ACARPC21011 - DEVELOPMENT OF NEW TESTING PROCEDURE FOR THE ASSESSMENT OF RESIN PERFORMANCE FOR IMPROVED ENCAPSULATED ROOF BOLT INSTALLATION IN COAL MINES

ACARPC21011 - DEVELOPMENT OF NEW TESTING PROCEDURE FOR THE ASSESSMENT OF RESIN PERFORMANCE FOR IMPROVED ENCAPSULATED ROOF BOLT INSTALLATION IN COAL MINES

In underground coal mining, the resin bond between the rock bolt and the strata is one of the critical elements of a roof
bolting system, yet the Australian coal industry does not have an agreed standard for bolting system evaluation. A program
of field and laboratory study was undertaken to examine various factors influencing the load transfer mechanism between
the bolt, resin and rock. As per ACARP project requirement, the entire study used M24, 21.7 mm diameter X-grade Jennmar
JBX bolts (APPENDIX B) and the standard Orica fast setting resin (APPENDIX Figure C). A series of Short Encapsulation
Pull Tests (SEPTs) were carried out in three mines with different geological conditions. These mines were Baal Bone,
Tahmoor and Gujarat NRE No.1. Additional studies included the evaluation of the anchorage performance along sections
of bolts installed in steel tubes and variations in the strength properties of resin depending on sample dimensions.
Furthermore, laboratory SEPTs were carried out on bolts installed in an overhead sandstone block mounted on a drill rig
under environmentally controlled conditions. Factors of importance considered to affect bolt installation in strata include;
borehole diameter, resin annulus thickness, installation time (including bolt spin to back and spin at back), the effect of
gloving and its impact on installation quality and load transfer variation along the length of the installed bolt. 24 bolts were
installed at each of Baal Bone and Tahmoor mines, and 16 bolts installed at Gujarat NRE No.1 mine. Installation of bolts in
steel tubes was carried out at Springvale Colliery and subsequently tested in the Wollongong University Laboratory. The
summary of the field studies found that:
 bolts installed in holes over-drilled by 50 mm resulted in relatively higher load transfer capacity for the given installation
time,
 bolts installed in 27 mm diameter holes performed relatively better than those installed in 28 mm holes,
 in some cases over-spinning was detrimental to the load transfer capacity of the installed bolt,
 the influence of gloving was reduced with over-drilling,
 strength properties of resin tested at different length to diameter ratios did not vary considerably. In general, the length
to diameter ratio of one was found to be a convenient dimension, and
 consistency of the strength values obtained from testing resin samples was dependent on the methodology of resin
mixing and casting.
Various laboratory procedures for testing resins and grouts properties were evaluated as suggested by British and South
African standards. Special emphasis was directed to the determination of the following resin /grout properties;
 Uniaxial Compressive Strength
 Young modules of elasticity
 Shear strength
 Creep tests.
The results from this evaluation revealed that some aspects of the British standards have shortcomings in sample
preparation, testing and presentation of the results. Therefore, a new sampling and testing procedure have been developed
as part of this study. Laboratory tests indicated that the proposed testing method is reliable, repeatable, easy to conduct and
produces meaningful results when compared to underground tests. The new testing procedure is considered to be
acceptable for testing resins used in Australia.
Because of the changes in emphasis on the project direction, this report is in two parts:
 Underground and the laboratory SEPT study findings, and
 Development of new testing procedures for the assessment of resin performance and a suggested method for SEPT.