Ninth International Conference on Permafrost ... - IARC Research

Non-Linear Analysis of the Thermal Characteristics of Permafrost Embankmentwith Crushed-Rock Revetment and Insulation on Qinghai-Tibet PlateauMingyi Zhang, Shuangyang Li, Shujuan Zhang, Yuanhong DongState Key Laboratory of Frozen Soil Engineering, Cold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy of Sciences, Lanzhou 730000, ChinaIntroductionThe embankment with crushed-rock revetment hasbeen widely used in the construction of the Qinghai-Tibetrailway/highway and is an effective measure to ensure thethermal stability of permafrost embankment (Lai et al. 2003,2004, Sun et al. 2004, Ma et al. 2002); however, becauseof the influence of global warming, it is difficult to protectthe underlying permafrost from warming, even thawing(Wang et al. 1996). Therefore, in order to sufficiently protectthe underlying permafrost, a numerical representation ofthe unsteady two-dimensional continuity, momentum, andenergy equations of thermal convection for incompressiblefluid in porous media (Nield et al. 1999, Kong et al. 2002) isused to analyze and compare the temperature characteristicsof the embankments with crushed-rock revetment, with andwithout insulation, under the global warming in this study.Results and DiscussionsBased on the temperature and geology conditions on theQinghai-Tibet Plateau (Cheng et al. 2003, Zhu et al. 1988,Qin, 2002, Lai et al. 2003), the temperature distributions ofthe three embankment models with crushed-rock revetment,with and without insulation (Fig. 1), constructed on July 15,are simulated and analyzed for 50 years.Figure 2 is the temperature distribution of the embankmentwith crushed-rock revetment (1.60 m thick), withoutinsulation on October 15, after 50 years of the construction. Itcan be seen from this figure that the location of the permafrosttable (0°C isotherm) is y = -2.39 m under the natural groundsurface, while that is y = -1.79 m in the centerline of theembankment and 0.60 m higher than that under the naturalground surface; furthermore, -0.2°C isotherm is high underthe slope foot of the embankment, while low in the middleof embankment.Figure 3 shows the temperature distribution of theembankment with crushed-rock revetment (2.0 m thick),without insulation on October 15, after 50 years of theconstruction. From this figure, we find that the groundtemperature distribution is similar to the embankment withcrushed-rock revetment (1.60 m thick), without insulation(Fig. 1). In detail, the permafrost table (0°C isotherm)is y = -2.39 m under the ground surface, while that is y =-1.69 m and 0.03 m in the centerline and side slope of theembankment, respectively.Based on the above the analyses, we can conclude thatthe embankments with crushed-rock revetment withoutinsulation have an active cooling effect on the underlyingpermafrost, but cannot effectively reduce the underlyingground temperature. Furthermore, their cooling effects arestrongest at the side slope foot, but weak in the middle. WeY(m)420-2-4-6-8-10-20 -15 -10 -5 0X(m)Figure 2. Temperature distribution of the embankment with crushedrockrevetment (1.60 m thick), without insulation on October 15,after 50 years of the construction (Unit: °C)4A30.0mB1:1.5B'CdC'' DE1:1.750.8m7.2m3.4mF5.0m0.4mG H''InsulationHCrushed-rock revetment30.0mI' I JY(m)20-2-43.0mNK-6MFigure 1. Embankment model with crushed-rock revetment.L30.0m-8-10-20 -15 -10 -5 0X(m)Figure 3. Temperature distribution of the embankment with crushedrockrevetment (2.0 m thick) without insulation on October 15,after 50 years of the construction (Unit: °C).359