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.