Effective electrode array in mapping karst hazards in electrical resistivity tomography

Abstract

When conducting environmental and engineering investigations in karst terranes, engineers and geologists often supplement exploratory borehole results with data gathered from surface geophysics to reduce the site-characterization cost and establish the most useful locations for borings or samples. When conducting resistivity investigations, a frequently occurring problem is the need to determine which of the many existing electrode configurations will respond best to the material changes in karst features. Each array has its advantages and disadvantages in terms of depth of investigation, sensitivity to horizontal or vertical variations, and signal strength. In the application presented in this paper, numerical forward modeling was conducted of dipole-dipole, Schlumberger, and Wenner arrays, and they produced markedly different anomaly shapes for a conceptual model of the development of a cover-collapse sinkhole. The resolution of the three above-mentioned arrays was further evaluated along a section of I-70 near Frederick, Maryland, where a sinkhole had occurred in the median of the highway. The image from the dipole-dipole array appeared to be better than those from the Wenner and Schlumerger arrays in displaying the sinkhole collapse area. However, they are all less effective than a mixed array, in which apparent resistivities from all the three arrays are combined and processed together in the model. Because the mixed array requires a significant increase in data collection, the dipole-dipole array appears to be the most effective and less costly configuration in mapping karst hazards areas. This conclusion was then confirmed by two case studies.

A Comparison of Self-Potential Tomography with Electrical Resistivity Tomography for the Detection of Abandoned Mineshafts

“…ERT is an established technique for environmental and engineering site investigation (Ogilvy et al, 1999;Chambers et al, 2002;Dahlin et al, 2002;Zhou et al, 2002). Specifically, it has been used to survey for uncharted mine galleries (Maillol et al, 1999) and subsurface cavities (van Schoor, 2002).…”

Electrical Resistivity Imaging of Suspected Seepage Channels in an Earthen Dam in Zaria, North-Western Nigeria

“…It is always necessary to consider further exploratory geophysical results gathered from the surface with borehole log data. This is to reduce the site characterization cost and establish the most useful locations for geological or geotechnical samples [21]. The results obtained based on 2D inversion of field data and borehole information, were interpreted to determine the depth and extent of shallow bedrock, thickness of overburden, aquifer etc.…”

“…To determine the resistivity distribution from measurements of potential differences is a non unique problem and its numerical solution is unstable: small variations in the data can cause large variations in the solution. Commonly used inversion methods provide unique and stable solutions by introducing the appropriate stabilizing function [21]. The main aim of the stabilizer is to incorporate a priori knowledge in the inversion process.…”

Determination of cavities using electrical resistivity tomography

“…Each of these parameters is related to one or more physical properties of the subsurface and to their spatial distribution (Chalikakis et al, 2011). For this type of problem, electrical resistivity tomography (ERT), is a popular choice due to the low costs of the survey and the high resistivity contrast that exists between the air-filled cavity and the surrounding formation (Van Schoor, 2002;Zhou et al, 2002). The cavities can be also partially or completely water-filled and, depending on the composition of the water, can have a resulting electrical conductivity ranging from very conductive to relatively resistive, compared to the host rock (Chalikakis et al, 2011).…”

“…A frequently occurring problem with ERT is the need to determine which of the many existing electrode configurations will respond best to the material changes. Each array has distinctive advantages and disadvantages in terms of depth of investigation, sensitivity to horizontal or vertical variations, and signal strength (Loke, 1997;Zhou et al, 2002). Comparison of the responses of dipole-dipole (DD), Wenner alpha (WA), Schlumberger (SCH), combined pole-dipole (CPD) electrode arrays have been computed using the 2D finite difference method and discussed in this paper.…”