## 3 Test Results and Microscopic Observation Analysis
### Influence of Rock Particle Size on Microbial-Solidified Soil-Rock Mixture  
According to the analysis of the above summary, it can be seen that the cementation effect of the soil-rock mixture with 50% and 60% rock block proportion is better. It can carry a large bearing capacity, and the unconfined compressive strength is relatively suitable. Therefore, the soil-rock samples with rock content of 50% and 60% were observed separately to find out the optimal particle size ratio of the soil-rock mixture. It provides a reference for subsequent research and engineering applications. The results show the following:  
1. Looking at Figures 7-9 below, under the condition that the bacterial solution concentration, cementation reagent concentration, and solution ratio remain unchanged when the rock block proportion is 50% for the soil-rock mixture with a particle size of 0.2-0.4 cm, as the sample is loaded, the stress increases with the increase in the strain. After reaching the peak, the stress gradually decreases, and the loading rate remains unchanged; therefore, the earliest maximum bearing capacity of the three particle sizes is D3-D2-D1, respectively; that is, the sample with a particle size of 0.6-0.9 cm shows a peak first, followed by a sample with a particle size of 0.4-0.6 cm, and finally a soil-rock mixture sample with a particle size of 0.2-0.4. When the rock block proportion is 60%, the earliest time for the three particle sizes to show the maximum bearing capacity is when D1, D2, and D3 show their peaks at the same time; that is, the sample with a particle size of 0.2-0.4 cm reaches the maximum bearing capacity first, and the sample with a particle size of 0.4-0.6 cm and a particle size of 0.6-0.9 cm basically has the maximum bearing capacity at the same time. The soil-rock mixture mixed with large-sized boulders has a large pore space. When compressed and squeezed, the internal pore space will be destroyed first, and the soil-rock mixture with small-sized boulders will reach the maximum bearing capacity faster than that;
2. It can be observed in Figure 9 that under the same loading rate and the same rock block proportion, in the rock block proportion of 20%, 30%, 40%, and 50%, under the same proportion of rock, the unconfined compressive strength decreases with the increase in particle size. When the rock content is 60%, the value of unconfined compressive strength first decreases and then increases with the increase in particle size. In the samples with low rock block proportion, the silt content is high, and the overall force is more inclined to the properties of silt during the loading and stressing process. During the compression process, the pores between the particles are destroyed, the bound water increases due to the shrinkage of the pores, and the bonding strength between the particles decreases, making it easier to be destroyed;
3. When the rock block proportion is low, the difference between the particle size ratio of the rock with small particle size and the soil particle size is relatively small, and it is easier to be cemented with the bacteria liquid to form a block. The compressive strength of the soil-rock mass is enhanced, so the unconfined compressive strength of the soil-rock mixture containing small-diameter rocks is higher than that of the soil-rock mixture containing large-diameter rocks under the same conditions. In the case of high rock block proportion, the large particle size of the rock and the soil particle size gap is large, and the pore space is large, giving the bacteria liquid more space for cementation and the required oxygen. At the same time, under the consolidation pressure of irregular boulders, the rocks with larger particle sizes have more particle contact points than those with smaller particle sizes.