| Under the state policy of the Belt and Road,the scale and quantity of national infrastructure construction are increasing rapidly,and the construction of tunnel projects has also increased rapidly.Many road and railway tunnels pass through the cold regions of Northeast China,Inner Mongolia and Qinghai.According to the investigation,the tunnel surrounding rock will undergo several times of freezing and thawing cycles every year during the actual operation of the tunnel,and the freezing and thawing will cause cracks in the rock mass.The gap water will frost heave and contract,so the crack in the surrounding rock will expand,and the deformation of the surrounding rock will increase,so the tunnel will be damaged in different degrees.The tunnels were built in cold area.There are many cases of tunnel instability and damage due to the freezing and thawing of surrounding rock,which brings great economic losses.The Quantai tunnel is located in the northeast of China.The groundwater type of the tunnel is mainly pore water and bedrock fissure water.Because of the seasonal change,the tunnel will show on freeze-thaw phenomenon.Based on the Quantai tunnel,this paper studies the damage degradation rule and tunnel stability under freeze-thaw cycle of tunnel surrounding rock.Firstly,through the rock freeze-thaw cycle test,the basic mechanical property change of rock is analyzed in the process of freeze-thaw cycle and the change rule of mechanical property is obtained.According to the test results,the rock damage model is deduced under the action of freeze-thaw load.According to the test results and damage model,the numerical analysis method is used to study the stability of Quantai tunnel.The main conclusions are as follows:(1)In terms of physical properties of surrounding rock,with the increase of freeze-thaw times,the quality of granite increases first and then decreases.After 100 cycles,the quality decreases by 0.24% compared with the initial state;In the process of freeze-thaw,the longitudinal wave velocity of granite decreases gradually,and the change speed increases first and then slows down.(2)In terms of rock mechanical properties,the compressive strength and tensile strength decrease with the increase of freeze-thaw cycles.The uniaxial compressive strength and tensile strength decrease by 61.67% and by 27.81% respectively after 100 freeze-thaw cycles,and the overall strength reduction is significant;In terms of mechanical properties of surrounding rock,the uniaxial compressive strength and tensile strength of granite decrease with the increase of freeze-thaw cycles,and the uniaxial compressive strength and tensile strength decrease by 61.67% and 27.81% respectively after 100 freeze-thaw cycles,and the elastic modulus decreases by 38.71%.(3)The physical and mechanical properties of surrounding rock decrease in the process of freeze-thaw,but the change rate of each stage is different,mainly divided into three stages: when the freeze-thaw cycle is 0-20 times,the change of physical and mechanical properties of granite is not obvious,which belongs to the stage of damage accumulation;when the freeze-thaw cycle is 30-70 times,the decline rate of physical and mechanical properties of granite is accelerated and the change is obvious after the damage accumulation to a certain extent During 80-100 cycles of freeze-thaw,the fracture part of granite is weakened by freeze-thaw,but the part without fracture is still hard,so the physical and mechanical properties of granite tend to be stable.(4)The stress-strain curve of surrounding rock can be divided into four stages.The failure mode is mainly splitting along the axial direction,the failure process is mainly crack propagation,local shear failure,and particle spalling on the surface during freeze-thaw.In this test,the failure mode of granite under freeze-thaw load is spalling + crack mode.(5)Based on the damage mechanics and the test results,the rock damage model is deduced under the action of freeze-thaw load.The damage model is basically consistent with the experimental curve,and the peak strength calculated by the damage model has little deviation from the uniaxial compressive strength obtained by the experiment,which can predict the strength change of rock under the action of freeze-thaw cycle.(6)The deformation and stress distribution of the surrounding rock of Quantai tunnel under the action of freeze-thaw are studied by numerical analysis.It is concluded that the deformation of the surrounding rock is increasing continuously in the process of 100 times of freeze-thaw cycles,and the deformation of the vault is the largest,with a maximum increase of 26.84%;the stress of the surrounding rock in the horizontal and vertical directions is also increasing,and the stress of the surrounding rock in the vault is the largest in the horizontal direction,and the stress of the surrounding rock in the vertical direction In the direction,the stress of surrounding rock at the arch waist is the largest.(7)Through three aspects of displacement,support force and plastic zone,the stability of surrounding rock of Quantai tunnel under the action of freeze-thaw is evaluated.It is concluded that the tunnel may lose its stability due to the excessive stress of support structure after 100 freeze-thaw cycles,which resulting in lining damage. |
PDF Full Text Request