A Study of Ground Penetrating Radar Methods in an Underground Stone Mine to Improve Ground Control
Baggett, Jonathan Gabriel
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This work focuses on the operational and safety issues associated with karst voids in large opening underground mines. Issues include water inrush, structural instability, and engineering uncertainty in these environments. Coupled with the fracturing prevalent in folded sedimentary rocks, karsts are complex and challenging ground control risks. Traditional methods of predicting karst void locations such as probe-drilling are impeded by the inconsistent spatial distribution and variable sizes of the features. Ground penetrating radar (GPR) is a geophysical technique that transmits radio waves into a medium and subsequently detects reflected waves via a receiver. The travel time and energy of received signals are then processed and interpreted. The difference in material properties between limestone and open karst voids causes strong reflections. This work summarizes a series of 2D and 3D GPR surveys for karst void mapping within a mine pillar and within sill pillars between mine levels in a large opening underground limestone mine. In this case study mine, karst voids are hazardous ground control risks that interact with geologic discontinuities, creating free blocks within the rock mass. As tunnels are advanced via blasting, unknown karst voids may be exposed and pose risks to mining personnel. The karst voids also form a hydrogeological network of water reservoirs with spatial locations throughout the rock mass that are difficult to predict with traditional methods such as drilling. While GPR has been utilized throughout several industries for anomaly detection, mapping, and validating other geophysical data sets, this technique has not seen the same proliferation within the mining industry. Regarding published literature, there is a lack of works that detail the applicability of GPR in underground mining scenarios. The aim of this work is to expand on previous methodologies establishing GPR as a useful tool in underground mining applications, and to discuss the benefits and limitations GPR data in such scenarios.
General Audience Abstract
This work focuses on the operational and safety issues associated with karst voids in large opening underground mines. Typical issues include water flooding into the tunnels and rocks falling out from the roof and walls, among other things. Sedimentary rock structures sometimes are geologically complex, and karst voids only add to that complexity. Engineers usually predict karst void locations with drilling or statistics, but this is often challenging as karst voids have various shapes and orientations. Ground penetrating radar (GPR) is a geophysical technique that sends electric signals into the rock; these signals can reflect off of karst voids and other anomalies. The travel time and energy of signals that come back to the antennas are then processed and interpreted. The difference in material properties between limestone and open karst voids causes strong reflections. This work shows a series of 2D and 3D GPR surveys for karst void mapping within a pillar in a stone mine and also below the floor of mine tunnels. In this mine, karst voids are very dangerous and the miners spend significant time and resources to ensure the tunnels walls are stable. As tunnels are blasted, hidden karst voids may be exposed and pose unpredicted risks to miners. The karst voids are also connected by cracks and discontinuities, providing a path for water to travel along. While GPR has been used in various ways among the construction, civil engineering, and tunneling industries, there is not enough literature pertaining to its benefits for mines. The goal of this work is to grow the available literature on GPR in mining and to talk about the best practices for GPR use as a means of improving health and safety for miners underground.
- Masters Theses