method statement for project joshua · method statement for ... cable laying, ploughing and shore...

____________________________________________________________________________________________________________________ ASN FO Sub Cable Installation Joshua 2014 June 4 - of 19 Alcatel-Lucent Submarine Networks. Confidential – Use Pursuant to Company Instruction

METHOD STATEMENT for PROJECT JOSHUA

SUBMARINE FIBRE OPTIC COMMUNICATIONS CABLE

SURVEY & INSTALLATION WORKS FROM HWM TO 12 NM

The marine operations required to install the systems include:

Cable Route Survey

Route Clearance

Pre-Lay Grapnel Run

Cable Surface Lay

Cable Burial

Landing

Crossings engineering

Post Lay Inspection and Burial

Cable Route Survey

The marine cable route survey is performed to define a cable routing that will maximise cable

survivability for acceptable system and component cost.

The route selected determines cable length and cable design (factors that the cable

manufacturer must understand), and establishes the methods to be followed for cable

deployment. The survey also generates a reference record that supports subsequent

maintenance and repair of the cable.

In water of depths less than 1000m, swath bathymetry, side scan sonar, seismic profiling and

a geotechnical survey will be performed. The nominal corridor to be surveyed is 500m wide,

which allows adjustment of the cable location if unfavourable conditions are found later. The

final installed cable will lie within the survey corridor.

In water of depths greater than 1000m, multibeam bathymetry only will be acquired.

It is common practice to bury the cable to a depth of about 1 meter in the sea bed in shallow

water sections (i.e. between 1000m and 15m of water depth), to protect it from hazards such

as fishing trawls.


Burial is done only where conditions allow - (e.g. in sandy and muddy sediments). Cable

route survey therefore incorporates burial assessment survey, which tests the mechanical

properties of the seabed along the route. Sediments are investigated by hydroacoustic

means (side scan sonar and sub-bottom profiler), and by intermittent physical samples (grab

samples or cone penetrometer tests).

Where plough burial of the cable is needed, surveys assist in the identification of routes that

avoid hydrothermal vents, seeps, areas of tectonic activity, seamounts, canyons and

dissected terrain, shallow water coral reefs and deep or cold water reefs, all of which are

unfavourable environments in which to attempt to bury cable (i.e. plough burial is not

practicable on these substrates).

Inshore cable route survey (0-15m water depth) is conducted using small boats and divers to

perform visual checks of the seabed and map the ideal route for the cable as it approaches

the shore. The inshore survey is normally conducted along a corridor about 200m wide, in

order to provide flexibility to adjust the cable routing to avoid hazards and minimise threats to

marine habitats.

If necessary the inshore survey may incorporate video footage or mapping of important

ecological zones, habitats and features on the approach to shore, to ensure that they will not

be damaged, or to support planning of mitigating and compensating measures for

unavoidable impacts.

Surveys (in conjunction with desk top studies and local consultations) highlight the existence

of other important coastal and littoral ecological complexes such as sea grass, mangrove

and dune formations, and important features such as marine and coastal conservation areas,

nesting sites and migratory routes.

The studies that precede cable laying serve to lower the probability of ecological impacts,

since in large part they are intended to identify routes for the buried cable that will avoid

seamounts, volcanoes, canyons, vents, seeps, deepwater reefs, carbonate mounds, and

dissected terrain – all areas that present problems for plough deployment, but which also are

often associated with above-average biodiversity and biological value.

Installation Vessels

ASN’s complement of vessels includes 140-meter cable ships, which have been designed as

powerful integrated cable installation vessels.

All vessels conform to MARPOL , including general requirements over the control of waste

oil, engine oil discharges and grey and black waste water discharges; prevention of pollution


by garbage from ships and prevention of air pollution; and maintain operating procedures for

dealing with incidents such as oil and waste spillages that potentially may threaten the

marine environment. One of the cable ships is accredited by the European Maritime Safety

Agency to perform maritime environmental protection activities.

