Behaviour of a weakly bonded residual soil subjected to monotonic and cyclic loading

Residual soils are found all around the world. Their behaviour is different from ‘classic’ soils due to the structure resulting from the geological formation processes, which can eventually undergo degradation under static and cyclic loads, with a decrease in both stiffness and strength. In this context, the aim of the present study was to evaluate the behaviour of weakly bonded residual soil in the face of loading and unloading cycles using field plate load tests. Preliminary field and laboratory tests were carried out to characterise the residual soil at the experimental site. Monotonic and cyclic plate load tests – with circular and square plates – were performed under three different load amplitudes. The results showed no shape effect of the loaded area for both monotonic and cyclic loading, considering the same loading pattern. Also, there is a threshold load, which indicates a yielding point and a change in soil behaviour and can be estimated from simple laboratory tests. Below this load, the residual soil presented a rigid behaviour even when subjected to cyclic loads.