Dynamic properties of Piedmont residual soils

Piedmont residual soils were formed by in-situ weathering of igneous and metamorphic rocks. In this research project, their dynamic properties (shear modulus and damping) were investigated by performing a combination of resonant column and torsional shear tests. These properties were evaluated with respect to confining pressure, shear strain amplitude, particle size distribution, cyclic frequency, and number of cycles and compared to results obtained from other studies reported in the literature. Totally 32 specimens of residual soils were tested. These residual soils were classified as MH, ML, SM-ML, and SM, according to the Unified Soil Classification System. The normalized shear modulus and damping values were found to be in the same range as reported by other authors for transported sands, silts, and clays. With increase in the shear strain amplitude, the normalized shear modulus decreased and damping increased at a rate faster than that for clays but slower than that exhibited by sands. An analytical model was established to predict the shear modulus and the damping ratio as a function of confining pressure and shear strain amplitude for four types of Piedmont residual soils.