| Multi-arch tunnel plays an important role.During the construction of multi-arch tunnel during the construction of mountain expressway,after the first tunnel excavation and pouring,it is often found that the first tunnel is cracked during the second tunneling process.Tunnel lining cracks will have a certain impact on the stability of tunnel structure.Analyzing the causes of cracks and taking reasonable measures to deal with them are crucial to ensure the safety and stability of the tunnel during construction and operation.In this paper,the cracks occurred in the second lining of the 1~#~5~#biased arch tunnel of Dazhongshan,and the results of crack investigation,cause analysis,theoretical analysis and numerical analysis were used to safely dispose the cracks.The main research contents of this paper are as follows:(1)Carry out detailed investigation and monitoring of cracks in the Dazhongshan tunnel group,investigate and analyze the relationship between crack location,shape,width,length and the depth of the bias angle,and summarize the distribution,variation and causes of the cracks in the second lining of the tunnel.(2)Based on the results of crack investigation,the cracks in the second lining of the tunnel are analyzed theoretically.The factors of bias pressure,construction technology and the interaction between the cracks and the sliding surface of the slope under bias pressure are analyzed.The bias load of the tunnel under bias pressure is calculated.The weak position of the tunnel under the bias pressure is determined and its safety is checked.It is obtained that near the shallow side of the middle partition wall under the effect of bias pressure is easier to break down.(3)MIDAS GTS/NX software is used to simulate the excavation process of tunnels under different working conditions,and the variation laws of stress field,displacement field and plastic zone of surrounding rock under different working conditions are analyzed.After the excavation of shallow side tunnels,the stress displacement between the arch wall and the vault top of the middle partition wall is larger,and the tension and compression stress concentration zone is formed.The deep side excavation disturbs the surrounding rock twice,resulting in the secondary disturbance of surrounding rock.The deformation of surrounding rock increases and the bending moment rotates to the inside,and the pressure of surrounding rock shifts from the outside to the inside.In this process,the surrounding rock moves backward from the left arch wall of the first tunnel to the vault.The eccentric load generated by the eccentric pressure is applied to the side of the back tunnel near the middle partition wall,while the surrounding rock and the middle partition wall on the slope side produce upward pulling force to prevent the rock sliding down and to prevent the deep-buried side tunnel.Under the complex tension and compression stress acting on the side of the road near the middle partition wall,the second lining concrete produces composite shear failure,which causes longitudinal cracks in the secondary lining of the arch waist,arch shoulder and vault area near the side of the middle partition wall.(4)Based on the results of crack investigation,numerical analysis and crack development,combined with crack width and length as well as site construction conditions,different types of cracks are treated by seam-riding grouting method and anchoring grouting method respectively,and the stability of the second lining crack and tunnel is monitored by buried stress and displacement observation equipment.The results show that the tunnel is safe.Both tunnel and crack are in stable state,which shows that the method adopted is reasonable and feasible. |
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