Research Into The Stratum Deformation Control And The Construction Optimization Of Aqueous Loess Tunnel

In recent years,the construction of urban subways in China has entered a rapid development stage.During the construction of subway tunnels,the shallow mining method has been widely used due to its flexibility,wide adaptability,and the small impact on the surrounding environment.However,how to ensure the stability of the surrounding rock and control the deformation of the stratum during the construction of the tunnel in the special stratum is still an urgent engineering problem to be solved.This paper takes the tunnel section(Taiyi Road Station to Xingqing Road Station)of Xi'an Metro Line 5 as the engineering background.Using the methods of theoretical analysis,numerical simulation and on-site monitoring,deformation control technology and construction optimization are studied,the deformation law and mechanical behavior of the tunnel are analyzed.The main research contents and results are as follows.(1)The main reasons for the deformation of the tunnel were analyzed.The advantages,disadvantages and adaptability of different reinforcement technologies were summarized.A reinforcement scheme for precipitation reinforcement,WSS grouting reinforcement,and reinforced by a small pipe grouting was proposed for this project.(2)The precipitation reinforcement scheme and grouting reinforcement scheme for the single-line tunnel was designed.The finite element software was utilized to analyze the seepage-stress coupling of the two reinforcement schemes.When the tunnel adopts the precipitation scheme to reinforce the stratum,the ground settlement increases with the increase of the depth of the precipitation,and the range of the ground settlement caused by the scheme is large,the ground settlement caused by precipitation accounts for 77 % of the total settlement.The ground settlement of the tunnel construction underthe grouting reinforcement scheme is only 12.5mm,which is much smaller than the precipitation reinforcement scheme.It is superior to the precipitation scheme in the aspects of ground deformation,surrounding rock stress,and plastic zone development.Thus,it is superior to the precipitation reinforcement scheme in lining mechanical.(3)The analysis of on-site monitoring data shows that the deformation laws of the ground under the two types of strata reinforcement schemes are different,but the deformation laws of the surrounding rocks in the tunnel are the same.The surface settlements under the precipitation reinforcement scheme are characterized by the precipitation stage,the tunnel excavation stage and the groundwater recovery stage,while the surface settlements under the grouting reinforcement scheme are characterized by the grouting stage,the tunnel excavation stage and the water loss stage of the tunnel.The deformation of the surrounding rock of the tunnel under the two reinforcement schemes is characterized by a rapid deformation stage,a slow deformation stage,and a final stable stage.(4)The optimization of the excavation sequence of the pilot tunnel during the construction of the double-track tunnel under the grouting reinforcement scheme utilizing the CRD method was carried out.According to the CRD construction method,different types of excavation sequences for each pilot hole are proposed.The comparison shows that construction scheme 1 is optimal in terms of strata deformation,surrounding rock stress,and plastic zone development.The stratum deformation law of construction scheme 1 was analyzed.It was found that when excavating the upper guide hole,the surface settlement increases and the maximum surface settlement position shifts to the right,while the maximum ground settlement and its position change are little when excavating the lower two guide holes.