The vessel does not require the use of its anchors to assist in any of the cable installation

operations – cable laying, ploughing and shore end landings are all performed using dynamic

positioning mode. The installation vessels can produce a high bollard pull (up to 130 tonnes)

for ploughing, which is essential for achievement of target burial depths for submarine cable

systems. Vessels are entirely self-sufficient throughout all cable installation operations.

Route Clearance (RC)

RC is performed to clear the cable path of obstacles such as out of service (OOS) cables

identified during the cable route survey, as these can be hazardous to both the vessel’s


installation equipment and the cable itself. RC is only carried out in areas where burial is

deemed necessary. RC excludes all works associated with ordnance, radio-active, or other

hazardous materials.

The Desk Top Study and the Marine Route Survey will establish positions of OOS cables

that may need to be removed from the proposed routes.

OOS cable sections are normally removed so as to clear a 500m corridor either side of the

centreline of the route. The cable ends will be left on the seabed.

RC is conducted using the same high navigational accuracy as used in the main lay

operations. Any recovered cable will be landed for proper disposal at suitably equipped

locations. Recovered repeaters, if any, will also be landed and disposed of according to

standard procedures.

The Vessel will position itself perpendicular and close to the Out Of Service cable

The usual method of RC uses a Deep Trenching Grapnel, lowered from the stern

The vessel moves towards the cable, allowing the fluke of the DTG to penetrate the

seabed and unbury the cable.

The vessel will continue to move until the cable is broken, leaving the two ends on the

seabed.

The vessel will then repeat grapnel runs to retrieve each end individually.

Once on the back deck, a section will be cut from the cable

Clump weights are attached to the cut cable ends.

The Vessel will return the ends to the seabed, leaving a space of 1km though which

the new cable will be installed

The Cable cut is kept onboard and disposed of onshore in the correct manner.

Pre Lay Grapnel Run (PLGR)

PLGR is carried out only along sections of the route where burial is intended. Undertaken

just before ploughing commences, PLGR is intended to clear the route of obstacles and

debris that could damage or obstruct the plough (rocks, fishing equipment, hawsers, anchor

chain, scrap, etc). One or an array of grapnels is towed along the length of the route to be

ploughed. The vessel moves at a speed that ensures that the grapnel(s) stay in continuous

contact with the seabed. Depth of penetration of the seabed by the grapnel is up to 40-80

cm. The grapnel is connected to the tow rope by means of a length of 30 metres of chain,


with a similar length of chain following the grapnel; the chain further assists in keeping the

grapnel in contact with the seabed. The forward motion and design of the Grapnels creates a

clear path by hooking any linear obstacle. The grapnels are retrieved to the vessels deck at

least every 20km, or when a large tension is registered by the vessel, as this will indicate that

an unidentified obstacle has been hooked. All retrieved debris are kept on board for further

safe disposal at port.

PLGR excludes all works associated with ordnance, radio-active, or other hazardous

materials.

PLGR operations would normally be carried out by a specially mobilised and fitted out vessel

capable of sustaining good slow speed positional control with good bollard pull capability.

The vessel would have sufficient deck space to mount a simple winch, simple guides and a

stern roller to deploy the grapnel(s) and stow any recovered debris. Alternatively, depending

on operational logistics and on the information obtained from the surveys, the PLGR

operation may be performed by the main lay vessel.

The PLGR vessel navigates along the route using the same position fixing systems as

employed by the main lay vessel – GPS. The route followed by the PLGR is maintained as

close as practicable to the selected ploughing route and is always maintained within the

swathe of the route surveyed during route selection.

As the vessel moves along the route the towing tension is monitored and the grapnel(s) is

recovered if the tension increases indicating that an obstruction has been hooked. As a

matter of routine grapnels are recovered and inspected at minimum intervals of 15km along

the route. Usually a single tow is made along the route but in areas where other marine

activity or debris amounts are high, additional runs may be made.

Cable laying - surface laying

In water depths exceeding 1000m the cable will be laid on the surface of the sea-bed.


Cable Laying – plough burial of cable

Plough burial of cable is usually performed in water depths of less than 1000m where the

seabed conditions allow.

