Excavation hazards and precautions:-
Most construction work involves some form of excavation of building foundatios, sewers and underground services. Excavation work involves the removal of soil or a mixture of soil and rock. Soil varies in it's nature. It could be fine sand which flows easily, and stiff clay which is more cohesive. Water is nearly always present in the soil, even if only as moisture. Heavy rain is a frequent cause of soil slip. The possibility of flooding presents the additional hazard which should always be considered. Cracks are caused by pressure release as soil is removed, or dried out in hot weather. These things makes excavations or trenching work highly dangerous and even some je the most experienced people get caught by the sudden and unexpected collapse of the unprotected sides of a trench. Buried under a cubic meter of soil, a person is unable to breathe due to pressure on the chest. Apart from getting any physical injury, one can quickly suffocate and even die with a comparatively small amount of soil weighing over 1 ton. The main cause of accidents resulting from excavation work are as follows:
•Workers trapped and buried in an excavation due to collapse of sides.
•Workers struck and injured by material falling into the excavation.
•Workers falling into the excavation.
•Unsafe and insufficient access incase of floods.
•Vehicles driven into or too close to the edge of an excavation, particularly while reversing, causing the sides to collapse.
•Poisoning caused by fumes heavier than air entering the excavation, e.g., exhaust fumes from the diesel and petrol engines.
#Some definitions for excavation activities are:
•Excavation -a cut, cavity, trench formed by earth removal or A process of digging of soil.
•Trench- a narrow excavation. The depth is greater than the width, but not wider than 15 feet.
•Shield-A structure able to withstand a cave-in and protect employees (also called box)
•Shoring- A structure that supports teh sides of an excavation and protects against cave-ins.
•Sloping- A technique that employs a specific angle of incline in the sides of the excavation. The angle varies based on assessment of impacting site factors.
#Hazards of excavation activity:
•Underground utilities.
•Underground gases.
•Underground water.
•Soil collapse
•Man, material, machine tools fall in to excavation pits
•Improper access.
•Vehicle collision.
•Machine failure
•Struck by moving machinery.
•Unauthorised operation and entry.
#Safety precautions:-
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The sides of the excavation or trench should be sloped or battered back to a safe angle of response, usually 45°, or be supported by timbering or other suitable means to prevent a collapse. The type of support necessary will be depend on type of excavation, the nature of ground and ground water conditions. Planning is vital. Make sure that there is enough material to support the length of teh trench to be cut, for the trench support must be installed without delay as the excavation progresses. At least random timbering or piling is required in all excavations, but excavation 1.2 meter or more depth should be provided with adequate timbering or sheeting close boarding or sheeting is required if the ground is unstable or lacks cohesion. Never work ahead of the trench support.
Shoring should be erected, altered or dismantled only by a competent worker operating under supervision. Wherever practicable, it should be installer before excavating to the final dephth of the trench-- it is necessary to begin when the trench is less than 1.2 meter deep. The excavation and installation of shoring should then proceed by stages untill full depth is reached. Ine should be fully aware of the procedures to follow to rescue a fellow worker trapped by a fall of earth. Workers often fall into excavations. Suitably high barriers should be erected (about 1 meter) to prevent falls. Projecting trench supports can often be used for this purpose.
#Control measures in points:-
CLICK "{Excavation safety animation}"
•Obtain permission from authority prior to starting the excavation.
•Ensure that no underground utilities are present is so isolate them.
•Soil testing should be done prior to excavation to identify underground gases and water, if they are present B. A. Set and dewatering facility should be provided.
•To prevent the collapse soil sloping, benching and shoring should be done.
•Excavated soil should be stacked away from the edge (at least 1.5 meters)
•A safe distance should be maintained from the edge of excavation and persons, machines etc.
•Barricade excavated area to prevent unwanted entry.
•Provided proper and safe access.
•Excavation related posters and sign boards should be displayed.
•Loose soil should be removed from the edges.
•Provide reverse guard to prevent vehicle collision while reversing a vehicle.
•All operators and drivers are competent and trained.
•Signal man(flag man) should be deployed.
•Maintain safe distance from moving machinery.
#Inspection:
Excavations should be inspected by a competent person before work begins and at least once a day where work is in progress. They should be thoroughly examined by a competent person once a week and a record must be kept for such inspections.
#Methods of Excavation.
The different methods of excavation are as follows:
•Vertical excavation: In this type of excavation, the trench is dug in such a way that all the layers are exposed in a vertical section. This type of digging usually occurs on complex urban sites with multiple periods of occupancy. Wheeler Box Grid System is an early vertical excavation method. In this method, the whole area is exposed with intact lines of earth left in place between squares of excavated areas. These guidelines, which reveal the strata, could be removed to show the important features.
•Keyhole excavation: In this type of excavation, instead of exposing the whole site, trenches are opened only around the identified d
Features. This method has been widely used in Roman military archaeology.
•Horizontal excavation/open area excavation: This method is generally employed on sites or large areas where an understanding of the site as a whole is required. It's is generally used on shallow sites with only one or two layers of occupancy, like abandoned settlement sites.
•Step trenching: This type of excavation is done on deep sites. In this case a large area is opened at the surface. This area diminishes as excavation proceeds downwards in a series of steps.
•Cofferdams: This type of excavation is carried out in areas where the excavation is deep and the sides are likely to collapse. In this case, sheet piling is erected around the extent of the area under investigation. This is particularly useful on waterlogged sites as it allows water to stay away from the site.
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