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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


> Air Drying Soft Pockets


> 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.


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.


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.


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.


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.


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.


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.


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.


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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