Assessment of karst activity at highway construction sites using the electrical resistivity method (Greene and Jefferson Counties, Missouri).

668101536Final report.PDFTech ReportOR 07-003KarstResistivity methodPavementsMissouriUniversity of Missouri--Rolla. Center for Infrastructure Engineering StudiesAnderson, Neil L.Apel, Derek B.Ismail, AhmedMissouri. Dept. of TransportationUniversity Transportation Centers Program (U.S.)United States. Dept. of Transportation. Research and Special Programs AdministrationNTL-HIGHWAY/ROAD TRANSPORTATION-Pavement Management and PerformanceNTL-HIGHWAY/ROAD TRANSPORTATION-Construction and MaintenanceUS Transportation CollectionTwo-dimensional (2-D) electrical resistivity data were acquired across and in proximity to active sinkholes at two MissouriDepartment of Transportation (MoDOT) highway-construction sites. Construction site #1 is located in Greene County, Missouri;site #2 is located in Jefferson County, Missouri.Two relatively dense grids (\ue2\u20ac\u1531A\ue2\u20ac? and \ue2\u20ac\u1531B\ue2\u20ac?) of electrical resistivity data were acquired at Greene County site #1 as part of ageotechnical investigation of a proposed interchange. Several active sinkholes with exposed throat diameters on the order of 1.5 fthad been discovered during a routine visual inspection of the site, and the District Geologist decided that a geophysicalinvestigation was warranted prior to routine boring. The primary objective of the electrical resistivity study was to determine ifsubstantive air-filled karstic cavities were present in the subsurface. Secondary objectives were to estimate depth to bedrock andidentify anomalous subsurface conditions that might compromise the integrity of the proposed intersection or complicateconstruction. The electrical resistivity data proved to be of significant utility. Substantive air-filled voids were not imaged on theresistivity profiles. A depth to bedrock structure contour map was generated for the site, and prominent clay-filled and apparentlyinactive karstic cavities were identified beneath segments of proposed new roadway.A relatively dense grid of electrical resistivity data was also acquired at Jefferson County site #2. These electrical resistivity datawere acquired because a previously unmapped, oval-shaped, clay-filled, sinkhole (approximately 50 ft x 35 ft x 15 ft; length xwidth x height) near the centerline of the northbound lanes effectively \ue2\u20ac\u153emptied\ue2\u20ac? overnight after overlying soil had been strippedby earth moving equipment. The supervising geologist authorized the acquisition of the geophysical data in order to image thesubsurface immediately beneath and adjacent to the sinkhole. The primary concern was that the sinkhole was underlain by a largeair-filled cavity. The interpretation of the resistivity data indicated the reactivated sinkhole was not underlain by a substantivecavity. Rather, the soil in the sinkhole appears to have \ue2\u20ac\u153flowed\ue2\u20ac? into the subsurface through solution-widened system of jointsthat do not underlie the sinkhole and probably do not pose a significant risk in terms of catastrophic collapse under load