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Context Sensitive Rock Slope Design Solutions

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3. Rock Excavation Methods

Breaking

Breaking is done with a hydraulic hammer (also known as a breaker or hoe ram), a percussion hammer fitted to an excavator that is typically used for demolishing concrete structures and is shown in Figure 23. It is used to break up rock in areas where blasting is prohibited due to environmental or other constraints. Like a ripper, a hydraulic hammer can be used in most rock types, although when sculpting a slope face, it works best in soft or moderately to highly fractured rock; existing discontinuities in the rock act as presplit lines, minimizing hammer- induced scars and fractures while creating a slope face that appears to be naturally weathered.

Photo. Application of a hydraulic hammer attached to an excavator.
Figure 23. Photo. Application of a hydraulic hammer attached to an excavator.

To allow for maximum downward pressure, the hammer is positioned perpendicular to the ground surface as shown in Figure 24. Hammering locations are spaced evenly in a grid-like fashion so that the end rock product is fractured into pieces that can be loaded and hauled. For slope excavations, the hammering angle should be not be parallel to the major discontinuity orientation, as this may cause fractures into the final slope face as Figure 25 shows.

Photo. A hydraulic hammer sculpting a rock face (the material to be removed has been outlined with common marking
                paint).
Figure 24. Photo. A hydraulic hammer sculpting a rock face (the material to be removed has been outlined with common marking paint).
Photo. A hydraulic hammer expanding a sculpted area, creating planting areas and more natural-looking slope variation.
Figure 25. Photo. A hydraulic hammer expanding a sculpted area, creating planting areas and more natural-looking slope variation.

After breaking, the excavated slope can be configured to look like a part of the natural landscape, with the addition of boulders and topsoil and reseeding with native vegetation as Figure 26 shows.

Photo. Completed rock slope prior to placement of topsoil and a native seed mix.
Figure 26. Photo. Completed rock slope prior to placement of topsoil and a native seed mix.

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