Document Type

Conference Paper

Publication Date


Publication Details

Ross Seedsman, Further Considerations on the Application of De-Bonded Cables, in Naj Aziz and Bob Kininmonth (eds.), Proceedings of the 16th Coal Operators' Conference, Mining Engineering, University of Wollongong, 10-12 February 2016, 9-15.


De-bonding of the central portion of long tendons has been suggested if they are installed in low strength rock prior to a significant stress change, be that either at the maingate corner or in installation roadways. The purpose of the de-bonded section is to allow a reduction of the strains applied to the cables during failure of the rock mass and so increase the chance of them surviving large shear movements. A recent application of de-bonded cables in a longwall installation roadway resulted in a major reduction in roof deformations from in excess of 100 mm to less than 3 mm. Assuming similar rock strengths and ground stresses, the de-bonded cables apparently prevented the onset of vertical dilation in the roof. Compared to an installed shear resistance of 183 kPa, shear stresses of up to 1.5 MPa are predicted in the roof immediately above the bolted horizon. A mechanism is proposed that involves the onset of brittle failure followed immediately by a large amount of sub-horizontal shear displacement. Because of the free length of the de-bonded cables the induced strains were insufficient to cause the cable to rupture. The de-bonded cable was post-tensioned and this led to the closure of some of the dilated bedding induced on the first pass.