The Research On Mechanical And Deformation Characteristics Of Rock-socketed Retaining Structure For Circular Anchor Pit With Inclined Rock Surface

The south anchorage of Zhenjiang Yangtze River Bridge is located in the mountain terrain,surrounded by mountains on the north and southeast.The overburden in anchorage area is mainly composed of residual clayey soil,consisting of silty clay and macadam silty clay.The height difference of strata below the overburden is large,with the rock surface of the north side(upstream side)up to about + 2.7m,and the south side(downstream side)is about-31.0 m,which is inclined distribution.A circular diaphragm wall and annular lining support scheme with outer diameter of 90 m and wall thickness of 1.5 m is adopted,according to the trend of strata,the diaphragm wall is in the form of step-like and unequal height,the top of the wall is 4.5 m,and the bottom of the wall is-17.4 ~-36.4 m,The upper part of the lining is closed and the lower part is not,and the bedrock excavation is divided in five layers.This support scheme is first applied to the anchor pit in China.and its deformation and mechanical characteristics are much more complex than those of rock-socketed retaining structure which is circular symmetric.In this paper,combined with the south anchorage of Zhenjiang Yangtze River Brridge project,the supporting characteristics of circular anchor pit with inclined rock surface are studied.with methods of numerical simulation and field measurement.First of all,based on MIDAS NX,the 3D model considering the distribution of inclined stratum is established to simulate various construction conditions of excavation,and the overall mechanical properties and deformation characteristics of the diaphragm wall and lining structure are analyzed.Especially,the change of radial displacement,overall deformation and circumferential stress of retaining structure from the high rock side to the low rock side,and the change of radial displacement and its maximum position,vertical stress,principal stress value of each section with the increase of excavation depth are studied emphatically.At the same time,compared with the research results of other rock-socketed diaphragm wall which is circular symmetric,the results show that the inflection point of radial displacement has a clear tendency to move up obviously;and the circumferential stress of diaphragm wall and lining structure gradually increased from the high rock side to the low rock side,consistent with the law of radial displacement.Secondly,for the different situations of rock-socketed length,bedrock elastic modulus,thickness of diaphragm wall and lining thickness combination,comparing the results of the multiple sets of models,it is concluded that the supporting behavior of circular pit with inclined rock surface is relatively sensitive to the thickness of diaphragm wall.Finally,suggestions for the reasonable value of influencing factors are given.Thirdly,according to the monitoring results of the south anchor pit of Zhenjiang Yangtze River Bridge,the variation law of monitoring data such as radial displacement,reinforcement vertical stress of diaphragm wall and reinforcement circumferential stress of lining structure are analyzed and summarized.Combined with the numerical simulation results,the comparison and analysis are carried out.The results of numerical analysis are consistent with the measured data,and it can provides reference for the design and construction of similar projects.