Trenching and Excavation

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Trenching and Excavation

• Subpart P

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Behold, the trench. No wider than 15 feet.
Otherwise, it is an excavation.
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Trench Cave-In Fatalities

• A Major Killer in Construction
• At least 50 fatalities per year, probably closer
  to 100.

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Trench Cave-Ins

• The leader in prosecutions of contractors for
  criminally negligent homicides. Also involuntary
  manslaughter.
• Significant OSHA fines associated with trench
  cave-ins
• Average Fine 5,124

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Competent Person

• Must be able to identify hazards (the potential
  for a cave-in)
• Must have the authority to take appropriate
  corrective actions

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Responsibilities of the Competent Person

• Recognize confined space hazards
• Specify any safety controls needed
• Oversee all tasks being performed
• Remove any workers not protected
• Remain present during excavation
• Observe protection being installed
• Remain present when workers in trench

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Duties of Competent Person

• Pre-inspect site and develop safety plan
• Design access for employees equipment
• Determine soil conditions
• Select protection system
• Monitor environmental conditions
• Communicate and inspect for worker safety

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Reclassification of Soil

• Recognize that soil types can change quickly.
• Evaluate soil conditions periodically
• If soil appears to be different, evaluate it
• Reclassify the soil if appropriate

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Be Vigilant with Inspections

• Prior to beginning work each day
• During work - as needed
• After a rainstorm or other natural change
• When conditions exist that might contribute to
  trench cave-ins

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Confined Space Concerns

• A means of egress shall be provided so the
  horizontal distance does not exceed 25 feet
• The atmosphere is oxygen deficient when the air
  contains less than 19.5 oxygen.

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No protection is needed in a trench when

• Material is solid rock
• Trench is less than 5 feet deep
• and
• competent person determines that there is no
  indication of a potential cave-in

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Things to Consider

• Surface Encumbrances
• Underground Installations
• Access and egress
• Hazardous atmospheres
• Water accumulation
• Stability of adjacent structures
• Fall protection
• Protection from falling objects
• Inspections

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Factors That Make Trench Walls Unstable

• Water
• Surcharge Loads and Other Loads
• Vibrations
• Previously Disturbed (Existing Utilities)
• Clay Seams
• Frozen Soil
• Lack of Soil Support
• Excavations under Structures

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Trench Wall Strength is Deceptive
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Conditions that Contribute to Cave-Ins
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Signs of Potential Trench Wall Collapse
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Adequate Slope?
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Adequate Slope?
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When must a P.E. be Consulted?

• Trenches over 20 feet deep
• Specially designed support systems
• When excavating near other structures
• Standard protection methods will not work
• Consider other conditions where a P.E. might be
  needed.

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Workers exposed to vehicular traffic

• Flaggers shall be provided and they shall wear
  warning vests or other garments made of
  reflectorized or high visibility material

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What is the weight of soil?

• It will vary with the type of material and the
  amount of water being contained, but it is in the
  general vicinity of about 100 pounds per cubic
  foot.
• Most soils are 2,000 to 3,000 pounds per CY

1 Cubic Yard
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Type A Soil

• Cohesive soil
• 1.5 ton per square foot or greater (unconfined
  compressive strength)
• but not fissured,
• not subject to vibration,
• not previously disturbed,
• not part of a sloped layer
• no other conditions to weaken its strength

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Type B Soil

• Cohesive soil
• Between .5 1.5 ton per square foot
• (unconfined compressive strength)

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Type C Soil

• Cohesive soil
• Less than .5 ton per square foot
• (unconfined compressive strength)
• Gravel, sand and loamy sand
• Submerged soil or soil with seeping water
• Layered soil with angle of 4H to 1V

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Means of Protection in Trenches

• Sloping the trench walls
• Trench Boxes
• Shoring System

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A 3/4H1V B 1H1V C 1.5H1V
20 max.
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Ladder Access and Egress
24 Max.
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Trench Box Available But Not Used!!!!
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Trench Box Available But Not Used!!!! 9
This is Stupid
This is Stupid
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Trench Box Too High Above the Trench Bottom
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Trench Box Too High Above the Trench Bottom 7
2 feet (max)
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Trench Box Set Too Low!!!!
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Trench Box Set Too Low!!!! 13
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Venturing Out of the Protection of Trench Box
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Venturing Out of the Protection of Trench Box
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Safe Inside the Trench Box
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Struck by Excavator Bucket 10
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Struck by Materials Falling into Trench Box 7
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Trench Shoring

• Little evidence that shoring practices are
  inadequate.
• Some dont shore when they should.
• Recognition of when shoring is needed is a
  problem.

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Trenching Safety is Very Important

• Avoid Mistakes
• Dont Bury Them

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