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Excavations and Trenching
29 CFR 1926 Subpart P
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Objectives
In this course, we will discuss the following: Excavat ions /Trenching: Subpart P
1926.650 - Scope, application, and definitions
applicable to this subpart
1926.651 - Specific excavation requirements
1926.652 - Requirements for protective
systems
1926 Subpart P
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Subpart P - Appendices
Appendix A - Soil Classification
Appendix B - Sloping and Benching
Appendix C - Timber Shoring for Trenches
Appendix D - Aluminum Hydraulic Shoring
Appendix E - Alternatives to Timber Shoring
Appendix F - Selection of Protective Systems
1926 Subpart P
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Definitions
Excavation Man-made cut, cavity, trench, or depression formed
by earth removal.
Trench
Narrow excavation
Depth is greater than the width, but not wider than 15
feet.
Shield Structure able to withstand a cave-in and protect
employees.
1926.650(b)
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Definitions
Shoring Structure that supports the sides of an excavation
and protects against cave-ins.
Sloping
Technique that employs a specific angle of incline
on the sides of the excavation.
1926.650(b)
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Competent person Must have specific training in and be knowledgeable
about:
Soils classification
Use of protective systems
Requirements of the
standard
Must be capable of
identifying hazards,andauthorized to
eliminate them.
1926.650(b)Definitions
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Weight of Soil
Weight of soil varies with type and moisture content.
One cubic foot weighs 110 pounds to 140 pounds.
One cubic yard (27 cubic
feet) of soil can weighmore than 3,000 pounds.
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Excavation Hazards
Cave-ins are the greatest risk.
Other hazards include: Asphyxiation due to lack of oxygen
Inhalation of toxic materials/fumes
Fire
Machinery moving near edge of
excavation causing a collapse
Severing underground utility lines
Falls
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Injury and Death
Excavating is one of themost hazardous
construction operations.
Most accidents occur intrenches 5-15 feet deep.
Usually no warning before
a cave-in.
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Specific Excavation Requirements
(a) Surface encumbrances
(b) Underground installations
(c) Access and egress
(d) Exposure to vehicular traffic
(e) Exposure to falling loads
(f) Warning system for mobile equipment (g) Hazardous atmospheres
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Specific Excavation Requirements
(h) Protection from hazards associatedwith water accumulation
(i) Stability of adjacent structures
(j) Protection of employees from loose rock orsoil
(k) Inspections
(l) Fall protection
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Surface Encumbrances
All surface encumbrancesthat create a hazard toemployees must beremoved or supported tosafeguard employees.
1926.651(a)
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Estimated location ofutility installations [sewer,
telephone, fuel, electric,
water lines] must be
determined prior toopening an excavation.
1926.651(b)(1)Underground Installations
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Exact location ofunderground
installations must be
determined by safe and
acceptable means.
1926.651(b)(3)Underground Installations
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1926.651(b)(3)Underground Installations
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Underground Installations 1926.651(b)(3)
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1926.651(b)(4)Underground Installations
Undergroundinstallations must be
protected, supported or
removed as necessary
to safeguard employees.
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1926.651(c)(1)(i)Structural Ramps
Structural ramps used for access or egressof equipment must be designed by a
competent person.
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1926.651(c)(2)Egress - Trench Excavation
Stairway, ladder, ramp,or other safe means of
egress must be located
in trench.
Required if trench 4 feet
or more in depth.
Lateral travel distanceno more than 25 feet.
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Ramp, ladder or stairs required at 4 feet or deeper.
25 feet 25 feet
1926.651(c)(2)Egress - Trench Excavation
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1926.651(c)(2)Egress - Trench Excavation
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Is this correct?
1926.651(c)(2)Egress - Trench Excavation
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Exposure to Vehicle Traffic
Employees exposed to public vehicular traffic
must wear warning vests or other suitable
garments marked with
or made of reflectorized
or high-visibility material.
1926.651(d)
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1926.651(e)
Employees must not be permitted to workunder loads handled by lifting or digging
equipment.
