Effect of Density on Critical Depth of Liquefaction in a Soil Deposit Containing Double Loose Sand Lenses

Large surface deformations due to liquefaction have been observed in many soil deposits which seem to feature good geotechnical characteristics. These deformations are often caused by the liquefaction of sand layers surrounded by clayey or silty soils called “sand lenses”. Liquefaction potential often decreases with increasing of depth. Hence, a specific depth of embedment of the lenses can be defined below which liquefaction would unlikely happen or the consequential surface deformation would be negligible. This depth is called critical depth. This research aims at studying the effects of the relative density of the sand within the lenses on the critical depth of liquefaction in a soil deposit containing double sand lenses. The soil deposit is simulated in plane strain condition using the computer code, FLAC (Version 4), which is based on finite difference method. Soil deformation, hysteresis loops, shear strain, shear stress, pore water pressure and effective stress in the sand lenses have been plotted during seismic loading. Results indicate that critical depth is strongly dependent on the relative density of the sand. The rate of change of the critical depth versus the standard penetration test number decreases with increasing relative density