Working in a trench is one of the most hazardous jobs in construction. Hundreds of people die and thousands are seriously injured each year due to cave-ins. Soil weighs between 90 and 140 pounds per cubic foot. Therefore, one cubic yard (3 ft. by 3 ft. by 3 ft.) can weigh as much as a small pickup truck. If a person is buried, there is little chance of survival. There are many things that can affect soil stability, such as the type of soil, water, and vibration. Soils saturated with water and previously disturbed soils are very dangerous to work in or around. But, don’t be fooled, even hard soil and rock that appears stable can cave in. Before entering a trench, the competent person at the jobsite must inspect the trench and the protection system to ensure that the trench is safe to enter. Always be sure that the trench walls are sloped, shored, or shielded with a trench box and that the trench is safe before you enter. There are recorded incidents of people buried and killed in trenches 3 to 4-ft. deep, so even shallow trenches must be inspected by a competent person before entering.
Source: https://www.nuca.com/tssd
An example of open cut sloping at the Stockport Wastewater Treatment Plant project (April of 2014), where Righter was the General Contractor.
