14_guide Osha Excavations Standard

7/27/2019 14_guide Osha Excavations Standard

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A Guide to

OSHA Excavations Standard

Bobby R. DavisSeries Editor

Division of Occupational Safety and Health

N.C. Department of Labor

1101 Mail Service Center

Raleigh, NC 27699-1101

Cherie Berry

Commissioner of Labor


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Occupational Safety and Health Program

Cherie Berry


OSHA State Plan Designee

Allen McNeely

Deputy Commissioner for Safety and Health

Kevin BeauregardAssistant Deputy Commissioner for Safety and Health

Acknowledgments

This edition ofA Guide to the OSHA Excavation Standardhas been updated to include material as prepared by the

Construction Education and Research Institute, Department of Civil Engineering at N.C. State University (principal

investigators were Paul P. McCain and David W. Johnston); U.S. Department of Labor, Occupational Safety and

Health Administration; U.S. Department of Health and Human Services (NIOSH); and OSHNC personnel

This guide is intended to be consistent with all existing OSHA standards; therefore, if an area is considered by thereader to be inconsistent with a standard, then the OSHA standard should be followed.

To obtain additional copies of this book, or if you have questions about N.C. occupational safety and health standards or

rules, please contact:


Bureau of Education, Training and Technical Assistance

1101 Mail Service Center

Raleigh, NC 27699-1101

Phone: (919) 807-2875 or 1-800-NC-LABOR (1-800-625-2267)

____________________

Additional sources of information are listed on the inside back cover of this book.____________________

The projected cost of the NCDOL OSH program for federal fiscal year 20072008 is $16,143,161. Federal funding provides approximately 32 percent ($5,180,570) ofthis total.

Printed 3/08


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ContentsPart Page

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1iiv

In t roduct ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1vii

1 C ommon S oil P roblems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1ii1

2 S oil Ty pes a nd P r essures . . . . . . . . . . . . . . . . . . . . . . . . . . . ii18

3 Met hods of P r ot ect ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii14

4 I ns ta lla t ion a n d R em ov a l of P r ot ect iv e S y st em s . . . . . . . . . . . . . . ii18

5 R es id en t ia l C on t ra ct or s a n d t h e E xca v a t ion s S t a n da r d . . . . . . . . . ii29

6 Wor ker Tr a in in g a n d J obs it e S a fet y . . . . . . . . . . . . . . . . . . . . . ii30

7 Sa fet y Checklist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii34

S uggest ed Rea din gs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii37

iii


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Foreword

There is no reason why anyone ever has to die in a trenching accident. Modern technology has provided us with a vari-

ety of excellent shoring systems and trench shields. The OSHA excavations standard provides us with a set of clearly

written and logical safety rules. Yet every year workers are killed and injured by cave-ins. Employers and employees can

expect N.C. Department of Labor safety inspectors to make the most detailed, professional inspections possible whenever

such accidents occur.

A Guide to the OSHA Excavations Standardexamines the standards different sections, offering many illustrations and

a safety checklist to help explain how to excavate and work safely in a trench. It also discusses the new rule concerningexcavating and residential construction.

In North Carolina, DOL inspectors enforce the federal Occupational Safety and Health Act through a state plan

approved by the U.S. Department of Labor. The N.C. Department of Labors Division of Occupational Safety and Health

offers many educational programs to the public and produces publications, including this guide, to help inform people

about their rights and responsibilities regarding occupational safety and health.

When looking through this guide, please remember DOLs mission is greater than just to enforce regulations. An equal-

ly important goal is to help people find ways to create safe workplaces. This booklet, like the other educational materials

produced by the N.C. Department of Labor, can help.

Cherie Berry


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IntroductionThe Occupational Safety and Health Administration issued its fi rst Excava tion an d Trenching

St anda rd in 1971 to protect w orkers from excava tion ha zards. S ince then, OSHA has am ended the st an -

da rd several t imes to increa se worker protection a nd to reduce the frequency an d severity of exca vat ion

a ccidents a nd injuries. Despite these efforts, exca vat ion-relat ed accidents resulting in injuries and fa ta li-

ties cont inue t o occur.

OSHNC ha s developed t his guide in effort to address requirements of the sta ndar d, a s w ell a s provide

informa tion for equipment opera tors, workers a nd a ll others a ssociated w ith t renching a nd excava ting t ohelp recognize haza rdous conditions t ha t could result in injury or a fat a lity. This guide discusses soil com-

position in moderat e detail t o provide a general overview of the various properties a ssociat ed wit h differ-

ent t ypes of soil. A general un dersta nding of the propert ies of soil is t he fi rst s tep in predicting the behav-

ior of soils in va rying condition. Some of the most common t ypes of soil conditions t ha t lea d t o trench a nd

exca va tion failure a re also discussed.

P roper t renching operat ions a re necessa ry to protect the w orkers fr om soil collapse. The ba sic trench-

ing opera tions tha t help ma ke a tr ench sa fe for w orkers a re described and illustr a ted. The methods of

shoring installation are also discussed briefl y. This document is not intended to be used as a step-by-step guideline in the excavation process.

OSHA has completely updated the excavations standard, with focus on the existing standard to simpli-

fy ma ny of the existing provisions, a dd a nd clarify defi nitions, elimina te duplica te provisions a nd a mbigu-ous la ngua ge, and give employers a dded fl exibility in providing protection for employees. In a ddition, th e

standard provides several new appendices. Appendix A to 1926.652 provides a consistent method of soil

classifi cation. Appendix B to 1926.652 provides sloping and benching requirements. Other appendixes

(a ppendixes C F) provide pictoria l examples of shoring a nd sh ielding devices, timber t a bles, hydra ulic

shoring tables, and selection charts that provide a graphic summary of the requirements contained in the

standard. For more information on the details of proper installation, please refer to the OSHA standard

on excavation (29 CFR 1926 Subpart P, which includes 650652 an d a ppendixes AF) an d to the

Suggested Readings in t his guide.

Scope an d App l i c a t i o n

OSHAs revised rule a pplies to a ll open exca vat ions ma de in the eart h s surfa ce, w hich includes trench-es. According to the OS HA construction sa fety a nd hea lth st a nda rds, 1926.650(b), a trench is referred t o

as a nar row excava tion made below the surface of the ground in which the depth is greater tha n th e

width the w idth not exceeding 15 feet (4.5 meters). An excava tion is a ny m a n-ma de cut, cavity, trench

or depression in t he eart h s surfa ce formed by ea rt h removal. This can include exca va tions for a nyt hing,

from cellars to highw a ys. The sta nda rd does not a pply t o house founda tion/basement exca va tions (includ-

ing th ose tha t become trenches by defi nition when formw ork, foundat ions or wa lls are const ructed) w hen

a ll of th e follow ing conditions a re present:

The house found a tion/ba sement exca va tion is less tha n 71/2 feet (2.5 meters ) deep or is benched for a t

lea st 2 feet (0.61 met ers) horizonta lly for every 5 feet (1.52 meters ) or less of vertical h eight ;

The minimum horizonta l w idth (exca va tion face to formwork/w a ll) a t the bottom of the excava tion is

a s w ide as pra ctica ble but not less tha n 2 feet (0.61 meters);

There is no wa ter, surface tension cra cks nor other environmenta l conditions present t ha t r educe the

stability of the excavation;

There is no heavy equipment opera ting in t he vicinity t ha t causes vibra tion to the exca vat ion w hile

employees are in t he exca va tion;

All soil, equipment a nd ma teria l surchar ge loa ds a re no closer in dista nce to the t op edge of the exca -

va tion tha n th e exca va tion is deep; how ever, when front end loaders a re used to dig the excava tions,

the soil surcharge load m ust be placed as fa r ba ck from the edge of the excava tion a s possible, but

never closer th a n 2 feet (0.61 meters).

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Work crews in the exca va tion a re the minimu m num ber needed to perform t he work; a nd

The work ha s been plann ed and is car ried out in a ma nner to minimize the time employees are in

the excavation.

These conditions a s a pplica ble to residentia l constr uction a re resta ted in a nother section of this guide,

Resi d e n t i a l Con t r a c t or s an d t h e Ex ca va t i on s St a n da r d .

The sta nda rd provides severa l options for designing tr ench protection mea sures. U nder certa in condi-

tions, the design of the trench protection mea sures must be prepa red by a registered professional engi-

neer.P roper selection an d insta llat ion of trench protection mea sures a re very import a nt. To comply w ith t he

standard, the employer must have a competent person: one who is ca pable of identifying existing a nd

predicta ble hazar ds in t he surroundings or w orking condit ions w hich a re unsa nita ry, ha zardous, or da n-

gerous to employees, and w ho has a uth orization to ta ke prompt corrective measures to elimina te th em.

This competent person has critical inspection responsibilities regarding excavations. This person must

inspect every exca vat ion a nd protective system un der his or her ca re daily, including a reas a djacent t o

a ny exca vat ion. Additional inspections must be conducted before sta rt ing w ork and a s needed th rough a

shift , for example, when a ny ha za rd-increasing occurrence (such as a ra instorm) ta kes pla ce. When th e

competent person fi nds a ny evidence of a sit ua tion tha t could result in a cave-in, protective syst em failure

or any other ha za rdous condition, employees are to be immedia tely removed from the dan ger ar ea unt il

the problem is fi xed.

Man y compa nies have esta blished a w ritt en policy tha t outlines specifi c safe tr enching pra ctices in

deta il. Such a policy should ensure a dequa te support for the tr ench a nd frequent inspections of the exca-

vation site to detect any change in the soil conditions. When this type of policy is enforced, all employees

underst a nd t heir responsibilities, w hich helps to a void unsa fe practices.

