Excavation & TrenchingExcavation & Trenching

These handouts and documents with attachments are not final, complete, or definitive instruments. This information is for guidance These handouts and documents with attachments are not final, complete, or definitive instruments. This information is for guidance purposes only. You should independently verify and satisfy yourself as to its accuracy. The AHBSIF does not assume any purposes only. You should independently verify and satisfy yourself as to its accuracy. The AHBSIF does not assume any

liability for damages arising from the use of this information or exhibits and attachments thereto and renders no opinion that liability for damages arising from the use of this information or exhibits and attachments thereto and renders no opinion that any of the terms, conditions, and/or cited federal standards in this document and the exhibits and attachments should be any of the terms, conditions, and/or cited federal standards in this document and the exhibits and attachments should be

explicitly followed by the fund member. Seek specific guidance from the appropriate regulator (OSHA) or professional advisor.explicitly followed by the fund member. Seek specific guidance from the appropriate regulator (OSHA) or professional advisor.

Dirt Work is Serious BusinessDirt Work is Serious Business Excavation cave-ins are one of the major sources Excavation cave-ins are one of the major sources

of fatalities within the construction industry.of fatalities within the construction industry. Trenching accidents on construction sites Trenching accidents on construction sites

account for an estimated 100 fatalities/year. account for an estimated 100 fatalities/year. 79% of trench fatalities occur in less than 15’ 79% of trench fatalities occur in less than 15’

excavations: 38% in less than 10’.excavations: 38% in less than 10’. Statistically most likely to be killed in an Statistically most likely to be killed in an

excavation:excavation: MaleMale Construction LaborConstruction Labor 20 to 30 years old20 to 30 years old

News ReleasesNews Releases► MichiganMichigan 09/29/10 09/29/10► A construction worker killed Wednesday in a trench collapse west of KalamazoA construction worker killed Wednesday in a trench collapse west of Kalamazooo

has been identified by police as Samuel Wilson, 58, of Burlington. has been identified by police as Samuel Wilson, 58, of Burlington. Wilson was installing sewer piping in a trench that was 8 feet deep and 3 feet Wilson was installing sewer piping in a trench that was 8 feet deep and 3 feet wide when the trench collapsed at 4:12 p.m., according to the Kalamazoo wide when the trench collapsed at 4:12 p.m., according to the Kalamazoo County Sheriff’s Office. At the time of the incident, Wilson, was working at the County Sheriff’s Office. At the time of the incident, Wilson, was working at the site of a house under construction in the 3200 block. Wilson was pronounced site of a house under construction in the 3200 block. Wilson was pronounced dead at the scene, deputies said.dead at the scene, deputies said.Undersheriff Pali Matyas said police planned to turn their investigation over Undersheriff Pali Matyas said police planned to turn their investigation over today to the Michigan Occupational Safety and Health Administration.today to the Michigan Occupational Safety and Health Administration.

► Nebraska Nebraska 06/05/1006/05/10► A Lewis and Clark Rural Water District employee died Friday after a trench A Lewis and Clark Rural Water District employee died Friday after a trench

collapsedcollapsed around him in northern Knox County. The incident killed 48-year-old around him in northern Knox County. The incident killed 48-year-old Galen Jueden of Hartington, Knox County Sheriff Jim Janecek said in a news Galen Jueden of Hartington, Knox County Sheriff Jim Janecek said in a news release. release. Jueden and another worker were replacing water lines in the trench, about 5 or Jueden and another worker were replacing water lines in the trench, about 5 or 6 feet deep, when it collapsed around Jueden at about 11 a.m. Friday, Sheriff's 6 feet deep, when it collapsed around Jueden at about 11 a.m. Friday, Sheriff's Capt. Ernest Ibach said. Capt. Ernest Ibach said. "He was only really buried about up to his waist," Ibach said. Telephone "He was only really buried about up to his waist," Ibach said. Telephone workers in the area pulled him from the trench and performed CPR, but neither workers in the area pulled him from the trench and performed CPR, but neither they nor rescue workers could revive him. Jueden was pronounced dead at the they nor rescue workers could revive him. Jueden was pronounced dead at the scene.scene.

OSHA’s Injury DataOSHA’s Injury Data The following hazards are most The following hazards are most

responsible for excavation related responsible for excavation related injuries;injuries; No protective systemsNo protective systems Failure to inspect the trench before and Failure to inspect the trench before and

during workduring work Improper spoils pile locationImproper spoils pile location Access/egress issuesAccess/egress issues

Defining a Competent PersonDefining a Competent Person One who is capable of identifying existing and One who is capable of identifying existing and

predictable hazards in the surroundings, or working predictable hazards in the surroundings, or working conditions which are unsanitary, hazardous, or conditions which are unsanitary, hazardous, or dangerous to employees, and who has dangerous to employees, and who has authorization authorization to eliminateto eliminate them. them.

