Sedimentary Environment and Subsidence of Soft Ground of Alluvial Deposits ('Chuseki-so') in Yokohama Lowland

A marked subsidence of soft ground has been occurring as a result of excessive pumping of groundwater due to industrial development and large-scale excavation due to construction works in Yokohama City. The zone in which the subsidence occurs is concentrated around river lowlands and the zone is composed of an extremely weak formation of alluvial deposits. In this paper, we examined the result of investigating the land subsidence, which is one form of ground environmental disaster. On the basis of the result of subsidence measurement, investigation of soil properties and the sedimentation environment of the past, the subsidence rate of the ground was compared with the sedimentation rate of alluvial deposits. As a result, the amount of subsidence inside a stratum is not uniform, and it is shown clearly that there is high correlativity in the sedimentation rate and subsidence rate.