Developed by Division of Occupational Safety and
Developed by Division of Occupational Safety and HealthHealth
August, 2009
August, 2009
Excavation and Trenching
Excavation and Trenching
The hazards of excavation &
The hazards of excavation &
trenching and how to control them
Excavation and Tenching Opeations
Excavation and Tenching Opeations
Course objective:
Course objective:
to provide a basic overview of
to provide a basic overview of
the excavation, trenching and
the excavation, trenching and
shoring regulations located in
shoring regulations located in
Part , chapter !"#$% '(C)
T
T
o
o
pics
pics
covere
covere
d
d
$
$ *azards of trenching & excavation*azards of trenching & excavation
$
$ +oil classification+oil classification
$
$ Trench protective sstems - shoring & slopingTrench protective sstems - shoring & sloping
$
$ .ther hazard controls.ther hazard controls
$
'hat is an Excavation/
An excavation is any peson!"ade cut, cavity,
tench, o depession in the eath#s suface$
A tench is an excavation
E"ployees "ust be potected fo" cave!in
%hen the excavation is & feet o "oe in
depth$
'ave!in potection is not e(uied %hen)
! Excavations ae "ade entiely in stable oc*+ o
! They ae less than & feet in depth and exa"ination of the gound by a co"petent peson povides no indication of a potential cave!in$
% 0atalities 1elated to Excavation (ctivities
in 'ashington +tate
%""2 - !332
Tpes of 4ncidents+oil collapse 5cave$in6 7 8
+truc9 b machiner 7
+truc9 b motor vehicle 7 %
+truc9 b falling object 7 %
Electrocution 7 %
The factors shown in this
illustration can create deadl conditions for wor9ers)
The spoils pile and the
e;uipment being too close to the vertical walls of the
trench are called <surcharge loads= which increase the li9elihood of collapse)
(dditionall, e;uipment
vibration, adverse weather conditions and ground water can change the condition and classification of the soil)
'hat ma9es trenches hazardous/
( <Competent Person= must ta9e all of these factors into consideration and re$evaluate the jobsite periodicall)
>efinitions
<Competent person= is someone who:
Can identif existing or predictable hazards in an excavation *as authorit to ta9e corrective actions as necessar
4s familiar with the >.+* excavation standards
4s 9nowledgeable in soil analsis and classification as well as the
erection, use, and precautions for the protective sstem on site
<1egistered Professional Engineer=51PE6 is:
a person registered as an engineer b the 'ashington +tate >epartment of ?icensing, 4(' Chapter %2)@ 1C'
This trench is well over A deep, cut into loose sand 5class C soil6, that is sloughing off the trench walls) The spoils pile is a suchaged load$ The shea %eight of the spoils not being set at least 2 feet bac* fo" the vetical face inceases the li*elihood of a cave!in and it adds to the depth of the tench$ f the tench is -. deep and the spoils pile is -. high diectly at the edge, the tench is no% /. deep1 A tench that is . deep could easily beco"e 3!. deep if the spoils pile is on the edge$
*azardous Trench Example
5conAt)6 The %eight 4 vibation of the tac*!
