# Study on Mechanical Properties of Fractured Sandy Mudstone Based on Triaxial Compression Experiment
## 3 Analysis of Triaxial Test Results
### Analysis of Stress-Strain and Acoustic Emission Characteristics of Specimens
During the post-peak crack acceleration stage, there is an intensive release of energy from the entire specimen after reaching peak strength. The energy series of the entire specimen is higher than that of a cracked rock specimen, leading to a rapid decrease in strength. The stress-strain relationship of fractured sandy mudstone differs from that of intact rock. The axial strain \(\varepsilon 1\) exhibits an inverted triangle shape near the peak stress, while the curve of intact rock samples shows an inverted U shape under the same confining pressure. This indicates that the failure form of fractured sandy mudstone is closer to brittle failure than that of intact rock. Additionally, after the loading exceeds the elastic deformation stage, a stress drop occurs in the rock specimen with cracks before reaching peak stress, which is caused by the closure of pre-existing cracks exceeding their yield strength \(\sigma c\). After fracture closure, occlusal contact under the fracture surface produces normal stress, strengthening the bearing capacity of the rock and causing a subsequent rise in stress value. Post-peak stress drop phenomena are more frequent in fractured sandy mudstone samples, with each stress drop accompanied by a surge in acoustic emission energy. In comparison to intact rock samples, energy release in fractured sandy mudstone occurs gradually step by step whereas it is released intensively as a single event for intact rocks; indicating that fractured rock samples have broken several times after reaching peak stress. According to acoustic emission data, both energy series and number of events for cracked samples are smaller than those for intact ones; suggesting that micro-cracks are more distributed in intact rock samples. Figure 3: Stress–strain curves and energy characteristics of rocks under different confining pressures. Based on the test results of specimens with cracks and intact specimens under varying confining pressures, it is observed that as the confining pressure increases, the values of \(\sigma\)c and \(\sigma\)t for all rock samples become closer. The \(\sigma\)c of intact rock samples clearly increases, while the slope of the straight line intersecting \(\sigma\)t decreases, and the strain required to reach the peak point becomes larger. This suggests a transition from brittleness to ductility in rock failure under confining pressure, leading to an increase in carrying capacity. Conversely, for specimens with cracks, plastic deformation is not significant initially; however, when the confining pressure exceeds 8 MPa, stress loading before reaching the peak point becomes more linear and stress drop amplitude reduces. This indicates an improvement in bearing capacity for rocks with cracks at higher confining pressures. These findings are consistent with research by [PERSON] [20] on fractured rocks under different confining pressures. Furthermore, analysis of \(\epsilon\)2 and \(\epsilon\)v data under different confining pressures reveals that \(\epsilon\)2 for specimens with cracks is larger than that of intact specimens due to expansion of tensile wing cracks dominated by prefabricated cracks. In contrast, failure in intact specimens tends towards instantaneous shear failure.