Study On The Reliability Of Thawing Settlement Of Permafrost Roadbed In The Qinghai-tibet Railway

Qinghai-Tibet Plateau permafrost is widely distributed,accounting for 69.5% of China's permafrost area,Q inghai-Tibet Railway is the highest elevation of the plateau railway in China and a great project of the Western Development,which has important military,economic and political significance.The key issue in the construction and maintenance of the Qinghai-Tibet Railway is to ensure the long-term stability and reliability of high-temperature high-ice permafrost roadbed with high heat sensitivity.Since the opening of the Qinghai-Tibet Railway in 2006,along the roadbed there have been varying degrees of melting deformation,and even cracking.Under the influence of the temperature rise of the Qinghai-Tibet Plateau and the disturbance of man-made engineering,the permafrost upper limit of the Q inghai-Tibet Plateau is gradually moving down,and the degradation and ablation of the ice layer is accelerated.This will accelerate the deformation of the railway.The deformation of the railway roadbed will directly lead to the bending of the rail,the lack of flatness,which will not only control the speed of the train,but also the larger uneven settlement deformation will reduce the comfort of passengers and traffic safety,increase the cost of maintenance.Based on the theoretical knowledge of permafrost,this paper analyzes the classification,distribution and disease mechanism of permafrost.Based on the analysis of thermal-hydro-mechanical coupling of permafrost roadbed,the finite element numerical simulation is carried out.Based on this,the RSM and the FOSM are used to solve the reliability index and failure probability of roadbed melting.The results are as follows:?1?By the influence of climate warming in the Q inghai-Tibet Plateau,the lowest temperature and maximum temperature of the subgrade in the 10 t h,the 30 t h,the 40 th,the 50 t h of the roadbed are increasing.The lowest temperature in the 10 t h year relative to the seco nd year increased from-12.8? to-12.6?,increased by 0.2?,the lowest temperature in the 50 t h year relative to the second year of the overall increase of 2.3?,the lowest temperature inside the roadbed in the slow.The highest temperature in the 10 t h year relative to the second year increased from 16? to 16.2?,increased by 0.2?,the maximum temperature in the 50 t h year relative to the second year increased by 2.3?,the maximum temperature inside the roadbed was slowly rising trend;The temperature of the top surface of the roadbed is the largest,and the temperature is below 10 m below the natural surface.The temperature is basically the same,and the change is the smallest,ground temperature is not affected by the outside temperature.?2?When the roadbed permafrost is frozen in January,the stress on the embankment slope and the slope foot is greatest.The temperature of winter ground temperature is reduced,the embankment slope and slope foot are low temperature areas.The freezing water in the subgrade is frozen and frozen to the low temperature freezing zone,and the volume of the soil increases,which leads to the increase of the tensile stress.By the influence of the temperature rise of the Q inghai-Tibet Plateau,the maximum tensile stress in the embankment is gradually reduced.When the roadbed permafrost settles in July,the maximum stress is mainly concentrated at 3m below the natural surface.The maximum compressive stress at the 3m below the natural surface is 0.92 MP,the 20 t h is reduced to 0.85 MP,the 40 t h is reduced to 0.32 MP,the 50 t h is reduced to 0.1MP,with the passage of time,the maximum value of sinking pressure decreases.?3?By the influence of the temperature rise of the Q inghai-Tibet Plateau,the X-direction displacement of the subgrade slope and the slope foot in the 10 t h,the 20 t h,the 30 t h,the 40 t h,the 50 t h of the roadbed is gradually increased,the Y-direction displacement decreases gradually in January,the displacement is the maximum near the boundary of the frozen soil subgrade,and the displacement in the Y direction gradually increases in July,and the maximum displacement is at the center of the top of the roadbed.?4?As the global warming,the probability of failure increased year by year,the 25 t h the probability of damage increased by 0.029% to 0.161%,roadbed melting deformation of the total within the acceptable range,the basic will not affect the reliability.35 years later,the probability of damage increased significantly,which may be a large number of high-temperature permafrost within the subterranean melting sedimentation occurred,the probability of damage up to 1.255% or more,the 50 t h sink more than 10 cm damage probability reached 5.281%,seriously more than engineering safety Permission scope should be taken to eliminate engineering measures.The change in reliability index is opposite to the probability of failure.In the 25 t h,the reliability index fell from 3.800 to 3.320,the 35^th year reliability index fell to 2.630,the 50 t h reliability index reached 2.011,is likely to affect the safe operation of the train.