OSHA30 ExcavationsPracticalApplications V6 SG

8/11/2019 OSHA30 ExcavationsPracticalApplications V6 SG

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Introduction

Practical Applications for Trenching and Excavation

Module Description

This module will cover some basic practical applicationsof the requirements found in subpart P, of the safetyand health regulations for construction, CFR 1926.Special emphasis and practical exercises relating toappendices B, C and D of the subpart will be presentedto convey the requirements of the regulation as itrelates to sloping, benching, shoring and alternativeprotective methods. Interpretation and use of theshoring tables will be discussed.

Approximate time: 45 minutes


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Introduction

Module Description

Not a substitute for standards.

Training should not be considered as substitute for

safety and health standards for general industry or

construction industry.

Employers and employees should be familiar,

comply with standards, rules, and regulations

applicable to their work.


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Introduction

References

Occupational Safety and Health Administration

(OSHA), 29 CFR 1926, Subpart P.

Excavations: Hazard Recognition in Trenching

and Shoring. OSHA Technical Manual (TED 1-0.15A), Section V - Chapter 2 (1999, January

20), 15 pages.


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Practical Exercise #1

What is the soil type?

Type A. Good compressive strength and

cohesiveness. wrong

Type B. Its not A, so it must be B. wrong

Possibly Type B, but probably Type C,

previously disturbed soil + train will createvibration. correct

The soil is probably type B, but could be downgraded all the way to type C. It has good compressive strength and good

cohesiveness as shown by the manual test performed earlier. However, we know the soil has been previously disturbed

because of the existing sewer line, and we can expect vibration from passing trains, so it cannot be classified as Type A.Type C is the safest choice, but more information would help.


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If you protect this excavation by sloping it,

how wide is the excavation at the top?

15 feet. wrong

30 feet. wrong

34 feet. correct None of the above. wrong


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Excavation = 34 Feet Wide

Your excavation will be 34 feet wide. Type B

soil gets a 1:1 slope, which means it will be 15

feet on each side, plus the 4 foot wide trench

for the pipe. Do you think that this is a good

solution for this situation? Consider all of thefactors presented in the scenario.

In this case, sloping is probably not a good idea. Since the railroad is only 15 feet away, sloping will undermine the track,

and you may end up with a train in your trench, and that would not be a good career move. Shoring would be a better

choice in these circumstances. It will provide protection and also reduce the chance for subsidence.


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What is the most likely soil type?

Type A wrong

Type B wrong

Type C correct

Unable to classify. wrong

Most likely this is type C soil. The tests indicate low cohesion and low strength. Also, if unable to classify the soil,then it must be assumed to be type C soil until sufficient information is developed to properly classify it otherwise.


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Type C soil. 2 foot wide trench in bottom.

10 feet deep. If you slope the excavation,

how wide is it at the top?

20 feet

22 feet

32 feet (correct answer)

40 feet


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32 Feet

Sloping this excavation would require a trench thatis 32 feet wide at the top. Type C requires a slopeof 1.5 to 1, or 15 feet each side for the 10 footdepth, plus the 2 feet for the pipe. 15 + 15 + 2 = 32feet.

This should result in a safe and legal excavation.

However, you need to think about the economics ofthis solution because that is a lot of soil to move. Ashoring system might make more sense in thissituation due to cost.


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Sloping Configurations

Type A Soil

Simple slope - general.

Configurations can be found in Appendix B ofSubpart P.

Twenty feet or less in depth.

If you are more than 20 feet, youre going to

need a Registered Professional Engineer. Type A, less than 20 feet deep. Maximum

allowable slope is :1.


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Type A Soil

Simple slope short term.

Exception for simple slope excavations in Type

A soil open 24 hours or less.

12 feet or less in depth.

Maximum allowable slope is :1.


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Type A Soil

Simple bench.

All benched excavations in Type A soil 20 feet

or less in depth.

Maximum allowable slope of 3/4 to 1.

Maximum bench dimension is four feet as

shown in the illustration.


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Type A Soil

Multiple bench.

Type A soil, 20 feet or less in depth.

Maximum allowable slope is :1.

Maximum bench dimension is four feet forthe bottom bench and five feet for

subsequent benches as shown in the

illustration.


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Type A Soil


Unsupported vertically sided lower portions.

Maximum vertical side of 3 1/2 feet.

The maximum slope for the upper portion is

to 1 as shown.


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Type A Soil

More than 8 feet, less than 12 feet.

Unsupported vertically sided lower portion.

Maximum vertical side of 3 1/2 feet.

Maximum allowable slope for the upper

portion is 1:1.


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Type A Soil


Vertically sided lower portion supported or

shielded.

Maximum allowable slope of 3/4:1 for the

upper portion of excavation.

The support or shield system must extend at

least 18 inches above the top of the vertical

side.


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Type B Soil

Simple slope.

Excavations 20 feet or less in depth.

Maximum allowable slope of 1:1.


