Comparative Study On Field Monitoring And Numerical Simulation Of Shield Tunneling Through The Ventilator Room With Small Clear Spacing

With the background of the extension line of Tianjin Subway Line One which directly shielding through Shuang Lin-Li Lou interval ventilator room engineering,this paper conducts a series of related research.The engineering is a two-lane tunnel with small clear spacing.The ventilator room is adjacent to the outer ring and the depth of surrounding underground pipelines is shallow.The reinforcement length of the soil near the entrance of the ventilator room is only 6m,which is far less than the conventional reinforcement length.In actual construction of shield tunnel,some temporary backfill measures are taken in the ventilator room to ensure the safety of the crossing process.Based on the above background,this paper uses the software of finite element analysis ABAQUS to have a three dimensional fluid-solid coupling simulation on the process of shield crossing,and the results are compared with field monitoring results.The main contents are as follows:(1)The key points and difficulties in the crossing construction of shield tunnel are analyzed.The field monitoring data are reorganized and the cross section settlement curves of each pipeline are drawn.The results show that the settlement curves are basically normal distribution,and the deformation of the pipeline is mainly concentrated in the vicinity of middle axis of the tunnel 3D(D is the outer diameter of tunnel)range.At the same time,for the excavation of tunnel with small clear spacing,the maximum settlement of each pipeline is near the midpoint of the middle axis of the two tunnels and slightly close to the right line tunnel.(2)With the establishment of ABAQUS three dimensional fluid-solid coupling model,the finite element simulation is arranged.The calculation results show that there is "bowl-shaped" sedimentation tank at the cross-section surface of soil.The deformation is concentrated around the tunnel 3D(D is the outer diameter of tunnel)range.In the tunnel excavating process of left and right lines,the soil subsidence varies greatly during the period of the shield cutting soil to the tail of shield machine away from the soil with a certain distance while the grouting incompletely coagulating.The maximum settlement is located near the midpoint of the axis between two tunnels and slightly close to the right line tunnel.(3)The monitoring values of underground pipeline settlement are compared with the results of simulation.The two are consistent with each other,which verifies the finite element simulation is more reasonable.At the same time,the settlement values of non-reinforced area soil,underground pipelines and reinforced area soil have a comparison,and the settlement value of reinforced area soil is the least one.The settlement of pipeline is slightly less than non-reinforced area soil.The result shows that pipeline structure itself has certain ability to resist deformation,but the effect is less obvious than the direct reinforcement of soil.(4)Changing the geometric model of ventilator room,having simulations of full backfill,partial backfill and non-backfill respectively inside the ventilator room,at the same time,combining with the dangerous situations such as horizontal displacement overrun and gushing water and sand in the entrance of the hole during the process of shield crossing tunnel with small clear spacing,this paper has a deep analysis on the changes under three conditions of diaphragm wall horizontal displacement and the soil excess pore pressure near the entrance of the hole.The results show that the changes of horizontal displacement and excess pore pressure of partial backfill are slightly larger than full backfill,while non-backfill is significantly larger than the other two.Relatively speaking,partial backfill is more economical and reasonable,which provides reference for the method of backfill in similar projects in the future.