Research On The Disaster Mechanism And Preventive Measures Of Subgrade Defect In Permafrost Regions Under The Double Thermal Effect Of Sunny-Shady Slope And Roadside Lake

The Qinghai-Tibet Project Corridor is an important strategic channel connecting Tibet and the mainland.There are many major linear projects such as the Qinghai-Tibet Highway,Qinghai-Tibet Railway,and high-voltage power transmission and transformation projects.With the further development of Tibet,the density of projects within the corridor will continue to increase.The corridor belt is in a 45° south-west direction,and the road engineering is affected by the shadow and Sunny-Shady Slope of the roadbed.Due to thermal melting and engineering soil borrowing along the corridor,a large number of roadside lakes exist.Due to the strong lateral water and heat erosion of the lakes,the water field and temperature field of the roadbed will also show strong asymmetric characteristics,and then induce engineering diseases.The influence of sunny-shady slope or roadside lakes on the heat transfer characteristics of frozen soil roadbeds has been reported in a large number of literatures,and the influence mechanism and coupling mechanism of the above-mentioned dual factors on the heat transfer process of frozen soil roadbeds are still to be further studied.Therefore,this paper uses the method of combining on-site monitoring and numerical calculation to carry out research on the disaster mechanism and prevention of subgrade diseases under the dual heat influence of the sunnyshady slope and the roadside lakes in the permafrost area.This article first takes the Qinghai-Tibet Highway as the main part of the study,and analyzes the distribution of the roadbed direction and roadside lakes from the West Datan to the Tanggula Pass,and selects the typical roadbed section at K2952+300 under the dual thermal effects of a typical Sunny-Shady Slope and roadside lakes.A temperature-moisture sensor is placed in the section to explore the internal water and heat migration of the roadbed.According to the monitoring data,the water and heat distribution law of the roadbed under the action of the Sunny-Shady Slope and the roadside lakes is analyzed,and the effect of the heat rod on the roadbed disease treatment is analyzed.In order to study the thermal impact of a single factor on the permafrost roadbed,an open system air-coupling model of permafrost roadbed was established through theoretical analysis.Based on the simulation results,the disaster-causing mechanism of permafrost roadbed diseases under the dual thermal effects of Sunny-Shady Slope and roadside lakes was investigated.Analys is according to the site disease status of the section,based on the energy balance theory of the frozen soil subgrade,a mechanical ventilation pipe is proposed to treat the asymmetric heat effect of the subgrade,and the treatment effect is verified and analyzed by numerical calculation.In summary,the following conclusions can be drawn:(1)80% of the roadbed in the section from Xidatan to Tanggula Pass of the Qinghai-Tibet Highway is southwestward,which is significantly affected by the sunny-shady slope effect.The sunny-shady slope effect of the roadbed from Xidatan to Kunlun Mountain Pass and Buxuequan to Wudaoliang is more serious.There are more than 900 roadside lakes within 250 meters along the highway,and there are more lakes on the roadside in the Tuotuo River and Chumar River areas;among them,the roadbed from the non-freezing spring to Wudaoliang are affected by both the sunny-shady slope and the roadside lakes.The thermal effect is the most obvious.(2)According to the analysis results of the monitoring data of typical cross-sections,the thermal rods are not ideal for the treatment of roadbed thermal disasters under the combined action of Sunny-Shady Slope and roadside lakes.The effect of their cooling performance is likely to cause local overcooling at the evaporating end,which manifests as the subgrade temperature field is distributed asymmetrically.Due to its strong radial refrigeration,the temperature gradient increases,and the water migrates to the freezing front,which causes radial frost heave,and finally causes serious engineering diseases such as longitudinal cracks.(3)Analyze the dual thermal effects of permafrost subgrades by establishing a numerical calculation model,systematically and quantitatively analyze the impact of Sunny-Shady Slope and roadside lakes on the thermal stability of subgrades in permafrost areas,and the study found that the Sunny-Shady Slope effect on permafrost subgrades The thermal influence is significantly stronger than the lateral thermal erosion of lakes,and the weight of the influence of the Sunny-Shady Slope effect gradually increases with the increase of the service life of the road.(4)The mechanical ventilation pipe foundation proposed based on the energy balance theory of frozen soil roadbed can effectively reduce the temperature of the roadbed body and the lower layer of the thawed frozen soil layer,and improve the asymmetry of the frozen soil roadbed under the dual thermal effects of the Sunny-Shady Slope and the lakes on the roadside Thermal effect,and the artificial upper limit of the permafrost at the center of the roadbed and the shoulder on Sunny-Shady Slope of the roadbed was raised by approximately 2.3 meters and1.5 meters respectively,during the five-year period of the ventilation pipe.