Freezing-thawing Stability Analysis Of Passenger Dedicated Tunnel Slope In Seasonal Freezing Area

With the rapid development of high-speed railway tunnel construction in China’s frozen area,the slope at the tunnel entrance is easily affected by freeze-thaw,and its stability cannot be ignored.Taking the slope at the entrance of the Limin Tunnel of the Harbin-Mudanjiang Passenger Line as the engineering background,this paper analyzes,evaluates and predicts the stability of the slope under freeze-thaw action through real-time dynamic monitoring,theoretical analysis and finite element numerical simulation,which provides a scientific reference for the maintenance and maintenance of the slope.The main work and research results are as follows:(1)According to the results of on-site investigation,deploy monitoring equipment and set up monitoring points to monitor them in real time.The data obtained from the monitoring points were sorted out and analyzed,and the results showed that the soil temperature of the slope showed a trend of first increasing and then decreasing with time,which was consistent with the change law of atmospheric temperature,but the average lag was about 7-11 days.The water content showed a trend of first decreasing and then increasing with time,which was consistent with the trend of local average daily precipitation.Affected by frost heave and thawing sedimentation,the horizontal and vertical displacement trends are the same as those of the sinusoidal function curve,the former showing a trend of first rising and then declining,and the latter showing a downward trend of first falling and then rising along the depth.(2)Based on ANSYS APDL finite element analysis software,the slope three-dimensional model was constructed,the slope thermal parameters were calculated through the moisture content monitoring data,and the sinusoidal function T=6.1+14×sin[2π/365(t-39.22)] was used as the upper boundary condition to calculate the slope temperature field,and the results showed that the change rate of the surface soil of the slope was greater than that of the soil inside the slope,and the soil temperature during the freezing period showed high internal and low surface.During the melting period,the soil temperature was high from the inside,low to low inside,and the surface height changed,and the maximum freezing depth was 1.41 m.(3)On the basis of the temperature field calculation results,the temperature load is converted into stress and applied to the model by indirect coupling,and the distribution and change law of slope displacement and stress are analyzed by the numerical simulation method of thermodynamic coupling.The results show that the maximum vertical displacement of the melting period of the No.2 monitoring point is-5.74 mm,and the displacement simulation results of the four monitoring points are compared with the monitoring data,and it is found that the change trend of the two is the same,and the maximum error is 1.85 mm.(4)Based on the numerical simulation results of thermodynamic coupling,the stability of the slope under different moisture content and different freeze-thaw cycles was analyzed,and the analysis results showed that with the increase of moisture content,the slope soil fell more obviously under the influence of self-gravity and temperature stress,the safety factor decreased,and the stability of the slope decreased.Under the same moisture content,slope stability decreases with the increase of the number of freeze-thaw cycles.Through the analysis,evaluation and prediction of the stability of slope under freeze-thaw,this paper provides a scientific reference for the maintenance and maintenance of slope.