Ruprecht-Karls-Universitšt Heidelberg

Terrestrial Systems > Soil Physics > Research > Porous Media and Soils

Modeling and measurement of crack formation in clay

Heiko Hoffmann, Hans-Jörg Vogel, Kurt Roth



The formation of cracks during desiccation is a common feature of clay soil. As a consequence,  hydraulic properties of the soil material cannot be considered to be constant - they vary with time in dependency of the  history in wetting and drying. This is one of the major difficulties for modeling flow and transport in such soils.
The task of this project is to find a simple model which describes the formation of cracks and which mimics the  physics of cracking. 
The starting point is a triangular lattice of nodes which are connected by springs.  Each spring has a stress threshold above which it breaks. This threshold is chosen to be Gaussian and was distributed at random. Desiccation is reproduced by reinforcing the springs. At one point, this leads to the  burst of the first spring and subsequently to a self organized formation of a crack pattern.

The image (left) shows a two-dimensional crack pattern obtained in an experiment with a mixture of bentonite and sand. Below is the pattern obtained by the simple model. A quantitative analysis in terms of size distribution of abggregates,  topology and distribution of angles  showed that our model output is in good agreement with the experiment.  (The quantification of crack patterns is illustrated in the lower right image: Distances to the next crack are indicated with grey levels, the skeleton of the crack provides information on topology and angles). 


 

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