Abstract: Based on the foundation pit project of the scientific research base of Gansu coalfield geology bureau, through the combination of on-site monitoring and numerical calculation, this paper analyzes the influence of the composite support system of prestressed anchor cable and row pile local plug high-pressure jet grouting pile on the seepage, deformation characteristics and potential failure forms of foundation pit slope during the excavation process under the action of existing buildings. The results show that the combined water stop curtain of row piles and local high-pressure jet grouting piles can effectively extend the groundwater seepage path and significantly reduce the groundwater seepage velocity. Although the existing buildings limit the vertical settlement of the surface soil in the excavation process to a certain extent, they also aggravate the lateral displacement of the soil, which increases the internal pressure of the jet grouting pile and greatly reduces the overall stability of the foundation pit. Under the action of existing buildings, the formation of two groups of potential fracture surfaces at the bottom of the foundation pit is the main reason for the great reduction of the stability of the foundation pit slope.

Key words: existing buildings, pile anchor support, finite element, foundation pit deformation