Office of Safety & Health Consultation
presents
Excavations & Trenching
Objectives
In this course, we will discuss the
following:
• Excavations/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
Subpart and Standard 1926.
Number of Serious Violations – FY 2013
3
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
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)
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)
Definitions
• 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,
and authorized to
eliminate them.
1926.650(b)
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 weigh
more than 3,000 pounds.
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
Injury and Death
• Excavating is one of the
most hazardous
construction operations.
• Most accidents occur in
trenches 5-15 feet deep.
• Usually no warning before
a cave-in.
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
Specific Excavation Requirements
• (h) Protection from hazards associated
with water accumulation
• (i) Stability of adjacent structures
• (j) Protection of employees from loose rock
or soil
• (k) Inspections
• (l) Fall protection
Surface Encumbrances
• All surface
encumbrances that create
a hazard to employees
must be removed or
supported to safeguard
employees.
1926.651(a)
Underground Installations
• Estimated location of
utility installations
[sewer, telephone, fuel,
electric, water lines]
must be determined prior
to opening an
excavation.
1926.651(b)(1)
Underground Installations
• When utility companies or
owners cannot respond to
request to locate underground
utility installations within 24
hours.
– Employer may proceed with
caution, provided detection
equipment, etc. is used to locate
utility installations.
1926.651(b)(2)
Underground Installations
• Exact location of
underground
installations must be
determined by safe and
acceptable means.
1926.651(b)(3)
Underground Installations
1926.651(b)(3)
Underground Installations
1926.651(b)(3)
Underground Installations
• Underground
installations must be
protected, supported or
removed as necessary
to safeguard
employees.
1926.651(b)(4)
Structural Ramps
• Structural ramps used for access or egress
of equipment must be designed by a
competent person.
1926.651(c)(1)(i)
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 distance
no more than 25 feet.
1926.651(c)(2)
Egress - Trench Excavation
25 feet
25 feet
Ramp, ladder or stairs required at 4 feet or deeper.
1926.651(c)(2)
Egress - Trench Excavation
1926.651(c)(2)
1926.651(c)(2)
Egress - Trench Excavation
• Is this correct?
Exposure to Vehicle Traffic
• Employees exposed to public vehicular traffic
must wear warning vests or other suitable
garments marked with or made or
reflectorized or high-visibility material.
1926.651(d)
Exposure to Falling Loads
• Employees must not be permitted to work
under loads handled by lifting or digging
equipment.
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 unloading
if equipment has proper cab
shield or canopy.
1926.651(e)
Warning System - Mobile Equipment
• Mobile equipment operated adjacent to
excavation and operator cannot see edge of
the excavation:
– Warning system
must be utilized.
• Barricades
• Hand or mechanical
signals
• Stop logs
1926.651(f)
Warning System - Mobile Equipment
Is this correct?
1926.651(f)
Hazardous Atmospheres
• Testing conducted before employees enter
the trench and regularly thereafter.
1926.651(g)(1)
Hazardous Atmospheres
• 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 OSHA’s Permissible Exposure Limits
(PEL)
1926.651(g)(1)
Hazardous Atmospheres
• Test at 4 feet if suspected
– LEL
– Oxygen
– CO
– H2S
– Petroleum
– Other toxics
1926.651(g)(1)
Emergency Rescue Equipment
1926.651(g)(2)(i)
Emergency Rescue Equipment
• Emergency rescue
equipment must be
readily available where
hazardous atmospheric
conditions exist or
expected to develop
during work.
– Breathing apparatus
– Safety harness and line
– Basket stretcher
1926.651(g)(2)(i)
Water Accumulation
• Employees must not work in
excavations where there is
accumulated water, or where
water is accumulating.
• Unless precautions taken to
protect workers:
– Water removal to control level of
water
– Special support or shield systems
1926.651(h)(1)
Water Accumulation
1926.651(h)(1)
Water Accumulation
• Water removal
equipment and
operations must be
monitored by a
competent person to
ensure proper
operation.
1926.651(h)(2)
Water Accumulation
• Excavations subject
to runoff from heavy
rains require an
inspection by a
competent person.
1926.651(h)(3)
Well Points Used to Remove Ground Water
What are the Hazards?
What are the hazards?
Stability of Adjacent Buildings
• Support systems such
as shoring, bracing,
or underpinning must
be provided to ensure
stability of structures.
1926.651(i)(1)
Stability of Adjacent Structures
• Excavation below the
foundation that could
pose a hazard shall not
be permitted except:
•
‘
– Underpinning provided
– Stable rock
– Registered professional
engineer (RPE) has
approved
1926.651(i)(2)
Underpinning
Underpinning to
prevent structural
failure.
1926.651(i)(2)(i)
Stability of Adjacent Structures
• Sidewalks, pavements and appurtenant
structure must not be undermined unless
supported to protect
employees from
collapse of such
structures.
1926.651(i)(3)
Protection of Employees
• Adequate protection
provided to protect
employees from loose rock
or soil that could pose a
hazard by falling or rolling
from an excavation face.
1926.651(j)(1)
Potential Problems
Extra load from
spoil pile
Fissures
Belly bulge
Protection of Employees
• Employees must be protected from
equipment or materials that could fall or roll
into excavations.
– Materials and
equipment must be
kept 2 feet from edge
of excavation or use
retaining devices.
1926.651(j)(2)
Rule: 2 Feet
1926.651(j)(2)
Two Feet From Edge
1926.651(j)(2)
Extra Surface Loading
1. What’s the Hazard?
2. See it now…
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 and
other events that could
increase hazards, e.g.,
snowstorm, windstorm,
thaw, earthquake, etc.
