Transcript RISK ASSESSMENT SEAWORKS - DOCKS

RISK ASSESSMENT
SEAWORKS - DOCKS - 1
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Dock structures for berthing vessels, loading and unloading cargo or
embarking and disembarking passengers, include:
piers projecting into the harbour with berths on either side;
quays continuous with the land and berths on one side;
dolphins for mooring vessels;
jetties for access to deep-water piers remote from the shore. These
structures are broadly of two types; open and closed. Open
construction consists of a deck of timber, steel, or reinforced or prestressed concrete supported on piles or cylinders. Closed
construction consists of mass wall construction which can be of
concrete blocks, mass concrete within steel sheet pile cells or
caissons and the like.
Structures contiguous with the shore often serve as large retaining
walls against which backfill or dredged material is placed.
CUNARD SUPER LINER PIER 90
NEW YORK HARBOUR
RISK ASSESSMENT
SEAWORKS - DOCKS - 2
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Settlement or failure of foundations and excavation slopes are
frequent causes of damage. The properties of the sea bed will need to
be investigated by bore holes and tests and will determine to some
extent the design of the foundations. Wherever possible, test loads
should be imposed on piled foundations. The design may allow for
some differential settlement.
There is also a risk of liquefaction of fine uniform sands when
subjected to vibration from earthquakes or blasting or piling
operations. Liquefaction of these materials can also occur where there
is inadequate drainage of deep excavations such as those required for
dry docks close to the sea.
Dock construction may include or be in close proximity to existing
roads, services, port buildings, warehouses, cargo-handling plant,
cold storage facilities, oil storage tanks and berths so that third party
liability exposures may require special consideration.
KINGSTON FORESHORE HARBOUR
WORKS
COEGA HARBOUR WORKS
COEGA HARBOUR
• Port Elizabeth - The deepwater harbour at Coega, positioned as
an important container terminal in sub-Saharan Africa, will start
business in October, 2009.
• Nosipho Damasane, general manager (sales logistics and
commercial) at Transnet Port Terminals, says that even though
operations will not begin with as much fanfare as expected,
because of the economic downturn, Transnet Port is committed
to this date.
• With the expected doubling in container volumes over the next
eight years, Transnet has spent more than R8bn to date on the
first phase, Transnet Port chief executive Solly Letsoalo
announced in Port Elizabeth on Tuesday.
• Volumes through the port have declined by about 20%
compared to a year ago, but it is expected that the new Coega
harbour will still handle 50 000 TEUs (20-foot containers) over
the first six months.
RISK ASSESSMENT
SEWAGE WORKS - 1
• There is now a worldwide awareness of pollution hazards and,
due to recent experiences, underwriters will be particularly
interested in sewage works. However, we are mainly concerned
with the construction hazards of such works. Contact beds
consist of watertight concrete tanks, frequently circular in
construction, filled with clinker on to which the sewage is
sprayed by revolving sprinklers.
• It is normal for a pump-house to be connected to the treatment
works and this will include the deepest point of excavation. The
methods of construction and the machinery involved are
normal.
• The hazards arising out of the construction of sewage works
include collapse of excavation works, flood, frost and third
party liability.
SEWAGE TREATMENT WORKS
RISK ASSESSMENT
SEWAGE WORKS - 2
• Collapse of excavations
• This could arise either in connection with the trench works for
ancillary pipelines or the excavations for the tanks. Information
should be supplied concerning the batters and support
methods for the sides of the excavations and the area available
to remove spoil. Excavations apart from that for the pump
house are not usually deeper than ten metres and no special
problems are presented.
RISK ASSESSMENT
SEWAGE WORKS - 3
• Flood
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Construction will frequently be in low-lying areas and the property is
consequently subject to damage by flooding from rainfall, nearby
rivers, or rising ground water. Information should be obtained on
ground conditions generally and on any nearby water which will affect
the water table levels. An additional flood risk can arise from
accidental or intentional disturbance of existing pipes, sewers or
structures.
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If there is a discharge into a river or sea, information should be
obtained on the method of protecting the works from inundation from
that source. If the discharge is into a river, a simple cofferdam may be
sufficient for the construction of the outfall and, if the river is tidal, a
valve chamber will be included to prevent back-up. An outfall into the
sea would be subject to the hazards described in earlier paragraphs
regarding pipelines and sea works.
