Observations on the consolidation characteristics and permeability of anglian Tills: Fid-Bau Portal

Observations on the consolidation characteristics and permeability of anglian Tills

Little, J.A.

Abstract The paper describes the results of a series of oedometer tests on undisturbed and reconstituted samples of lodgement till from the Vale of St Albans, Hertfordshire. The tills are found in an area near the postulated southern margin of the Anglian ice sheet in the UK, in close association with commercially exploited fluviatile (proto-Thames) and glaciofluvial sands and gravels. A technique is described for the undisturbed sampling of these matrix supported tills directly in the rings subsequently used for oedometer testing. An investigation of the directional dependence of permeability in these tests necessitated a frame of reference within which sampling of the tills could take place. A new technique is described which utilised the measured clast fabric vector in each till for this purpose. Reasons are presented explaining why estimates of the maximum preconsolidation pressure from the test results consistently underestimate the probable maximum ice thickness above these lodgement deposits during Anglian times. A parallel series of oedometer tests carried out on ‘control’ samples of soil reconstituted from the screened matrix of the tills has provided a means of comparing directly the coefficients of consolidation and permeability for reconstituted and undisturbed till. In this way, it is argued, insight may be gained into the many and diverse effects on soil behaviour resulting from complex post-depositional processes operating during the Holocene.