trench rev1

7/27/2019 Trench Rev1

1/119

Excavations and Trenching

29 CFR 1926 Subpart P


2/119

Objectives

In this course, we will discuss the following: Excavat ions /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


3/119

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


4/119

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)


5/119

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)


6/119

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,andauthorized to

eliminate them.

1926.650(b)Definitions


7/119

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 weighmore than 3,000 pounds.


8/119

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


9/119

Injury and Death

Excavating is one of themost hazardous

construction operations.

Most accidents occur intrenches 5-15 feet deep.

Usually no warning before

a cave-in.


10/119

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


11/119

Specific Excavation Requirements

(h) Protection from hazards associatedwith water accumulation

(i) Stability of adjacent structures

(j) Protection of employees from loose rock orsoil

(k) Inspections

(l) Fall protection


12/119

Surface Encumbrances

All surface encumbrancesthat create a hazard toemployees must beremoved or supported tosafeguard employees.

1926.651(a)


13/119

Estimated location ofutility installations [sewer,

telephone, fuel, electric,

water lines] must be

determined prior toopening an excavation.

1926.651(b)(1)Underground Installations


14/119


15/119

Exact location ofunderground

installations must be

determined by safe and

acceptable means.



16/119



17/119

Underground Installations 1926.651(b)(3)


18/119


Undergroundinstallations must be

protected, supported or

removed as necessary

to safeguard employees.


19/119

1926.651(c)(1)(i)Structural Ramps

Structural ramps used for access or egressof equipment must be designed by a

competent person.


20/119

1926.651(c)(2)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 distanceno more than 25 feet.


21/119

Ramp, ladder or stairs required at 4 feet or deeper.

25 feet 25 feet



22/119



23/119

Is this correct?



24/119

Exposure to Vehicle Traffic

Employees exposed to public vehicular traffic

must wear warning vests or other suitable

garments marked with

or made of reflectorized

or high-visibility material.

1926.651(d)


25/119

1926.651(e)

Employees must not be permitted to workunder loads handled by lifting or digging

equipment.

Exposure to Falling Loads


26/119

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 unloadingif equipment has proper cab

shield or canopy.


27/119

1926.651(f)Warning System - Mobile Equipment

Mobile equipment operated adjacent toexcavation and operator cannot see edge ofthe excavation:

Warning systemmust be utilized.

Barricades

Hand or mechanicalsignals

Stop logs


28/119

Warning System - Mobile Equipment 1926.651(f)

Is this correct?


29/119

Hazardous Atmospheres

Testing conducted before employees enter the

trench and regularly thereafter.

1926.651(g)(1)


30/119

1926.651(g)(1)

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 OSHAs Permissible Exposure Limits

(PEL)

Hazardous Atmospheres


31/119

Test at 4 feet if suspected LEL

Oxygen

CO

H2S

Petroleum

Other toxics

1926.651(g)(1)Hazardous Atmospheres
http://www.msanorthamerica.com/catalog/catalog537.htmlhttp://www.msanorthamerica.com/catalog/catalog500083.html


32/119

Emergency Rescue Equipment 1926.651(g)(2)(i)


33/119

1926.651(g)(2)(i)Emergency Rescue Equipment

Emergency rescue

equipment must be

readily available where

hazardous atmospheric

conditions exist orexpected to develop

during work.

Breathing apparatus

Safety harness and line

Basket stretcher


34/119

1926.651(h)(1)Water Accumulation

Employees must not work inexcavations where there is

accumulated water, or where

water is accumulating.

Unless precautions taken toprotect workers:

Water removal to control level of

water

Special support or shieldsystems


35/119

Water Accumulation 1926.651(h)(1)


36/119

Water removalequipment and

operations must be

monitored by a

competent person toensure proper

operation.



37/119


Excavations subject torunoff from heavy

rains require an

inspection by a

competent person.


38/119

Well Points Used to Remove Ground Water


39/119


40/119

What are the hazards?


41/119

1926.651(i)(1)Stability of Adjacent Buildings

Support systems suchas shoring, bracing, or

underpinning must be

provided to ensure

stability of structures.


42/119

Stability of Adjacent Structures

Excavation below thefoundation that could

pose a hazard shall not

be permitted except:

Underpinning provided

Stable rock

Registered professional

engineer (RPE) has

approved

1926.651(i)(2)


43/119

Underpinning toprevent structural

failure.

1926.651(i)(2)(i)Underpinning


44/119

Stability of Adjacent Structures

Sidewalks, pavements and appurtenant

structure must not be undermined unless

supported to protect

employees from

collapse of suchstructures.

1926.651(i)(3)


45/119

Adequate protection

provided to protect

employees from loose rock

or soil that could pose a

hazard by falling or rollingfrom an excavation face.

Protection of Employees 1926.651(j)(1)


46/119

Belly bulgeFissures

Extra load from

spoil pile

Potential Problems


47/119

Employees must be protected from equipment

or materials that could fall or roll into

excavations.

Materials and

equipment must bekept 2 feet from edge

of excavation or use

retaining devices.

Protection of Employees 1926.651(j)(2)


48/119

Rule: 2 Feet 1926.651(j)(2)


49/119

Two Feet From Edge 1926.651(j)(2)


50/119

Extra Surface Loading


51/119

1. Whats the Hazard?


52/119

2. See it now


53/119

1926.651(k)(1)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 andother events that could

increase hazards, e.g.,

snowstorm, windstorm,

thaw, earthquake, etc.


54/119

Inspections

Frequency of testing should be increased ifequipment is operating in trench as well as if

welding, cutting, or burning is done in trench.

1926.651(k)(1)


55/119

Fall Protection 1926.651(l)(1)

Walkways provided when crossing over

excavation.

