| Summary: | 碩士 === 國立成功大學 === 土木工程學系碩博士班 === 101 === Due to the geographically special environment, large amount of low plasticity slity sand with fines widely spread in Southwestern Taiwan. The low plasticity silt sand is easy to lose due to the internal erosion effect and result to piping failure in many underground excavation cases. Therefore it is necessary to investigate the properties of low plasticity slity sand under condition of internal erosion.
In previous study, the internal erosion properties of low plasticity silty sand under sudden pressure difference has been investigated by using Flexible Wall Pin Hole apparatus (FWPH). In this study both FWPH test and undrained triaxial test are used to study the effect of fines content on the resistance of internal erosion and the steady state behavior of the low-plasticity silty sand.
The test results indicated that the resistance of internal erosion of low plasticity sand would decrease as the effective confining pressure or void ratio increases; while as fines content increases, there is a decreasing trend of resistance of internal erosion, but it world increases at 30% fines content, which world be packed most closely. The degree of soil particles packing density is the principal condition affected the resistance of internal erosion of soil.
The steady state line obtained from test results showed that as the effective stress and void ratio of the silty sand below the steady state line, it will not cause piping failure by internal erosion; on the other hand, it will cause failure. In summary, low plasticity silty sands may increase the resistance of internal erosion by improving the density of the soil or reduce the groundwater level, and the steady state line of soil may be used as the reference for engineering design to determine if failure condition of erosion may occur.
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