EXCAVATION SAFETY

CONTENTS
1.WHAT IS EXCAVATION 2.WHAT IS TRENCH 3.TYPES OF SOIL 4.SLOPEING

5.BENCHING
6.SHORING 7.BARRICATION 8.PLANT AND MACHINERY 9.ACCESS AND ESCAPE

EXCAVATION
Excavation means any man-made cavity or depression in the earths surface, including its sides, walls, or faces, formed by earth removal. IS CODE FOR (EXCAVATION WORK CODE OF SAFETY ) IS 3764:1992

TRENCH
Trench means an excavation having a depth greater than its width measured at the bottom

TYPES OF SOIL
There are three types of soils 1.Type A 2.Type B 3.Type C

Stability decreases through A to B to C.

AS PER MIOSHAS
Soil means any of the following: (a) Clay a very fine textured soil that derives its resistance to displacement from cohesion and may be: (i) Soft clay a clay-type soil that has an unconfined strength of less than 1.0 ton per square foot. (ii) Medium clay, sometimes called plastic a clay-type soil that has a minimum unconfined strength of 1.0 ton per square foot. (iii) Firm soil a clay-type soil that is resistant to forces causing rupture or displacement. A firm clay has a minimum

SLOPING SYSTEM

Slope means the acute angle formed by the side of a trench or excavation and the horizontal plane Sloping system is that maximum allowable slope for excavation less than 20 feet or 6.9meters.
soil type Stable rock Type A Type B Type C Height depth ratio Vertical 3/4:1 1:1 1*1/2:1 Slope angle 90deg 53deg 45deg 34deg

BENCHING AND SLOPPING

(1) The angle of repose shall be flattened when an excavation has water conditions, silt materials, loose boulders, or areas where erosion, deep frost action, or slide planes appear.
(2) When benching the side of an excavation, the vertical rise shall not be more than 5 feet and the step back shall extend at least to the angle of repose as required .

SHORING
The horizontal cross members used in the shoring system is called braces or struts, that bear against the uprights or stringers. When a shoring system is used, the system shall be designed and used to resist the added pressure when heavy equipment, material handling equipment, or material is located near an excavation.

Timber has been used traditionally for shoring. Aluminium shores using hydraulic jacks to hold then in place are also used these days.

They are economical and lighter weight, can installed and dismantled easily and have longer life
They are also more safer than timber.

As far as possible , the installation of shores should be done from the surface i.e vertical shores should be placed from surface and the horizontal brace should be installed just below the surface from above.

The operator should go down in the trench with the help of the ladder which is long enough to install the next lower brace. Similarly all other .
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When the removal of shoring is planned, the possible collapse of trench sides should be anticipated. If the trench is likely to cave in on removal of shores, the worker to go down on the ladder and remove this brace after which other should be remove from bottom to top.

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The removal of shoring is hazardous work. A worker never be permitted to engage in this work single handled. All lose stone , projecting lumps of earth should be removed from trenches . The excavated slides of the trench should be adequately guarded. On steep slopes , workers should not be permitted to work on top of one anoher.
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There is the tendency to dump the excavated material just on the edge of the trench when excavation is done manually . The material may slide back into the trench or apply additional load on shoring. A provision of clear berm of width not less than one third of the final depth of the excavation is recommended.

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BARRICADING
When deep excavation is going on there is likelihood of the public or cattle frequenting the area ,suitable protective fencing (barricading) should be erected and also sufficient number of notice boards and danger signals should be provided to prevent accidents by falling in excavated trenches/pits.

For excavated sites close to public roads/pathways the area notice boards should have lights during darkness hours.

Barriers or covering should be provided to excavations, shafts , pits and openings having a vertical fall distance of more than 2 meters , except during the period necessary for the access of persons and movements of plant , equipment and materials.

PLANT AND MACHINERY

The machinery used in the excavation are Excavators Power shovels

Draglines
Trucks etc.

ACCESS TO ESCAPE
The workers should be able to escape fast in the event of any mishap during excavation. It is recommended that one ladder should be provided for every 15 meters or fraction there of in the case of relatively less hazardous work.

OTHER PRECAUTIONS
Many accidents occur due to fall in unfenced trenches such accidents are common during the rainy season . Fences , guards or barricades should be erected to prevent persons or livestock from falling into excavated pits /trenches. At night time all public side walks and walkways should be adequately illuminated , and warning lights placed at proper sites to ensure safety of pedestrian and vehicular traffic.

Side walls tend to become unstable during monsoons , so they should be braced in the wet season.
It is possible that harmful gases and fumes are present in the trench. Gases , vapours and their metabolites absorbed by a human organ create morphological abnormalities and the individual develops symptoms of poisoning. To prevent such mishaps , dilution and exhaust ventilation system should be used to reduce the concentration of gases matter to the recommended hygiene standards.

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Explosive mixed gases may also be present in a trenches . Air containing more than 1.5 percent of flammable gases by volume is dangerous . Gases and fumes should be rendered harmless or discharged at points that are sufficiently remote from the trenches. No internal combustion engine should be operated in trench unless adequate precautions are taken. While excavating near or below the building foundations , the latter should be supported by shoring ,bracing or underpinning as long as the trench remains open.

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PPE
All the workers working in the excavated pit or trench should be provided with all the personal protective equipments as required for the job undertaken . PPEs like Safety helmet Ear plugs

Goggles
Safety shoes

Self contained breathing apparatus if required etc.

REFERENCES
NICMAR(CONSTRUCTION SAFETY MANAGEMENT) NCP 32. WWW.MICHIGAN.GOV/MIOSHASTANDARDS. PROFESSOR SVS RAJA PRASAD NOTES. INTRODUCTION TO EXCAVATION SAFETY AND SHORING DESIGN

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