Residual Soil Settlment Related to the Weathering Profile

Residual soils are the in-place residue from rock weathering. They differ greatly from the better understood deposited soils in that their particle arrangements and mineralogy reflect both the degree of weathering and the structure of the parent rock. They are neither homogeneous nor isotropic. Like deposited soils they consolidate under load, but the soil compressibility is related empirically to the void ratio of the undisturbed material instead of to the usual index properties. Because most of the more compressible residual soils are partially saturated, their settlements develop far more rapidly than those of clays, usually within the first year after loading. Conventional laboratory tests and analyses based on in-situ pressuremeter tests can be used for predicting settlements. The conventional analyses tend to over predict settlement by about 25 percent; the pressuremeter results appear to be more scattered, but on the average the predictions are closer to the measured settlements.