Competency for Subpart P requires knowledge of the Competency for Subpart P requires knowledge of the following:following:1)1) Soils analysisSoils analysis2)2) The use of protective systemsThe use of protective systems3)3) The requirements of this standardThe requirements of this standard

A cubic yard of soil weighs approx. 2700 lbs!

Competent Person Competent Person ResponsibilitiesResponsibilities

Authority to stop workAuthority to stop work Inspection of excavationsInspection of excavations

DailyDaily Pre-shiftPre-shift As neededAs needed After rainAfter rain Any increasing hazard occurrenceAny increasing hazard occurrence

Testing for hazardous Testing for hazardous atmospheresatmospheres

Inspection of material and Inspection of material and equipmentequipment

Monitoring of water removalMonitoring of water removal Visual TestsVisual Tests Manual TestsManual Tests

Mechanics of a Cave-InMechanics of a Cave-In Stress cracks form back Stress cracks form back

from edge due to ground from edge due to ground surface tension and shear surface tension and shear forces.forces.

Cracks occur from about Cracks occur from about 1/3 to 2/3 of the depth of 1/3 to 2/3 of the depth of the excavation back from the excavation back from its edges.its edges.

Cracks take away the soils Cracks take away the soils ability to maintain a strong ability to maintain a strong vertical face. vertical face.

The weight of the earth The weight of the earth above is transferred to the above is transferred to the lower portions of the lower portions of the excavation wall.excavation wall.

Mechanics of a Cave-InMechanics of a Cave-In Excavation bottoms are the first to fail.Excavation bottoms are the first to fail. Support for the upper part of excavation Support for the upper part of excavation

is left hanging only by shear and reduced is left hanging only by shear and reduced tension forces.tension forces.

The uppermost portion of the vertical wall The uppermost portion of the vertical wall collapses into the excavation. collapses into the excavation.

Soil, like concrete, is normally strong in Soil, like concrete, is normally strong in compression but not strong in tension.compression but not strong in tension.

Figures 1 and 2 two detail the scenario.Figures 1 and 2 two detail the scenario.

Mechanics of a Cave-InMechanics of a Cave-InFig. 1

Fig. 2

Soil ClassificationSoil Classification

Cohesive Granular

SandSiltClay

Stronger + - WeakerMore Cohesion – Less Cohesion

Soil Classification – Visual Soil Classification – Visual TestsTests

Observe samples of soil that Observe samples of soil that are excavated. are excavated. If it stays in clumps it is If it stays in clumps it is

cohesive cohesive If it breaks up easily its If it breaks up easily its

granular granular Check the sides of the opened Check the sides of the opened

excavation and adjacent excavation and adjacent surfaces for signs of cracking.surfaces for signs of cracking.

Check for existing utilities, Check for existing utilities, underground structures, and underground structures, and previously disturbed soil. previously disturbed soil.

Check for layered soils. Check for layered soils. Be aware of surface water, Be aware of surface water,

seeping water, and water seeping water, and water collection in the base.collection in the base.

Be aware of the machinery Be aware of the machinery running near the cut. Vibration running near the cut. Vibration can affect stability.can affect stability.

Soil Classification – Manual Soil Classification – Manual TestsTests

ManualManual(Bare Hands)(Bare Hands)

MechanicalMechanical(Device)(Device)

PlasticityPlasticity Pocket PenetrometerPocket Penetrometer

Dry StrengthDry Strength Shear VaneShear Vane

Thumb PenetrationThumb Penetration

Plasticity – Dry StrengthPlasticity – Dry Strength PlasticityPlasticity – Mold a moist or wet sample of soil into – Mold a moist or wet sample of soil into

a wet ball and attempt to roll it into threads as thin a wet ball and attempt to roll it into threads as thin as 1/8-inch in diameter. Cohesive material can be as 1/8-inch in diameter. Cohesive material can be successfully rolled into threads without crumbling. successfully rolled into threads without crumbling. If at least a two-inch length of 1/8-inch thread can If at least a two-inch length of 1/8-inch thread can be held on one end without tearing, the soil is be held on one end without tearing, the soil is cohesive.cohesive.

