Research Of The Influence Included By Deep Excavation Pit On Surrounding Environment In Karst Area And Engineering Application

With the acceleration of urbanization in China,the exploitation and utilization of underground space are gradually becoming large-scale and intensive.However,the development of underground space and the surrounding complex environment influence and restrict each other.Due to the existence of buried karst in Guangzhou area,it is easy to occur trench collapse of the retaining structure,water gushing in the foundation pit,ground collapse and uneven settlement of the surrounding environment,resulting in casualties and damage to construction machinery.It is only increases the construction period,but also increases the cost.In view of the above problems,this study studied the influence of excavation pit in karst area on the surrounding response using three-dimensional finite element simulation method.The main research contents and results are as follows:(1)The basic physical test,triaxial consolidation drainage test,triaxial loading and unloading test,resonance column test and standard consolidation test were carried out to obtain the soil physical parameters,which provide reliable basis for the establishment of finite element model.(2)By comparing the numerical simulation data with the in-situ test data,the influence of foundation pit excavation on surrounding structures is studied in many aspects.The results show that with the increase of excavation depth,the top of diaphragm wall is spring back in the vertical direction.In the horizontal direction,the displacement of the top of the wall has no obvious rule,while the lateral displacement of rock-socketed diaphragm wall shows a spindle shape with smaller ends and larger middle.The lateral displacement of diaphragm wall without rock-socketed type and with insufficient buried depth shows that the toe of diaphragm wall has a large displacement.The surface settlement is in groove shape,and the surface settlement increases with the increase of the depth of foundation pit.The settlement of pile and the soil displacement field have a great correlation.The settlement of end-supported pile is small,while the settlement of friction pile is relatively large.(3)Based on the three-dimensional model of excavation of Tongdewei excavation,the effects of treatment of karst cave on the response of surrounding structures caused by excavation of excavation are studied in many aspects.The results show that the untreated karst cave increases the surface settlement outside the diaphragm wall near the foundation pit,and the settlement decreases with the increase of the distance from the karst cave.The effect on the lateral displacement of the diaphragm wall is negligible.The numerical analysis of the parameter sensitivity of the grouting material shows that the surface settlement,wall deflection,bridge pier settlement and bridge inclination can be reduced by the treatment of karst cave.However,with the increase of the grouting modulus,the influence on the surrounding environment is very small.Changing the permeability of grouting material under water level has little effect on excavation.(4)Based on the three-dimensional model of Tongdewei foundation pit excavation,the effect of MJS(Metro Jet System)reinforcement treatment on the response of surrounding structures caused by foundation pit excavation was studied in many aspects.The results show that the MJS piles can effectively reduce the deformation and displacement of the surrounding soil caused by the excavation of the foundation pit,and achieve the purpose of reducing the disturbance.A series of parameter studies were carried out by changing the parameters of MJS pile.The results show that the reinforcement effect can be increased with the increase of MJS pile diameter or row number,but when the pile diameter or row number of MJS increases to the critical value,the lateral displacement of diaphragm wall and the settlement of bridge pier will not be reduced.The strengthening regional of MJS pile is sufficient to cover the required reinforcement range.Excessively increasing the reinforcement area length will not have much effect on reducing the disturbance of the surrounding environment caused by the excavation of the foundation pit.There is an optimal distance between the diaphragm wall and MJS pile to minimize the disturbance.The optimal burial depth of MJS pile is the depth reaching the rock strata.Enhance the modulus of MJS pile can reduce the settlement of foundation and wall.