Lin Jinshi, Zhuang Yating, Huang Yanhe, Jiang Fangshi, Lin Jinglan, Ge Hongli. Shear strengths of collapsing hill in red soil as affected by soil moisture under different experimental methods[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2015, 31(24): 106-110. DOI: 10.11975/j.issn.1002-6819.2015.24.017
    Citation: Lin Jinshi, Zhuang Yating, Huang Yanhe, Jiang Fangshi, Lin Jinglan, Ge Hongli. Shear strengths of collapsing hill in red soil as affected by soil moisture under different experimental methods[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2015, 31(24): 106-110. DOI: 10.11975/j.issn.1002-6819.2015.24.017

    Shear strengths of collapsing hill in red soil as affected by soil moisture under different experimental methods

    • Abstract: Gully erosion (especially from a permanent gully) is a widespread phenomenon in many agricultural landscapes and it is a serious land management issue in many parts of the world. Gully erosion occurs randomly in sediment from the gully bank deposited into a slump. Thus,simulation of the gully bank retreat condition is important. In order to understand the erosion mechanism of permanent gully, it's key to know that the variation of gully wall's shear strength. However, different experimental methods get different results. Therefore, characteristics of shear strength vary with soil water content were studied in permanent gully's red soil layer, by using direct shear and tri-axial shear method. Soil samples were collected from the Longmen catchment of Anxi County, Fujian Province, in southeast China. The samples were pre-treatment according to the experimental standers, then the samples were tested for different confining pressure (100, 200, 300, 400 kPa) and various volumetric soil moisture (from 10% to 30%). Results showed that the highest cohesive force of soil reaches 80 kPa when soil moisture content changed from 10% to 15% under the direct shear test. The increase in volumetric soil moisture content (from 15% to 25%), cohesive force and internal friction angle gradually reduced to a minimum. The cohesive force were less than 5 kPa in most of the soil samples when soil moisture was over 25 %, and the internal friction angle was also reduced from 38° to 25°. In tri-axial shear test, with the increase in soil moisture content, cohesive force and internal friction angle decreased to a minimum in tri-axial shear test. The cohesive friction angle decreased more than 65% in most of the samples, and the internal friction angle showed the same trend. There are similar results of tri-axial shear and direct shear test. However, the cohesive forces of tri-axial shear test were greater than the direct shear test. However, internal friction angles of tri-axial shear test are lower than direct shear test. There were two reasons causing the variation between those two methods. First, discrete soil samples preparation. All the soil samples, which used in direct shear test, were undisturbed samples. However, there were remolded samples were used in tri-axial shear test. Although the remolded samples can get a uniform test piece, it breaks the "natural" connection between soils particles, compare to undisturbed samples. Second, different failure modes of soil samples in direct shear test and tri-axial shear test. In the direct shear test, shear planes is inherent and not drained in the test, breakage of test piece estimated based on the theory. However, it usually disagrees with the actual conditions and difficult to control the drained. In tri-axial shear test, it can be complete not drained, and the shear planes are not fixed. This means the shear breakage of the test piece can be close to the natural situation in tri-axial shear test. This research provides a quantified evaluation of different test method in shear strength. Therefore, it is wise to choose a better method according to the demand for further research.
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