## 2 Experimental Test and Machine Learning Technique  
### Sample Preparation and Uniaxial Compression Test  
To execute the uniaxial compression test, we obtained the granite (RG-2) from KAERI (Korea Atomic Energy Research Institute) in Daejeon, South Korea. (Figure 2). KURT was constructed for the purpose of simulating the radioactive waste disposal environment [29]. With consideration of the practical purpose for achieving the required depth, the tunnel has a downward slope of 10% and a size of 6 \(\times\) 6 m. The geological formation of KURT generally comprises Mesozoic two-mica granite, and detailed topographic and geological information and host rock conditions of this site can be found in the literature [29]. Ten granite samples were collected from 56.2 to 60.8 m depth and made by satisfying the NX size suggested by ISRM (2007) [30] as shown in Figure 3. The flatness of the initial and end surfaces was adjusted to less than 0.02 mm. A uniaxial compression test was carried out and the deformation and failure behavior of samples were observed. The average ratio of length to diameter for specimens is 2.4, which is somewhat lower than 2.4 suggested by ISRM (2007) [30]. Biaxial strain gauges (AP-11-TS50N-120-EC, CAS) with a data logger (UCAM 20 PC, KYOWA) were attached to the rock surface for monitoring the rock deformation according to the vertical stress level in increments of 0.2 MPa/s (Figure 4). The tests were conducted by increasing the loading rate of 0.19-0.21 MPa/s on the specimens using the stress-controlled mode to simulate the progressive damage of rocks. Figure 5 shows a representative stress-strain curve for sample No. 2. A description of this curve will be given in Section 2.2. Testing times from the stress initiation to the rock failure were recorded as 9-17 min. The descriptive statistics for the rock properties are summarized in Table 1.  
Figure 4: Bi-axial strain gauge and eight acoustic emission sensors attached to the specimen surface. The strain gauge was installed to the center of the vertical axis and AE sensors were attached in a spiral direction for a wide range of crack detection. Figure 3: Ten granite specimens to be used in the compression test. These were obtained from the RG-2 section in KURT which comprises Mesozoic two-mica granite. Figure 2: Korea Underground Research Tunnel (KURT) located in Daejeon, South Korea. This facility was constructed for the purpose of simulating the radioactive waste disposal repository. Simultaneously, eight AE sensors (AE603 SW-GA), which have a sensitivity of 115 dB, a valid frequency of 30-300 kHz, and a resonance frequency of 60 kHz, were used to acquire AE signals. For ensuring reliable data, the sensors were attached to the rock specimen using an epoxy bond (Araldite Rapid corporation: relative density of \(-1.17\) at 25 Celsius, specific acoustic impedance of \(12.8\times 10^{6}\) kg/m\({}^{2}\cdot\) s), eliminating the air and minimizing the measurement error in the acoustic impedance [31]. The AE voltage was amplified to 60 dB for detection efficiency using a preamplifier. As a data acquisition system, a RECTUSON 10-channel analyzer was used, where the peak definition time, hit definition time, and hit locking time were specified as 50, 100, and 500 us to extract the signal concerning rock crack. The threshold of a lower limit for AE signal detection was set to 65 dB. Additionally, only signals obtained from the sensor attached to the middle of the specimen were considered under the detected condition by more than 6 out of 8 AE sensors. The AE voltage was amplified to 60 dB for detection efficiency using a preamplifier. To remove the noise of AE signals, filtering with wavelet transform was used. The specifications of equipment used for the uniaxial compression test are summarized in Table 2.