## 2 Materials and Methods  
### Material Characteristics and Sample Preparation  
It is extremely challenging to obtain undisturbed core samples in permafrost [26]. Therefore, artificially prepared frozen samples were used in this research. According to the research from [PERSON] and [PERSON] [29; 30], the soil/rock threshold was set at \(\mathrm{d_{s/rt}}=0.05\) L\({}_{\mathrm{c}}\), where L\({}_{\mathrm{c}}\) is the diameter of specimens. Two types of cylindrical samples (61.8 mm (diameter) \(\times\) 125 mm (height) and 61.8 mm \(\times\) 50 mm) were fabricated for uniaxial compression testing and Brazilian testing, respectively. Therefore, we selected 2.0 mm as the soil/rock threshold. The plastic limit, liquid limit, and plasticity index of the soil were about 18.8%, 31.3%, and 12.5, respectively; the Cu and C\({}_{\mathrm{c}}\) were 31.58 and 0.77, respectively. For rock blocks, according to the sample preparation standard (Standard for Soil Test Method GB/T 50123-1999) [31], the diameters of rock blocks should be less than 12.36 mm (61.8 \(\times\) 0.2 = 12.36 mm). Moreover, the geometries and strengths of rock blocks are the main factors that affect the mechanical properties of the soil-rock mixture [32; 33; 34]. Accordingly, albaster blocks were chosen for testing, which are mostly made up of CaCO\({}_{3}\) and SiO\({}_{2}\). The particles have a density of 2.59 g/cm\({}^{3}\) with a smooth surface. The point-load strength of the particles is about 6.5 MPa. We calculated the roundness, sphericity, and the ratio of the perimeter and area of projection contour using the Image-Pro Plus (IPP) software package [35]. The mean roundness, sphericity, and ratio values were 1.132, 0.729, and 0.536, respectively. In order to acquire albaster blocks with a rough and porous surface and maintain similar macroscopic particle shapes with natural albaster blocks, we treated the blocks with a hydrochloric acid solution (HCI) with a solubility of 5 mol/L for 15 min, then washed the albaster blocks with distilled water. The angles of repose of the 2 albaster blocks were 35\({}^{\circ}\) and 43\({}^{\circ}\), respectively. Moreover, the arithmetical mean deviations of the profiles (R\({}_{\mathrm{a}}\)) were calculated as follows [36]:  
\[\mathrm{R_{a}}=\frac{1}{n}\sum_{i=1}^{n}\lvert y_{\mathrm{i}}\rvert \tag{1}\]  
As shown in Figure 1c, the R\({}_{\mathrm{a}}\) values of the 2 blocks were 13.24 \(\upmu\)m (from 9 samples), and 99.14 \(\upmu\)m (from 11 samples), respectively. All materials and corresponding parameters are shown in Figure 1.  
The mixture ratio, water content, dry unit weight, and frozen temperature are the important factors that determine the strength and deformation characteristics of FSRMs. According to earlier literature [37; 38], the strength of a SRM is jointly controlled by rock blocks and soil particles when the rock block content is 25%-75%. To obtain universal research conclusions and avoid the breakage of rock blocks during sample preparation, we selected the volumetric block proportion (VBP) of 40%. In the literature, when the water content is increased above saturation, the unfrozen water film thickness increases and pore ice begins to dominate the sample, where the strength is then reduced [24]. Considering the plastic limit (18.8%) and liquid limit (31.3%) of soil, research object, and sample preparation method, it is difficult to maintain the shape of sample at higher soil water content during sample preparation; moreover, it is not representative of frozen soil at lower soil water content. Therefore, the soil water content of 25% was selected. For the soil dry unit density, in general, the strength of frozen soil increases with an increase in unit weight; however, because most of natural SRMs are obtained from the loose colluvium and sediment, the soil dry weight of 1.7 g/cm\({}^{3}\) was chosen.