Predicting the excavation damaged zone within brittle surrounding rock masses of deep underground caverns using a comprehensive approach integrating in situ measurements and numerical analysis

Excavation Damaged Zone (EDZ) scope is important for optimizing excavation and support schemes in deep underground caverns. However, accurately predicting the full EDZ scope within the surrounding rock masses of deep underground caverns during excavation remains a pressing problem. This study presents a comprehensive EDZ scope prediction approach (CESPA) for the brittle surrounding rock masses of deep underground caverns by coupling numerical simulation with quantitative analysis of borehole wall images and ultrasonic test results. First, the changes in both P-velocity () and joint distribution of the surrounding rock masses before and after excavation damage are captured using ultrasonic tests and borehole digital cameras. Second, the quality Q-parameters of the surrounding rock mass before and after excavation damage are preliminarily rated with the rock mass descriptions provided by borehole wall images, and the rock mass -parameter values are determined according to the –borehole depth curves. Third, the Q-parameter ratings are further finely adjusted by updating the related Q-values to be similar with the Q-values estimated by -parameter values. Fourth, the initial and residual mechanical parameters for the rock mass deterioration model () are estimated by the adjusted Q-parameter ratings based on the modified Q-based relations, and the elastic modulus deterioration index () threshold to describe the EDZ boundary is determined with the -parameter values. Finally, EDZ scope is predicted using the elastoplastic numerical simulation with and based on the mechanical parameter estimates and threshold. Analyses of applications in Sub-lab D1 in Jinping II project show that CESPA can provide a reliable and operable solution for predicting full EDZ scopes within the brittle surrounding rock masses of deep underground caverns.