No Slide Title - ClickSafety · Introduction •Practical ... appendices B, C and D of the subpart...

Introduction

• Practical Applications for Trenching and Excavation • Module Description • This module will cover some basic practical applications

of the requirements found in subpart P, of the safety and health regulations for construction, CFR 1926. Special emphasis and practical exercises relating to appendices B, C and D of the subpart will be presented to convey the requirements of the regulation as it relates to sloping, benching, shoring and alternative protective methods. Interpretation and use of the shoring tables will be discussed.

• Approximate time: 45 minutes

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.

Introduction

• Objectives • Upon completion of this module, the student:

– Should be aware of the sloping and benching requirements for types A, B and C soils.

– Know where to locate and to use the shoring tables for both timber shoring and aluminum hydraulic shoring.

– Understand the basic requirements for using trench boxes or shields as an alternative to sloping or shoring.

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.

Introduction

• Build on Knowledge • Test knowledge with practical exercises,

cover additional information: sloping configurations, and specific shoring applications using tables from appendices located in Subpart P of OSHA Construction Standards.

Practical Exercise #1

• Using What You’ve Learned • Now let’s use some of what we have learned

about soils analysis, trenches and excavations. We’ll present some information to you about various field situations. You will be required to evaluate the information, use available resources, such as tables from Subpart P, and determine appropriate solutions for each scenario. Ready? Let’s get started.


• The Facts #1 • Visually nothing unusual • Soil from your excavation:

– Very hard to dent with your thumb when dry. – Can be made into a ball and makes a ribbon like a fishing

worm when you perform the wet thread test. • Replacing an existing sewer line 15 feet from a railroad. • Excavation is dry. • You plan to dig 15 feet deep and need a 4 foot wide

trench in bottom.


What is the soil type? • Type A. Good compressive strength and

cohesiveness. wrong • Type B. It’s not A, so it must be B. wrong • Possibly Type B, but probably Type C,

previously disturbed soil + train will create vibration. 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.


• 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


• 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 the factors 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.


• The Facts #2 • You are excavating for a 24 inch water line.

The soil in this excavation can be molded into a ball, but does not hold together. The soil is sandy, with large grains. There is no evidence of previous disturbance, and the soil is dry. You are in an open field 300 feet from any road or other activity.


• 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.


• 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


• 32 Feet • Sloping this excavation would require a trench that

is 32 feet wide at the top. Type C requires a slope of 1.5 to 1, or 15 feet each side for the 10 foot depth, plus the 2 feet for the pipe. 15 + 15 + 2 = 32 feet.

• This should result in a safe and legal excavation. However, you need to think about the economics of this solution because that is a lot of soil to move. A shoring system might make more sense in this situation due to cost.

Sloping Configurations

• Type A Soil • Simple slope - general. • Configurations can be found in Appendix B of

Subpart P. • Twenty feet or less in depth. • If you are more than 20 feet, you’re going to

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

allowable slope is ¾:1.


• 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 ½:1.


• 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.


• Type A Soil • Multiple bench. • Type A soil, 20 feet or less in depth. • Maximum allowable slope is ¾:1. • Maximum bench dimension is four feet for

the bottom bench and five feet for subsequent benches as shown in the illustration.


• 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 ¾

to 1 as shown.


• 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.


• 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.


• Type B Soil • Simple slope.

– Excavations 20 feet or less in depth. – Maximum allowable slope of 1:1.


• 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.


• 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 feet

as shown in the illustration.


• 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.


• Type C Soil • Simple slope.

– 20 feet or less in depth. – Maximum allowable slope of 1 1/2:1.


• 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.


• 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 ¾ to 1. – The slope for the type B soil can be no greater

than 1 to 1.


• Layered Soil • Type C over Type A.


shown in the illustration. – The slope for the type A soil can be no greater

than ¾ to 1. – The slope for the type C soil can be no greater

than 1 ½ to 1.


• Layered Soil • C over B.


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 ½ to 1.


• 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 bottom

layer, controls the slope for the entire excavation, limiting it to no greater than 1 to 1.

– Inferior soil as bottom layer will control slope for entire excavation.


• Layered Soil • A over C.


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 ½ to 1.


• Layered Soil • B over C.


shown in the illustration. – Again, type C as the bottom layer controls this

slope configuration. Maximum slope is 1 ½ to 1 for the entire excavation.

Shoring

• Shoring Tables • Shoring is any mechanical system used to prevent

collapse 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.

Shoring

• Shoring Tables • Internet: • Or you can easily access the tables using the

Internet 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. Click on Appendix D to view shoring tables for Aluminum Hydraulic shores. You’ll have to scroll down to view the tables.

