## 3 Results and Discussion  
### The Failure Pattern under Compression and Brazilian Testing  
The temperature data show that relatively stable temperatures of \(-26\pm 1\), \(-15\pm 1\), and \(-7\pm 1\)\({}^{\circ}\)C were maintained for 5-7 min during compression testing. Meanwhile, the peak stresses could be reached within 3-4 min. The Brazilian test samples were analyzed directly, and the peak loads could be reached within 2-3 min. For the current work, it is sufficient to investigate the strength difference of FSRMs under different temperatures. Figure 4: Testing system: (**a**) acoustic emission (AE) system; (**b**) ultrasonic plus velocity (UPV) system. Figure 3: The testing apparatus and method: (**a**) uniaxial compression test; (**b**) sketch of the testing system; (**c**) thermometer probe; (**d**) Brazilian test. The typical stress-strain curves of FSRM samples under different frozen temperatures are plotted in Figure 5. Under uniaxial compression, the stress-strain curves followed a similar pattern. At the beginning stage of the loading, all the curves had a transient concave upward section. Subsequently, all samples exhibited an elastic behavior wherein stress was linearly proportional to strain. After the yielding stress was reached for the sample with a frozen temperature of \(-30\)\({}^{\circ}\)C, the stress showed a sharp increase to the peak stress strength point and decreased rapidly; however, for the samples with frozen temperatures of \(-10\)\({}^{\circ}\)C and \(-20\)\({}^{\circ}\)C, the stress data showed a yielding plateau. The stress slowly increased to the peak point, then decreased gradually. The samples with different frozen temperatures showed different failure modes. For the samples with frozen temperatures of \(-10\) and \(-20\)\({}^{\circ}\)C (Figure 5b,c), no obvious penetrating cracks were observed, even when the strain reached 12%. The bulging deformation and short split fracture parallel to the compression axis were the main failure modes at the stress post-peak stage. For the sample with a frozen temperature of \(-30\)\({}^{\circ}\)C (Figure 5d), the obvious inclined shear cracks and axial tension cracks were observed at the stress post-peak stage. The samples exhibited greater shear failure, and the bulging deformation was not relatively obvious. Within the local area of the shear cracks, small amounts of rock fragments were observed, and rock powder was mainly distributed around the rock fragments. This implies that the shear dislocation extrusion damage of interlocking angular rock blocks was the main block destruction mechanism. On the contrary, all the ice-rock mixture samples showed obvious axial cracks at the peak point, and the axial stress decreased rapidly after the peak strength point. The loading curves and corresponding failure modes of the FSRM disk samples containing rough rock blocks under the Brazilian test are depicted in Figure 6. A tortuous failure surface adjacent to the loading surface, instead of a splitting fracture as in the homogeneous sample, was the main failure mode for FSRMs under Brazilian testing here. In addition, rock fragments could be observed in the central failure surface, and the number of rock fragments increased with a decreasing temperature. On the basis of the fracture surface morphology of rock blocks in Figure 6d, we found that rock block tensile damage was the main destruction mechanism. We could not see the obvious breakage of rock blocks  
Figure 5: Failure patterns of frozen soil–rock mixtures (FSRMs) under uniaxial compression: (**a**) stress-strain curves; (**b**) failure pattern of the FSRM at \(-10\)\({}^{\circ}\)C; (**c**) failure pattern of the FSRM at \(-20\)\({}^{\circ}\)C; (**d**) failure pattern of the FSRM at \(-30\)\({}^{\circ}\)C; (**e**) rock block fragments in the internal crack of the FSRM at \(-30\)\({}^{\circ}\)C.  
in the ice-rock mixture samples and FSRM samples containing smooth rock blocks.