This document is not intended to be a guideline for compliance with all pertinent OSHAregulations but rather an overview of safe practices in trenching operations. Though theguide is not intended to be inconsistent with OSHA standards, if an area is considered by thereader to be inconsistent, the OSHA standard should be followed.

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1

Common Soil ProblemsThis guide highlights the requirements in the updated standard for excavation and trenching opera-

tions, provides meth ods for protecting employees ag a inst cave-ins, a nd describes safe w ork practices for

employees. A necessar y fi rst s tep in pla nning t he approach to an y tr enching or oth er exca vat ion project is

to understa nd w ha t could go w rong. This understa nding can help avoid many of the problems associat ed

with excava tion.

The t erms soila nd eartha re commonly referred to in the exca va tion process to describe the na tur a lly

occurring ma teria ls uncovered on a project. S oil conditions va ry fr om one site t o the next. S oil ma y be

loose or pa rtia lly cemented, orga nic or inorga nic. However, most soils ca n be referred to a s a mixture or

a n a ccumula tion of minera l gra ins tha t a re not cemented together. An exception is ha rd rock, which

remains fi rm a fter exposure to the elements.

Soi l fa i lu reis defi ned a s th e collapse of pa rt or all of an excava tion w a ll. The most common soil fa ilure

is ty pica lly described as a n unexpected sett lement, or cave-in, of an excava tion. Soil sliding is t he most

common fa ctor lea ding t o soil failure.

P roper plann ing a nd supervision can a void the unsa fe working conditions caused by soil sliding. Unless

such sa fety precautions ha ve been implemented, sliding soil fa ilure ca n occur in a ll types of exca va tions(including sloped t renches an d exca vat ions w ith bra ced t rench boxes). See fi gure 1.

Over v i ew : Soi l M echa n i cs

A number of str esses an d deforma tions can occur in a n open cut or t rench. For example, increa ses or

decrea ses in moisture content can a dversely affect the st a bility of a tr ench or exca va tion. The follow ing

diag ra ms show some of the more frequently identi fi ed ca uses of trench failure.

Tensi on cr acks. Tension cra cks usua lly form a t a horizont a l dista nce of one-ha lf to thr ee-qua rters times

the depth of the t rench, measured from t he top of the vertical fa ce of the t rench. See fi gure 2 for a ddition-

al deta ils.

Figure 1Sl i d i n g F a i l u r e

1

Tension CrackFailed Soil Mass


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Figure 2

Tens i on C r ack

Sl i d i ngor sluffi ng ma y occur as a result of tension cra cks, as illustra ted in fi gure 3.

Figure 3

S l i d i n g

Toppl ing. In a ddit ion to sliding , tension cra cks ca n caus e toppling. Toppling occurs w hen th e trench svertical fa ce shea rs a long t he tension cra ck line an d topples into the exca va tion. See fi gure 4.

Figure 4

Topp l i n g

2

TensionCrack

H

.5 to .75 H

Sliding

Toppling


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Subsidence and B ul gin g. An unsupported excava tion ca n create a n unba lan ced str ess in the soil,

w hich, in t urn, causes subsidence at the sur face and bulging of the vertica l face of the t rench. If uncor-

rected, this condition can cause fa ce failure a nd entr a pment of workers in the trench. See fi gure 5.

Figure 5

Subsi d ence an d Bu l g i n g

H eavi ng or Squeezing. B ottom hea ving or squeezing is caused by the downw ar d pressure creat ed by thew eight of adjoining soil. This pressure causes a bulge in the bottom of the cut, a s illustra ted in fi gure 6.

Hea ving a nd squ eezing can occur even wh en shoring or shielding ha s been properly insta lled.

Figure 6

H eav i ng o r Squeez ing

3

Bulge

Subsidence

HeaveSoil

Weight


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Boi l ingis evidenced by a n upwa rd w at er fl ow int o the bott om of the cut. A high w a ter t a ble is one of

the causes of boiling. Boiling produces a quick condition in t he bottom of th e cut a nd ca n occur even

w hen shoring or tr ench boxes a re used. See fi gure 7.

Figure 7

Bo i l i n g

Uni t Weight of Soi l srefers to the w eight of one unit of a part icular soil. The w eight of soil varies w ith

ty pe an d moist ure content . One cubic foot of soil ca n w eigh from 110 pound s t o 140 pounds or more, a nd

one cubic met er (35.3 cubic feet) of soil can w eigh m ore th a n 3,000 pounds.

A sa fe slope can be defi ned as t he maximum a ngle of the edge wa ll or ba nk of an excava tion at which

sliding w ill not occur. The uniq ue mixt ures of th e different ty pes of soil (sa nd, cla y, silt a nd r ock) necessi-

ta te different sa fe slopes from one excava tion site to the next.

There ar e other complica ting fa ctors t ha t can result in sliding soil failures. During a n exca vat ion, visi-

bly different la yers of soil ma ybe uncovered. Ea ch of those layers ma y call for different sa fe slopes. It is

essentia l to plan y our exca vat ion a round the most gra dua l (ra ther t ha n steepest) safe slope for all of the

different soil types and la yers encount ered during the exca va tion.

Another complica ting fa ctor is t ha t soil composition mixtures ma y va ry signi fi cant ly from one ar ea of

the project t o anoth er. Dur ing a n exca va tion, as the soil composition changes, t he sa fe slope for t rench

w a ll excava tion also changes. Thus, a cross a n exca va tion site, the slope of the ba nk ma y need to be differ-

ent t o provide a sa fe working environment .

Sliding a nd other m odes of failure ca n a lso occur in soils tha t a re not densely compacted. For exa mple,

a trench th a t is m a de close to a previously dug trench is very unst a ble. If uncompacted soil is discovered,

the norma l sa fe slope for dense soil will not be enough t o prevent sliding. B ra cing or furt her sloping ma y

be necessa ry.

If cra cks a re observed in rocky t ypes of soil, sliding ha s a lready occurred. These cracks should signa l

tha t a more gra dua l slope for excava tion is needed beca use the rocky soil is very susceptible to slides a ndother ty pes of fa ilure.

Excava tions tha t ha ve been sta ble for long periods ar e also subject t o sliding ty pes of failure. After pro-

longed exposure t o the elements, t he moisture content in th e soil ma y increase. This increase in m oistur e

ma y be due to va rious ca uses, such a s ra infall or a broken wa ter line. The extra soil moisture tends to

speed up sliding soil failures.

Determ ining t he correct sa fe slope ca n be quit e diffi cult for certa in ty pes of soil. The OSH A sta nda rd

ha s developed a simple method of determining sa fe exca va tion ba nk slopes for different soil types. This

new method w ill be discussed in more deta il in a la ter section of this document.

4

WaterTable

Boiling


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Soil failure ca n occur for a ny num ber of reasons. Fa ctors th a t increase th e cha nces of soil failure a re:

1. excessive vibra t ion

2. surface encumbrances

3. weather condit ions

Cave-i n s an d P r o t ec t i ve Supp o r t Syst em s

Excavation workers are exposed to many hazards, but the chief hazard is danger of cave-ins. OSHArequires t ha t in a ll exca vat ions employees exposed to potentia l cave-ins mu st be protected by sloping or

benching t he sides of the exca va tion, by supporting the sides of the excava tion, or by placing a shield

betw een the side of the exca va tion an d the w ork area . Designing a protective system can be complex

because of the number of factors involved-soil classifi cation, depth of cut, w a ter content of soil, changes

due to wea th er a nd clima te, or other operat ions in t he vicinity. The sta nda rd, however, provides several

different methods and approaches (four for sloping and four for shoring, including the use of shields)* for

designing protective syst ems th a t ca n be used to provide the required level of protection a ga inst ca ve-ins.

One method of ensuring the sa fety a nd hea lth of workers in an exca vat ion is to slope the sides to an a ngle

not st eeper th a n one an d one-ha lf horizonta l to one vertical (34 degrees mea sured from t he horizonta l).

These slopes must be exca va ted t o form confi gura tions tha t a re in accorda nce w ith t hose for Type C soil

found in appendix B of the st a nda rd. A slope of this gr a da tion or less is considered sa fe for a ny t ype of

soil. (See fi gure 8).Figure 8

Type C Soi l

S im p l e S lope Excava t i on

All simple slope excava tions 20 feet (6.11 meters) or less in depth mu st ha ve a ma ximum a llow a ble

slope of 1.5:1. A second desig n m ethod, w hich can be a pplied for both sloping a nd sh oring, involves usin g

tabulated data, such as tables and charts, approved by a registered professional engineer. These data

must be in wr it ing and must include suffi cient explan a tory informa tion to ena ble the user to ma ke a

selection, including t he criteria for determ ining th e selection a nd t he limits on the use of the da ta . At

least one copy of the informa tion, including th e identity of th e registered professiona l engineer w ho

a pproved the da ta , must be kept at the w orksite during construction of the protective system. U pon com-

pletion of the system, the da ta ma y be stored a w ay from t he jobsite, but a copy must be ma de ava ilable

upon request t o OSH NC. Contr a ctors ma y a lso use a t rench box or shield tha t is either designed ora pproved by a registered professional engineer or is bas ed on ta bulat ed dat a prepa red or approved by a

registered professional engineer. Timber, alum inum or other suita ble mat erials m a y a lso be used. OSHA

sta ndar ds permit the use of a trench shield (also known as a welder s hut ) a s long as t he protection it pro-

vides is equa l to or grea ter th a n th e protection tha t w ould be provided by the appropria te shoring system.

(See fi gure 9.)

5

*See appendix F to the sta nda rd for a complete overview of all options.

