Laboratory Investigation into the Effect of Particle Sizes on Shear Wave Parameters Using Bender Elements Test Results

Abstract

Evaluating the influences of soil particle size on the dynamic behavior of soils during wave propagation has been an important issue in geotechnical engineering. Heretofore, the effects of particle size on shear wave velocities in soils have been examined using various experimental techniques. Most research in this regard so far have been carried out over a limited range of particle sizes, and the results have indicated contrasting effects of particle size on shear wave velocity (Vs). However, there has not been a comprehensive and unambiguous outcome describing the influences of particle size on Vs in soils. This research aims to experimentally investigate the effects of a wider range of particle sizes on Vs, wave shape, and frequency content of the shear waves transmitted in soil specimens. To this aim, a bender element apparatus embedded in a triaxial cell were used to minutely measure shear wave parameters of ten groups of local dry sandy soils, R1 (d50 = 0.225 mm) to R10 (d50 = 7.14 mm) samples. Moreover, dry tamping methods were employed to provide comparable samples at a similar initial void ratio of 0.8. Various amounts of frequency (5–12 kHz) and various confining pressures (50–500 kPa) were conducted on the identically prepared clean sand samples. Based on the results, it was observed that, for samples with mean particle sizes between 0.225 mm (R1) and 1.290 mm (R6), the Vs increased with the particle diameter, but for samples with mean particle sizes between 1.290 mm (R6) and 7.140 mm (R10), an increment in the particle diameter caused the Vs to decrease. It can be inferred that particle size influences the shape of the received signals such that the frequency content of the received signals, in both fine- and coarse-grained soils, are quite similar; however, medium-sized soils have a higher frequency content and a higher Vs, as well.