| Based on the Tianjin Metro Line 1 shield engineering in silty clay layer, this paper takes the model test as the main research method, combined with the theoretical analysis and numerical simulation, which analyzed the mechanical response of weak surrounding rock stratum and existing pile.(1) The similar model test system of shield construction is designed, which realizes the automatic push and shield tail synchronous grouting. According to 1:100 geometric similar ratio, I have developed a similar lining materials and mass ratio:clean quartz sand (1mm in diameter):paraffin:steel fiber (0.2mm in diameter and 5mm in length)=15:90:1. It has been verified the silty clay geology in Tianjin area can be simulated by cleaning sand, barite powder, Vaseline in accordance with the ratio of 8:3:1. Test shows that the reference range of shield grouting filling coefficient is 1.4-1.6 in silty clay layer and grouting has a significant effect on the displacement control of soft surrounding rock and pile.(2) Designing Group(n=11) 33 orthogonal model test, respectively discusses the different tunnel depth (1D,2D,3D), different branch support (soil excavation, lining and grouting support) and pile-tunnel relative position (the level from tunnel longitudinal vertical plane 1D,2D,3D, and the vertical from tunnel axis horizontal plane 0.5D,0D,-0.5D), we studied the displacement and stress response of surrounding rock and pile body and verify the applicability of PIV technology in geotechnical test, which can be used to observe internal displacement and partical migration of soil. The K value reference range is given by the comprehensive analysis of each working condition.(3) Without grouting and lining support, the progressive collapse will occur at H/D=1-3. With grouting and lining support, the soil settlement obtain effective control and the earth pressure is more uniform than non supporting. The influence range of the arch waist radial pressure is 1.5D by filter diffusion method and the pressure drop is more than 10% in the area of 1D-2D when grouting ratio is 1.5. The phenomenon of flow around pile is obvious. The greater the depth of shield tunnel, the smaller the K value. In the presence of the pile, the influence of shield tunneling on the surrounding rock pressure is increased, which verified the shielding effect of pile body. The larger span ratio, the bigger the pile bending moment and the smaller the displacement of pile top. When the horizontal distance between the pile and tunnel is increased, the bending moment and the displacement of the pile top are decreased. When the pile end is located under the arch of the tunnel, the negative bending moment is generated, which maximum value is located at the arch waist.According to the response of surrounding rock and pile body, the surrounding rock is divided into 5 main regions, which key control factors are given. The numerical model verifies the basic data, law of the similar model test and the rationality of the surrounding rock region division. |
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