An industry-standard cable plough weighs approximately 12 tonnes in water. It is deployed

from the stern of the installation vessel and towed behind the ship, burying the cable into the

seabed, usually to a depth of 1 m, as it progresses along the route.

As the plough is towed through the seabed its share blade and inclined cutting disk lift a

wedge of substrate. As the plough progresses forwards, this sediment is dropped back into

the trench, emplacing the cable at the bottom of a relatively undisturbed sediment wedge.

Plough share cuts wedge of sea bed substrate

Wedge displaced; cable positioned in trench

Plough passes, wedge replaced over cable


A combination of specialist cable lay software and DGPS control the position of the ship and

plough to achieve accurate cable positioning, using thrusters and propellers and with no

need for anchors.

Plough burial achieves a maximum burial depth of 2m (depending on seabed type). The

width of the trench is 0.2m (the width of the plough share). The plough will not be deployed

in areas where steep or side slopes prevent it, or where the route crosses an in-service cable

or pipeline.

Following plough burial of the cable a ca 4m strip footprint coincident with the passing of the

plough (width of the plough share incision, plus the tracks of the skids and stabilisers),

remains visible for a period that will vary depending on nature of the substrate and local

seabed hydrodynamics and sedimentation.

In certain demanding environments where there is a soft sea bead and/or high intensity

shipping activity that poses an elevated threat to the cable, deep burial requirements may be

stipulated. For example in Singapore port limits, cables must be buried to a depth of 10m in

the seabed. Such deep burial is achievable with specialised jetting and rock cutting

equipment

Shore-end Landing – Direct Landing Method Statement

Where possible cables are brought to shore directly from the main-lay cable ship (where this

is not possible a “separate” shore end is required). Such shore-end operations are usually

completed within one day.

Operational planning


Preparations for the operation are often made the previous day. Various resources and pre-

requisites are assembled:

Subcontract plant hire

Beach access arrangements for heavy plant and Local Authority agreement.

Permits for the cable installation on the fore-shore.

Route planning to avoid of ‘altercourses’ in the ‘pull-in’.

If ‘altercourses’ exist, what methods are to be used to secure the cable.

Design of post installation cable protection.

Commissioning of divers and support facilities.

Execution

Prior to the cable landing operation, divers will place a marker buoy at the inner limit of the

cable laid by the Cable Vessel. This marks the start position of the proposed shore end

route. Divers may identify gullies / slopes along the route centre line, through which the

cable can be routed, and will again mark their position(s) using marker buoys.

During the shore end landing operation the Cable Vessel will position itself as close as

reasonably practicable to the first marker buoy.

The laying vessel will approach the shore to the agreed cable launching position, or to the

limit deemed acceptable by the Master and maintain this position by use of its dynamic

positioning technology. Once the vessel has achieve a stable station keeping condition the

cable floated off the stern of the vessel and pulled into the beach using a winch or tractor.

This will enable the cable to be initially aligned as close as possible to the target route

selected by the divers. During the pull-in operation, additional slack cable (approx 10m to

15m) will be pulled inshore of the anchor points installed by the divers.


Cable being floated ashore viewed from the vessel stern

The pull can be provided by one of three methods:

a separate work-boat to haul the cable end.

a hauling line which, is passed around a sheave placed on the beach, and

then returned to the laying vessel which provides the hauling tension itself.

most commonly, a hauling line which is passed around a beach sheave but

which is hauled by means of beach equipment e.g. a tractor hauler.

A heavy excavator will be used as “anchor point” for quadrant. The quadrant will allow the

pulling rope and cable to be pulled along the beach in a 90 degree angle from the direction of

landing. Normal beach pulling will require one excavator to pull the rope attached to the

cable for a distance of 100-200 m along the beach.

Cable/rope will be secured every time the excavator will have to go back to perform a new

pull. These beach pulls will continue until all the required cable is safely landed on the beach.


The main lay vessel will pay out cable with floats at the same rate/speed as the excavator

performing the beach pulls.

Cable being hauled ashore around a quadrant. The cable ship is seen in the distance.

An area on the beach of approximately 250 x 15 m is needed for beach pulls to bring the

cable end to shore.

