Macro and micro analysis on deformation characteristics of fine sand under different groundwater table change

Abstract

By using the samples of fine sand in Shanghai’s seventh layer, creep tests were performed to investigate the deformation characteristics of fine sand under different groundwater table change. It was revealed that the creep of fine sand is closely related to groundwater table change: when the effective force caused by groundwater table change is smaller than pre-consolidation force, the deformation is mainly elastic. When effective force caused by groundwater table change is bigger than pre-consolidation force, the compression deformation is large and the rebound is small; and the deformation is mainly viscoelastic plastic when equal to pre-consolidation stress. Through the scanning electron microscope (SEM) analysis it was found that creep of fine sand is dominated by the slip of particles, not by the breaking of particles. And the fine sand particles are squeezed under the load induced by the groundwater table change, and the particles slide along the indirect contact surface of the particles, resulting in the continuous adjustment of position and relative displacement. Mercury injection test shows that the pore size distribution of fine sand has little change before and after the test.