Study of evaluation method of anti-uprush stability of foundation pit with thick interbedded soil layers in Wuhan

Aiming at the foundation pit with thick interbedded soil in Wuhan, considering the gravity, friction and cohesion of thick interbedded soil, a calculation model of anti-uprush of foundation pit with thick interbedded soil was established, and a calculation method of the anti-uprush stability of foundation pit with thick interbedded soil was proposed. Taking the foundation pit of Wuhan Huarun Wanxiang as an example, the calculation results of the model proposed in this paper are compared with the Technical Specification for Ｒetaining and Protection of Building Foundation Excavations (JGJ120—2012) and existing literatures. The results show that when the thick interbedded soil was regarded as multiple thin aquifer layers and the pressure method is used to judge the uprush instability, the uprush instability area is only limited to the range of 1~2 m at the top of the thick interbedded soil, so the thick interbedded soil can be regarded as an impermeable layer instead of aquifer. Because most of the thick interbedded soil in Wuhan area is more than 2 m, the calculation results of the Technical Specification for Ｒetaining and Protection of Building Foundation Excavations (JGJ120—2012) tend to be conservative. The safety factor of anti-uprush is calculated as 3.5 in the model of anti-uprush of foundation pit with thick interbedded soil which considering the gravity, friction and cohesion of thick interbedded soil, while the safety factor of anti-uprush calculated by the pressure balance method adopted by the code under the same site conditions is 1.5, the calculation result of anti-uprush stability model is about 2.2 times than the Technical Specification for Ｒetaining and Protection of Building Foundation Excavations (JGJ120—2012). Therefore, the stability of anti-uprush at the bottom of the pit calculated by this method will be better than that calculated by this method. It is more practical and economical to rely on soil gravity to resist inrush damage, but this conclusion still needs to be tested by a lot of engineering practice. This study is a useful exploration for redefining the role of interbedded soil in the anti- uprush of foundation pit.