Exposure to Falling Loads
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1926.651(e)Exposure to Falling Loads
Stand away from equipment that is being loaded or
unloaded.
Equipment operators may
stay in their equipment
during loading and unloadingif equipment has proper cab
shield or canopy.
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1926.651(f)Warning System - Mobile Equipment
Mobile equipment operated adjacent toexcavation and operator cannot see edge ofthe excavation:
Warning systemmust be utilized.
Barricades
Hand or mechanicalsignals
Stop logs
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Warning System - Mobile Equipment 1926.651(f)
Is this correct?
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Hazardous Atmospheres
Testing conducted before employees enter the
trench and regularly thereafter.
1926.651(g)(1)
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1926.651(g)(1)
Less than 19.5% or more than 23.5% oxygen
A combustible gas concentration greater than
20% of the Lower Flammable Limit (LFL)
Concentrations of hazardous substances that
exceed OSHAs Permissible Exposure Limits
(PEL)
Hazardous Atmospheres
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Test at 4 feet if suspected LEL
Oxygen
CO
H2S
Petroleum
Other toxics
1926.651(g)(1)Hazardous Atmospheres
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Emergency Rescue Equipment 1926.651(g)(2)(i)
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1926.651(g)(2)(i)Emergency Rescue Equipment
Emergency rescue
equipment must be
readily available where
hazardous atmospheric
conditions exist orexpected to develop
during work.
Breathing apparatus
Safety harness and line
Basket stretcher
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1926.651(h)(1)Water Accumulation
Employees must not work inexcavations where there is
accumulated water, or where
water is accumulating.
Unless precautions taken toprotect workers:
Water removal to control level of
water
Special support or shieldsystems
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Water Accumulation 1926.651(h)(1)
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Water removalequipment and
operations must be
monitored by a
competent person toensure proper
operation.
1926.651(h)(2)Water Accumulation
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1926.651(h)(3)Water Accumulation
Excavations subject torunoff from heavy
rains require an
inspection by a
competent person.
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Well Points Used to Remove Ground Water
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What are the hazards?
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1926.651(i)(1)Stability of Adjacent Buildings
Support systems suchas shoring, bracing, or
underpinning must be
provided to ensure
stability of structures.
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Stability of Adjacent Structures
Excavation below thefoundation that could
pose a hazard shall not
be permitted except:
Underpinning provided
Stable rock
Registered professional
engineer (RPE) has
approved
1926.651(i)(2)
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Underpinning toprevent structural
failure.
1926.651(i)(2)(i)Underpinning
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Stability of Adjacent Structures
Sidewalks, pavements and appurtenant
structure must not be undermined unless
supported to protect
employees from
collapse of suchstructures.
1926.651(i)(3)
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Adequate protection
provided to protect
employees from loose rock
or soil that could pose a
hazard by falling or rollingfrom an excavation face.
Protection of Employees 1926.651(j)(1)
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Belly bulgeFissures
Extra load from
spoil pile
Potential Problems
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Employees must be protected from equipment
or materials that could fall or roll into
excavations.
Materials and
equipment must bekept 2 feet from edge
of excavation or use
retaining devices.
Protection of Employees 1926.651(j)(2)
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Rule: 2 Feet 1926.651(j)(2)
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Two Feet From Edge 1926.651(j)(2)
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Extra Surface Loading
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1. Whats the Hazard?
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2. See it now
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1926.651(k)(1)Inspections Competent Person
Daily and before the start of each shift.
As dictated by the work
being done in the trench.
After every rain storm andother events that could
increase hazards, e.g.,
snowstorm, windstorm,
thaw, earthquake, etc.
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Inspections
Frequency of testing should be increased ifequipment is operating in trench as well as if
welding, cutting, or burning is done in trench.
1926.651(k)(1)
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Fall Protection 1926.651(l)(1)
Walkways provided when crossing over
excavation.
Standard guardrail
installed when more
than 6 feet abovea lower level.
