Geotechnical Site Characterization with 3-D Seismic Waveform Tomography

不可预料的场地条件，如具有嵌入的低速异常(软土或空洞)的高度可变的土壤和岩层，在基础施工期间和之后会造成严重的问题。了解这些异常情况至关重要，因为这些异常情况可能导致结构损坏或坍塌，从而导致重大财产损失和偶尔的生命损失。该奖项支持基础研究，以提供量化嵌入异常所需的知识，并以高分辨率表征不同的土壤/岩层。这项研究的结果将加速经济和实际地实施创新的无损检测(NDT)方法，以保护和改善我国的基础设施。开发的分析可用于从毫米到数百米的不同尺度的材料成像和表征，用于几个工程应用，如评估岩土地下场地条件、桥梁基础冲刷、混凝土结构组件和沥青路面。这项研究的目的是从地面地震波场中获得三维地下结构在米级尺度上的横波(S波)和纵波(P波)速度剖面特征。地下结构由土壤、岩石和由空气或水填充的空隙组成。为了实现这一目标，这项研究将包括：(I)发展地震波场的三维全波形反演(3D-FWI)分析，以高分辨率(米像素)表征地下场地条件；(Ii)通过全尺度野外实验验证三维全波形反演分析。由于地震波的传播特性受到异常和地层界面的调制，因此将使用完整的地震面波场来量化埋藏的异常并表征不同的土壤/岩层。地震波场是利用地面均匀二维网格上的传感器和震源通过地球物理测试获得的，然后进行反演以提取三维地下波速结构。这项研究将解决小尺度层析成像的固有问题，包括瑞雷波分量占优势、波激励不一致、衰减强、先验信息差以及近地表土壤/岩石高度可变。利用测量的波形数据中包含的全部信息，FWI分析有望提供比目前实践中使用的方法更详细和准确的材料表征，后者只使用部分测量数据。这将在工程地球物理领域产生新的知识，这是朝着使用有效的地球物理方法进行现场勘察以改进基础和其他岩土结构设计的关键一步。

Unanticipated site conditions such as highly variable soil and rock layers with embedded low-velocity anomalies (soft soils or voids) cause significant problems during and after construction of foundations. Knowledge of the anomalies is crucial, as the anomalies can cause structural damage or collapse that can result in significant property damage and occasional loss of life. This award supports fundamental research to provide the knowledge needed to quantify embedded anomalies and characterize variable soil/rock layers at high resolutions. Results from this research will accelerate economical and practical implementation of innovative non-destructive testing (NDT) methods for protecting and improving our nation's infrastructure. The developed analysis can be used for material imaging and characterization at various scales from millimeters to hundreds of meters for several engineering applications such as evaluation of geotechnical subsurface site conditions, bridge foundation scour, concrete structural components, and asphalt pavements. The goal of this research is to characterize both shear wave (S-wave) and compression wave (P-wave) velocity profiles of 3-D subsurface structures at meter scales down to 30 meter depth from surface-based seismic wave fields. The subsurface structures consist of soil, rock, and voids filled by air or water. To achieve the goal, the research will include (i) to develop a three-dimensional full waveform inversion (3-D FWI) analysis of seismic wave fields for high-resolution (meter pixel) characterization of subsurface site conditions, and (ii) to verify the 3-D FWI analysis by full scale field experiments. Full seismic surface wave fields will be used to quantify embedded anomalies and characterize variable soil/rock layers, as the propagation properties of seismic waves are modulated by the anomalies and layer interfaces. The seismic wave fields are acquired from geophysical testing using sensors and sources located in uniform 2-D grids on the ground surface, and then inverted for the extraction of 3-D subsurface wave velocity structures. The research will address inherent issues of small scale tomography including dominant Rayleigh wave components, inconsistent wave excitation, strong attenuation, poor a priori information, and highly variable of near surface soil/rock. Using full information contained in the measured waveform data, the FWI analysis is expected to provide more detailed and accurate characterization of materials than methods currently used in practice, which use only portions of the measured data. This will result in new knowledge in the area of engineering geophysics, and it is a critical step toward using an effective geophysical method for site investigations to improve design of foundations and other geotechnical structures.