Liquefaction proneness of stratified sand-silt layers based on cyclic triaxial tests

Abstract

Most studies on liquefaction have addressed homogeneous soil strata using sand or sand with fine content without considering soil stratification. In this study, cyclic triaxial tests were conducted on the stratified sand specimens embedded with the silt layers to investigate the liquefaction failures and void-redistribution at confining stress of 100 kPa under stress-controlled mode. The loosening of underlying sand mass and hindrance to pore-water flow caused localized bulging at the sand-silt interface. It is observed that at a silt thickness of 0.2H (H is the height of the specimen), nearly 187 load cycles were required to attain liquefaction, which was the highest among all the silt thicknesses with a single silt layer. Therefore, 0.2H is assumed as the optimum silt thickness (topt). The silt was placed at the top, middle and bottom of the specimen to understand the effect of silt layer location. Due to the increase in depth of the silt layer from the top position (capped soil state) to the bottom, the cycles to reach liquefaction (Ncyc,L) increased 2.18 times. Also, when the number of silt layers increased from single to triple, there was an increase of about 880% in Ncyc,L. The micro-characterization analysis of the soil specimens indicated silty materials transported in upper sections of the specimen due to the dissipated pore pressure. The main parameters, including thickness (t), location (z), cyclic stress ratio (CSR), number of silt layers (n) and modified relative density (Dr,m), performed significantly in governing the liquefaction resistance. For this, a multilinear regression model is developed based on critical parameters for prediction of Ncyc,L. Furthermore, the developed constitutive model has been validated using the data from the present study and earlier findings.

Keywords

• Cyclic triaxial tests
• Soil stratification
• Soil liquefaction
• Regression model