2.1 Specimen preparation
The specimens are made of the common C15 cement mixed with sand and quicklime, with a composition of C15 cement:sand:quicklime = 1:3:1.5. The coagulant is slaked lime, which is used in the same amount as cement. For the systematic rock bolt, the #45 steel is selected and processed into a threaded steel rod with a strength class of 8.8 (Figure 1(c)). The threaded rod shows a yield strength of 640 MPa, a tensile strength of 800 MPa, and a diameter of 5 mm. For the advancing conduit, it is made of the 45# carbon steel pipe (Figure 1(d)). The outer diameter of the steel pipe is 6 mm, and the wall thickness is 1 mm. The specimens of 100 mm × 100 mm × 100 mm were prepared through the cast-iron mold. During pouring, a steel tube with an outer diameter of 22 mm was placed in the middle of the test mold to reserve a round hole with a diameter of 20 mm. The specimen was poured in four times, with a thickness of 20 mm, 30 mm, 30 mm, and 20 mm, respectively. After the first three pourings, five bolts with a length of 25 mm and a diameter of 5 mm were evenly prepared along the round hole, as shown in Figure 1(a). The bedding structure is simulated by uniformly laid 100-mesh mica sheets with a thickness of 0.2 mm, and the bedding spacing is 20 mm. The prepared specimens were cured at room temperature for 28 days, and then they were used for laboratory uniaxial compression tests. For the size and the loading mode of specimens, refer to Figure 1(b).