Volume 31, Issue 6 (November 2008)
Determination of Diffusion Characteristics of Intact Rock Mass: A Critical Evaluation
Intact rock mass is the most suitable geological formation for disposing of hazardous wastes. Hence, for safety assessment, establishment of contaminant transport mechanism(s) in/through the rock mass becomes essential. Conventional diffusion cells have been employed by earlier researchers for establishing diffusion characteristics of the intact rock mass. However, due to extremely low porosity of the intact rock mass, the time required for obtaining the “break-through curve” runs into a few months, during which maintaining the ambient conditions becomes extremely difficult. To overcome these limitations, researchers have resorted to accelerated diffusion tests, in the recent past. Several analytical models have been developed by the earlier researchers, which can be employed for determining diffusion characteristics of the intact rock mass. This calls for a comparative study of the diffusion characteristics obtained from these models so as to establish their suitability. With this in view, diffusion characteristics of the intact rock mass of different types were established by conducting accelerated diffusion tests and employing these models. In addition, diffusion characteristics of the intact rock mass were determined based on the concept of cumulative concentration accumulation of ionic species (CCAIS) in the measuring reservoir. It has been found that the models reported in the literature over-predict the diffusion coefficients for the intact rock mass. The superiority of CCAIS model, has been demonstrated by computing the hydraulic conductivity of the intact rock mass and comparing it with the centrifuge modeling results.