Undrained Static Response of Loose and Medium Dense Silty Sand of Mostaganem (Northern Algeria)

Abstract

Critical undrained shear strength of sandy soils is a fundamental parameter in stability analysis. This will help to evaluate the occurrence of flow deformation under liquefaction phenomena. A precise evaluation of the undrained liquefaction strength is very important for the design of soil structures such as earth dams, building foundations and soil densification process which can avoid catastrophic failure due to soil instability. In this work, laboratory investigation on natural and on reconstituted soil specimens of silica sands was carried out to enable the analysis of its mechanical behavior. Several concepts have been proposed by many researchers in order to characterize instability of silty sands. However, a review of studies published in the literature indicates that no clear conclusions can be drawn as to what manner the variation of fine content affects the mechanical behavior. The present paper is an attempt to experimentally describe mechanical behavior and theoretically justify such response of loose and medium dense sand by means of critical state parameters. Two distinct stress path tendencies have been shown in this study. In undrained conditions, loose samples show amplified contractive phase with fine content ranging from 0 to 30%, while medium dense samples exhibit a contractive phase followed by a dilative phase with fine contents beyond 30%. In this study, it has been shown that the strength of sand fabric of carrying loads becomes weaker and the critical state parameter increases with the increase in fine content leading to the reduction of normalized critical undrained shear strength.