Initial static shear effect on cyclic liquefaction behaviour of sand

Abstract

Evaluation of soil liquefaction potential plays a key role in geotechnical earthquake engineering design since liquefaction is a major cause of earthquake-induced damages. While the evaluation procedure works well for free-field level ground conditions, the existence of initial static driving shear stress under earth dams or buildings complicates the issue. To address the insufficiency in current understanding, this paper presents an experimental study of the initial shear effect on the liquefaction resistance of sand, focusing mainly on the dependence of the effect on the initial state and sand type. A large number of cyclic triaxial tests have been conducted on two standard silica sands under a wide range of initial shear stress, density and confining pressure. Three distinct cyclic responses are identified to be dependent on the initial state and degree of stress reversal. The test results indicate that while the initial shear effect on loose sand can be beneficial or detrimental, that on dense sand is always favourable. However, a sufficiently high level of initial shear or confining stress could reverse the effect on dense sand. A new concept, termed as threshold a, is presented along with the zero reversal line to effectively characterise the initial shear effect. The insufficiency of the existing empirical Kα correlation chart is also examined against the experimental data.