Detection of Buried Mine Shafts by Ground Conductivity Mapping - Two Examples from the Walloon Coalfield (Belgium)

AbstractIn order to evaluate quickly and cost effectively the detailed shallow sub-surface geology of a 300 ha area in the West Midlands, geophysical techniques were used in conjunction with shell and auger drilling. Since the area contains one of the largest landfill sites of its type in Europe and is crossed by a river which is abstracted for drinking water within a short distance downstream, it was important to determine the geology and hydrogeology in some detail.Previous geological surveys of the area, which included the drilling of over 80 boreholes for sand and gravel extraction, indicated the presence of up to 5 m of highly variable sandy overburden overlying Keuper Marl. It was apparent from an initial desk study that despite the large number of boreholes the geology had been completely misinterpreted.A ground conductivity map was produced using a Geonics EM-31 which rapidly gave a picture of the general structure and identified targets for drilling and Offset Wenner resistivity soundings. The geophysics revealed the presence of a major buried channel cutting deeply into the marl, which was later confirmed in several places by drilling. Surface outcrops of clay or marl could be identified using the ground conductivity values alone.The use of the geophysical techniques has considerably reduced the cost and time of the investigation and has allowed the major effort to be concentrated in problem areas.

Download Full-text

Delineation of Management Zones for Site-Specific Information about Soil Fertility Characteristics through Proximal Sensing of Potato Fields

Agronomy ◽

10.3390/agronomy10121854 ◽

2020 ◽

Vol 10 (12) ◽

pp. 1854

Author(s):

Humna Khan ◽

Aitazaz A. Farooque ◽

Bishnu Acharya ◽

Farhat Abbas ◽

Travis J. Esau ◽

...

Keyword(s):

Soil Fertility ◽

Prince Edward Island ◽

Tuber Yield ◽

Sampling Strategy ◽

Time Domain Reflectometry ◽

Specific Information ◽

Proximal Sensing ◽

Site Specific ◽

Management Zones ◽

Ground Conductivity

The delineation of management zones (MZs) has been suggested as a solution to mitigate adverse impacts of soil variability on potato tuber yield. This study quantified the spatial patterns of variability in soil and crop properties to delineate MZs for site-specific soil fertility characterization of potato fields through proximal sensing of fields. Grid sampling strategy was adopted to collect soil and crop data from two potato fields in Prince Edward Island (PEI). DUALEM-2 sensor, Time Domain Reflectometry (TDR-300), GreenSeeker were used to collect soil ground conductivity parameter horizontal coplanar geometry (HCP), soil moisture content (θ), and normalized difference vegetative index (NDVI), respectively. Soil organic matter (SOM), soil pH, phosphorous (P), potash (K), iron (Fe), lime index (LI), and cation exchange capacity (CEC) were determined from soil samples collected from each grid. Stepwise regression shortlisted the major properties of soil and crop that explained 71 to 86% of within-field variability. The cluster analysis grouped the soil and crop data into three zones, termed as excellent, medium, and poor at a 40% similarity level. The coefficient of variation and the interpolated maps characterized least to moderate variability of soil fertility parameters, except for HCP and K that were highly variable. The results of multiple means comparison indicated that the tuber yield and HCP were significantly different in all MZs. The significant relationship between HCP and yield suggested that the ground conductivity data could be used to develop MZs for site-specific fertilization in potato fields similar to those used in this study.

Download Full-text

On the measurement of ground conductivity at VLF

IRE Transactions on Antennas and Propagation ◽

10.1109/tap.1958.1144590 ◽

1958 ◽

Vol 6 (3) ◽

pp. 273-277 ◽

Cited By ~ 16

Author(s):

J. Wait ◽

A. Conda

Keyword(s):

Ground Conductivity

Download Full-text

EARTH CONDUCTIVITY DETERMINATIONS EMPLOYING A SINGLE SUPERCONDUCTING COIL

Geophysics ◽

10.1190/1.2035912 ◽

1976 ◽

Vol 41 (6) ◽

pp. 1184-1206 ◽

Cited By ~ 8

Author(s):

H. F. Morrison ◽

William Dolan ◽

Abhijit Dey

Keyword(s):

Large Scale ◽

Low Frequency ◽

High Sensitivity ◽

Input Resistance ◽

Measurement Sensitivity ◽

Superconducting Wires ◽

Superconducting Coil ◽

Airborne Electromagnetic ◽

Earth Conductivity ◽

Ground Conductivity

A low‐frequency airborne electromagnetic prospecting method has been developed which exploits the inherent low resistance of a superconducting coil. Changes in the input resistance of this coil are monitored in the presence of the conducting earth. The response of the system, the change in the input resistance, is proportional to the quadrature secondary magnetic field at the transmitter, although unlike two‐coil systems, the response does not decrease with increasing frequency. This research has demonstrated that superconducting wires, large scale nonmetallic cryostats, the requisite measurement circuitry, and an appropriate data acquisition system are realizable in a practical flight configuration. The unicoil presents the following significant advantages in electromagnetic prospecting: 1) The measurement sensitivity is not limited by the relative coil motion experienced by two‐coil systems. 2) Ample field strength may be supplied to override ambient noise. 3) Optimum frequencies for specific geologic sections are easily implemented in the range of 10 to 2000 Hz. 4) Maps of ground conductivity may be obtained because precise thermal stability is maintained and the measurement, therefore, is absolute. 5) The point source observation minimizes analytic complexity. 6) The combination of the foregoing features with multiple frequency operation, yields a system of potentially high sensitivity and unprecedented depth of exploration. The unicoil system also possesses some disadvantages: 1) An operational complexity results from the cryogenic procedures required in the field, and 2) the heavy sensor requires a large helicopter.

Download Full-text