RISK ASSESSMENT
SEWAGE WORKS - 4
• Frost
• There is a substantial amount of mass concreting involved and,
if frost can be expected, having regard to the area and period of
construction, frost can be added to the major perils excess
clause.
• Third party liability
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• There is unlikely to be any nearby property, unless the work is
an extension of an existing sewage works. Pipework to the
works will present the hazards described earlier.
• Exposure to flood is the main risk and the estimated maximum
loss will depend on the number of adjacent excavations being
worked upon at any one time.
RISK ASSESSMENT
TUNNELS - 1
• Tunnels may be major civil engineering projects in their own
right, or, like diversion tunnels for dams, a comparatively small
part of larger schemes. Tunneling methods may be employed
for road and rail tunnels through mountains, under rivers and
harbours and for turbine halls, surge chambers, access
tunnels, tailraces and temporary diversion tunnels,
underground railway networks, sewers and water supply
schemes.
• Methods of tunneling
• There are basically three types of tunnel construction:
• bored tunnels constructed underground;
• cut and cover tunnel constructions from ground surface;
• immersed tube tunnels constructed on sea or river bed.
• These are described below.
CHANNEL TUNNEL
UNDER-SEA BETWEEN ENGLAND & FRANCE
RISK ASSESSMENT
TUNNELS - 2
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BORED TUNNELS
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The methods of tunneling depend on the nature of the ground through
which the tunnel is bored, the two conditions being rock tunneling and
soft ground tunneling.
• Rock tunneling
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In tunneling through rock, the traditional method of excavation is by
drilling and blasting ahead of the tunnel face, removing the rock spoil
by trucks or rail cars and supporting the exposed sides and roof of the
tunnel, where necessary, by timber struts or steel ribs and sheeting.
Excavation is followed by the construction of an in situ concrete lining
where additional permanent support is necessary or where a smooth
or watertight surface is required.
GOTHENBURG RAIL TUNNEL
KATTLEBERG MOUNTAIN
TUNNEL BORING MACHINE
RISK ASSESSMENT
TUNNELS - 3
• Where the tunnel is to convey water at high pressure, a steel
lining may be fixed to the concrete. Later developments in rock
tunneling include:
• multi-boom drilling machines and controlled blasting by microsecond delay detonating;
• full face and boom-cutter excavation machines for all but the
hardest rock;
• mechanised spoil-loading and handling equipment;
• increasing use of rock bolting and sprayed concrete for
providing temporary and permanent rock support.
RISK ASSESSMENT
TUNNELS - 4
• Soft ground tunneling
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There are basically three methods of soft ground tunneling:
by hand;
by hand using shields;
by machines with shields.
In soft and hard clays, soft materials, and weakly cemented
sands, tunneling by these methods is relatively easy and the
ground is sufficiently self-supporting to enable prefabricated
linings to be erected immediately behind the excavation.
RISK ASSESSMENT
TUNNELS - 5
• In cohesion-less materials such as sand, and in loose waterbearing ground, it is essential to keep water away from the
excavation face by applying compressed air to the face or by
treating the ground beforehand.
RISK ASSESSMENT
TUNNELS - 6
• Ground treatment can comprise injection of grouts (chemical,
clay or cement-based) or ground freezing (brine ammonia or
liquid nitrogen) or ground water lowering.
• Tunneling by hand
• Small tunnels in soft ground can be excavated by hand tools,
powered manually or by compressed air. The exposed
earthfalls are temporarily secured by timbering and then
permanently secured by prefabricated linings of cast-iron or
concrete
RISK ASSESSMENT
TUNNELS - 7
• Tunneling by hand with shields
• Excavation for large tunnels in soft ground calls for the use of a
shield that consists essentially of a steel cylindrical casing to
support the ground at and behind the excavation face and that
is jacked forward as work advances. In subaqueous or
cohesion-less ground, a diaphragm can be incorporated in the
shield to enable excavation at the face to be carried out in a
compressed-air chamber.
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TUNNELLING SHIELD USED
TO CONSTRUCT THE THAMES TUNNEL
TUNNELLING SHIELD USED ON XINYI LINE
TAIPEI METRO SYSTEM
RISK ASSESSMENT
TUNNELS - 8
• Tunneling by cutting machine and shield
• Considerable advances have taken place in the development of
full-face cutting machines incorporated within the front face of
shields. In difficult ground, these include diaphragms with
controlled outflow of excavated materials and in recent
developments have included the use of bentonite to retain the
face and facilitate the forward movement of the shield. In very
difficult environments, earth pressure balancing machines are
used in preference to bentonite. They work by balancing
extraction rates (via a screw conveyor) against the rate of
advance controlled by the thrust rams.
