Laboratory investigation on hydrothermal response of the open crushed-rock layer to rainfall infiltration in permafrost regions

Abstract

Under the condition of warming and wetting trend on Qinghai-Tibet Plateau due to climate change, summer rainfall infiltration alters the change of the hydrothermal state and may impact the cooling performance of crushed-rock interlayer embankment. Herein, two experimental models with the 1.4-m-thickness (M1) and 0.6-m-thickness (M2) crushed-rock layer (CRL) were conducted in an environmental simulator experiencing the freezing and thawing cycles. The hydrothermal response to rainfall events was investigated and quantified by analyzing the variations of measured soil temperatures, volumetric water contents, and heat fluxes. Thermal observations show that rainfall infiltration caused heat advection and resulted in step change of soil temperature at depth. Rainfall infiltration reduced the surface temperature of the CRL, but warmed the soil layer at depth by up to 2.13 °C. The average temperature of the base soil layer under the action of concentrated rainfall basically showed an increasing trend. In particular, the CRL with a smaller thickness (M2) had a more significant thermal response to rainfall event. In addition, the moisture pulse, experiencing a step increase and following a gradual decrease caused by rainfall water infiltration, appeared several hours earlier than the temperature pulse. Moreover, infiltrated water produced an additional energy to warm the soil at depth, with maximum heat flux of 12.13 W/m2 and 79.90 W/m2 for the M1 and M2, respectively. The infiltrated water accumulated at the top of base soil significantly delayed the refreezing processes in cold period due to the latent heat effect. The net founding of this study provide an insight into improving the design crushed-rock embankment in permafrost regions.