Real-Time Measurement of Shear Zone Development in Soil Models Using Time Domain Reflectometry

*9908342穿孔这项研究的目标是开发一种基于时域反射仪(TDR)的方法，实时检测和测量土壤结构离心机模型中的内部剪切带的发展。TDR类似于雷达，因为电压沿着同轴电缆脉冲，以检测电磁故障。当电缆埋入变形的地质材料中时，电缆会剪切并反射一小部分电压。在试验过程中测量内部剪切区发展的能力将提供一个强有力的工具来研究在各种载荷条件下土体的行为。它还将允许对物理模型行为与数值预测进行比目前可能的更全面的比较。通过对超固结粘土边坡的模拟，展示了内部剪切带发育的实时测量的优势。先前对超固结粘土边坡的离心机研究表明，突然的破坏涉及到沿不同的破坏表面的块状运动。除了该项目的仪器方面提供的好处外，研究人员还将评估颗粒大小、土壤抗剪强度和硬度以及灌浆对土壤TDR测量的影响。最后，这项工作的结果将有助于TDR在土壤中的现场应用。该项目分为四个主要任务：1)TDR仪器的开发；2)实验室可行性测试；3)离心机开发测试；以及4)超固结粘土斜坡的离心机模拟。在第一项任务中，研究人员将使用改进的直接剪切仪来确定土壤颗粒大小、土壤强度和灌浆包覆对使用不同TDR电缆进行剪切位移测量的影响。在第二项任务中，调查人员将进行小型和大型承载能力模型试验，以评估TDR探测多个剪切带的能力、数据的质量和重复性，以及选定电缆在这些条件下的稳健性。在第三项任务中，将在佛罗里达大学使用一台半径为1.85米、最大加速度为100克、最大有效载荷约为70公斤的土工离心机进行承载能力测试，以证明TDR系统在非离心机环境中工作的能力。将评估TDR测量的准确性和可靠性，并将离心机结果与大规模精细测试进行比较。最后一项任务是利用新的仪器来评估超固结边坡的内部剪切发展。在超固结的黏土斜坡上，我们会进行长期和短期的测试，而这些斜坡均装有TDR电缆和LVDT仪器。目标是确定内部剪切位移是否在破坏之前发生；是否可以在地表移动之前检测到剪切位移；以及这些位移的位置与斜坡的内部应力状态之间的关系。

***9908342PierceThe objective of this research is to develop a time domain reflectometry(TDR)-based method of detecting and measuring, in real-time, the development ofinternal shear zones within centrifuge models of soil structures. TDR isanalogous to radar in that voltage is pulsed along a coaxial cable to detectelectromagnetic faults. When a cable is embedded in a deforming geologicmaterial, the cable shears and reflects a small percentage of voltage. Theability to measure internal shear zone development during testing will providea powerful tool to investigate the behavior of soil subjected to a wide varietyof loading conditions. It will also allow more comprehensive comparisons ofphysical model behavior to numerical predictions than currently possible. Theadvantages of real-time measurement of internal shear zone development will bedemonstrated through the modeling of overconsolidated clay slopes. Priorcentrifuge studies of overconsolidated clay slopes have shown that suddenfailures involve block-type motion along a distinct failure surface. Inaddition to the benefits provided by the instrumentation aspects of thisproject, the investigators will evaluate the effects of grain size, soil shearstrength and stiffness, and the use of grout on TDR measurements in soil. Finally, the results of this work will aid in the development of field use ofTDR in soils.The project is divided into four main tasks: 1) TDR instrumentationdevelopment; 2) laboratory feasibility testing; 3) centrifuge developmenttesting; and 4) centrifuge modeling of overconsolidated clay slopes. In thefirst task, the investigators will use a modified direct shear device todetermine the effects of soil grain size, soil strength and grout encapsulationon shear displacement measurements using different TDR cables. In the secondtask, the investigators will conduct small- and large-scale bearing capacitymodel tests to evaluate the ability of TDR to detect multiple shear zones, thequality and reproducibility of the data, and the robustness of selected cablesunder these conditions. In the third task, bearing capacity tests will beconducted at the University of Florida using a geotechnical centrifuge with aradius of 1.85m, a maximum acceleration of 100g and a maximum payload ofapproximately 70kg to demonstrate the ability of the TDR system to work in acentrifuge environment. The accuracy and reliability of TDR measurements willbe evaluated and centrifuge results will be compared to the large-scalelaboratory tests. The final task utilizes the new instrumentation to evaluateinternal shear development in overconsolidated slopes. Long-term andshort-term tests on overconsolidated clay slopes instrumented with TDR cablesand LVDTs will be conducted. The objectives are to determine if internal sheardisplacements occur prior to failure; if shear displacements can be detectedprior to surface movement; and how the location of these displacements relatesto the internal stress-state of the slopes.***