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
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
Sloping trench walls is carried out
mechanically, while supervisors check the
installation of trench protection and look for
potential hazards prior to work starting
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
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)
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
Excavations and Inspections
• Inspections conducted before
work starts, throughout shifts
and after rainstorm or snow/ice
thaw
• Excavations inspected for:
- Evidence of possible caveins
- 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.
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
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
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
Place barriers and warning signs
around deep excavations.
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
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 caveins 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.
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).
Prepared by: Andy Britten December 03