Howard Taylor

Site classification for seismic hazard assessment

Started: March 2013
Supervisor: O'Sullivan, C., Sim, W.W.
Funding: EPSRC

Background

Dam engineers worldwide have acknowledged that one of the most significant threats to dam integrity is internal erosion, which is the progressive washing out of soil particles under water seepage. This has been the subject of extensive investigations by laboratory testing as well as analytical and numerical modeling, all of which has led to the development of various empirical filter design criteria which are used in practice today.  

Much of the existing research indicates that one of the key factors controlling the potential for internal erosion is the size of void “constrictions” formed between the filter particles, which will determine whether any mobile soil particles can fit through the void network and hence whether they can be washed out. To date, the sizes of these void constrictions have either been estimated based on the particle size distribution and some simplified geometric approximations, or the constriction sizes have been determined by numerical algorithms, again relying on simplified geometric conditions. In this study, x-ray micro computed tomography (micro-CT) and state of the art image analysis techniques will be used to provide observations and measurement of void constrictions in real soil structures. It is hoped that these observations may then shed new light on the accuracy and applicability of the filter design criteria used in engineering practice.   

Research aims

  1. Develop a tool-kit of image analysis techniques to locate and measure void constrictions.
  2. Produce and analyse micro-CT images of real soils, with a range of particle size distributions, particle shapes and relative densities. This will include investigation of materials which are expected to be internally stable/unstable.
  3. Improve our qualitative understanding of the 3D void space formed between soil particles and investigate the characteristics of void constrictions.
  4. Investigate quantitative relationships between particle size/shape/packing and constriction sizes.
  5. Assess the implications of the above on existing dam filter design criteria.

Fig 1
Figure 1: Example micro-CT image of soil particles (Leighton Buzzard sand), showing void constrictions

HOWARD TAYLOR

Howard TaylorPhD Candidate - Geotechnics 
Department of Civil & Environmental Engineering 
Imperial College London SW7 2AZ 
h.taylor13@imperial.ac.uk