Effect of fines content and plasticity on liquefaction susceptibility of sand matrix soils

Abstract

Empirical evidences revealed that not only clean sand is susceptible to soil liquefaction hazard but the sand matrix soils (sand contains little presenting fines) are also liquefiable. Most of previous studies focused on the compositional characteristic as main causes in influencing the liquefaction susceptibility and neglected the plasticity of plastic fines. An experimental based study has been carried out aimed to develop the liquefaction susceptibility chart that considers the coupled effects of fines content and plasticity to predict the liquefaction susceptibility of sand matrix soils. The sand matrix soils were reconstituted by mixing low plastic kaolin and high plastic bentonite to the poorly graded sand at different percentages by weight. The soils were tested with triaxial apparatus under isotropically consolidated undrained condition. The results of strain controlled monotonic triaxial compression tests using Mohr-Coulomb failure criterion showed that with the increased of fines, the role of frictional resistance of sand was slowly replaced by the cohesion resistance coming from the plasticity of sand matrix soils. The concept of threshold fines content was verified through the results analysed using critical state failure criteria. The results of stress controlled two-way cyclic triaxial tests on clean sand showed that liquefaction resistance of the sand is proportional to cyclic stress ratio, effective consolidation pressure and density index. The standardised condition to test the sand matrix soils were at loose state condition and confined with low effective consolidation pressure using 1 Hz cyclic loading to simulate earthquake condition. Liquefaction susceptibility increases with the increases of fines content and in reverse trend after exceeded threshold fines content. Sand matrix soils with more plasticity have more resistance towards liquefaction. Based on statistical analysis, a multivariable liquefaction susceptibility equation was formulated. Using the equation, the assessment charts that considered the effect of fines content (in the form of density ratio) and the effect of plasticity (in term of plasticity ratio) were developed.