Collaborative Research: Evaluation of 2D vs 3D Multielectrode Resistivity for the Characterization of Shallow Karst

CMS-0201015PI: Mary RothInstitution: Lafayette college标题：“合作研究：浅岩溶特征的2D vs 3D多电极电阻率评估”在可溶基岩（如石灰岩和白云岩）地区的天坑是施工期间成本超支和结构失效的原因之一。这些地区占美国的15%，自1975年以来，宾夕法尼亚州中东部因地陷造成的损失估计超过3000万美元。这些问题的发生频率可以通过改进定位引起天坑的地下空洞的方法来降低。二维地电阻率测试已被证明是有用的，但由于假设了二维几何形状，这种方法确定孔隙大小和方向的能力有限。二维电阻率线附近和直线下方的特征会影响结果。三维电阻率测试耗时，除非使用数千个电极，否则无法为岩土工程调查提供足够的细节。在本项目中，通过比较两种现场方法，改进了电阻率数据的解释。第一种方法将多条二维电阻率线合并到三维模型中。第二种方法是从多个较小的、重叠的3D调查中开发大型3D数据集。这两种方法都应该能够通过从实际数量的电极收集的数据中开发3D电阻率模型来确定空洞的几何形状。为了验证这些方法，绘制了一个天然地下洞穴的几何图形，并将洞穴上的电阻率结果与实际洞穴几何图形进行了比较。这项计划将有助改善天坑地区的调查策略。应该注意到这个项目的另外两个特点。首先，该项目是在其他研究人员使用过的地点进行的。对现场条件的进一步描述将鼓励更多的合作，以测试新的调查方法。其次，该项目涉及本科院校与研究生院校的合作。这种合作将鼓励学生获得研究生教育。

CMS-0201015PI: Mary RothInstitution: Lafayette CollegeTitle: "Collaborative Research: Evaluation of 2D vs 3D Multielectrode Resistivity for the Characterization of Shallow Karst"Sinkholes in areas with soluble bedrock (e.g., limestone and dolomite) are a cause of cost overruns during construction and of structural failures. These areas can be found in 15% of the United States and estimated costs of failures caused by sinkholes in eastern central Pennsylvania since 1975 exceed 30 million dollars. The frequency of these problems can be reduced by improving methods for locating subsurface voids that cause sinkholes. Two-dimensional earth-resistivity testing has been demonstrated to be useful, but because 2D geometry is assumed, this method has limited ability to determine void size and orientation. Features adjacent to the 2D resistivity line and directly below the line affect the results. Three-dimensional resistivity tests are time-consuming and do not provide sufficient detail for geotechnical investigations unless thousands of electrodes are used.In this project, interpretation of resistivity data is being improved by comparing two field methods. The first method incorporates multiple 2D resistivity lines into three-dimensional models. The second method develops large 3D data sets from multiple smaller, overlapping 3D surveys. Both approaches should be able to determine void geometry by developing a 3D resistivity model from data collected with a practical number of electrodes. To test the methods, the geometry of a natural subsurface cave is being mapped and resistivity results over the cave are compared to actual cave geometry. The project will result in an improved investigation strategy for sites located in sinkhole areas. Two additional features of this project should be noted. First, the project is being conducted at a site that has been used by other researchers. Further characterization of the conditions at the site will encourage additional collaboration to test new investigation methods. Second, the project involves collaboration of an undergraduate institution with a graduate institution. Such collaboration will encourage students to obtain post-graduate education.