Influence of coupling and properties of encapsulating mortars on the anchoring capacity of rock bolts

Rock bolts are the most widely used support elements in rock excavations. Some bolts anchor themselves and others require encapsulants to attach to the wall of the holes. The coupling of the rock bolts in the walls of the drill holes and the properties of the mortars with which the rigid bars are installed are aspects that have been little studied; basically, due to the difficulty of obtaining specimens of bolts installed in rock. The specimens where the couplings and properties of the encapsulants were analyzed were obtained by installing the bolts in ST, a method that facilitated the preparation of specimens of different shapes, sizes and quantities necessary to obtain reliable results and then relate them to their AC. It is shown that no bolt couples 100 % to the wall of the holes. In the case of inflatable bolts (Hy and Sw) and constriction bolts (SS), strips of openings are generated, reducing their coupling to 55.82 % (STD = 38 mm); 51.96 % (STD = 41 mm) and 45.31 % (STD = 37 mm), respectively, for any BL and reaching the corresponding AC of 15.23 t; 15.23 t and 7.44 t. In the RB, the porosity and plastic wrappers of the encapsulants reduce their coupling and adhesion, the effects of which could not be quantified due to the impossibility of longitudinally sectioning entire RB installed with different encapsulants. The RBRC has better adhesion, reaching an AC of 17.37 t (STD = 36 mm and BL = 0.90 m). The encapsulants with the highest and lowest porosity are CG and RC, respectively, with their AC of 11.25 t and 17.37 t. The RBCC and RBCG have the lowest and highest roughness, respectively, and their AC 13.89 t and 11.25 t (STD = 36 mm and BL = 0.90 m). The hardness of the encapsulants is in the following order CG > RC > CC, but their AC in RC > CC > CG. The order of the densities is CC > RC > CG and the AC, RC > CC > CG. RC at 400 °C, becomes ash, losing its physical and chemical properties. In all cases the RB is offset with respect to the ST axis. The order of water absorption is RC