## 2 Experimental Materials and Methodology
### Experimental Device and Procedure  
An indigenously developed continuous loading system was designed and fabricated for this investigation. The experiments were conducted in the nanoVoxel-4000 micro-CT facility (Tianjin Sanying Precision Instruments Co., Ltd., Tianjin, China) under ambient conditions (25 \({}^{\circ}\)C). The integrated system comprised (1) a servo-controlled loading actuator, (2) an acoustic emission (AE) monitoring module, and (3) a four-dimensional X-ray computed tomography (4D-XCT) imager (Figure 1). Key geometric and operational parameters are summarized in Table 2.  
AE monitoring and CT scanning were synchronized during sandstone compression (Figure 1a). Throughout the loading process, mechanical loading equipment and AE devices continuously collected data, while CT scans captured internal structures at different loading moments. Rock strain gauges on the mechanical loading system measured compressive strain in sandstone specimens (Figure 1b). The CT scanning system acquired images of sandstone's internal structural configurations (Figure 1c). AE signal amplifiers were adjusted to monitor acoustic emissions during loading (Figure 1d). During the scanning process of sandstone samples, the position of the loading piston will not move. Since the piston is fixed at the designated position during the scanning process, the scanning image of the sandstone sample will not be affected.  
Figure 1: Experimental device and procedure: (**a**) Real-time 4D-XCT scanning and AE monitoring during in-suit continuous uniaxial compression; (**b**) Strain gauge during in-suit loading process; (**c**) CT scanning; (**d**) AE sensors and AE signal amplifier.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Sample** \\ **Grouping** \\ \end{tabular} } & \multirow{2}{*}{**Specimen**} & \multirow{2}{*}{**Mass (g)**} & \begin{tabular}{c} **Diameter** \\ **(mm)** \\ \end{tabular} & \begin{tabular}{c} **Height** \\ **(mm)** \\ \end{tabular} & \begin{tabular}{c} **Porosity** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **Dry** \\ **Density** \\ **(m/s)** \\ \end{tabular} & \begin{tabular}{c} **P-Wave** \\ **Velocity** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **Uniaxial Peak** \\ **Velocity** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **Elasticity** \\ **Strength** \\ **(\%/MPa)** \\ \end{tabular} & \
\begin{tabular}{c} **Poisson’s** \\ **Ratio** \\ \end{tabular} &
\begin{tabular}{c} **Radius Size** \\ **(L/mm)** \\ \end{tabular} \\ \hline \multirow{4}{*}{R-1} & R-1-1 & 432.25 & 50.00 & 100.02 & 9.75 & 2.37 & 2175 & 37.58 & 4.18 & 0.26 & 784 \\  & R-1-2 & 430.89 & 50.02 & 99.98 & 9.77 & 2.36 & 2166 & 29.55 & 4.17 & 0.28 & 826 \\  & R-1-3 & 431.56 & 49.98 & 99.96 & 9.74 & 2.38 & 2186 & 44.21 & 4.20 & 0.25 & 817 \\  & R-1-4 & 403.78 & 50.02 & 99.98 & 9.76 & 2.37 & 2172 & 39.24 & 4.18 & 0.27 & 821 \\ \hline \multirow{4}{*}{R-2} & R-2-1 & 429.48 & 50.00 & 100.02 & 9.78 & 2.35 & 2162 & 26.88 & 4.16 & 0.28 & 799 \\  & R-2-2 & 432.46 & 50.02 & 100.02 & 9.75 & 2.37 & 2186 & 46.52 & 4.19 & 0.27 & 842 \\  & R-2-2 & 431.30 & 50.02 & 100.00 & 9.74 & 2.37 & 2173 & 38.73 & 4.19 & 0.26 & 852 \\  & R-2-4 & 430.75 & 49.98 & 100.04 & 9.74 & 2.37 & 2167 & 29.54 & 4.18 & 0.27 & 834 \\ \hline \multirow{4}{*}{R-3} & R-3-1 & 432.77 & 50.00 & 99.96 & 9.75 & 2.37 & 2181 & 40.06 & 4.19 & 0.25 & 831 \\  & R-3-2 & 430.25 & 49.98 & 99.98 & 9.74 & 2.37 & 2171 & 35.32 & 4.17 & 0.26 & 823 \\  & R-3-3 & 432.09 & 50.04 & 100.00 & 9.75  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**Device** & **Configuration** & **Parameters** & **Device** & **Configuration** & **Parameters** & **Device** & **Configuration** & **Parameters** \\ \hline  & Loading & Servo control & & & U.S. PAC & & & Tianjin Sanying \\  & system & system & & & company, & & & Precision \\  & Loading & Servo control & & &