Welcome to SafeWork SA's tool box series
on avoiding utility strikes.
This series is all about avoiding utility strikes
while digging or working near overhead power lines.
This is the third episode, Excavation Work.
Excavation work can introduce
many high-risk work activities.
In this toolbox, we'll be looking at
excavating techniques to minimise those risks.
Excavations are any activities that penetrate the soil.
It could be as simple as using a shovel to dig a hole,
using an excavator to dig a trench,
or using a vacuum truck to remove soil.
Excavation work should be carefully planned
before work starts so it can be carried out safely.
Before starting any excavation activities,
you must take all reasonable steps to obtain
current underground essential services information,
and locate all services within the areas you are working.
Toolbox 1 and 2 explain this in more detail.
For all mechanical excavation activities,
it is good practice to use a permit to excavate,
as this will help clearly define persons
with key responsibilities, the scope of works,
preliminary planning requirements,
including permits from relevant authorities,
specific controls and hold points
with respect to identifying and locating services.
A permit to excavate helps work crews
understand the process.
A permit to excavate will need to be completed
by someone who has been trained
and deemed competent by your organisation.
However, everyone is responsible for making sure
that all steps on the permit
have been completed and are understood.
Excavation work can introduce
many high-risk construction work activities.
A documented SafeWork Method Statement
will need to be developed for those activities
identifying site specific hazards
and the appropriate risk controls.
The SWMS must also describe
how the control measures are to be implemented,
monitored and reviewed,
and should include what actions are required
in the event of contact with gas or electricity lines.
Prior to excavating,
ensure all relevant Personal Protective Equipment
is available on site, as identified in the SWMS.
When planning an excavation consider the following.
Have all access authorisations been confirmed?
Are there man-made structures?
Have overhead power lines been identified
if mechanical excavation or large plant is to be used?
Have all underground assets been physically located
and marked prior to breaking ground?
Have you notified all persons
who are affected by the work prior to commencing?
Will the planned trench be close
to pedestrian or vehicle traffic?
Is Work Zone Traffic Management required?
Barricading, cones and traffic control are examples of this.
Is the excavation going to be within a rail corridor?
If so has the appropriate authority been notified,
approved spotter engaged,
and the required rail safety induction undertaken?
Is there a risk of falling into the trench
during the day or night?
If so, consider covering or barricading the trench area.
Do exposed services need to be protected
from falling objects?
If the work is being performed on or near a country road,
give consideration to the level of compaction density
on the verge of the road,
as it may not be as solid as that on a major road.
How big will the trench need to be?
Can workers safely move around the site,
for example in and out of the trench,
and the movement of plant and equipment?
Are ladders required to assist workers
safely get in or out of the trench?
Consider an emergency situation
where you needed to rescue a worker from the trench.
Plan how you would get them out.
If the excavation is greater than 1.5 metres deep,
you must install trench support,
shoring, battering, or benching.
What equipment will be in use?
If it is needed in the trench
how will you get the tools and equipment in and out?
How long will trench be open for?
The longer it is exposed to the elements,
the greater the risk of collapse.
All open excavations and assets
shall be secured in a safe manner
when there are no workers on site.
Operators of excavators and backhoes
must be trained and competent
prior to operating any machinery on site.
If mobile plant is in use,
ensure all workers remain outside
the operator's blind spots.
Operators can often have
severely restricted visibility
of ground workers or nearby pedestrians,
particularly those close to the plant.
Consider the placement of the spoil.
Where possible, place it on the low side
or opposite to previous excavation
at least 1 meter from the zone of influence.
Consider heavy fleet accessing the site;
all need space planning, safe bringing to site,
use, and removal.
Also consider possible weight effects on trench sides.
Heavy loads should not be located
in the zone of influence of an excavation,
unless the ground support system installed
has been designed by a competent person,
for example, a geotechnical engineer, to carry such loads.
The zone of influence will depend on the ground conditions.
It is the zone in which there may be an influence
on the excavation, including possible ground collapse.
Some soils are more stable than others.
The type of soil is one of the factors
that determine the chance that an excavation may cave in.
Hard cohesive is very stable.
Clay is an example of a hard cohesive material.
Soft cohesive is less stable.
This generally includes crushed rock, silt,
and soils containing an equal mixture of sand
and can incorporate silt material.
Non cohesive is even less cohesive.
Gravel and coarse sand are examples.
Consider the soil's granularity.
This refers to the size of the soil grains;
the larger the grains, the less stable the soil.
For example, clay has very small grains.
Saturation means how much water soil will absorb.
Saturated soils are subject to slumping.
Cohesiveness means how well soil holds together.
Remember, clay is a cohesive soil.
When adjoining man-made structures,
all soil types will lose their normal cohesiveness.
They will not bond to man-made materials
like concrete, brick and metal.
Also man-made structures
may introduce a large downward force on the soil below.
For this reason, excavating near man-made structures
requires special safety consideration.
Normal battering and benching designs
may have to be revised around man-made structures.
More soil removal may be required.
If in doubt seek professional engineering advice.
So, in summary:
Conduct appropriate searches
for overhead and underground utilities.
Where high risk construction work has been identified,
complete a documented SWMS based on a risk assessment
and consider a permit to excavate process.
Notify the public and protect them
from machinery and fall hazards.
Consider traffic management.
Consider the proximity of machinery to workers
and the sides of the trench.
Machinery operators must have
the appropriate training and competency.
Consider trench depth and size.
Workers need to enter and exit the trench safely
and must have the appropriate
personal protective equipment and tools.
Is the trench at risk of collapse?
Conduct analysis of soil type
and length of exposure to the elements.
Support the trench appropriately.
Practice emergency procedures regularly.
Toolbox 4 of the series
outlines the safe approach limits for people
and minimum safe clearance distances for machinery
when working near overhead power lines.
For more information on workplace safety,
visit safework.sa.gov.au
or call us on 1300 365 255.
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