Document Type

Conference Paper

Publication Date


Publication Details

P. Craig and B. Murnane, In-situ pull testing of cable bolts encapsulated with injection polyurethane, 13th Coal Operators' Conference, University of Wollongong, The Australasian Institute of Mining and Metallurgy & Mine Managers Association of Australia, 2013, 131-136.


Polyurethane (PUR) injection into underground coal mine strata has been practiced in Australia as early as 1985. The ACARP report C100019 discussed several case studies of which one included PUR injection into resin anchored, pre-tensioned hollow central tube cable bolts. In cases of rapid response to accelerating strata movement it is the preference of site geotechnical personnel to install immediate pre-tensioned cable support, followed by re-consolidation of the strata through injection of grout or PUR. Cementitious grouting of cable bolts has two operational time restrictions; 1) 24-48 h restrictions can be placed on roadway widening or longwall chock removal while waiting for the grout to achieve adequate strength and 2) a 24 h restriction being placed on PUR injection after grouting has taken place to avoid unwanted chemical reactions and heat generation. In the last few years, more mines, faced with time critical ground support, have been utilising hollow cable bolts as the support and the means of injecting PUR into the strata. The main reason is time, 24 h lost to cementitious grout curing could be used in stabilising the strata by PUR injection into distant fractures, and operationally 24 h gained on a longwall move represents a large financial advantage. It has been considered that foregoing cementitious grouting of cables and replacing it with PUR will reduce the load transfer of the cable bolt, but no readily available data exists on how much reduction in bond strength occurs. Underground short encapsulation cable pull tests were conducted at Springvale Colliery comparing cementitious grout against PUR at both 24 h and nine days cure time.