A Geophysical Investigation of Near Vertical Boreholes in the Roof of an Underground Tunnel in a Coal Mine

ABSTRACT: 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.