EAGER: Deformation Induced Soil Fracturing - Multi-Scale Multi-Physics Mechanism and Early Detection

这个早期概念探索性研究奖助金(AGIRE)项目研究了土体因地面沉降、山体滑坡或地震而沉降和变形时在土壤中发展的多尺度和多物理过程的基础科学。它为一种新的土壤破裂理论模型寻找实验证据。然后，这些发现将被用于开发一种现场监测工具，提供土壤破裂的早期预警。该项目特别利用岩土工程中的以下两个问题作为基于案例的研究的一部分。第一个问题与美国许多地区普遍存在的地下水开采引起的地面沉降有关。例如，在加利福尼亚州的圣华金河谷，超过一半的山谷下沉超过0.3米；据报道，一些地区下沉10米，下沉速度超过0.3米/年。当地下水开采井附近发生差异压实和局部地质变化时，可能会在周围的地面上产生裂缝。这种地面沉降引起的断裂带可能宽达200m，由多个平行的分支裂隙和地块组成。据报道，这些功能对关键的已建基础设施造成了数十亿美元的损失。然而，目前还没有能够有效地对土壤裂缝发育进行预警的监测技术。第二个问题与为降低洪水风险而修建的河堤深防渗墙可能因地震造成的破坏有关。例如，加利福尼亚州的大萨克拉门托地区是美国灾难性洪灾风险最高的地区之一。该地区依赖于老化的堤坝系统，目前正在进行大规模的堤防改造。一个典型的改进措施包括安装深防渗墙和额外的填充物来抬高堤坝，以减轻堤坝的渗漏破坏。在地震期间，由于堤防系统变形，这些墙可能会有破裂的危险。因此，在未来的洪水事件中控制渗漏的能力可能会丧失。同样，需要一个预警监测系统来评估在运营期间发生这种土壤破裂的风险。当土壤破裂发生时，它可能是局部性的和规模相关的，因此很难预测破坏的位置。土壤破裂过程中的这种不确定性可能会导致重大的工程问题，任何提供早期检测的监测技术都是必要的。为了改变我们对土壤破裂过程的基本认识，需要实验证据来支持新的理论模型和工具来在现场测量它。本项目旨在探索变形引起的土体裂隙萌生和扩展过程中发生的多物理、多尺度土-孔隙水相互作用的实验证据，并论证高分辨率分布式光纤应变传感技术检测土体破裂早期特征的可行性。该项目的主要目标是(I)检验在变形引起的土壤裂缝萌生和扩展过程中发生的多物理和多尺度土壤-孔隙水相互作用的实验证据，以及(Ii)论证高分辨率分布式光纤应变传感技术用于检测土壤破裂的早期特征的可行性。在本工程中，将在土梁试件上进行一系列的抗弯试验，在试件中埋入微型孔压传感器和光纤传感电缆。该项目将研究土体裂缝萌生和扩展过程中超孔压的产生和消散。假设高分辨率分布式光纤应变传感技术能够捕捉到断裂过程区内不同微观尺度的破坏模式。将研究该技术用于基于现场的土壤破裂早期预警系统的可行性。

This EArly-concept Grant for Exploratory Research (EAGER) project investigates the fundamental science of multi-scale and multi-physics processes of fractures that develop in soil while a soil mass is settling and deforming due to land subsidence, landslides or earthquakes. It seeks experimental evidence of a new theoretical model of soil fracturing. The findings will then be used to develop a field monitoring tool that provides early warning of soil fracturing. The project specifically utilizes the following two problems in geotechnical engineering as part of a case scenario-based study. The first problem is related to land subsidence induced by groundwater extraction that is prevalent in many areas of the United States. For example, in the San Joaquin Valley, California, more than half of the valley has subsided in excess of 0.3m; subsidence of 10 m and a rate of more than 0.3m/year has been reported in some areas. When differential compaction occurs near groundwater extraction wells and local variations in geology, cracks may develop in the surrounding ground. Such land subsidence induced fracture zones may be as much as 200 m wide and consist of multiple parallel, branching fissures and graben blocks. These features are reported to cause billions of dollars of damage to critical built infrastructure. However, monitoring technology that effectively gives early warning to soil fracture development is not available at present. The second problem is related to possible earthquake-induced damage of deep cut-off walls used in river levees that are constructed to reduce its flood risk. For example, the Greater Sacramento area in California is among the most at-risk regions in America for catastrophic flooding. The area relies on an aging system of levees, and massive levee improvements are currently underway. A typical improvement involves installation of deep cut off walls with additional fill to raise the levee in order to mitigate under-seepage failure of the levees. During an earthquake, the walls can be at risk of fracturing as the levee system deforms. As a consequence, the ability to control seepage in a future flooding event may be lost. Again, an early warning monitoring system is needed to assess the risk of such soil fractures during the lifetime of operation.When soil fracture occurs, it is likely to be localized and scale-dependent and therefore the locations of the failure will be difficult to predict. This uncertainty in the soil fracturing process can potentially lead to significant engineering issues and any monitoring technology that provides early detection is needed. To make a step change in our fundamental understanding of soil fracturing process, experimental evidence that supports new theoretical models and tools to measure it in the field are required. This project aims to explore for the experimental evidence of multi-physics and multi-scale soil-pore water interaction occurring during deformation induced soil fracture initiation and propagation and to demonstrate the feasibility of high resolution distributed fiber optic strain sensing technology for detecting an early signature of soil fracturing. The primary goals of the project are (i) test for experimental evidence of multi-physics and multi-scale soil-pore water interaction occurring during deformation induced soil fracture initiation and propagation, and (ii) to demonstrate the feasibility of high resolution distributed fiber optic strain sensing technology for detecting an early signature of soil fracturing. In this project, a series of flexural tests will be performed on soil beam specimens, in which miniature pore pressure transducers and fiber optic sensing cables will be embedded. The project will investigate the excess pore pressure generation and dissipation during the soil fracture initiation and propagation process. It is hypothesized that different micro-scale failure modes inside a fracture process zone would be captured by high resolution distributed fiber optic strain sensing technology. The feasibility of the technology for a field-based early warning system against soil fracturing will be examined.