Dynamic Properties of Fine Grained Soils in South of Tehran

Shear modulus, damping ratio and shear wave velocity profiles are important input parameters in site response analysis. For seismic microzonation in south of Tehran, many field and laboratory studies were performed. Field investigations include seismic refraction, down-hole, SASW and SPT while laboratory tests encompass stress controlled cyclic triaxial and resonant column tests on undisturbed samples of low to medium plastic silty materials. This paper presents dynamic properties of fine grained soils in south of Tehran through field and laboratory studies. Based on field geoseismic investigations, new Vs-N(SPT) correlations for fine grained soils are presented. Also laboratory test results reveal that effective confining pressure at stage of consolidation has a remarkable effect on both strain dependent shear modulus and damping ratio of very low plastic soils but by increasing soil plasticity this effect disappears. Evaluation of plasticity effects on deformation properties shows that for PI<12, plasticity index does not have any outstanding effect on these properties, while by increasing PI, shear modulus ratio will increase and damping ratio will decrease.