Trenching and Shoring

UNIVERSITY of

NORTHERN COLORADO

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Injury and Death

Excavating is one of the most hazardous construction operations

Most accidents occur in trenches 5-15 feet deep

There is usually no warning before a cave-in

Trenching Related Deaths

2000 to 2006………..271 trenching fatalities

Rules Underground Utilities must be located and marked before excavations

begin Employees are not allowed in the excavation while heavy equipment

is digging All employees on an excavation site must wear hard hats Employees shall be removed from the trench during a rainstorm Do NOT work under raised loads Stand away from equipment that is being loaded or unloaded to avoid

being struck by falling materials or spillage Trench that is 4 feet or greater in depth requires a trench inspection

form filled out by the competent person. All excavations or trenches 4 feet or greater in depth shall be

appropriately benched, shored, or sloped. Excavations or trenches 20 feet deep or greater must have a

protective system designed by a registered engineer.

Inspection Form

To be completed by Competent Person

Review FormTurn completed

forms into EHS.

Soil classification

Type A Fine grainedDoesn’t crumbleHard to break up when dry

Type BGranular: coarse grainsLittle or no clay contentCrumbles easily when dry

Clay Loam

Clay

Silty loam

Loam

Angular gravel

Soil Classification

Type C Granular soil: very

coarseMinimal cohesionExamples:

o Sando Gravelo Loamy sando Submerged soil or soil

with freely seeping watero Submerged rock that is

not stable.

Sand

Gravel

Loamy sand

Definitions

“Competent person” is someone who: Can identify existing or predictable hazards in an excavation Has authority to take corrective actions as necessary Is familiar with the DOSH excavation standards Is knowledgeable in soil analysis and classification as well as

the erection, use, and precautions for the protective system on site

Definitions

• Excavation – a man-made cut, cavity, trench, or depression formed by earth removal.

• Trench – a narrow excavation. The depth is greater than the width, but not wider than 15 feet.

• Shield - a structure able to withstand a cave-in and protect employees

• Shoring - a structure that supports the sides of an excavation and protects against cave-ins

• Sloping - a technique that employs a specific angle of incline on the sides of the excavation. The angle varies based on assessment of impacting site factors.

• Cave-in – The separation of soil or rock material from the side of an excavation.

Design of Protective Systems

The employer shall select and construct : slopes and configurations of sloping and benching

systems support systems, shield systems, and other

protective systemsShield - can be permanent or portable. Also known

as trench box or trench shield.Shoring - such as metal hydraulic, mechanical or

timber shoring system that supports the sides Sloping - form sides of an excavation that are

inclined away from the excavation

Materials and Equipment

Equipment used for protective systems must not have damage or defects that impair function.

If equipment is damaged, the competent person must examine it to see if it is suitable for continued use.

If not suitable, remove it from service until a professional engineer approves it for use.

Benching Benching can be used in conjunction with sloping. Benching is NOT allowed in Type C soil.

The bottom vertical height of the trench must not exceed 4 feet.

Benches must be below the maximum allowable slope for that soil type.

(example: A 10-foot deep trench in Type B soil must be benched back 10 feet in each direction, with the maximum of a 45 degree angle.)

SlopingMaximum allowable slopes for excavations

less than 20 feet based on soil type and angle to the horizontal are as follows:

Soil Type Height/Depth Ratio Slope Angle

Type A ¾ : 1 53 degrees

Type B 1 : 1 45 degrees

Type C 1½ : 1 34 degrees

Shoring

A support system for trench faces used to prevent movement of soil, underground utilities, roadways, and foundations.

Three types of shoring:Aluminum HydraulicTimberPneumatic

Shielding Shielding also known as Trench Boxes focus on protecting from

cave-ins. Workers must enter and leave the shield in a protective manner

(ladder or ramp) Workers may NOT remain in the shield while the shield is being

moved.

Inadequate Protective System

This excavation has inadequate support posts and egress access

This worker is in a trench with no protective system, that is not sloped or benched and has no means of egress

Hazardous Conditions

The weight and vibrations of the crane makes this a very hazardous condition.

They should not be working under this crane.

Warning Systems

The following steps should be taken to prevent vehicles or people from falling

Barricades must be installed where necessary

Hand or mechanical signals must be used as required

Trenches left open overnight shall be fenced and barricaded

Ingress / EgressAccess to and exit from the trench requires the following conditions:

Trenches 4 feet or more in depth should be provided with a fixed means of egress

Spacing between ladders or others means of egress must be that the worker will not travel more than 25 feet laterally to the nearest egress

Ladders must be secure extending a minimum of 36 inches above the landing

Metal ladders should not be used when electrical utilities are present

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Improper Means of Egress

A stairway, ladder, or ramp must be present in excavations that are 4 or more feet deep, and within 25 feet of the employees

The ladder should extend 3ft above the excavation

Two ladders lashed together are not an adequate means of egress

Hazardous Atmospheres If there is any possibility that the excavation could

contain a hazardous atmosphere, testing must be conducted prior to entry. (example: Natural gas line may warrant this)

Test excavations more than 4 feet before an employee enters the excavation for: Oxygen deficiency High combustible gas concentration High levels of other hazardous substances

All operations involving atmospheric testing will require Confined Space Entry procedures to be used. Continuous monitoring may be required.

Oxygen should be between 19.5% - 23.5%

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Water is Hazardous

When water is present in an excavation it is extremely hazardous to enter

Methods for controlling standing water and water accumulation must be provided

University of Northern Colorado

Environmental Health & Safety

351-1963 or 351-1149

Call for questions or concerns!“Protect Yourself”