Abstract

This paper gives the results of mineralogical and engineering classification tests and one-dimensional consolidation and swelling tests on undisturbed and reconstituted samples of a number of different lodgement tills from the Vale of St Albans in Hertfordshire. These tills are presumed to be of Anglian age and mark the approximate southernmost Quaternary ice advance in the area. They are interbedded with fluvioglacial sands and gravels which were deposited on the proglacial fringe of a retreating ice mass, and other sands and gravels which are associated with a former course of the Thames in the Vale. In mineralogical tests the tills were found to contain crystalline calcite; this could lead to cementing in undisturbed samples which would be broken down during preparation of reconstituted samples.

The results of oedometer tests show little evidence of compression or consolidation anisotropy in clast fabric orientated, undisturbed samples. Differences in the compression and swelling characteristics of undisturbed and reconstituted samples attributable to calcite cementing were observed, particularly at the lowest consolidation pressures during initial loading. Differences in permeability between the undisturbed and reconstituted samples were also found to be greatest at the lowest consolidation pressures during initial loading. Examination of the swelling characteristics revealed a marked threshold effect shown by significant variations in the swelling index associated with changes from loading to unloading and from swelling to reloading.

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