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Excavations
1926 Subpart P
 EXCAVATION

◦ Any man-made cut, cavity, trench, or depression in an
earth surface that is formed by earth removal.
◦ Cave-ins are much more likely to result in worker
fatalities than other excavation-related accidents.

TRENCH
◦ A narrow excavation (in relation to its length) made
below the surface of the ground.
◦ The depth of a trench is greater than its width, and
the width (measured at the bottom) is not greater
than 15 ft (4.6 m).
Soil Mechanics
A number of stresses and deformations
can occur in an open cut or trench.
 For example, increases or decreases in
moisture content can adversely affect the
stability of a trench or excavation.
 The following diagrams show some of the
more frequently identified causes of
trench failure.

Excavations

1926.651(b)
◦ Locate underground utilities and installations
Means of Access/Egress

1926.651(c)
◦ Required in excavations 4 feet or deeper
◦ Provide means of egress
◦ Maximum lateral travel distance in 25 feet
Hazardous Atmospheres

1926.651(g)
◦ Excavations 4 feet or deeper where
hazardous atmospheres can reasonably exist
◦ Oxygen deficiency, oxygen enriched
◦ Toxic gases, flammable vapors
◦ Provide ventilation and/or PPE
Emergency Rescue Equipment

Emergency rescue equipment is required when
a hazardous atmosphere exists or can
reasonably be expected to exist.
 Requirements are as follows:


◦ Respirators must be of the type suitable for the
exposure.
Attended (at all times) lifelines must be provided when
employees enter bell-bottom pier holes, deep confined
spaces, or other similar hazards.
Employees who enter confined spaces must be trained.
Control of Water

1926.651(h)
◦ PROTECT EMPLOYEES FROM THE
ACCUMULATION OF WATER
◦ MONITOR WATER REMOVAL EQUIPMENT
Protection of Employees

1926.652(a)
◦ Protect employees in the excavation from
cave-ins in excavations 5 feet and deeper
 Protection could be required at depths less than 5
feet if there is an indication of a potential cave-in,
work activities warrant protection, etc.
 Not required for excavations made entirely in
stable rock
Protection Systems
1926.652
 Sloping and benching
 Shielding, support, or other protective
system

Stable Rock
Stable rock is natural solid mineral matter
that can be excavated with vertical sides
and remain intact while exposed.
 It is usually identified by a rock name such
as granite or sandstone.

TYPE A SOILS
Examples of Type A cohesive soils are
often: clay, silty clay, sandy clay,
clay loam.
 Compressive forces of 1.5 tsf or greater

TYPE B SOILS
Type B soils are: angular gravel; silt; silt
loam; previously disturbed soils unless
otherwise classified as Type C
 Compressive forces greater than .5 tsf but
less than 1.5 tsf

TYPE C SOILS
Type C soils include granular soils such as
gravel, sand and loamy sand, submerged
soil, soil from which water is freely
seeping, and submerged rock that is not
stable.
 Compressive forces .5 tsf or less

Soil Field Tests

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Thumb test
Plasticity
Pocket
penatrometer
Torvane shear
Sedimentation
Thumb Penetration Test
ASTM test designation D 2488
 Retrieve a large clump of undisturbed spoil
 Attempt to penetrate the soil with the tip of
the thumb
 Type A soil can be penetrated only with
great force
 Type B will penetrate to the full length of the
thumb nail
 Type C will penetrate easily several inches
and can be molded by light finger pressur

Plasticity Test




Roll a moist sample
of spoil into a ball
Roll the ball out into
a 1/8" by 2 " thread
If this can be done,
hold it on end
If it remains
suspended without
tearing the soil is
cohesive
Pocket Penetrometer

POCKET PENETROMETER.
Penetrometers are directreading, spring-operated
instruments used to determine
the unconfined compressive
strength of saturated cohesive
soils.

Once pushed into the soil, an
indicator sleeve displays the
reading.

The instrument is calibrated in
either tons per square foot
(tsf) or kilograms per square
centimeter (kPa).

However, Penetrometers have
error rates in the range of ±
20-40%.
Torvane Shear






Select fresh clod or
block of undisturbed
soil from spoil pile
Cut a smooth surface
on the clod
Insert vanes of device
into the soil
Retract vanes to show
foot imprint
Set indicator at zero
Hold device firmly
against soil and twist
in clockwise manner
until soil fails in shear
Consistency
Term
Shear Strength,
psf
Unconfined
Compressive
Strength, psf
Very Soft
<250
<500
Soil Type
TYPE “C”
Soft
250-500
500-1000
Medium
500-1000
1000-2000
Stiff
Stiff
1000-1500
1500-2000
2000-3000
3000-4000
Very Stiff
Hart
2000-4000
>4000
4000-8000
>8000
TYPE “B”
TYPE “A”
Sedimentation Test
Flat bottom container at
least 7 inches high
 Fill glass jar
 5 inches of water on top of
soil
 1 1/2 inches of soil

