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The vertical–horizontal curtain system (VH curtain) is sometimes utilized in foundation pit dewatering under complex hydrogeological conditions. However, the working mechanism of this system when the horizontal curtain is semi-permeable and cannot completely cut off the bottom aquifer remains unknown. A transparent soil physical model test was performed to reveal the water control mechanism of the VH curtain system with a semi-permeable horizontal curtain. A multi-point inert tracer with a high-speed camera was used to photograph the seepage process. The seepage mode was revealed via a model test. With the Shanghai deep tunnel project as background, a numerical simulation was performed to understand the utilization of the VH curtain. The influence of horizontal curtain position, horizontal curtain thickness, horizontal curtain hydraulic conductivity, and VH curtain combination form on the seepage path around the foundation pit and on the drawdown of water level inside and outside the pit were studied. Results provide a basis for the engineering application of the VH curtain pumping well system. [ABSTRACT FROM AUTHOR]

Partial expansion was observed in stratified subsidence during foundation pit dewatering. However, the phenomenon was suspected to be an error because the compression of layers is known to occur when subsidence occurs. A slice of the subsidence cone induced by drawdown was selected as the prototype. Model tests were performed to investigate the phenomenon. The underlying confined aquifer was generated as a movable rigid plate with a hinge at one end. The overlying layers were simulated with remolded materials collected from a construction site. Model tests performed under the conceptual model indicated that partial expansion occurred in stratified settlements under coordination deformation and consolidation conditions. During foundation pit dewatering, rapid drawdown resulted in rapid subsidence in the dewatered confined aquifer. The rapidly subsiding confined aquifer top was the bottom deformation boundary of the overlying layers. Non-coordination deformation was observed at the top and bottom of the subsiding overlying layers. The subsidence of overlying layers was larger at the bottom than at the top. The layers expanded and became thicker. The phenomenon was verified using numerical simulation method based on finite difference method. Compared with numerical simulation results, the boundary effect of the physical tests was obvious in the observation point close to the movable endpoint. The tensile stress of the overlying soil layers induced by the underlying settlement of dewatered confined aquifer contributed to the expansion phenomenon. The partial expansion of overlying soil layers was defined as inversed rebound. The inversed rebound was induced by inversed coordination deformation. Compression was induced by the consolidation in the overlying soil layers because of drainage. Partial expansion occurred when the expansion exceeded the compression. Considering the inversed rebound, traditional layer-wise summation method for calculating subsidence should be revised and improved. [ABSTRACT FROM AUTHOR]