Excavating & Trenching
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:MaleConstruction Labor20 to 30 years old
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 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 analysis2) The use of protective systems3) The requirements of this standard
A cubic yard of soil weighs approx. 2700 lbs!
Competent Person Responsibilities
Authority to stop work Inspection of excavations
– 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 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
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-InFig. 1 Fig. 2
Soil Classification
Cohesive Granular
SandSiltClay
Stronger + - WeakerMore Cohesion – Less Cohesion
Soil Classification – Visual Tests 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
Thumb Penetration Test 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.
This test can be used to estimate the unconfirmed compressive strength of cohesive soils.
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
Shear Vane 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
Soil or Rock Type
Maximum Allowable Slopes for Excavations Less than 20’
Unconfined Compressive 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°).
Benching
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 Call1-800-292-8525 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
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
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
Electric – RedGas/Oil – YellowComm./CATV –
OrangeWater – BlueSewer – GreenProposed Exc. –
WhiteTemp. Survey - Pink
See Appendix “C”
Protective Systems
Reasons for Needing a Protective 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 SystemsTimber Shoring
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 SystemsHydraulic Shoring
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 SystemsTrench Boxes
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 SystemTraditional shoring concept
with less excavationChanneled posts are pressed
into place by excavatorPanels 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.
Hazardous Atmospheres
All testing must be performed from outside the space
Hazard may be generated from existing conditions inside excavation– Methane– Natural Gas– Petroleum
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
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
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 ChecklistUtilities locations identified and marked
Access/ Egress points and routes free from obstruction
Potentially Hazardous Atmosphere tested before and during shift
Water accumulation monitored before and during shift
Emergency Rescue Equipment on site and ready for duty
Spoils piles at least two feet back from excavation edge
Employees and machinery protected from traffic
Soil classification performed by Competent Person
Employees protected from falling loads
Shoring systems inspected before and during shift
Proper fall protection for cross over points
Daily inspection performed by a competent person before and during the shiftInspection includes the trench, the area around it, and protective systems
Excavations ≥ 20’ in depth have engineered protection systems
Stability of adjacent structures secured and shored
Hauling Safety
Training Requirements
• OSHA does not have specific training requirements for employees using motor vehicles and mechanized equipment on the job.
• They do however have a general training requirement:– “Each employer shall instruct each employee in the
recognition and avoidance of unsafe conditions and the regulations applicable to his work environment to control or eliminate any hazards or other exposure to illness or injury”
Training• It’s critical that employers
provide stringent Lockout/Tagout procedures and training for employees who work under the dump body and to isolate and sufficiently and safely block the dump bed prior to doing the assigned work
General Requirements• An employer must insure that the equipment is
inspected regularly.• Any damaged or improperly functioning parts
must be repaired immediately.• Operators must be familiar with the operator’s
manual supplied by the manufacturer.• Operators must conduct a pre-operation
inspection before each use.
Pre-Operation Inspection
Brake System Hydraulics
Pedestrian Warning Devices
Fluid Levels, Battery Connections
Tires Pins and Bushings
Operator Controls Mirrors
Cab Conditions Wheel Chocks
Operator Safety Systems Fire Extinguisher
Frame and Bed Operators Manual
Stability Considerations
Stability is adversely affected by one or more of the following factors:
The unit is not on a level surface when dumping
A large amount of material is in the upper portion of the raised box
Material does not flow out of the top portion of the box
The rear wheels settle unevenly as the load moves to the rear during dumping
Stability Considerations (cont’d)
Stability may also be affected by the truck’s mechanical condition:
Poor rear suspension systems on one side of the vehicle
Uneven tire pressures in rear wheels
Worn or inadequate components of the lifting system such as pins and lifting cylinders
Loading Safety
• Loading of box front to back must meet allowable gross weight and axle weight limitations
• If material is likely to flow poorly, lighten up the load in the top end of the box.
Dumping Safety
• Be aware of soft or uneven surfaces and inadequately compacted fill
• Before dumping ensure tailgate is unlocked and vehicle is on a reasonably level surface
• Before spreading material from a moving truck, ensure entire length of travel is reasonably level
• Do not dump when parked next to other trucks
• Warn workers in area to stay clear of dumping trucks
Vehicle Maintenance
Performing maintenance work or troubleshooting activities underneath the dump body of a dump truck presents special hazards to maintenance or servicing
personnel
OSHA 1926.600(a)(3)(i)
• Requires that “heavy machinery, equipment, or parts thereof which are suspended or held aloft…shall be substantially blocked or cribbed to prevent falling or shifting before employees are permitted to work under or between them.”
OSHA 1926.601(b)(10)
Requires that in construction settings, trucks with dump bodies shall be equipped with positive means of support, permanently attached, and capable of being locked in position to prevent accidental lowering of the body while maintenance or inspection work is being done.
Maintenance Safety
• Make sure these procedures are followed prior to repair:– Hydraulics blocked or
cribbed– Engine stopped– Controls in neutral– Brakes set– Wheels chocked
Maintenance Safety (cont’d)
Causes for the sudden movement of the dump truck bed include the following:Inadvertent control operationInadvertently pulling a release cableHydraulic failurePremature reconnecting of an air lineFailure of the blocking device
Truck Bed Blocking
Acceptable blocking Unacceptable blocking
Highway Safety
• Cover the load when driving on the road to avoid flying debris that could cause an accident.
• When on the road, drive at or below the speed limit. Dump trucks are not designed for speed and can easily tip on curves.
Jobsite Considerations• Soil Conditions
– Be aware of weather conditions that can impact the work surface (rain, drought, etc.)
– Previously excavated soil– Areas destabilized by high traffic
• Terrain– Steep grades– Uncleared lots and excessive undergrowth can hide
dangerous terrain• Traffic
– In addition to jobsite traffic, also be aware of auto and pedestrian traffic
– Never block loading or transition areas
Jobsite Considerations
• Emergency Routes– Never block important access paths on the jobsite
• General Safety– Check clearances– Loaded truck generally has right-of-way– Operate within the design limits of the truck– If spotters are provided, have direct communication with
them– Use hand signals if needed
Dump Truck Hand Signals
Spill Containment
• If materials such as fuel or lubricants are discharged into soil or water, they must be contained and cleaned up properly
• Spill napkins and absorption pads should be readily available
• Any spill on land in excess of 25 gallons is reportable
• Any release of petroleum into water is reportable
Spill Containment
• Emergency Management Association (State) 334-263-7594
• National Response Center 800-424-8802
• No quantity is too small for clean-up• Soil must be excavated completely and
transferred to suitable containers for transport