Abstract

Terzaghi K. (1936) ‘A fundamental fallacy in earth pressure computations’, Boston Society of Civil Engineers, complains that strain does not enter the theory, and concludes that

‘The fundamental assumptions of Rankine’s earth pressure theory are incompatible with the known relation between stress and strain in soils, including sand. Therefore the use of this theory should be discontinued’

. Terzaghi also taught that his re search student Hvorslev M. J. (1937) had determined the nature of Coulomb’s cohesion in soils and that the plasticity of clay is due to surface chemistry of clay mineral grains.

However the error that Rankine’s made was to adopt Coulomb’s soil strength equation. Observed behaviour of soil can be explained well by the mechanics of an aggregate of fine solid grains saturated with an incompressible pore fluid. Indeed if there is a layer of hard grains of powdered ice on Titan’s surface, saturated with and eroded by precipitation and flow of liquid methane, then the landforms on the surface of Titan could be similar to those on Earth, and the geography recognisable.