Effects of Initial Conditions on Debris-Flow Mobilization: Flume and Ring-Shear Experiments

9803991 Iverson临界状态土壤力学的概念为理解土壤和岩石的静态块体移动到快速变形的泥石流中的机制提供了基础。 临界状态的原则表明，土壤的初始体积密度，有效应力，和水力扩散率确定的体积密度和孔隙压力发生故障期间的变化。 这些变化可以导致从缓慢的、缓慢的故障转变为广泛的、快速的故障和流动（NRC，1985）。 然而，几乎所有的尝试，以评估临界状态的土壤行为已被限制到标准的工程方法，主要是实验室三轴试验不排水（密封）条件下。 这些试验强调的是能够破坏结构的小应变，但既不能复制排水条件，也不能复制快速滑坡和泥石流所特有的非常大的剪切应变（1）和应变率（s-1）。 因此，虽然临界状态概念在原则上被广泛接受，但很少或没有数据可以测试它们对泥石流大而快速变形特性的适用性（Stark等人，1997）。我们建议收集必要的实验数据，以扩展和应用临界状态土壤行为的原则，泥石流动员。 利用两个独特的设施，将进行两套互补的实验：在美国地质调查局泥石流水槽进行的大规模泥石流启动实验和在爱荷华州州立大学使用环剪装置进行的高应变实验室测试。 以前的泥石流启动实验使用美国地质调查局水槽测量孔隙压力的变化之前，在斜坡故障和触发泥石流动员。 我们将探讨这些孔隙压力增加的原因和范围内的初始条件下，他们发生的进行类似的测试，在美国地质调查局水槽中，初始容重是系统地变化和地下土壤变形连续测量。 辅助试验将提供第二种手段，研究伴随着破坏的体积密度和孔隙压力的耦合变化，这种变化可能引发或抑制泥石流的流动。

9803991IversonConcepts of critical-state soil mechanics provide a foundation for understanding the mechanisms by which static masses of soil and rock mobilize into rapidly deforming debris flows. Critical-state principles indicate that soil initial bulk density, effective stress, and hydraulic diffusivity determine changes in bulk density and pore pressure that occur during failure. These changes can cause a transition from slow, creeping failure to widespread, rapid failure and flow (NRC, 1985). However, virtually all attempts to assess critical-state soil behavior have been limited to standard engineering methodologies, primarily laboratory triaxial tests under undrained (sealed) conditions. Such tests emphasize the small strains that can damage structures, but can replicate neither the drainage conditions nor the very large shear strains ( 1) and strain rates ( s-1) that characterize rapid landslides and debris flows. Thus, while critical-state concepts are widely accepted in principle, little or no data exist to test their applicability to large, rapid deformations characteristic of debris flows (Stark et al., 1997).We propose to collect the experimental data necessary to extend and apply the principles of critical-state soil behavior to debris-flow mobilization. Using two unique facilities, two sets of complementary experiments will be conducted: large-scale debris-flow initiation experiments at the U.S. Geological Survey debris-flow flume and high-strain laboratory tests using a ring-shear device at Iowa State University. Previous debris-flow initiation experiments used the USGS flume to measure changes in pore pressure preceding and during slope failure and trigger debris-flow mobilization. We will explore the causes of these pore-pressure increases and the range of initial conditions under which they occur by conducting similar tests at the USGS flume in which the initial bulk density is varied systematically and subsurface soil deformation is measured continuously. Ancillary tests will provide a second means of studying the coupled changes in bulk density and pore pressure that accompany failure and that may either instigate or suppress the mobilization of debris flows.