Progressive Failure of Slopes and Excavations as Fracture Problems

本研究的目的是建立断裂模型，并提供实验数据，用于评估内聚摩擦材料的渐进破坏相关条件。该方法的基础包括分析断裂的扩展，其中理论模型是应力和位移的精确表示，结果将呈现(1)体积内的剪切带（斜坡），以及(2)自由表面附近的裂纹扩展（挖掘）。对体积型不稳定性的分析将包括(a)各种形状的裂缝，例如圆形和对数螺旋形；(b)非线性和时变行为，如塑性和粘弹性。对表面型不稳定性的分析将包括：(a)自由表面附近裂纹的萌生和扩展，包括相互作用；(b)与钻孔或隧道有关的自由表面的曲率。新型实验装置将用于测量扩展剪切带的断裂特性和剥落失稳现象。评估渐进式破坏条件的方法基于对分段均匀介质（允许分层系统）的超奇异边界积分方程的使用，该介质具有界面（接缝、断层）和多个开口（漂移、竖井）等特征。超奇异积分方程的主要优点是它提供了一种处理不连续面和其他离散曲面的方便方法。超奇异边界积分方程包含位移不连续和牵引力，这些值表征了表面上的相互作用。这一强大的技术将有助于深地下科学与工程实验室评估在一个体积内和接近自由表面的开挖断裂条件。知识转移与研究计划紧密结合，通过互动分析软件与更广泛的岩土工程社区进行交流和接触。一般的K-12教育计划将利用斜坡和挖掘的熟悉度和美学吸引力来吸引广泛的学习者。将设计和制作小型展品，通过对弱胶结砂岩断裂的实验来演示渐进破坏。

The objective of this research is to develop fracture models and provide experimental data that can be used to assess conditions associated with progressive failure in cohesive, frictional materials. The basis for the method involves analyzing the propagation of a fracture, where the theoretical model is an exact representation of the stresses and displacements, and the results will be presented for (1) shear banding within a volume (slopes), and (2) crack growth near free surfaces (excavations). The analyses for volume-type instabilities will include (a) various shapes of the fracture, e.g. circular and log spiral; and (b) nonlinear and time-dependent behavior, e.g.plasticity and viscoelasticity. The analyses for surface-type instabilities will include the (a)initiation and growth of cracks near a free surface, including interactions; and (b) curvature of the free surface associated with a borehole or tunnel. Novel experimental apparatus will be used to measure the fracture characteristics of propagating shear bands and spalling instability phenomena. The approach to evaluate the conditions for progressive failure is based on the use of the hypersingular boundary integral equation for a piece-wise homogeneous medium (layered systems are allowed), with features such as interfaces (joints, faults) and multiple openings (drifts, shafts). The main virtue of hypersingular integral equations is that they present a convenient means to deal with discontinuities and other discrete surfaces. Hypersingular boundary integral equations contain the displacement discontinuities and tractions, the values that characterize the interactions at the surfaces. This powerful technique will be useful to evaluate conditions of fracture within a volume and near a free surface for excavations at the Deep Underground Science and Engineering Laboratory. Knowledge transfer is tightly integrated into the research program, where exchange and engagement with the broader geotechnical engineering community will be accomplished through software for interactive analysis. A general K-12 education program will use the familiarity and esthetic appeal of slopes and excavations to engage a broad spectrum of learners. Small exhibits will be designed and fabricated to demonstrate progressive failure through experiments on fracture of a weakly cemented sandstone.