6 DISCUSSION
In this paper, the laboratory experimental method is used to obtain the mechanical properties and the deformation characteristics of the rock with holes and anchors, and to obtain the supporting mechanism of the support structures on the holes and the surrounding rock. However, there are several crucial factors that require further explanation and discussion.
The specimens are made of similar materials with good homogeneity, and the dispersion of the test data is small. There are still several factors that require adequate attention during the tests. The first factor is the distribution of the bolts. During the arrangement process, the bolts should be distributed as evenly as possible. However, in the process of arranging the specimens layer by layer, the bolts can easily deviate, the ideal state is that when the five bolts, shown in Figure 6(4), are all on the same level. The second factor is that the epoxy resin with high plastic deformation ability should be used in the tests in order to simulate the shotcrete layer. Therefore, during the tests, no concrete cracking and peeling, and flaking off of the concrete layer on similar engineering sites were observed. After the tests, the specimens were broken, and the simulated concrete components (Figure 10(d)) were taken out carefully, and the plastic deformation of the concrete layer was observed. Although this experimental result is different from that of the actual engineering projects, it is obviously beneficial for maintaining the integrity of the tunnel. The last and important factor is that the loading fracture process of the specimens was not observed by the real-time CT scanning observation. How to prepare smaller-scale specimens with holes and anchors for the real-time observation and study more microscopic dimensions in order to observe and analyze the law of crack evolution is an important question that should be discussed in the next step.
In this paper, the analytical formulas related to the stress and displacement of the surrounding rock in the anchored area and the non-anchored area under the action of supporting components are discussed. Based on the test results, it is concluded that the bolts primarily realize the anchoring effect by changing the stress state of the surrounding rock in the anchoring area and by improving the mechanical parameters of the surrounding rock. The anchoring area demonstrates the functions of weakening, arresting, and changing the propagation path of cracks, which thus improves the bearing capacity of the surrounding rock. It is important to note that the theoretical analytical formula is obtained under ideal and simplified conditions, which can qualitatively well explain the action mechanism of support structures on the stress state of the surrounding rock, but the calculation and test results can show a certain deviation if the theoretical analytical formula is used to quantitatively calculate the stress displacement. For example, the calculation in the process of the installation of bolts is based on the assumption that the bolts are evenly arranged on the same plane. The installation quality of bolts in the actual engineering projects (including the laboratory tests in this article) is significantly affected by human factors. It is often difficult to maintain the installation angle of the bolts and the grouting quality, which thus affects the anchoring effect of the bolts.