Experimental study on the inhibitory effect of bolting position on crack propagation in cavity-containing sandstone

This study systematically investigated the effects of seven bolt anchorage positions on the mechanical behavior and failure of single-hole sandstone specimens using uniaxial compression tests and PFC2D simulations, with emphasis on crack-propagation suppression. The results showed that: (1) Anchorage position strongly influenced the stress-strain response, mechanical parameters, crack initiation, and final failure morphology. When the bolt passed through the cavity center (1#) or was tangent to the cavity crown (2#), both strength and stiffness decreased, the pre-peak response showed multiple stress drops, and post-peak failure remained brittle. By contrast, anchoring 12-18 mm from the cavity center (3#-4#) increased strength and E, and the post-peak response shifted from brittle to more ductile (plastic-like) behavior. Position 3# yielded the best overall performance, with peak strength, E, secant modulus, and crack initiation stress increasing by 42.72%, 44.61%, 71.93%, and 44.39%, respectively. (2) Failure patterns depended on bolt location: near-cavity anchoring promoted stress concentration and a V-shaped crown collapse; intermediate anchoring (3#-5#) produced a distinct partitioned failure between upper and lower regions; more distant anchoring (6#-7#) increased damage severity and led to more complex fracture morphologies. (3) Simulations indicated that position 3# achieved the highest energy storage capacity (Kmax = 0.91) and the greatest resistance to instability, whereas position 2# showed the lowest capacity (Kmin= 0.29) and the highest failure susceptibility. Positions 4#-5# formed a favorable range in which higher bolt axial forces generated a localized displacement field that inhibited crack growth and confined the damage zone. These findings show that selecting an appropriate anchorage position can markedly improve stiffness, load capacity, and crack resistance of cavity-containing sandstone, providing quantitative guidance for bolt layout in engineering practice.