20' Maximum

11/2

1


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Su r f a c e Encum b r a n ces

Hea vy loa ds such as la rge equipment, heavy m a teria ls or la rge spoil piles ca n be too heavy for th e soil

to support , resulting in a cave-in. These loads a re referred t o a s sur face encumbran ces. They pose differ-

ent t ypes of da ngers (see fi gure 3). For exam ple, lar ge spoil piles ma y hide t ension cra cks th a t w ould oth-

erw ise signa l tha t a sliding soil failure may occur.

Figure 11

Su r f a ce Encum b ra nces

Existing s ite featu res such as buildings, curbs, trees, utility poles a nd other str uctures a djoining the

exca va tion a rea ma y be considered a s ty pes of surfa ce encumbra nces. These extr a loa ds can pla ce morestr ess on the sides of an exca va tion tha n the w a lls ca n sa fely ca rry. Sh oring, bra cing, underpinning or

some combinat ion of safety mea sures should be provided, as n ecessar y, to protect w orkers a nd t o prevent

movement of the soil beneath the a djacent load.

In cases w here the space is limited and hea vy loa ds must be located nea r a n exca vat ion, the trench

w a lls must be braced or shored as needed to sa fely support t his extra w eight.

Wea t h er Con d i t i on s

Weat her is an importa nt fa ctor in determining soil conditions. More importa ntly, changing w eat her

conditions ma y signa l a cha nge in the pressures exert ed by the soil on th e side w a lls of a t rench.

Excess wa ter from ra in or melting snow int eracts w ith th e soil, increasing the pressure on the exca va-t ion and shoring system. For insta nce, a ra instorm can t urn a sta ble trench wa ll that required only light

bra cing into a ma ss of loose soil tha t requir es heavy bra cing.

Freezing usua lly indica tes a ra ther sta ble ground condition, unless th e frost line is exceeded during exca -

va tion. The fr ost l i ne phenomenonis depicted in fi gure 12. If y ou excava te or shore frozen ground, be aw a re

th a t a nother potent ial problem existstha wing. A sudden tha w can be a s dangerous as a ra instorm.

Figure 12

Reg ion o f Soi l F r eez i ng

Excessively dry conditions can a lso be dangerous. As moistur e content decrea ses, some dry soils lose

their ability to stick together. This lack of cohesionma y result in a sliding t ype of soil fa ilure. In m a ny of

the sit ua tions described above, dewateringor extra shoring ma y be required a s necessary t o ensure the

sa fety of your w orkers. See fi gures 16 a nd 17 in part 2 for more informa tion about dew a tering.

7

Tension CrackThese loads not only createforces too heavy for the soilto carry, but also cover upand signs of failure.

w=

Ground level

Water level

Frost lineThe water above the frost line can freeze

The water below the frost line does not freeze


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2

Soil Types and Pressures

Soi l Cha r a c t er i st i c s

The OSH A exca va tions sta nda rd recognizes an d a llow s a va riety of soil class ifi cation systems under

certain conditions. A special simple soil classifi cation system used by OSH A for exca vat ion planning a nd

protection is included in the standard. If that classifi cation sys tem is str ictly followed, trench protection

syst ems can be designed for man y situa tions wit hout th e approval of a r egistered professiona l engineer.

In t he soil class ifi cation system used by OSH A, the terms used to identify soil types ar e draw n lar gely

from an other syst em, commonly used for construction in Nort h Ca rolina , ca lled the U nited Soil

Classifi cation Sy stem. B oth syst ems a re based upon the engineering propert ies of soils and a re concise

a nd eas ily associa ted w ith a ctual soil behavior. The OSH A syst em can be applied in the la bora tory or the

fi eld. The terms used for classifi cation ar e based upon the soil part icles, including th e quan tity of the va r-

ious sizes of soil par ticles a nd t he qua lities or char a cteristics of the very fi ne gra ins. The principa l ty pes

of soil ma y be divided into tw o genera l classes a ccording to gra in size. Coarse-gra ined soils a re gra vel and

sa nd. Fine-gra ined soils are silt a nd clay.

The composition or texture of a soil is a critical factor in its stability. The more cohesive the soil parti-cles, the more th e entir e soil mass t ends to stick together ra ther t ha n crumble. How ever, it is importa nt

to remember t he time element involved in cuts. If an excavated cut is to be left open for long periods of

time, cohesive forces ma y not w ithst a nd exposure to w eat her conditions. When fresh fi ll dirt is n ot prop-

erly compacted, subsequent exca va tions in the sa me a rea result in a lmost no cohesion properties; thus, a

greater w idth ma y be required to mainta in a st a ble slope.

The soil found a t a site is usua lly a mixture of one or more of the ba sic types listed below. From the

a mounts of each soil type blended t ogether to form th e actua l soil conditions, descriptive soil terms a re

combined in t he order of low est content t o highest content . For exa mple, soil clas sifi ed as silty clay is a

mixture of mostly cla y w ith n oticeable but lesser a mounts of silt . The single term loam is used to

describe a m ixture of clay, sand a nd silt .

The t ypes of soil found most often include:Soil Type Characteristics of Soil Type

Clay Cla y is a very, very fi ne-gra ined soil. In genera l, wa ter moves very slow ly th rough cla y.La rge am ounts of ra infall ma y pond on the surface and eva pora te before being absorbed.

Sand Sa nd is a gran ular soil. The shape of individual gra ins ma y be round or a ngular. San dysoils tend to ha ve large pores, allowing faster groundwat er a bsorption. In most situat ions,

sa ndy soil is the easiest to compact wit h vibra tion.

Silt Silt has properties intermediate between fi ne san d an d clay. Silt is th e most sensitive tochanges in soil moisture content . Silt t ends to crumble wit h drying .

Det er m i n a t i o n o f Soi l Type

B y gr ouping different t ypes of soils (described a bove) a ccording to requ irements for sa fe exca va tion, the

excava tion sta ndar d has defi ned four soil classifi cations (provided below). For a deta iled explan a tion of

OSH A cla ssifi cation syst em, plea se see a ppendix A of the exca vat ion st a nda rd. OSH A categorizes soil and

rock deposits into four ty pes, A thr ough D, a s follows:

Stable Rockis natur al solid mineral ma tter t hat can be excava ted with vert ical sides and r emaininta ct while exposed. It is usually identi fi ed by a rock na me such a s gra nite or sa ndstone. Determining

w hether a deposit is of this type ma y be diffi cult unless it is know n w hether cracks exist a nd w hether or

not the cracks run into or a wa y from the excava tion.

8


15/46

Type A soils a re cohesive soils wit h a n unconfi ned compressive strengt h of 1.5 tons per sq ua re foot(144 kP a ) or grea ter. Exa mples of Type A cohesive soils a re clay, silty cla y, sa ndy clay, cla y loam a nd, in

some ca ses, silty clay loa m a nd sa ndy cla y loam . (No soil is Type A if it is fi ssured, is subject to vibra tion

of a ny t ype, has previously been disturbed, is pa rt of a sloped, layered syst em wh ere the layers dip into

the exca va tion on a slope of four horizont a l to one vertical or great er, or ha s seeping w a ter.)

Type B soils a re cohesive soils wit h a n unconfi ned compressive strength g rea ter t ha n 0.5 tons persqua re foot (48 kPa ) but less t ha n 1.5 (144 kPa ). Exa mples of Type B soils a re a ngula r gr a vel; silt ; silt

loa m; previously dist urbed soils unless otherw ise class ifi ed as Type C; soils tha t m eet the un confi ned

compressive strengt h or cementa tion requir ements of Type A soils but a re fi ssured or subject t o vibra tion;dry un sta ble rock; an d lay ered systems sloping into th e trench at a slope less tha n four horizonta l to one

vertical (only if the ma teria l would be classi fi ed a s a Type B soil).

Type C soils a re cohesive soils wit h a n unconfi ned compressive strength of 0.5 tons per square foot (48kP a ) or less. Type C soils include gra nula r soils such a s gra vel, sand a nd loamy sa nd, submerged soil, soil

from wh ich w a ter is freely seeping, a nd submerged rock tha t is not st a ble. Also included in th is cla ssifi ca -

tion is mat erial in a sloped, layered syst em wh ere the layers dip into the exca vat ion or ha ve a slope of

four horizonta l to one vertical or gr eat er.

Layered geological strata.Where s oils a re confi gured in la yers, i.e., where a lay ered geologic struc-tur e exists, t he soil must be clas sifi ed on the ba sis of the soil class ifi cation of the w eakest soil layer. Ea ch

layer ma y be classifi ed individually if a more sta ble la yer lies below a less sta ble layer, i.e., w here a Type

C soil rests on t op of sta ble rock.

The sta nda rd a lso conta ins other importa nt criteria th a t mus t be examined to class ify soils properly.

Importa nt: 1. The labora tory t esting process an d compressive strengt h calculations must be conducted

under th e direction of a registered professiona l engineer. The OSH A sta nda rd requires t ha t t he excava -

tion protection syst em be designed by a registered professional engineer wh en the depth of the exca va tion

exceeds 20 feet or w here unusua l site conditions exist. 2. The ma nua l fi eld test ing a lternat ive permitted

under th e sta nda rd does not requ ire the a pprova l of a r egistered professiona l engineer under certa in spe-

cifi c conditions. How ever, a t leas t one visual test a nd one manu a l test a re required to class ify soil accord-

ing t o the OS H A met hod. The specifi c manual and visual fi eld tests a re listed a nd described in th e sta n-

dard .

Test Equ i p m en t an d M et h ods f or Eva l u a t i n g Soi l Type

Man y kinds of equipment a nd methods a re used to determine the ty pe of soil prevailing in an a rea, a s

described below.

