Load/settlement prediction for large-diameter bored piles in Mercia mudstone

A semi-empirical method has been developed which can predict the characteristics of large-diameter, bored, cast in situ piles in Mercia mudstone, at every stage of loading up to the ultimate state. The analysis is based on mathematical representation of: (a) the mobilization of shaft resistance and end bearing with increasing pile settlement; (b) the variation in load sharing between the pile shaft and base; (c) where present, the additional influence of compressible soil debris on settlement at pile base level; and (d) the effect of nonlinear stress–strain behaviour of concrete on pile compression, hence settlement. The predictive method has been validated against a large database of full-scale pile tests in Mercia mudstone and other cohesive soils. The database comprised test piles with or without instrumentation and having a wide range of diameters and lengths. In every case, the predictive capability is judged to be accurate and satisfactory. The method is also capable of dealing with special circumstances whereby a pile is specifically constructed to support load purely in shaft resistance or end bearing. The improved predictive capability of this method, in pile analysis, is expected to result in a more cost-effective construction.