Evaluation of Dynamic Properties and Liquefaction Studies for Sandy Soil—A Case Study

Abstract

Dynamic properties of sandy soils, viz. shear modulus (G) and damping ratio (D), are the most important properties for designing geotechnical structures that involve dynamic loading of soils and soil–structure interaction. Liquefaction phenomenon is the most common cause of ground failure during earthquake which has produced severe damage to the structures all over the world. In this paper, a case study has been considered for Shahpurkandi Dam Project which is located on the Ravi River in Pathankot district of Punjab, India. The project also consists of 55.5 m high concrete gravity dam. The main purpose of the project is to generate electricity up to 206 MW and provide irrigation to Punjab and Jammu and Kashmir. The dam foundation consists of different strata of sand lenses at different depths. Efforts are made to study the effect of earthquake on liquefaction potential for these sand lenses at different depths. Undisturbed samples were collected from the sandy soil deposited below the foundation and carried out grain size analysis, proctor density, relative density, resonant column and cyclic simple shear tests in the laboratory for determining the material properties and liquefaction study. The liquid limit, plastic limit and plasticity index were also determined. The dry density and the moisture content of the material vary from 1.5 to 1.68 gm/cc and 8.7 to 14.2%, respectively. The relative density of the material varies from 50 to 73%. Resonant column tests were conducted for 70% relative density with the varying confining pressure from 1 to 4 kg/cm2 and determined shear modulus and damping ratio. Effect of confining pressure was studied on dynamic properties of sandy soil. The study shows that the shear modulus increases and damping ratio decreases with increase in confining pressure. Also, it is observed that the damping ratio varies from 1.18 to 2.8% and shear modulus varies from 770 to 2000 kg/cm2 for the confining pressure ranging from 1 to 4 kg/cm2. The high value of shear modulus indicates that the sand is dense. It is also observed that the damping ratio increases and shear modulus decreases with increase in shear strain amplitude. Undrained cyclic simple shear tests were conducted on saturated soil specimens and determined cyclic strength which is required for evaluating the liquefaction potential of sandy soil. Seed’s simplified procedure has been used to evaluate liquefaction potential for the studied material. The study shows that the cyclic strength of the soil at different depths is more than the cyclic shear stresses induced due to earthquakes of two magnitudes (6.5 and 8.0). Liquefaction potential study shows that the sandy soil deposits are sufficiently dense and are not susceptible to liquefaction for the considered earthquake magnitudes.