Study On The Cooling Mechanism And Adaptivity Of Crushed-Rock Berm Structure In Stabilizing The Qinghai-Tibet Railway On Permafrost

Following the trend of global warming, the stability of embankment in permafrost regions becomes a key problem during the construction and operation of Qinghai-Tibet railway. The crushed-rock revetment is one of the active measures in maintaining embankment on permafrost in Qinghai-Tibet railway. Due to the prominent effect of thermal insulation and the convenience in construction, the crushed-rock revetment becomes the most preferred technique in reinforcing and maintaining embankment in permafrost, specially, during the running of the railway.This Ph.D dissertation mainly concerns the construction of Qinghai-Tibet railway and stability maintaining of embankment in permafrost during its operation. For this purpose a field test on the crushed-rock slope structurte in the Qingshuihe experimental section of the Qinghai-Tibet railway was conducted, both the thermal regime and the setttlement of the roadbed using the different crushed-rock berm structure were monitored and analyzed. A numerical model for the roadbed thermal regime prediction considering the crushed-rock berm stuture was presented, several cases were simulated for conventional roadbed and the roadbed with the crushed-rock berm of differnet size. The climate warming effect was also studied in the computation.Both the in-situ test and the numerical simulation showed the possitive effect of the crushed-rock berm structure in protecting the permafrost under the roadbed. The shading effect and the variation of heat conductivity of crushed-rock can substantially reduce the energy intrance into the roadbed in the warm season and enhance the cooling in the cold season, hence the permafrost table can be maintained. The diferential settlement can also be adjusted by using different size of the crushed-rock berm sturcture.Based on the analysis of the results of in-situ test and the numerical simulation, the application condition, method and optimization of the crushed-rock berm structure in design were recommended.