| Project Detail |
The engineering analysis of geotechnical structures such as building foundations, tunnels or embankments, is usually made assuming that the soil acts as a continuous material, as if it were, for example, a metal. The tests that we carry out to characterise soil therefore utilise samples that have a representative number of particles, often millions, within them. The problem with this approach is that the soil behaviour is extremely complex, much more so than most other materials, resulting from the soil actually consisting of discrete particles with water filled voids between, and also the fact that these particles have a natural rather than man made origin, which can affect their shape, strength and arrangement. The extreme complexity of the equations we might use to characterise soil then means that our research understanding of soil behaviour is rarely fully implemented in engineering design.
In recent years increased computing power has led to the increasing use of discrete approaches in the analysis of soils, in which individual soil particles are modelled. In such an analysis it is important to model accurately the key characteristics of the particles that will influence the overall behaviour of the soil mass; their shapes, strengths, the arrangement that they have relative to each other and how they behave when they touch. Advances have been made in all of these areas, with the exception of the particle contact behaviour, which in recent years has been the special interest of Professor Coop, who has developed a new apparatus with which to investigate this aspect.
Having understood the contact behaviour, we will be in a good position to create a virtual or "Avatar" model of soil particles, at least for sands size and above, and this is the aim of this research. The vehicle for doing this is to address the practical engineering problem of modelling particles of railway ballast used to support rail track, the ballast in this sense being regarded as a large grained sand. Collaborating with noted experts on ballast behaviour at Nottingham University (Professor McDowell) and Southampton University (Dr. Zervos), and with contributions on soil particle shape description from Dr Baudet of UCL, the research will create a virtual model of several typical ballasts, capturing their shapes, arrangement, any damage that occurs during loading by the trains as well as, most crucially, the contact behaviour between particles. Such a model could then be used both in research and engineering design, but the first step will be to validate that it is successful. This can only be done by comparing the output of discrete numerical analyses using the model particles with "real events". The most convenient real events are "triaxial" tests, which are conventional continuum type tests in which a cylindrical sample of many particles is loaded and the response monitored. These are difficult tests and ultimately the aim of this type of research would be to render them obsolete as we then rely only on the new particle scale tests and modelling. |
