Study On Construction Influence And Reinforcement Control Technology Of Small Distance Parallel Shield Tunnel

In order to solve the problem of more and more serious traffic jams in major cities,the construction of underground traffic engineering represented by metro rail transit is in full swing.With the continuous construction of urban metro,the metro line network is becoming more and more intensive,and the distance between tunnels is also becoming smaller.In addition,the pile foundation of high-rise buildings in cities is generally deep and the underground pipe network lines are complex The tunnel section is generally avoided by adjusting the line type and reducing the tunnel spacing,which often results in the situation of small spacing(the clear distance is less than 1 times the tunnel diameter)tunnel construction.Due to the small distance between the lines,there are complex mechanical problems and construction problems between the new tunnel and the adjacent existing subway tunnel structure.If the construction control is not proper,it is easy to cause engineering accidents such as ground subsidence and collapse,segment cracking and water leakage.Therefore,how to effectively control the influence of small distance shield construction on the existing tunnel and surrounding strata is an urgent technical problem to be solved in the development of urban subway.Based on the construction of the 4th bid section of the north extension section of Guangzhou Rail Transit Line 8,this paper studies the ground settlement caused by the construction of the small spacing shield tunnel and the change rule of the stress on the leading segment under the two reinforcement control technologies.The main contents include: through the field monitoring and measurement of the small spacing shield construction,this paper studies the ground caused by the construction of the small spacing shield tunnel under the two reinforcement control measures The change rule of surface settlement and additional stress of leading segment.The numerical simulation method is used to model and analyze the shield construction with small spacing,to study the influence law of the subsequent shield construction on the surface settlement and the stress deformation of the first segment,and to compare and analyze the reinforcement effect of the two control technologies.Finally,combining the field monitoring data and the numerical simulation results,the main conclusions are as follows:(1)According to the summary and analysis of the field monitoring results,the ground settlement experienced the process of slow change,rapid change and stable change during the shield construction with small spacing;in the horizontal ground settlement,the ground settlement near the two tunnels was greater than that far away from the two tunnels,and the ground settlement directly above the first tunnel crown was greater than that directly above the second tunnel crown;the shield passed through Before and after the first segment,the additional stress of the first segment is mainly in the state of compressive stress,and the change is relatively stable.During the process of the shield passing the first segment,the additional stress of the first segment will increase abruptly,mainly in the state of tensile stress.The additional stress of the first segment is reflected in: 45 ° oblique additional stress > circumferential additional stress > Longitudinal additional stress.(2)Based on the numerical calculation and analysis of the three construction conditions of unreinforced,grouting reinforcement in tunnel and isolation column reinforcement: the maximum value of ground settlement caused by the excavation of subsequent shield tunnel will be slightly greater than that caused by the excavation of prior shield tunnel,and the surface settlement curve of grouting reinforcement in tunnel is V-shaped,and the surface settlement curve of isolation pile reinforcement is W-shaped;construction with small spacing The ground settlement,internal force deformation and additional stress caused by the leading segment all show significant regularity,that is,the influence of the leading segment in the process of passing through the leading segment is the largest,there is a sudden change in numerical value,and the arch waist near the leading segment of the following shield is the most affected,and the segment is mainly compressed;both reinforcement methods have a great impact on the small spacing shield tunnel The effect of construction has a good control effect,but the effect of isolated pile is better than that of grouting in tunnel.(3)Through the comparison between the numerical calculation results and the field monitoring results,the change trend of the two is basically the same,which shows that the numerical model has a high accuracy,and also shows that the monitoring method of attaching strain gauge on the surface of the tunnel to the additional stress collection of the first segment is feasible and has practical application value.At the same time,it also proves that the influence of the two reinforcement measures on the construction of controlling the small spacing is significant Therefore,the reinforcement control technology and monitoring method in this paper can provide some reference for the construction design and monitoring of similar small spacing related projects in the future.