Why is glacial till unsuitable for building?

Answer 1

Glacial till is in fact very commonly used in building. It is over consolidated and so is very stiff making it a very good founding material as there is very little settlement.

This also means that it has a very high shear strength by the standards of soils so can be used to form very stable embankments and cuttings.

There can however be practical problems with the use of glacial tills as there may be large cobble and boulder sized clasts within the clay matrix which can make excavation of cuttings difficult and also hamper the driving of piles for deep foundations.

Also some clays (which may be present in glacial till) are more "active" than others. Activity in this context is a term used to describe their shrink swell potential, as some clays undergo significant volume changes depending on their moisture content. This can cause cyclical shrinking and swelling of the clay / glacial till depending on seasonal variations in rainfall and temperatures.

In embankments and cuttings, this deformation leads to a strain softening behaviour which can ultimately result in the formation of a slip surface causing a failure in slopes.

In founding materials composed of glacial till, this behaviour can lead to differential settlements that can cause damage to structures and underground services.