Mechanical characteristics of cohesive gravelly soils under bidirectional cyclic loading

The behavior of soils under seismic loading is a critical aspect of geotechnical engineering, particularly in regions prone to strong earthquakes. Soils are subjected to complex cyclic loading conditions combining both vertical and horizontal stresses under strong seismic excitations. However, previous experimental studies seldom considered the effect of horizontal cyclic stresses on soils, especially for cohesive gravelly soils. To address this limitation, this study aims to conduct a series of large-scale cyclic triaxial tests on gravelly clay sample with various gravel contents subjected to dynamic confining pressures (represented as DCP stress path η), more closely replicating the actual conditions soils encounter during seismic events. The features of cyclic stress-strain responses, effective stress paths (p-q) and excess pore water built-ups are firstly analyzed. The test results showed the axial strains at failure are increased with the increasing of DCP stress path η. The effect of the gravel content on the dynamic characteristics of gravelly clay is furtherly discussed in detail. Moreover, a unified formula incorporating axial strains, excess pore pressure, and gravel contents was established that can provide a good reference for predicting dynamic behaviors in cyclic triaxial tests with different DCP stress paths η. The test results will help to identify potential failure mechanisms, evaluate the soil’s resilience, and inform the development of improved seismic design practices for soil-infrastructure in earthquake-prone areas.