Evaluation of trenching, ground penetrating radar (GPR) and electrical resistivity tomography (ERT) for sinkhole characterization

Abstract

This paper explores the suitability and advantages of combining the trenching technique with geophysical surveys [ground penetrating radar (GPR) and electrical resistivity tomography (ERT)] for sinkhole characterization in a mantled karst area. The approach is applied to two active sinkholes concealed by anthropogenic deposits and formed by contrasting subsidence mechanisms; collapse and sagging. The ERT section acquired across the collapse sinkhole images the clayey fill of the depression as an obvious low resistivity area, showing the approximate location of the sinkhole edges. Spatially dense GPR surveys provide information on the position of the boundaries of the concealed subsidence structures and their three‐dimensional (3D) internal geometry, revealing the dominant subsidence mechanism. We illustrate the impact of several factors on the quality of the GPR data such as sinkhole size, nominal frequency of the antennas, antenna shielding, and the presence of backfilled excavations and above‐surface objects. Trenches provided detailed information on the subsurface structure of the sinkhole, subsidence magnitude, partitioning of the strain, and the position of the sinkhole edges, especially when they are deep enough and excavated across the central sector and perpendicular to the boundaries. The stratigraphic and structural relationships observed in the trench were then used to infer the spatial evolution of the sinkholes (e.g. enlargement), their kinematic behavior (episodic versus progressive), and to differentiate discrete subsidence events and their associated magnitude. Numerical dates were used to estimate average subsidence rates and the recurrence of subsidence events. Such integrated data sets may be used as an objective basis to forecast the future behavior of potentially damaging sinkholes and to assess the associated hazard and risk. Copyright © 2013 John Wiley & Sons, Ltd.

The application of GPR and ERI in combination with exposure logging and retrodeformation analysis to characterize sinkholes and reconstruct their impact on fluvial sedimentation

“…GPR systems encompass a transmitting antenna that generates electromagnetic (EM) radio waves (typically in the 25 to 2000 MHz frequency range) that travel through the subsurface, a receiver antenna that captures the reflected EM wave signals, and a control unit that digitally records the time delay and strength of the signal. Carbonel et al, 2014Carbonel et al, , 2015Rodríguez et al, 2014). Wave reflections are related to changes in the EM impedance due to variations in the physical properties of the subsurface material (i.e.…”

“…The most common configuration consists in actively transmitting an electrical current pulse through electrodes, galvanic-coupled to the ground, while the potential induced to the ground is recorded at specific locations in other electrodes according to a specific array. Therefore, ERI and GPR can provide complementary results for sinkhole investigation (Kruse et al, 2006;Carbonel et al, 2014Carbonel et al, , 2015De Giorgi and Leucci, 2014). Since deformation structures (e.g.…”

“…Gutiérrez et al, 2014). An essential aspect for effective risk mitigation is the precise mapping and characterization of the existing sinkholes, since damage is frequently related to concealed karst depressions buried by natural or man-made deposits Carbonel et al, 2014Carbonel et al, , 2015. Most investigations dealing with sinkhole characterization using subsurface methods have focussed on collapse sinkholes underlain by cavernous carbonate bedrock, and utilize near-surface geophysical methods in combination with geotechnical boreholes (van Schoor, 2002;Zhou et al, 2002;Kruse et al, 2006;Valois et al, 2011;Festa et al, 2012;Nouioua et al, 2013;Youssef et al, 2013).…”

Investigation of suspected gulls in the Jurassic limestone strata of the Cotswold Hills, Gloucestershire, England using electrical resistivity tomography

“…Carbonel et al, 2014;Rodríguez et al, 2014) and, in comparison to ERT, provides faster data acquisition and thus smaller cost. However, its investigation depth is constrained by the resistivity of the investigated formation, where lower resistivities lead to lower penetration depths.…”

Facing Engineering Problems in the Fragile Karst Environment

“…An essential step, regardless of the mitigation strategy, is the construction of comprehensive sinkhole inventories and a detailed characterization of the critical sinkholes. The latter typically require the combination of multiple techniques such as geomorphological mapping, geodetic measurements like InSAR, geophysical exploration, drilling, trenching (Carbonel et al 2013), stability analyses. In areas with abundant data, there is the possibility of quantitatively developing and evaluating sinkhole susceptibility and hazard models, which provide an assessment of the probability of occurrence of new sinkholes in each portion of the territory (Galve et al 2012).…”