Excavations and Trench Protection

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 dont 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 trenchs edge. 9.
False. Inspect excavations daily, throughout the
shift, and after conditions change. 10. 1-1/2
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

• 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

• 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 excavations edge
• Ravelling, or small amounts of material (i.e.,
  pebbles) trickling into excavation

Supervisor and Safety Advisor carry out hazardous
atmosphere checks prior to any work starting. A
trained watchman stands by.
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

• 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

• 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

• 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 (3/41)
• Type B 4 feet (1.3m) horizontal to 4 feet (1.3m)
  vertical (11)
• Type C 6 feet (1.8m) horizontal to 4 feet (1.3m)
  vertical (1-1/21)
• 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 workers head is
  not buried, soil exerts great pressure and
  prevents chest expansion
• Immobilized by soils 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