Laboratory pull-out tests of cable bolts are conducted using specimens of two types of cables made of plain and bulbed strands installed in steel pipes filled with cement grout. In order to investigate the mechanical behaviors of cable bolts and the mechanism of grout bond failure, the pressure of radial confinement and locations of acoustic emission events were measured during the pull-out tests. After the tests, the failure planes generated inside the steel pipe specimen were visualized by means of X-ray CT technology in two-dimensional slices and in three-dimensional images. Based on the results, the supporting effects of cable bolts were discussed.
Cable bolting has been used for the reinforcement for underground structures due to its Workability and economical efficiency. Recently, it was used for the pre-reinforcement of the crown part of a large cross section tunnel installed from a TBM-driven pilot drift in a tunnel for the Second Tomei Highway in Japan and establishment of the rational support system including rock and cable bolts was pursued (Tanaka et al. 2000). The support mechanism of cable bolting has been investigated. Yazici & Kaiser Conducted the pull-out tests of cable bolts and found the generation of the radial cracks in grout and of shear failures along the boundary between grout and cable strands. The constitutive equations for the cable bolt have also been proposed in the literature (Kaiser et al. 1992; Hyett et at 1992 & 1995). The authors have visualized, by means of an X-ray CT scanner, the failure plane generated around rock and cable bolts inside the specimen made of cement grout and concrete, and have discussed the grout bon failure mechanism (Ito et al. 2001; Obara et al. 02), It would be still said on the current situation that modes of the bond failure 111 the grout around a cable bolt are only conceptually known and have not been qualitatively and quantitatively well investigated. In this study, pull-out tests of cable bolts are conducted using specimens of two types of Cables made of plain and bulbed strands installed in steel pipes filled with cement grout. The mechanical behaviors of cable bolts during the pull-out tests are investigated. Specifically, the pull load, cable bolt displacement, acoustic emission events and strains on the steel pipe specimen are measured during the pull-out tests. Moreover, applying an X-ray CT to the tested specimens, the failure planes generated inside the steel pipe are visualized in two-dimension and in three-dimension, Based on these visualized images, the grout bond failures occurring around the cable bolts were discussed.
A cable bolt of 15.2mm in diameter is made of seven-wire strand (each approximately 5mm in diameter). As shown in Figure 1, two types of cable bolts are used: a plain strand that has a consistent cross-section shape and a bulbed strand that has partially inflated bulbs.
The overview and the schematic diagrams of the specimens for the pull-out tests are shown in Figures 2 and 3.