Pocket Pene t r omete r . P enetrometers a re direct-rea ding, spring-operat ed instrum ents used to deter-

mine t he unconfi ned compressive strengt h of sa tur a ted cohesive soils. Once pushed into the soil, an indi-

cator sleeve displays t he reading. The instrum ent is calibra ted in either tons per squa re foot or kilogra ms

per squa re centimeter. However, penetrometers ha ve error ra tes in th e ran ge of 2040 percent .

1. Sh earva ne (Torvane). To determine th e unconfi ned compressive strengt h of the soil with a s hear -

va ne, the blades of the va ne a re pressed into a level section of undisturbed soil, a nd t he torsional

knob is slow ly tu rned unt il soil fa ilure occurs. The direct ins tru ment read ing must be multiplied by

2 to provide results in t ons per sq ua re foot or kilogram s per squa re centim eter.

2. Thumb P enetra tion Test. The thumb penetra tion procedure involves a n a tt empt to press the thumb

fi rmly into the soil in question. If t he thumb ma kes a n indentat ion in t he soil only w ith grea t diffi -

culty, the soil is probably Type A. If th e thum b penetra tes no furth er tha n th e length of the thumb

na il, it is probably Type B soil, and if the th umb penetra tes th e full length of the thumb, it is Type C

soil. The thum b test is subjective a nd is th erefore the lea st a ccura te of the thr ee methods.

3. Dry S trengt h Test. Dry soil tha t crumbles freely or wit h modera te pressure into individua l grains is

gra nular. Dry soil tha t fa lls into clumps tha t subsequently break int o smaller clumps (a nd the sma ll-

er clumps can be broken only wit h diffi culty) is probably clay in combinat ion w ith gr avel, san d or silt .

9


16/46

If the soil breaks into clumps that do not break into smaller clumps (and the soil can be broken only

with diffi culty), t he soil is considered un fi ssured unless th ere is visual indication of fi ssuring.

Pl as t i c i t y o r Wet Th r ead Test . This test is conducted by molding a moist sa mple of the soil into a ball

an d at tempting to roll it into a t hin thread a pproximat ely 1/8 inch (3 millimeter s) in dia met er (thick) by 2

inches (50 millimeters) in length. The soil sample is held by one end. If the sample does not break or tear,

th e soil is consider ed cohesive.

Visua l Test . A visual test is a qua litat ive evaluat ion of condit ions around the site. In a visual test , the

entire exca va tion site is observed, including th e soil adjacent t o the site a nd t he soil being exca vat ed. If

the soil rema ins in clumps, it is cohesive; if it a ppea rs t o be coarse-gra ined sa nd or gra vel, it is considered

gra nula r. The evalua tor a lso checks for any signs of vibra tion.

Dur ing a visual t est, the eva lua tor should check for crack-line openings along the fa ilure zone tha t

w ould indicat e tension cra cks, look for existing ut ilities tha t indicat e tha t t he soil ha s previously been

distur bed, an d observe the open side of th e exca va tion for indications of lay ered geologic structuring.

The evaluator should also look for signs of bulging, boiling or sluffi ng, as w ell a s for signs of surfa ce

wa ter seeping from the sides of the excava tion or from the wa ter ta ble. If there is stan ding wa ter in the

cut, the eva lua tor should check for quick conditions. In a ddition, the area a djacent t o the exca va tion

should be checked for signs of founda tions or other intr usions into the fa ilure zone, an d t he evalua tor

should check for surchar ging a nd t he spoil dista nce from th e edge of the excava tion.

Ea r t h P r essu r es

An a ppreciat ion of the need for shoring can be based on an underst a nding of eart h pressures. The

a mount of ea rth pressur e exerted upon the side wa ll of any excava tion depends upon the w eight a nd

depth of the soil tha t it su pport s.

Earth pressure dist r ibut ionsvar y w ith t he type of soil, depth of exca vat ion a nd moisture conditions.

Exa mple distributions a re shown in fi gur e 13.

The center of the ear th pressures is norma lly found between one-ha lf an d tw o-third s of the depth of a

simple exca va tion. However, addit iona l eart h pressures result from surfa ce encumbra nces a nd differ-

ences in soil la yer cohesiveness. All of these fa ctors in fl uence the actua l center of pressure at a n exca va -

tion site.

Figure 13

Pr essu r e D i st r i b u t i o n s on th e S i de Wa l l s o f an Excava t i o n

10

Sand and GranularSoils

Soft Clay

Trench WallPressure

Stiff Clay


17/46

As a general r ule of thu mb, th e center of pressure will be a t a low er depth w hen cohesion is poor (as in

fresh fi ll dirt , w a ter-bearing sa nd or loose ground). Where cohesion is high, t he center of pressure will be

higher (as in good compa ct soil). The loca tion of the center of pressure can change a fter a cut is ma de

unless support is provided to prevent ear th movement.

Regar dless of the soil type, as t he depth of the trench increases, the ma gnitude of pressures on th e full

height of the exca va tion also increa ses. The presence of ground w a ter a dds hydr osta tic pressure a ga inst

the w alls of the trench a s shown in fi gur e 14.

Figure 14

Wate r Pr essu r e

Ef f ec t s o f Wat er a n d R em ed i es

The nat ura l wa ter ta ble can cause ma ny ty pes of problems. For example, trenches exca va ted below t he

na tura l wa ter ta ble in sandy soils and soft clay a re highly susceptible to heaving, as il lustrat ed in fi gure

15. Hea ving is the seepa ge of wa ter a t t he bott om of the tr ench causing t he soil to be pushed upw a rd.This heaving is a signal tha t a failure may occur.

Figure 15

Hea v i n g

11

Ground watertable

Water

Pressure

Added effect of water pressure

Water TableDry Soil

Granular Saturated SoilHeave

GranularSoil

Water Movement


18/46

Wet conditions a t t he bott om of a tr ench ma y present a nother problem. If t he bott om of the t rench

begins to puff a nd bubble and t he eart h rises, a quicksand condition is occurring. This is a lso a signa l

tha t a failure may occur.

If hea ving or quicksand conditions a re expected, dew a tering s hould be considered prior to beginning a n

excava tion. Dew at ering drast ically reduces t he presence of w at er a nd t he addit ional pressure it causes.

Without dew a tering, hea vier timbers w ould be needed to support th e extra pressures ca used by the

w a ter. The tw o most frequently used dewa tering syst ems ar e well-points a nd sump pumps.

The wel l -poin t system(illustra ted in fi gure 16) is a very popular method of dewa tering. L oca ted on a

line 2 or 3 feet, or furt her, behind th e sheeting, w ell-points a re inserted t o the depth of the excava tion

w ith spa cing betw een the w ell-points va rying from 3 to 8 feet.

Figure 16

Wel l -Po in t

Well-points a re pipes w ith a point a t t he low er end a nd a screen or fi lter over perforat ions a long 3 or 4feet of the lower ends of the pipes. There are two types of well-points:

s those driven with a ma ul

s those that ar e jet ted in

The selection of the size of the w ell-points a nd t he required s pacing a re ba sed upon site conditions a nd

the type of excavation to be accomplished.

Above the ground, well-point pipes are connected by piping to a high-capacity pump. Pumping keeps

the w a ter level below the bottom of the exca va tion so tha t only a moist soil condition w ill be encountered

with in the exca vat ion.

The w ell-point s ystem should ha ve a capacity suf fi cient t o remove an y in fl ow of wa ter a s quickly as itoccurs. The depth limit of t his m ethod s pra ctica l effectiveness is a pproximat ely 1520 feet, a lthough t he

theoretical limit is just u nder 34 feet since the meth od depends upon pumping suction. G rea ter depths

can be a chieved by ar ra nging w ell-points int o tw o or more vertical st a ges, or by deep-w ell pumping, tha t

is, locating t he pump a t a low er elevat ion.

Dewatering does not permit any substantial excavation without providing ground support. Although

the dewatered soil will usually be fi rmer tha n it wa s before dewa tering, working condit ions ma y st il l be

unsafe. Shoring, or ba nk w alls a t a safe slope, should be used in dewa tered ground in t he same ma nner

as in any other excava tion.

12

Header

Sand andgravel filter

Inflow pipecovered with

filtering screen

Head

Jetting HolesLowered water table

ContinuousSheeting

Ground

Trenchbraces

Riser


19/46

The second common t ype of dew a tering syst em is t he sump pum pa s depicted in fi gur e 17.

Figure 17

Sump Pum p

Sump pumping, a s contra sted w ith w ell-pointing, has several a dvant ages. Sump pumps:

s can be insta lled q uickly by inexperienced la bor

s require less space and ca use less interference on t he site

s can be a dded or removed easily to meet requ ired pumping ca pacity

s can be sta rted by simply sw itching on th e pow er supply beca use no ba lan cing or turn ing is required

s do not freeze in cold w eat her beca use of the fas t, high volume fl ow of wa ter

s ma y be removed from one sump a nd used elsewh ere if needed

s usua lly cost less t ha n w ell-points

13

Discharge pipe to a distant point

Pump

Suction pipe

Wire mesh

Coarse sand andgravel filter

Bracing

Lowered water table

Sides supported bysheeting until filter andbracing are installed


20/46


21/46

Spa ced Sh eet i n g

Another popular method of protection is called spa ced sheeting. I t is a lso referred t o as spot s horing.

