| The double-arch tunnel has a smooth line shape,small lead footprint and high space utilization rate.It has important positive significance for line layout,land acquisition and demolition,and overall project investment of complex terrain mountain highways,especially medium and short tunnels.The advantage is even greater.However,the shortcomings of the double-arch tunnels,such as cumbersome construction procedures,high technical requirements,and long construction period,cannot be ignored.Especially when considering factors such as slag discharge and construction organization,the main hole excavation adopts asymmetric excavation of left and right holes,which makes the tunnel space effect mor e obvious,which makes the load change of the stratum and the load conversion of the lining structure more complicated.In particular,the partition wall of the tunnel is often in a state of complex stress and is highly susceptible to damage.In order to alleviate the influence of asymmetric excavation on the stress and stability of the middle partition wall,the design of a double-arch tunnel in western Guangdong adopts the method of one-side temporary support of the middle partition wall,that is,the vertical spacing of the fourth-grade surrounding rock area is 0.8m.The ?108 steel pipe support and the V-class surrounding rock area are backfilled with 50 cm thick gravel soil and 50 cm concrete laterally.Based on this project,this paper studies the effect and optimization design of adjusting the complex stress state distribution of the middle partition wall for the temporary support of the IV and V surrounding rock areas and the different support strengths of the same support form.The research contents and results are as follows:(1)On the basis of literature collection and analysis,the factors affecting the stability of the partition wall of the multi-arch tunnel are summarized and analyzed.The best way to maintain the stability of the partition wall is to support the method.The principle and calculation method of force analysis of the partition wall of the double-arch tunnel.(2)For the supporting project,the tunnel engineering finite element method and the large-scale finite element analysis software MIDAS/GTS were used to establish the three-dimensional temporary support plan for each of the five groups of IV and V surrounding rock sections during tunnel construction.The finite element analysis model is used to obtain the general rule of the force of the partition wall in the tunnel excavation construction.Through comparison and analysis with the design scheme,the optimization result of the temporary design support scheme of the middle partition wall is obtained.When the vertical spacing of the ? 108 steel pipe is 75 cm and the longitudinal spacing is 80 cm,the displacement stress of the left and right monitoring points is most balanced when the 50-cm thick gravel soil and C25 concrete are backfilled for the V-class surrounding rock.(3)Computational analysis results show that in the construction process of the IV and V surrounding rock sections,the force law of the five medium-wall temporary support schemes is that the spacing of the steel pipe supports is reduced and the support strength is improved.The displacement of the finite element model monitoring point is reduced,the stress is increased,and the temporary support to maintain the balance of the left and right partition walls is the key to safe construction.For Class IV surrounding rock,the temporary support on the right side of the middle partition wall adopts ?108 steel pipe with vertical spacing of 75 cm and longitudinal spacing of 80 cm.For V-class surrounding rock,when backfilling 50 cm thick gravel soil and C25 concrete,the displacement stress changes of the left and right monitoring points are the most.Balanced,it can be used as a recommended solution for temporary support.The practical engineering practice verifies the rationality and reliability of the results. |
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