Abstract:
The properties of the residual clays derived from in situ weathering of the Waitemata group sandstones and siltstones found around Auckland are known to surprisingly variable. In addition it is known that the permeability of the material decreases rapidly as the effective consolidation pressure is increased. A possible contribution to both the variability and the rapid decrease in permeability might be the void structure of the soil. The advent of micro CT scanning equipment provides an opportunity to examine the void size distribution in the material. Discussed in this note are some preliminary results on small specimens of the soil. These indicate that at low effective confining pressures there are some quite large macro-voids. These are found to be greatly diminished in size when the effective confining pressure reaches about 200 kPa. From very low effective consolidation pressures up to about 200 kPa the permeability decreases by more than two orders of magnitude.