RISK ASSESSMENT
TUNNELS - 9
• CUT AND COVER TUNNELS
• This method is often preferred for the construction of shallow
tunnels, such as for underground railway systems. The normal
procedure is to excavate the site in the open after having
protected the sides by means of close piling, or steel sheet
piling, or diaphragm walls. The base, sides and roof of the
tunnel are then formed in the open pit that is finally back-filled,
and the surface or roadway reinstated.
• An alternative method, which is employed where it is important
for the roadway or ground level to be reinstated as quickly as
possible, is achieved by close piling both sides of the route of
the proposed tunnel and then casting in a shallow excavation
the concrete roof of the tunnel bearing upon the piles. The
ground surface can then be reinstated and the tunnel
excavated beneath the already formed roof.
CUT AND COVER TUNNEL
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ANCHOR PILES
TIE BAR
SHEET PILES
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PROPOSED TUNNEL
BACKFILL MATERIAL
RISK ASSESSMENT
TUNNELS - 10
• IMMERSED TUBE TUNNELS
• The immersed tube tunnel is becoming an increasingly popular
method of crossing rivers and waterways. This method entails
the prefabrication of sections of the tunnel, usually in concrete
but occasionally in steel, which are then sunk into position,
aligned and joined together. The jointing of the sections
involves the use of divers and complicated systems of airlocks.
Individual sections of concrete tunnel, which will probably be
constructed in a dry dock and towed into position, may weigh
as much as 25 000 tonnes.
MARMARAY IMMERSED TUNNEL
THE WORLD’S DEEPEST
RISK ASSESSMENT
TUNNELLING HAZARDS - 1
• Although tunneling has been practiced for several thousands
of years, despite considerable development of scientifically
based methods of site investigation and design, it remains
substantially an art. The success of any tunnel project will
depend largely upon the accuracy with which the site
investigations can predict ground conditions, the adequacy of
the consulting engineer's planning and design to meet the
actual conditions, and the preparedness and ability of the
contractor to deal with the hazards encountered.
RISK ASSESSMENT
TUNNELLING HAZARDS - 2
• The prediction of ground conditions is based on careful
geological mapping from the surface, and subsurface
exploration by boreholes and adits at selected points along the
tunnel route carried out during the planning of the project.
Where hazardous ground is predicted, it is now common
practice for more detailed exploration to be carried out during
construction by probing ahead of the tunnel face with long
boreholes or, in the case of large tunnels, by driving small pilot
tunnels. The geological features of the site are among the most
important factors in assessing the risk.
RISK ASSESSMENT
TUNNELLING HAZARDS - 3
• A tunneling project basically involves the creation of a selfsupporting or artificially supported space or void within a
section of a ground mass, which prior to excavation was in a
stabilised state of local equilibrium. The stresses and
pressures disturbed by the excavation will be transferred to the
tunnel surfaces. If these stresses or pressures are not
effectively relieved or checked, it is inevitable that there will be
problems for the contractor and consequently losses for the
insurer.
• Exposure to air, and possibly water, may initiate chemical and
other weathering processes not previously present, which
lining, grouting and other work must take into account. The
permeability of the ground mass, the water table and variations
brought about by temporary surface conditions should be
investigated.
RISK ASSESSMENT
TUNNELLING HAZARDS - 4
• However, the contractor can rarely be entirely confident as to
the conditions expected as local weathered zones, faults,
fissures, dykes, discontinuities, aquifers, voids, made up
ground and even past mine workings can seriously upset
predictions and, with conditions very different from those of
the surrounding rock mass, present unexpected hazards of
inundations. Especially when compressed air is used, the risks
of fire and explosion can be very serious in all tunnels.
RISK ASSESSMENT
TUNNELLING HAZARDS - 5
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The hazards to be expected in bored tunnels are:
rockfalls and rockbursts;
collapse of tunnel sides falls of hanging;
inrush of water;
inrush of soil or broken rock;
fire and explosion;
heave or subsidence of ground surface.
