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Water and Gas Movement in Mx80 Bentonite Buffer Clay

Published online by Cambridge University Press:  01 February 2011

Stephen T. Horseman ,
Jon F. Harrington  and
P. Sellin
Stephen T. Horseman
Affiliation:
British Geological Survey, Keyworth, NG12 5GG, UK (stho@bgs.ac.uk/+44 115 9363261)
Jon F. Harrington
Affiliation:
British Geological Survey, Keyworth, NG12 5GG, UK (stho@bgs.ac.uk/+44 115 9363261)
P. Sellin
Affiliation:
Svensk Kärbränslehantering AB (SKB), Stockholm, Sweden (patrik.sellin@skb.se/+46 8 6624974).
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Abstract

This paper describes a long-term laboratory test designed to examine the sensitivity of gas flow in Mx80 buffer bentonite subject to a constant volume boundary condition. A constant volume and radial flow (CVRF) apparatus was designed to enable gas flow from a centrally located injection filter to be independently monitored at three sink-filter arrays mounted around the circumference of the clay specimen. Axial and radial total stresses and internal porewater pressure were continuously monitored. Gas entry, breakthrough and peak gas pressures were found to be systematically higher under constant volume boundary conditions than under previously reported constant stress and radially-constrained test conditions [6, 9, 10]. The observation that gas pressures are sensitive to test boundary conditions supports the hypothesis that gas entry is accompanied by dilation of the bentonite fabric. Gas penetration of the clay caused a substantial increase in total stress and internal porewater pressure. Abrupt drops in gas pressure, accompanied by similar drops in total stress, were interpreted as fracture propagation events. The outflow of gas was always non-uniformly distributed between the sinks. Furthermore, the distribution of flow between sinks often changed abruptly during the course of an experiment indicating that gas pathways were very unstable. When gas injection stopped, the gas pressure and rate of outflow spontaneously declined with time. Under constant volume conditions, the gas pressure at the asymptote exceeded the internal porewater pressure by an amount equal to the capillary pressure. In constant volume tests on clay with high water saturation, capillary pressure has a value close to the measured swelling pressure of the clay.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 807: Symposium Scientific Basis for Nuclear Waste Management XXVII , 2003 , 715
Copyright
Copyright © Materials Research Society 2004

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References

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