Research On The Mechanism And Control Measures Of Large Deformation Of Sandstone And Mudstone Wall Rock In Huipaishan Tunnel

With the continuous development of my country’s economy and society,the transportation industry has been able to maintain a sustained and rapid development trend,and more and more railway projects have been built in the vast western region.Due to the complex geological structure and complex lithology in the western region,the construction of tunnels in these areas is more difficult.The large deformation of sandstone and mudstone wall rock is one of the more typical examples,which brings great trouble to the construction.Based on the Huipaishan Tunnel of Yumo Railway,this paper conducts in-depth research on related theoretical and practical problems,and conducts research through indoor experiments,theoretical analysis,numerical simulation,and on-site monitoring.The physical and mechanical parameters of the surrounding rock were studied,and the large deformation mechanism of the surrounding rock of the Huipaishan Tunnel was analyzed through theoretical analysis and measured data.The control measures for the large deformation of the tunnel were proposed,and FLAC-3D software was used for numerical simulation and on-site simulation.Monitoring and measurement are supplemented by verification.The main conclusions are as follows:(1)The test data of the rock obtained by the conventional triaxial compression test of the rock can be well represented by the Mohr Coulomb strength envelope.The Hoek-Brown strength criterion can be transformed into reasonable rock mass parameters,and further transformed to obtain the rock mass physical and mechanical parameters required by the Mohr-Coulomb criterion.(2)The main influencing factors of the large deformation of the surrounding rock of the Huipaishan Tunnel are lithology,geological structure,in-situ stress,water and excavation.Use the theory of elastoplastic mechanics to analyze the deformation of the surrounding rock.Considering that the ground stress is equal pressure and unequal pressure,the maximum deformation of the surrounding rock varies greatly.The surrounding rock is mudstone.The most prominent only when the surrounding rock is mudstone.And through the large deformation DK297+865～DK297+905 arch settlement and surrounding convergence data analysis,the results of the aforementioned elastic-plastic analysis are verified.(3)Measures to control the large deformation of sand and mudstone surrounding rock of Huipaishan Tunnel are proposed.The step method is adopted for excavation,and the large deformation section with a buried depth of less than 105 m is reinforced by partial grouting of the vault.The initial support is made of C25 shotcrete and I20 b steel frame.Through numerical simulation,the maximum settlement of the tunnel vault is 15.18mm;The maximum invert bulge is 15.67mm;the horizontal displacement value at the left side wall is the largest,and the maximum displacement value is 9.08 mm.The large deformation section with a buried depth of more than 250 m enlarges the scope of grouting reinforcement.At the same time,the initial support is made of C30 shotcrete and I20 b steel frame.The length of the steps is 3.6m,7.2m,and 10.8m.Through numerical simulation,the length of the steps is changed from 3.6m.During the whole process of m growing to 10.8m,the maximum settlement deformation of the dome is from 51.72 mm to 59.97mm;the maximum uplift deformation of the invert is from53.42 mm to 65.00mm;the maximum horizontal displacement of the left side wall is from32.63 mm to 45.10 mm,the right side The maximum horizontal displacement of the side wall is from-32.79 mm to-45.29 mm.However,the entire deformation is within the control standards of the tunnel,which can ensure that the deformation during the construction process is controlled.(4)Analyzing the displacement monitoring data of the DK295+970～DK296+042 section and the measured data of the steel arch in the test section,the data changes greatly in the initial stage of excavation,then gradually decrease,and finally gradually reach stability.The minimum final value of the dome settlement data of each section is 51.6mm and the maximum is 60.2mm;the minimum final value of the peripheral convergence is 64.7mm and the maximum is 93.6mm.The stresses of the steel arches eventually show negative values,indicating that the steel frame is under compression,and the maximum stress is-126.987 MPa.The left and right side stresses at the same position of the steel arches are not much different,which indicates the symmetrical distribution of the stress state of the tunnel.The stress of the frame is lower than the yield strength of the steel,and the supporting structure is safe.The final stable deformation value of the surrounding rock is similar to that of the numerical simulation,and both are within the safe range.The joint effect of surrounding rock and supporting structure has reached stability.It can provide reference for the construction of similar projects.