The Deformation Rules Of Changzhou Deep Foundation Pit Excavation And A Optimized Design For The Enclosure Structure

In the recent years,in order to address the issues of the crowded above-ground space and transport congestion,the exploitation of the underground space has been promoted,and the construction of subways has grown vigorously,leading to the rapid development of the deep foundation pit projects.The No.1 and No.2 lines deep foundation pit projects of Changzhou subway are featured with high technology requirements,difficult construction and high risks,calling for a high-standard foundation pit deformation control.Therefore,at the beginning of the Changzhou subway construction,it is important to conduct theoretical study on the foundation pit design and construction,in order to learn the deformation rules of the subway station deep foundation pit in Changzhou’s typical stratum conditions.This paper focuses on the construction of No.1 and No.2 lines of Changzhou subway,applies the method which combines measured data statistics and numerical simulation analysis,and conducts a study on the deformation rules of Changzhou subway station foundation pit excavation and the parameters of the enclosure structure.The main study and results are presented as below:(1)the typical stratigraphic distribution of Changzhou areas is collected,the stratigraphic profile of Changzhou No.1 and No.2 subway line construction sites is drawn,different subway station foundation pit types are classified and main design parameters for foundation pit enclosure structure are collected.(2)The in-situ monitoring data of 38 stations of Changzhou No.1 and No.2 subway lines are collected,and the deformation rules of Changzhou subway station foundation pit excavation are analyzed systematically using measured data statistics.The maximum lateral deformation of the enclosure structure is between 0.09%～0.37%H,and the depth is mainly concentrated near 0.8H.The maximum ground surface settlement is between 0.04%H and 0.24%H,and most of the ground surface settlement out the pit is characterized with the concave distribution.Both the erect column and top of the wall show rebound during the excavation of the foundation pit.The force of the first concrete support is too high,and the axial force of the other steel support is not effective.(3)ABAQUS is applied to conduct simulation on the general rules of typical station foundation pit deformation.The influence of design and construction parameters on the foundation pit deformation is studied and the availability of an optimized design for the supporting structures is discussed.The insertion ratio of the enclosure structure of Changzhou subway station is suitably set in range of 0.7～0.8.The wall thickness of 800 mm is widely applicable to the foundation pit of Changzhou subway station,and can be increased or decreased according to the geological conditions and surrounding environment.Drilled bitten pile and SMW pile have certain feasibility under the geological conditions of Changzhou area,and can be tried as alternatives to the diaphragm wall.Rigid joints have better shear and bending resistance than flexible joints,and can prevent the joints from over-large deformation and large-area seepage.The excavation of foundation pits requires reasonable vertical and horizontal division,the excavation sequence of each division must be fixed and the over excavation must be prevented.