Heat transfer analysis of thawing behavior in artificially frozen subway cross passage under seepage conditions

The thawing process of artificially frozen strata has received growing attention in engineering practice. Groundwater seepage significantly influences thawing behavior in highly permeable sandy gravel strata. To expedite the thawing and meet strict engineering schedules, forced thawing techniques are often employed. However, predicting the variation in stratum thawing temperature under the combined effects of multiple factors remains challenging. This unpredictability results in a lack of a reliable quantitative basis for assessing the environmental impacts of thawing. This study conducted model tests to systematically investigate the temperature distribution within strata during both natural and forced thawing. Then, the soil freezing characteristic curve of sandy gravel was incorporated to optimize a heat-hydraulic coupling numerical model. Furthermore, the influences of multiple key factors on stratum thawing were analyzed in detail. Finally, suggestions for selecting stratum thawing methods were proposed, and the implementation scheme for forced thawing was optimized. The findings indicate that increases in groundwater seepage velocity and temperature can effectively accelerate stratum thawing, and natural thawing is sufficient to meet the thawing requirements in most engineering scenarios. Compared with natural thawing, forced thawing can reduce the thawing duration by 83.71%, making it more suitable for strata with low seepage velocity and temperature. The optimized forced thawing method not only ensures thawing efficiency but also minimizes the waste of excess heat. These research outcomes provide valuable technical guidance for the selecting thawing methods in similar engineering projects.