Grain-scale mechanics of quartz sand under normal and tangential loading

- Normal and tangential contact behavior was studied at quartz grain contacts.
- Pre-loading and pre-shearing effects were investigated.
- Ploughing mechanism dominated the behavior at greater normal loads.
- Hertzian response was observed with initial plastic deformation.
- The apparent contact area was measured experimentally with image analysis.

The study provides some insights into the grain scale mechanical behavior of quartz sand grains at their contacts. It is achieved by conducting laboratory experiments with a custom-built apparatus. A variety of tests were performed exploring the effects of pre-loading and pre-shearing on the inter-particle coefficient of friction, the tangential and normal contact behavior. Microscopic observations are made on the grain surfaces before and after shearing through image processing. Images showed that ploughing dominates the contact behavior at relatively larger normal loads, but a similar behavior was not apparent at very small loads. The apparent radius of the contact area of the grains was quantified both experimentally and theoretically using Hertz fitting. It was shown that theoretical and experimentally derived contact areas matched at relatively greater normal loads but not at smaller normal loads.