Fractal model for erosion mass of bentonite colloids

Compacted bentonite has been considered as a candidate buffer material in underground repository for the disposal of high-level radioactive waste. Bentonite erosion caused by groundwater flow may take place at the interface of compacted bentonite and fractured granite. Bentonite colloids formed at the outer part of a bentonite buffer could expand and release into rock fractures during erosion by seeping groundwater. A novel idea is proposed to estimate bentonite erosion mass in consideration of fractal structure of bentonite colloids in this paper. The erosion model for accumulated bentonite erosion mass under various geochemical conditions is presented on the basis of fractal model for bentonite colloids. The erosion model presents the relation between accumulated volume of water flow and accumulated erosion mass of bentonite colloids in terms of a power law. The exponent parameter is related to fractal dimension (D) of bentonite colloids, and expressed as D/(6 − D). A number of data from different tests are used to verify the erosion model for bentonite erosion mass, and the results from all tests were well matched the prediction of the proposed erosion model.