1926.651(k)(1)
Inspections
• Frequency of testing should be increased if
equipment is operating in trench as well as if
welding, cutting, or burning is done in trench.
1926.651(k)(1)
Fall Protection
• Walkways provided when crossing over
excavation.
• Standard guardrail
installed when more
than 6 feet above
a lower level.
1926.651(l)(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
1926.652(a)(1)
Sliding
Toppling
Tension Crack
Bulging
Heaving or Squeezing
Soil
Weight
Soil
Weight
Methods of Protection
• Sloping and benching
• Shoring (spaced sheeting, closed sheeting)
• Trench shield
• Other occasionally used systems
1926.652
Protective Systems
• Protective systems
shall have capacity to
resist without failure
all loads applied or
transmitted to the
system.
1926.652(a)(2)
Installation and Removal
• Support systems must be installed and
removed in a manner that protects
employees from
cave-ins.
1926.652(e)(1)(ii)
Installation and Removal
• Removal must begin
at, and progress from,
the bottom of the
excavation.
• Members released
slowly to note any
indication of possible
failure of remaining
members.
1926.652(e)(1)(V)
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 be
permitted.
1926.652(e)(2)(i) and (g)(2)
Deadly Trench Collapse
What’s the hazard?
What’s the hazard?
What’s the hazard?
What’s the hazard?
What’s the hazard?
What’s the hazard?
What’s the hazard?
Soil Classification
• Contains definitions
• Sets forth requirements
• Describes acceptable visual and
manual test for use in classifying
soils
Appendix A
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
Soil types
Appendix A
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
• Unconfined
compressive strength
– Load per unit area at
which a soil will fail in
compression
Note: Estimated in the
field by use of a pocket
penetrometer, thumb
penetration test, and
other methods
Appendix A
Thread Test
• Roll into thread
• At least 2 inches in length
• Longer unbroken
thread means more
cohesive
Appendix A
Ribbon Test
• Roll soil into a cigar shape
• Pinch between thumb and finger
• Longer ribbon means
more cohesive
Appendix A
Thumb Penetration Test
Appendix A
Pocket Penetrometer
Appendix A
Type A Soil
• Most stable: clay, silty clay, and hardpan
• Not fissured
• Not subjected to vibration
of any type
• Never been previously
disturbed
• No seeping water
Unconfined compressive strength
greater than 1.5 tons per square foot
(tsf)
Appendix A
Type B Soil
• Medium stability: silt, sandy
loam, medium clay and
unstable 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
vibration
Unconfined compressive strength
less than 1.5 tsf and greater than
0.5 tsf
Appendix A
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
• Contains definitions
• Sets forth requirements
• Configurations of sloping and
benching
Appendix B
Allowable Slopes
Soil Type
Height/Depth
Ratio
Slope Angle
Stable rock
Vertical
90°
Type A
¾:1
53°
Type B
1:1
45°
Type C
1½:1
34°
Type A (short term)
½:1
63°
(For a maximum excavation depth of 12 ft)
Table B-1
Excavations Made in Type “A” Soil
Simple Slope
Excavations Made in Type “A” Soil
Simple Slope – Short Term
Excavations Made in Type “A” Soil
Simple Bench
Excavations Made in Type “A” Soil
Unsupported Vertically-Sided Lower Portion
Excavations Made in Type “A” Soil
Unsupported Vertically-Sided Lower Portion
Excavations Made in Type “A” Soil
Multiple Bench
Excavations Made in Type “A” Soil
Support or Shield System
Excavations Made in Type “B” Soil
Simple Slope
Excavations Made in Type “B” Soil
Single Bench
Excavations Made in Type “B” Soil
Multiple Bench
Excavations Made in Type “B” Soil
Support or Shield System
Excavations Made in Type “C” Soil
Simple Slope
Excavations Made in Type “C” Soil
Support or Shield System
Excavations Made in Layered Soils
A over B
Excavations Made in Layered Soils
A over C
Excavations Made in Layered Soils
B over A
Excavations Made in Layered Soils
B over C
Excavations Made in Layered Soils
C over A
Excavations Made in Layered Soils
C over B
Benching
Benching and Sloping
Timber Shoring for Trenches
• 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
Appendix C
Aluminum Hydraulic Shoring
• 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
Appendix D
Figure No. 1
Vertical Aluminum Hydraulic Shoring (Spot Bracing)
18” Max..
Vertical Rail
Vertical
Spacing
4’ Max.
Hydraulic Cylinder
2’ Max.
Figure No. 2
Vertical Aluminum Hydraulic Shoring (With Plywood)
Horizontal
Spacing
Vertical
Rail
Hydraulic
Cylinder
18” Max.
Vertical
Spacing
Plywood
4’ Max.
2’ Max.
Figure No. 3
Vertical Aluminum Hydraulic Shoring (Stacked)
Horizontal Spacing
Hydraulic
Cylinder
Vertical
Spacing
4’ Max.
Vertical Rail
2’ Max.
Figure No. 4
Aluminum Hydraulic Shoring Waler System (Typical)
Horizontal Spacing
Upright
Sheeting
Waler
2’ Max.
Vertical
Spacing
4’ Max.
Hydraulic
Cylinder
Alternatives to Timber Shoring
Appendix E
Alternatives to Timber
Shoring
Appendix E
Selection of Protective Systems
• 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).
Appendix F
Your Questions?