•
Place lid on jar and
shake
– Set jar down
– Rotate slightly
– Larger particles settle out
immediately
– Wait 30 seconds
– Mark jar
– Silt after several minutes
– Fine clays in an hour
– Make second mark
Sloping Options
NO STEEPER THAN 1 1/2
HORIZONTAL TO 1 VERTICAL (34
DEGREES)
 OSHA TABULATED DATA (SOIL
CLASSIFICATIONS)
 OTHER TABULATED DATA
 REGISTERED PROFESSIONAL
ENGINEER DESIGN

Slopes for Types of Soil
Stable Rock (Vertical) 90 degrees
 TYPE A - (3/4 Horiz. TO 1 Deep) (53
degrees)
 TYPE B - (1 Horiz. TO 1 Vertical)(45
degrees)
 TYPE C - (1 1/2 Horiz. TO 1 Deep)(34
degrees)

Shoring
Provision of a support system for trench
faces used to prevent movement of soil,
underground utilities, roadways, and
foundations.
 Shoring or shielding is used when the
location or depth of the cut makes
sloping back to the maximum allowable
slope impractical.

Types of Shoring
There are two basic
types of shoring,
timber and aluminum
hydraulic
 Shoring systems
consist of posts,
wales, struts, and
sheeting.

Hydraulic Shoring

Hydraulic shoring
provides a critical
safety advantage over
timber shoring
because workers do
not have to enter the
trench to install or
remove hydraulic
shoring.
Hydraulic Shoring


Hydraulic shoring provides a critical safety
advantage over timber shoring because
workers do not have to enter the trench to
install or remove hydraulic shoring.
Other advantages of most hydraulic systems
are that they:
◦ are light enough to be installed by one worker;
◦ are gauge-regulated to ensure even distribution
of pressure along the trench line;
◦ can be adapted easily to various trench depths
and widths.
Installing/Removing Shoring
All shoring should be installed from the
top down and removed from the bottom
up
 Hydraulic shoring should be checked at
least once per shift for leaking hoses
and/or cylinders, broken connections,
cracked nipples, bent bases, and any other
damaged or defective parts

Shielding
Trench boxes are different from shoring
because, instead of shoring up or
otherwise supporting the trench face,
they are intended primarily to protect
workers from cave-ins and similar
incidents.
 The space between the trench boxes and
the excavation side are backfilled to
prevent lateral movement of the box.

Trench Boxes



The box should extend
at least 18 in above the
surrounding area if there
is sloping toward
excavation.
This can be
accomplished by
providing a benched area
adjacent to the box.
Earth excavation to a
depth of 2 ft below the
shield is permitted, but
only if the shield is
designed to resist the
forces
Trench Boxes
The box should extend at least 18 in above the
surrounding area if there is sloping toward
excavation.
 This can be accomplished by providing a
benched area adjacent to the box.
 Earth excavation to a depth of 2 ft below the
shield is permitted, but only if the shield is
designed to resist the forces

Spoil Pile
There is also a hazard from excavated
material and equipment outside of the
excavation falling or rolling down into the
trench.
 Temporary spoil must be placed no closer
than 2 ft from the surface edge of the
excavation

Materials and Equipment
Employees must also be protected from
excavated materials or equipment that
could pose a hazard by falling or rolling
into the excavation
 This is achieved by placing and keeping
materials and equipment at least 2 feet
back from the edge of the excavation.

Competent Person
Employers are required
to have a competent
person on site when
trenching and
excavation work is in
progress.
 This person should be
knowledgeable of the
cave-in hazards and
have sufficient authority
to act when necessary.


The designated competent
person should have and be
able to demonstrate the
following:
◦ Training, experience, and
knowledge of: - soil analysis,
- use of protective systems
◦ Ability to detect: conditions that could result
in cave-ins, - failures in
protective systems, hazardous atmospheres, and
- other hazard
◦ Authority to take prompt
corrective measures
Inspections
Daily inspections of the excavation,
adjacent areas and protective systems
should be made by a competent person.
 The inspections should be made at the
start of the work shift and as deemed
necessary throughout the shift.

Inspection Frequency

The following guide specifies the
frequency and conditions requiring
inspections:
◦ Daily and before the start of each shift.
◦ As dictated by the work being done in the trench.
◦ After every rain storm.
◦ After other events that could increase hazards, e.g., snowstorm,
windstorm, thaw,
earthquake, etc.
◦ When fissures, tension cracks, sloughing, undercutting, water seepage,
bulging at the bottom, or other similar conditions occur.
◦ When there is a change in the size, location, or placement of the spoil pile.
◦ When there is any indication of change or movement in adjacent structures.