This m ethod, shown in fi gure 19, involves placing spaced timber shores, bracing, trench jacks, piles or

other m at erials in a ma nner strong enough t o resist the pressures surrounding the exca vat ion. Sheeting

consists of vertical planks u sed ar ound the boundar y of the proposed exca va tion. Horizonta l bra ces

extend betw een the vertical planks t o support the sheeting. The horizonta l trench bra ces ma y be wooden

or telescoping meta l pipes. The meta l bra ces a re ty pica lly used w hen t he w idth of th e trench exceeds 5

feet. It is import a nt t o remember tha t a ll mat erials selected for use must be in good condition.

Figure 19

Spaced Sheet i ng

Cl ose Sh eet i n g

This met hod involves the pla cement of continuous solid sheeting a long t he entire lengt h of a trench

exca va tion. An exam ple is show n in fi gure 20. The sa me types of mat erials used in spa ced sheeting can be

used in close sheeting. Timber sheeting or steel sheet piles may be selected for use depending on the cir-

cumsta nces. As a general rule of thum b, steel sheeting becomes more cost effective when the depth of a

planned excava tion exceeds 15 feet. E a ch of th e ma jor components of this sys tem h a s been labeled in fi g-

ure 20. Cleat s ma y a lso be used to fast en the strut s to the wa les and prevent slipping or falling out.

15

Sheeting

Wales with jack screws


22/46

Figure 20

Close Sh eet i ng

T r ench Sh i el d

Contr a ctors a lso ma y use a t rench shield, a prefa bricated movable str ucture often composed of steel

plat es welded to a h eavy st eel fra me (see fi gure 21). Some trench shields are composed of aluminum or

fi berglass. OSH A sta nda rds permit th e use of a t rench shield as long as t he protection it provides is equa l

to or grea ter t ha n th e protection tha t w ould be provided by th e appropria te shoring syst em. Employees

must know t o work only w ithin t he protection of the sh ield. Also, if a slide sta rts , workers must know

tha t t hey should not run out of the shield into the pat h of the slide.

16

Continuous sheet pilingJack screw

Wale

Metal brace or strut


23/46

Figure 21

T r ench Sh i e l d

Ot h er Systems

Some other sy stems t ha t a re used occa sionally include:

Freezing th e moist or sa tur a ted soil by the circulation of low -tempera tur e brine through piping dri-

ven into th e soil

Injection of chemical or other gr outing int o the soil to solidify a nd fi ll cra cks a nd spa ce surrounding

the individua l soil par ticles t o solidify the soil mass

17


24/46

4

Installation and Removal of Protective SystemsTo ensure t he sa fety of the w orkers a nd t he integrity of the job, it is essentia l to insta ll the va rious

types of trench protection properly. The standard requires the following procedures for the protection of

employees when insta lling support syst ems:

securely connect members of support s yst ems, safely insta ll support systems,

never overloa d members of support syst ems, an d

install other structural members to carry loads imposed on the support system when temporary

removal of individual members is n ecessar y.

In a ddition, the st a nda rd permits exca va tion of 2 feet (0.61 meters) or less below the bottom of th e

members of a support or shield system of a t rench if:

1. the system is designed to resist the forces calculat ed for t he full depth of the tr ench, a nd

2. there a re no indica tions, wh ile the trench is open, of a possible ca ve-in below the bottom of the sup-

port system.Also, the inst a llat ion of support syst ems must be closely coordina ted w ith t he exca va tion of tr enches.

As soon a s w ork is completed, the exca va tion should be back-fi lled a s th e protective system is disma ntled.

After t he exca va tion ha s been cleared, w orkers sh ould slowly r emove the protective syst em from th e bot-

tom up, ta king care to release members slowly.

Sl o p i n g a n d B en c h i n g

As mentioned earlier, one method of trench protection can be accomplished by sloping the sides of the

tr ench to th e safe a ngle specifi ed by OSH A exca vat ion st a nda rds. The trench is sloped on both sides.The sa fe ang le to slope the sides of an exca va tion var ies with different kinds of soil and must be deter-

mined on ea ch individua l project. When a n exca va tion ha s a high w a ter t a ble condition, silty ma teria l or

loose boulders, or when it is being dug in a rea s w here erosion, deep frost or sliding is a pparent, t he sa fean gle is more gradua l (tha t is, fl atter) (see fi gur e 22).

Figure 22

S l o p i n g

Problems Associated With Sloping and Benching

1. The spoil accumulated from digging a trench must be placed a bove and a wa y from the side wa lls of

the exca va tion. Otherw ise, the w eight of the spoil might creat e an un sa fe condition. OSH A requires

tha t t he spoil be kept 2 feet or m ore from t he edge of th e exca va tion or prevented fr om falling or

rolling int o the exca vat ion by t he use of reta ining devices. This procedure usua lly requires a w ide

storage a rea .

18

Determine safe slopefrom standard

Too steep

2 ft. minimum,greater distanceis preferred

Spoil


25/46

2. Wide excava tion area s can expose footings or cause dam age t o the wa lls of an adjacent structure

and thereby pose additional hazards to employees.

3. Wide exca vat ion a rea s can expose or place utilities (such as electric pow er, telephone, wa ter, gas,

storm dr a in or sewer lines) a bove the a ngle for a sa fe slope, causing t he unsupported collapse an d

failure of the utility line.

4. Wide areas of excava tion require the use of lar ge equipment. There may also be haza rds in t he

movement of the equipment a cross a lar ger exca va tion. For exa mple, exca va tion under or adjacent

to electric power lines crea tes a serious ha za rd t o workers an d th e public.

5. To prevent t he collapse of a n unsu pport ed bench in a n exca va tion 8 feet or less in depth, t he a llow -

a ble height of a bench a t t he base of a n exca va tion must be 31/2 feet or less. The collapse of one bench

can cause a low er bench t o fail in a situa tion wh ere multiple benches ha ve been exca va ted. For Type

A soil, for exam ple, the st a nda rd req uires tha t m ultiple benches ha ve an overa ll slope (from the t op

of one side of an excavation to the bottom) of 3/4 horizonta l t o 1 vertical (see fi gur e 23).

Figure 23

Un suppo r t ed Ver t i c a l l y S i ded Lowe r Po r t i o nMa x im um E i gh t Feet i n D ep th

The cont ra ctor shouldfi

rst m a ke a determina tion of the soil types at t he excava tion site using the soilclassifi cation syst em used by OSH A or one of the other a cceptable methods described in th e sta nda rd.

Next, th e contr a ctor sh ould consider potentia l sloping a nd benching problems, such a s t hose described

a bove. Fina lly, aft er considering a ll other protection t ha t m a y be necessar y to ensure sa fe working condi-

tions, the contr a ctor can d etermine if sloping (a nd possibly benching) is the best m ethod to use at tha t

site. Figur e 24 defi nes th e ma ximum a llow a ble slopes for excava tions less tha n 20 feet deep. This fi gure is

shown as t a ble B -1 in the standa rd.

Figure 24

Max i mu m A l l owab l e Sl o p es

19

8' Max

3/4

1

3 ' Max1/2

All excavations more than 8 feet but not more than 12 feet in depth with unsupportedvertically sided lower portions must have a maximum allowable slope of 1:1 and amaximum vertical side of 31/2 feet.

Soil or rock type Maximum allowable slopes (H:V)1

for excavations less than 20 feet deep3

Stable rock Vertical (90)Type A2 34:1 (53)Type B 1:1 (45)Type C 112:1 (34)

Notes:

1 Numbers shown in parentheses next to maximum allowable slopes are anglesexpressed in degrees from the horizontal. Angles have been rounded off.

2 A short-term maximum allowable slope of 12H:1V (63) is allowed in excava-tions in Type A soil that are 12 feet (3.67 m) or less in depth. Short-term maxi-mum allowable slopes for excavations greater than 12 feet (3.67 m) in depthshall be 34H:1V (53).

3 Sloping or benching for excavations greater than 20 feet deep shall bedesigned by a registered professional engineer.


26/46


27/46

Figure 26

Sl ope Configu r a t i o n s: Exca va t i o n s i n L a yer ed So i l s

21

20' Maximum

3/4

1

Type A SoilSimple Slope Excavation

20' Maximum

1

1

Type B SoilSimple Slope Excavation

20' Maximum

11/2

1

Type C SoilSimple Slope Excavation

Type A Soilover

Type C SoilType A

Type C

1

1

11/2

11/2

Type B Soilover

Type C SoilType B

Type C

1

1

11/2

11/2

Type A Soilover

Type B Soil

Type B

Type A1

1

1

1

Type C Soilover

Type B SoilType C

Type B

1

11

11/2

Type B Soilover

Type A SoilType B

Type A

1

1

1

3/4

Type C Soilover

Type A SoilType C

Type A

1

1

11/2

3/4


28/46

In case of an emergency, w orkers m ust be able t o lea ve the t rench quickly. According to OS HA regula-

tions, wh en employees ar e required to be in trenches 4 feet deep or more, adeq ua te mea ns of exit, such as

a ladder or st eps, must be provided a nd loca ted so as t o require no more th a n 25 feet of lat eral t ra vel.

Sup por t Systems, Sh i el d Systems a n d O th er Pr o tec t i ve Systems

When a trench is exca va ted, employees wh o are to w ork in the exca va tion must be protected from cave-

ins. In a ddition to the bra cing described earlier, the contr a ctor should consider exca va ting a w ider ar ea

tha n th e minimum necessa ry. Such ad ditional exca va tion provides a more comforta ble working environ-

ment in t he trench. In addit ion, this extra working area ma y provide a mea ns for workers t o escape unex-pected crises, such a s fa lling objects or debris. Another common sense st ra tegy for sa fety in trenches

requires ma na gers to reduce risk by limiting t he number of workers in the trench at a ll times. The only

w orkers a llow ed in the trench should be those who ar e absolutely needed to perform t he ta sk at ha nd.

