Thawing warm permafrost of quicklime (CaO) piles and their optimization design

As a sustainable ground improvement technique, quicklime (CaO) piles have demonstrated considerable potential in frozen soil engineering applications. This study systematically investigates the thermochemical behavior of quicklime piles in thawed-warm permafrost, focusing on their exothermic behavior, expansion, and moisture absorption capability. Comprehensive laboratory experiments involving six physical models constructed with two representative soils from Northeast China's Mo'he Airport and the Lanzhou Loess District, coupled with 55 numerical simulation cases, were conducted. Critical parameters like soil temperature evolution, heat flux distribution, volumetric moisture content, and density variations during frozen soil thawing were quantitatively analyzed. The results reveal that the thawing radius of quicklime piles is strongly correlated with three primary factors: volumetric ice content (θ_i), initial soil temperature (T₀), and quicklime weight ratio (QWR). Under otherwise identical conditions, the thawing radius demonstrates a positive linear relationship with QWR. Soil densification within the thaw-affected zone significantly improved, with average dry density increasing by ≥5 %. When arranged in triangular configurations with a pile spacing ≤3d (where d represents pile diameter), the inter-pile soil exhibited effective compaction characteristics (average squeeze coefficient ≥ 0.93). Field validation is recommended to verify inter-pile soil compression performance for a pile spacing exceeding 3d. The results substantiate that quicklime pile technology provides an effective dual-function solution for thermal stabilization and mechanical reinforcement in warm permafrost regions. This research establishes a theoretical framework and technical guidelines for optimizing quicklime pile applications in permafrost engineering.