Dry StrengthDry Strength – If the soil is dry and crumbles on – If the soil is dry and crumbles on its own or with moderate pressure into individual its own or with moderate pressure into individual grains or fine powder it is granular. If its dry and grains or fine powder it is granular. If its dry and breaks into clumps, but the clumps can only be breaks into clumps, but the clumps can only be broken with difficulty, it may be a clay combination.broken with difficulty, it may be a clay combination.

Thumb PenetrationThumb Penetration

Thumb Penetration TestThumb Penetration Test Type AType A: These soils can be : These soils can be

indented by the thumb, but indented by the thumb, but penetration takes great penetration takes great effort.effort.

Type BType B: Easily indented, : Easily indented, can be penetrated with can be penetrated with somewhat less effort than somewhat less effort than type A.type A.

Type CType C: This type of soil : This type of soil can be easily penetrated up can be easily penetrated up to several inches by the to several inches by the thumb and can be molded thumb and can be molded with light finger pressure.with light finger pressure.

This test can be used to estimate the This test can be used to estimate the unconfirmed compressive strength of unconfirmed compressive strength of cohesive soils.cohesive soils.

Pocket PenetrometerPocket Penetrometer Probes the soil with a Probes the soil with a

small tube-like plungersmall tube-like plunger Device is pressed into Device is pressed into

soil to calibration marksoil to calibration mark Spring loaded piston Spring loaded piston

displaces the scale displaces the scale ringring

Produces a Produces a compressive strength compressive strength reading rated in reading rated in tons/sq.fttons/sq.ft

Shear VaneShear Vane Hand-held instrument used Hand-held instrument used

for determining soil strength for determining soil strength Provides reading in kPa Provides reading in kPa

(kiloPascal, Unit of Pressure)(kiloPascal, Unit of Pressure) Vane blade is pushed into Vane blade is pushed into

the soil and device is rotated the soil and device is rotated at predetermined rate (ex: 1 at predetermined rate (ex: 1 revolution/minute)revolution/minute)

Reading is obtained when Reading is obtained when soil fails soil fails

Devices come with different Devices come with different ranges and features ranges and features

Extension rods are available Extension rods are available to increase the to increase the measurement depthmeasurement depth

Slope ConfigurationsSlope ConfigurationsSoil or Soil or Rock Rock TypeType

Maximum Allowable Maximum Allowable Slopes for Slopes for Excavations Less Excavations Less than 20’than 20’

Unconfined Unconfined CompressivCompressive Strengthe Strength

Stable Stable RockRock

Vertical Vertical 9090°° ______________

Type AType A ¾ to 1¾ to 1 5353°° ≥ ≥ 1.5 tons/sq 1.5 tons/sq ftft

Type BType B 1 to 11 to 1 4545°° .5 - 1.5 tons/sq .5 - 1.5 tons/sq ftft

Type CType C 1½ to 11½ to 1 3434°° ≤ ≤ .5 tons/sq .5 tons/sq ftft

SlopingSloping When combination soils are When combination soils are

encountered, and the soil encountered, and the soil beneath is of lesser beneath is of lesser cohesion than the soil cohesion than the soil above, the slope will be above, the slope will be that of the less cohesive that of the less cohesive soil.soil.

When sloping with a When sloping with a shoring system in place, shoring system in place, the top edge of the cut the top edge of the cut must be 18” below the top must be 18” below the top edge of the shoring system.edge of the shoring system.

A shoring device does not A shoring device does not affect the soil type affect the soil type dimensions of the dimensions of the continuing slope.continuing slope.

Short Term Maximum Allowable Short Term Maximum Allowable SlopesSlopes

A short term A short term maximum allowable maximum allowable slope is a special slope is a special situation for Type A situation for Type A soil.soil.

An excavation in Type An excavation in Type A soil that is open for A soil that is open for less than 24 hours and less than 24 hours and 12 feet or less in 12 feet or less in depth, can have a depth, can have a maximum allowable maximum allowable slope of 1/2H:1V (63slope of 1/2H:1V (63°).°).

BenchingBenching Can stand alone or in Can stand alone or in

combination with slopingcombination with sloping Type C soils cannot be Type C soils cannot be

benchedbenched In multiple bench In multiple bench

situations, max bench situations, max bench height of first bench is 4’height of first bench is 4’

In bench-slope In bench-slope combinations, max combinations, max bench height of first bench height of first bench is 3.5’bench is 3.5’

Foundation/Basement Foundation/Basement ExcavationsExcavations The depth of the The depth of the

foundation/basement trench foundation/basement trench cannot exceed 7½ feet deep cannot exceed 7½ feet deep unless you provide other cave-unless you provide other cave-in protection. in protection.

Keep the horizontal width of Keep the horizontal width of the foundation trench at least 2 the foundation trench at least 2 feet wide. Mind surface feet wide. Mind surface encumbrances. encumbrances.

