Research On Mechanical Performance Of Composite Retaining And Protection Structure For Super Large And Deep Foundation Excavations

In recent years,with the rapid development of China's economy and the rapid growth of urban population,the high-rise buildings and super large underground works has been built.The Haikou Twin Towers in Hainan Province are the tallest building in Hainan Province,building height 428.3m.The foundation pit is the first deep foundation pit in Hainan Province,the depth of the foundation pit in tower area is 25.4m.The cast-in-situ piles + underground diaphragm wall + prestressed anchor composite retaining structure is adopted.In order to ensure the quality of construction and reduce the difficulty of construction.It is particularly important to study the mechanical properties of composite retaining structure for super large and deep foundation pit.Reliable retaining methods and a good bearing system are the key to the success of super deep excavation engineering.In this article,the first deep foundation pit in Hainan province is taken as an example.The method of mutual verification between in-situ monitoring and numerical simulation is adopted.The mechanical performance of reinforced concrete cast-in-situ piles + underground diaphragm wall + prestressed anchor composite retaining structure are studied.Compared with the in-situ monitoring data,the effectiveness and rationality of the finite element software PLAXIS simulation of the retaining structure is verified.The interaction between the retaining structure of the upper cast-in-situ piles and the retaining structure of the lower diaphragm wall is revealed.It shows the change rule of the internal force in the time and space of the diaphragm wall,the influence of insertion ratio and rigidity on the mechanical properties of diaphragm wall is discussed.Research indicates:(1)the interaction between the two retaining structure is limited.(2)During the excavation process of the foundation pit,the maximum bending moment of the diaphragm wall is always located near the excavation face of the foundation pit,the curvature of the bending moment curve decreases gradually with the increase of excavation depth and axial tension of anchor.(3)When the insertion ratio of diaphragm wall increases,the maximum bending moment moves upward,and it is linear relationship with the soil depth of the diaphragm wall.(4)With the rigidity of the diaphragm wall increases moderately,the horizontal displacement of the structure decreases,but the location of the maximum bending moment does not change significantly.The research results can provide theoretical basis and practical experience for the design of composite retaining structure of super large and deep foundation pit.