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High-speed high-stress ring shear tests on granular sods and clayey soils
| Authors: | Hiroshi Fukuoka, Kyoji Sassa |
| Year: | 1991 |
| Type: | General Technical Report |
| Station: | Pacific Southwest Research Station |
| Source: | In: Rice, Raymond M., technical coordinator. 1991. Proceedings of the IUFRO technical session on geomorphic hazards in managed forests; 5-11 August 1990; Montreal, Canada. Gen. Tech. Rep. PSW-GTR-130, Berkeley, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; p. 33-41 |
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Abstract
The purposes of this study is to obtain exact knowledge of the influences on friction angle during shear by shearing speeds. Ring shear tests on sandy and clayey materials have been carried out with a newly developed High-speed High-Stress Ring Shear Apparatus to examine if there are some changes in the frictional behaviors of these materials at high shearing speeds of O.O1cm/sec-100cm/sec and high normal stress of 0-3.8kgf/cm2. Samples used for tests were glass beads, tennis court sands in the university campus, the Toyoura standard sands (uniform beach sands) and bentonite clays. All tested samples were dry.Although result on the glass beads showed that the friction angle during shear was independent of shear speed under the normal stress up to 3.8kgf/cm2, 2 ~ 5 degrees of change in friction angle were observed on the tennis court sands, the Toyoura standard sands and the bentonite clays. In the tests on the Toyoura standard sands and the bentonite clays, friction angle increased as the shear speed increased. On the contrary, friction angle during shear of the tennis court sands decreased at a shearing speed of 100cm/sec.
Change in grain size distribution implies that heavy crushing or grinding of particles occurred during shear. The grain size distribution become wider during shear by grain crushing in samples except glass beads. It could result in the increase of density and accordingly increase of the friction angle. Crushing or grinding of grains during shear can change the shape of grains. The Toyoura standard sands have round shape, because they are beach sands, it may become angular by crushing during shear. On the contrary, the tennis court sands have angular shape because they are taken from mountain slopes, it may become round by grinding during shear. Round grains have a small friction angle. It may be interpreted that the tennis court sands had a smaller friction angle during shear because of the change of angular grains to round grains by grindings. Hence, it can be said that the friction angle is affected by crushing or grinding of grains during shear, which appears in a higher normal stress and a greater shear speed (shear distance).