Plan the foundation trench Plan the foundation trench work to minimize workers in work to minimize workers in the trench and the length of the trench and the length of time they spend there. time they spend there.

Inspect the trench regularly.Inspect the trench regularly. Stop work if any potential for Stop work if any potential for

cave-in develops and fix the cave-in develops and fix the problem before work starts problem before work starts again. again.

Utilities LocationUtilities Location Alabama One CallAlabama One Call

1-800-292-8525 or 8111-800-292-8525 or 811 Must call at least 48 Must call at least 48

hours in advancehours in advance Service is available Service is available

Monday through Monday through Friday, 7:00 am to Friday, 7:00 am to 5:00 pm5:00 pm

All utilities are marked All utilities are marked in a standardized color in a standardized color codecode

Utilities LocationUtilities Location Excavators must observe a tolerance zoneExcavators must observe a tolerance zone The width of the facility on a horizontal plane, The width of the facility on a horizontal plane,

at least 18” on either side of the outside edgeat least 18” on either side of the outside edge If relocation is If relocation is

necessary, necessary, excavator must excavator must coordinate with coordinate with facility facility owner/operatorowner/operator

Utilities LocationUtilities Location When estimated location of When estimated location of

underground installations are underground installations are approached, exact location shall be approached, exact location shall be determined by safe/acceptable meansdetermined by safe/acceptable means(hand digging, soft dig, pot hole, etc.)(hand digging, soft dig, pot hole, etc.)

While excavation is open, underground While excavation is open, underground installations shall be protected, installations shall be protected, supported or removed as necessary to supported or removed as necessary to safeguard employees.safeguard employees.

Uniform Color CodesUniform Color Codes Electric – RedElectric – Red Gas/Oil – YellowGas/Oil – Yellow Comm./CATV – Comm./CATV –

OrangeOrange Water – BlueWater – Blue Sewer – GreenSewer – Green Proposed Exc. – Proposed Exc. –

WhiteWhite Temp. Survey - PinkTemp. Survey - Pink

See Appendix “C”

Protective SystemsProtective SystemsReasons for Needing a Protecive SystemReasons for Needing a Protecive System

Existing utility lines, roadways, or structural Existing utility lines, roadways, or structural foundations intruding on the maximum foundations intruding on the maximum allowable slope.allowable slope.

No right-of-way permit for sloped No right-of-way permit for sloped excavation.excavation.

The vertical face excavation is beyond the The vertical face excavation is beyond the safety slope.safety slope.

The gravitational force will cause soil The gravitational force will cause soil raveling, cave-ins, or slope stability failures raveling, cave-ins, or slope stability failures from the vertical face.from the vertical face.

Protective SystemsProtective SystemsTimber ShoringTimber Shoring

System uses reinforced wood sheets or planks in an upright or sheet configuration to System uses reinforced wood sheets or planks in an upright or sheet configuration to reinforce the vertical cutreinforce the vertical cut

Walers support the system horizontally against the outer wallWalers support the system horizontally against the outer wall Struts support the system horizontally from side to sideStruts support the system horizontally from side to side

Struts

Walers

Protective SystemsProtective SystemsHydraulic ShoringHydraulic Shoring

Uses alloy struts Uses alloy struts (aluminum, steel) to (aluminum, steel) to support system side to sidesupport system side to side

System does not require System does not require entry for installation or entry for installation or removalremoval

Significantly lighter than Significantly lighter than timber systems timber systems

Provides even distribution Provides even distribution of pressure along the of pressure along the trench line trench line

Can utilize "preloading" to Can utilize "preloading" to use the soil's natural use the soil's natural cohesion to prevent cohesion to prevent movement movement

Adapts easily to various Adapts easily to various trench depths and widths. trench depths and widths.

Protective SystemsProtective SystemsTrench BoxesTrench Boxes

The width of the trench should exceed the width of the The width of the trench should exceed the width of the box to facilitate ease of movementbox to facilitate ease of movement

Clearance prevents stresses on the trench box that could Clearance prevents stresses on the trench box that could lead to failure during cave-inlead to failure during cave-in

Trench boxes may sit on 2’ of excavated soilTrench boxes may sit on 2’ of excavated soil

Protective SystemsProtective SystemsPro Tec Slide Rail SystemPro Tec Slide Rail System

Traditional shoring concept Traditional shoring concept with less excavationwith less excavation

Channeled posts are pressed Channeled posts are pressed into place by excavatorinto place by excavator

Panels are inserted into post Panels are inserted into post channelschannels

System utilizes the soils System utilizes the soils natural compressive strengthnatural compressive strength

Fast installation and removalFast installation and removal System conforms to a wide System conforms to a wide

variety of excavation typesvariety of excavation types

Access/ EgressAccess/ Egress A stairway, ladder, ramp, or other safe A stairway, ladder, ramp, or other safe

means of egress shall be located in trench means of egress shall be located in trench excavations that are 4 feet or more in excavations that are 4 feet or more in depth and require no more than 25 feet of depth and require no more than 25 feet of lateral travel for employees.lateral travel for employees.

