The particle scale mechanics of sands

Nevertheless, a continuum approach is usually applied to soil as for other materials, so design is by means, for example, of a finite element programme. The equations used to represent the soil behaviour that might be used in such an approach are often then highly complex as they try to capture a behaviour that is actually particulate.

In the future, we might therefore abandon our continuum approach when we design soil structures such as foundations or tunnels and instead try to model every particle of the soil individually using a discrete element approach rather than finite element. Current attempts to do this often use simplistic spherical soil particles, but soon we will be able to use realistic shapes. What is missing is the mechanics of the individual particles and this project addressed that aspect of the problem.

Innovative new apparatus were developed to test individual particles, examining the behaviour when two sand particles touch and also how, when they are loaded together far enough, they break. The results have shown that the mineralogy, size, shape and roughness of the particles controls their contact behaviour and their strength and that neither the way sand particles break nor the load-deflection behaviour up to breakage correspond very well with currently accepted theories.