For Working Faces
- Note and map the location of structural discontinuities (i.e., joints, faults, and bedding planes) and underground mine workings relative to the existing highwall and in the direction of mining.
- Anticipate unstable highwall conditions in the vicinity of intersecting structural discontinuities and underground mine workings.
- Design highwalls for stability in local geological conditions including stratification, structural discontinuities, rock strength, groundwater seepage, and underground mine workings.
- Shorter highwalls and wider benches can improve highwall stability by reducing overburden load and the amount of material that could become unstable.
- Surface runoff diversions and groundwater drains can improve highwall stability by reducing erosion and internal water pressure.
- Frequently inspect highwalls in the work area, especially after rainfalls, snowmelts, freeze/thaw events, and blasting.
- In addition to mass stability, situations were rockfall conditions may be present need to be considered. The stability of detached blocks should be evaluated. Sloping or irregular faces can cause a falling rocks to be projected away from the face.
- Excessive amounts of rainfall, runoff, or pooled water behind the crest, rapid freezing and thawing, or blast vibrations may destabilize the highwall.
- Inspect all portions a highwall (i.e., the toe, the face, and especially behind the crest) from several different angles.
- Cracks in the face or behind the crest, bulging at the toe, and fallen rocks at the toe may be signs of instability.
- Report noticeable changes in the condition of the highwall to supervisory personnel.
- Avoid exiting vehicles and equipment when working near a highwall.
- Avoid placing yourself between equipment and the toe or crest of a highwall.
- Operate mobile equipment perpendicular to a highwall face to minimize exposure.
- Do not undercut the highwall face.
For Permanent Faces:
- Installing canopies (steel sets, arches, tunnel liners, etc.) at mine portals can protect personnel from falling debris.
- Wire mesh, screening, or other rock fall catchments can be installed on permanent highwalls to protect workers from rock falls where blocky conditions exist.
- Avoid unprotected access to the toe of a non-working highwall by posting warning signs and installing properly designed berms or other barriers at a safe distance.