P.I. Meldrum

British Geological Survey

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O. Kuras

British Geological Survey

Jonathan Chambers

British Geological Survey

Paul Wilkinson

British Geological Survey

R.D. Ogilvy

British Geological Survey

P.B. Wilkinson

British Geological Survey

David Gunn

British Geological Survey

S. Uhlemann

Center for Urban Waters

E. Haslam

British Geological Survey

Russell Swift

British Geological Survey

Arnaud Watlet

University of Mons

Cooperative Institutions

British Geological Survey

Natural Environment Research Council

University of Nottingham

University of Leicester

Loughborough University

Science and Technology on Surface Physics and Chemistry Laboratory

Amrita Vishwa Vidyapeetham

University of Mons

Lawrence Berkeley National Laboratory

University of Almería

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A trial 4D cross-borehole electrical resistivity tomography (ERT) for detecting and monitoring subsurface leakage and contaminant transport, supporting the decommissioning of legacy silor at the Sellafield Site, UK

O. Kuras Paul Wilkinson P.I. Meldrum L. Oxby Sebastian Uhlemann

Nuclear decommissioning

Electrical Resistivity Tomography

Leakage (economics)

Source

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Citations (2)

Tracking the Movements of Electrodes on an Active Landslide over Time Using Only Time-lapse Resistivity Data

Near Surface 2009 - 15th EAGE European Meeting of Environmental and Engineering Geophysics (2010)

P.B. Wilkinson Jonathan Chambers P.I. Meldrum David Gunn O. Kuras

The movements of permanently installed monitoring electrodes on an active landslide will cause artefacts in the resulting resistivity images if their positions are not continuously updated and incorporated in the inversion. In this paper we investigate the effects of electrode movements on time-lapse resistivity tomography using a simple analytical model and real data. The correspondence between this model and the data is sufficiently good to be able to predict the electrode movements with reasonable accuracy. We show that the model can be used to invert the downslope displacements of the electrodes from their original baseline positions using only the time-lapse ratios of the apparent resistivity data. The example datasets are taken from an electrode array on an active lobe of a landslide. We show that the electrode positions can be recovered to an accuracy of 4% of the baseline electrode spacing, which is sufficient to correct the artefacts in the resistivity images. Using a time-lapse sequence of resistivity data, we demonstrate that this technique can be used to track the movement of the landslide over time to the same level of accuracy.

Electrical Resistivity Tomography

Tracking (education)

Electrode array

10.3997/2214-4609.20144815

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Monitoring of Agricultural Hydrodynamics and Investigation of Geophysical Relationships in African Alfisols using Electrical Resistivity Tomography

Russell Swift Jonathan Chambers James Boyd Tongai Mtangadura Elijah Phiri

A full understanding of the moisture regimes in agricultural soils is critical when considering a climatic future that is potentially both drier and hotter. The study of near-surface hydrodynamics necessitates a high temporal frequency of measurements to allow the capture of fast-moving processes. In addition to this, heterogeneities in soils, coupled with spatially variable moisture contents, mean that point sensors alone can miss valuable information when studying soil hydrodynamics.The sensitivity of Electrical Resistivity Tomography (ERT) to soil water content means that it is ideally suited to studying soil hydrodynamics. As a non-invasive technique, it is able to effectively capture spatial heterogeneities, while repeating ERT measurements at short time intervals enables the monitoring of rapid soil moisture changes.In order to study Conservation Agriculture (CA) - an agricultural technique shown to have increased water and heat stress resilience - we collect frequent ERT measurements (&#8804; daily) over a long period of time (> 2 years) using PRIME - a low-cost, low-power, ERT monitoring instrument developed by the British Geological Survey. Our equipment is permanently installed at three agricultural observatories in southern Africa (Malawi, Zimbabwe, and Zambia), and is complemented by many co-located point sensors monitoring soil temperature, water content, and matric potential.We compare the hydrodynamics - derived from ERT data - found under CA, with those under conventional agricultural tillage methods, to better understand the root of CA&#8217;s resilience to hot and dry weather conditions. We use laboratory measurements together with the high number of co-located point sensor measurements to build pedological / geophysical relationships for each site, comparing those derived from laboratory scale samples to those derived from in-field measurements.

