Precise grading of surrounding rock based on numerical calculation of jointed rock mass

Abstract

In this study, grading of surrounding rock was based on rock mass basic quality (BQ) according to Chinese specifications. A numerical approach was used to construct a synthetic rock mass model (SRMM) to represent the jointed rock mass and then obtain the strength of the rock mass. To construct a discrete fracture network, intact rock was represented by the bonded particle model and joint behaviour was represented by a smooth joint model. In a case study (Hongtuzhang tunnel), the micro properties of granite cores with different degrees of weathering were determined and the representative elementary volume of the surrounding rock was set as 15 × 15 m. Five slightly weathered, three slightly to moderately weathered and two moderately weathered granite surrounding rock mass models were established based on the probability distribution of joint sets in each borehole, and the conversion BQ value was acquired according to the calculated strength of the SRMM. The surrounding rock grades obtained using geological surveys were found to be higher than those predicted by the numerical method. The numerical calculation was consistent with actual excavation of rock mass at a borehole.