trenching and shoring university of n orthern c olorado
TRANSCRIPT
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”