Underhand cut-and-fill mining has allowed for the safe extraction of ore in many mines operating in weak rock or highly stressed, rockburst-prone ground conditions. However, the design of safe backfill undercuts is typically based on historical experience at mine operations and on the strength requirements derived from analytical beam equations. In situ measurements in backfill are not commonplace, largely due to challenges associated with instrumenting harsh mining environments. In deep, narrow-vein mines, large deformations and induced stresses fracture the cemented fill, often damaging the instruments and preventing long-term measurements. Hecla Mining Company and the Spokane Mining Research Division of the National Institute for Occupational Safety and Health (NIOSH) have worked collaboratively for several years to better quantify the geomechanics of cemented paste backfill (CPB), thereby improving safety in underhand stopes. A significant focus of this work has been an extensive in situ backfill instrumentation program to monitor long-term stope closure and induced backfill stress. Rugged and durable custom-designed closure meters were developed, allowing measurements to be taken for up to five successive undercuts and measuring closures of more than 50 cm and horizontal fill pressures up to 5.5 MPa. These large stope closures require the stress–strain response of the fill to be considered in design, rather than to rely solely on traditional methods of backfill span design based on intact fill strength. Furthermore, long-term instrument response shows a change in behavior after 13–14% strain, indicating a transition from shear yielding of the intact, cemented material to compaction of the porosity between sand grains, typical of uncemented sand fills. This strain-hardening behavior is important for mine design purposes, particularly for the use of numerical models to simulate regional rock support and stress redistribution. These quantitative measurements help justify long-standing assumptions regarding the role of backfill in ground support and will be useful for other mines operating under similar conditions.

NIOSH ground control safety research program at Spokane, Washington, is exploring applications of photogrammetry to rock mass and support monitoring. This paper describes two ways photogrammetric techniques are being used. First, photogrammetric data of laboratory testing is being used to correlate energy input and support deformation. This information can be used to infer remaining support toughness after ground deformation events. This technique is also demonstrated in a field application. Second, field photogrammetric data is compared to crackmeter data from a deep underground mine. Accuracies were found to average 8 mm, but have produced results within 0.2 mm of true displacement, as measured by crackmeters. Application of these techniques consists of monitoring overall fault activity by monitoring multiple points around the crackmeter. A case study is provided in which a crackmeter is clearly shown to have provided insufficient information regarding overall fault ground deformation. Photogrammetry is proving to be a useful ground monitoring tool due to its unobtrusiveness and ease of use.

Rockbursts are a serious hazard to workers in deep and high stress mines. Researchers with the

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Deformation and support conditions in underground mines are typically monitored through visual inspection and geotechnical instrumentation. However, the subjectivity of visual observation techniques can result in ambiguous or incomplete analyses with little quantifiable data. Monitoring displacements with conventional instrumentation can be expensive and time-consuming, and the information collected is typically limited to just a few locations. Moreover, conventional methods usually provide vector rather than tensor descriptions of geometry changes, the latter of which offer greater insight into rock movements and potential ground fall hazards. To address these issues, researchers from the National Institute for Occupational Safety and Health's Spokane Mining Research Division have developed and evaluated photogrammetric systems for ground control monitoring applications in underground mines. In cooperation with the Hecla Mining Company, photogrammetric surveys were conducted over a three-year period at the Lucky Friday mine in northern Idaho, United States of America, as underhand cut-and-fill mining methods were used to mine Ag-Pb-Zn ore in rockburst-prone ground conditions at depths approaching 2,100 metres. A photogrammetric system was developed for underground use at the mine that is not only mobile, rugged, and relatively inexpensive, but also capable of producing measurements comparable to conventional displacement-measuring instrumentation. This paper describes the components of the photogrammetric system, discusses the use of point cloud analyses from photogrammetric surveys to monitor bulk deformation in underground entries, and explains the advantages of full tensor descriptions of three-dimensional (3D) ground movement, particularly in regard to the interpretation of potential movement along fault intercepts. The practical use of photogrammetry to augment measurements from conventional instruments, such as crackmeters, is presented, as well as the use of photogrammetric data in conjunction with 3D visualisation software to synthesise and integrate complex information from diverse sources including geology, mining configuration, seismicity, and geotechnical instrumentation.