In rock tunneling, falls are usually due to broken or crushed
rock, often associated with faults. In certain rocks containing
expansive clay minerals, enormous pressures, particularly at
great depth, can be expected on the tunnel sides causing
collapse. Below the water table, heavy flows of water and loose
materials are usually associated with faulted or broken rock or
with cavernous rock such as limestone. Explosive gases are
often found in coal-bearing shales. Toxic gases can occur in
volcanic rocks.
RISK ASSESSMENT
TUNNELLING HAZARDS - 6
• In soft tunneling, the main hazards are the inrush of water and
loose soil. In shallow tunnels, the resulting surface settlement
can be large. Conversely, when tunneling with compressed air,
there is a risk of the pressure lifting the ground.
• In cut and cover tunneling, the principal hazards are collapse of
the excavation, inundation by heavy rain or flood water, or
failure of the dewatering system and the consequent damage to
constructional plant.
• With immersed tube tunnels, problems arise from the sheer
size of the individual sections, their construction on land, and
their subsequent launching, towing and positioning on site.
These problems will be much greater if the tunnel is being
constructed in a busy shipping channel, or if the site is in a
windstorm or earthquake area.
FALL OF HANGING
• NOTE HOW THE ROOF HAS COLLAPSED, OR, THERE HAS
BEEN A FALL OF HANGING
• ROOF BOLTING OR GUNNITING MAY HAVE PREVENTED THIS
COLLAPSE.
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MOUNTAIN
ROOF COLLAPSE
TUNNEL
ROOF RUBBLE
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CLEARLY, THE COLLAPSE COULD EXTEND RIGHT TO THE TOP OF THE
MOUNTAIN OR HILL. AS RUBBLE IS REMOVED, SO WILL MORE DEBRIS FALL
IN. SHOULD THE TUNNELLERS NOT HAVE BEEN WORKING WITHIN A
SHIELD? THERE MAY HAVE BEEN SERIOUS INJURIES OR LOSS OF LIFE.
TUNNELLING HAZARDS
COLLAPSE OF ROOF – FALL OF HANGING
HOW WILL THIS AFFECT DEBRIS REMOVAL
• MANY UNDERWRITERS DO NOT CONSIDER THE EXTENT TO
WHICH DEBRIS REMOVAL FOLLOWING FALLS OF HANGING,
• PRESSURE BURST OR COLLAPSE OF ROOF CAN RESULT IN
• CUMULATIVE LOSSES.
• IT IS NOT ENOUGH JUST TO PLACE A LIMIT OF INDEMNITY
FOR EACH EVENT OF DEBRIS REMOVAL, CLEARLY THERE
SHOULD ALSO BE A LIMIT AS TO THE AMOUNT OF DEBRIS
REMOVAL AND RESTORATION OF THE NEAT LINES OF THE
TUNNEL OR SHAFT, IT IS SUGGESTED THAT A LIMIT OF SAY 5
METRES AT 90 DEGREES FROM THE TANGENT OF THE NEAT
LINE OF THE TUNNEL OR SHAFT OR ALTERNATIVELY AN
OVERALL LIMIT OF INDEMNITY DURING THE PERIOD OF
INSURANCE
• WHAT IF THERE IS AN UNEXPECTED MUD RUSH?????
TUNNELLING HAZARDS
COLLAPSE OF ROOF – FALL OF HANGING
HOW WILL THIS AFFECT DEBRIS REMOVAL
• FALL OF HANGING OR COLLAPSE OF ROOF
• PRESSURE BURST
• OR COLLAPSE OF
• WALL
RISK ASSESSMENT
TUNNELLING HAZARDS - 7
• Conditions and special provisions that an insurer may wish to
apply to the property section of the policy include:
• a warranty on the length of unsupported surface where lining,
grouting, or rock bolting are necessary;
• a force majeure exclusion[1];
• a warranty on standby pumping and other necessary
emergency facilities;
• a clear definition of debris removal and cleaning up costs;
• an exclusion of abandonment or constructive total loss;
• an exclusion of overbreak.
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[1] However, the term “force majeure” is best avoided and if
possible a more specific term used clearly stating the risks
excluded
RISK ASSESSMENT
TUNNELLING HAZARDS - 8
• THIRD PARTY LIABILITY
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Each of the basic methods of tunneling has its own special hazard in
relation to the property of third parties, but the main ones are
subsidence, collapse, vibration, withdrawal or weakening of support,
and damage to underground services along the route of the tunnel.
