Tree Based Machine Learning Framework for Stability Evaluation of Square Tunnels in Sloping Rock
摘要
This study presents a hybrid computational intelligence framework for assessing the stability of square tunnels excavated in sloping rock masses following the Generalized Hoek–Brown failure criterion under surcharge loading, with the objective to develop a rapid and interpretable predictive tool for estimating the stability number (Ns). Adaptive Finite Element Limit Analysis (AFELA) was employed to simulate tunnel behaviour, and a database comprising 2700 numerical simulations was used by considering the effects of cover-depth ratio (C/H), slope inclination (θ), Geological Strength Index (GSI), material constant (mi), and normalized uniaxial compressive strength (σci/γH). The dataset was integrated with tree-based machine learning models, including Classification and Regression Tree (CART), Chi-square Automatic Interaction Detector (CHAID), and Exhaustive CHAID (Ex-CHAID), for predicting Ns. Performance evaluation indicated that the CHAID model outperformed the CART and Ex-CHAID models, achieving the highest prediction accuracy with testing values of R² = 0.820 and RMSE = 3.755, while Taylor diagram analysis further confirmed its superior agreement with observed values. SHAP analysis revealed that GSI was the most influential parameter, followed by mi and C/H, whereas σci/γH and θ exhibited comparatively lower influence on tunnel stability. The proposed AFELA–machine learning framework provides a computationally efficient, reliable, and interpretable approach for tunnel stability assessment in sloping rock mass conditions.