# Study on Shear Mechanism of Bolted Jointed Rocks: Experiments and CZM-Based FEM Simulations
## 3 Laboratory Experiments  
### Preparation of Rock Specimens  
With the start of the construction of China's oil reserve bases, a number of large underground water sealed oil depots are under preparation. An underground oil depot is mainly an oil storage tank formed by the fissure water in the rock and the surrounding rock of the cavern. Because of the rheological properties of the joints in the surrounding rock, even if the external conditions do not change with time, the structure of the surrounding rock will continue to adjust, which can lead to change in the stability of the surrounding rock. Under complicated long-term loading and unloading conditions, the long-term stability of underground caverns is even more complex and dynamic. It is thus crucial to understand the mechanistic behavior of bolted jointed rock for the safety evaluation of underground water sealed oil storage caverns. Based on the Huangdao oil depot in China, the shear characteristics of bolted jointed rock are studied in this work. The rock in this area is mainly granite. Rock-like materials were used to conduct laboratory experiments, In order to avoid large variability in the experiment results caused by natural sampling. There are two main types of specimens used in our laboratory experiments. The first type is standard cylindrical with a length of 100 mm and a diameter of 50 mm. The second is rectangular parallelepiped with a length of 200 mm, a width of 100 mm and a height of 100 mm. Orthogonal design of experiments was used to determine the optimum proportion of materials for all specimens. The quantity of material by mass was CA270 cement: 0.5-1 Corundum: 0-0.5 mm corundum: \(-45\upmu\)corundum: Water reducer ADS3: Water reducer ADW1: Water = 1: 2.4: 1.4: 1.2: 0.018: 0.042: 0.4. The joint surface curve was selected from ten standard Joint Roughness Coefficient (JRC) curves proposed by [PERSON] (1978, 1980). The standard JRC curves were discretized and re-divided using CAD as shown in Figure 2. Three JRC curves with different roughness, JRC2-4, JRC10-12 and JRC18-20, labeled S1, S2, and S3, were used in the experiment. As shown in Figure 3. The specimens were first put into the curing box and kept under constant temperature and humidity conditions for 28 days, and then taken out for the experiments.  
The bolts were made of metal aluminum and divided into three different types: 1060 aluminum alloy, characterized by strong plasticity, high elongation (up to 25%), labeled as MG1; 6063 aluminum alloy with medium hardness, high strength and elongation of 15%, labeled as MG2; LY12 high-hardness aluminum alloy, with high strength, poor plasticity, and 5% elongation, labeled as MG3. Specific physical and mechanical parameters are listed in Table 1. In order to bolt the rock joints, two couplings of rough joints were aligned, inserted into experiment bolts, and bolted with bolting agent. The diameter of bolts is 10 mm and the length is 100 mm [30]. The bolted piece was cured at room temperature for  
Figure 3: Cylinder and shear specimen dies.  
Figure 2: Standard Joint Roughness Coefficient (JRC) Graph (Modified after [PERSON] [15; 16]).  
approximately 10 days. The bolted specimens are shown in Figure 4. The labels of the different types of specimens are provided in Table 2.  
We use these three different types of metal aluminum to represent three different types of bolts to carry out our experiments to explore the shear failure mechanisms of different bolted jointed rocks.