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

CMS-0201015PI：Mary RothInstitution：Lafayette CollegeTitle：“合作研究：用于表征浅层岩溶的2D和3D多电极电阻率的评估”具有可溶基岩的地区(如石灰岩和白云岩)中的空洞是施工期间成本超支和结构故障的原因。这些地区覆盖了美国15%的地区，自1975年以来，宾夕法尼亚州中东部的天坑造成的破坏估计损失超过3000万美元。这些问题的出现频率可以通过改进定位引起天坑的地下空洞的方法来减少。二维地电阻率测试已被证明是有用的，但由于假设为二维几何，该方法在确定空洞大小和取向方面的能力有限。与二维电阻率线相邻且位于该线正下方的要素会影响结果。三维电阻率测试非常耗时，除非使用数千个电极，否则无法为岩土勘察提供足够的细节。在这个项目中，通过比较两种现场方法来改进对电阻率数据的解释。第一种方法将多条2D电阻率线合并到三维模型中。第二种方法从多个较小的、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建立3D电阻率模型来确定空洞的几何形状。为了测试这些方法，正在绘制一个天然地下洞穴的几何图形，并将该洞穴上方的电阻率结果与实际的洞穴几何形状进行比较。该项目将改进对位于天坑区域的地点的调查战略。应该注意到这个项目的两个附加功能。首先，该项目是在一个已经被其他研究人员使用的地点进行的。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，该项目涉及本科生机构和研究生机构的合作。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.