Excavation

Excavation blog contains following points in details

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.

There are two types of excavation-

1. Mechanical 2. Manual