Optimization Study On Construction Scheme Of Large Span Multi-arch Tunnel

The multi-arch tunnel is a typical structural form of the highway tunnel.Its compact structure and fluent connection between the roads play a unique advantage in the construction of highway tunnels.From the perspective of the overall planning of highway traffic,there are many irreplaceable advantages.Although the multi-arch tunnel has a high initial investment,is difficult to construct and has a long construction period,it has great potential for environmental protection and energy conservation in the later stage of operation.As the construction of the multi-arch tunnel continues to deepen,many problems have arisen in terms of construction,design,monitoring,and operation.At present,the technology of construction equipment for multi-arch tunnels is relatively backward,and the traditional design of the guide tunnel design section is too conservative to be conductive to the development of large-scale modern excavation equipment.The design of the multi-arch tunnel is similar to the engineering analogy,and the current tunnel design specifications are too restrictive for the relevant provisions of the multi-arch tunnel.Lag,there are widespread problems such as unreasonable design support strength,complicated construction procedures,and high construction costs;monitoring measurement is insufficient for the stability of surrounding rock and dynamic construction control,and it does not provide practical and effective solutions to the bias problem of the partition wall.Ground monitoring means;in the course of operation after the completion of the multi-arch tunnel,the treatment of the emerging diseases is not timely enough that the spread of the disease endangers the stability of the tunnel.Taking the single sidewall method of the middle guide hole as the basic construction method,the effect of different construction sequences on the entire tunnel structure was studied when the center line of the middle guide hole was shifted from the middle line of the partition wall.It is found that when the pilot hole is one of the first excavation sides and the first hole is excavated and deep buried,the disturbance to the surrounding rock is small.In view of the construction plan for multi-arch tunnels in shallow sections and other special sections,the following research work has been carried out based on Chongqing Zhaojia twin-Arch Tunnel:(1)ANSYS finite element analysis software was used for numerical simulation.The mechanical behaviors of different construction methods in Zhaojia twin-Arch Tunnel were studied,and the results were compared and analyzed with the actual field monitoring data.The results show that the finite element numerical results are smaller than the actual measurement results,but the laws and trends are shown.Can make reasonable suggestions for the construction,and draw a conclusion that the sidewall method of the middle guide tunnel is a reasonable construction method for the Zhaojia twin-Arch Tunnel.(2)In order to ensure that both the excavation of the middle guide tunnel and the placement of the partition wall can be carried out simultaneously,the slag discharge operation of the middle guide hole can be smoothly implemented while guaranteeing space for the placement of the partition wall as a formwork,and a moderate expansion is proposed.The guide hole size is offset by the construction method of the placement position of the partition wall,and the influence of the construction method on the entire tunnel structure is simulated on the basis of different construction sequences using the finite element analysis software ANSYS.The analysis results show that the construction method of expanding the size of the middle guide hole and shifting the middle partition wall is feasible.When the middle guide hole is biased towards the first excavation side,and the excavation is first performed on the deep buried side,the disturbance to the surrounding rock is small,and the risk of excavation is reduced.(3)In order to study the problem of reasonable excavation footage in the method of deflecting mid-holes in the shallow-buried biased geological belt,a three-dimensional finite element model was built using ANSYS for numerical simulation of excavation.Through analysis,the results showed that the excavation length during construction of the middle-middle-hole tunneling method.When the distance is 1m,the safety excavation footage of the tunnel structure can be ensured.When the tunneling length is2 m,the local tension of the initial branch of the tunnel is too large which is not suitable as a reasonable footage length.(4)In order to balance the effect of horizontal thrust on the partition wall after the excavation of the first hole,the current conventional practice is to carry out lateral steel support or backfilling concrete on the other side of the partition wall.This process changed the bias status of the partition wall better but the later demolition work took time and wasted material.In order to reduce backfilling operations and speed up construction progress,it is proposed to change the shape of the middle guide hole,adjust the structure of the middle partition,and reduce the backfilling or backfillingconstruction method in the case of the partial middle guide tunnel.Use Ansys to perform the construction simulation analysis.The construction method is different.The effect on the entire tunnel structure under the order.The study found that by changing the shape of the middle guide hole and adopting a reasonable excavation sequence of the main hole,the tunnel excavation can be safely implemented,and it is reasonable to use the deep burying side first.