Once the cable end has reached its proper position and sufficient cable has been brought

ashore, the cable end will be opened and the fibres tested towards the ship to ensure that

the cable has not suffered any damage during the landing operation.

Once the cable has been secured on the beach it is then positioned in accordance with the

RPL. Whilst the cable is held in position, the floats are removed by the divers so that the

cable is sunk on its correct line. This work is carried-out from the beach towards the ship.

It is essential that a number of support vessels are to hand to recover the severed floats

which should be returned to the laying vessel.

The vessel will now be standing-to a cable end. Care is required at this juncture to ensure

that the vessel does not allow ‘loops’ to form at cable touchdown. To this end the vessel

should not be allowed to ‘wander’ and the vessel should hold a positive lead on the cable.

The vessel will normally hold station at the cable-end until such time as the beach joint is

completed. However, if station keeping circumstances are difficult it is preferable that the

vessel moves a little further off-shore. This will give the vessel more sea-room and, with

increasing water depth, reduce the chances of a variable cable lead.

On completion of the pull-in operation, the cable will be stoppered off to ensure that the slack

cable is secured, prior to cutting off the cable floats and laying the cable down onto the

seabed. By manoeuvring the vessel and controlling the tension of the cable during the lay

down operation the cable can be laid down as close as possible to the optimum route.


Following completion of cable testing, the vessel will depart and the divers will release the

slack cable from inshore and where necessary move the cable manually, using the slack

cable available, to finalise the position of the cable on the seabed. This process will exploit

natural features on the seabed, such as channels and gullies, to protect the cable and

minimise “suspensions”.

With planned preparation prior to each of the shore ends, controlled lay down during the

shore end landings and post lay utilisation of slack cable, shore ends can be laid close to the

required final position in good conformity with sea bed topography.

Inspection

Once the cable has been sunk into position and the beach joint has been commenced, it is

usual for a diver video inspection of the landing to be carried-out. The inspection is required

to:

Confirm that action was taken, during cable replacement, to avoid small local

suspensions

Record the status of the installation to demonstrate to the System Owners that the

landing has been successfully carried-out (or where corrective work is still required).

Video equipment is required for instant replay as soon as the video tape is available from the

divers.

Precision of cable positioning – expected tolerance for deviation within the 12 nm.

Cable lay and touchdown positioning is normally based on a mathematical model which for

some much more advanced applications may work as a 3 D cable model and use current


vector information as well from different layers in the water column – within certain depth

ranges.

Very precise cable positioning may be required and achieved in shallow water (within safe air

diving range) in connection with cable landing operations, where divers can normally support

manual cable placement out to around 25 m of water depth.

Based on experience and previous system laid and inspected by ROV, typical positioning

accuracy figures could be summarised as follows:

Water Depth Range Precision

10m – 100m: +/- 10-15m

100m – 1000m: +/- 10% WD

1000m – 2000m: +/- 7% WD

> 2000m +/- 5% WD

Submarine Cable Cross section

Please see separate specification - OALC4 Cable Specs.pdf

Embedded:

OALC4 Cable Specs.pdf

Shore-end cable protection and fixing – Articulated Pipe

Cables laid across rocky seabed will be protected by the installation of articulated pipe (AP) ,

which is fitted by divers after the cable has been landed. AP is extensively used by the

submarine cable industry to provide cable protection in the near-shore area where burial is

impracticable for environmental or engineering/technical reasons.

AP pipe can be installed with minimal impact to existing marine environmental conditions,

both during installation and in the longer term. AP is readily colonised by marine flora and

fauna. Like the cable, AP is non-toxic and inert in the marine environment, though in certain

situations it may be oxidised by sulphur reducing bacteria.


The cable with the AP attached will be buried across the beach, both for system security and

environmental and public safety reasons, usually to a depth of 2 meters.


The cable trench is usually dug with hydraulic digging machinery and the beach will be

reinstated at the end of burial.

Shore-end cable protection and fixing – burial methods in shallow waters

Plough burial operations are not normally possible in shallow water of less than 15 meters

depth, due to the size of the plough and the draught of the cable vessels. Consequently,

where such areas have suitable sea-bed characteristics the cable can be buried by other

means.

