In order to investigate the effect of anchor spacing on the interaction between full-length bonded anchor rods

an approximate solution of stress distribution in the anchorage section of double anchor rods based on the Mindlin solution was derived. By combining with the single and double anchor static load pullout model tests

the effect of changing anchor spacing on the stress distribution

ultimate bearing capacity and final damage pattern of double anchor rods were obtained. The results show that the decrease in spacing makes the axial stress and lateral friction resistance of the anchor rods uniform. The axial stress increases with the decrease in spacing

and the middle of the anchorage section has the largest increase. When the anchor system enters the damage phase

the depth of the rock damage around the anchor system increases with decreasing spacing

and the area of the damage cone increases and changes from inverted cone damage of a single anchor to compound damage mode. When the spacing is too small

the increase in the number of anchor rods is very limited for improving the bearing capacity. In order to exert the joint effect of anchoring

the spacing of anchor rods should be not less than 10 D (D is the diameter of the anchor rod)

and the spacing should be larger in soft rock.