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Excavation, Trenching & Shoring
Safety •Presented by
•Presented by
–R. W. Smith
Excavation Safety Is
Based On 4 Things
•Understanding soil
•Competent Person
•Inspections
•Inspections
•Correct Set Up
•Protection
Excavation Safety
•Dangers of Excavation
–Suffocation
–Crushing
–Crushing
–Drowning
–Loss of circulation
Excavation Safety
•Why is it important?
•Any hole dug in the earth is an unnatural
situation
situation
•Nearly 300people die each year from
excavation accidents
•Over 3000people are injured in excavation
accidents each year
•Majority occur in less than 15feet
•How Excavation
is done in
other countries
•We’re much safer
•We’re much safer
Or Are We?
Or Are We?
Why Do Trenching Accidents
Occur?
•False Sense of Security
•Thought the soil was stable
•Conditions changed overnight
•Conditions changed overnight
•(Known to be out of compliance)
Excavation Hazards
•Cave In
•Falling Objects
•Hazardous Atmospheres
•Hazardous Atmospheres
•Utilities
•OSHA Inspections & Citations
Excavation Safety
•Results from:
•…being aware of hazard
•…making good choices
•…making good choices
•…following through on those choices
Why You Need To Know This
•OSHA Requirement:
–“The employer shall instruct each employee in
the recognition and avoidance of unsafe
the recognition and avoidance of unsafe
conditions and the regulations applicable to his
work environment to control or eliminate any
hazards or other exposure to illness or injury.”
OSHA 29 CFR 1926.21 b 2
•Protect Yourself!
Most Frequent OSHA Violations
of Excavations
•General Req
•Protective Systems
•Head Protection
•Head Protection
•Training
•Material Handling Equipment
•Ladders
Why You Need To Know This
•Remember:
–OSHA requirements are a legal minimum of
safety that must be followed. Your employers
safety that must be followed. Your employers
policies must be equal to or greater than these
legal requirements
Understanding Soil
Mechanics of a Cave In
Mechanics of a Cave In
Mechanics of a Cave In
Worksite Analysis Steps
•Soil Composition
•Surface & Subsurface Water
–Or dryness
–Or dryness
•Location & Identity of Utilities
•Traffic& Nearby Structures
•Depth of Excavation
•Time excavation open
•Climatic conditions
Worksite Analysis Steps
•Hazardous Atmospheres
Worksite Analysis Steps
•Hazardous Atmospheres
•Excavations near sewers, landfills,
hazardous substances storage area
hazardous substances storage area
•Test atmospheres when deeper than 4 feet
•Ventilation or appropriate PPE
•Rescue & Emergency Equipment
Surface & Subsurface Water
•Change in moisture affects stability
•Surface Runoff Water
–Use dikes &/or ditches to divert
–Use dikes &/or ditches to divert
•Leaching water in Excavation
–Must pump out water
–Cave-in protection more critical
Utilities
•Contact IOWA ONE CALL
•When nearing depth of utilities, must hand
digdig
•Uncovered utilities may need support
•Watch for overhead utilities
–Maintain at least 10 ft clearance from energized
lines
24
Traffic & Nearby Structures
•Traffic, work, equipment add vibration &
weight increasing cave in potential
•Use barricades, signage, cones, flagger, stop
•Use barricades, signage, cones, flagger, stop
logs to protect site & public
•Do not dig adjacent or under a structural
wall with out support or an “ok” from a
Registered Professional Engineer
Traffic & Nearby Structures
•Excavation must be secured from
unauthorized access by the public by
barricades, signs, etc.
barricades, signs, etc.
•If excavation is to be left open &
unattended, it must be secured (ex. Snow
fence, etc.)
