Study On The Influence And Regionaldivision Of Orthogonal Tunnels Based On Strength Reduction Method

This article relies on the“National Key R&D Program Topic 6:Structural Risk Monitoring,Key Technology and Demonstration of Safety Control for Typical Construction Projects Adjacent to Existing Urban Roads/Bridges/Tunnels”,using FLAC~3DD finite difference software,based on strength reduction method,take the displacement mutation theory as a criterion,analyzed the safety of 121 kinds of orthogonal tunnels and single tunnels in different surrounding rock grades,different tunnel sections,different upper and lower tunneling forms,and different net distances.The main conclusions are as follows:(1)When the tunnels are orthogonal,under the condition of the surrounding rock selected in this article,as the net distance of the tunnel increases,the safety factor is always greater than 1 or less than 1,that is,the orthogonal tunnels are always in a stable or non-steady state.The larger the net distance,the better the surrounding rock parameters,the shallower the buried depth,the smaller the tunnel cross-section,the greater the safety factor;(2)In general,when the new tunnel is upper,the safety factor increases with the increase of the net distance,and the trend gradually slows down.When the new tunnel is lower,the safety factor increases or increases first and then decreases as the net distance increases.The change in the safety factor of orthogonal tunnels mainly depends on the tunnel depth and net distance.(3)Whether the new tunnel is upper or lower,when the net distance is small,the difference between the safety factor of the orthogonal tunnels and the smaller value of the safety factor of the single tunnel(?k)decreases rapidly with the increase of the net distance.As the net distance increases,the change trend of?k slows until it is 0.In order to fit the relation between?k and net distance better,take into account the simplicity of the fitting function,this paper uses the reciprocal of the quadratic function or the reciprocal of the primary function to fit,and can obtain better fitting results.(4)Most of the critical points of the impact range under various conditions are between0.5D and 1.5D,94.4%of the total working condition.The critical point is 1.0D which is the largest,50%.(5)When the surrounding rock level,tunnel depth,new and existing tunnel sections are all the same,the unimpeded net clearance critical point of the new tunnel is greater than or equal to the unaffected net clearance critical point when the new tunnel is put on.(6)The worse the surrounding rock grade and the larger the tunnel hole diameter,the greater the unimpeded net clearance point.In general,The smaller the tunnel safety factor,the greater the critical point of influence.