L‐ and CORNER‐arrays for 3D electric resistivity tomography: an alternative for geophysical surveys in urban zones

Abstract

Three‐dimensional electric resistivity tomography surveys carried out on heavily urbanized areas represent a cumbersome task since buildings, houses, or other types of obstacles do not allow parallel electric resistivity tomography lines to be deployed. This paper proposes applying any four‐electrode configuration to provide subsurface information in complex urban areas. Such a procedure allows acquiring information beneath a construction by simply surrounding the structure of interest by a series of electric resistivity tomography profiles. Apparent resistivity is obtained from ‘L’‐ and ‘Corner’‐shaped profiles, where alternations between current and potential electrodes are carried out in an automatic way. Four ‘L’‐arrays and four ‘Corner’‐arrays are employed in a square geometry that allows surrounding the studied target to cover the subsurface. The first mentioned array will provide deep information. The second array will cover more of the shallow subsurface information. For the ‘L‐’ and ‘Corner’‐arrays, a mixture of traditional arrays are employed, like the Wenner–Schlumberger, axial, equatorial, azimuthal, and perpendicular dipole arrays. Two synthetic examples are presented to demonstrate the possibilities of the proposed electric arrays. A resistive cube set at the centre of a working cube is modelled. The ‘L‐’ and ‘Corner‐’ arrays are capable to detect such a model; however, dimensions are exaggerated. Later on, an extended wall model is dealt with. Similar results as in the first synthetic example are obtained in terms of geometry and resistivity. However, depth to the top of the wall model is not adequately recovered in comparison with the traditional methodology. Finally, the ‘L’‐ and ‘Corner’‐arrays are applied in an archaeological site named El Pahñu, located in Central Mexico. The new methodology described here is compared with the traditional 3D procedure employing a grid of electric resistivity tomography transects. As expected, the approach discussed in this investigation produced a reasonable solution towards the central portion of the working cube. However, shallow resistive anomalies (size about the electrode interval) were not fully detected, in comparison to a traditional 3D survey, where parallel lines forming a grid could be deployed. The reason is that no electrodes were set towards the central portions of the structure under study. However, the L‐ and Corner‐arrays are more sensitive to anomalies produced by deeper objects, which cannot be observed in the traditional method, especially when objects are located in between the electric resistivity tomography transects.

2D‐ERT Survey for the Identification of Archaeological and Historical Structures beneath the Plaza of Santo Domingo, Mexico City, Mexico

“…These obstacles are reflected in the shallower portion (down to a maximum depth of 2.7 m) of the electrical image (Figure 12), where high and low-resistivity anomalies of small dimensions are detected. In addition, the profile coincided with four concrete injection points (large high-resistivity anomalies below 3 m of depth; anomaly centres at X = 10, 32, 50 and 70 m), derived from the geotechnical engineering works carried out in 2009 to reinforce the soil, provide stability to the temple and stop its deterioration and continuous fracturing caused by processes of differential subsidence (Santoyo, 2010).…”

“…The water in this lake was mostly saline. So, highly water-saturated clay soils are usually found at an average depth of 4 to 6 m (Barrera and Islas, 2013;Santoyo, 2010). The continuous water extraction and drying of the lake have produced several subsidence problems in this region throughout the city's history.…”

“…In the past three decades, the ERT method has been rapidly and successfully developed, particularly after the improvement of automatic devices capable of acquiring large amounts of data (Griffiths and Turnbull, 1985;Tejero-Andrade et al, 2015). Simultaneously, efficient inversion algorithms have also been designed to interpret the collected apparent resistivity data for solving 2D (Loke, 1994) and 3D (Loke and Barker, 1996) tasks.…”

Real-Time Three-Dimensional Imaging of Soil Resistivity for Assessment of Moisture Distribution for Intelligent Irrigation

“…), which can be measured by the same device with the addition of various optional sensors. Although three-dimensional moisture measurements have been conducted previously [21][22][23], the ease of electrode installation and removal is an essential feature of the present device, making it attractive for multi-unit use in the agricultural field. By implementing the described system, farmers can significantly improve the efficiency of agricultural irrigation, leading to more food production with less water.…”

3D assessment of an underground mine pillar by combination of photogrammetric and geoelectric methods

“…Some small artifacts appear in the result in the vicinity of strong working faces (near anomaly A1) and near anomaly A3. Because of the inherent loss of sensitivity in the center of the pillar, the detection capability of A3, as suggested by Tejero-Andrade et al (2015), should be lower. In this study, we assume that the favorable context of our synthetic model facilitates the detection of A3.…”