Field Investigation and Prediction of Responses of Far-Field Ground and Groundwater to Pumping Artesian Water in Deep Excavations

Abstract

Pumping artesian water is mandatory in deep excavation above a shallow confined aquifer with a high piezometric head. In this study, a comprehensive monitoring program is performed to investigate the responses of far-field ground and groundwater to the pumping of artesian water in deep excavations. The artesian water level was monitored by observation wells, and the pore pressures along the depth were monitored by a cluster of vibrating wire piezometers. The ground surface settlement and subsurface settlement were surveyed by level instruments and multiple position extensometers, respectively. These measured data are analyzed comprehensively and thoroughly. Moreover, a simplified prediction method of far-field groundwater drawdown and ground surface settlements induced by dewatering is proposed. Results indicate that the response of artesian water levels is closely related to the discharge and recharge flow. Because of the vertical drainage, the pore pressures in the lower portion of the aquitard above the confined aquifer decrease slightly during the dewatering process. However, the pore pressures in poorly conductive soils barely increase during the short dated recharge. The developments of the ground surface settlements are consistent with the artesian water level. The ground surface beyond 4He settled significantly after dewatering, and the influence zone of dewatering on ground surface settlements extended to 1He, where He represents the final excavation depth. The measured data reveal that dewatering in the confined aquifer resulted in the compression of all soil layers. The comparison between predicted results and the monitoring data confirms the practicability of the proposed method.