction (VPI) and soil parameters on the response of pavement.