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Conference Paper

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This conference paper was originally published as Aziz, N, An Update of Roof Bolt Research at the University of Wollongong, in Aziz, N (ed), Coal 2004: Coal Operators' Conference, University of Wollongong & the Australasian Institute of Mining and Metallurgy, 2004, 215-224.


The influence of surface profile on load transfer mechanisms of bolts has been studied under both the constant normal stiffness (CNS) and constant normal load (CNL) conditions. Testing under CNS condition was conducted in a specially constructed constant normal stiffness shearing apparatus, whereby the flattened surface of a bolt section was pulled against the image of cast resin sample under constant stiffness conditions. Testing under CNL conditions included the conventional pull testing of an encapsulated section of bolt anchored in a borehole, and the short encapsulation push test. The conventional pull testing involved pull testing of three different profiled bolts in three different diameter holes. The pull tests were carried out both insitu and in the laboratory. Parameters examined, in addition to bolt surface profile, were the resin annulus thickness and the effectiveness of resin mixing in the hole. The credibility of push testing, in short steel cylinder sleeves, was examined by pulling the bolt out of the cylindrical sleeve instead of pushing. Also tested in short sleeve, was the possibility of changing the load transfer capability of a bolt by changing its surface profile. A numerical simulation study has recently been incorporated to enhance the current programme of research carried out at the School of Civil, Mining and Environmental Engineering, The University of Wollongong. The numerical study included the modeling of both the short encapsulation push/ pull test as well as shear stress simulation across joints. The conclusions drawn were that the bolt surface profile is an important parameter affecting the load transfer capacity of the bolt/rock interface, that the anchorage strength of resin encapsulation is influenced by the effectiveness of resin mixing, and the annulus thickness, and the short encapsulation push test underestimates the peak shear load and peak load displacement.

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