Erosion of valley-floor bedrocks by sediment-laden flows

(1)没有定量研究基岩侵蚀由于泥沙流动进行。为了获得关于这个问题的初步知识，首先使用循环水槽进行了无沉积物水流对基岩侵蚀的实验室实验。由水泥、沙子和水混合制成的人造岩石被用来模拟野外的实际岩石。在这些具有不同强度的模拟岩石中，凹进具有各种开口的狭缝。为了研究狭缝内和狭缝周围的流动，还使用中性浮力浮子进行了可视化实验。当水流入狭缝内部时，水颗粒撞击狭缝的下边缘，对边缘产生压缩力，使得该部分比其他部分更快地被侵蚀。当狭缝的开口变大时，侵蚀更剧烈。随着岩石强度的降低，开孔的影响越来越明显。当下边缘的侵蚀达到某一临界值时，水颗粒不再对边缘施加压力。作用在上下边缘上的侵蚀力的差异变小，导致两个边缘之间的相对高度恒定。(2)利用循环水槽进行了恒定流速水流对基岩侵蚀的试验研究。这里使用的岩石样本是从野外收集的，具有不同的强度。使样品经受流的剪切力。结果表明：（1）土壤侵蚀与时间呈线性关系，即土壤侵蚀量随时间的增加而增加;平均侵蚀速率R与岩石抗压强度S_c的关系可用R = 0.17（4.3 - 1 nS_c）表示，其中R和S_c的单位分别为mm/hr和kg/cm ^2。

(1) No quantitative studies on bedrock erosion due to sediment-laden flows have been conducted. In order to obtain a rudimentary knowledge on this subject a laboratory experiment on bedrock erosion by water flows without sediments was first performed using a recirculating flume. Artificial rocks made of a mixture of cement, sand, and water were used to simulate actual rocks in the field. In these simulated rocks having different strengths a slit was indented with various openings. To examine a flow in and around the slit, a visualization experiment was also conducted using neutral buoyant floats. When water flows into the interior of the slit, water particles hit the lower edge of the slit to act compressive force on the edge, so that this part is eroded more rapidly than the other part. The erosion is more vigorous as the opening of the slit becomes larger. The effect of opening tends to be more marked as the rock strength decreases. When erosion of the lower edge attains a certain critical value, water particles act no more compressive force on the edge. Difference in erosive force acting on the upper and lower edges becomes small, resulting in constancy of the relative height between the two edges.(2) An experiment using a recirculating flume was performed to investigate bedrock erosion due to sediment-laden flows with a constant speed. Rock samples used here were collected from the field and had different strengths. The samples were subjected to shear force of the flows. The result showed that (1) the erosion occurs linearly with time, i.e., no temporal variation in erosion rate is present, and (2) the relationship between average erosion rate, R , and compressive strength of rocks, S_c , can be expressed by R = 0.17(4.3 - 1n S_c ) where the units of R and S_c are mm/hr and kg/cm^2, respectively.