| Summary: | 碩士 === 中原大學 === 土木工程研究所 === 98 === Disc shearing may produce lateral displacement of sand particles to enhance the sand strength and to make the sand grains closely packed.
The study is to investigate the effect of disc diameter on the disc shearing behavior of sand. In previous small size disc shearing experiments, the specimen ring is 200 mm in diameter and the disc diameter is 198 mm. This provide the sand specimen a laterally confined condition. In previous mid-size disc shearing experiments, the specimen diameter increases to 600 mm and the disc diameter is 200 mm. These reduce the lateral confinenet condition in the sand specimen. This experimental study use the 600 mm test tank and a new disc of diameter
of 150 mm, together with the 200 mm diameter disc.
Mai-Liao and Ottawa sand are used as soil samples with different grain characteristics. The specimen is 600 mm in diameter and 150 mm in hight, and the initial relative density is 50%. The disc shearing
is operated under both constant static load and unit angle of rotation. The disc settlement, the amount of sand surface heaving, the change in lateral
earth pressure, and cone penetration resistance are observed.
The test results show that, as the accumulated angle of rotation is the same, the effect of disc diameter on the specimen compression is a function of sand grain characteristics. Multilayer sand sample with reinforced material (i.e. filter paper), has smaller settlement as result
of disc shearing.
For the change in lateral earth pressure, when the accumulative angle of rotation less than 30°, the lateral earth pressure increases with increasing accumulated angle of rotation； when the accumulated angle of rotation exceeds 30°, the lateral earth pressure keeps about the same. The 200 mm disc is close to the side of the tank so that the change in
lateral earth pressure is higher than that induced by the 150 mm disc.
The cone penetration resistance data show that disc shearing causes an unern change；qc increases under the disc center and qc decreases under the disc edge. The qc after 200 mm disc rotation is higher than the
qc after 150 mm disc rotation.
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