Study On The Deformation Control Of Three-hole Parallel Tunnel With Shallow Burial And Small Clearance

With the increase of the scale of urban rail transit construction and the improvement of the development speed,the multi-hole tunnel engineering is gradually increasing,especially the parallel tunneling construction of small distance shield tunnel and mine tunnel.For the road crossing project of shallow buried three-hole parallel tunnel with small clear distance,the tunneling construction process of each tunnel is affected by complex factors such as excavation unloading,formation loss,soil disturbance of surrounding rock and stress and strain superposition.In this paper,Jinan rail transit R3 phase I civil engineering,shallow buried three hole small clear distance tunnel under the long Ding Avenue Project as the background.Through the establishment of three-dimensional finite element numerical model,the paper systematically studies the road surface settlement and deformation,the vertical and horizontal displacement of each tunnel,the interaction between the tunnels and the blasting construction of the mining method caused by the whole process of the excavation of the three hole small clear distance tunnel,and puts forward reasonable and effective reinforcement measures through comparative analysis.The specific research contents are as follows:(1)The three-dimensional numerical model is established by the finite element software,and the whole process from excavation to penetration of the three hole small clear distance tunnel is simulated and analyzed.The results show that in the three construction stages of tunnel excavation without reinforcement,the displacement and deformation of each tunnel and the surface settlement of the upper highway gradually have the superposition effect,especially in the place with the minimum clear distance.In the third stage,the displacement deformation is beyond or close to the allowable range of deformation control,in which the vertical displacement of the mining tunnel and the surface settlement of the upper highway area are relatively large,so corresponding reinforcement measures should be taken.(2)The three-dimensional finite element blasting dynamic analysis models of different tunnel clear distance(0.4d,0.6d,0.8d,1D,etc.)are established respectively for the blasting construction of single pilot tunnel of mining tunnel(CD method),and the rules of blasting vibration velocity variation of each component of each tunnel and surface under different clear distance are studied.The results show that the peak vibration velocity of highway surface and tunnels is larger at 0.4d and 0.6d without reinforcement,which has exceeded or near the safety allowable standard value.With the increase of clear distance,the peak vibration velocity gradually decreases.The larger value of blasting vibration velocity of tunnel with mining method is mainly concentrated in the arch waist and side wall;the larger value of vibration velocity of shield tunnel is mainly concentrated in the arch waist of tunnel near the middle rock column area;therefore,it is necessary to focus on the vibration absorption and reinforcement measures for the small clear distance below 0.8d.(3)The three-dimensional numerical model of three hole small clear distance tunnel with grouting reinforcement and isolation pile(bored pile)reinforcement measures is established respectively,and the effects of the two reinforcement schemes are compared.The results show that the two reinforcement schemes can effectively control the displacement and deformation of each tunnel,the surface settlement of the highway and the blasting vibration of the mining tunnel.Among them,the use of isolation pile reinforcement can isolate the tunnel and its surrounding rock mass extending to the road surface into three approximately independent single hole tunnel areas,so as to better reduce the interaction between the tunnels,resist the impact of blasting vibration on the surrounding rock mass of the side wall and the shield tunnel,and there is almost no superposition effect in the rock column area.Combined with the calculation results,it can be seen that the reinforcement scheme of isolated pile(bored pile)is slightly better than that of grouting.(4)According to the field measurement and comparative analysis,the laws of tunnel displacement and road surface settlement are basically consistent with the three-dimensional numerical simulation results.