Protective Systems
Sloping to protect workers can be done by cutting back the trench wall at an angle inclined away from the excavation not steeper than a height/depth ratio of 1.5:1, according to the sloping requirements for the type of soil.
Options for Sloping and Benching
Follow these requirements for sloping in Class C soils:
- Always provide a way to exit a trench-such as a ladder, stairway or ramp-no more than 25 feet of lateral travel for employees in the trench.
- Keep spoils at least two feet back from the edge of a trench.
- Make sure that trenches are inspected by a competent person prior to entry and after any hazard-increasing event such as a rainstorm, vibrations or excessive surcharge loads.
Maximum allowable slopes for excavations less than 20 ft. (6.09 m) based on soil type and angle to the horizontal are as follows:
Allowable Slopes
| Soil Type | Height/Depth Ratio | Slope Angle |
|---|---|---|
| Stable Rock | Vertical | 90 degrees |
| Type A (Clay) | 3/4:1 | 53 degrees |
| Type B (gravel, silt) | 1:1 | 45 degrees |
| Type C (sand) | 1 1/2:1 | 34 degrees |
| Type A (short term) | 1/2:1 | 63 degrees |
Source: OSHA Technical Manual, Sec V. Chap. 2, Excavations: Hazard Recognition in Trenching and Shoring .
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5-8. What is the maximum allowable slope for type A soil?
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