The TUBEX grouted friction tube system for rock support
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A new friction tube device, TUBEX (TUBe for EXcavation), proposed by Prof. B. Stimpson for use in mining and civil engineering as a support/reinforcing element for rock excavations has been tested in laboratory conditions. The device utilizes the interference fit with the borehole wall of well-known friction tubes as the Split Set and the Cotter Pin Rock Stabilizer. Its uniqueness is, however, in the components added to the system and the functions they perform. Compared to the standard friction tubes, TUBEX has higher strength, provides longer term support, and has a rock grouting capability. A short 37.4 cm long TUBEX prototype was tested in axial loading using pull-out tests and push-in tests with grouts of varying strengths and stiffnesses. The strength of TUBEX grouted with w/c = 0.25 ratio grout was found to be comparable to the strength of Atlas Copco's expandable Swellex. A full length (1-2 m) device is, however, expected to provide anchorage of 14-18 tonnes, a value which greatly exceeds the capacities of all currently available friction rock stabilizers. This increased strength is achieved by means of metal studs on the external surface of the tube. These studs can indent the rock during and after insertion of the device into the borehole depending on the hardness of the rock. Numerical modelling, using linear elastic finite elemen analysis, was carried out to investigate the influence of indentation and interface strengths (rock/grout, metal/grout) on failure. Laboratory testing in direct shear is needed to determine the high shear capacities that are anticipated, and a full-scale prototype should be manufactured for field trials.