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To reduce ground displacements induced by dewatering and excavation in foundation engineering, it is crucial to predict the ground displacements before construction. Two types of analyses, i.e., transient analysis (TA) and steady state analysis (SSA), are often used to predict ground displacements. To facilitate appropriate use of the two analyses in this study, both TA and SSA are carried out for a large-scale excavation in Shanghai, China. The calculations include groundwater table, ground settlement, and horizontal displacement. Comparisons between the calculated results and the measured results are made. Both the calculated and the measured results suggest that the deep mixing soil walls and diaphragm walls play an important part in preventing groundwater seepage and constraining soil movement. The calculated results show similar tendencies to the measured results, although the magnitudes were different. The comparisons indicate that TA is more accurate, and it is appropriate for detailed analysis of construction processes. SSA requires less calculation and is suitable for preliminary evaluation. [ABSTRACT FROM AUTHOR]

Dewatering-induced ground settlement is an important issue, and there a cumulative effect in stratified soil settlement. Detailed research of the stratified soil settlement devotes to a better evaluation of ground settlement. To better investigate the dewatering-induced stratified settlement characteristics of the soil strata in Shanghai, an intensive field-monitoring program was carried out for the excavation of an underground metro station, which involved the dewatering of confined aquifers in urban areas. Analyses of monitoring results suggest that the groundwater tables dropped steadily. The ground settlement decreased with an increasing distance from the excavation, and the maximum ground settlement was less than the allowable value. The results for stratified settlement monitoring showed that the ground settlement was less than the settlement at the bottom of the soft soil clay layer, which indicates that the clay layer swelled during dewatering in the underlying soil layer. This special phenomenon, referred to as dewater-caused soil expansion, has not been reported in the existing literature. This project acts as a special case study and provides a basic insight into this phenomenon. [ABSTRACT FROM AUTHOR]