Electrical Resistivity Tomography

10.5194/egusphere-egu22-8137

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A linked geomorphological and geophysical modelling methodology applied to an active landslide

Landslides (2021)

James Boyd Jonathan Chambers Paul Wilkinson M. V. Peppa Arnaud Watlet

Abstract Moisture-induced landslides are a global geohazard; mitigating the risk posed by landslides requires an understanding of the hydrological and geological conditions present within a given slope. Recently, numerous geophysical studies have been attempted to characterise slow-moving landslides, with an emphasis on developing geoelectrical methods as a hydrological monitoring tool. However, landslides pose specific challenges for processing geoelectrical data in long-term monitoring contexts as the sensor arrays can move with slope movements. Here we present an approach for processing long-term (over 8 years) geoelectrical monitoring data from an active slow-moving landslide, Hollin Hill, situated in Lias rocks in the southern Howardian Hills, UK. These slope movements distorted the initial setup of the monitoring array and need to be incorporated into a time-lapse resistivity processing workflow to avoid imaging artefacts. We retrospectively sourced seven digital terrain models to inform the topography of our imaging volumes, which were acquired by either Unmanned Aerial Vehicle (UAV)-based photogrammetry or terrestrial laser ranging systems. An irregular grid of wooden pegs was periodically surveyed with a global position system, from which distortions to the terrain model and electrode positions can be modelled with thin plate splines. In order to effectively model the time-series electrical resistivity images, a baseline constraint is applied within the inversion scheme; the result of the study is a time-lapse series of resistivity volumes which also incorporate slope movements. The workflow presented here should be adaptable for other studies focussed on geophysical/geotechnical monitoring of unstable slopes.

Electrical Resistivity Tomography

Geohazard

10.1007/s10346-021-01666-w

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Citations (30)

Capacitive Resistivity Imaging With Towed Arrays

15th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems (2003)

O. Kuras R.D. Ogilvy D. Beamish P.I. Meldrum C. Paul Nathanail

Capacitive resistivity (CR) is an emerging technique which can extend the scope of DC resistivity to environments where galvanic measurements tend to fail, for example on engineered structures (roads, pavements), dry soil or frozen ground. Low frequencies (say 1 to 25 kHz) allow for capacitive coupling between sensors and the ground, but theoretical equivalence with the DC case is only achieved in a low-induction number mode of operation associated with quasi-stationary fields. Under such conditions, conventional DC interpretation schemes are applicable to CR data. In general, the transfer impedance across a four-point capacitive array is a complex function of frequency and geometry. For standard geometries with plate-wire sensors on the surface, typical survey parameters and moderate electrical properties of the subsurface, responses are strongly inphase. However, there are circumstances under which the quadrature component is non-negligible so that significant phase-shifts are observed and a phase-sensitive expression for apparent resistivity is more adequate. We have validated these fundamental properties of CR by measuring the fully complex voltage (magnitude and phase) with a prototype CR instrument developed by BGS. The nature of the CR technique facilitates dynamic measurements with towed multi-offset arrays, which we have employed for the collection of low-noise, highly repeatable apparent resistivity data at centimeter intervals. Such data allow near-surface electrical tomographic imaging at resolutions that would be impractical to achieve with conventional DC resistivity. We conclude that capacitive resistivity imaging (CRI) has the potential to become a key tool for environmental and engineering site investigation surveys in the built environment.

10.3997/2214-4609-pdb.190.ele03

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Citations (3)

Assessment of ground-based monitoring techniques applied to landslide investigations

Geomorphology (2015)

S. Uhlemann Alister Smith Jonathan Chambers Neil Dixon Tom Dijkstra

A landslide complex in the Whitby Mudstone Formation at Hollin Hill, North Yorkshire, UK is periodically re-activated in response to rainfall-induced pore-water pressure fluctuations. This paper compares long-term measurements (i.e., 2009–2014) obtained from a combination of monitoring techniques that have been employed together for the first time on an active landslide. The results highlight the relative performance of the different techniques, and can provide guidance for researchers and practitioners for selecting and installing appropriate monitoring techniques to assess unstable slopes. Particular attention is given to the spatial and temporal resolutions offered by the different approaches that include: Real Time Kinematic-GPS (RTK-GPS) monitoring of a ground surface marker array, conventional inclinometers, Shape Acceleration Arrays (SAA), tilt meters, active waveguides with Acoustic Emission (AE) monitoring, and piezometers. High spatial resolution information has allowed locating areas of stability and instability across a large slope. This has enabled identification of areas where further monitoring efforts should be focused. High temporal resolution information allowed the capture of ‘S’-shaped slope displacement-time behaviour (i.e. phases of slope acceleration, deceleration and stability) in response to elevations in pore-water pressures. This study shows that a well-balanced suite of monitoring techniques that provides high temporal and spatial resolutions on both measurement and slope scale is necessary to fully understand failure and movement mechanisms of slopes. In the case of the Hollin Hill landslide it enabled detailed interpretation of the geomorphological processes governing landslide activity. It highlights the benefit of regularly surveying a network of GPS markers to determine areas for installation of movement monitoring techniques that offer higher resolution both temporally and spatially. The small sensitivity of tilt meter measurements to translational movements limited the ability to record characteristic ‘S’-shaped landslide movements at Hollin Hill, which were identified using SAA and AE measurements. This high sensitivity to landslide movements indicates the applicability of SAA and AE monitoring to be used in early warning systems, through detecting and quantifying accelerations of slope movement.

