Abstracts of our staff presentations.
A Geophysical Investigation of Near Vertical Boreholes in the Roof of an Underground Tunnel in a Coal Mine
Patrick Mah, P.Geo.
DMT Geosciences Ltd., Calgary, Alberta, Canada
Brian Wong, P. Eng.
Teck Coal Ltd., Sparwood, British Columbia, Canada
Torsten Gorka, Dipl. Geol.
DMT GmbH & Co., KG, Essen, Germany
As part of a tunnel roof reinforcement feasibility study, five vertical boreholes were drilled in the roof of an underground tunnel and were logged using unconventional wireless geophysical instruments specifically designed for challenging operational environments. The program was completed in conjunction with a broader drilling program to understand the overlying lithology and bedrock structure as a basis for reinforcement against future planned close proximity mining activities. The tunnel serves as the only corridor for raw coal conveyance from the mine operations to the process plant. The geotechnical investigation was conducted without disruption to the processing plant and conveyance infrastructure.
The geophysical investigation was crucial in supporting the assessment of the jointing and bedding characteristics of the rock mass as well as the lithology. This data was used to evaluate basic tunnel support requirements through closed form analytical solutions to estimate maximum support capacities for the general types of support systems, and to allow for the estimation and evaluation of mining impacts using a series of 2-D finite element numerical models in the PLAXIS™ software suite. The operational challenges encountered in the geotechnical investigation were helpful to highlight potential constructability issues for future tunnel reinforcement works.
A Novel Case Study on Achieving Site Closure - EM31 and Pseudo-3D OhmMapper Surveys, Calibrated with Physical Analytical Soil Data, to Create Impacted Soil Volume Estimates before Remediation
Adam Peake, P.Geo.
DMT Geosciences Ltd., Calgary, AB, Canada
David Barcham, GIT
Pinchin Ltd., Calgary, AB, Canada
Volume estimation and three-dimensional mapping of salt-impacted soils is an integral part of both remediation and risk management activities in order to create accurate budgets, alternative remedial options, or properly characterize the site for risk management. This paper reviews a case study documenting the process and final results after the combined acquisition and interpretation of novel geophysical survey data using innovative techniques for mapping chloride contaminated soils in the vicinity of a historical pipeline release. For this case study, a start to finish methodology can be recognized, highlighting impacted soil volume estimates compared to actual impacted soil volumes removed from site during a remedial excavation to achieve site closure.
The geophysical methods utilized include frequency domain electromagnetics (EM31) and advanced pseudo-3D capacitively coupled resistivity (OhmMapper) surveys. EM31 and pseudo-3D OhmMapper data are first used to image the contaminated area and target for an intrusive Phase II Environmental Site Assessment (ESA). The Phase II ESA soil sampling and laboratory analysis of soil conductivity and chloride content was then performed and compared to the applicable regulatory criteria. Geophysical survey data is then compared to the sampled soil data to correlate actual laboratory measured soil properties with the non-intrusive geophysical survey results in order to map the chloride impacted soil volumes.
Application of the Subsoil Salinity Tool (SST) to create a Tier 2 Regulatory Guideline for closure and subsequent re-evaluation of the geophysical survey data is conducted to estimate the volume of impacted soil where remediation is required.
Further discussions of data collection, soil analytical correlation, pipeline interference, and limits to contaminant characterization are addressed based on actual events.