Standard guardrail

installed when more

than 6 feet abovea lower level.


56/119

1926.652(a)(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


57/119

Sliding


58/119

Toppling


59/119

Tension Crack


60/119

Bulging


61/119

Heaving or Squeezing

Soil

Weight

SoilWeight

M th d f P t ti


62/119

Methods of Protection

Sloping and benching

Shoring (spaced sheeting, closed sheeting)

Trench shield

Other occasionally used systems

1926.652


63/119

1926.652(a)(2)Protective Systems

Protective systems

shall have capacity toresist without failure

all loads applied or

transmitted to the

system.


64/119

1926.652(e)(1)(ii)Installation and Removal

Support systems must be installed and

removed in a manner that protects employeesfrom cave-ins.

I t ll ti d R l


65/119

Removal must begin

at, and progress from,

the bottom of the

excavation.

Members released

slowly to note any

indication of possible

failure of remainingmembers.

Installation and Removal 1926.652(e)(1)(V)


66/119

1926.652(e)(2)(i) and (g)(2)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 bepermitted.

Deadl Trench Collapse


67/119

Deadly Trench Collapse


68/119

Wh t th h d?


69/119

Whats the hazard?

Wh t th h d?


70/119

Whats the hazard?

Wh t th h d?


71/119

Whats the hazard?

Wh t th h d?


72/119

Whats the hazard?

Wh t th h d?


73/119

Whats the hazard?

Whats the hazard?


74/119

Whats the hazard?

Whats the hazard?


75/119

Whats the hazard?

Soil Classification


76/119

Contains definitions

Sets forth requirements

Describes acceptable visual and

manual test for use in classifying

soils

Soil Classification Appendix A

Definitions A di A


77/119

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

Appendix A

Soil types

Definitions A di A


78/119

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 A di A


79/119

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 pocketpenetrometer, thumb penetration test, and other

methods

Appendix A

Thread Test A di A


80/119

Roll into thread

At least 2 inches in length

Longer unbroken

thread means more

cohesive

Thread Test Appendix A

Ribbon Test A di A


81/119

Roll soil into a cigar shape

Pinch between thumb and finger

Longer ribbon means

more cohesive

Ribbon Test Appendix A

Thumb Penetration Test Appendix A


82/119

Thumb Penetration Test Appendix A

Pocket Penetrometer Appendix A


83/119

Pocket Penetrometer Appendix A

Type A Soil Appendix A


84/119

Type A Soil

Most stable: clay, silty clay, and hardpan

Not fissured

Not subjected to vibrationof any type

Never been previouslydisturbed

No seeping water

Unconfined compressive strength

greater than 1.5 tons per square foot

(tsf)

Appendix A

Type B Soil Appendix A


85/119

Type B Soil

Medium stability: silt, sandy

loam, medium clay andunstable 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 vibrationUnconfined compressive strength

less than 1.5 tsf and greater than

0.5 tsf

Appendix A

Type C Soil Appendix A


86/119

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 Appendix B


87/119

Contains definitions

Sets forth requirements

Configurations of sloping and benching

Sloping and Benching Appendix B

Allowable Slopes Table B-1


88/119

Allowable Slopes

Soil Type Height/Depth

Ratio

Slope Angle

Stable rock Vertical 90

Type A : 1 53

Type B 1 : 1 45

Type C 1 : 1 34

Type A (short term) : 1 63

(For a maximum excavation depth of 12 ft)

Table B-1

Excavations Made in Type A Soil


89/119


Simple Slope



90/119


Simple Slope Sho rt Term



91/119

Simple Bench




92/119

Unsupported Vert ical ly-Sided Lower Port ion




93/119


Unsupported Vert ical ly-Sided Lower Port ion



94/119


Mult ip le Bench



95/119

ca at o s ade ype So

Support o r Shield System

Excavations Made in Type B Soil


96/119

Simple Slope




97/119

Sing le Bench




98/119


Mult ip le Bench



99/119



Excavations Made in Type C Soil


100/119


Simple Slope



101/119



Excavations Made in Layered Soils


102/119


A over B



103/119


A over C



104/119

y

B over A



105/119

y

B over C



106/119

y

C over A



107/119

y

C over B


108/119

Benching and SlopingBenching

Timber Shoring for Trenches Appendix C


109/119

g

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

Aluminum Hydraulic Shoring Appendix D


110/119

y g

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

Vertical Aluminum Hydraulic Shoring (Spot Bracing)Figure No. 1


111/119

18 Max..

Vertical

Spacing

4 Max.

2 Max.

Vertical Rail

Hydraulic Cylinder

Vertical Aluminum Hydraulic Shoring (With Plywood)Figure No. 2


112/119

Vertical

Rail

18 Max.

Vertical

Spacing

4 Max.

Plywood

Hydraulic

Cylinder

2 Max.

Horizontal

Spacing

Vertical Aluminum Hydraulic Shoring (Stacked)Figure No. 3


113/119

Horizontal Spacing

Vertical

Spacing

4 Max.2 Max.

Hydraulic

Cylinder

Vertical Rail

Aluminum Hydraulic Shoring Waler System (Typical)Figure No. 4


114/119

Horizontal Spacing

2 Max.

Vertical

Spacing

4 Max. Hydraulic

Cylinder

Waler

Upright

Sheeting


115/119

Alternatives to Timber Shoring Appendix E


116/119

Selection of Protective Systems Appendix F


117/119

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).

Thank You For Attending!


118/119

Final Questions?

1-800-NC-LABOR

(1-800-625-2267)

www.nclabor.com

Handouts


119/119

Place all handouts at the end of this presentation.

trench rev1

Documents