- Excavation Definition
- Type of soil
- Hazards
- Control Measures
Excavation Definition
Any man mad cut, cavity, trench or depression on the surface of ground is called excavation.
Excavation is also one type of confined space and if O2 level is between 19.5% to 23.5% by volume in the air work to be allowed.
Type of soil
Type A
Most stable: clay, silty clay, and hardpan (resists penetration). No soil is Type A if it is fissured, is subject to vibration of any type, has previously been disturbed, or has seeping water.
Type B
Medium stability: silt, sandy loam, medium clay and unstable dry rock; previously disturbed soils unless otherwise classified as Type C; soils that meet the requirements of Type A soil but are fissured or subject to vibration.
Type C
Least stable: gravel, loamy sand, soft clay, submerged soil or dense, heavy unstable rock, and soil from which water is freely seeping.
Shielding (shield system) means a structure that is able to withstand the forces imposed on it by a cave-in and thereby protect employees with the structure.
Shields can be permanent structures or can be designed to be portable and moved along as work progresses. Also known as trench box or trench shield.
Shoring (shoring system) means a structure such as a metal hydraulic, mechanical or timber shoring system that supports the sides of an excavation and which is designed to prevent cave-ins.
Sloping (sloping system) means a method of protecting employees from cave-ins by excavating to form sides of an excavation that are inclined away from the excavation so as to prevent cave-ins.
The angle of incline varies with differences in such factors as the soil type, environmental conditions of exposure, and application of surcharge loads.
Maximum allowable slopes for excavations less than 20' based on soil type and angle to the horizontal are as follows:
Trench (trench excavation) means a narrow excavation (in relation to its length) made below the surface of the ground. In general, the depth is greater than the width, but the width of a trench is not greater than 15 feet.
If forms or other structures are installed or constructed in an excavation as to reduce the dimension measured from the forms or structure to the side of the excavation to 15 feet or less, the excavation is also considered to be a trench.
Hazards in excavation
- Water accumulation
- Cave-in – sudden & unexpected fall of excavated wall/soil
- Underground / above utilities
- Presence of toxic gases & lack of O2
- People, Materials, Vehicles falling
- Adjacent structure collapse
- Physical, Chemical, Biological Hazards
- Lack of illumination/ ventilation
- Slip &trip
- Traffic disruption
- Access/ egress inconvenience
- Electrocution
- Fire hazard
- Struck by moving machinery (Excavator, Dumper)
Control Measures
- Work permit
- Dewatering
- Shoring/ Shielding/ Sloping/ Benching/ barricading
- Location of map
- Use of detector, scanner , trial pit
- Isolate/ de-energize above ground utilities & keep safe distance
- Gas detector/ O 2 level checking
- Ventilation ( vacuum & forced cleaner)
- Respiratory protection
- Barricading, sign boards, stop logs, guard rails, proper lighting, warning sign
- Traffic diversion, if required, heavy vehicles must stopped passing nearby
- Unauthorized entry restricted
- PPE like helmet, safety shoes should be used
- Keep the excavated soil at least 5 feet distance
- Excavated sides should be sloped bake to a safe angle
- Hand excavation should be done at the present of UG pipes or cables place
- Cutting shall be done from top to bottom
- All narrow trenches 4 feet or more deep shall be supplied at least one ladder
- While excavating on the slope on the slope whose height is over 10 feet men should use safety belts