As th e trench is backfi lled, th e braces an d plan ks can be removed for reuse. If insta lled a nd removed prop-

erly, vertical planks a nd t rench bra ces ma y be used severa l times. Spa ced sheeting is shown in fi gur e 27.

Figure 27

Spaced Sheet i ng

Cl ose Sh eet i n g

When t he soil is unst a ble, the exca va tion should be supported a long t he entire a rea of the exposed

tr ench w a lls. This can be done by insta lling continuous sheeting tha t extends t he full depth of the tr ench,

a s depicted in fi gure 28. Ta bles ha ve been provided in th e sta nda rd for t he selection of timber sizes for

va rious exca va tion depths a nd w idths. The timber sizes listed in th e ta bles are for genera l reference only

a nd a re not adequa te for a ll soil conditions. B e sure to read t he informa tion tha t expla ins how to refer-

ence the ta bles properly.

22

Trench jack

Uprights


29/46

Very unst a ble soil conditions w ill require the sh eeting to be driven prior t o digging, wit h t he bra cing

insta lled as exca va tion proceeds. If steel sheeting is used, a pile driver will be necessar y for insta llat ion.

For w ooden sheeting, a pneumat ic hamm er is often used. The sheeting should extend one foot a bove the

surrounding g round to help prevent pipe, tools or equipment from fa lling into the t rench.

Figure 28

Close Sh eet i ng

Tr ench Sh i el d s

OSH A regulat ions a llow the use of port a ble trench boxes or sh ields in lieu of fi xed shoring systems a s

long a s a n equiva lent or gr eat er level of employee protection is provided. In deeper tr enches, the t rench

shield approach is often th e safest. The shields may be ma de wit h top and bott om sections for a da pta bili-

ty to deep and shallow excavations.

Tren ch boxes or shield s:

s ma y be production type or custom ma de of steel, a luminum or other equivalent ma teria l

s must be regularly inspected and properly maintained

s must be properly used under the dir ection of a competent person

Trench boxes a re different from shoring beca use, instea d of shoring up or otherw ise supporting t hetr ench fa ce, they a re intended prima rily t o protect w orkers from cave-ins a nd simila r incidents. The exca -

va ted a rea betw een the outside of the trench box and the fa ce of the tr ench should be a s sma ll as possible.

The space betw een the tr ench boxes a nd t he exca va tion side are ba ckfi lled to prevent la tera l movement of

the box. Shields may not be subjected t o loads exceeding those wh ich t he syst em w a s designed to wit h-

stand.

23

Braces

Sheet piles

Cleats

Stringers


30/46

Combined use. Trench boxes ar e generally used in open a reas , but t hey a lso may be used in combina -tion w ith sloping a nd benching. The box should extend a t least 18 inches (0.45 meters) above the sur-

rounding a rea if there is sloping t owa rd excava tion. This can be accomplished by providing a benched

ar ea a djacent to the box.

Ea rt h exca vat ion t o a depth of 2 feet (0.61 meters) below the sh ield is permit ted, but only if the shield

is designed to resist the forces calculated for the full depth of the trench a nd t here ar e no indica tions

while the trench is open of possible loss of soil from behind or below the bottom of the support system.

Conditions of this type require observa tion on the effects of bulging, heaving a nd boiling a s w ell as sur -

charging , vibra tion, adjacent str uctures, etc., on exca vat ing below the bottom of a sh ield. Ca reful visualinspection of the conditions mentioned above is the prima ry a nd most prudent a pproa ch to ha za rd identi-

fi cation a nd cont rol.

Figure 29

S lope an d Sh i el d Config u r a t i o n s

Exa m pl es o f Oth er System s

Man y shoring systems a re introduced to the ma rketplace ea ch year. The structura l supporting mem-

bers ar e typica lly ma de of wood or meta l. For most of these systems, t he horizonta l trench ja cks or braces

a re activa ted using a ir or hydra ulic pumps. These types of systems a re illustr a ted in fi gur e 30.

24

Type A SoilSupported or shielded

Vertically sided lower portion

Support or shield

system

20' Maximum

1

18" Minimum

3/4

Type B SoilSupported or shielded


Support or shield

system

20' Maximum

1

18" Minimum

1

Type C SoilSupported or shielded


Support or shieldsystem

20' Maximum 1

18" Minimum

11/2


31/46

Figure 30

A i r S h or i n g or H y d r a u l i c Sh o r i n g

Shor i n g Types

Shoring is t he provision of a support syst em for trench fa ces used t o prevent m ovement of soil, under-

ground utilities, roa dw a ys a nd foundat ions. Shoring or shielding is used when the loca tion or depth of the

cut ma kes sloping back to the ma ximum a llow a ble slope impra ctica l. Shoring syst ems consist of posts,

wales, struts and sheeting. There are two basic types of shoring, timber and aluminum hydraulic. See fi g-

ures 31 and 32.

Hydraulic shoring. The trend toda y is towa rd th e use of hydr a ulic shoring, a prefabricat ed struta nd/or wa le system ma nufa ctured of alum inum or steel. Hydra ulic shoring provides a critical sa fety

a dva nta ge over timber shoring because workers do not ha ve to enter th e trench to insta ll or removehydra ulic shoring. Other advan ta ges of most hydra ulic systems ar e that they:

Are light enough t o be inst a lled by one w orker;

Are ga uge-regula ted t o ensure even dist ribution of pressure a long t he tr ench line;

Ca n ha ve their tr ench faces preloaded to use t he soils na tur a l cohesion to prevent movement; an d

Ca n be ada pted easily to various trench depths a nd w idths.

All shoring should be insta lled from t he top dow n a nd removed from the bottom up. Hydr a ulic shoring

should be checked a t lea st once per shift for leakin g hoses a nd/or cylinders, broken connections, cra cked

nipples, bent ba ses, and a ny other da ma ged or defective part s.

25

18" Maximum

Verticalspacing

4' Maximum

2' Maximum

Vertical rail

Hydraulic cylinder

Aluminum hydraulic shoring

Examples of trench jacksused in pneumatic (air)and hydraulic shoring


32/46

Figure 31

Shor i n g Va r i a t i o n s: T y p i ca l A l um i n um H yd r a u l i c Sh or i n g I n s t a l l a t i on s

Pneumatic shoring w orks in a m a nner similar to hydra ulic shoring. The primar y difference is tha tpneumat ic shoring uses a ir pressure in place of hydra ulic pressure. A disad van ta ge to the use of pneu-

ma tic shoring is tha t a n a ir compressor must be on site. Air shoring involves using compressed air

instead of hydra ulic fl uid to expand t he trench ja cks into position. Using t he air t ype of system, pins a re

put in pla ce to lock the jacks w hen a desired level of sta bility ha s been achieved. For t he removal of thistr enching syst em, air is a ga in injected into the jacks to extend th em, allowing t he pin to be removed.

These types of jacks are popular since they a re cleaner t ha n hydr a ulic jacks and t here is no danger from

the leaka ge of fl uids or other lubrication.

1. Screw jacks. Screw jack systems differ from hydra ulic an d pneuma tic systems in tha t t he struts of a

screw jack syst em must be adjusted ma nua lly. This crea tes a h a za rd beca use the worker is required

to be in th e trench in order to a djust the st rut . In a ddition, uniform preloading cannot be achieved

with screw jacks, and their weight crea tes han dling diffi culties.

2. Single-cylinder hydra ulic shores. Shores of this type are genera lly used in a wa ter system, as an

assist to t imber shoring syst ems, and in sha llow trenches wh ere face sta bility is required.

26

Vertical Aluminum Hydraulic Shoring(Spot Bracing)

Vertical Aluminum Hydraulic Shoring(With Plywood)

Vertical Aluminum Hydraulic Shoring(Stacked)

Aluminum Hydraulic Shoring Waler System(Typical)

VerticalRoll

VerticalRoll

VerticalRoll

Plywood

HydraulicCylinder

HydraulicCylinder

HydraulicCylinder

HydraulicCylinder

UprightSheeting

Wale


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3. U nderpinning. This process involves sta bilizing adjacent stru ctures, founda tions and other intru-

sions tha t ma y ha ve an impa ct on the exca vat ion. As the term indicat es, underpinning is a proce-

dure in w hich the foundat ion is physically r einforced. Underpinning sh ould be conducted only under

the direction of and w ith t he approval of a r egistered professiona l engineer.

Figure 32

Sh o r i n g V a r i a t i o n s

The exca va tions sta nda rd provides four options for the design of support syst ems, shield systems a nd

other protective syst ems. A summa ry of the options follow s.

Option 1. The soil conditions encountered at the site must fi rst be class ifi ed using t he soil class ifi cation

syst em used by OSH A (a ppendix A of the sta nda rd). B a sed on t he soil class ifi cation and other project con-

ditions, the contra ctor ma y select a t imber shoring system using the informa tion conta ined in appendix C

or an a luminum hy dra ulic shoring system using t he informa tion conta ined in appendix D. The informa -

tion conta ined in appendix D should only be used when th e man ufa cturer s dat a for an hydra ulic system

ar e not a vailable. The informa tion in appendix D includes ta bles t ha t detail the m aximum vert ical a nd

horizonta l spacings tha t m ay be used w ith va rious a luminum member sizes and various hydraulic cylin-der sizes.

Option 2. The ma nufa cturer s ta bulated da ta provided w ith commercially a vailable support systems,

shield systems or other protective syst ems ma y be used if jobsite conditions a nd m ethods of use are in

str ict a ccordance with t he design intent of the syst em.

Option 3. Other ta bulated da ta , such a s ta bles a nd charts, prepared by a registered professiona l engi-

neer for use under t he conditions a t t he site ma y be used for t he design of support syst ems, shield sys-

tems a nd other protective systems.