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1926.652(a)(1)Protection of Employees
Employees in an
excavation must be
protected from cave-ins
by adequate protective
system. Except when:
Made entirely in stable rock
Excavation is less than 5
feet deep and examined by
competent person
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Sliding
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Toppling
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Tension Crack
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Bulging
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Heaving or Squeezing
Soil
Weight
SoilWeight
M th d f P t ti
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Methods of Protection
Sloping and benching
Shoring (spaced sheeting, closed sheeting)
Trench shield
Other occasionally used systems
1926.652
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1926.652(a)(2)Protective Systems
Protective systems
shall have capacity toresist without failure
all loads applied or
transmitted to the
system.
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1926.652(e)(1)(ii)Installation and Removal
Support systems must be installed and
removed in a manner that protects employeesfrom cave-ins.
I t ll ti d R l
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Removal must begin
at, and progress from,
the bottom of the
excavation.
Members released
slowly to note any
indication of possible
failure of remainingmembers.
Installation and Removal 1926.652(e)(1)(V)
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1926.652(e)(2)(i) and (g)(2)Installation and Removal
Excavations of material to a level not greater
than 2 feet below
the bottom of the
support system or
shield must not bepermitted.
Deadl Trench Collapse
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Deadly Trench Collapse
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Wh t th h d?
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Whats the hazard?
Wh t th h d?
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Whats the hazard?
Wh t th h d?
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Whats the hazard?
Wh t th h d?
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Whats the hazard?
Wh t th h d?
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Whats the hazard?
Whats the hazard?
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Whats the hazard?
Whats the hazard?
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Whats the hazard?
Soil Classification
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Contains definitions
Sets forth requirements
Describes acceptable visual and
manual test for use in classifying
soils
Soil Classification Appendix A
Definitions A di A
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Definitions
Cohesive soil
Clay, or soil with a high clay content, which has
cohesive strength
Does not crumble
Can be excavated with vertical side slopes
Plastic when moist
Hard to break up when dry
Appendix A
Soil types
Definitions A di A
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Definitions
Granular soil
Gravel, sand, or silt, with little or no clay content
No cohesive strength
Cannot be molded when moist
Crumbles easily when dry
Note: Some moist granular soils exhibit
apparent cohesion
Appendix A
Definitions A di A
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Definitions
Unconfined compressive strength Load per unit area at which a soil will fail in
compression
Note: Estimated in the field by use of a pocketpenetrometer, thumb penetration test, and other
methods
Appendix A
Thread Test A di A
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Roll into thread
At least 2 inches in length
Longer unbroken
thread means more
cohesive
Thread Test Appendix A
Ribbon Test A di A
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Roll soil into a cigar shape
Pinch between thumb and finger
Longer ribbon means
more cohesive
Ribbon Test Appendix A
Thumb Penetration Test Appendix A
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Thumb Penetration Test Appendix A
Pocket Penetrometer Appendix A
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Pocket Penetrometer Appendix A
Type A Soil Appendix A
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Type A Soil
Most stable: clay, silty clay, and hardpan
Not fissured
Not subjected to vibrationof any type
Never been previouslydisturbed
No seeping water
Unconfined compressive strength
greater than 1.5 tons per square foot
(tsf)
Appendix A
Type B Soil Appendix A
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Type B Soil
Medium stability: silt, sandy
loam, medium clay andunstable dry rock
Previously disturbed soils
unless otherwise classified
as type C
Soils that meet the
requirements of Type A
but are fissured or subject
to vibrationUnconfined compressive strength
less than 1.5 tsf and greater than
0.5 tsf
Appendix A
Type C Soil Appendix A
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Type C Soil
Least stable: gravel, loamy sand, soft clay
Submerged soil or dense,heavy unstable rock
Soil from which water is
freely seeping
Unconfined compressive strength 0.5
tsf or less
