Patterns and Prediction of Thaw Settlement and Thaw Compression in Permafrost

Permafrost foundations are prone to settlement during thawing, resulting from both thaw settlement and thaw-induced compression. The relative contributions of these components are strongly influenced by soil structure and loading conditions. Therefore, clarifying their interaction and identifying the conditions for significant compressive deformation are essential for accurate predictions. Laboratory tests were conducted to determine the thaw-settlement and thaw-compression coefficients. A new index, the thaw proportion of thaw settlement, was introduced to quantify the relative contributions of the two deformation components. By combining this ratio with compressive strain characteristics, criteria for identifying significant thaw-compression deformation and the corresponding load–porosity conditions were established. In addition, multiple machine learning models were developed, and their predictive performance was systematically evaluated. The main findings are outlined as follows: (1) The thaw proportion of thaw settlement is controlled by soil type, natural water content, dry density, and external load, with clear differences among soil types. It increases with water content, but decreases with increasing dry density and load. (2) Significant thaw-compression deformation is defined by a compressive strain of 8%, and the corresponding load–porosity conditions are identified. (3) Machine learning models effectively predict permafrost deformation. After Bayesian Optimisation (BO), performance improves markedly, with the BO-Support Vector Machine (SVM) model achieving the highest accuracy for thaw-settlement-coefficient prediction (R2 = 0.85), and the BO-Extreme Gradient Boosting (XGBoost) model performing best for post-thaw compressive strain (R2 = 0.95).