Effect of Loading Frequency on Small-Strain Shear Modulus of Soils

Abstract

The effects of loading frequency on small-strain shear modulus of various types of soils were investigated by using resonant column (RC) and torsional shear (TS) tests. Both RC and TS tests were performed with a same piece of equipment, eliminating variability due to preparing "identical" samples. Tested soils include washed mortar sand, ten compacted subgrade soils, and 37 undisturbed natural soils. Frequency effect was investigated at small strain where the effect of the number of loading cycles is negligible. Loading frequency has almost no effect on the stiffness of the washed mortar sand. The stiffness of undisturbed natural soils and compacted subgrade soils increase linearly as a function of the logarithm of loading frequency, and the effect of loading frequency was quantified. The frequency effect on undisturbed natural soils varies from 0.15% to 9.15% per log cycle of loading frequency and that of compacted subgrade soils ranges from 4.5% to 8.4%. The frequency effect on the natural sandy soils is not negligible but the value is less than 3.5%. The frequency effect of undisturbed natural soils was well correlated with index properties such as the plasticity index, void ratio, and water content, and it increases as each index property increases. The frequency effect on natural sandy soils was difficult to correlate with soil index properties and is affected by the characteristics of fine particles included in the soils.