| Popis: |
Debris flows contain solid particles of various sizes. The gaps between large particles contain fine-grained sediment, and this is known to maintain high pore pressures. Inverse grading in which large particles become increasingly concentrated towards the surface of the flow is also known to occur. Therefore, to determine the flow behavior, it is important to clarify the grain-size distribution for not only large particles, but also fine sediment in the depth direction of the flow. In the present study, we generated a debris flow by eroding riverbed material consisting of large particles and fine-grained sediment in an experimental flume, and measured the concentration of different sized particles in layers at three different depths. The test results showed that the highest concentration of large particles was in the middle layer. The highest concentration of fine-grained sediment was in the bottom layer, and this concentration decreased towards the surface of the flow. Inverse grading was observed from the bottom layer to the middle layer; however, no noticeable inverse grading occurred from the middle layer to the upper layer. The reason for this kind of concentration distribution is considered to be that there was insufficient turbulence in the gaps between large particles in the bottom layer, and so fine-grained sediment settled, while in the upper layer, interstitial turbulent stress developed and fine-grained sediment was dispersed. We calculated the concentration distribution of fine-grained sediment from the middle to the upper layer on this basis, and the results were in general agreement with the measured distribution in the dispersion region. |