Option 4. Support syst ems, shield systems a nd other protective syst ems not using options 1, 2 or 3

(above) must be approved by a registered professional engineer.

There is other importa nt informa tion in the sta nda rd th a t mu st be review ed to execute one of thesedesign options correctly.

O t h er H a za r d s

Falls and Equipment

In a ddit ion to cave-in ha zards an d seconda ry ha zards related to cave-ins, there are other haza rds from

w hich workers mus t be protected dur ing exca va tion-relat ed w ork. These ha za rds include exposure t o

falls, fa lling loa ds a nd mobile equipment. To protect employees from t hese ha za rds, OS HA requires th e

employer t o ta ke the following precaut ions:

27

Upright Sheeting

Screwjack

WalePneumatic/hydraulic jacks

Screw jack


34/46

Keep mat erials or equipment th a t might fall or roll into an exca va tion at least 2 feet (0.61 meters)

from th e edge of exca va tions, or ha ve reta ining devices, or both.

Provide warning systems such as mobile equipment, barricades, hand or mechanical signals, or stop

logs to a lert operat ors of the edge of an excava tion. If possible, keep the gra de aw a y from the exca va -

tion.

P rovide sca ling to remove loose rock or soil or inst a ll protective barr ica des a nd other equ ivalent pro-

tection t o protect employees a ga inst falling r ock, soil or ma teria ls.

P rohibit employees from w orking on faces of sloped or benched exca vat ions a t levels a bove otheremployees unless employees at low er levels a re a dequa tely protected from th e ha za rd of falling,

rolling or sliding mat erial or equipment.

P rohibit employees under loa ds th a t a re ha ndled by lifting or digging equipment. To avoid being

str uck by an y spilla ge or fa lling mat erials, require employees to sta nd a w a y from vehicles being

loa ded or unloaded. If cabs of vehicles provide adequ a te protection from fa lling loa ds dur ing loading

an d unloading opera t ions, the opera tors ma y rema in in them.

Water Accumulation

The sta nda rd prohibits employees from w orking in exca va tions where w a ter ha s accumulat ed or is

a ccumula ting unless a dequa te protection has been ta ken. If wa ter removal equipment is used to control

or prevent w a ter from accumulat ing, the equipment an d operat ions of the equipment must be monitoredby a competent person t o ensure proper use.

OSH A sta nda rds a lso require tha t diversion ditches, dikes or other suita ble mea ns be used to prevent

surface wat er from entering an excava tion and t o provide adequat e draina ge of the ar ea a djacent to the

exca va tion. Also, a competent person must inspect excava tions subject to runoffs from hea vy ra ins.

Hazardous Atmospheres

U nder th is provision, a competent person must test excava tions grea ter t ha n 4 feet (1.22 meters) in

depth as w ell a s ones wh ere oxygen defi ciency or a ha za rdous at mosphere exists or could reasonably be

expected t o exist, before an employee enters t he exca va tion. If h a za rdous conditions exist, contr ols such

a s proper r espira tory protection or vent ilat ion m ust be provided. Also, controls used to reduce at mospher-

ic conta mina nts to a cceptable levels must be tested regula rly. Where a dverse at mospheric conditions ma y

exist or develop in a n exca va tion, the employer a lso must provide a nd ensure t ha t emergency rescue

equipment, (e.g., breathing apparatus, a safety harness and line, basket stretcher, etc.) is readily avail-

a ble. This equipment must be at tended wh en used.

When an employee enters bell-bottom pier holes and similar deep and con fi ned footing exca va tions, the

employee must w ear a ha rness w ith a lifeline. The lifeline must be securely at ta ched to the har ness an d

must be sepa ra te from an y line used to ha ndle ma teria ls. Also, wh ile the employee wea ring t he lifeline is

in the exca va tion, an observer must be present t o ensure th a t t he lifeline is working properly and t o

maintain communication with the employee.

Access and Egress

U nder th e sta nda rd, th e employer must provide safe access a nd egress to all exca va tions. According to

OSH A regula tions, w hen employees a re required to be in t rench exca vat ions 4 feet deep (1.22 meters) or

more, adequa te mea ns of exit, such as la dders, steps, ram ps or other sa fe means of egress, must be pro-

vided and be with in 25 feet (7.62 meters) of lat era l tra vel. If str uctura l ram ps are used as a mea ns of

access or egress, they must be designed by a competent person if used for employee access or egress, or a

competent person qua lifi ed in str uctura l design if used by vehicles. Also, structura l members used for

ra mps or runw a ys must be uniform in thickness an d joined in a ma nner to prevent t ripping or displace-

ment.

28


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5

Residential Contractors and the Excavations StandardResidential builders an d contra ctors fa ce a un ique set of circumsta nces wh en building homes. B oth the

federal and North Carolina departments of labor have recognized that residential construction sites can

be very different from commercial sites a s they rela te to pa rt of the OSHA Exca va tions St a nda rd (29 CF R

1926.652). To addr ess a ccepted residential building pra ctices a s t hey rela te t o the st a nda rd, both a gencies

ha ve adopted similar occupa tiona l safety a nd hea lth enforcement policies for exca vat ions on resident ialsites.

Residential builders in North Carolina must follow the N.C. Department of Labor s version of th is poli-

cy. The depa rt ment s policy suspends 29 CF R 1926.652 for house founda tion a nd ba sement excava tions a t

residential sites w hen all of the following conditions a re present:

The house found a tion/ba sement exca va tion is less tha n 71/2 feet in d epth or is benched for a t lea st 2

feet horizonta lly for every 5 feet or less of vertical height.

The minimum horizonta l w idth (exca va tion face to formwork/w a ll) a t the bottom of the excava tion is

as wide a s pract icable but not less tha n 2 feet .

There is no wa ter, surface tension cra cks or other environment a l conditions present t ha t r educe the

stability of the excavations.

There is no heavy equipment opera ting in t he vicinity t ha t causes vibra tion to the exca vat ion w hile

employees are in t he exca va tion. All soil, equipment a nd ma teria l surchar ge loa ds a re no closer in

dista nce to the t op edge of the exca vat ion th a n t he exca va tion is deep; however, wh en front-end loa d-

ers a re used to dig the exca vat ions, the soil surcha rge loa d must be placed as fa r ba ck from the edge

of the exca vat ion a s possible, but never closer t ha n 2 feet.

Work crew s in th e excava tion a re the minimu m num ber needed to perform t he work.

The work ha s been plann ed and is car ried out in a ma nner to minimize the time employees are in

the excavation.

29


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6

Worker Training and J obsite Safety

Suggest ed Com pa n y Po l i c y

One of the most importa nt responsibilities of fi eld and offi ce ma na gement is plann ing for safety. Most

on-the-job problems a nd a ccidents d irectly result from improper pla nning. C orrecting mista kes in sh oring

a nd/or sloping aft er w ork has begun s low s down t he opera tion, adds to the cost a nd increases t he possibil-

ity of an excavation failure.

Contr a ctors should develop safety checklists to ma ke certa in tha t t here is enough informa tion about

the jobsite and t hat all needed items, such a s sa fety equipment, a re on ha nd.

To help ensure s a fety in tr enching a nd excava tions, these specifi c conditions sh ould be t a ken into

account:

Soil types a nd lay ers

Traffi c

Nearn ess of structur es and t heir condition

Surfa ce an d ground w at er condit ions

The wa ter t a ble elevat ion

Overhead and underground utilities

Weather

These an d other conditions ca n be determ ined by jobsite st udies, observat ions, t est borings a nd consul-

ta t ions w ith local offi cials a nd ut ility compan ies. U nderground insta llat ionssewer, telephone, wa ter,

fuel and electric lines tha t ma y be encountered in the exca va tion must be loca ted before sta rtin g the job.

If underground inst a llat ions a re uncovered, OSH A regulat ions require th a t th ey be properly supported.

The contr a ctor m ust conta ct the ut ility compan ies involved and inform them of the proposed w ork before

sta rt ing t he trench or excava tion.

Compan ies should establish a safety a nd health progra m. This importa nt aspect of the w ork is put into

place before th e job sta rts . Field a nd offi ce personnel should become familiar with the company policies

a nd guidelines outlined in th eir company s a fety program . The progra m is often put in w riting t o solidify

a nd commun ica te the compa ny s position w ith rega rd t o jobsite sa fety. Additionally, OSH A has specifi c

tr a ining requirement s for a ll employees who a re required to enter confi ned or enclosed spaces.

Cooperat ion from supervisors, employee groups an d individua l employees is necessar y t o ensure t ha t

sa fety policies ar e implemented effectively. In a ddition, each supervisor m ust underst a nd his or her

degree of responsibility for providing a sa fe working environment.

The cooperation of all employees requires their recognition of safety hazards and the necessary safety

preca utions. Employees should be t ra ined in t he following a reas:

1. Ha zards associa ted with t renching and excavat ing

2. Soi l ident ifi cation

3. Sa fe slopes for different soil types a nd condit ions

4. P roper insta l la t ion and shoring

5. St ress pat terns on trench w alls from soil and spoil , equipment, and vibrat ion caused by equipment

and t ra ffi c

6. Effects of adjacent buried utilities, building founda tions and length y exposure to the elements on

trench side walls a nd other excava tions

30


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7. Effects on tr ench a nd exca vat ion conditions from severe weat her, such a s excess wa ter, freezing t em-

peratures, unexpected heat or prolonged drying

8. Recognit ion of buried drums, containers, tanks a nd w ells

Employees should be trained to follow proper procedures to involve the electrical power company,

healt h depar tm ent, a nd other a gencies upon th e discovery of unforeseen objects such as w ells, sewa ge

disposal systems, cemeteries, and historic or architectural artifacts.

