Objective of EXCAVATION Precautions
Awareness about EXCAVATION Precautions to engineer and supervisors are very important to make early arrangements to avoid any delay in work completion and all the work should be done is safe manner and as per the legal and company standards.
BEFORE WORK STARTS
In order to begin excavation work with minimum risk to men, plant and equipment and to enable the work to proceed without interruption, the following factors shall be considered before the job starts:
- size and purpose of the excavation;
- nature of the ground including the proximity of made-up ground;
- Stability of adjacent structures;
- position of underground obstructions such as pipes, electric cables, and other utilities;
- position of structures of archaeological and historical interest (in known areas)
- weather and soil moisture conditions, especially high water table
- sources of soil vibrations (highway traffic, machinery, etc.)
- adjacent roads and footpaths
- method of excavation
Consideration of these factors will indicate the safety measures that must be implemented to proceed with the job and whether the sides of the excavation can be sloped and benched to a safe angle or whether other protective systems will be required. It is important to provide adequate and suitable protective systems for use whenever excavation work is to be carried out to a depth of 1.2 meters (4 feet) or more. Excavation work to a depth of less than 1.2 meters (4 feet) may also require protective systems.
The required Permit to work and Excavation Permit shall be obtained prior to excavation work commencing in a Restricted Area. For excavation work outside a Restricted Area, only an Excavation permit is required.
IDENTIFICATION OF ALL UNDERGROUND UTILITIES
Whenever the presence of underground pipes, cables, vessels, or structures is known or suspected, mechanical excavators shall not be used until all such obstructions have been exposed by hand digging. Mechanical excavators shall not be used within 3 meters (10 feet) of any such obstruction and including, wellheads and exposed pipes. In certain and special circumstances, this critical distance may be evaluated, modified, and supervised by an authorized and qualified person. Pneumatic breakers shall only be used where necessary to break concrete or other hard surfaces.
GENERAL Excavation PRECAUTIONS
Shoring Protective Systems
As soon as an excavation reaches a depth of 1.2 meters (4 feet) suitable shoring shall be installed or the sides sloped back to a safe angle. Shoring may be of timber or any other suitable material, such as steel sheet piling.The determination of the angle of slopes, benches, or the choice and design of other protective systems shall be based on evaluation of pertinent factors such as:
- Type of soil
- Depth of cut
- Possible variations in water content of the material while the excavation is open
- Anticipated changes in materials from exposure to air, sun, or water
- Loading imposed by structures, equipment, overlying material, or stored material
- Vibrations from equipment, blasting, traffic, or other sources.
Excavations shall not be sloped at an angle greater than one and one-half horizontal to one vertical (340 measured from the horizontal). All excavations shall be inspected after any rain.
A qualified and authorized person shall design the shoring system. The system design shall meet accepted engineering requirements according to the above pertinent factors. Materials used shall be in good serviceable condition, and timbers shall be sound, free from large or loose knots, and of proper dimensions.
Temporary crossings for personnel shall be provided over any trench in access of 1.0 m in depth.
Temporary crossings should be at least 600 mm wide and provided with handrails.
Portable trench boxes may be used for the protection of personnel in lieu of a shoring system or sloping.
Trench boxes shall be designed, constructed and maintained to provide protection equal to or greater than the sheeting or shoring required.
All pits, trenches and excavations shall be roped off and provided with suitable warning signs.