Engineering in stiff sedimentary clays

The papers to the Symposium in Print are reviewed, looking in particular for insights and applications available to practising designers.† The papers display the complexity of the behaviour of stiff clays, and the very high level of expertise committed to researching it. The features of behaviour described, and to some extent quantified, are very important in understanding observed phenomena in conventional civil engineering situations. Studies of the stratigraphy of London Clay, as an example, show some helpful consistency across the deposit when results are plotted relative to its base, but also show that it is not a single, uniform material. Engineering at greater depth and with thermal effects, as required for nuclear repositories, provides some new challenges, involving both unfamiliar parameters and more familiar problems of characterising stiffness, strength and permeability, especially in bonded materials, set in a context of higher stresses. The combination of high-quality laboratory studies with field observations of full-scale behaviour remains essential to the development of geotechnical engineering, and both are well represented in the papers to the Symposium.