Traffic & Nearby Structures
•Use barricades,
signage, cones,
signage, cones,
flagger, stop
logs to protect
site & public
Depth
•Deep excavations have greater potential for
cave in due to greater exposed surface area
•Decision Process
•Decision Process
–If over 20 ft. deep, must use Registered
Professional Engineer OR
–Use tabulated data from a RPE
–If under 20 ft. depth can use OSHA standards
or RPE
Time Excavation Open
•Ground is moving entire time even if you
can’t see it
•Longer Excavation is open, more likely to
•Longer Excavation is open, more likely to
experience cave in
Climate
•Drying, Rain, Freezing & Thawing will
decrease stability
Soil Analysis
•Use one Visual Test & one Manual Test
•Soil Types
–A
–A
–B
–C
–Stable Rock
Soil Type A
•Cohesive soil
•Unconfined Compressive Strength over
3000 psf
3000 psf
•Previously undisturbed
•No fissures
•No traffic or equipment vibration
•Examples: clay, silty clay loam, sandy clay
loam
Type C Soil
•Least Stable
•Compressive strength less than 1000psf
•Submerged
•Submerged
•Leaching water
•Examples: gravel, sand, loamy sand
Type B Soil
•Not A or C
•Most Soil
•Compressive Strength from 1000 to 3000
•Compressive Strength from 1000 to 3000
psf
•Fissured
•Previously disturbed
•Examples: silt, silty loam, sandy loam, Silty
clay loam, sandy clay loam
Stable Rock
•Natural solid mineral matter that can be
excavated with vertical sides and remain
intact while exposed
intact while exposed
•None in Iowa
video
Visual Tests
•Observe soil as it is dug out of the trench
•Look at face of wall & material coming out
of trench
of trench
•Observe particle size
–Gravel: anything larger than a pencil lead
–Sand: smaller than gravel down
–Granular appearance
–Somewhat “sticky” when wet; not when dry
41
Visual Tests
•Silt
–Particles cannot be seen w/ naked eye
–not necessarily “sticky”
–not necessarily “sticky”
•Clay
–Particles cannot be seen w/ naked eye
–“sticky”
Visual Tests
•Clumping
–Gravel & Sand don’t clump unless frozen
–Fine sand may clump by breaks up easily
–Fine sand may clump by breaks up easily
–Silt & Clay typically stay in clumps
•Silt can be crushed when dry
•Clay is sticky & slippery when wet
•Clay is very hard when dry
Visual Tests
•Cracks & Fissures in ground & wall
–Cracks indicate partial failure of wall
–Spalls are falling chips of soil which indicate
–Spalls are falling chips of soil which indicate
moving ground
–Trickling soil indicates instability
•Existing Utilities
•Layering
Visual Tests
•Water
–Presence creates instability; not volume
–Standing water
–Standing water
–Seeping water (creates a shiny appearance)
–Trickling Water
–Runoff
•Sources of Vibration
–Highways, Railroad, Manufacturing equipment,
construction equipment
46
Manual Tests
•Plasticity Test
•Undisturbed sample of soil
•Adjust moisture to consistency of modeling
•Adjust moisture to consistency of modeling
clay
•Roll sample to 1/8 inch thickness & hold by
one end
•If 2 inches long or more, it is clay soil
Manual Tests
•Sand/Sedimentation Test
•Fill olive jar with soil
•Estimate % of sand
•Estimate % of sand
–80% or more sand is classified as sand
–70% sane + 30 % silt is loamy sand
–85% sand + 15% clay is loamy sand
Manual Tests
•Dry Strength
•If dry sample crumbles on own or with little
pressure, it is granular, gravel, sand, or silt
pressure, it is granular, gravel, sand, or silt
•If it shrinks or cracks upon drying, it is
mostly clay
•If it shrinks or cracks upon drying &
smaller pieces are hard to break it may
fissured soil (also look for discoloration
along cracks)
Manual Tests
•Thumb Penetration
•Undisturbed sample or clod
•Cut smooth surface with knife
•Cut smooth surface with knife
•Press thumb into smooth surface
–Readily indented by requires great effort to
penetrate = Type A
–Easily penetrate several inches = Type C
–Partial penetration = Type B
Manual Tests
•Pocket Penetrometer
•Done similarly to Thumb Penetration test
•Gives numeric measurement of compressive
•Gives numeric measurement of compressive
strength
Manual Tests
•Shearvane or Torvane Shear Test
