Research On Inrush Disaster Control Of Deep Foundation Pit In Soft Soil Area

Confined water with high water level has always been a major problem in the excavation process of foundation pits.If it is not handled properly,it will lead to serious foundation pit accidents.Relying on the foundation pit inrush accident of the deep foundation pit project of the crossriver tunnel on the north bank of the Yangtze River,based on the basic theory of groundwater seepage,a two-dimensional seepage model was established for the target foundation pit with the help of the groundwater seepage simulation software Visual MODFLOW,from the perspective of decompression and precipitation outside the pit,to analyze and study the management of sudden surge accidents caused by confined water.Using ABAQUS numerical simulation software,the fluid-structure coupling analysis method is used to simulate and study the influence of foundation pit excavation and dewatering on the foundation pit deformation.The following conclusions are obtained by comparing the monitoring data and numerical simulation analysis data:(1)For deep foundation pits with drop-bottom water-stop curtains,when the deep confined water in the pit surges in the foundation pit,the decompression and dewatering measures outside the pit are taken,and the effect is obvious;(2)The mixed well structure has better dewatering effect and higher efficiency than the conventional dewatering well structure;when the size of the filter tube is 2/3 of the thickness of the confined aquifer,the precipitation effect is better;(3)In general,the surface settlement value outside the pit is greatly affected by the excavation of the foundation pit,and increases with the excavation depth of the foundation pit.After decompression and precipitation outside the pit,the surface subsidence value has a sudden change,and the abrupt change is about 2 times of the normal construction condition,which changes with the decompression and precipitation;(4)The horizontal displacement of the enclosure structure follows the excavation of the foundation pit,and the maximum horizontal displacement occurs near the excavation surface of the foundation pit.For the long-strip foundation pit,the influence of the foundation pit inrush accident on the horizontal displacement of the longitudinal envelope structure is greater than that of the horizontal envelope structure.(5)The axial force of the inner support gradually increases with the construction of the foundation pit,and the installation of the lower support will reduce the axial force of the upper support.After decompression and precipitation outside the pit,the axial force of each layer of support is significantly reduced.(6)Theexcavation of the foundation pit,and the uplift increases with the increase of the excavation depth.After decompression and precipitation outside the pit,the uplift of the basement decreases significantly.