Impact response of unsaturated sandy soil under triaxial stress

Abstract Sandy soil is a common geotechnical material, which differs from sand because of its visco-plasticity. The effects of strain rate, moisture content, degree of compaction, and stress state on the dynamic mechanical properties of sandy soil were studied by using a split-Hopkinson pressure bar (SHPB). These four factors were determined by dimensional analysis. The relationship between the dimensionless compressive strength and the influencing factors was revealed by a second regression analysis based on experimental data. The results show that unsaturated sandy soil exhibits strain-rate strengthening between 500 s−1 and 2200 s−1. Sandy soil can be always enhanced by increasing the moisture content and degree of compaction. The mechanical properties of the sandy soil specimens with 100% and 97.5% degrees of compaction are similar, but both are significantly better than those at 95% degree of compaction. Specimens with 15% moisture content are twice as stronger as the others. At the same strain rate, the mechanical performance of the sandy soil under the restraint of the steel sleeve is much less than that of the aluminum alloy sleeved sandy soil specimens. This difference can reach 50% as the strain rate increases to 2100 s−1. This is related to the triaxial stress state and dynamic Poisson's ratio of the sandy soil within the sleeve. The strength of polycarbonate (PC) sleeved specimens is always very low because the restraining effect of the PC sleeve is almost negligible. The mechanical response of sandy soil constrained by a PC sleeve is similar to that obtained in a uniaxial compression test.