Impact Analysis Of Mudstone Expansion On The Stability Of Tunnel Lining

With the development of my country’s railways,as of the end of 2020,the total mileage of my country’s railway operations has exceeded 145,000 kilometers,of which 16,798 tunnels are currently in operation,with a total length of approximately 19,630 kilometers.However,the construction of railway tunnels will inevitably pass through the swelling mudstone area.However,the swelling,softening and shrinking characteristics of the mudstone in contact with water will cause the tunnel lining structure to become unstable,which will seriously affect the safety of tunnel construction and subsequent operation and maintenance.It is currently in the tunnel project.A special type of problem.This paper takes a railway tunnel in an expansive mudstone area as the research object.First,the basic physical properties and expansion characteristics of the mudstone sample are tested to determine the expansion grade of the sample;secondly,the indoor tunnel scale model test is combined with numerical simulation.Methods,comparative analysis of the deformation characteristics of the tunnel lining;finally,summarized the failure mode of the tunnel lining in the mudstone area,which provides a theoretical basis and comparative analysis data for similar research.The main research contents and conclusions of this paper are as follows:(1)Sampling of mudstone in the tunnel on site.Liquid-plastic limit test,density test,Xray diffraction test,free swelling rate test and cation exchange capacity tests were carried out indoors to determine the basic expansibility index of the mudstone sample.The standard judges that this kind of mudstone is weakly expansive mudstone.(2)Design an indoor tunnel scale model test based on similarity theory.By changing the water content of mudstone to simulate the expansion of the surrounding rock of the tunnel in contact with water,the impact of the swelling force of mudstone on the tunnel lining structure is tested,including the swelling force of the surrounding rock,the value of lining deformation,Strain value and water content change value.During the test,it was found that the water content of the surrounding rock of the tunnel showed an "S"-shaped distribution with the water injection time,which was summarized as three stages of "stabilization stage-sharp increase stage-restabilization stage";the expansion force of the surrounding rock around the tunnel lining was The distribution law of "near big,far small",that is,the farther away from the tunnel lining,the smaller the expansion force,and vice versa;the maximum test value of expansion force appears at the invert,about 36 k Pa,and the minimum expansion force appears at The arch waist is about9 k Pa.(3)Test the deformation value of the inner surface of the tunnel lining and the stress value of the outer surface of the lining.Through the time-deformation time history curve,it is found that after 360 h of water injection,with the increase of water injection,the deformation values of different parts of the tunnel lining all increase.Among them,the deformation of the invert and the vault has the maximum value,and the arch waist The amount of deformation of the arch has a minimum;the deformation of the dome and the inverted arch shows a tendency to squeeze inward,and the deformation of the arch waist and arch feet shows a tendency to expand outward.Monitoring the variation of lining stress by pasting strain gauges at 1/2 and 1/4 of the longitudinal outer wall of the tunnel lining model,the analysis found that within the test water content range,the lining stress is proportional to the water content of the surrounding rock.At this time,there is a maximum stress at the invert and a minimum stress at the arch waist,which is consistent with the lining deformation law.(4)Based on the finite element analysis software,the swelling deformation and force of the mudstone tunnel are simulated,and the deformation and force of the tunnel lining in the indoor model test are compared and analyzed.The results show that the vault and invert positions are more prone to failure forms such as vault subsidence and invert heave,and the lining change trend obtained by numerical simulation is basically consistent with the change trend of indoor tunnel model test.In the paper,through the indoor tunnel scale model test and numerical simulation method,the stability of the tunnel structure in the expansive mudstone area under the expansion force load is analyzed mechanically,and the accuracy of the indoor tunnel scale model test results is verified,which can be similar the research provides a theoretical basis.