## 2 Laboratory Uniaxial Compression Test
### Test Results
#### 2.3.2 Influence of Rock Content on Strength Responses Under Compression Testing  
Table 4 presents the elastic modulus, UCS, and the axial strain corresponding to the UCS of the soil-rock mixture specimens with varying rock contents. The incorporation of rock blocks within soil-rock mixture significantly enhances its resistance to deformation induced by external forces compared to the pure soil material. However, the mechanical properties of soil-rock mixture exhibit a notable deterioration trend as rock content increases, particularly when the rock content exceeds 15%. Figure 7 illustrates that the elastic modulus, UCS, and the axial strain corresponding to UCS exhibit a distinct decreasing trend as the rock content increases. Notably, the latter two indices present exponential and linear decline, respectively. Additionally, the time required for the specimen to achieve uniaxial compression strength (UCS) and complete failure consistently decreases as rock content increases.  
From the point of view of material composition, the appearance of a rock block should provide strength for the whole material through its own strength on one hand and through cooperation with the soil matrix and other rock blocks on the other hand. However, under uniaxial compression conditions, the soil-rock interface derived from the emergence of the rock block plays a negative role in the mechanical characteristics. The failure mode of the soil-rock mixture specimen with 30% rock content indicates that local failures predominantly occur near the rock blocks, with cracks propagating along the soil-rock interface, resulting in complex crack distributions. The strength of soil-rock mixture under the uniaxial compression conditions compared to that of the soil matrix also decreases, which means the strength provided by the increasing soil-rock interface is obviously weaker than that of the initial soil matrix. Additionally, the decrease in mechanical properties becomes more pronounced as rock content exceeds 15%, which correlates with the particle distribution characteristics. As shown in Table 3, the D\({}_{60}\) value increased rapidly from about 0.3 mm to 0.87 mm as the rock content rose from 10% to 30%. Previous researches  
\begin{table}
\begin{tabular}{l l l l l l l} \hline \hline
**Index** & & & & **Value** & & \\ \hline Rock content/(\%) & 0 & 5 & 10 & 15 & 20 & 25 & 30 \\ Elastic modulus/MPa & 24.29 & 21.45 & 21.73 & 24.92 & 21.28 & 24.00 & 18.32 \\ UCS/kPa & 816.24 & 684.14 & 650.09 & 701.46 & 544.17 & 568.79 & 435.75 \\ Axial strain corresponding to UCS/(\%) & 3.36 & 3.19 & 2.99 & 2.82 & 2.56 & 2.37 & 2.38 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Mechanical properties of soil–rock mixture with varying rock contents.  
Figure 6: Failure modes of soil–rock mixture specimens with varying rock contents as (**a**) longitudinal fracture; (**b**) shear fracture; (**c**) multiple shear fracture.  
have indicated that particle sizes ranging from D\({}_{10}\) to D\({}_{60}\) play a critical role in the forming of the soil skeleton. With increasing rock content, the particle size that governs the structure of the soil-rock mixture also increases, and for materials with high rock content, rock blocks play a vital role in defining structural characteristics. The disturbance influence of rock blocks and the soil-rock interfaces on the soil matrix becomes more evident.  
Therefore, the soil-rock interface presents complex and variable influence on the mechanical characteristics of soil-rock mixture, and its mechanism represent critical issues warranting further analysis.