Study On Deformation Characteristics And Controlling Measures Of Unsymmetrically Loading Tunnels In Bedding Strata

Because of the bedding distribution of the rock mass,the geological bias of the tunnel is often caused.In this case,the deformation and stress of the surrounding rock and the supporting structure are more complicated than the unbiased tunnel.Especially,when the number of bedding distributions is large and the spacing is small,the effect is more obvious,the supporting structure usually causes severe deformation and damage and the collapse of the tunnel face.Therefore,it is particularly important to study the deformation and stress characteristics of surrounding rocks and supporting structures during the construction of a unsymmetrically loading tunnel in bedding strata.This article relies on the part of the bedding strata of the Mengsong No.2 tunnel in the Yuxi-Mohan section of the China-Laos Railway as an engineering object.Based on the existing theoretical research,the combination numerical simulation analysis and on-site monitoring measurement was used to study the deformation and stress characteristics of the supporting structure and surrounding rock in the bedding layer and the biased section.and proposed an optimization scheme for the support structure of the tunnel with biased layers.The main research contents and conclusions include the following aspects:(1)The equivalent model and mechanical behavior of jointed rock masses,and the calculation method of surrounding rock pressure of a bedding biased tunnel are introduced.(2)Research on the deformation and stress of surrounding rocks and supporting structures by formulating on-site monitoring schemes,installing monitoring instruments and data processing for the asymmetrical pressure tunnel in bedding strata section.The research results show that: The deformation of the supporting structure before the excavation of the lower step accounts for 70% of the total deformation.The maximum horizontal convergence of the arch waist position is 217.3mm.The pressure of the surrounding rock is distributed in the form of “right large and left small”,and the stress of the steel arch frame is expressed the characteristics of “upper-large and lower-small” and “right-larger and left-smaller”.That the surrounding rock stress on the upper step is greater than that on the lower step and the supporting structure is not coupled with the deformation and deformation,and the structural damage occurs before the deformation instability occurs.(3)By simulating the impact of tunnel excavation on the surrounding rock and supporting structure of the asymmetrical pressure tunnel in bedding strata section,the results show that the vertical displacement value of the left arch waist is smaller than the displacement value of the right arch waist,and the tunnel appears asymmetric deformation,the deformation is mainly concentrated on the cross-section of the upper bench,and the entire tunnel is in a state of obvious asymmetrical pressure.(4)By establishing a three-dimensional numerical model of different strata thickness and inclination angle of the bedding rock mass,in order to investigate the deformation forces of the surrounding rock and the initial support during the construction of the tunnel in the bedding strata.The research results show that: The horizontal displacement,maximum shear stress value,and anchor axial force of the rock gradually decrease as the thickness of the rock layer continues to increase.The horizontal displacement,maximum principal stress and anchor axial force of surrounding rock increase with the increase of the rock inclination.It can be seen that the greater the thickness of the rock formation,the better the integrity of the surrounding rock,the greater the inclination of the rock formation,and the worse the stability of the surrounding rock.(5)Proposed three optimization schemes for the initial support structure of the asymmetrical pressure tunnel,and compared and analyzed the stress conditions of the surrounding rock and support structure under the three support schemes.The research results show that: the optimal solution is to keep the anchor length and other support parameters unchanged by changing the angle of all the anchor rods on the left side of the upper bench.For the subsequent construction of the asymmetrical pressure tunnel,it is recommended to increase the section size and reinforcement of the supporting structure on the bias side of the tunnel.