Transcript Subpart P - Excavations

Excavation & Trenching
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Seek specific guidance from the appropriate regulator (OSHA) or professional advisor.
Dirt Work is Serious Business
Excavation cave-ins are one of the major sources
of fatalities within the construction industry.
 Trenching accidents on construction sites account
for an estimated 100 fatalities/year.
 79% of trench fatalities occur in less than 15’
excavations: 38% in less than 10’.
 Statistically most likely to be killed in an
excavation:

 Male
 Construction Labor
 20 to 30 years old
News Releases
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Michigan 09/29/10
A construction worker killed Wednesday in a trench collapse west of Kalamazoo has been
identified by police as Samuel Wilson, 58, of Burlington.
Wilson was installing sewer piping in a trench that was 8 feet deep and 3 feet wide when
the trench collapsed at 4:12 p.m., according to the Kalamazoo County Sheriff’s Office. At
the time of the incident, Wilson, was working at the site of a house under construction in
the 3200 block. Wilson was pronounced dead at the scene, deputies said.
Undersheriff Pali Matyas said police planned to turn their investigation over today to the
Michigan Occupational Safety and Health Administration.
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Nebraska 06/05/10
A Lewis and Clark Rural Water District employee died Friday after a trench collapsed
around him in northern Knox County. The incident killed 48-year-old Galen Jueden of
Hartington, Knox County Sheriff Jim Janecek said in a news release.
Jueden and another worker were replacing water lines in the trench, about 5 or 6 feet
deep, when it collapsed around Jueden at about 11 a.m. Friday, Sheriff's Capt. Ernest
Ibach said.
"He was only really buried about up to his waist," Ibach said. Telephone workers in the
area pulled him from the trench and performed CPR, but neither they nor rescue workers
could revive him. Jueden was pronounced dead at the scene.
OSHA’s Injury Data
 The
following hazards are most responsible
for excavation related injuries;
 No protective systems
 Failure to inspect the trench before and during
work
 Improper spoils pile location
 Access/egress issues
Defining a Competent Person
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One who is capable of identifying existing and predictable
hazards in the surroundings, or working conditions which
are unsanitary, hazardous, or dangerous to employees,
and who has authorization to eliminate them.
Competency for Subpart P requires knowledge of the
following:
1) Soils analysis
2) The use of protective systems
3) The requirements of this standard
A cubic yard of soil
weighs approx.
2700 lbs!
Competent Person Responsibilities
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Authority to stop work
Inspection of excavations
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Daily
Pre-shift
As needed
After rain
Any increasing hazard occurrence
Testing for hazardous atmospheres
Inspection of material and
equipment
Monitoring of water removal
Visual Tests
Manual Tests
Mechanics of a Cave-In
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Stress cracks form back from
edge due to ground surface
tension and shear forces.
Cracks occur from about 1/3
to 2/3 of the depth of the
excavation back from its
edges.
Cracks take away the soils
ability to maintain a strong
vertical face.
The weight of the earth
above is transferred to the
lower portions of the
excavation wall.
Mechanics of a Cave-In
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Excavation bottoms are the first to fail.
Support for the upper part of excavation is left
hanging only by shear and reduced tension
forces.
The uppermost portion of the vertical wall
collapses into the excavation.
Soil, like concrete, is normally strong in
compression but not strong in tension.
Figures 1 and 2 two detail the scenario.
Mechanics of a Cave-In
Fig. 1
Fig. 2
Soil Classification
Cohesive
Stronger +
Clay
Granular
More Cohesion – Less Cohesion
Silt
- Weaker
Sand
Soil Classification – Visual Tests
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Observe samples of soil that are
excavated.
 If it stays in clumps it is
cohesive
 If it breaks up easily its granular
Check the sides of the opened
excavation and adjacent surfaces
for signs of cracking.
Check for existing utilities,
underground structures, and
previously disturbed soil.
Check for layered soils.
Be aware of surface water, seeping
water, and water collection in the
base.
Be aware of the machinery running
near the cut. Vibration can affect
stability.
Soil Classification – Manual Tests
Manual
(Bare Hands)
Mechanical
(Device)
Plasticity
Pocket Penetrometer
Dry Strength
Shear Vane
Thumb Penetration
Plasticity – Dry Strength

Plasticity – Mold a moist or wet sample of soil into a wet
ball and attempt to roll it into threads as thin as 1/8-inch in
diameter. Cohesive material can be successfully rolled into
threads without crumbling. If at least a two-inch length of
1/8-inch thread can be held on one end without tearing,
the soil is cohesive.

