Analysis method of radon release during underground cavern excavation

Radon release during underground engineering excavation is mainly from the newly generated fracture surfaces of the rock mass rupture, and the accurate prediction of radon release depends on the quantitative characterization of the rock mass rupture. To examine the correlation between radon release and rock mass rupture, a series of triaxial compression radon release tests were carried out and the effective radon exhalation rate (J_eff) was defined, a linear function of rock fracture area and radon release was developed. Based on the continuous-discontinuous element method (CDEM), a quantitative equation between rock fracture degree (D) and radon release by numerical model for triaxial compression tests was obtained. Subsequently, a synthetic rock mass (SRM) method combining discrete fracture network (DFN) model and CDEM was used to analyze the scale dependence of radon release from rock mass rupture, and the representative element volume (REV) size of the radon release from rock mass rupture was determined. Radon release increases exponentially with increasing sample size. Radon release increases and then decreases with the increase of joint dip angle, however, radon release increases with the increase of joint trace length amplification factor. Additionally, an underground powerhouse excavation model to derive the evolution of radon release from the surrounding rock with the number of excavation layers was established. The results of this research can provide a basis for radon pollution control during underground engineering excavation.