Benching

There  are two type of benching ,simple and multiple.The type of soil determines the horizontal to vertical ratio of the benched side.As a generlal rule the bottom  vertical heightr.. of the trench must not exceed
 4 feet for the first trench.Subsequent benches may be up to a maximum of 5 feet vertical in type.A soil and 4 feet in type  b soil to a total trench depth of 20 feet .All subsequent benches must be below the maximum allowable slope for that soil type .For type B soil the trench excavation is permitted in cohesive siol.                                                                                                                                                e

Pre excavation requirments

In order to carryout the excavation work safety and to minimise the risk .the following factors shall be concidered before the excavation starts.

Size and purpose of excavation.

Nature of the ground including the proximityof made up ground.

Stability of adjuscent structures.Position of underground obstructions such as pipes ,electric cables and other utilities.

Position of structures of archieological and historical interest.

wether and moisture conditions high water table.

Sourse of soil vibration (high way traffic,mechinery etc.)

Adjucent road and fott path.

Method of excavation.

Slopping

Slopping is method of excavation in which the sides of  an excavation are laid back to safe angle to prevent cave ins. Trench boxes are generally used in open  areas but they also may be used in combination with slopping and benching.The boxes should extend atleast 18 inches above the surrounding area, if there is slopping towards excavation.This can be accomplished by providing a benched are adjusted to the box.Earth excavation to a depth of 2 feet below the shield is permitted.