Dry Strength – If the soil is dry and crumbles on its own
or with moderate pressure into individual grains or fine
powder it is granular. If its dry and breaks into clumps, but
the clumps can only be broken with difficulty, it may be a
clay combination.
Thumb Penetration
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This test can be used to estimate the
unconfirmed compressive strength of cohesive
soils.
Thumb Penetration Test
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Type A: These soils can be
indented by the thumb, but
penetration takes great effort.
Type B: Easily indented, can
be penetrated with somewhat
less effort than type A.
Type C: This type of soil can
be easily penetrated up to
several inches by the thumb
and can be molded with light
finger pressure.
Pocket Penetrometer
Probes the soil with a
small tube-like plunger
 Device is pressed into
soil to calibration mark
 Spring loaded piston
displaces the scale ring
 Produces a
compressive strength
reading rated in
tons/sq.ft
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Shear Vane
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Hand-held instrument used for
determining soil strength
Provides reading in kPa
(kiloPascal, Unit of Pressure)
Vane blade is pushed into the
soil and device is rotated at
predetermined rate (ex: 1
revolution/minute)
Reading is obtained when soil
fails
Devices come with different
ranges and features
Extension rods are available to
increase the measurement
depth
Slope Configurations
Maximum Allowable
Soil or
Unconfined
Rock Type Slopes for Excavations Compressive
Less than 20’
Strength
Stable Rock
Vertical
90°
_______
Type A
¾ to 1
53°
≥ 1.5 tons/sq ft
Type B
1 to 1
45°
.5 - 1.5 tons/sq ft
Type C
1½ to 1
34°
≤ .5 tons/sq ft
Sloping
When combination soils are
encountered, and the soil
beneath is of lesser cohesion
than the soil above, the
slope will be that of the less
cohesive soil.
 When sloping with a shoring
system in place, the top
edge of the cut must be 18”
below the top edge of the
shoring system.
 A shoring device does not
affect the soil type
dimensions of the continuing
slope.

Short Term Maximum Allowable
Slopes
A short term maximum
allowable slope is a
special situation for
Type A soil.
 An excavation in Type
A soil that is open for
less than 24 hours and
12 feet or less in
depth, can have a
maximum allowable
slope of 1/2H:1V (63°).
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Benching
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Can stand alone or in
combination with sloping
Type C soils cannot be
benched
In multiple bench
situations, max bench
height of first bench is 4’
In bench-slope
combinations, max bench
height of first bench is 3.5’
Foundation/Basement Excavations
The depth of the
foundation/basement trench
cannot exceed 7½ feet deep
unless you provide other cave-in
protection.
 Keep the horizontal width of the
foundation trench at least 2 feet
wide. Mind surface encumbrances.
 Plan the foundation trench work
to minimize workers in the trench
and the length of time they spend
there.
 Inspect the trench regularly.
 Stop work if any potential for
cave-in develops and fix the
problem before work starts again.

