The behaviour of lightly loaded piles in swelling ground and implications for their design Available to Purchase

This paper describes the results of experiments on instrumented piles from a shrinkable/expansible clay site in Kent. On this high-plasticity London Clay site, the ground had been desiccated to a considerable depth by trees which were felled in 1990, resulting in approximately 160 mm of ground heave. The data obtained from the site are used to investigate design methods for lightly loaded bored piles in swelling clays. It is concluded that: in stiff clays, under seasonal shrinkage and swelling near trees, shear stresses may quickly reach a peak value which appears to be associated with the fully softened strength, ϕ′_cv, and at large displacement reach a limiting value that appears to be associated with residual strength, ϕ′_r; application of ‘normal’ α factors to desiccated soil strengths in ground that is swelling is likely to lead to a significant overestimate of maximum shear stress. A design framework in which ultimate and serviceability limit states are examined explicitly, rather than through a single factor of safety, is recommended as being more appropriate for lightly loaded piles in swelling ground.