skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Case histories of electrical resistivity and controlled-source magnetotelluric surveys for the site investigation of tunnel construction

Abstract

In tunnel construction, the information regarding rock mass quality and the distribution of weak zones is crucial for economical tunnel design and to ensure safety. Usually, the rock mass grade is estimated by observing recovered cores obtained by drilling or by physical parameters calculated in a laboratory using core samples. However, the high drilling cost limits the number of boreholes; furthermore, rough terrains can reduce the access of drilling machines to the survey sites. In such situations, surface geophysical methods such as electrical resistivity or controlled-source magnetotelluric (CSMT) can provide a rough estimate of the rock mass condition over the planned tunnel route. These methods can also map weak zones (faults, fractures, coal bearing zones, and cavities), which are characterized by a lower resistivity than the surrounding fresh rock mass. We present two successful applications of the electrical resistivity and CSMT methods to the site investigation of tunnel construction over a rough terrain. The first example demonstrates that the boundary of the bedrock and weak zones related to the distribution of coaly shale and coal seams were estimated to extend beyond a few hundred meters below the rough surface. The second example shows that the developing direction and depth ofmore » cavities, which are mainly related to the weak zones in limestone, were successfully interpreted by a three-dimensional (3-D) electrical resistivity survey with the aid of borehole test results.« less

Authors:
; ; ; ;  [1]
  1. Samsung Engineering & Construction Co., Gyeonggi Do (Republic of Korea). Research Institution of Technology
Publication Date:
OSTI Identifier:
20862117
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Environmental and Engineering Geophysics; Journal Volume: 11; Journal Issue: 4
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; GEOPHYSICAL SURVEYS; TUNNELS; PLANNING; RESISTIVITY SURVEYS; MAGNETOTELLURIC SURVEYS; MAPPING; GEOLOGY; COAL SEAMS; GEOLOGIC STRATA; SHALES; CAVITIES; LIMESTONE; SITE CHARACTERIZATION

