Variation in anchorage performance of a high capacity modified bulb cable bolt under differing conditions in a weak confining medium

Cable bolts are increasingly being used for ground reinforcement due to their high load carrying capacity, tendon length and flexibility that affords easy installation. There are a variety of cable bolt designs on the market and while many have been tested, few studies have examined anchorage performance in a weak confining medium that approximates behaviour in coal. This paper presents the results of testing a high capacity cable bolt, the MW9 indented cable bolt, in weak material of differing borehole diameters and grout strengths. Both the standard recommended borehole diameter of 42 mm and an oversize borehole of 52 mm were examined in combination with the standard high strength grout strength of 80 MPa and a lower strength of 62 MPa. In weak grout, borehole diameter had minimal effect on the peak load carrying capacity with only a 6% reduction in capacity from an increase in borehole diameter from 42 mm to 52 mm. However, with the strong grout, there was a 7% increase in peak load carrying capacity with borehole diameter. In the standard borehole diameter, increasing grout strength reduced the peak load carrying capacity by 4% whereas there was a 10% in the oversized borehole. In the vast majority of tests, failure occurred at the bolt/grout interface.