Development, trials and testing of an innovative method to improve strength characteristics of hollow cable bolts

The 70 t Sumo is a resin point-anchored, pre-tensioned, post-grouted hollow cable bolt for tunnel roof support, particularly in poor ground conditions. An innovative ancillary product to the 70 t Sumo is the Booster cable, which is designed to reinforce the Sumo and enhance the systems shear and tensile performance. The Booster cable is an 11 mm 7-wire PC strand with a nominal breaking load of 15 tonnes, which is inserted into the hollow centre tube of the 70 t Sumo after grouting, while the grout is still pliable. Theoretically, the Booster can increase the tensile and shear capacity of the 70 t Sumo by up to 20%. The Booster reinforced 70 t Sumo is useful in high demand conditions where additional support strength is required without the need to install new support. This paper will present results from laboratory tests undertaken to quantify the tensile and shear characteristics of the 70 t Sumo reinforced with the Booster cable. A case study of a support trial using Booster reinforced 70 t Sumo cable bolts at a Dendrobium is also presented in this paper. The Booster cable successfully reduced 70 t Sumo cable bolt densities by 25%, from four cables per meter to three.