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