What is Maximum Allowable Slope?
Per OSHA, Maximum allowable slope means the steepest incline of an excavation face that is acceptable for the most favorable site conditions as protection against cave-ins, and is expressed as the ratio of horizontal distance to vertical rise (H:V). [Source]
Of note: Maximum Allowable Slope is a term that has replaced Angle of Repose, which due to conflicting and inconsistent definitions led to confusion as to the meaning of this phrase.
Maximum Allowable Slope by Soil Type
Maximum allowable slopes for excavations less than 20 ft (6.09 m) based on soil type and angle to the horizontal are as follows [Source]:
- Maximum allowable slope for Stable Rock is a vertical Height:Depth ratio / 90° Slope angle.
- Maximum allowable slope for Type A soil is a ¾:1 Height:Depth ratio / 53° Slope angle.
- Maximum allowable slope for Type B soil is a 1:1 Height:Depth ratio / 45° Slope angle.
- Maximum allowable slope for Type C soil is a 1½:1 Height:Depth ratio / 34° Slope angle.
|Soil type||Height:Depth ratio||Slope angle|
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