Thickness Calculation of Accumulative Damaged Zone by Rock Mass Blasting Based on Hoek–Brown Failure Criterion

Abstract

Tunnel excavation by cyclic blasting caused accumulative damages to the surrounding rocks, reducing the intactness of the rock mass. The blasting impact contributes to the formation of an excavation damaged zone (EDZ) around the tunnel, which may induce disasters such as surrounding rock failure and roof collapse, hazarding the construction safety. This study, in view of Lame’s equation and Hoek–Brown’s failure criterion, deduced the equation of the strength reduction coefficient and established a method to calculate cyclic blasting disturbance factor D based on the wave velocity decrease rate. After modifying Hoek–Brown criterion parameters mb and s based on the geological strength index, a method to calculate the thickness of the EDZ near the tunnel face was established, which quantified the EDZ range under the cyclic blasting disturbance. Subsequent theoretical calculations demonstrated a “three-stage” variation trend of the EDZ under cyclic blasting and revealed the EDZ thickness variation law with different excavation radii, initial stresses, rock strengths of surrounding rocks, disturbance factors, and lateral pressure coefficients.