Research Of New Supporting Structure System Of Trench Cutting Assembled Diaphragm Wall

Trench cutting Remixing Deep wall(TRD)with the H-beam is one of the commonly supporting methods in the construction industry.On the basis of integrating the elements of building industrialization and considering the concept of green building advocated by the current state,this paper puts forward a new method of foundation pit support,namely,Trench cutting Assembled underground Diaphragm wall(TAD method).In the TAD method,the precast concrete piles are inserted into the cement-soil groove which is formed in advance,and then the individual precast piles are connected by effective connection measures such as tenon,so that the complete wall can play the role of soil retaining and water cutting,and the tiny disturbance goal of deep excavation retaining in dense urban areas can be realized.Considering the new construction method has not been large-scale application,the academic and engineering have not yet reached a complete conclusion on its performance of soil retaining,water stopping and deformation control.In order to provide guidance and reference for the development and application of the TAD construction method,this paper is based on the in-situ test of the prefabricated underground diaphragm wall carried out in a test site in Dajiangdong,Hangzhou,combined with measured data analysis,finite element numerical analysis and theoretical analysis.(1)On the basis of the in-situ tests carried out at a site in the Hangzhou,so that the variation rules of bearing behavior of TAD retaining structure during excavation can be studied by measuring the data of deep soil displacement,wall bending moment,surface settlement outside the pit and groundwater level.It can be found that with the increase of excavation depth,the bending moment of the wall increases gradually,and the maximum bending moment point moves down continuously until it reaches the peak near the excavation face.When the TAD wall is used as the supporting structure,the displacement of deep soil and the surface settlement outside the pit can be controlled effectively during the excavation stage,and it has a certain isolation effect on the groundwater level.(2)According to the construction scheme based on the in-situ test,the calculation model is established by the finite element software PLAXIS-3D.And then,the structure stiffness,the cement wall thickness and different ways of connection between the top of TAD wall bearing performance of influence can be studied,optimization structure and construction method are put forward for the weak joints of TAD wall in vertical splinting.It is found that when the stiffness of TAD wall is larger,the deformation of the retaining structure is smaller,while the bending moment is larger.Roof connection during excavation can reduce the deformation of the wall and change the absolute value of bending moment at the top of TAD wall.When TAD wall as a supporting structure,the cement wall thickness and strength of the stage of foundation pit excavation have less effect on the deformation of supporting structure,the TAD wall as the basement exterior wall structure,and in the process of the main structure construction,the thicker the cement wall is,the smaller the wall deformation is.The optimal combination of the cement wall width should be choose when the TAD wall is considered as the “Two Walls Combined into one” diaphragm wall.(3)Considering the joint position of concrete in TAD wall splicing process,a method for calculating the reduction coefficient is proposed,which can easily obtain the stiffness parameters required in the finite element software.Based on the beam method of elastic foundation,the calculation of the stiffness parameter in the FRWS software can get a more reasonable calculation value.The TAD has a good development prospect in the densely constructed areas with limited surface space.It should be equipped with real-time information monitoring equipment in combination with the unique soil conditions of each place,so as to use the trench cutting assembled diaphragm wall in the foundation pit engineering more scientifically and safely.