3D Block Erodibility: Dynamics of Rock-Water Interaction in Rock Scour
3D Block Erodibility: Dynamics of Rock-Water Interaction in Rock Scour
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3D 块侵蚀性：岩石冲刷中岩水相互作用的动力学
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发表时间：
2015
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通讯作者：
M. George
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作者：
M. George
作者：乔治·迈克尔·弗里曼 | 乔治·迈克尔·弗里曼顾问：西塔尔，尼古拉斯 |摘要：摘要三维块侵蚀性：岩石冲刷中岩石与水相互作用的动力学作者：迈克尔·弗里曼·乔治（Michael Freeman George）工程哲学博士 - 土木与环境工程加州大学伯克利分校尼古拉斯·西塔教授（主席）流水对岩石的侵蚀是自然景观演变中不可或缺的过程，也是水坝、水坝等关键基础设施的严重危害。溢洪道、桥梁和隧道。去除单个岩石块是发生岩石冲刷的主要机制之一。本研究研究了 3D 地质结构对岩石块可蚀性的影响，旨在了解该过程的基本力学并开发块可蚀性的预测框架。为此，建立了一个多方面的研究计划。对加利福尼亚州北部内华达山脉原型场地的实地调查被用作开发一系列广泛的水力模型实验的基础，并辅以基于 3D 块理论的理论确定性和随机分析。过去的实验研究仅限于实验室环境中简化的立方体或矩形块几何形状，有关 3D 块周围的流体动力压力以及随后的块对流体动力载荷的响应的数据非常少。对于更复杂的块体形状（自然界中常见的情况），这种几何形状的简化可能会产生问题，因为岩体内不连续性的 3D 方向很大程度上影响块体的可移除性、运动学和稳定性。因此，本研究的一个主要重点是从现场和实验室环境中获得与 3D 非立方块几何形状相关的水力和岩体参数的高分辨率实验数据集。现场工作是在加利福尼亚州北部一个坝址的活跃侵蚀的无衬砌岩石溢洪道的原型环境中进行的。使用光探测和测距（LiDAR）扫描获得高分辨率岩体数据，该扫描允许对岩体参数变异性进行统计表征，以用于概率冲刷预测模型。在现有的块模具中铸造了两个装有仪表的人造岩石块，以捕获泄漏事件期间的流体动力压力和块位移。然而，加利福尼亚州北部的气候条件阻止了水库在这些区块上泄水，因此迄今为止尚未收集到任何数据。还建立了一个按比例的物理水力模型，大致代表了上述现场的条件。实验室模型的优点是能够研究在现场环境中不易实现的广泛变量和流动条件。对于该模型，构建了一个可相对于流动方向旋转的仪器化 3D 块体模具，以研究不连续方向对块体侵蚀性的影响。正如预期的那样，发现块可蚀性阈值高度依赖于流向。这可归因于与下游方向上的块体模具几何形状以及通道底部上方的块体突出的相对轮廓相关的运动学约束的变化。观察到三种独立的块响应类型，它们与块运动阻力密切相关。由无量纲平均动态压力系数 Cp 表示的压力值被确定为块模具取向、湍流强度、块突出高度和流速的函数。总体而言，块体表面上的平均动水压力足以满足评估模型块体稳定性的要求。因此，本文提供的数据可以应用于各种流动条件。还开发了基于可靠性的块体理论框架，用于在给定与岩石冲刷过程中的固有变化性相关的参数不确定性的情况下评估3D块体可蚀性。块理论提供了严格的分析方法来识别可拆卸块、确定潜在故障模式并评估 3D 块稳定性。使用块理论极限平衡和运动学约束方程以伪静态方式评估块稳定性。块体侵蚀阈值的理论预测与高湍流和低湍流水力模型测试获得的预测结果非常吻合。当使用移动关节摩擦角时，在某些情况下观察到了改进的预测。通过对北加州现场的两个示例分析，证明了基于可靠性的块理论方法的适用性。对溢洪道中的可移除块进行了识别和确定性分析，以确定其侵蚀阈值。基于激光雷达数据集的统计分析，包括岩体参数的变异性，以计算具有最低侵蚀阈值的块体的破坏概率。参数重要性的 FORM 分析表明，块体突出高度、其次是岩石节理方向和流速是对块体稳定性影响最大的变量，而节理摩擦角相对较小。从设计角度来看，该方法的好处是可以将 3D、特定地点的地质结构信息纳入岩体可蚀性评估中。场地参数的变化可以通过概率的方式来解决，以对最容易受到侵蚀的位置进行分类，并确定影响岩块稳定性的最有影响力的变量。这可以导致更有效的冲刷修复设计以及更集中的现场和实验室工作来研究对系统影响最大的参数。此外，可靠性数据对于设计者和基础设施所有者在特定站点的决策和风险管理方面非常有用。
Author(s): George, Michael Freeman | Advisor(s): Sitar, Nicholas | Abstract: Abstract3D BLOCK ERODIBILITY: DYNAMICS OF ROCK-WATER INTERACTIONIN ROCK SCOURbyMichael Freeman GeorgeDoctor of Philosophy in Engineering – Civil a Environmental EngineeringUNIVERSITY OF CALIFORNIA at BERKELEYProfessor Nicholas Sitar, ChairErosion of rock by flowing water is an integral process in the evolution of natural landscapes as well as a critical hazard for key infrastructure such as dams, spillways, bridges and tunnels. The removal of individual blocks of rock is one of the primary mechanisms by which rock scour can occur. This research examined the influence of 3D geologic structure on erodibility of rock blocks with the aim to understand the basic mechanics of the process as well as to develop a predictive framework for block erodibility. To do this, a multifaceted research program was established. Field investigation of a prototype site in the Sierra Nevada Mountains in northern California was used as a basis for the development of an extensive series of hydraulic model experiments, which were complemented by theoretical deterministic and stochastic analyses based on 3D block theory.Past experimental studies have been limited to simplified cubic or rectangular block geometries in laboratory settings, with very little data regarding hydrodynamic pressures surrounding 3D blocks and subsequent block response to hydrodynamic loading. For more complex block shapes (as often found in nature), such simplifications in geometry can be problematic as the 3D orientation of discontinuities within the rock mass largely influence block removability, kinematics and stability. Accordingly, a major focus of this research was to obtain a high resolution experimental data set from both field and laboratory settings for hydraulic and rock mass parameters pertaining to 3D non-cubic block geometries.Field work was carried out in a prototype setting at an actively eroding unlined rock spillway