Appendix A
Sloping and Benching Appendix B
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Contains definitions
Sets forth requirements
Configurations of sloping and benching
Sloping and Benching Appendix B
Allowable Slopes Table B-1
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Allowable Slopes
Soil Type Height/Depth
Ratio
Slope Angle
Stable rock Vertical 90
Type A : 1 53
Type B 1 : 1 45
Type C 1 : 1 34
Type A (short term) : 1 63
(For a maximum excavation depth of 12 ft)
Table B-1
Excavations Made in Type A Soil
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Excavations Made in Type A Soil
Simple Slope
Excavations Made in Type A Soil
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Excavations Made in Type A Soil
Simple Slope Sho rt Term
Excavations Made in Type A Soil
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Simple Bench
Excavations Made in Type A Soil
Excavations Made in Type A Soil
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Unsupported Vert ical ly-Sided Lower Port ion
Excavations Made in Type A Soil
Excavations Made in Type A Soil
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Excavations Made in Type A Soil
Unsupported Vert ical ly-Sided Lower Port ion
Excavations Made in Type A Soil
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Excavations Made in Type A Soil
Mult ip le Bench
Excavations Made in Type A Soil
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ca at o s ade ype So
Support o r Shield System
Excavations Made in Type B Soil
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Simple Slope
Excavations Made in Type B Soil
Excavations Made in Type B Soil
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Sing le Bench
Excavations Made in Type B Soil
Excavations Made in Type B Soil
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Excavations Made in Type B Soil
Mult ip le Bench
Excavations Made in Type B Soil
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Support o r Shield System
Excavations Made in Type B Soil
Excavations Made in Type C Soil
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Excavations Made in Type C Soil
Simple Slope
Excavations Made in Type C Soil
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Excavations Made in Type C Soil
Support o r Shield System
Excavations Made in Layered Soils
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Excavations Made in Layered Soils
A over B
Excavations Made in Layered Soils
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Excavations Made in Layered Soils
A over C
Excavations Made in Layered Soils
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y
B over A
Excavations Made in Layered Soils
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y
B over C
Excavations Made in Layered Soils
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y
C over A
Excavations Made in Layered Soils
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y
C over B
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Benching and SlopingBenching
Timber Shoring for Trenches Appendix C
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g
Need to determine soil classification
Presentation of information
Basis and limitations of the data
Use of tables
Examples to illustrate the use of tables
Notes for all tables
Aluminum Hydraulic Shoring Appendix D
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y g
Need to determine soil classification
Presentation of information
Basis and limitations of the data
Use of tables
Example to illustrate the use of the tables
Footnotes, and general notes
Vertical Aluminum Hydraulic Shoring (Spot Bracing)Figure No. 1
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18 Max..
Vertical
Spacing
4 Max.
2 Max.
Vertical Rail
Hydraulic Cylinder
Vertical Aluminum Hydraulic Shoring (With Plywood)Figure No. 2
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Vertical
Rail
18 Max.
Vertical
Spacing
4 Max.
Plywood
Hydraulic
Cylinder
2 Max.
Horizontal
Spacing
Vertical Aluminum Hydraulic Shoring (Stacked)Figure No. 3
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Horizontal Spacing
Vertical
Spacing
4 Max.2 Max.
Hydraulic
Cylinder
Vertical Rail
Aluminum Hydraulic Shoring Waler System (Typical)Figure No. 4
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Horizontal Spacing
2 Max.
Vertical
Spacing
4 Max. Hydraulic
Cylinder
Waler
Upright
Sheeting
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Alternatives to Timber Shoring Appendix E
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Selection of Protective Systems Appendix F
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Illustrates a graphic summary of requirements
contained in subpart P for excavations 20 feet or
less in depth.
Protective systems for use in excavations more
than 20 feet in depth must be designed by a
registered professional engineer in accordance
with 1926.652(b) and (c).
Thank You For Attending!
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Final Questions?
1-800-NC-LABOR
(1-800-625-2267)
www.nclabor.com
Handouts
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Place all handouts at the end of this presentation.
Recommended