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

临界状态土力学的概念为理解静止的土体和岩石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，土体初始体积密度、有效应力和水力扩散系数决定了破坏过程中发生的体积密度和孔压的变化。这些变化可能导致从缓慢、缓慢的失败过渡到广泛、快速的失败和流动(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，主要是不排水(密封)条件下的实验室三轴试验。这类测试强调的是可以破坏建筑物的小应变，但既不能复制排水条件，也不能复制以快速滑坡和泥石流为特征的非常大的剪切应变和应变率(S-1)。因此，虽然临界状态的概念在原则上被广泛接受，但很少或根本没有数据来测试它们对泥石流大而快速变形特征的适用性(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原理到泥石流动员中。利用两个独特的设施，将进行两套互补的实验：美国地质调查局泥石流水槽的大规模泥石流引发实验和爱荷华州立大学使用环形剪切装置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勘探局的水槽来测量斜坡崩塌之前和期间的孔压变化，并引发泥石流动员。我们将通过在USGS水槽上进行类似的试验来探索孔压升高的原因和初始条件的范围，在USGS水槽中，系统地改变初始容重，并连续测量地下土体的变形。辅助试验将提供第二种手段来研究伴随着破坏的体积密度和孔压的耦合变化，这些变化可能会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.