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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Practical Exercise #1
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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Practical Exercise #1
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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Practical Exercise #2
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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Practical Exercise #2
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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Practical Exercise #2
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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Sloping Configurations
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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Sloping Configurations
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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Sloping Configurations
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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Sloping Configurations
Type A Soil
8 feet or less in depth.
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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Sloping Configurations
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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Sloping Configurations
Type A Soil
20 feet or less in depth.
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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Sloping Configurations
Type B Soil
Simple slope.
Excavations 20 feet or less in depth.
Maximum allowable slope of 1:1.
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Sloping Configurations
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
shown in the illustration.
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Sloping Configurations
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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Sloping Configurations
Type B Soil
20 feet or less in depth.
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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Sloping Configurations
Type C Soil
Simple slope.
20 feet or less in depth.
Maximum allowable slope of 1 1/2:1.
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Sloping Configurations
Type C Soil
20 feet or less in depth.
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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Sloping Configurations
Layered Soil
Type B over Type A.
20 feet or less in depth.
Maximum allowable slope for each layer as
shown in the illustration.
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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Sloping Configurations
Layered Soil
Type C over Type A.
20 feet or less in depth.
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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Sloping Configurations
Layered Soil
C over B.
20 feet or less in depth.
Maximum allowable slope for each layer as
shown in the illustration.
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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Sloping Configurations
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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Sloping Configurations
Layered Soil
A over C.
20 feet or less in depth.
Maximum allowable slope for each layer as
shown in the illustration.
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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Sloping Configurations
Layered Soil
B over C.
20 feet or less in depth.
Maximum allowable slope for each layer as
shown in the illustration.
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
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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Aluminum Hydraulic Shoring
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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Aluminum Hydraulic Shoring
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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Aluminum Hydraulic Shoring
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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Aluminum Hydraulic Shoring
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
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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Aluminum Hydraulic Shoring
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.