An engineering evaluation index of thermal asymmetry in subgrade and its optimal design in cold regions

In cold regions, thermal budget between ground and atmosphere rebalances after linear engineering is constructed. The local surface morphology and strike of subgrade could cause asymmetric thermal boundary conditions, although most of conventional subgrades is geometrically symmetric. The asymmetric thermal boundaries bring the sunny-shady slope effect, which is investigated in most studies by comparing the temperatures difference between symmetric positions. This is one-dimensional analysis when modeling a two-dimensional subgrade profile, which cannot well describe the asymmetric geothermal field, not to mention the uncertainty of the coupling effects of thermal conditions and filling modes due to asymmetry. This study proposes an engineering evaluation index, thermal static moment (TSM). The bigger TSM value is, the more asymmetric the geothermal field is. Based on this method, the difference and distribution characteristics of temperature profile were analyzed. An optimal subgrade filling mode was proposed based on TSM evaluation. The TSM difference was smaller for optimized mode than that of conventional mode, so the thermal regime of the optimal filling mode was better.