1. EXCAVATION AND TRENCH PROTECTION
DANGER
Deep Excavation
IS YOUR TEAM WORKING IN OR AROUND EXCAVATIONS. UNSTABLE EXCAVATIONS AND TRENCH WALLS CAN COLLAPSE, CRUSHING OR TRAPPING WORKERS. DEEP EXCAVATIONS CAN CAUSE SERIOUS INJURY OR DEATH IF A PERSON FALLS INTO THEM. LEARN HOW TO RECOGNISE DANGER AND PROTECT YOURSELF AND YOUR WORKMATES? READ THE INFORMATION BELOW AND DECIDE WHAT CHANGES CAN BE MADE TO THE WAY YOU WORK AND YOUR WORKING ENVIRONMENT TO MAKE IT A SAFER PLACE
TEST YOURSELF
1. Describe two signs of soil distress:
2. Describe why a worker buried up to the neck would not be able to breathe: ___________________________
3. When working in a 4 ft (1.2m) trench, there must be an exit within 25 feet (8m). True or False? ______________________________
4. Shielding is designed to prevent an excavated wall from caving in. True or False ?
______________________________
5. Name a portable device used for shielding: ______________________________
6. How does water or rain impact the classification of soil?
7. Trenches near landfills may not contain enough oxygen to support life. True or False? ___________________________
8. Describe a way to protect trench workers from falling soil or objects: ___________________________
9. Excavations need to be inspected only after they are first dug. True or False
___________________________
10. If you don’t know the soil type, what slope angle should you use to be safe? _____________
Answers
1. Signs of soil distress include cracks, slumping, bulging, sinking edge, or trickling pebbles.
2. The soil exerts great pressure on the chest, which prevents chest expansion.
3. True.
4. False. Shoring prevent cave-ins and shielding protects workers from a cave-in.
5. A trench box is a portable device that is used for shielding.
6. Rain or water decreases the stability of soil. Saturated soil can be very unstable.
7. True. The trench might be filled with a heavy gas (from the landfill) that displaces oxygen.
8. Remove loose soil by scaling, provide protective barriers, keep material 2 feet (0.60cm) from trench’s edge.
9. False. Inspect excavations daily, throughout the shift, and after conditions change.
/2 feet (0.45cm) horizontal for every vertical foot. So a 10 foot (3.1m) deep trench would slope out 15 feet (5m).
What is a Trench?
A narrow excavation deeper than it is wide
No more than 15 feet (5m) wide at bottom
What is a cave-in?
Soil or rock that suddenly falls or slides into an excavation
Can entrap, bury, injure or immobilize
Soil gravitates downward, pressure pushes soil inward toward the trench
Bottom third of wall typically fails first
Soil above the collapsed lower wall follows
Trench Boxes
Often designed to stack
Never use sheeting to extend the height
Can be used in conjunction with sloping and benching
No one permitted inside when being raised or lowered
Excavations and Inspections
Inspections conducted before work starts, throughout shifts and after rainstorm or snow/ice thaw
Excavations inspected for:
Evidence of possible cave-ins
Indications of failure of protective systems
Potential hazardous atmosphere
If hazardous conditions are found, workers are not permitted to work
Signs of Soil Distress
Fissures or cracks
Slumping of material
Bulging or heaving of material at the bottom l
Sinking of excavation’s edge
Ravelling, or small amounts of material (i.e., pebbles) trickling into excavation
Conditions Causing Soil Distress
Nearby vibrating machinery
Nearby heavy, moving loads
Seeping water or rain
Hot, dry weather
Freeze and thawing of soil
Supervisor and Safety Advisor carry out hazardous atmosphere checks prior to any work starting. A trained watchman stands by.
Falling Soil or Equipment
Protect workers from loose rock/soil that may fall from an excavation face
Carry out scaling to remove loose soil
Install protective barricades, such as shoring or shields
Protect workers from material or equipment that could fall into the excavation
Keep material/equipment 2 feet (0.6m) from edge
Use retaining devices
Adjacent Structures
Excavations might endanger stability of buildings, walls, other structures
Sidewalks, pavement not to be undermined unless supported to prevent collapse
Shoring, bracing, or underpinning used to ensure stability for employee protection
Water Accumulation
Workers have drowned in the water at the bottom of a trench or excavation
Never work in an excavation where water is accumulating without proper precautions
Special shoring or shield system
Water removal system in operation
Place barriers and warning signs around deep excavations.
Sloping trench walls is carried out mechanically, while supervisors check the installation of trench protection and look for potential hazards prior to work starting
Hazardous Atmospheres
Excavations near sewers, landfills, hazardous substances storage areas may contain gasses
Test atmosphere when deeper than 4 feet (1.3m)
Ventilation or appropriate PPE
Rescue and emergency equipment ready
Other Trenching Issues
Mark underground utilities
Stand away from lifting/digging equipment
Use warning systems or barricades
Always use the correct PPE
Trenches 4 feet deep or more must have exit means within 25 feet of every worker
Use fall protection
Worker on top watches excavation walls to warn trench workers of potential hazards
Remember
Cave-ins occur suddenly and can entrap, bury, or injure
Soils have varying stability that determines the appropriate protection
Be aware of signs of soil distress
Be aware of hazards associated with working around excavations
Carry out JSA before you start work
Sloping and Benching
Sloping: this means angling of walls at an incline to help stabilize the slope
Benching: cutting a series of steps to angle the walls
Soil type determines angle of slope / bench
Type A: 3 feet (1.0m) horizontal to 4 feet 1.3m vertical (3/4:1)
Type B: 4 feet (1.3m) horizontal to 4 feet (1.3m) vertical (1:1)
Type C: 6 feet (1.8m) horizontal to 4 feet (1.3m) vertical (1-1/2:1)
Benching is not permitted for Type C soil
Shoring
Support walls designed to prevent cave-in
Usually built in place and designed by an engineer
Components include: uprights (sheeting), wales, and cross braces
Shielding
Withstands forces of a cave-in and protects employees within
Permanent or portable
Trench boxes
Depending on soil stability it may not be necessary to slope trench walls. Required slope must be determined by a qualified engineer.
Cave-in Injuries
Soil weighs 125 lbs per cubic foot or 170kgs per cubic meter.
A worker can be crushed by soil, rock, or an object
Suffocation can occur even if worker’s head is not buried, soil exerts great pressure and prevents chest expansion
Immobilized by soil’s suction effect
Soil Classification is determined by
Grain size
Saturation
Cohesiveness
Unconfined compressive strength
Know Soil Types
Type A - dense and heavy clay (most stable)
Type B - silt, sandy loam, medium clay
Type C - gravel, loamy sand, soft clay (least stable)
Purpose designed trench protection boxes must be used in unstable soils. Ensure they are used, protect yourself
Working alone in a trench without supervision is dangerous and NOT permitted!
Do not work on sides of sloped or benched excavation above other workers
Prepared by: Andy Britten December 03