Manual Tests
•Drying Test
•Tests for fissures & hardness
•Sample 1” by 6”
•Sample 1” by 6”
•Dry slowly
•Cracking during drying indicates fissures
•Easily breads after drying, is granular or
fissured
Competent Person
•“One who is capable of identifyingexisting
and predictable hazards in the surroundings
or working conditions which are unsanitary,
or working conditions which are unsanitary,
hazardous, or dangerous to employees, and
who has the authorityto take prompt
corrective measures to eliminate them”
Competent Person
•Required on every site
•Must be identified by contractor/employer
•Can have more than one Competent Person
•Can have more than one Competent Person
•Must conduct inspections
–Daily
–Periodic
–After weatherchange
–After significant time of unattended trench
Competent Person
•Misconception: Competent Person is
responsible for site so that he will be held
responsible in case something goes wrong
responsible in case something goes wrong
•Competent person is designated to take
steps to ensure employees safety
Inspections
•Soil Typing (including visual & manual
tests)
–Fissures
–Fissures
–Slumping or material from excavation face
–Bulging or heaving of material at the bottom of
excavation wall
–Sinking of excavation edge
–Ravelling or small amounts of material trickling
into excavation
Inspections
•Water
•Selection & condition of sloping, shoring,
or trench boxes
or trench boxes
•Utilities notified
•Access
Inspections
•Spoil pile location (at least 2ft. back from
trench)
•Cracks/fissures
•Cracks/fissures
•Vibration
•Structures, tress, other
•Atmospheric testing
•Barricades, stop logs, traffic control
•Correct PPE
60
Hazardous Atmospheres
•Trench may have hazards similar to
Confined Space
•Example locations:
•Example locations:
–Landfill areas
–Hazardous Material storage areas
–UST’s
Hazardous Atmospheres
•Must test for hazardous atmosphere
–Oxygen not less than 19.5%
–Flammable not over 10% LEL
–Flammable not over 10% LEL
–Toxic gases not over PEL’s
–No other hazards
Employee Protection
•All excavations more than 5ft. deep
required employee protection
•Not every scenario can be fore thought…
•Not every scenario can be fore thought…
exercise good, safe judgement within these
guidelines
Employee Protection
•Protect employees from loose soil that may
fallfrom excavation face
–Scaling to remove loose material
–Scaling to remove loose material
–Protective structures such as shields or shoring
•Protect employees from material or
equipment that could fall into trench
–Keep material 2 ft.from edge
–Use retaining device
65
Trench Boxes
•Often designed to stack
•Never use sheeting to extend height
•Can be used in conjunction with sloping &
•Can be used in conjunction with sloping &
benching
•No one permitted inside the box while being
raised or lowered
Trench Box
Shoring & Protective Systems
•Must be installed from top down
•Cannot have employees in trench but
outsideof protective system
outsideof protective system
•Access can be no more than 25ft. from
employee
•Ladders must extend 3ft. above upper
contact point
14 ply (Finland form)
FinForm or Finboard
must be 3/4” minimum
thickness.
Std. Plywood must be at
least 1-1/8”.
2 inch diameter cylinders, at this width,
shall have structural steel tube (3.5 x 3.5
x 0.1875) oversleeves, or structural
oversleeves of manufacturer's
specification, extending the full,
collapsed length.
Shores
1926.651(c)(2) Means of egress
•Means of egress from trench excavations.
A stairway, ladder, ramp or other safe
means of egress shall be located in trench
77
means of egress shall be located in trench
excavations that are 4 feet (1.22 mm) or
more in depth so as to require no more than
25 feet (7.62 m) of lateral travel for
employees.
78
79
80
81
Sloping Type A Soil
Sloping Type A Soil
Under 12 ft; Open less than 24 hr
84
85
Benching Type A Soil
Sloping Type B Soil
Benching Type B Soil
Sloping Type B Soil
Straight Wall Allowance
Sloping + Trench Box
Sloping Type C Soil
QUESTIONS?
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