Constitutive Modeling and Mechanical Response of Weak Expansive Soils Under Loaded Wetting–Drying Cycles
摘要
This study aims to investigate the degradation mechanism of weakly expansive soil under loading and wetting–drying (W–D) cycles and to establish a corresponding constitutive model. Triaxial shear tests were conducted on specimens subjected to W–D cycles under different hydraulic pathways. The effects of cycle number, W–D cycles amplitude, and external loading on soil strength parameters were analyzed. Furthermore, a modified theoretical model and a machine learning-based constitutive relationship were established. Results indicate that W–D cycling induces soil deterioration, with reductions in peak shear strength and cohesion. Compared to cohesion, the internal friction angle exhibits lower sensitivity to cycling. The degradation effects intensify with decreasing loads and increasing W–D amplitudes. Fracture analysis reveals that structural damage serves as the primary mechanism for mechanical deterioration. Regression relationships between parameters of the Mohr–Coulomb and Duncan-Chang models and influencing factors were established using experimental data. A modified Duncan-Chang model (R2 = 0.90) was proposed after optimizing regression coefficients via a Genetic Algorithm. Concurrently, an artificial neural network (ANN)-based constitutive model (R2 = 0.99) was developed. By integrating global surrogate models (decision tree regressor) and local surrogate models (Local Interpretable Model-Agnostic Explanations), a comprehensive interpretability framework was achieved. Both theoretical and machine learning models effectively captured the stress–strain behavior of weak expansive soils, with the ANN model demonstrating superior accuracy. In addition, through hyperparameter tuning and surrogate modeling, machine learning frameworks can attain enhanced practicality and interpretability.