Study On Groundwater Control For Foundation Pit Engineering And Its Influence On Existing Composite Foundation

Groundwater control, which is an important part of foundation pit engineering, aim at ensuring dry space for the construction of subsurface structure and avoid falling water tables affect the safety of surroundings around foundation pit. Different groundwater control methods lead to different drawdown curves of surroundings around foundation pit, which have a significant impact on the existing building foundation. This paper summarized methods of groundwater control for foundation pit engineering, studied the design and calculating method of groundwater control with vertical cut-off walls basing on simulation by ABAQUS, data fitting by Origin, comparison of measured data and other methods, and analyzed the influence of different groundwater control methods on deformation and force of composite foundation outside the excavation pit, acquired the following conclusions:(1) According to practical engineering and considering different combinations of dewatering, cutting off water and recharge, the groundwater control system for foundation pit engineering was divided into three kinds of control models, including open groundwater control model, enclosed groundwater control model and semi-enclosed groundwater control model, and the design and calculating method of each model were clearly showed.(2) Setting cut-off walls can effectively reduce the scope of the ground surface settlement outside the excavation pit which was caused by the decline of the water table inside the excavation pit, and slow the downward trend of water level to reduce the adverse impact of differential settlement on adjacent buildings or structures(3) Different groundwater control model had different groundwater curve outside the excavation pit, having important influence on nearby composite foundation. CFG-pile composite foundation inclined toward the excavation pit after dewatering. The horizontal displacement of all pile tops without cut-off walls were less than that with cut-off walls. The settlements of all pile tops without cut-off walls were greater than that with cut-off walls. When setting cut-off walls in the actual project, attentions needed to be taken to avoid the horizontal deformation of adjacent buildings or structures may be caused by the water head difference between two sides of cut-off walls.(4) The change rule of mechanical behaviors of CFG-pile composite foundation due to different groundwater control methods were basically the same. Setting cut-off walls can effectively reduce the increment of pile-soil stress ratio and shorten the expanded scope of the negative friction of CFG-pile, which were both caused by the decline of the water table.