at a dam site in northern California. High resolution rock mass data was obtained using light detection and ranging (LiDAR) scanning which permitted statistical characterization of rock mass parameter variability for use in a probabilistic scour prediction model. Two instrumented artificial rock block were cast in existing block molds to capture hydrodynamic pressures and block displacements during spill events. Climatic conditions in northern California, however, prevented reservoir discharges on the blocks such that no data to date have been collected.A scaled physical hydraulic model, loosely representing conditions at the above field site was also performed. The advantage of the laboratory model was the ability to investigate a broad range of variables and flow conditions not readily achievable in a field setting. For the model, an instrumented 3D block mold was constructed that could be rotated with respect to the flow direction to study the influence of discontinuity orientation on block erodibility. As would be expected, the block erodibility threshold was found to be highly dependent on the flow direction. This can be attributed to changes in kinematic constraints associated with the block mold geometry in the downstream direction as well as the relative profile of block protrusion above the channel bottom. Three separate block response types were observed which are closely associated with block kinematic resistance. Pressure values, represented by the dimensionless average dynamic pressure coefficient, Cp, were determined as a function of the block mold orientation, turbulence intensity, block protrusion height, and flow velocity. Overall, the average hydrodynamic pressures on block faces were found to be adequate in the evaluation model block stability. Accordingly, the data presented herein may be applied to a variety of flow conditions.A reliability-based, block theory framework was also developed for evaluation of 3D block erodibility given parameter uncertainty associated with the inherent variability within the rock scour process. Block theory provides a rigorous analytical methodology to identify removable blocks, determine potential failure modes, and assess 3D block stability. Block stability is evaluated in a pseudo-static manner using block theory limit equilibrium and kinematic constraint equations. Theoretical predictions for block erodibility threshold compare well with those obtained from hydraulic model testing for both high and low turbulence flows. Improved prediction was observed for some cases when a mobilized joint friction angle was used.Applicability of the reliability-based, block theory methodology was demonstrated through two example analyses for the field site in northern California. Removable blocks from the spillway channel were identified and analyzed deterministically to determine their erodibility threshold. Variability in rock mass parameters was included based on statistical analysis of the LiDAR data set to calculate the failure probability of the block with the lowest erodibility threshold. FORM analysis for parameter importance indicates block protrusion height, followed by rock joint orientations and flow velocity, are the most influential variables on block stability, while joint friction angle is relatively insignificant.From a design standpoint, the benefit of the proposed methodology is that 3D, site-specific geologic structure information can be incorporated into evaluation of rock mass erodibility. Variability in site parameters can be addressed in a probabilistic manner to classify locations most susceptible to erosion as well as identify the most influential variables affecting rock block stability. This can lead to more efficient scour remediation designs as well as more focused field and laboratory efforts to investigate parameters with the most impact on the system. Furthermore, reliability data can be useful for designers and infrastructure owners in decision making and management of risk at a specific site.