Limestone Cave Collapse Evolution As an Analog for Long-Term Rock Behavior

长期岩石行为对于理解岩石边坡、地下开挖、大坝和桥梁基础、国家纪念碑和其他关键岩石结构的退化和破坏非常重要。天然地下洞穴是研究长期岩石行为的理想地质模拟，因为气候相对稳定，并且数千年来积累在洞穴底部的岩崩保存完好。 在这项研究中，岩石退化和故障在亚利桑那州南部的Kartchner洞穴的演变将进行调查，使用放射性测年和国家的最先进的地质力学技术的独特组合。 首先，为了确定过去10万年来洞穴中发生的岩崩的演变，将使用U-TH和碳测年法。 由于Kartchner是一个活的洞穴，许多落石块上都有洞穴沉积物，因此将在这些洞穴沉积物的底部采集小岩芯进行测年。 其次，新一代地面激光雷达扫描仪将用于获得洞穴几何形状和洞穴底部落石碎片的详细三维点云。 详细的点云沿着辐射数据将用于重建过去10万年的洞穴几何形状。最后，将使用Abaqus有限元程序进行三维建模。将在Abaqus中实施基于亚临界裂纹扩展的随时间变化的损伤模型，以模拟洞穴塌陷演变。由于亚利桑那州南部容易受到小到中等水平的地震灾害，因此也将考虑洞穴的地震荷载。Kartchner洞穴提供了了解长期岩石行为的独特机会，其结果应该引起岩石力学科学家和工程师以及岩溶和洞穴专家的极大兴趣。 这项研究的结果将用于开发和验证长期强度模型或亚临界裂纹扩展模型，以正确预测长期岩石行为。 Kartchner洞穴也是向公众传达地质力学的理想平台，公众可以进入2.4英里的通道，每年吸引超过15万游客。 作为这项研究的一部分，将在Kartchner游客中心建立一个互动的地质力学展示柜，洞穴导游将在他们的日常图尔斯旅游中提供地质力学信息。 本研究的结果将有望在洞穴破裂和天坑发育方面提供新的发现。 这项研究的结果可能会揭示过去的地震事件在亚利桑那州南部的时间，因此将感兴趣的地震学家和地质学家研究第四纪断层。

Long-term rock behavior is important for understanding the degradation and failure of rock slopes, underground excavations, dam and bridge foundations, national monuments, and other critical rock structures. Natural underground caverns are an ideal geologic analog for studying long-term rock behavior, because of the relatively constant climate and the preservation of rockfalls that accumulate on the floor of the cave over thousands of years. In this study, the evolution of rock degradation and failure in the Kartchner caverns in southern Arizona will be investigated, using a unique combination of radiometric dating and state-of-the-art geomechanics techniques. First of all, to date the evolution of rockfall that has occurred in the cave over the last 100,000 years, both U-TH and Carbon dating will be used. Because Kartchner is a live cave, speleothems occur on many of the rockfall blocks, and small cores will be taken at the base of these speleothems for dating. Secondly, a new generation ground-based LIDAR scanner will be used to obtain detailed three-dimensional point clouds of the cavern geometry and also of the rockfall fragments on the floor of the cave. The detailed point clouds along with the radiometric data will be used to reconstruct the cave geometry over the past 100,000 years. Finally, three-dimensional modeling will be conducted using the Abaqus finite element program. A time-dependent damage model based on subcritical crack growth will be implemented in Abaqus to simulate cave collapse evolution. Seismic loading of the cave will also be considered, since southern Arizona is susceptible to small to medium levels of seismic hazard.Kartchner caverns provides a unique opportunity to understand long-term rock behavior, and the results should be of great interest to rock mechanics scientists and engineers as well as karst and cave specialists. The results of this research will be used to develop and validate long-term strength models or subcritical crack growth models to correctly predict long-term rock behavior. Kartchner caverns is also an ideal platform to communicate geomechanics to the general public, with public access to 2.4 miles of passages and attracting over 150,000 visitors each year. As part of this research, an interactive geomechanics display case will be established in the Kartchner visitor center, and cave tour guides will provide geomechanics information on their daily tours. The results of this research will hopefully provide new findings in the areas of cave breakdown and sinkhole development. The results of this research might reveal the timing of past seismic events in southern Arizona, and therefore will be of interest to seismologists and also geologists studying Quaternary faulting.