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

[80399]临界状态土力学的概念为理解土壤和岩石的静态块体动员成快速变形的泥石流的机制提供了基础。临界状态原理表明，土体初始容重、有效应力和水力扩散系数决定了破坏过程中容重和孔隙压力的变化。这些变化可以导致从缓慢的、缓慢的失效到广泛的、快速的失效和流动的转变（NRC, 1985）。然而，几乎所有评估临界状态土壤行为的尝试都局限于标准的工程方法，主要是在不排水（密封）条件下的实验室三轴试验。这些试验强调可以破坏结构的小应变，但既不能复制排水条件，也不能复制具有快速滑坡和泥石流特征的非常大的剪切应变(1)和应变率（s-1）。因此，尽管临界状态概念在原则上被广泛接受，但很少或根本没有数据可以测试其对泥石流大而快速变形特征的适用性（Stark等人，1997年）。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原理到泥石流动员。使用两个独特的设备，将进行两套互补的实验：在美国地质调查局的泥石流水槽进行大规模的泥石流启动实验，以及在爱荷华州立大学使用环剪装置进行高应变实验室测试。先前的泥石流启动实验使用USGS水槽来测量边坡破坏之前和期间孔隙压力的变化，并触发泥石流动员。我们将在美国地质勘探局的水槽中进行类似的试验，系统地改变初始容重，并连续测量地下土壤变形，从而探索这些孔隙压力增加的原因和发生这种情况的初始条件范围。辅助试验将提供第二种方法来研究伴随破坏而来的体积密度和孔隙压力的耦合变化，这些变化可能引发或抑制泥石流的动员。

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.