Study of cement-grout penetration into fractures under static and oscillatory conditions

摘要

Grouting of the rock surrounding high-level waste (HLW) can serve to minimize groundwater flow around it and thereby to retard erosion of waste-embedding clay (buffer) and transport of possibly released radionuclides. Earlier attempts have shown the efficiency of superimposing the injection pressure with oscillations for bringing cement-rich grouts into narrow fractures using organic superplast-icizers. However, these are short-lived and can produce radionuclide-bearing organic colloids, and should be replaced by inorganic agents. Portland cement in grouts is not long lived and low-pH cements are preferable as is also reduction of the cement content to an absolute minimum. The present study describes the composition and performance of candidate grouts in laboratory experiments with injection into plane-parallel slots with different aperture. The study included development of a simple and quick method for estimating the viscosity on the construction site for adapting the grout recipe to the injectability of the rock. A simple theoretical model for predicting grout penetration gives fair agreement with laboratory data. The longevity of the grout under various conditions is believed to be sufficient for use in HLW repositories implying waste placement in very deep holes.