Airborne EM mapping of rockslides and tunneling hazards

Pfaffhuber, Andreas Aspmo; Grimstad, E.; Domaas, Ulrik; Auken, Esben; Foged, Nikolaj; Halkjær, Max

doi:10.1190/1.3480009

Cited by 18 publications

(10 citation statements)

References 3 publications

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“…Review papers by Dahlin (2001) for direct current (DC) methods and Tekzan (1999) and Everett (2012) for induction EM methods provide overviews of the large range of applications in which near-surface geologic information is useful. Among the most recent studies, one can find various applications such as aquifer vul-nerability mapping (Röttger et al, 2005), landslide hazards (Pfaffhuber et al, 2010;Supper et al, 2013), clay mapping (Donohue et al, 2012), agriculture regulation (Refsgaard et al, 2014), and overburden mapping Oluwafemi and Oladunjoye, 2013). Most of those studies rely on the mapping of clay geologic units because of their particular mechanical and hydraulic properties, which play key roles in geotechnical (e.g., landslides, construction) and hydrogeological (e.g., groundwater flow modeling, pollution plumes) problems.…”

Section: Introductionmentioning

confidence: 99%

Assessment of near-surface mapping capabilities by airborne transient electromagnetic data — An extensive comparison to conventional borehole data

et al. 2014

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A newly developed helicopter transient electromagnetic (TEM) system has the ability to measure very early times within just a few μs after the turn off of the primary current. For such a system, careful calibration and accurate modeling of the electromagnetic (EM) response is critical to get true resistivities of the very shallow geologic layers. We discovered that this leads to resolution of the same level or in some cases even better than what can be obtained from airborne frequency EM systems. This allowed a range of important applications where high and accurate resolution is mandatory, e.g., geotechnical applications such as urban planning, railroad and road investigations, landslides or distribution of raw materials, and assessing aquifer vulnerability. We evaluated the results of a pilot survey covering the Norsminde catchment south of Aarhus, Denmark, where we found that near-surface layers (top 30 m) can be mapped with an accuracy of a few meters in a complicated glacial sedimentary environment. The mapping of the geologic layers was assessed by a detailed analysis in which we developed a general methodology for crosschecking the EM and borehole data. This methodology is general and can easily be adapted to other data types and surveys. After rating the quality of the boreholes based on a list of predefined criteria, we concluded that the EM data matched with about three-quarters of the boreholes located within less than 15 m from the closest EM soundings. The remaining quarter of the boreholes fell into two groups in which half of the boreholes were of very poor quality or had inaccurate coordinates. Only eight of all the boreholes could not be reproduced by the data, and we attributed this to be caused by very strong lateral or vertical geologic variations not resolvable by the TEM technique.

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Section: Introductionmentioning

confidence: 99%

Assessment of near-surface mapping capabilities by airborne transient electromagnetic data — An extensive comparison to conventional borehole data

et al. 2014

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“…Wynn (2006) carries out airborne TEM survey for aquifer delineation up to a depth of 400 m in Upper San Pedro River basin, Cochise County, South Eastern Arizona using aircraft at a nominal terrain-clearance of 120 m. Now, HTEM with terrainclearance of 30 m have been developed. Pfaffhuber et al (2010Pfaffhuber et al ( , 2011 use it for mapping clays associated with tunneling hazards and active rock slides in western Norway. The information obtained from HTEM can be used for further detailing on the ground wherever required.…”

Section: Airborne Electromagnetic Surveysmentioning

confidence: 99%

The time domain electromagnetic method

Chandra¹

2015

Groundwater Geophysics in Hard Rock

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“…The aim of the geophysical survey was general geological mapping along the proposed route, as well as identification of faults, fractures and dykes which may have been problematic for tunnel construction. Pfaffhuber et al (2010) use a transient AEM system to assess landslides and potential tunnelling hazards in Norway. This paper presents a method for automatic estimation of geoelectrical boundaries.…”

Section: Introductionmentioning

confidence: 99%

Assessing the presence of hard rock along a gas pipeline alignment with airborne EM

Christensen

Reid²

2012

ASEG Extended Abstracts

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Over the past decades, airborne electromagnetic (AEM) surveys have mostly been used in connection with mineral exploration and a variety of issues in hydrogeophysical mapping. However, increasingly, AEM is used for a wide range of geotechnical purposes: pollution mapping, geotechnical assessment on road and freeway alignments, bathymetry, and depth to bedrock. We present an investigation using a helicopterborne transient electromagnetic system along the planned trace of a gas pipeline. Oil and gas pipelines are often buried at a depth of a few meters and the cost of construction depends critically on whether the subsurface is composed of soft sediments that can be easily excavated or hard rock formations that require much heavier equipment and possibly have to be blasted. The aim of the AEM survey was to distinguish between the soft, relatively conductive sediments and the hard, relatively resistive bedrock in the upper few meters of the subsurface. Data were collected with a rather small transmitter moment, but a high repetition frequency that simultaneously allowed high acquisition speed, and reliable data quality. Measurements were inverted with 1D models with both vertical and lateral constraints to produce model sections along flight lines. A novel method of statistical analysis of the set of equivalent models for each inverted model, calibrated against boreholes, improved the estimates of the presence of hard rock along the flight lines.

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Airborne EM mapping of rockslides and tunneling hazards

Cited by 18 publications

References 3 publications

Assessment of near-surface mapping capabilities by airborne transient electromagnetic data — An extensive comparison to conventional borehole data

Assessment of near-surface mapping capabilities by airborne transient electromagnetic data — An extensive comparison to conventional borehole data

The time domain electromagnetic method

Assessing the presence of hard rock along a gas pipeline alignment with airborne EM

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