Various kinds of Shallow Water Burial Tool (SWBT) may be used to accomplish the burial.

The SWBT is a system that employs water jetting to cut trenches of depths of 0.5 m to 1m in

the sea bed, in water up to 20 meters water depth, under the manual control of divers. There

is no instrumentation on the burial tool.

The SWBT is usually connected to a pump on a barge or pontoon on which provides high

pressure pumped water. Using the high pressure water directed as jets through nozzles on a

jetting “sword” the SWBT cuts into the seabed a channel no wider than the sword itself.

Sediment will be generated and dispersed to varying degree depending on the seabed

substrate characteristics.

Cable installation at crossings of other cables and pipelines

Where the route of the cable crosses in-service telecom or power cables, oil and gas

pipelines or other seabed installations, it is not possible to plough without interruption.

Buried in-service cables can be located by use of tone detection equipment. If necessary this

may be followed by careful excavation with diver’s jetting/ROV tools to allow verification and

identification.

The plough is raised and lowered either side of the intersection (creating a “plough skip” or

interruption in the ploughed alignment). This may be done 100-500 meters either side of the

intersection, the margin of safety depending on factors like crossing angles, complexity of the

seabed installations, etc.

Alternative means must be used to achieve cable burial at and around crossing points to

avoid any risk of damage to in-situ infrastructure while ensuring that the new cable is also

protected. Divers or ROV then perform the cable burial precisely around the intersection

using jetting or other tools.


Pipeline crossings may be protected by use of concrete mattressing, “uraduct” (a plastic

sleeving on the cable to reduce friction with pipe casing) or, rarely, by rock dumping.

The International Cable Protection Committee publishes guidelines intended to assist the

cable and pipeline industries to adopt harmonised approach in relation to crossings and ASN

attempts to observe these wherever possible. ICPC Recommendation number 3

recommends the considerations to be borne in mind in relation to crossings of telecom and

power cables.

In the event that it was proposed that a power interconnector be installed across the telecom

cable, in the normal course of events the owners of the crossing power cable would seek a

“no objection” or “agreement to cross” from the owners of the crossed telecom cable.

Normally this process involves provision by the crossing power cable owner of details of the

crossing point location, the physical characteristics of the power cable, details of how the

cable is armoured, buried or otherwise protected and an explanation of the methods by

which the power cable owner proposes to install the power cable at and around the crossing

point. It is usually the case that cable owners can agree quite quickly on a mutually

acceptable crossing engineering solution. In some cases cable owners may seek to achieve

formal legal “crossing agreements” that set out the parties’ respective roles and

responsibilities and define how liabilities may be assigned in the event that damages occur

either at the time of installation or as a result of maintenance and repair works that may take

place on either system during its operational lifetime. (see Appendix One) .

Final Route Map

A copy of the “as laid” route map will be made available to the licensing authority following

completion and acceptance by the customer, of the project.


APPENDIX ONE – CROSSINGS

CROSSING & BURIAL PROCEDURE

This section provides a description of the basic processes to be used for the safe crossing of existing in-service telecommunications cables. This crossing has been unavoidable, and is based on ICPC (International Cable Protection Committee) Recommendations, in particular, ICPC Recommendation #02 - Recommended Routing and Reporting Criteria for Cables in Proximity to Others. Cable routing was also based on ICPC recommendations, as well as SEACOM recommendations & requirements.

Detailed position information has now been obtained from a route survey operation, including bathymetry (MBES), Side Scan Sonar (SSS), Sub-bottom Profiler (SBP), and where appropriate, magnetometers.

The cable system will be installed from a main lay cable ship (e.g. the CS Ile de Sein), and the majority of this length will be buried. For the burial operations, a burial depth below the seabed as listed in Section 3 will be targeted, using a cable plough deployed from the cable ship. The cable to be installed is from the ASN OALC4 product line, with the specific cable type XXCXXX.

