RESEARCH ON QUANTITATIVE IDENTIFICATION OF RUPTURE EVOLUTION AND PRECURSORY ANOMALY OF ROCK BRIDGE UNDER THE WETTING-DRYING CYCLES

To investigate the rupture evolution and precursory anomalies of the rock bridge in a rock slope containing a locking segment under wetting-drying cycles, we conducted uniaxial compression tests on rock bridge specimens subjected to different numbers of wetting-drying cycles. Utilizing digital image correlation(DIC)technology, we measured the full-field deformation of the specimens in real-time during the loading process, identifying crack growth types by solving displacement vectors. Additionally, we introduced the covariance matrix to quantitatively describe the discreteness of multiple components of the strain field. A method to identify precursory anomalies in the rock bridge strain field was proposed, and the influence of wetting-drying cycles was analyzed. The results indicate that with an increase in the number of wetting-drying cycles, the crack initiation stress and compressive strength of the rock bridge gradually deteriorate. As cracks develop in the rock bridge, the displacement vectors of surrounding rocks show significant differences, identifying two basic types of cracks: tensile cracks and shear cracks. The axial stresses required for crack initiation and propagation decrease with an increase in the number of wetting-drying cycles. The evolution process of the effective variance of the strain field can be divided into three stages: initial differentiation, stable differentiation, and accelerated differentiation. When the shear crack initiates, the effective variance of the specimen under dry conditions abruptly increases, while the effective variance of the specimen under wetting-drying cycles shows accelerated growth, serving as a precursor. The precursor stress level and time level of the specimen under wetting-drying cycles are lower than those under dry conditions due to the softening effect induced by the wetting-drying cycles.