Citation Formats

Kwon, H.S., Song, Y., Yi, M.J., Chung, H.J., and Kim, K.S. Case histories of electrical resistivity and controlled-source magnetotelluric surveys for the site investigation of tunnel construction. United States: N. p., 2006. Web. doi:10.2113/JEEG11.4.237.
Kwon, H.S., Song, Y., Yi, M.J., Chung, H.J., & Kim, K.S. Case histories of electrical resistivity and controlled-source magnetotelluric surveys for the site investigation of tunnel construction. United States. doi:10.2113/JEEG11.4.237.
Kwon, H.S., Song, Y., Yi, M.J., Chung, H.J., and Kim, K.S. Fri . "Case histories of electrical resistivity and controlled-source magnetotelluric surveys for the site investigation of tunnel construction". United States. doi:10.2113/JEEG11.4.237.
@article{osti_20862117,
title = {Case histories of electrical resistivity and controlled-source magnetotelluric surveys for the site investigation of tunnel construction},
author = {Kwon, H.S. and Song, Y. and Yi, M.J. and Chung, H.J. and Kim, K.S.},
abstractNote = {In tunnel construction, the information regarding rock mass quality and the distribution of weak zones is crucial for economical tunnel design and to ensure safety. Usually, the rock mass grade is estimated by observing recovered cores obtained by drilling or by physical parameters calculated in a laboratory using core samples. However, the high drilling cost limits the number of boreholes; furthermore, rough terrains can reduce the access of drilling machines to the survey sites. In such situations, surface geophysical methods such as electrical resistivity or controlled-source magnetotelluric (CSMT) can provide a rough estimate of the rock mass condition over the planned tunnel route. These methods can also map weak zones (faults, fractures, coal bearing zones, and cavities), which are characterized by a lower resistivity than the surrounding fresh rock mass. We present two successful applications of the electrical resistivity and CSMT methods to the site investigation of tunnel construction over a rough terrain. The first example demonstrates that the boundary of the bedrock and weak zones related to the distribution of coaly shale and coal seams were estimated to extend beyond a few hundred meters below the rough surface. The second example shows that the developing direction and depth of cavities, which are mainly related to the weak zones in limestone, were successfully interpreted by a three-dimensional (3-D) electrical resistivity survey with the aid of borehole test results.},
doi = {10.2113/JEEG11.4.237},
journal = {Journal of Environmental and Engineering Geophysics},
number = 4,
volume = 11,
place = {United States},
year = {Fri Dec 15 00:00:00 EST 2006},
month = {Fri Dec 15 00:00:00 EST 2006}
}
  • The use of measurement while drilling (MWD) resistivity tools in boreholes 8{1/2} in. and greater in diameter has evolved over the past 10 years from a little-used, qualitative service to a routinely used quantitative service in directional, horizontal, and extended-reach wells. Today`s applications include reconnaissance logging, geosteering, pore pressure evaluation, wireline replacement, and enhanced formation evaluation. Over the last several years, there has been an increasing trend worldwide toward drilling smaller boreholes to optimize the costs of tubulars and gain greater drilling efficiencies. Until recently, there have been no MWD resistivity tools available for logging 6-in. diameter boreholes. A newmore » multiple-depth-of-investigation MWD resistivity sensor housed in a nominal 4-3/4 in. diameter drill collar has been developed for use in slimhole drilling operations. This new MWD resistivity sensor provides eight different depths of investigation in any mud type and allows for derivation of the flushed zone resistivity, true resistivity, and the diameter of invasion across a wide range of formation resistivities. The tool is designed for boreholes larger than 5-7/8 in. in diameter and can be used in medium-radius drilling applications. Extensive operations in the North Sea, Gulf of Mexico, south Texas, Middle East, Alaska, and Australia have demonstrated a variety of applications. Slimhole MWD resistivity has been shown to have use in geosteering horizontal wells to maintain and optimize wellbore placement. Additionally, it allows determination of true formation resistivity and diameter of invasion for formations with invasion effects and provides for application of advanced modeling techniques to enhance formation evaluation and log interpretation.« less
  • A magnetotelluric survey was conducted at accessible locations around Mount Hood, Oregon. Thirty-eight tensor magnetotelluric (MT) and remote telluric stations were set up in clusters around the volcano except for the northwest quadrant, a wilderness area. Because of limited access, station locations were restricted to elevations below 1829 m. On the basis of the MT results, three areas were later investigated in more detail using a large-moment, controlled-source electromagnetic (EM) system. One-dimensional interpretations of EM and MT data on the northeast flank of the mountain near the Cloud Cap eruptive center and on the south flank near Timberline Lodge showmore » a similar subsurface resistivity pattern: a resistive surface layer 400--700 m thick, underlain by a conductive layer with variable thickness and resistivity of <20 ohm m. It is speculated that the surface layer consists of volcanics partially saturated with cold meteoric water. The underlying conductive zone is presumed to be volcanics saturated with water heated within the region of the central conduit and, possibly, at the Cloud Cap side vent. This hypothesis is supported by the existence of warm springs at the base of the mountain, most notably Swim Warm Springs on the south flank, and by several geothermal test wells, one of which penetrates the conductor south of Timberline Lodge. The mT data typically gave a shallower depth to the conductive zone than did the Em data. On the other hand, MT was better for resolving the thickness of the conductive layer and deeper structure. The MT data show evidence for a moderately conductive north-south structure on the south flank below the Timberline Lodge and for a broad zone of late Tertiary intrusives concealed on the southeast flank.« less
  • A magnetotelluric survey, with a reference magnetometer for noise cancellation, was conducted at accessible locations around Mount Hood, Oregon. Thirty-eight tensor magnetotelluric (MT) and remote telluric stations were set up in clusters around the volcano except for the northwest quadrant, a wilderness area. Because of limited access, station locations were restricted to elevations below 1829 m, or no closer than 5 km from the 3424-m summit. On the basis of the MT results, three areas were later investigated in more detail using a large-moment, controlled-source electromagnetic (EM) system developed at Lawrence Berkeley Laboratory and the University of California at Berkeley.more » One-dimensional interpretations of EM and MT data on the northeast flank of the mountain near the Cloud Cap eruptive center and on the south flank near Timberline Lodge show a similar subsurface resistivity pattern: a resistive surface layer 400-700 m thick, underlain by a conductive layer with variable thickness and resistivity of <20 ohm m. It is speculated that the surface layer consists of volcanics partially saturated with cold meteoric water. The underlying conductive zone is presumed to be volcanics saturated with water heated within the region of the central conduit and, possibly, at the Cloud Cap side vent. This hypothesis is supported by the existence of warm springs at the base of the mountain, most notably Swim Warm Springs on the south flank, and by several geothermal test wells, one of which penetrates the conductor south of Timberline Lodge. The MT data typically gave a shallower depth to the conductive zone than did the EM data. This is attributed, in part, to the error inherent in one-dimensional MT interpretations of geologically or topographically complex areas. On the other hand, MT was better for resolving the thickness of the conductive layer and deeper structure. The MT data show evidence for a moderately conductive north-south structure on the south flank below the Timberline Lodge and for a broad zone of late Tertiary intrusives concealed on the southeast flank.« less
  • When measurements from a borehole are available, using such data to aid in the inversion of surface measurements may offer considerable benefits. This possibility has been recognized with regard to seismic data in exploration for hydrocarbons. In geothermal exploration, resistivity data from surface measurements and well logs may offer the best synergism. An example is given by using a resistivity log and magnetotelluric (MT) data from the East Mesa field.
  • Aeromagnetic map and electrical resistivity sounding data obtained along eight traverses were examined at two sites across the Katsina-Ala River. The principal goals of this exercise were to define depths to the bedrock, bedrock relief, geologic structures, define the nature of the superficial deposit, and select probable minor and major axes for hydroelectric power dams. The aeromagnetic map shows that the basement rocks trend roughly northeast-southwest, which correlates with the strike of foliation measurements made on rock outcrops along the river channel. A network of cross cutting lineaments, suspected to be faults/fractures that trend approximately northeast/southwest and northwest/southeast, was alsomore » delineated from the magnetic map. The depths to the bedrock estimated from resistivity depth sounding data at site 1 generally vary from 1--53.1 m. Depths to the bedrock estimated at site 2 range from 1.9--19.5 m. The superficial deposit varies from clay to sandy clay, to clayey sand (with boulders in places), and to sand and laterite. The bedrock relief is relatively flat and gently undulates along most of the traverses, with an overall dip towards the river channel. Traverses E-F or I-J at site 1 and K-L at site 2 are probable dame axes. These traverses are characterized by relatively thin overburden thicknesses and rock heads dipping toward the river channel, thereby reducing the likelihood of water seepages from the flanks of the proposed dam axes.« less