Laboratory Investigation of the Pore Pressure Built-Up in Moving Debris
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Debris flow poses significant threat to property and human life mainly as a result of its high sediment concentrations and mobility. For the purpose of predicting debris flow mobility and mitigating potential damage, considerable attention has been drawn to the development of debris flow physical models. Despite of the achievements, a thorough mechanism accounting for the built-up and maintaining of pore pressure within the shearing layer of debris flow has not been made available mainly due to the lack of experiment data. In viewing of that situation this study developed a coaxial-cylinder apparatus and conducted two series of tests concerning pore pressure built-up in samples of varying solid fraction concentration (by volume) and fine grain content (by weight) at differing rotational velocity. The first series of tests show that when solid fraction concentration increase from 20% to 50%, pore pressure built-up tends to be higher. The second series of tests exhibit that similar pattern can apply except for samples with 80% and 100% silt content. This peculiarity together with grain size analyses before and after experiment give rise to a postulation that mixing rods shearing may be responsible for the constant pore pressure built-up, while «most breakable grain sizes may exist and have led to the extraordinarily low peak values and prolonged decline in samples with rich silt content through dilatancy. Nonlinear relationship between pore pressure built-up and rotational velocity was found in all tests. Initial stagnation and transitional stage were observed for most samples; plausible explanations have been proposed. Owing to some limitations, future work is expected on the microscopic mechanism of sediment dilatancy, the properties of «most breakable grain sizes and practical application.