Study On The Design Method Of The Supporting Structure Of The Prestressed Anchor Bolt Oriented With Steel Tube

With the continuous development of the national economy,China's urbanization process has been accelerating,and various urban high-rise buildings and underground projects have emerged,resulting in a large number of deep foundation pit projects.With the increase of excavation scale and depth,the difficulty of foundation pit construction is also bigger,especially in areas with high water content and poor physical and mechanical properties such as collapsible loess or soft soil.And the higher requirements for anchoring technology in the construction of deep foundation pits is needed.The prestressed anchor flexible support structure is widely used in the field of deep foundation pit engineering due to its good stress and deformation characteristics.However,the ordinary prestressed anchor is not enough to handle some complicated environmental conditions since it must be pre-formed during construction and difficult to form holes and collapse holes easily in soft soil.Moreover,there are still problems such as difficulty in controlling the position of the tunnel and difficulties in bolting the jack,for anchors with large anchorage depth and long length.The supporting structure of the prestressed anchor bolt oriented with steel tube is proposed based on the in-depth understanding of the characteristics of the existing prestressed anchor flexible support structure.And it's design method and stability are studied combining the theoretical and numerical methods.The main conclusions drawn are as follows:(1)Based on the existing prestressed anchor flexible supporting structure,to avoid the hole forming process of the anchor rod,a new the prestressed anchor bolt oriented with steel tube without pre-forming holes,simple construction and good stress is proposed.The structural form and construction process are introduced in detail,and the working mechanism of the structure is divided into three parts:guiding principle,grouting principle and force transmission principle.(2)The earth pressure on the side wall of the foundation pit is calculated by select the empirical earth pressure distribution mode,then the channel steel beam net is divided into beams and columns and calculated separately,the length and cross-sectional area of the prestressed anchor bolt oriented with steel tube are designed subsequently,so that the design method of the prestressed anchor bolt oriented with steel tube is completed.And the design example is given.(3)Firstly,the foundation pit instability mode is classified and its causes arediscussed.Then,the stability calculation model of the prestressed anchor bolt oriented with steel tube is established with the circular slide method,the method of determining the most dangerous slip surface is given.Combining with an example,the most dangerous slip surface is found by MATLAB programming,and the stability of foundation pit supported the prestressed anchor bolt oriented with steel tube is evaluated.(4)The finite element calculation model of the prestressed anchor bolt oriented with steel tube supporting foundation pit is established and calculated by Abaqus finite element software.The deformation of the side wall of foundation pit and the distribution law of the axial force of anchor rod are analyzed by the finite element simulation results.It is found that the structure supporting foundation pit can achieve good stability effect indeed.