Inclinometer

Piezometer

Tiltmeter

Temporal resolution

10.1016/j.geomorph.2015.10.027

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Citations (172)

The use of a semi‐structured finite‐element mesh in 3‐D resistivity inversion

Geophysical Prospecting (2022)

M.H. Loke Paul Wilkinson O. Kuras P.I. Meldrum Dale F. Rucker

Abstract Calculating the electric potential for 3‐D resistivity inversion algorithms can be time consuming depending on the structure of the mesh. There have been generally two approaches to generating finite‐element meshes. One approach uses a structured rectangular mesh with hexahedral elements on a rectangular model grid. The distribution of model cells can be designed to follow known boundaries, and directional roughness constraints can be easily imposed. A 1‐D wavelet transform that takes advantage of the regular arrangement of the model cells can also be used to reduce the computer time and memory required to solve the smoothness‐constrained least‐squares equation. However, the structured rectangular mesh uses an unnecessarily fine mesh in parts of the model that are far away from the electrodes where the potential changes gradually. A second approach uses an unstructured mesh with tetrahedral elements created automatically by a mesh generation program with finer elements nearer the electrodes and coarser elements in the more remote regions. This generates a mesh with a much smaller number of nodes. The disadvantage is that an irregular model grid is normally used. We examine an alternative approach that combines structured and unstructured meshes. We employ a regular model grid with a finer mesh near the surface and a coarser mesh in deeper regions using a combination of hexahedral and tetrahedral elements. The semi‐structured mesh reduces the calculation time by more than three times compared with a structured mesh. An adaptive semi‐structured mesh that also uses a coarser mesh for model cells near the surface if they are more than one unit electrode spacing from the nearest electrode was also developed for surveys with non‐uniform data coverage. For the Bonsall Leys field survey, which used a capacitively coupled mobile system and collected a data set with nearly a million electrode positions, the adaptive mesh reduces the calculation time by about 80%. The calculation time can be further reduced by about 93% when it is combined with a mesh segmentation method.

Hexahedron

Tetrahedron

Laplacian smoothing

Volume mesh

T-vertices

Adaptive Mesh Refinement

10.1111/1365-2478.13260

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Citations (2)

Three-dimensional geophysical anatomy of an active landslide in Lias Group mudrocks, Cleveland Basin, UK

Geomorphology (2010)

Jonathan Chambers Paul Wilkinson O. Kuras Jonathan R. Ford David Gunn

Electrical Resistivity Tomography

Escarpment

Debris flow

Geotechnical investigation

Geologic map

10.1016/j.geomorph.2010.09.017

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Citations (157)

Sand and Gravel Deposit Evaluation Using Electrical Resistivity Tomography

Near Surface 2009 - 15th EAGE European Meeting of Environmental and Engineering Geophysics (2009)

Jonathan Chambers P.B. Wilkinson A. Weller O. Kuras P.I. Meldrum

In this study, we assess the suitability of ERT for UK sand and gravel deposit assessment. To this end, we have reviewed the characteristics of deposits in terms of geological setting, thickness and heterogeneity to inform our survey design strategy. We have collated existing data on the electrical properties of UK sand and gravel, reviewed previous examples of ERT sand and gravel surveys, and undertaken detailed geophysical studies at seven potential or active sand and gravel extraction locations in East Anglia and the East Midlands.

Electrical Resistivity Tomography

10.3997/2214-4609.20147079

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Citations (1)

Performance Assessment of Novel Electrode Materials for Long-term ERT Monitoring

Proceedings (2015)

O. Kuras P.B. Wilkinson P.I. Meldrum Russell Swift Sebastian Uhlemann

Summary We present results of a laboratory study of novel electrical resistivity tomography (ERT) sensor materials, whose performance has been assessed in terms of suitability for long-term geoelectrical monitoring. The study has addressed concerns over the longevity of buried ERT sensors required to support nuclear decommissioning at the Sellafield Site in the UK. Electrodes made from three candidate materials and installed in a bentonite grout were subjected to accelerated measurements and electrochemical analyses were carried out on both pristine and used electrodes after extraction from the laboratory tanks. Electrical contact resistance showed significantly different behaviour for stainless steels compared with platinised titanium. Pt-Ti sensors displayed outstanding properties and their stability under operational conditions was remarkable. Their susceptibility to ERT noise, which was expected to be worse due to their higher nobility, was only marginally greater than that of stainless steels. No tangible advantage in terms of electrical performance was found for using higher-grade varieties of stainless steel over a conventional 316L-based design. Crucially, both steel types were affected by the growth of carbonate scales when buried in bentonite. This fundamental process may well be (at least partially) responsible for the frequently encountered increase in contact resistance of stainless-steel electrodes over time.

Bentonite

Nuclear decommissioning

Contact resistance

Electrochemical noise

10.3997/2214-4609.201413777

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Citations (2)