Influence of index properties on the cyclic failure of fine-grained soils

Abstract

The purpose of this study is to develop an easy procedure to diagnose the cyclic behavior of fine-grained soils, leading to liquefaction.There are approaches to this problem with reference to liquid limit (wL), plasticity index (PI), clay content, (C%), in-situ water content compared to the liquid limit (wn/wL), average grain size (D50), and liquidity index (IL). Previous research has indicated that fine-grained soils defined as “sand-like” are prone to liquefaction. There is consensus that liquefiable silty soils have “sand like” characteristics. In the transition from sandy to clayey, it is generally accepted that it would be appropriate to make a judgment by making use of mechanical testing and that clayey soils do not liquefy.This paper presents the results of dynamic triaxial shear testing (CTX), where excess pore water pressures and axial strains are evaluated compared to the physical properties to reach the threshold for cyclic failure. Samples of undisturbed soil procured from different locations of the city of Adapazarı, Turkey, were subjected to CTX testing. The results were interpreted in the light of the physical properties to arrive at a judgment of cyclic failure.Being able to identify a liquefaction prone fine grained soil by merely measuring a few physical properties without resorting to arduous cyclic testing would be an advantage to the practising engineer. This however necessitates the elimination of the ‘gray zone’ for which most researchers recommended the use of cyclic testing.The main finding of this study is that samples reaching double strain amplitude (DSA) of <5% in the CTX test contain no sand and have a clay content of 20% or more. An attempt to establish a relationship between sensitivity to cyclic loading and physical properties is also made.