Behaviours of groundwater and strata during dewatering of large-scale excavations with a nearby underground barrier

Abstract

When an excavation is close to an existing underground structure which exactly penetrates aquifers, the structure would exert water-blocking (WB) and soil-blocking (SB) effects by changing the groundwater seepage and restricting the strata movement. These two barrier effects would make the dewatering-induced behaviours of groundwater and strata be different from the case with no nearby structure. In this study, a typical metro station was selected as an underground barrier, and its barrier effect on the responses of groundwater and strata to dewatering of adjacent large-scale excavations were numerically investigated. Results indicate that regardless of the excavation scale, the overall water yield of the excavation would be reduced by considering the WB effect, while in the meantime, the induced groundwater drawdown would be enlarged, meaning the number of the designed pumping wells could be reduced to achieve the same dewatering effect. The strata behaviour under barrier effect is more complicated, depending on the coupled action of the WB and SB effects; both the excavation width (B) and the distance of station to the excavation (D) could largely affect the intensity of the WB and SB effects, further determining the ground settlement amount (either larger or smaller than that without barrier effect). Designers should consider the barrier effect based on practical D and B to realize the optimal or economic design and meanwhile to prevent the appearance of unexpected large responses of groundwater and strata during dewatering construction.