The influence of genetic processes on some geotechnical properties of glacial tills

Abstract

Summary The principle characteristics of debris in transport by glaciers are described and the way in which this material is subsequently deposited as till. Three principal types of till are described, lodgement till, melt-out till and flow till, which can be related to typical sediment/landform models and which can form a good basis for site investigation planning. A proglacial/sub-glacial sediment association and land system is defined, in which lodgement till and proglacial outwash are the principal sediments, and in which drumlins, fluted moraines and push moraines, and kettle holes and eskers are the principal landforms. A supraglacial sediment association and land system is also defined, in which a suite of supraglacial sediments and landforms are superimposed on the subglacial/proglacial land system. The sediments comprise flow till, melt-out till and supraglacial outwash sediments, and the landforms largely comprise kame moraines. A third land system, the glaciated valley land system comprises chiefly medial and lateral moraines, in which the till is derived supraglacially from flanking valley sides, and kame terraces. Till genesis influences the geotechnical properties of tills through its control on several important characteristics: grain-size distribution and its spatial variation; the stress history of the till; the nature of the sequence in which the till lies, e.g. the presence of stratified horizons; and jointing in the till. Post-depositional processes which change these characteristics are also important. The processes considered are: post-depositional wetting and drying; freezing and thawing; remoulding; and downward percolation of fines.