Research on Reinforcement and Excavation Control of the Launching Hole of Subway Shield Tunnels in Soft Clay
Shield tunneling is one of the key links in subway tunnel construction,characterized by high risks,heavy waterproofing tasks,and strong soil disturbance.Taking the shield tunneling starting from Xinjiayuan East Station to Xinjiayuan Station on Line B1 of Binhai New Area in Tianjin as an example,the reinforcement range of soft clay at the starting end was determined based on the thin plate theory.A joint reinforcement scheme of'three-axis mixing pile+2-row high-pressure rotary jet grouting pile'was proposed according to the mechanical characteristics of crossing soft clay,and the excavation control parameters at the starting end were analyzed.The surface settlement curve was obtained using on-site measurement methods.The results show that the soil reinforcement scheme can meet the requirements of shear resistance,tensile strength,and anti-seepage of the reinforced soil at the tail of the shield;reinforcement area excavation thrust≤1 200 kN,propulsion speed≤10 mm/min,cutter head speed≤1 r/min;non reinforced area excavation thrust≤3 000,the advance speed is30-40 mm/min,and the speed of the cutterhead is 1-1.51 r/min;the monitoring shows that the maximum surface settlement occurs near the excavation face,and the surface settlement in front of the tunnel face approaches 0 after twice the excavation length;the peak value of surface subsidence increases with the increase of excavation length,and the rate of surface subsidence increases rapidly when the tail of the shield shell detaches from the reinforcement area.
soft claysubway shield tunnelingthree-axis mixing pilereinforcement at launching holeexcavation control
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