Delineation of rockburst fractures with ground penetrating radar in the Witwatersrand Basin, South Africa

Abstract

The depth of mining in the gold mines of the Witwatersrand Basin, South Africa is continuously increasing, with several mines already stoping at depths exceeding 3500 m. Due to the high stresses imposed on the rock mass in these deep level mines, a high potential for rockbursts exists. Rockbursts cause injuries and deaths to the workers and lost production time. One of the techniques for reducing the severity of damage of face-bursts (a class of rockbursts where the mining face is ejected into the excavation) is preconditioning. Ground Penetrating Radar (GPR) is used to quantify the change in fracture pattern with preconditioning. It is found that both the intensity and depth to which fracturing occurs ahead of the mining face increased, thereby delineating the area of influence of the preconditioning blast. This allowed the establishment of the optimum preconditioning methodology. To further enhance the understanding of the controlling factors involved, a rockburst was simulated in the tunnel sidewall of a crosscut in a deep level mine. GPR is again used to depict the fracture pattern before and after the synthetic rockburst. The radar scans show a new set of blast-hole parallel fractures, whilst nearer the sidewall, dilation and a slight increase in length of pre-existing fractures occurred. In both cases it is shown that GPR represents a useful tool for rock mechanics practitioners in defining the most suitable strategies for minimizing the damaging effects of rockbursts. r

Comprehensive geophysical prediction and treatment measures of karst caves in deep buried tunnel

“…The penetration depth decreases with increasing conductivity. Higher frequencies do not penetrate as far as lower frequencies, but give better resolution (Davis and Annan, 1989;Grodner, 2001;Bristow and Jol, 2003;Reynolds, 1997;Zhang et al, 2010).…”

“…The GPR method, a nondestructive geophysical technique, was first proposed and developed in 1956 (Cook, 1975), and had been applied to image the rock mass from underground excavations for more than 50 years (Grodner, 2001). The GPR method is based on the contrast in electrical properties of the materials and cannot be used to derive mechanical parameters.…”

Prediction of tunneling hazardous geological zones using the active seismic approach

“…; Moser and Howard ; Sénéchal G., Rousset, and Gaffet ). Each prediction technique is based on the presence of contrast in specific physical properties of the surrounding rock, e.g., the dielectric constant and the acoustic impedance (Grodner ; Schrott and Sass ; Yaramanci ).…”

“…These methods include the tunneling seismic prediction (TSP) (Sattel, Frey, and Amberg 1992), the ground-penetrating radar method, and the infrared detecting method (Ashida 2001;Gritto et al 2004;Alimoradi et al 2008;Moser and Howard 2008;Sénéchal G., Rousset, and Gaffet 2013). Each prediction technique is based on the presence of contrast in specific physical properties of the surrounding rock, e.g., the dielectric constant and the acoustic impedance (Grodner 2001;Schrott and Sass 2008;Yaramanci 2004).As a non-destructive HGZ prediction method, the TSP technique, which is based on the reflection of elastic waves, is good at predicting HGZs with prominent reflection interfaces such as faults, bedding plane, and karst cavity boundaries (Zhao, Jiang, and Zhao 2006). It has large prediction range (>100 m) and is convenient to operate (Song, Cho, and Chang 2012;Schrott and Sass 2008).At the end of 1970s, Dresen, Freystatter, and Sommer (1977) applied the channel wave method to detect tunneling HGZs.…”

“…These methods include the tunneling seismic prediction (TSP) (Sattel, Frey, and Amberg 1992), the ground-penetrating radar method, and the infrared detecting method (Ashida 2001;Gritto et al 2004;Alimoradi et al 2008;Moser and Howard 2008;Sénéchal G., Rousset, and Gaffet 2013). Each prediction technique is based on the presence of contrast in specific physical properties of the surrounding rock, e.g., the dielectric constant and the acoustic impedance (Grodner 2001;Schrott and Sass 2008;Yaramanci 2004).…”