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EXCAVATIONS Malcolm McIntyre CFIOSH
Excavations
What is an excavation?
trench for a pipeline
strip foundation
pad foundation
large basements
motorway cutting
tunnel (under the road or under the sea)
Hazards in Excavations
Tree roots
Rats/wildlife
Contaminated land
Unexploded ordnance
Underground
chambers
Poor lighting
Inadequate workforce
Children
Explosives (failure in
use)
Earthquakes
Hazards in Excavations
Collapse of sides of excavation
Fall of people and machines into the excavation
Fall of materials into the excavation
Unsafe access
Undermining nearby structures etc
Hazardous atmosphere / confined space
Flooding
Underground services/Overhead power lines
Failure of support system
Working outside limits of support
Vehicle movements
Excavations
Why do excavations collapse?
Mechanical failure of soil
Breakdown of soil caused by moisture
Failure of soil caused by vibration
Extra loading on sides of excavation
Excavation on previous excavations
Side of excavation being struck by a heavy load
Variation of soil type
Trench Collapse Scenarios > Typical Site Conditions
Spoil
Tension
Cracks
Native
Soil
Fill
Old Utility Trench
(Crossing Utility)
Bedding Material
Previously
Disturbed
Areas Old Utility Trench
(Parallel Utility)
Trench Collapse Scenarios
Soft Zone Failure
Stable
Soft
Zone
Stable
Layered soils
Trench Collapse Scenarios
> Air Drying Soft Pockets
Trench Collapse Scenarios
> Rotational Failure Wedge Failure
Trench Collapse Scenarios > Effects of Water
Rain
Ground Water
Water Accumulation
Surface Run Off
Stable Ground
Soft Saturated Zone
Excavation Support Basic Principles
Battered Sides
Safest method - accidents
very rare.
Excavations battered to
safe angle of repose -
dependent on soil type.
Specialist advice needed
in waterlogged ground as
some system of
dewatering will be needed
to improve stability.
Excavation Support Basic Principles
Double Sided Support
Forces exerted by the earth
are transmitted from one
side of the excavation to the
other by walings and
horizontal struts.
Most excavations lend
themselves to “Standard”
support systems or
“Proprietary systems.
Some excavations will,
however, need detailed
design by competent people.
Excavation Support Basic Principles
Single Sided Cantilever
Support
Can only be used:
in ground conditions which
are sufficiently stable to
provide the necessary
resistance to balance the
overturning forces or
where the effects of
superimposed loads and
their stability is not critical.
Must always be designed by
a competent person.
Pe
rmit
to
Excavate
Open & Close Boarding
Open Sheeting using Steel Sheets
and Jacks
Boxes (Modular Strutted Support
Walls)
Sh
ield
/ D
rag
Bo
x
Hyd
rau
lic S
tru
ts /
Wa
lin
gs
Plate Lining Systems
Guarding Excavations
Guarding Excavations
Where vehicles are used for
tipping materials into an
excavation, safety measures
such as well anchored stop
blocks, should be used to
prevent the vehicle overrunning
the edge.
Stop blocks must be placed at a
sufficient distance from the edge
to avoid the danger of it
breaking away under the weight
of the vehicle.
Reversing must be done under
the direction of a banksman.
Excavations: Safety Checklist
Prior to commencing work: check the health and safety plan for excavations
check and approve the risk assessment / method statement.
Decide how to prevent access to the excavation, especially children.
check the soil type and decide on support work.
check whether excavation will affect nearby buildings etc.
seek advice if excavating below existing foundations of adjacent building.
Excavations: Safety Checklist Prior to commencing work (continued):
locate position of all services, mark and/or
disconnect
provide adequate supply of material for support work,
barriers and correct notices.
Check for overhead power lines
check provision of adequate lighting.
check that adequate ladders are available for
access.
determine the method of excavating, and the method
by which the support work will be installed and
removed.
Excavations: Safety Checklist
Whilst work is in progress:
ensure only sound material is used.
ensure that approved and safe methods are adopted
for the installation of support work.
ensure that all working surfaces are safe.
install support work as soon as excavation sides are
trimmed.
ensure all support work is secure.
Excavations: Safety Checklist
Whilst work is in progress (continued):
continually check for signs of overstress or damage
to support work.
continually check for any water or soil seeping
through the support work.
check for signs of the earth peeling or cracking at
unsupported faces.
check that ladders are maintained, secured and used
correctly.
Excavations: Safety Checklist
Whilst work is in progress (continued):
check for unhealthy atmosphere.
ensure that spoil heaps are kept back from the edge
of the excavation.
ensure that there are adequate barriers, notices and
warning lights.
when pumping, ensure there are adequate sumps
and that soil is not being drawn from behind support
work.
Excavations: Safety Checklist
Whilst work is in progress (continued): check that the edges of excavations are provided
with top and mid guard-rails at all places where there is a danger of persons falling 2 metres or more, or falling and injuring themselves.
bridges and gangways should be provided with handrails and toeboards.
ensure that stopblocks for dumpers, tipping lorries etc. are provided, well anchored and used.
ensure that passing traffic is kept well back from the edge of excavation.
Excavations: Safety Checklist
Whilst work is in progress (continued): ensure that the correct method of withdrawing
support work is used.
ensure that persons are not working too close to machines or each other.
ensure that the correct PPE is being used.
ensure that persons are wearing suitable ear defenders when piling is taking place.
ensure that machine operators have the best possible vision of the work which is in progress.
Excavations: Safety Checklist
Whilst work is in progress (continued): ensure that services are marked, protected and
adequately supported when exposed in excavations.
ensure any backfilling is carried out correctly.
carry out inspections daily, prior to each shift, after use of explosives or after inclement weather, especially frost and rain.
ensure that a proper record of all inspections is made and signed by a competent person.
ARE THE CONTRACTORS WORKING TO THEIR METHOD STATEMENT?
Insp
ecti
on
Rep
ort
REGISTER - INSPECTION REPORT OF SCAFFOLDS, EXCAVATIONS, COFFERDAMS,
CASSIONS & PERSONAL SUSPENSION EQUIPMENT
CONSTRUCTION (HEALTH, SAFETY AND WELFARE) REGULATIONS 1996
1. Name and address of person for whom inspection was carried out.
2. Site address 3. Date and time of inspection
4. Location and description of workplace (including any plant, equipment or materials)
inspected.
5. Matters which give rise to any health and safety risks.
6. Can work be carried out safely?
7. If not, name of person informed.
8. Details of any other action taken as a result of matters identified in 5 above.
9. Details of any further action considered necessary.
10. Name and position of person making the report.
11. Date report handed over.
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DAY MONTH YEAR TIME (24 CLOCK)
Y/N
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