Cyclic and Post-cyclic Shear Behaviour of a Granite Residual Soil – Geogrid Interface

The dynamic frictional properties of the soil-geosynthetic interface play an important role in the design and stability analysis of geosynthetic-reinforced soil structures under repeated loadings, such as those induced by compaction, traffic and earthquakes. This paper describes a laboratory study carried out using a large-scale direct shear test device, aiming to investigate the cyclic and post-cyclic behaviour of an interface between a granite residual soil and a biaxial woven geogrid. In the cyclic direct shear tests, the interface was subjected to 40 cycles of sinusoidal displacement, with semi-amplitude and frequency ranging from 1-10 mm and 0.05-0.5 Hz, respectively. To evaluate the effect of the cyclic loading on the interface shear strength, monotonic direct shear tests were performed immediately following the cyclic tests. The results indicated that the loading frequency has little impact on the interface shear stiffness during the loading cycles. In contrast, the influence of the displacement semi-amplitude on the interface stiffness was found to be significant. The cyclic loading did not lead to the degradation of the post-cyclic interface shear strength. The post-cyclic peak shear strength tended to increase with the semi-amplitude of the shear displacement, which may be associated with an increase in soil density.