The spatial distribution of excavation damaged zone around underground roadways during blasting excavation

Knowledge of the degree and depth of the excavation damaged zone (EDZ) resulting from drill-and-blast excavations has important influences on the design and construction of deep underground tunnels. However, the spatial distribution of EDZ around underground tunnels subjected to the combined effect of blast loading and in situ stress unloading is still under discussion. In this study, the dependences of the spatial distribution of EDZ in an underground tunnel on the variations of in situ stress conditions, excavation dimensions and rock strength were investigated using a combined method of field measuring and numerical modelling. Field measurements of EDZ in an underground mine were first conducted using the non-metallic acoustic technique. Subsequently, a blast excavation model concerning the combined effect of blast loading and in situ stress unloading was developed and calibrated against the field-measured data. Finally, the EDZs induced by various in situ stress conditions, tunnel shapes, and dimensions as well as rock strengths were simulated. The field measurement results indicate that larger highly damaged zones are generated at the roadway crown and sidewall, whereas smaller intensively damaged zones are induced at the roadway shoulder. The average depth of EDZ around the tested roadways, with an overburden of 355 m to 915 m, varies from 0.36 m to 1.72 m. The numerical results show that in situ stress, excavation dimension, and rock strengths significantly impact the depth of EDZ. More specifically, lateral pressure coefficient and the shape of the roadway cross section play a predominant role in controlling the distribution pattern of EDZ, and the magnitude of in situ stress, excavation dimension, and rock strength mainly contribute to the depth of EDZ. Furthermore, the special phenomenon of zonal disintegration in the surrounding rock mass occurs around highly pre-stressed underground roadways.