The design and performance of soil improvement solutions in a deep collapsing residual soil

The stratigraphy, geotechnical characteristics and behaviour of a deep mantle of highly cemented residual sandstone of Pliocene age on the southern Mocambique coastal plain are described. The performance of both soil improvement and deep foundation solutions at natural moisture content as well as "wetted-up" conditions founded within the collapsing sod fabric are outlined. The results of three soil improvement test areas as well as an extensive trial pile test programme for a large Aluminium Smelter Complex are evaluated and discussed. The key issues of foundation choice and performance where metastable soils are encountered are put forward. The changes in soil moisture regime beneath the Smelter site due to changes in the boundary conditions as well as extreme climatic events are tabulated and discussed. Recommendations on the design of foundations in the unique conditions encountered on the Smelter site are given and conclusions are reached on controlling critical aspects of foundation performance in this problematical soil.