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Type B Soil

Single bench.

All benched excavations 20 feet or less in

depth.

Maximum allowable slope of 1:1.

Maximum bench dimension is four feet as



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Type B Soil

Multiple bench.

Type B soil, 20 feet or less in depth.

Maximum allowable slope is 1:1.

Maximum bench dimensions are four feetas shown in the illustration.


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Type B Soil


Vertically sided lower portion.

Must be shielded or supported to a height at

least 18 inches above the top of the vertical

side.

All such excavations shall have a maximum

allowable slope of 1:1 for the upper portion.


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Type C Soil

Simple slope.


Maximum allowable slope of 1 1/2:1.


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Type C Soil


Vertical sided lower portion.

Shielded or supported to a height at least 18

inches above the top of the vertical side.

All such excavations shall have a maximum

allowable slope of 1 1/2:1 for the upper

portion.


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Layered Soil

Type B over Type A.


Maximum allowable slope for each layer as


The slope for the type A soil can be to 1.

The slope for the type B soil can be no greater

than 1 to 1.


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Layered Soil

Type C over Type A.


Maximum allowable slope for each layer asshown in the illustration.

The slope for the type A soil can be no greaterthan to 1.

The slope for the type C soil can be no greaterthan 1 to 1.


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Layered Soil

C over B.




The slope for the type B soil can be no greater

than 1 to 1.

The slope for the type C soil can be no greater

than 1 to 1.


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Layered Soil

A over B.

20 feet or less in depth. Maximum allowable slope for each layer as shown

in the illustration.

As seen, in this case the type B soil as the bottomlayer, controls the slope for the entire excavation,limiting it to no greater than 1 to 1.

Inferior soil as bottom layer will control slope forentire excavation.


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Layered Soil

A over C.




As seen, the entire slope is again controlled by

the bottom layer, in this case type C soil with a

slope no greater than 1 to 1.


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Layered Soil

B over C.




Again, type C as the bottom layer controls this

slope configuration. Maximum slope is 1 to

1 for the entire excavation.


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Shoring

Shoring Tables

Shoring is any mechanical system used to preventcollapse of an excavation.

Shoring: OSHA standards subpart P: Appendix C, timber shoring.

Appendix D, aluminum hydraulic shoring.

Other shoring systems must be designed by a

Registered Professional Engineer. Hard copy of the standards? Go to subpart P,

appendix C or D, and locate the tables.


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Shoring

Shoring Tables

Internet:

Or you can easily access the tables using theInternet at www.osha.gov Click on the weblink.

This will take you to the Construction Standards,1926 Subpart P Excavations. Click on Appendix C

to view the shoring tables for Timber shoring. Clickon Appendix D to view shoring tables for AluminumHydraulic shores. Youll have to scroll down to viewthe tables.

http://www.osha.gov/pls/oshaweb/owasrch.search_form?p_doc_type=STANDARDS&p_toc_level=1&p

_keyvalue=Construction


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Shoring

Key Terms

Uprights are the vertical boards placed against the

soil. Uprights can also be called sheeting and mayneed tongue and groove to retain water.

Cross brace refers to the timber running across the

excavation, which holds the uprights in place.

Wales, or walers are the timbers that run parallel

to the excavation and provide support for the

uprights.


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Shoring

Using The Tables

Minimum sizes of members are specified for use in

different types of soil. Six tables of information, two for each soil type.

The soil type must first be determined.

Selection of size and spacing of members is based

on: Depth and width of trench.

Horizontal spacing of cross braces.


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Shoring

Using The Tables

1. Where a choice is available, choose the

horizontal spacing of the cross braces beforedetermining the size of any member.

2. Then, using soil type, width and depth oftrench, and horizontal spacing of cross braces

you can read from the appropriate table: The size and vertical spacing of the cross braces. The size and vertical spacing of the wales.

The size and horizontal spacing of the uprights.


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Timber Shoring

Timber Shoring

Tables.

Remember, Soil classification is still required touse the tables.

Tables C1.1 through C2.3 are based on soil types.C1 series uses oak while the C2 series uses Douglas

fir. Dimensions refer to actual dimension, not the

nominal dimension. So, 4x4 means 4 inches by 4inches, not 3.5 by 3.5.

http://www.clicksafety.com/ucp/images/pdf/courseware/TABLE%20C%20-%201.3.pdf


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Timber Shoring

Lets Practice

Using the tables.

You have type B soil. Shore it with oak timber.

Use the table in appendix C of subpart P for oakand type B soil. The next screen will provide youwith those tables.

The trench: 13 feet deep X 5 feet wide. You maywant to write down these trench dimensions, soyoull have them handy if you cant rememberthem.


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Aluminum Hydraulic Shoring


Appendix D in Subpart P in OSHA constructionstandards. Soil classification is required to properly determine

appropriate installation.

Hydraulic shoring can be installed vertically in Type Aand B soils using tables D1.1 and D1.2.