Must be designed by a competent person.Must be designed by a competent person. Boards must be of uniform thickness and Boards must be of uniform thickness and

structurally sound, also must be equipped structurally sound, also must be equipped with cleats to prevent tripping on ramp with cleats to prevent tripping on ramp applications. applications.

Hazardous AtmospheresHazardous Atmospheres All testing must be All testing must be

performed from outside performed from outside the spacethe space

Hazard may be generated Hazard may be generated from existing conditions from existing conditions inside excavationinside excavation MethaneMethane Natural GasNatural Gas PetroleumPetroleum

Hazard may be generated Hazard may be generated from surroundingsfrom surroundings Carbon MonoxideCarbon Monoxide

Hazardous AtmospheresHazardous AtmospheresExposures to harmful levels of atmospheric Exposures to harmful levels of atmospheric

contaminants can be prevented by:contaminants can be prevented by: Testing for oxygen deficient air with a tester Testing for oxygen deficient air with a tester

at no less than four feet in depth. at no less than four feet in depth. (Concentrations should lie between 19.5% (Concentrations should lie between 19.5% and 23.5%)and 23.5%)

Flammable gas testingFlammable gas testing Toxic atmosphere testing.Toxic atmosphere testing. Testing as often as is necessary to ensure Testing as often as is necessary to ensure

safe atmosphere at all times safe atmosphere at all times

Standard SpecificsStandard Specifics All spoils piles and equipment must be kept at All spoils piles and equipment must be kept at

least 2’ back from the excavation’s edge.least 2’ back from the excavation’s edge. Employees must not be exposed to falling Employees must not be exposed to falling

loads at any time.loads at any time. Employees must be provided with and wear Employees must be provided with and wear

warning vests when exposed to trafficwarning vests when exposed to traffic Excavations greater than 5’ in depth must be Excavations greater than 5’ in depth must be

sloped, benched, or utilize a protective sloped, benched, or utilize a protective system.system.

Water accumulation must be controlled at all Water accumulation must be controlled at all timestimes

Standard SpecificsStandard Specifics Surface encumbrances must be removed or Surface encumbrances must be removed or

supported i.e. trees, telephone poles, fire hydrantssupported i.e. trees, telephone poles, fire hydrants If a ramp must be constructed, handrails and If a ramp must be constructed, handrails and

decking must meet established requirements.decking must meet established requirements. Employee ramps must be designed by a Employee ramps must be designed by a

competent person.competent person. Physical protection must be provided at all Physical protection must be provided at all

remotely located excavations.remotely located excavations. Structural ramps used to support equipment must Structural ramps used to support equipment must

be designed by a Registered Professional Engineerbe designed by a Registered Professional Engineer

Excavation ChecklistExcavation ChecklistUtilities locations identified Utilities locations identified and markedand marked

Access/ Egress points and Access/ Egress points and routes free from obstructionroutes free from obstruction

Potentially Hazardous Potentially Hazardous Atmosphere tested before and Atmosphere tested before and during shiftduring shift

Water accumulation Water accumulation monitored before and during monitored before and during shiftshift

Emergency Rescue Equipment Emergency Rescue Equipment on site and ready for dutyon site and ready for duty

Spoils piles at least two feet Spoils piles at least two feet back from excavation edgeback from excavation edge

Employees and machinery Employees and machinery protected from trafficprotected from traffic

Soil classification performed Soil classification performed by Competent Personby Competent Person

Employees protected from Employees protected from falling loadsfalling loads

Shoring systems inspected Shoring systems inspected before and during shiftbefore and during shift

Proper fall protection for cross Proper fall protection for cross over pointsover points

Daily inspection performed by Daily inspection performed by a competent person before and a competent person before and during the shiftduring the shiftInspection includes the trench, Inspection includes the trench, the area around it, and the area around it, and protective systemsprotective systems

Excavations Excavations ≥ ≥ 20’ in depth 20’ in depth have engineered protection have engineered protection systemssystemsStability of adjacent structures Stability of adjacent structures secured and shoredsecured and shored