Quantitative evaluation of supporting effect of prestressed rock bolt in jointed surrounding rock tunnel

Abstract In engineering practice, surrounding rock is commonly dissected by joints and thus becomes discontinuous, which can readily trigger instability and failure. Prestressed rock bolts provide effective reinforcement for jointed surrounding rock; however, current design still relies largely on experience and engineering analogy. Therefore, a quantitative evaluation of bolting effectiveness is necessary to guide engineering practice. By combining theoretical analysis and numerical simulation, the prestress-induced stress compensation of rock bolts is quantified. The results show that: (1) for a single bolt, the peak vertical stress compensation is approximately 20 kPa in intact rock and decreases to about 16 kPa when a joint is present; (2) for a three-bolt system, stress superposition forms a reinforced compressive zone, and the peak vertical stress compensation increases to about 35 kPa in intact rock and 27 kPa in jointed rock; (3) on the joint surface, the normal and tangential stress compensations increase from about 13 kPa and 3 kPa (single-bolt case) to about 25 kPa and 7 kPa (three-bolt case), respectively; (4) at the tunnel scale with systematic bolting, prestressing increases the near-boundary radial stress by approximately 0.2–0.3 MPa and improves global stability; (5) although the absolute magnitude of direct stress compensation is modest compared with rock strength, direct shear simulations indicate a clear strengthening mechanism: under a 100 kN prestress level, the equivalent cohesion increases by about 13.5% and the internal friction angle increases by about 40.3%, leading to a marked improvement in the overall stability of jointed surrounding rock.