2 Guoyu, Li 2007 Lanzhou State Key Laboratory of Frozen Soil Engineering 151 Qinghai-Tibet Railway, Awning board, Crushed rock, Permafrost, Cooling effect, Thermal diode The embankment with crushed rock is a type of effective, active cooling structure in subgrade engineering in permafrost regions. But it needs strengthening techniques in warm permafrost regions under the impact of climate warming and human activities according to recent researches in-situ. Researchers have proposed a New Composite Slope Protection (NCSP) of the embankment, which is comprised of Awning Board and Crushed Rock Slope Protection (ABCRSP). Investigations found that it had better cooling effect. However, the cooling effect under various influencing factors, design optimization of parameters and structural stability need further study deeply and systematically. Aimed at the above problems, the detailed researches are conducted. And some main research achievements can be obtained as follows.Firstly, the mathematic formulas of heat transfer for the embankment with crushed rock slope protection are set up in different zones. And the General Controlled Formula (GCF) is proposed based on the controlled formulas for the crushed rock considering as the porous media by introducing Stream Function. Then the different discretization formulas based on the different discretizing scheme using the Finite Volume Method are derived. The researches mentioned above make a solid foundation of theory for the simulation and analysis of the thermal stability for the crushed rock embankment in permafrost regions.Secondly, based on the previous researches, the influencing factors and variations of the thermal conductivity for various soils are further studied deeply. In addition, more accurate multiple regression forecasting models for various soils were set up based on the experimental data. For the ice-rich frozen soil, which characterize complex relation between thermal conductivity and influencing factors, forecasting model of Artificial Neural Network (ANN) was established. Presenting of these models has provided new methods and helped convenience choosing the accurate conductivity in practical engineering.Thirdly, by considering the impact of air temperature difference between daytime and nighttime and the wind velocity difference between warm months and cold months on cooling effect of the embankment with open crushed rock slope protection at Beiluhe Test Section along the Qinghai-Tibet Railway, its temperature field, velocity field and heat flow are simulated and analyzed quantitatively. The results show that a certain cooling effect occurs for the crushed rock slope protection under the influence of the forced convection of the cold air during nighttime in warm months. And it has “heat shield” effect due to solar shading during warm months. During cold months, the stronger convective heat transfer occurs in it. The key type of heat transfer for the crushed rock slope protection is forced convection. But the distinct wind difference results into the apparent heat discrepancy between warm months and cold months. The main mechanisms of the cooling effect for the open crushed rock slope protection is including its “heat shield” effect, the cooling effect due to air temperature difference between daytime and nighttime and heat discrepancy resulting from the different wind velocity during warm months and cold months. It also deposits about 20 per cent of the total “cold energy” in winter in a year. If the climate warming and human activities are taken into account, the embankment with crushed rock slope protection in warm permafrost regions needs be strengthened and remedied. Fourthly, researchers have proposed the ABCRSP due to need for the strengthening techniques for the crushed rock slope protection under the influence of climate warming and human activities. Based on the investigation about the NCSP, the cooling effect and heat transfer characteristics under the various influencing factors are simulated and discussed systematically. The thickness and particle size of the crushed rock are optimized based on the results of the temperature field. These results and conclusions can provide the good ideas and references for the design and construction for the NCSP and crushed rock slope protection, and get the detailed training samples for the development of the Intelligentizing Analysis System for Qinghai-Tibet Railway (IASQTR). Then the cooling mechanisms of the NCSP are studied based on the investigating results and discussions. The awning board acting as a part of the NCSP can shade sunlight, obstruct warm wind in summer and snow in winter. The crushed rock slope protection acting as the other part of the NCSP has “thermal diode” effect and can shield the second radiation from the warmer awning board to the slope protection.Fifthly, the Open Composite Slope Protection (OCSP), which means that the air under the awning board can flow and exchange with the air outside freely, is put forward and the cooling characteristics and cooling effect are analyzed and discussed in this paper. The results show that the boundary conditions including open and closed boundary conditions have great influence on the cooling effect of the NCSP under the special geographic condition on Qinghai-Tibet Plateau. The OCSP has better cooling effect and high cooling rate. It is recommended to be adopted in building the subgrade engineering in warm permafrost regions, which is advantageous to cooling the embankment and protecting permafrost beneath the subgrade. Then the cooling mechanisms for the OCSP are studied. The researches show that it is different from that for the Closed Composite Slope Protection (CCSP). The fluid beneath the awning board has “siphon effect”, “channeling effect” and “chimney effect” under the influence of the forced convection of the outside air. These effects have resulted into better cooling effect on the embankment. The awning board still plays a great role on the cooling effect by solar shading, warm wind and snow obstructing. In addition, the cooling effect of the NCSP under different height are compared and analyzed. Note that the height of awning board has less impact on its temperature field. So the designs should be based on the results of the structural stability not that of the thermal stability when the awning board is designed. Sixthly, the stability of the awning board affiliated to the NCSP is one of most important problems. Its stability analysis and structural parameter optimization are performed based on the research of the wind load on the awning board under the influence of ultimate wind velocity. Meanwhile the reasonable ranges of height, space, buried depth and steel type for awning board are given according to the simulation tests.Seventhly, based on the results and discussions mentioned above from the temperature field, velocity field and heat flow of the embankment with NCSP and the analysis for the structural stability of the awning board, the design principles for the NCSP are proposed primarily. These can provide the scientific basis for design, construction and maintenance of the NCSP, and that the emphasis should be made on cooling effect and structural stability. Construction cost and convenience should be considered secondly. Additionally, the detailed design of the various parameters for the NCSP are discussed and studied.