Utilities Location
Alabama One Call
1-800-292-8525 or 811
 Must call at least 48
hours in advance
 Service is available
Monday through
Friday, 7:00 am to
5:00 pm
 All utilities are marked
in a standardized color
code
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Utilities Location
Excavators must observe a tolerance zone
 The width of the facility on a horizontal plane, at
least 18” on either side of the outside edge
 If relocation is
necessary,
excavator must
coordinate with
facility
owner/operator
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Utilities Location
 When
estimated location of underground
installations are approached, exact location
shall be determined by safe/acceptable
means (hand digging, soft dig, pot hole,
etc.)
 While excavation is open, underground
installations shall be protected, supported or
removed as necessary to safeguard
employees.
Uniform Color Codes
See Appendix “C”
 Electric
– Red
 Gas/Oil – Yellow
 Comm./CATV –
Orange
 Water – Blue
 Sewer – Green
 Proposed Exc. –
White
 Temp. Survey - Pink
Protective Systems
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Reasons for Needing a Protecive System
Existing utility lines, roadways, or structural
foundations intruding on the maximum
allowable slope.
No right-of-way permit for sloped excavation.
The vertical face excavation is beyond the
safety slope.
The gravitational force will cause soil raveling,
cave-ins, or slope stability failures from the
vertical face.
Protective Systems
Timber Shoring
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System uses reinforced wood sheets or planks in an upright or
sheet configuration to reinforce the vertical cut
Walers support the system horizontally against the outer wall
Struts support the system horizontally from side to side
Struts
Walers
Protective Systems
Hydraulic Shoring
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Uses alloy struts (aluminum,
steel) to support system side
to side
System does not require
entry for installation or
removal
Significantly lighter than
timber systems
Provides even distribution of
pressure along the trench
line
Can utilize "preloading" to
use the soil's natural
cohesion to prevent
movement
Adapts easily to various
trench depths and widths.
Protective Systems
Trench Boxes
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The width of the trench should exceed the width of the box to
facilitate ease of movement
Clearance prevents stresses on the trench box that could lead to
failure during cave-in
Trench boxes may sit on 2’ of excavated soil
Protective Systems
Pro Tec Slide Rail System
 Traditional shoring concept
with less excavation
 Channeled posts are pressed
into place by excavator
 Panels are inserted into post
channels
 System utilizes the soils
natural compressive
strength
 Fast installation and removal
 System conforms to a wide
variety of excavation types
Access/ Egress
A stairway, ladder, ramp, or other safe means of
egress shall be located in trench excavations
that are 4 feet or more in depth and require no
more than 25 feet of lateral travel for
employees.
 Must be designed by a competent person.
 Boards must be of uniform thickness and
structurally sound, also must be equipped with
cleats to prevent tripping on ramp applications.
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Hazardous Atmospheres
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All testing must be
performed from outside
the space
Hazard may be generated
from existing conditions
inside excavation
 Methane
 Natural Gas
 Petroleum
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Hazard may be generated
from surroundings
 Carbon Monoxide
Hazardous Atmospheres
Exposures to harmful levels of atmospheric
contaminants can be prevented by:
 Testing for oxygen deficient air with a tester at no
less than four feet in depth. (Concentrations
should lie between 19.5% and 23.5%)
 Flammable gas testing
 Toxic atmosphere testing.
 Testing as often as is necessary to ensure safe
atmosphere at all times
Standard Specifics
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All spoils piles and equipment must be kept at
least 2’ back from the excavation’s edge.
Employees must not be exposed to falling loads at
any time.
Employees must be provided with and wear
warning vests when exposed to traffic
Excavations greater than 5’ in depth must be
sloped, benched, or utilize a protective system.
Water accumulation must be controlled at all
times
Standard Specifics
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Surface encumbrances must be removed or
supported i.e. trees, telephone poles, fire hydrants
If a ramp must be constructed, handrails and
decking must meet established requirements.
Employee ramps must be designed by a
competent person.
Physical protection must be provided at all
remotely located excavations.
Structural ramps used to support equipment must
be designed by a Registered Professional Engineer
Excavation Checklist
Utilities
marked
locations identified and
Access/
Egress points and routes
free from obstruction
Potentially
Hazardous Atmosphere
tested before and during shift
Water
Emergency
Rescue Equipment on
site and ready for duty
Spoils
Employees
and machinery
protected from traffic
Soil
Employees
Shoring
loads
protected from falling
Proper
fall protection for cross
over points
Excavations
≥ 20’ in depth have
engineered protection systems
Stability
of adjacent structures
secured and shored
accumulation monitored
before and during shift
piles at least two feet back
from excavation edge
classification performed by
Competent Person
systems inspected before
and during shift
Daily
inspection performed by a
competent person before and
during the shift
Inspection includes the trench, the
area around it, and protective
systems