Shear strength properties of Hilti Plain and Indented Strand cable bolts

An investigation into the performance of two 22 mm diameter, 60 tonne tensile strength capacity Hilti cable bolts in shear was conducted using the double shear testing apparatus at the laboratory of the School of Civil, Mining and Environmental Engineering Faculty of Engineering and information sciences, University of Wollongong. The tested cable bolts were (a) Hilti19 wire HTT-UXG plain strand and (b) Hilti 19 wire HTT-IXG spirally indented strand cable bolt, with indentation only on the surface of the outer strands. Both cable bolts were of sealed wire construction type, consisting of an outer 5.5 mm diameter strand layer overlying the middle 3 mm diameter wire strands. Both layers are wrapped around a single solid 7 mm diameter strand wire core. The double shearing test was carried out in 40 MPa concrete blocks, contained in concrete moulds. The cable bolts were encapsulated in concrete using Minova/ Orica FB400 pumpable grout. Prior to encapsulation, each cable bolt were pretensioned initially to 50 kN axial force. A 500 t capacity servo controlled compression testing machine was used for both tests, and during each test the vertical shear displacement was limited to 70 mm on travel. The rate of vertical shear displacement was maintained constant at 1 mm/min. The maximum shearing load achieved for the plain strand cable was 1024 KN, while the indented cable peak load was 904 kN, before the cable bolt strands began to individually snap, which lead to the cable bolt break up into two pieces. It was found that indentation of the cable bolt’s outer strand weakened both the tensile and shearing strength.