# Study on Mechanical Properties of Fractured Sandy Mudstone Based on Triaxial Compression Experiment
## 3 Analysis of Triaxial Test Results
### Influence of Confining Pressure on Specim Strength and Deformation  
It is evident from the examination of stress-strain curves that, under varying confining pressures, the mechanical characteristics of specimens with fractures and unbroken specimens differ. As seen in Figure 4, the peak strength of specimens under various confining pressures was extracted for examination in order to more intuitively depict the impact of confining pressure on the strength of sandy mudstone. Figure 4 illustrates how the peak strength of the sandy mudstone specimen rises as confining pressure does. A specimen with cracks has a lower peak strength than an intact specimen, and its average strength is only 15% of the intact specimen's strength. When the confining pressure is 8 MPa, the strength of both intact and fractured specimens rises the highest in comparison to the strength under uniaxial conditions. There is a 53% increase in peak strength for whole specimens and a 28% increase for broken specimens. It is evident that confining pressure has less of an impact on the strength of cracked sandy mudstone. The peak axial and circumferential strains of intact and fractured sandy mudstone at various confining pressures are shown in Figure 5. The picture shows that the axial strain of the intact specimen progressively rises with increasing confining pressure, whereas the axial strain of the fractured specimen gradually decreases. This suggests that prefabricated  
Figure 4: Peak strength of rock specimens under different confining pressures. fractures are more difficult to break and shut at higher confining pressures. The impact of fracture on the collapse of rocks progressively diminishes. The lateral strain of the intact rock specimen is positively associated with the confining pressure, while the lateral strain of the fissure specimen rises first and subsequently declines as the confining pressure increases, based on the peak circumferential strain data. Consistent with the axial strain data, the dilatation of fissured rock reduces as the confining pressure loading exceeds 16 MPa. The rock is less susceptible to expansion deformation when axial strain is reduced, which also encourages circumferential strain reduction. The data of cracked and intact specimens at the elastic deformation stage were fitted and analyzed in order to investigate the impact of confining pressure on the elastic modulus E of rock. As a result, the elastic modulus E of sandy mudstone under various confining pressures was obtained, as illustrated in Figure 6. The picture illustrates a positive correlation between the confining pressure and the elastic modulus E of both the crack specimen and the whole specimen. In other words, a higher confining pressure corresponds to a higher elastic modulus. The intact specimen's growth slope is greater than the fractured specimen's, suggesting that the intact specimen's elastic modulus is more susceptible to confining pressure. The average elastic modulus of unbroken sandy mudstone under the same confining pressure is 3.51 times that of cracked rock. The aforementioned findings demonstrate that confining pressure can increase the elastic modulus of sandy mudstone. Conversely, the elastic modulus of fractured rock is less susceptible to confining pressure because of the higher density of microcracks and numerous secondary cracks brought on by tensile stress during the failure process. On the other hand, the medium inside the rock is more compact, the secondary fractures have low density, and the whole specimen contains shear cracks throughout the failure process. Therefore, the resistance to deformation of cracked sandy mudstone is much lower than that of whole rock, the larger the confining pressure. The greatest stress at which a rock can return to its initial condition upon unloading is known as the yield strength of rock, or elastic limit [28]. It is also a crucial metric for assessing the mechanical characteristics of rock.