Main Lay Crossing Procedure

The vessel will simultaneously lay and plough-bury the cable. This is done by pulling the cable burial plough behind the vessel, along the seabed, and allowing the cable to pass through the share of the plough. This process allows the cable to be buried below the seafloor.

In order to avoid damage to any in-service cables or pipelines, the installation plan includes a plough recovery (PLUP) from the seabed at a safe distance before the identified crossing location of each crossing. The cable will then be surface laid towards the crossing point.

After surface laying the new cable over the in-service cable, the subsequent plough re-launch (PLDN) is located an agreed distance from the crossing point. This installation method is in keeping with the ICPC guidelines. The highly accurate (GPS) positioning systems that are used to navigate the main-lay vessel and installation plough provide a guarantee that all vessel and plough positions are know at all times better than +/- 10m accuracy, and so the exclusion zone from the crossed cable is sufficient to guarantee the safety of all cable crossings.

While ICPC guidelines recommend a ±500m “no-plough corridor” at crossings, with modern navigation systems it is often possible for this to be reduced to ±250m. If the in-service cable is positively located using modern survey techniques & equipment such as magnetometers, and it matches the reported database position, with the acceptance of the cable owner, it is proposed that the PLUP/PLDN positions be reduced to ±250m.

Slack will be installed in the new cable in the surface laid area, to ensure the cable is laid on the seabed along the agreed corridor.

Depending on cable configurations, no additional protection may be required – e.g. if cable types are matched as much as possible to the crossed in-service cable (i.e. armour on armour, as per ICPC Recommendation #2). Additionally, if the crossed cable is buried, there is no possibility of relative movement of the cables causing abrasion.

The following illustrations show a typical main lay cable crossing procedure:


STEP 1: Cable plough buried to PLUP location (250m or 500m away from in service cable)

STEP 2: Plough recovered to deck

STEP 3: New cable surface laid across existing in service cable

STEP 5: Plough launched at PLDN location (250 or 500m away from existing cable)

Seabed

Surface Lay

250m or 500m

Surface Lay

In-Service Cable

Water Level

In-Service Cable

Seabed

Surface Lay

Water Level

In-Service Cable

Seabed

250m or 500m

Water Level

In-Service Cable

Seabed

250 or 500m

Water Level


STEP 6: Ploughing operations resume

Post Lay Burial Procedure

In areas where burial is planned, Post Lay (or remedial) Burial PLB will be performed on the new cable where it has been left unburied at the crossing location. This burial will be performed by a work class ROV using water jetting.

Prior to any ROV burial operation, an inspection pass is made by the ROV, using video, sonar and other detection equipment such as TSS440. This should allow the positive location of the crossed cable. During ROV operations, if possible, a tone can be applied to the crossed cable from the terminal station, to assist in location.

A Post Lay Burial (PLIB) vessel with ROV (Remotely Operated Vehicle) is used. The ROV usually has 2 modes of manoeuvring, either free-swimming or tracked, and has two water jet arms that are lowered into the seabed, opening a narrow trench to the target burial depth in the seabed into which the cable falls. If the crossed cable is surface laid, the new cable will be buried close to the touchdown point either side of the crossed cable. If the crossed cable is already buried to a known depth, the new cable will be buried to close proximity to the crossing location, and then the ROV jetting legs will be retracted to provide a safe clearance during the crossing. Once safely on the other side, the ROV jetting legs will be redeployed to the target depth.

When operating in close proximity to the crossed cable, the ROV will be in free-swimming mode, and should pose no risk to the pipeline, and so there are no risks associated with this burial strategy. Positioning during this operation will also be according to GPS (ie better than ±10m).

Seabed

Surface Lay

250-500m

Surface Lay

In-Service Cable

19 / 19

1. CROSSING INFORMATION

All information below is “as found” after survey.

Ref Crossed System Name

Cable Status

Latitude (WGS-84)

Longitude (WGS-84)

Depth (m)

Cum KP Dist (km)

New Cable Type

New cable to be Buried?

Crossing Angle

Nearest Repeater (km)

Crossed Cable Type

Method Located

Change from Previous Crossing Pack?

1

method statement for project joshua · method statement for ... cable laying, ploughing and shore...

Documents