Optimizing Machine Learning Models for Predicting Rock Cohesion and Angle of Internal Friction: A Comparative Study of Lithological Analysis, Robustness Assessment, and SHAP Explanations

Rock cohesion (c ) and angle of internal fricti on (φ ) are core parameters for rock mass stability analysis and engineering design; however, traditional triaxial tests are costly and time-consuming, limiting engineering efficiency.Based on a total of 199 sets of measured data from four rock types (shale, limestone, quartzite, and quartz-mica schist) in the Himalayan region, this study uses P-wave velocity (V_p ), density (ρ ), uniaxial compressive strength (UCS), and tensile strength (TS) as input variables. It employs four models—Support Vector Regression (SVR), Random Forest (RF), multilayer perceptron (MLP), and extreme gradient boosting (XGBoost) to predictc andφ . Hyperparameters were tuned using grid search and Bayesian optimization. We compared unified modeling with rock-type-specific modeling, performed interpretability analysis using SHAP, and tested robustness by introducing Gaussian noise. The results show that XGBoost produced the best predictions atc (test setR^2 = 0.9901, RMSE = 0.512 MPa), while the Bayesian-optimized SVR model yielded the best results atφ (R^2 = 0.9776, RMSE = 0.744°). Rock-type-specific modeling improved theR^2 for limestone atφ by 0.3541; the SHAP contribution for UCS and TS exceeded 70%; Random Forest demonstrated the best noise resistance, with a decrease inR^2 of less than 0.04 under 10% noise. In summary, the strategy proposed in this paper allows for the selection of prediction schemes based on data quality and lithological differences, providing a feasible approach for rapidly obtaining rock strength parameters.