# The Influence of Radial Stress on Mechanical Properties of Anchorage Structure
## 1 Introduction  
Since the 1960s, anchorage structure, as a temporary and permanent reinforcement component, has been widely used in civil engineering and mining engineering [1; 2; 3; 4; 5; 6]. The main components of an anchorage system are the tendon, an anchorage head assembly, and the grouting body. The tendon is generally made of steel, while the grouting body is usually made of resin or cement mixture [7]. The tensile anchorage structure mainly provides the anchorage force needed in the engineering support through the shear stress between the bolt and grouting body, as well as between the grouting body and surrounding rock mass. The schematic diagram of the anchorage system is shown in Figure 1. Therefore, most of the observed anchoring failures in practice occur at one of the two interfaces: Bolt-grout and rock-grout interfaces [8; 9; 10]. In the design of the tensile anchorage structure, the determination of the anchorage length is one of the most critical problems in anchorage design. However, the determination of anchorage length is mainly controlled by the shear stress of these two interfaces. How to determine the anchorage length of the anchorage structure is a challenge for designers. The key to solve this problem is how to obtain the distribution of interfacial shear stress. Since the anchorage structure has been used in engineering, many scholars have carried out relevant research works in this field. There is no doubt that the material properties and surface shape of a bolt, the mechanical properties ofthe grouting body and rock, and the size and roughness of a borehole have a great influence on the shear stress distribution at the interfaces of anchorage structure [10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22]. However, it is undeniable that the radial stress of the interface has a significant effect on the interfacial shear stress because at the bolt-grout and grout-rock interfaces, the initiation and growth of debonding involves frictional sliding. [PERSON] et al. [23] also believed that the bond strength of fully grouted cable bolts was primarily frictional, which depended on the pressure at the cable-grout interface. Similarly, many scholars have reached the same conclusion [14; 14; 24]. In specific engineering practice, the current design codes have a minimum requirement for the buried depth of the anchorage section of an anchorage structure. For example, according to the \"Technical Code for Building Slope Engineering\" [11], the thickness of the overburden soil layer of anchorage section should not be less than 4 m, and the thickness of the overburden rock should not be less than 2 m and the \"Technical Specification for Retaining and Protection of Building Foundation Excavations\" [25] also stipulates that the thickness of the overburden soil layer of anchorage section should not be less than 4 m, while in the \"Technical Specification for Ground Anchors\" [26], the value should not be less than 4.5 m. The purpose of the above codes to limit the minimum thickness of overburden layer is to ensure that there is enough confining pressure around the anchorage section, which is the premise that the interface of anchorage structure can provide the anchorage force. In the specific design of the anchorage structure, it is difficult to quantitatively consider the beneficial effect of confining pressure caused by the thickness of the overburden layer, which may lead to a relatively conservative design. In conclusion, the radial stress acting on the interface of anchorage section has a significant effect on the interfacial shear stress. Surprisingly, there are relatively few studies on this aspect. In this study, according to the phenomenon of the splitting failure of samples found in the laboratory test, the influence of radial stress on the mechanical properties of the anchorage structure is studied by theoretical analysis and numerical simulation.