• Different replacement materials significantly influence the temperature distribution within the permafrost foundation. • The replacement cushion changes the spatial and temporal moisture distribution in the shallow foundation. • Moisture migration caused by the replacement cushion challenges the long-term maintenance of foundation mechanical properties. • The water permeability and thermal conductivity of the replacement material are critical factors affecting the water-heat distribution and evolution. Road hazards in the permafrost regions of the Qinghai-Tibet Plateau have become increasingly severe due to climate change, environmental shifts, and engineering-related thermal effects. Replacement cushions play a pivotal role in enhancing the stability and durability of highway foundations. In combined with the replacement cushion design of the Gonghe-Yushu Freeway, this study employs numerical simulations to analyse the water-heat distribution in foundations under three replacement materials: fine sand, coarse sand, and gravel. The findings reveal that the gravel cushion exhibits excellent temperature regulation, effectively reducing the heat transfer from the subgrade to the underlying foundation. However, shallow meltwater invades the deeper foundation, leading to increased magnitude and oscillation amplitude of unfrozen water content in the permafrost beneath the replacement cushion. The moisture migration caused by replacement cushioning adversely affects the long-term maintenance of foundation mechanical properties. Therefore, adopting the replacement method in engineering practice should be approached cautiously, with careful consideration of the climate, environment, and topographic features of the road area.
Gao et al. (Wed,) studied this question.