Geotechnical properties of the Quaternary sediments in Shanghai

The subsoil of Shanghai is composed of Quaternary sediments of the Yangtse River estuary. The center of the city has undergone a man-induced subsidence due to water pumping in the confined multi-aquifer system located in these sediments. Together with a sedimentological study of the post-Pleistocene conditions of deposition and accumulation, an accurate geotechnical study has been completed on the basis of all the available data from identification, oedometer and triaxial tests. Size analysis, X-ray analysis, compressibility characteristics, void ratio, preconsolidation pressures, permeabilities are considered taking into account the sedimentary sequence. Some relations between parameters are deduced and the hydrodynamic parameters are related to compaction parameters in order to predict their coupled and non-linear effects on the subsidence phenomena. Conclusions consist in the determination of the zones where different sensitivities to compaction are evaluated in these Quaternary formations.