## 4 Effect of Oil-Water Infiltration on Rock Mechanical Properties
### AE Characteristics of Damaged Rock Samples with Different Liquid Contents
This indicates that, upon entering the failure stage, crack development in the rock specimen undergoes a sudden transformation, and the drastic internal structural changes generate a large number of intensive AE signals. Figure 12 shows the relationship between the maximum AE ringing count rate and the cumulative ringing count at failure with soaking time. As the soaking time increases, both the maximum AE ringing count rate and the cumulative AE ringing count at failure decrease. For the dry sample, the maximum AE ringing count rate reaches 378 counts, and the cumulative count is 88,279 counts. For the sample soaked for 8 h, the maximum AE ringing count rate is 282 counts, and the cumulative count is 37,109 counts. For the sample soaked for 16 h, the maximum AE ringing count rate is 94 counts, and the cumulative count is 22,614 counts. rringing count rate is 69 counts, and the cumulative count is 17,288 counts. Compared to the dry sample, these parameters are reduced by 81.7% and 80.4%, respectively. This indicates that the \"water-rock interaction\" weakens the mechanical strength of the rock, and the oil-water mixture has a significant impact on the AE characteristics during the uniaxial compression process. AE signals can not only characterize the time and frequency of internal rock structural damage but also reflect the types of cracks and failure modes inside the rock. This phenomenon can be used for crack characteristic analysis during the rock failure process [24]. The microcracks in the rock during loading mainly include tensile cracks and shear cracks. By analyzing the RA and AF values from the AE monitoring data, the types of internal cracks can be identified. RA (ms/v) is the ratio of rise time to amplitude, and AF (kHz) is the ratio of ringing count to duration. Research has shown that low AF and high RA values typically represent the occurrence or development of shear cracks, while high AF and low RA values indicate the occurrence or development of tensile cracks [25]. Due to the clear distinction in damage and AE characteristics of water-soaked specimens, this study used the traditional proportional clustering method to plot an AF-RA graph. The selection of K value is based on the measured maximum values of AF value and RA value of the acoustic emission signal during the experimental process, in order to determine the maximum scale values of AF value and RA value, and then determine the K value for experimental data analysis [26]. The calculated K value is 30, which meets the requirements of the general rock K value range of 1-200. Based on AE monitoring results from the experiment, the RA-AF scatter plots for rock samples in different liquid-soaked conditions are shown in Figure 13. In Figure 13, the scatter plot is divided into a tensile crack zone on the upper left and a shear crack zone on the lower right, with the coordinate axis at 45\({}^{\circ}\) as the boundary. Data points near the boundary line represent a mixed zone of tensile and shear cracks inside the rock sample. In the diagram, the crack sketches are shown, with red representing tensile cracks and green representing shear cracks. Figure 12: Maximum AE ringing count rate and cumulative ringing count during destruction as a function of soaking time curve. It can be observed from Figure 13 that under uniaxial loading, the AF values of the damaged rock samples range from 0 to 240 kHz, and the RA values range from 0 to 6 ms/v. The highest data density is near the origin, and the density gradually decreases as it moves away from the origin. In the dry state, the AF values of the damaged rock samples are mostly distributed between 0 and 180 kHz, and the RA values are mostly between 0 and 6 ms/v. The RA-AF parameters are distributed on both sides of the tensile and shear crack regions, with a wide and dense distribution of data points, indicating that the crack development inside the sample is complex, and the failure mode of the rock is a composite failure primarily caused by tensile damage.