There are three major components of a fully grouted roof boltwhich primarily determine its ability to develop and sustain load: thesteel rebar, the resin annulus, and the rock/grout interface. The untensioned,fully grouted roof bolt is subjected to loading only when thesurrounding rock deforms. Vertical rock deformation is generally aresult of strata sagging and bedding plane separation, whereas horizontaldeformation is typically a result of bedding plane sliding. Thesetwo types of deformation create different types of internal loads withinthe roof bolt, tensile stress for vertical rock deformations and shearstress for horizontal rock deformations. Also, as a result of the mutualload transfer between the rock and bolt, shear stress will be developedalong the grout/rock interface. According to the exact bolt loadingconditions, different failure modes may occur: bolt axial failure,bolt shear failure, and shear failure along the grout/rock interface.Understanding these possible failure modes and their root causes isthe key to eliminating roof failures in underground mines employingfully grouted resin bolts.Using ABAQUS 5.8, a finite element model was developed tosimulate the components of the fully grouted bolt and its interactionwith the surrounding roof strata. Several models were conducted toinvestigate how load transfer occurs between the rock and the boltunder different geological and mining conditions. The effects of beddingplane location and properties, and strata sequence on bolt stabilitywere studied. Also, the effects of hole roughness on bolt stabilitywere discussed. Bolt axial failure was not observed within therange of the studied parameters; however, a combination of highoverburden depth, a bedding plane located at 2 to 3 ft from the roofline or a low coefficient of friction along the bedding plane causedstrata sliding and shears failure in the bolt. Also, in the case of aweak immediate roof, the shear stress at the grout/rock interfacecould exceed its ultimate capacity lead to slippage.
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