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, Australian Centre for Geomechanics, Perth, pp. 579-587.
In an attempt to provide the best support system for rock excavations, the designers of ground support are constantly seeking ways to create rockbolts that meet a variety of demands. Load capacity, corrosion resistance and ease of installation are arguably the most important criteria used in any design. In seismic conditions, appropriate ductility is also a key performance parameter. Often, when designing or adapting rockbolts to specific environments, the ease of installation is not given the consideration that mine operators in particular require. The plethora of two pass rockbolt systems gives evidence to this fact.
This paper describes two rockbolts that have been designed to achieve industry requirements for strength, corrosion protection and ductility. Importantly, these bolts are not only designed to be installed in one pass, but are designed to be installed into standard 45 mm diameter drill holes. The requirement to match the installation needs of mine operators has resulted in rockbolts that are user friendly, whilst still providing all the engineering requisites of geotechnical practitioners.
The first bolt, B1, is 38 mm in diameter, with a nominal ultimate tensile strength of 20 t. The use of resin glue (a high density polyethylene sheath) and surrounding grout, provides at least three levels of corrosion protection to the core tendon. Fixation to the rock mass via the resin glue provides a stiff external support whilst the inner tendon can be manufactured as stiff or ductile, thus providing appropriate support for low or high stress rock environments.
The second bolt (Stiff Split Set®, patent pending) capitalises on the significant increases in frictional strength provided by the internal grouting of normal frictional stabilisers. In such cases, frictional strength can typically increase by a factor of four. The design of the bolt enables a simple one pass grouting method that occurs during bolt installation as opposed to a secondary expensive and time consuming process, that takes place after the bolt has been installed. The one pass grouting process speeds up the tunnelling or mining process considerably.
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