Study on Rock Mass Classification Methods Used in the Geological Disposal of High-level Radioactive Waste

Abstract

The conventional methods of rock quality classification mainly focus on the constructability of rock mass, while the long-term safety requirements of the high-level radioactive waste (HLW) disposal are not considered. Therefore, two rock suitability classification methods for geological disposal projects, the Rock Suitability Criterion (RSC) and the QHLW methods were systematically compared by evaluating the rock suitability of the ONKALO site for geological disposal in Finland. The suitability of the ONKALO site was analyzed by evaluating the permeability, geochemical condition, and integrity of rock mass, according to the RSC method. Meanwhile, the QHLW method was used to evaluate the rock mass suitability by analyzing the fault zone influence, hydrogeochemical characteristics, temperature influence, permeability, strength-stress ratio, and integrity of rock mass. Then, the advantages and disadvantages of the two methods were discussed. We found that the results obtained with RSC are consistent with those with QHLW. While RSC gives more detailed chemical properties of groundwater and mechanical characteristics of rock mass, QHLW performs better in evaluating the permeability of rock mass. Besides, RSC is a qualitative or semi-qualitative method with some site-specific criteria, while the QHLW is a quantitative method with higher universality. Based on the above results and conclusions, a new version of QHLW at the tunnel scale was finally proposed by incorporating the advantages of RSC.