Detailed information with regard to the age, value and distance from
the tunnel of any third party property must be obtained and,
preferably, a photographic record or survey made by a suitable firm.
This should enable the contractor successfully to refute many
frivolous claims that are put forward after work has commenced by
demonstrating that the damage was present before work started.
It is especially necessary for blasting to be carried out by qualified and
experienced personnel and a very strict check kept on the type of
explosive used, the maximum amount of any charge and the method
of firing.
RISK ASSESSMENT
TUNNELLING HAZARDS - 9
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If the sub-soil permits the use of a boring machine, which is the
method of tunneling least hazardous to third party property, much will
depend on the depth of the tunnel below the surface and below the
foundations of existing third party property. The greater the depth of
tunnel, the less the risk of damage to underground services.
The cut and cover method of construction for shallow tunnels such as
underground railway systems, however, presents a very real risk of
damage to underground services and the fullest information should be
sought from the appropriate civic authority regarding the precise
position of such services as electricity, gas, telephone, water, sewers
and the like.
With the immersed tube tunnel, there is very heavy potential exposure
linked to the towing and sinking procedures of the various
prefabricated units.
RISK ASSESSMENT
TUNNELLING HAZARDS - 10
• The risk will be reduced substantially if the fairway to shipping
is closed during the operation of sinking and bedding the units
in the prepared trench.
• An insurer making a comparison between shaft sinking and
tunneling will see both favourable and unfavourable features. It
is very much easier with a vertical or near-vertical shaft to
investigate the ground conditions using boreholes, and
consequently the geological data is likely to be much more
complete and precise. Geological problems should, therefore,
be capable of being investigated to a greater degree of
accuracy and the appropriate precautions taken.
RISK ASSESSMENT
TUNNELLING HAZARDS - 11
• The effectiveness of these precautions and the
avoidance of losses would, however, depend as
much upon the competence and the experience of
the engineers and contractors as to the particular
rock faults encountered
RISK ASSESSMENT
TUNNELLING HAZARDS - 12
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The difficulties of dealing with flooding are greatly increased if the
water is encountered at the considerable depths to which many shafts
are sunk. Insurers must make appropriate enquiries about provisions
for pumping and grouting.
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The considerable vertical distances involved in this type of shaft
sinking can greatly increase the risk of damage to constructional
plant, as well as to the works. Any equipment that may be accidentally
dropped could easily sustain and inflict considerable damage. Much
heavy equipment is used in shaft sinking, for example, the kibbles
used for removing rock to the surface may be carrying 15 tonnes or
so. With some mines, once the initial sink and shaft collar have been
completed and the headgear structure has been built, a sophisticated
system for winding can be installed and this usually incorporates
many elaborate safety precautions.
RIVER LOCKS FOR WATER TRANSPORT
• A lock is a device for raising and lowering boats
between stretches of water of different levels on
river and canal waterways. The distinguishing
feature of a lock is a fixed chamber in which the
water level can be varied; whereas in a caisson lock,
a boat lift, or on a canal inclined plane, it is the
chamber itself (usually then called a caisson) that
rises and falls.
• Locks are used to make a river more easily
navigable, or to allow a canal to take a reasonably
direct line across land that is not level.
POUND LOCKS
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A pound lock is a type of lock that is used almost exclusively nowadays on
canals and rivers. A pound lock has a chamber (the pound) with gates at both
ends that control the level of water in the pound. In contrast, an earlier design
with a single gate was known as a flash lock.
Indirect evidence suggests that pound locks may have been used in antiquity
by the Ptolemaic Greeks and the Romans.
Pound locks were used in ancient China during the Song Dynasty (960–1279
AD), having been pioneered by the government official and engineer Qiao
Weiyo in 984. They replaced earlier double slipways that had caused trouble
and are mentioned by the Chinese polymath Shen Kuo (1031–1095) in his book
Dream Pool Essays (published in 1088), and fully described in the Chinese
historical text Song Shi (compiled in 1345):
The distance between the two locks was rather more than 50 paces, and the
whole space was covered with a great roof like a shed. The gates were 'hanging
gates'; when they were closed the water accumulated like a tide until the
required level was reached, and then when the time came it was allowed to flow
out.
The water level could differ by 4 or 5 feet at each lock and in the Grand Canal
the level was raised in this way by 138 feet (42 m).
LOCK ON MOSCOW WATERWAY
LOCK IN RIVER NECKAR
HEIDELBERG, GERMANY