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CONTENTS
Volume 3, Number 2, June 2011
 

Abstract
The effect of non-plastic fines (silt) on liquefaction and pore pressure generation characteristics of saturated sands was studied through undrained stress controlled cyclic triaxial tests using cylindrical specimens of size 50 mm diameter and height 100 mm at different cyclic stress ratios and at a frequency of 0.1 Hz. The tests were carried out in the laboratory adopting various measures of sample density through various approaches namely gross void ratio approach, relative density approach, sand skeleton void ratio approach, and interfine void ratio approach. The limiting silt content and the relative density of a specimen were found to influence the undrained cyclic response of sand-silt mixtures to a great extent. Undrained cyclic response was observed to be independent of silt content at very high relative densities. However, the presence of fines significantly influenced this response of loose to medium dense specimens. Combined analyses of cyclic resistance have been done using the entire data collected from all the approaches.

Key Words
stress controlled; gross void ratio; sand skeleton void ratio; interfine void ratio; limiting silt content; cyclic response.

Address
H.K. Dash: Department of Civil Engineering, College of Engineering and Technology (CET), Biju Patnaik University of
Technology (BPUT), Bhubaneswar, India - 751003
T.G. Sitharam: Department of Civil Engineering, Indian Institute of Science, Bangalore, India - 560 012

Abstract
This note presents an analytical solution for the determination of the shape factor of a flush bottom piezometer in a uniform, isotropic, and incompressible deep soil deposit. The deduced shape factor is compared to published values obtained by approximate methods. Depending on the selected value, the difference may reach 11%.

Key Words
hydraulic conductivity; shape factor; flush bottom piezometer; analytical solution; comparisons.

Address
Vincenzo Silvestri, Christian Bravo-Jonard and Ghassan Abou-Samra: Department of Civil, Geological, and Mining Engineering, Ecole Polytechnique, P. B. 6079, Station Centre-Ville, Montreal, Quebec, Canada H3C 3A7

Abstract
The methods of design available for geocell-supported embankments are very few. Two of the earlier methods are considered in this paper and a third method is proposed and compared with them. In the first method called slip line method, plastic bearing failure of the soil was assumed and the additional resistance due to geocell layer is calculated using a non-symmetric slip line field in the soft foundation soil. In the second method based on slope stability analysis, general-purpose slope stability program was used to design the geocell mattress of required strength for embankment. In the third method proposed in this paper, geocell reinforcement is designed based on the plane strain finite element analysis of embankments. The geocell layer is modelled as an equivalent composite layer with modified strength and stiffness values. The strength and dimensions of geocell layer is estimated for the required bearing capacity or permissible deformations. These three design methods are compared through a design example. It is observed that the design method based on finite element simulations is most comprehensive because it addresses the issue of permissible deformations and also gives complete stress, deformation and strain behaviour of the embankment under given loading conditions.

Key Words
geocell; reinforcement; embankment; soft ground; design; composite model; finite element analysis.

Address
G. Madhavi Latha: Department of Civil Engineering, Indian Institute of Science, Bangalore - 560 012, India

Abstract
The electrical conductivity of a soil-water system is related to its engineering properties. By measuring the soil electrical conductivity, one may obtain quantitative, semi-quantitative, or qualitative information to estimate the in-situ soil behavior for site characterization. This paper presents the results of electrical conductivity measured on compacted kaolin clay samples using a circular two-electrode cell in conjunction with a specially designed compaction apparatus, which has the advantage of reducing errors due to sample handling and increasing measurement accuracy. The experimental results are analyzed to observe the effects of various parameters on soil electrical conductivity, i.e. porosity, unit weight, water content and pore water salinity. The performance of existing analytical models for predicting the electrical conductivity of saturated and unsaturated soils is evaluated by calculating empirical constants in these models. It is found that the Rhoades model gives the best fit for the kaolin clay investigated. Two general relationships between the formation factor and soil porosity are established based on the experimental data reported in the literature and measured from this study for saturated soils, which may provide insight for understanding electrical conduction characteristics of soils over a wide range of porosity.

Key Words
compaction; electrical conductivity; formation factor; kaolin clay; salinity.

Address
J.K. Lee and J.Q. Shang: Department of Civil and Environmental Engineering, The University of Western Ontario
London, Ontario N6A 5B9, Canada

Abstract
Traditional design methods of bearing capacity of shallow foundations are deterministic in the sense that they do not explicitly consider the inherent uncertainty associated with the factors affecting bearing capacity. To account for such uncertainty, available deterministic methods rather employ a fixed global factor of safety that may lead to inappropriate bearing capacity predictions. An alternative stochastic approach is essential to provide a more rational estimation of bearing capacity. In this paper, the likely distribution of predicted bearing capacity of strip footings subjected to vertical loads is obtained using a stochastic approach based on the Monte Carlo simulation. The approach accounts for the uncertainty associated with the soil shear strength parameters: cohesion, c, and friction angle,

Key Words
stochastic analysis; Monte Carlo; bearing capacity; shallow foundations; strip footings.

Address
Mohamed A. Shahin: Department of Civil Engineering, Curtin University, WA 6845, Australia
Eric M. Cheung: Mainroads Western Australia, Perth, Australia


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