## 2 Comparison and Analysis of Pullout Tests on Bolts and Compression Tests on an Anchored Rock Mass  
Surrounding rocks of underground caverns generally contain structural planes, including fractures and faults, which decrease their stability, making it necessary to support the surrounding rock with bolts (Figure 1). It can be seen that anchored surrounding rocks are stressed in three directions, with only one free face in the cavern direction. When surrounding rocks are deformed, it drives the deformation of bolts, which generates tensile force. The tensile force on such bolts suppresses the deformation of the surrounding rocks, improving the stability of the surrounding rock stability.  
To test the installation quality of bolts in the field, pullout tests are commonly conducted on bolts. On this basis, to enable relevant research via laboratory tests, the tests are simplified as pullout tests on bolts, as shown in Figure 2a. The test system is composed of a bolt, a bearing plate, grout, and a rock mass. A displacement constraint is applied to the surrounding rocks in the tests, and tensile force is applied to the outer end of the bolt. After the bolt is deformed under stress, the rock mass is also deformed due to the transfer effect of grouts. In the process, the bolt is the actively stressed member, while surrounding rocks are passively stressed. In the compression test on anchored rock mass (Figure 2b), after applying stress to the surrounding rocks, the surrounding rocks are deformed under stress, which is transferred by grouts to cause deformation and generation of tensile force in the bolt. In addition, the deformation of surrounding rocks also causes displacement of the bearing plate towards the free face, which drives the bolt to deform and generate tensile force. In the process, surrounding rocks are the actively stressed member, and the bolt is passively stressed.  
Figure 1: Stress state on rock surrounding a cavern [29].  
Compared with pullout tests on bolts, the relationship between surrounding rocks and bolts in terms of deformation in compression tests on anchored rock mass better matches reality. That is, the deformation of surrounding rocks drives the deformation of bolts via the transfer effect of the grout and bearing plate. Generating tensile force in the bolt constrains the deformation of the surrounding rock, thus realizing the anchoring effect.  
Additionally, [PERSON] et al. [29] compared the two test methods through numerical simulation. Two types of surrounding rocks (intact and fractured rock mass) are involved in the computation. The stress distribution on the bolts in an intact rock mass obtained using the two test methods is basically consistent. In fractured rock mass, the stress distribution law of bolts in the pullout tests is similar to that of a homogeneous rock mass; nevertheless, fractures exert a significant influence on the stress distribution of the bolts in compression tests on anchored rock mass, resulting in two peaks on the stress distribution curves.  
Therefore, compared with pullout tests on bolts, compression tests on an anchored rock mass confer certain advantages when studying the mechanical properties of bolt supports, especially for heterogeneous rock mass. However, there remain certain shortcomings in the existing research into the mechanical properties of bolt supports based on compression tests on an anchored rock mass, so this aspect was further explored in the current research.