Precompression design for secondary settlement reduction

A large water treatment plant is to be built on soft deltaic deposits. Precompression has been selected as the method for achieving the required ground improvement. An instrumented preload test has been carried out to obtain reliable information on precompression performance. Distributions of displacements throughout the foundation depth, obtained using sliding micrometer extensometers, have proved extremely useful for identifying the mechanisms of behaviour controlling ground deformation. The magnitudes of displacements are largely dependent on the overconsolidation state of the soil. As primary consolidation settlements take place rather quickly, they can be largely controlled by applying a preload over a limited period. The main design criterion therefore concerns secondary settlements. Laboratory and field data indicate clearly that overconsolidating the soil, even in moderate amounts, significantly reduces the secondary compression rate. The performance of an unloading stage in the preload test provi...