Trench Rescue Operations

Introduction

Construction is one of the most hazardous industries in the U.S., with excavation being one of the most hazardous types of construction work. The accident of special concern in excavation is a cave-in, the seperation of material from the side of the excavation into the excavation.

Photograph used with permission from Lancaster FD Battalion Chief David McEchern

Definitions

An excavation is any man-made cut, cavity, trench, or depression in the earth surface, formed by earth removal.

A trench is defined as a narrow excavation (in relation to its length) made below the surface of the ground.

A lip refers to the area at the top of both side of the trench.

The toe is the area on both side of the floor of the trench.

The belly refers to the space between the lip and the toe of the trench.

The spoil refers to the soil rocks or other materials removed from the trench.

Types of Collapses

• Lip slide Often caused by piling the excavated spoil too close to the edge, thereby creating a load on the lip of the trench. This is the most common type of collapse.

• Belly in or wall slough A collapse caused when a large mass of soil falls from the side of a trench and leaves a large overhand. The most difficult to stabilize.

• Side wall shear A collapse caused when an entire wall of earth shears aways from the side.

Factors Influencing Trench Stability

• Soil type
• Moisture
• Recent excavation
• Freezing and thawing
• Surcharged loads
• Shock and vibration
• Interesting trenches
• Multiple collapses
• Toe slough

OSHA Recognized Protective Systems

Sloping Method of cutting back the sides of an excavation to a safe slope

Shield system Permenent or portable structures that my be used inside a trench. Also known as trench boxes.

Shoring A system of uprights (vertical members of a trench shoring system) which bear against the soil, walers (horizontal members of a trench shoring system) which hold the uprights against the soil, and braces (cross members of a trench shoring system) which force the walers tightly against the uprights.

-- TonyCantu - 22 Apr 2005