Tables D1.3 and D1.4 call for horizontal installationwith wales and uprights for types B and C soils.

Type A soil wont need sheeting (uprights) whereas,Type B may, and Type C will.

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10934


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Example #1

You have type A soil, 12 feet deep and 6 feet

wide.

What is the maximum horizontal and vertical

spacing, and what diameter shoring is

required?

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10934


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Typical Installations

Aluminum hydraulic shoring.

Lets also look at typical installations of aluminumhydraulic shoring.

This first one is for vertical hydraulic shoring, orspot bracing, and is the simplest example we will

consider. Incidentally, when vertical shores are used, there

must be a minimum of three shores spacedequally, horizontally, in a group.


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Vertical Aluminum Hydraulic Shoring With

Plywood

The requirements indicate that Plywood shall

be 1.125 inch thick softwood or 0.75 inch thick,

14 ply, arctic white birch (Finland form).

Plywood is not intended as a structuralmember, but only for prevention of local

raveling (sloughing of the trench face) between

shores.


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Vertical Aluminum Hydraulic Shoring

(stacked)

This would typically be used in trenches too

deep for single shores.

Remember the shores are installed from the

top down and removed from the bottom up


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Aluminum Hydraulic Shoring Waler System

Note that the shores or wales are installed

horizontally, whereas the uprights, or sheetingis vertical.

This application would typically be used in type

C soils.


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Caution

It is not intended that the aluminum hydraulic

specification apply to every situation that may beexperienced in the field. These data weredeveloped to apply to the situations that are mostcommonly experienced in current trenchingpractice. For shoring systems for use in situations

that are not covered by the data in appendix D,seek help from the manufacturer, distributor or aRegistered Professional Engineer.


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Other Shoring

Pneumatic Shoring

Pneumatic shoring works in a manner similar

to hydraulic shoring. The primary difference is that pneumatic

shoring uses air pressure in place of hydraulicpressure.

A disadvantage to the use of pneumaticshoring is that an air compressor must be onsite.


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Other Shoring

Screw Jacks

Screw jack systems differ from hydraulic and

pneumatic systems in that the struts of ascrew jack system must be adjusted manually.

This creates a hazard because the worker isrequired to be in the trench in order to adjust

the strut. In addition, uniform "preloading"cannot be achieved with screw jacks, and theirweight creates handling difficulties.


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Trench Boxes

A Shield or Shield System

Shield:

Structure able to withstand forces imposed by a cave-in

and thereby protect employees within the structure. Can be permanent structures or portable to move along

as work progresses.

Can be pre-manufactured or job-built in as specified insubpart P of the construction safety standard.

In trenches are usually referred to as "trench boxes" or"trench shields."


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Trench Boxes

Trench Boxes

Different from shoring because, instead of shoringup or otherwise supporting the trench face, they

are intended primarily to protect workers fromcave-ins and similar incidents.

The excavated area between the outside of thetrench box and the face of the trench should be as

small as possible and backfilled to prevent lateralmovement of the box.

Shields may not be subjected to loads exceedingthose which the system was designed to withstand.


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Trench Boxes

Combined Use

Trench boxes are generally used in open areas, but

they also may be used in combination with slopingand benching, as we saw when we discussedsloping configurations.

The box should extend at least 18 in. above thesurrounding area if there is sloping towardexcavation. This can be improved by providing abenched area adjacent to the box.


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Trench Boxes

Excavation Depth

Earth excavation to a depth of 2 ft. below the

shield is permitted, but only if the shield is: Designed to resist the forces calculated for the full

depth of the trench.

There are no indications while the trench is open ofpossible loss of soil from behind or below thebottom of the support system.

Conditions require observation.

Careful visual inspection is prudent.


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Trench Boxes

Employee Protection

Employees shall be protected from the

hazard of cave-ins when entering or exiting

the areas protected by shields.

Employees shall not be allowed in shields

when shields are being installed, removed,

or moved vertically.


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Trench Boxes

End Protection

At times trench shields will be used in

excavations where there is exposure due to

unprotected ends of the shield.

These open ends must be protected by

means of additional engineered panels or

approved sheeting when they are exposed

to a potential cave-in.


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Trench Boxes

Trench Boxes: Stacking

If the trench is deep and stacking shields is

required: Use manufacturers specifications for installation.

Be sure that the shields are pinned according to the

manufacturers specification.

No exposure to suspended load overhead,

especially during installation or removal

process!


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Summary

Summary

Weve reviewed field applications of therequirements found in Subpart P of the OSHA

construction standards. Weve provided samples of challenges that

contractors face with excavation activities. We cantcover all possible types of exposures or situations.

Become familiar with detailed informationcontained in the appendices discussed here. Go tothem as described earlier, and study them until youare comfortable with the requirements.


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Summary

Get Help

If you need it, get help.

Good sources of assistance:

Local shoring dealer.

Distributor or manufacturer.

Registered Professional Engineer. OSHA Consultation.

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