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

Shoring

• Key Terms – Uprights are the vertical boards placed against the

soil. Uprights can also be called sheeting and may need 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.

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.

Shoring

• Using The Tables • 1. Where a choice is available, choose the

horizontal spacing of the cross braces before determining the size of any member.

• 2. Then, using soil type, width and depth of trench, 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.

Timber Shoring

• Timber Shoring • Tables.

– Remember, Soil classification is still required to use 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 4 inches, not 3.5 by 3.5.

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

Timber Shoring

• Let’s Practice • Using the tables.

– You have type B soil. – Shore it with oak timber. – Use the table in appendix C of subpart P for oak

and type B soil. The next screen will provide you with those tables.

– The trench: 13 feet deep X 5 feet wide. You may want to write down these trench dimensions, so you’ll have them handy if you can’t remember them.

Aluminum Hydraulic Shoring

• Aluminum Hydraulic Shoring • Appendix D in Subpart P in OSHA construction

standards. – Soil classification is required to properly determine

appropriate installation. – Hydraulic shoring can be installed vertically in Type A

and B soils using tables D1.1 and D1.2. – Tables D1.3 and D1.4 call for horizontal installation

with wales and uprights for types B and C soils. – Type A soil won’t 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


• 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


• Typical Installations • Aluminum hydraulic shoring.

– Let’s also look at typical installations of aluminum hydraulic shoring.

– This first one is for vertical hydraulic shoring, or spot bracing, and is the simplest example we will consider.

– Incidentally, when vertical shores are used, there must be a minimum of three shores spaced equally, horizontally, in a group.


• 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 structural member, but only for prevention of local raveling (sloughing of the trench face) between shores.


• 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


• Aluminum Hydraulic Shoring Waler System – Note that the shores or wales are installed

horizontally, whereas the uprights, or sheeting is vertical.

– This application would typically be used in type C soils.


• Caution • It is not intended that the aluminum hydraulic

specification apply to every situation that may be experienced in the field. These data were developed to apply to the situations that are most commonly experienced in current trenching practice. For shoring systems for use in situations that are not covered by the data in appendix D, seek help from the manufacturer, distributor or a Registered Professional Engineer.


• Caution • Tables in appendix D not adequate: • Vertical loads on cross braces exceed 100 lb. gravity

load. • Surcharge loads: equipment over 20,000 pounds. • Lower portion of trench shored, remaining portion

of trench sloped or benched unless: – Sloped portion is sloped at less than 3:1. – Members selected from tables for use at depth

determined from top of overall trench, not from toe of slope.

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 hydraulic pressure.

• A disadvantage to the use of pneumatic shoring is that an air compressor must be on site.

Other Shoring

• Screw Jacks • Screw jack systems differ from hydraulic and

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

• This creates a hazard because the worker is required to be in the trench in order to adjust the strut. In addition, uniform "preloading" cannot be achieved with screw jacks, and their weight creates handling difficulties.

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 in

subpart P of the construction safety standard. • In trenches are usually referred to as "trench boxes" or

"trench shields."

Trench Boxes

• Trench Boxes • Different from shoring because, instead of shoring

up or otherwise supporting the trench face, they are intended primarily to protect workers from cave-ins and similar incidents.

• The excavated area between the outside of the trench box and the face of the trench should be as small as possible and backfilled to prevent lateral movement of the box.

• Shields may not be subjected to loads exceeding those which the system was designed to withstand.

Trench Boxes

• Combined Use • Trench boxes are generally used in open areas, but

they also may be used in combination with sloping and benching, as we saw when we discussed sloping configurations.

• The box should extend at least 18 in. above the surrounding area if there is sloping toward excavation. This can be improved by providing a benched area adjacent to the box.

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 of

possible loss of soil from behind or below the bottom of the support system.

– Conditions require observation. – Careful visual inspection is prudent.

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.

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.

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

manufacturer’s specification.

– No exposure to suspended load overhead, especially during installation or removal process!

Summary

• Summary • We‘ve reviewed field applications of the

requirements found in Subpart P of the OSHA construction standards.

• We’ve provided samples of challenges that contractors face with excavation activities. We can’t cover all possible types of exposures or situations.

• Become familiar with detailed information contained in the appendices discussed here. Go to them as described earlier, and study them until you are comfortable with the requirements.

Summary

• Get Help – If you need it, get help. – Good sources of assistance:

• Local shoring dealer. • Distributor or manufacturer. • Registered Professional Engineer. • OSHA Consultation.

No Slide Title - ClickSafety · Introduction •Practical ... appendices B, C and D of the subpart...

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