Case Analysis of Water Gushing in a Deep Foundation Pit Caused by Local Defects

Water gushing is a common engineering geological disaster in the process of foundation pit construction. Its successful judgment directly affects the safety of engineering construction. Taking the case of water gushing at the bottom of the foundation pitas as a research object, the mechanism and treatment of water gushing in foundation pits, the stability against water gushing, and its influencing factors are analyzed with a field investigation, field testing, and theoretical calculation. The calculation formula for the safety factor and critical thickness of the foundation pit against surges, considering the influence of multiple factors, is deduced. The influence of the height of the confined water level, the thickness of the water-resisting layer, the shear strength of the soil mass, the reinforcement depth of the soil mass in the pit, and the diameter of the bearing pile in the pit on the safety factor of the foundation pit surge are expounded. In addition, measures such as the reinforcement of the soil mass in the passive area in the pit, the increase in the thickness of the water-resisting layer, and the reduction in the confined water level are proposed to improve the anti-surge stability of the foundation pit. A new monitoring method is proposed for characterizing uplift deformation at the bottom of the pit without affecting normal construction. The research results show that: (1) the minimum safety factor against surges, considering multiple factors, is 1.455, and the critical thickness is 5.87 m, which is in line with specifications. (2) Measures such as reinforcing the soil in the passive zone of the pit, increasing the thickness of the water-insulating layer, and lowering the bearing pressure level are used to improve the stability of the pit against surges. (3) The pit, obtained by the pit bottom counter-pressure, pumping water out of the pit, and the timely construction of the pit bottom bedding to block the program, exhibits a measured maximum bottom plate pressure of 115.189 kPa, and the deformation corresponding to the method proposed in this paper is 1.406 mm, which is better disposed in the field. The research results provide a reference basis for the judgment of anti-surge stability of foundation pits and similar engineering applications.