2.2 Experimental plan
Seven types of support conditions, namely, rough tunnel, systematic rock
bolt support, systematic rock bolt, and shotcrete support, systematic
rock bolt and shotcrete and steel arch support, steel pipe support,
steel pipe, and shotcrete support, and steel pipe and shotcrete and
steel arch support, are considered. The shotcrete is simulated by using
the epoxy resin with a thickness of 2 mm. The steel arch is composed of
304 stainless-steel pipes with an inner diameter of 20 mm. During the
installation process, the steel pipe was put into the reserved cavity,
and then the epoxy resin was injected into the pores between the outer
wall of the steel pipe and the surrounding rock by using a syringe. Each
support mode has been tested by the rocks with beddings angles of 0° and
90°, and the mechanical properties of the rock with holes and the
failure of the surrounding rock under different support methods have
been studied. In order to reduce the dispersion effects, three specimens
were prepared for each case, and the ids and the support methods of the
specimens are shown in Table 1.
The MTS815 rock mechanics testing system was used for the uniaxial
compression tests of the anchored specimens with holes. The displacement
control method was used as the loading type of the specimens, and the
loading speed was controlled at 0.1 mm/min. During the test, a
high-definition camera was used for recording the development and
penetration of the surface cracks of the specimens, and the development
process of the internal cracks in the holes was recorded by using the
industrial endoscope apparatus.
Before and after the test, a German Siemens SOMATOM Scope X-ray Spiral
CT Scanner was used to perform the non-destructive scanning of the
specimens in order to detect the development and distribution of the
internal cracks of the specimens. The spatial resolution of the CT
scanner was 0.35 mm × 0.35 mm, the contrast resolution was 3 Hu, and the
layer thickness was 0.75 mm.