An example of a compan y sa fety and health program in a ct ion is a wr it ten policy tha t ensures tha t a ll

employees in all excavations will be protected from cave-ins. All company personnel will be expected to dotheir part to enforce this policy.

On -t h e-J ob Fol l ow -U p

Once the job gets underw a y, each employer sh ould keep itself informed of th e sa fety a spects of the pro-

ject a s w ell as t he progress of th e work. This is called on-the-job foll ow-upa nd involves a series of inspec-

tions t o detect ha za rds a nd correct jobsite situa tions before cave-ins or other a ccidents occur. When ma n-

a gement requires da ily reports, acts on the reports a nd ma kes personal visits to the jobsite, it ma y feel

mor e con fi dent t ha t everyone is meeting job safety responsibilities.

Spec i a l H ea l t h an d Sa f et y Con si d er a t i ons

Competent person. The designat ed competent person should ha ve and be able to demonst ra te th e fol-lowing:

Tra ining, experience an d know ledge of:

- soil a na lysis;

- use of protective systems; and

- requirements of 29 CF R P a rt 1926 Subpart P.

Ability to detect:

- conditions that could result in cave-ins;

- failures in protective sys tems;

- haza rdous at mospheres; a nd

- other ha za rds including those associat ed wit h con fi ned spa ces.

Auth ority to ta ke prompt corrective measur es to eliminat e existing a nd predicta ble ha za rds a nd to stop

work w hen required.

Surface crossing of trenches. Surface crossing of trenches should be discouraged; however, iftr enches must be crossed, such crossings a re permitt ed only under t he following conditions:

Vehicle crossings must be designed by a nd inst a lled un der t he supervision of a registered professional

engineer.

Wa lkwa ys or bridges mus t be provided for foot t ra ffi c. These str uctures mu st:

- ha ve a sa fety fa ctor of 4;

- have a minimum clear width of 20 inches (0.51 meters);

- be fi t ted with standa rd ra i ls ; and

- extend a minimum of 24 inches (0.61 meters) past the surface edge of the trench.

Ingress and egress. Access to a nd exit fr om the t rench require t he following conditions:

Trenches 4 feet or more in depth should be provided w ith a fi xed means of egress. Spa cing betw een lad-

ders or other mean s of egress must be such tha t a w orker w ill not ha ve to tr a vel more tha n 25 feet la t-

erally t o the near est mea ns of egress. Ladders m ust be secured and extend a minimum of 36 inches (0.9

meters) a bove the lan ding. Metal la dders should be used wit h caut ion, par ticularly w hen electric utili-

ties are present.

31


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Exposure to vehicles. Procedures to protect employees from being injured or killed by vehicle traf fi cinclude:

P roviding employees with a nd requiring them to wear wa rning vests or other suitable garments

ma rked with or made of refl ectorized or high-visibility ma teria ls. Requiring a designa ted, tra ined fl a g-

person along with signs, signals an d ba rricades w hen necessary.

Exposure to falling loads. Employees must be protected from loads or objects falling from lifting ordigging equipment. P rocedures designed to ensure t heir protection include:

Employees are not permitted to work under raised loads. Employees are required to stand away fromequipment that is being loaded or unloaded. Equipment operators or truck drivers may stay in their

equipment during loading a nd unloading if th e equipment is properly equipped w ith a cab shield or

adequate canopy.

Warning systems for mobile equipment. The following steps should be taken to prevent vehiclesfrom accidenta lly falling into the tr ench:

B ar ricades must be installed w here necessary. Ha nd or mecha nical signa ls must be used as required.

St op logs must be insta lled if there is a da nger of vehicles falling into th e trench. Soil should be gra ded

a w a y from the exca va tion; this w ill assist in vehicle control and cha nneling of run-off wa ter.

Hazardous atmospheres and confined spaces. Employees must not be permitt ed to work in haz-a rdous a nd/or toxic a tm ospheres. Such a tm ospheres include those wit h:

Less th a n 19.5 percent or more tha n 23.5 percent oxygen; combustible gas concentra tion grea ter t ha n

20 percent of th e lower fl ammable limit; and concentrations of hazardous substances that exceed those

specifi ed in th e Threshold Limit Va lues for Airborne C onta mina nts esta blished by the America n

Conference of Governmental Industrial Hygienists.

All operat ions involving such at mospheres must be conducted in a ccordance wit h OS HA requirements

for occupat iona l hea lth a nd environmenta l contr ols (see Subpa rt D of 29 CP R 1926) for personal protec-

tive equipment a nd for lifesaving equipment (see Subpa rt E, 29 CF R 1926). En gineering contr ols (e.g.,

ventilat ion) a nd respirat ory protection ma y be required.

When testi ng for atm ospher ic cont am in ant s, the foll owin g shoul d be consid er ed:

Testin g should be conducted before employees ent er th e trench a nd sh ould be done regula rly t o

ensure th a t t he trench rema ins sa fe. The frequency of testing s hould be increased if equipment is

opera ting in th e trench. Testing frequ ency should a lso be increa sed if w elding, cutt ing or burning is

done in the trench.

Em ployees required to w ear r espirat ory protection must be tr a ined, fi t-tested a nd enrolled in a res-

pirat ory protection program . Some trenches qualify a s confi ned spa ces. When th is occurs , compli-

an ce with t he Con fi ned Space Sta ndar d is also required.

Emergency rescue equipment. Emergency rescue equipment is r equired w hen a ha zardous a tmos-phere exists or can r easona bly be expected to exist. Requirements a re a s follows:

Respirat ors must be of the t ype suita ble for the exposure. Em ployees must be t ra ined in their use,

an d a respirat or program must be inst ituted.

Attended (at all times) lifelines must be provided when employees enter bell-bottom pier holes, deep

con fi ned spaces or other similar ha zards.

Employees who enter con fi ned spaces must be tra ined.

Standing water and water accumulation. Methods for controlling sta nding wa ter a nd w at er accu-mula tion must be provided and should consist of the follow ing if employees a re permitted t o work in the

excavation:

U se of specia l support or shield syst ems a pproved by a registered professional engineer

Wa ter removal equipment, i.e., w ell pointing , used a nd m onitored by a competent person

32


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Sa fety ha rnesses a nd lifelines used in conforma nce with 29 CF R 1926.104

Surfa ce wa ter diverted aw ay from the trench

Em ployees removed from th e trench during ra instorms

Trenches ca refully inspected by a competent person a fter ea ch ra in a nd before employees a re permit-

ted t o re-enter t he tr ench.

Inspections. A competent person must inspect t he trench a nd document a ny fi ndin gs. The follow ingguide s pecifi es the frequ ency a nd conditions requiring inspections:

Da ily and before the sta rt of each shift

As dictat ed by the w ork being done in the tr ench

After every ra instorm

After other events tha t could increase ha zards, e.g. snowst orm, windstorm, tha w, earthq uake, etc.

When fi ssures, tension cra cks, sloughing, undercutt ing, wa ter seepage, bulging a t t he bott om or

other similar conditions occur

When there is a change in the size, location or placement of the spoil pile

When th ere is any indica tion of cha nge or movement in a djacent str uctures.

33


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7

Safety Checklist*FOR A SAFE J OB SI TE TRE NCH ING OP ER ATION, THE ANSWER TO EACH OF THE FOLL OW-

I N G S H O U L D B EYES.

YES NO

General Protection Requirements

____ ____ Are all w alkwa ys, runw ays an d sidewalks clear of exca vat ed mat erial or other obstructions?

____ ____ Are a ll undermined sidewa lks shored to ca rry a minimum live loa d of 125 pounds per squa re

foot?

____ ____ Are pla nks laid par a llel to the length of w a lk and fas tened together aga inst displacement if

used for ra ised wa lkwa ys, runwa ys or sidewa lks?

____ ____ Are plan ks uniform in thickness?

____ ____ Are cleat s on ra mps provided wh en ra mps a re used in lieu of steps?

____ ____ Are all employees enga ged in excava tion, trenching an d shoring provided wit h th e appropria te

training and personal protective equipment?

____ ____ Are employees exposed to vehicular t ra ffi c wea ring wa rning vests ma rked with or ma de of

refl ectorized or high visibility ma teria l?

____ ____ Are employees prohibited from being under suspended loads ha ndled by lifting a nd other

heavy equipment?

____ ____ Are da ily inspections ma de of exca va tions, trenching a nd shoring?

____ ____ If evidence of possible ca ve-ins or slides is a pparent , does a ll w ork stop until t he necessa ry

preca utions ha ve been ta ken to safeguar d all th e employees?

Specific Excavation Requirements

____ ____ P rior to opening an exca va tion an d/or trench, ha s a n effort been ma de to determine if anyunderground insta llat ions w ill be encount ered?

____ ____ Did y ou conta ct utility compan ies before exca va ting?

____ ____ Did you remove a ll trees, boulders an d other surfa ce encumbra nces before exca vat ing w a s

begun?

____ ____ Are the w a lls an d fa ces of all exca va tions in w hich employees ar e exposed to dan ger from mov-

ing ground guar ded by a shoring syst em, ground sloping or some other equiva lent mean s?

____ ____ Are exca va tions inspected by a competent person after every ra instorm or other ha za rd-

increa sing occurrence to determine if a dditional protection a ga inst slides and cave-ins is nec-

essary?

____ ____ Did you store or reta in exca vat ed or other ma teria ls at least 2 feet or more from the edges of

the excavation?

____ ____ Do sides, slopes and faces of all exca va tions meet a ccepted engineering r

Documents

14_guide Osha Excavations Standard