## 5 Method to Prepare Similar Materials Simulating Weak Rock Mass  
Via discrete element analysis, the mathematical relationships between the RFCA and mechanical properties such as elastic modulus, cohesion, and internal friction angle were proposed. According to this, a method to prepare the similar material is presented. The flowchart of the method is shown in Figure 15.  
Figure 14: Macroscopic crack expansion in numerical modelling and laboratory tests with different RFCAs. Figure 15: Flowchart of method to prepare similar materials simulating weak rock mass. Obtain the original parameters of weak surrounding rock mass:  
Mechanical parameters such as elastic modulus, cohesion, friction angle, etc., for prototype rock mass are usually obtained from the field measurements, laboratory tests, or empirical methods. Derive the target parameters of similar materials by the similarity principle:  
The target parameters of similar materials can be solved by the similarity principle on the basis of the original parameters. Gravity, Poisson's ratio, and the internal friction angle of the similar material are equivalent to those of the prototype rock mass, whereas the elastic modulus and cohesion are solved by dividing the stress geometric similarity scale. Select the basic components of similar materials:  
The basic components of similar materials simulating weak rock mass are proposed, and a summary is shown in Table 6. As in Table 6, the similar material for the rock mass is mostly composed of three parts: aggregates, binder, and modifying agent. Aggregates are produced by barytes, sand and iron powder, etc. The binder refers to a white emulsion, gypsum, cement, epoxy resin, silicone rubber, rosin, et al. The modifying agent refers to water, alcohol, and gasoline. The main purpose of the modifying agent is to mix the proportions of the similar materials. Referencing Table 6, the coarse aggregate of the similar material is sourced from quartz sand, and barytes are selected as fine aggregates. The binder and modifying agent are gypsum and water, respectively. Determine the proportions of the components of similar materials:  
Several sets of compression tests for different RFCAs and the ratio of the binder should be conducted. Based on the test results, coefficients of Equations (4), (7), and (8) are derived. Hence, relationships between the elastic modulus, cohesion, friction angle, and RFCA are obtained. Substituting the target mechanical parameters into the relationships, the \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Rock Mass Classification** & **Aggregates** & **Binder** & **Modifying Agent** \\ \hline limestone & barytes, river sand & gypsum & water \\ \hline clay & barytes, quartz sand & vaseline & water \\ \hline sand & barytes and quartz sand, or & & water \\  & full quartz sand & & \\ \hline fractured rock mass & barytes, quartz sand & rosin & alcohol \\ \hline fractured rock mass & quartz sand & cement, gypsum & water \\ \hline weak rock mass for class IV & barytes, fine sand, flyash & & machine oil \\ and class V & & & \\ \hline rock mass for class V & Lanzhou loess, sand & cement, gypsum & water \\ \hline rock mass for class IV & barytes, yellow sand & gypsum & laundry detergent, water \\ \hline rock mass for class V & barytes, river sand & gypsum & \\ \hline rock mass for class IV & barytes, yellow sand & gypsum & laundry detergent, water \\ \hline rock mass for class IV & barytes, sand & starch & water \\ \hline rock mass for class IV & barytes, quartz sand & gypsum & water \\ \hline rock mass for class IV & river sand & cement, gypsum & water \\ \hline Relatively soft rock mass & barytes, sand & silicone rubber, epoxy resin & gasoline \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Aggregates, binder, and modifying agent of similar materials for simulating multiple kinds of weak rock mass. range of the RFCAs can be obtained. It should be noted that the unit weight of the similar material depends heavily on barite power.