In marine construction operations driving piles in an excavated pit is extremely dangerous. To provide the greatest protection to employees, OSHA requires the walls of the pit to be sloped to the required angle during sheet piling installation.
It is essential to ensure the pit is at the correct angle to limit the possibility of wall collapse when using of pile driving equipment in an excavated pit. The angle required is based on the types of soil in and surrounding the pit.
There are four options for sloping requirements, depending in part on the three soil classifications. The classifications are determined by the soil’s strength and relative cohesiveness. The person who decides the soil type must have experience identifying existing and predictable hazards in this type of worksite.
The first option can be used in all excavations. This requires using an angle not steeper than 1½ (horizontal) to 1 (vertical), which is 34 degrees measured from the horizontal. This is the most conservative angle for the allowable slope and can be used in all soil types.
Option two can be used for excavations of 20 feet or less. These provide slope angles depending on the particular soil classification. If it is determined that the site’s soil is as either rock, an angle larger than 34 degrees can be selected for the maximum allowable slope.
The third option allows for a sloped angle to be selected from tabulated data, such as tables and charts that are approved by an engineer. The tabulated data must be in written form and include all of the following:
(a) identification of the parameters that affect the selection;
(b) identification of the limits of use of the data; and
(c) explanatory information as may be necessary to aid the user in making the correct selection.
The last option requires an engineer to determine the proper sloping and benching system.
While there is no minimum length or height requirement for the sheet-piling to extend above the surface grade of an excavation. Sheet-piling is a type of shield or support system. There are some basic guidelines provide by OSHA:
For excavations, less than 20 feet, which have vertically sided lower portions, a shield or support must extend to a height of at least 18 inches above the top of the vertical side.
For excavations greater than 20 feet, a registered engineer will be required to determine any minimum sheet-pile height requirements for the site plans.
In these situations, the extended sheet-pile protects the workers from objects or debris falling in the pit. In addition, employee protection is also provided by scaling the slopes to remove loose material from the face that could pose a hazard by falling or rolling into the excavation.
Additionally, employee protection must be provided by placing and keeping materials and equipment at least 2 feet from the edge of the excavation.
Benching can be used in conjunction with sheet-piles regardless of soil classification. However, the excavated pits can only have a maximum depth of 20 feet. In making that measurement, you must start from the original grade, not at the base of the slope.
An excavation greater than 20 feet deep, which can use options 3 or 4 above, must be designed by an engineer. An engineer is also required when a site has unusual conditions.