hoe also inceases the pobability of a collapse$
The e"ployees %o*ing in the
tench ae exposed to)
! ovehead ha5ads 6no had hats7, and
! tench collapse %ithout a potective syste"
t does not appea that safe
access o egess has been povided$8
8 A stai%ay, a"p, ladde o othe safe "eans of egess "ust be located so
%o*es don.t have to tavel "oe than 23 feet lateally in the tench$
(nother hazardous trench example
eaby heavy e(uip"ent and the spoils pile diectly on the ight edge of the excavation both ceate a suchage load$ The potective yste" in this photo does not extend fa enough up the tench to povide ade(uate potection fo the t%o %o*es in the tench$
Process for +afe Trench 'or9
4dentif 9nowledgeable competent person
Chec9 and verif above and below ground utilit
locations, an adjacent structures or surface encumbrances, and water table
>etermine soil classification through testing
Choose the correct protective sstem for soil tpe Berif protective sstem installation and set$up Provide safe access
Compl with re;uirements specified in the
Excavation, Trenching, and +horing regulations)
Conduct dail inspections prior to the start of wor9,
0irst: ou must locate utilities before
digging
Go to:www.callbeforeyoudig.org
or
Call %$233$!$
4tAs 0ree
Dou are re;uired to to call for utilit locates
and once the locates have been identified
onsite, the emploer must do an exact locate
as specified by:
'(C !"#$%$#5!65c6
:;hen excavation opeations appoach the location of undegound
installations, the exact location of the installations shall be dete"ined by safe and acceptable "eans$<
'h do ou need to do exact utilit locates/
ecause the are rarel spot$on, and olderinstallations ma not show up on current utilit maps)
Controlling heav vehicle surcharge loads
'hat does the $degree angle represent/
4t represents the zone of
influence or affected area) 4n other words, it represents the shear plane 5wea9est area6, at which the excavation or trench wall will fail, and that is wh it should alwas be 9ept clear of heav e;uipment or machiner, and the spoils pile, unless the trench can be properl shored)
Controlling water accumulation
'ater accumulation in a trench is hazardous because it erodes and changes soilG which means the stabilit of the soil is li9el wea9ened)
Prevent water accumulation b using sump pumps, or create diversion ditches and di9es for natural drainage of streams
interrupted b the excavation or in anticipation of heav
rainwater runoff, or consult with an 1PE)
+pecial supports or shield sstems ma be needed if water accumulates on the trench floor)
'ater (ccumulation Control +stem
'ater accumulation hazards should be prevented b either using a
special support or shield sstems designed for water drainage issues, or water removal to control the
level of accumulating water, or use of a safet harness and lifeline b wor9ers inside excavation)
'ater controlled through the use of pumps and other e;uipment setups must be monitored b a competent person to ensure proper operation) >iversion ditches, di9es, or other suitable means should be used to prevent surface water or rainwater from entering and accumulating in the excavation)
A %ate contol syste" that got out of hand1
Classifing +oils
4t is important to correctl classif soil tpe
before selecting and using a protective sstem)
4n order to classif soil, at least one visual test
and one manual test are re;uired to determine
if the soil is Tpe (, Tpe , or Tpe C)
=ost enginees agee that less than 3> of the soil in ;ashington can be classified as Type A, and as soon as the Type A soil is distubed, it "ust be do%n gaded to a Type ?$
+oil characteristics
Tpe (:
Hood cohesive soil with a highcompressive strength such as: cla, silt cla, sand cla, cla loam and cemented soils such as caliche, duricrust and hardpan
Tpe :
Cohesive soil with a moderatecompressive strength such as: silt, silt cla, sand cla, cla loam, silt loam, sand loam, angular
gravel 5similar to crushed roc96, an previousl disturbed fissured or soil or subject to vibration
Tpe C:
Cohesive soil with a low compressive strength such as: granular soils including gravel, sand, and loam sand or submerged soil or roc9 that is not stable or soil from which water is freel seeping+oil classification
Tpe <(=
- 0ine grained
- >oesnAt crumble
- *ard to brea9 up when dr - Examples:
I Cla
I *ardpan
I +ilt or sand cla, cla loam
'lay @oa"
'lay
As "oe oganic "atte, silt and sand 6 togethe *no%n as loa"7 gets "ixed in and as the gains get lage, the classification %ill be degaded to type ?$ As the "ix has less and less clay and oganic "atte in it beco"ing close to pue sand o gavel it
+oil Classification
Tpe (
Even if soil has high cla content and is plastic when
moist, it cannot be classified as <Tpe (= if it is:
$fissured,
$has been previousl disturbed, or
$subject to vibration from
heav traffic, etc) This soil is fissued changing the classification fo" A to ?
