Contractors and utilities often ask the UndergroundSafety staff this very question. We created this Slope Calculator (for soil) to provide you with the excavation requirements with each method.
As always, the safety of your employees is the most important consideration.
If you choose to use a manufactured protective system (for example, underground shield, hydraulic shoring, or a slide rail system), only cubic yards of material will have to be excavated, temporarily stored, and replaced. That's a % reduction from sloping. Also, surface restoration costs will be lower, and the overall job will take less time.
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When sloping at depths greater than 20 feet, OSHA says that a Registered Professional Engineer, licensed in the state where the work is to be performed, must determine the proper angle of slope. See OSHA's Subpart P, Excavations, for requirements.
These are the MINIMUM SLOPING REQUIREMENTS, including the OSHA-required spoil and equipment set-backs. Additional material may need to be excavated, as determined by the onsite Competent Person, to provide a safe workplace.
Construction techniques and equipment usage must be in accordance with all governmental regulations and manufacturer's instructions. All orders placed with UndergroundSafety, including training, are subject to the terms, conditions, and warranty limitations in UndergroundSafety's rental and sales agreements.