Advanced geotechnical monitoring technology to assess ground support effectiveness

Abstract

Deformation at the surface of excavations in hard rock often occurs on a millimetre scale, which means the movements cannot be readily detected through visual inspection. These slight rates of deformation can lead to cracking, bulking, wedges and even loss of material that may go unnoticed or be deemed unimportant until significant rehabilitation is needed. The impact of such deformation on ground support capacity over time is difficult to assess quantitatively. Other than visual inspections, traditional excavation monitoring technologies typically entail point measurements, such as with extensometers, prisms or convergence measurement systems. The scanning and surveying of specific excavation cross-sections are also used. The authors of this paper have tested a new technology for underground monitoring. GroundProbe’s Geotech Monitoring LiDAR (GML) system has millimetre-range accuracy and measures the rate of deformation at the rock surface with high precision in each pixel of a 360° image. The system can measure the rate of deformation of ground support elements and the surrounding rock or shotcrete surface at any given time, in any drive, intersection or stope entry. This technology was tested in two different hard rock underground environments through a process of experimentation and validation. The GML system was used to monitor large critical infrastructure with shotcrete walls and roofs, compare bolt displacements in different geological contexts and stress environments, and monitor the rock mass and ground support response to stope and development blasts. The impact of bolt spacing and bolt type on rock surface deformation was also measured. Testing of the technology to date has demonstrated clear value and has the potential to assist ground control engineers by providing visual records and quantitative assessments of rock mass deformation and ground support performance. Advanced deformation monitoring can be a valuable asset for optimising ground support design and monitoring ground support performance.