Design practice of deep and complex foundation pit based on local conditions and displacement control

A foundation pit excavation was located in Beijing urban area with a depth of approximately 16.5 meters, with a local deepened area of up to 20.4 meters. Surrounding the excavation were numerous utility lines and residential buildings, as well as multiple layers of groundwater within the excavation depth range. The groundwater control design utilized a thick overlapping bottom-fall curtain wall to effectively solve the problem of groundwater seepage, suppressed the additional settlement of surrounding soil layers, and played a positive role in controlling the deformation of surrounding buildings. According to the local condition, emergency depressurization wells were set up around the excavation and in the local deepened area, effectively ensuring the construction of water-submerged anchor rods and playing a positive role in preventing the sudden surge of confined water. The foundation pit support design adhered to the principle of displacement control, combining numerical and theoretical calculations to predict the deformation of deep foundation pit. A standard for the displacement control of support structures was proposed, and different stiffness support systems were selected based on the degree of sensitivity of the surrounding environment. Specific requirements were also made for the construction process of anchor rods and water control measures to effectively ensure the safety and normal use of the foundation pit and surrounding environment while saving time and costs.