Dynamic properties and liquefaction behaviour of cohesive soil in northeast India under staged cyclic loading

Estimation of strain-dependent dynamic soil properties, e.g. the shear modulus and damping ratio, along with the liquefaction potential parameters, is extremely important for the assessment and analysis of almost all geotechnical problems involving dynamic loading. This paper presents the dynamic properties and liquefaction behaviour of cohesive soil subjected to staged cyclic loading, which may be caused by main shocks of earthquakes preceded or followed by minor foreshocks or aftershocks, respectively. Cyclic triaxial tests were conducted on the specimens prepared at different dry densities （1.5 g/cm3 and 1.75 g/cm3） and different water contents ranging from 8% to 25%. The results indicated that the shear modulus reduction （G/Gmax） and damping ratio of the specimen remain unaffected due to the changes in the initial dry density and water content. Damping ratio is significantly affected by confining pressure, whereas G/Gmax is affected marginally. It was seen that the liquefaction criterion of cohesive soils based on single-amplitude shear strain （3.75% or the strain at which excess pore water pressure ratio becomes equal to 1, whichever is lower） depends on the initial state of soils and applied stresses. The dynamic model of the regional soil, obtained as an outcome of the cyclic triaxial tests, can be successfully used for ground response analysis of the region.

Property estimation of free-field sand in 1-g shaking table tests

Experimental data taken from free-field soil in 1-g shaking table tests are valuable for seismic studies on soil-structure interaction.But the available data from medium-to large-scale shaking table tests were not abundant enough to cover a large variety of types and conditions of the soil.In the study,1-g shaking table tests of a 3-m-height sand column were conducted to provide seismic experimental data about sand.The sand was directly collected in-situ,with the largest grain diameter being 2 cm and containing a water content of 6.3%.Properties of the sand were estimated under the influence of white noise plus pulse and earthquake motions,including the settlement,the dynamic properties of the sand column,and the three soil layers′shear modulus degradation relationships.The estimated properties were then indirectly verified by means of finite element analysis.Results show that the estimated parameters were effective and could be used in numerical modeling to reproduce approximate seismic responses of the sand column.