'lues fo peviously distubed soil) soil discoloation, lac* of vegetation, you dig and discove pipes o so"ething else$ f the %o* odes ae specific to eplacing existing
+oil classification
Tpe
- Hranular: coarse grains - ?ittle or no cla content - Crumbles easil when dr - Examples:
I Silt$fine mineral particles in size between cla and sand
I Loam$from fragments of roc9 deposits in water
I Angular gravel$crushed roc9$the angular nature of the individual roc9s provides some resistance to movement
Silty loa"
+oil Classification
Tpe C *
- Hranular soil: ver coarse - Jinimal cohesion
- Examples:
I +and I Hravel
I ?oam sand
I +ubmerged soil or soil with freel seeping water
I +ubmerged roc9 that is not stable)
Sand
avel
* Tpe C is the most common soil classification in 'ashington)
Tpes of Protection +stems
I +loping and enching
I +horing +stem
$ Timber, (luminum$*draulic
$ +hield +stem
$ +teel +hield ox, (luminum ox
'hat are the protective sstem re;uirements/
Fse protective sstems when there is potential
for cave$in for Class (, , and C soils:
- Under 4’ deep if a potential for a cave$in exists - 4’ to 20’ deep
I +loping or enching 5benching is not an option in C soil6 I +hield or +horing
- Over 20’ deep $ protective sstem must be
designed b 1egistered Professional Engineer or approved in manufacturerAs tabulated data
+loping
+loping is the process of removing soil to
eliminate the chance of a cave in)
The re;uired maximum allowable slope is
determined b the class of soil)
The re;uirements are as follows:
! Bo each foot of tench depth, the atio of slope "easued fo" the tench edge at gound height "ust be)
+oil Tpe ( -
K to % 5@L6
+oil Tpe -% to % 5L6
+horing
+horing is one of the most common used methods of wor9er
protection) 4t is light$ weight, portable and eas to install)
The manufacturer
provides tabulated data with the shoring that
provides the limitations, precautions, re;uired
spacing and proper use)
This photo shows an example of aluminum hdraulic shoring)
+hields
+hields are manufactured b a number of companies and are designed to protect wor9ers
wor9ing within the confines of the shield)
Chec9 tabulated data for the
maximum allowable depth it can be used) The tabulated data
must accompan the shield when it is being used)
(dditionall, the shield must be designed b a 1egistered
Professional Engineer, be in good condition, and used properl)
+hields That >onAt Ho (ll
The 'a To The ottom)))
Excavation of material to a level no deeper than ! feet below the bottom of the members of a support sstem is permitted onl if:
$ the sstem is designed to resist the forces
calculated for the full depth of the trench,
$ there are no indications while the trench is open of a possible loss of soil from behind or below the bottom of the support
1PE$>esigned Protective +stem
( 1egistered Professional Engineer can
design a protection sstem for use on a
specific project)
The 1PE will consider the soil tpe and
conditions as well as other concerns that
might exist at the excavation site)
The sstem must be used as designed b
the 1PE)
Even with an 1PE, the Competent Person
must still perform dail inspections
.ther +horing Jethod Examples
Just be designed b a registered
Provide safe entr and exit
( trench that is A or more in depth must have a safe means for wor9ers to get in and out of the trench)
( means of egress is re;uired to be within !A of lateral travel)
The most common method for access is a straight ladder or an extension ladder) 4f a ladder is
used, it must extend a minimum of @A above the landing) The use of step ladders is not permitted)
.ther means could be a stairwa or ramps or other means as designed b a 1PE)
?ocating the method of
uc9ets of excavators, bac9hoes, etc)
are not to be used as a means of egress)
=ost 'o""on Tenching Ciolations
o cave$in protective sstem being used when
re;uired b soil classification, depth, and code
Excessive surcharge load 5spoils piles too close
to excavation wall or e;uipment or traffic too
close to excavation operations6
o accessNegress for excavations feet or
more in depth
An E"ploye only %o*ing in an unpotected
excavationtench can be cited by DOSH$
f the e"ploye is %o*ing in the tench alone
6no e"ployees in the tench7 %ithout using a
potective syste", the e"ploye can be cited
since, in the event of a cave!in, you ae
exposing evey e"ployee to cave!in ha5ads if
they u"p into the excavation to atte"pt escue$
Jore information and training
.nline Training course:
4.+* $Trench +afet (wareness
OSHA e!Tool) OSHA 'onstuction eTool) Tenching and Excavation
Oegon OSHA ) :Excavations Safe Gactices< publication) http)%%%$cbs$state$o$usoshapdfpubs2/&$pdf
http)%%%$lni$%a$gov%ishaulesconstuctionHT=@29!/33I/$ht"