EFFECT OF CROSS WALL HEIGHT ON ENCLOSURE WALL DEFLECTION INCURRED BY PUMPING TEST BEFORE BULK EXCAVATION

Dewatering before bulk excavation is able to cause centimeter-level wall deflection, while the commonly-used inner strut system cannot effectively limit the wall deflection at deep location. Recently, aiming at the inner cross-wall system frequently used to achieve sectionalized construction in soft soil area, some scholars proposed a deformation-control idea of making use of cross wall and optimizing its layout, which effectively restricts the dewatering-induced deformation. This paper aims to further optimize the arrangement of the cross wall to ensure the deformation control effect under the most economical conditions. It investigates the influence of cross wall height on the enclosure wall deflection incurred by dewatering before bulk excavation. Based on an actual foundation pit, a series of numerical simulations are conducted to explore the deformation characteristics of enclosure wall incurred by dewatering before bulk excavation under different pumping depths and cross wall height. On this basis, this paper proposes the optimized layout of cross wall in depth direction. Results show that the layout of cross wall in depth direction has a great influence on its deformation control effect. Specifically, the installation of cross wall within the pumping depth can significantly reduce the retaining wall deflection triggered by pumping, while the installation of cross wall below the pumping depth has a very limited effect on the control of retaining wall deformation. In order to take into account both the economy and deformation control effect, this paper recommends to set the cross wall top at 0.33-0.67H_d above the pumping depth(H_d) and set the cross wall bottom at H_d. When there are deeply-buried structures outside the pit which are sensitive to deformation, it should be better to extend the cross wall bottom downward by 1/3H_f to achieve the deformation control of deeply buried structures, where H_f is the distance between the pumping depth location to the retaining wall bottom.