corrib onshore pipeline brief of evidence - construction by eamon · pdf file ·...

Corrib Onshore Pipeline Construction – Eamon Kelly

CORRIB ONSHORE PIPELINE

BRIEF OF EVIDENCE - CONSTRUCTION

BY EAMON KELLY

1 QUALIFICATIONS, EXPERIENCE AND ROLE IN PROJECT

My name is Eamon Kelly and I am the Senior Onshore Pipeline Engineer, responsible for the construction of the Corrib Onshore Pipeline.

I am a Chartered Engineer, having qualified from University College Cork (UCC) with a degree in Civil Engineering. I completed a Diploma in Project Management at Dublin University. I also successfully completed a Certified Diploma in Accounting and Finance, accredited by ACCA. I am a member of Engineers Ireland. I am a former member of Gas Technical Standards Committee, Ireland and I am also an Honorary Life Member of the Pipeline Industries Guild.

My experience includes gas pipeline route selection, site investigation, landowner management, construction supervision and management. I have been involved in Project & Construction Management of various aspects of the following Bord Gáis Éireann (BGE) transmission/distribution projects since 1985:

1985/86 Cork - Dublin Gas Pipeline;

1986/87 Clonmel - Waterford Pipeline and associated spurs;

1987/88/89 Dublin - Dundalk Pipeline (NEP2);

1989 - 1990 Santry – East Wall Road Transmission Pipeline. Project Manager responsible for routing and construction management;

1990 - 1991 Dunleer – Virginia / Bailieborough Transmission Pipeline;

1991- 2002 Variety of managerial positions, responsible for design, planning, financial assessment and construction management of distribution network and connections;

2002 – 2004 General Manager BGE Northern Ireland. Responsible for design, planning and Contractor appointment for the North West Transmission Pipeline (Carrickfergus-Derry). Responsible for preliminary route selection and appointment of Consultants to Dublin-Belfast Gas Pipeline; and

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2004 – 2006 Distribution Operations Manager. Responsible for all Republic of Ireland distribution activities, including design, planning, safety, response management and all network construction.

Prior to involvement with BGE in 1985, I was engaged as a Site Engineer on sewerage/water projects in Tallaght, Naas, Clondalkin, Drogheda and Clonmel. I was also engaged as Site Engineer on construction of a tailings dam in Navan, a major sand embankment reservoir in Drogheda, a sea outfall pipeline and Resident Engineer on a variety of bridges and associated roads including the East Link Toll Bridge. I have extensive site and construction experience on a variety of infrastructure projects but particularly on pipeline projects.

2 SCOPE OF EVIDENCE

I will outline the proposed construction methods to be used along the pipeline route from the High Water Mark (HWM) at Glengad to the termination of the onshore pipeline at Bellanaboy Bridge Gas Terminal. As I discussed last year, the proposed construction methods have been developed in consultation with various environmental specialists, each of whom will outline their evidence later in separate statements to the Oral Hearing. These discussions ensured that methods were developed that would avoid or minimise environmental impact.

In general the land based construction methods (apart from those associated with the tunnelling process) have not changed significantly since the description provided in my Witness Statement for Construction at the Oral Hearing for the Corrib Onshore Pipeline in 2009. Consequently, this Witness Statement will refer to the Witness Statement submitted in 2009 for methodologies and techniques that remain unchanged and will only focus on those areas of construction that have changed since 2009.

I will also outline the proposed method of installing, testing and commissioning the pipeline, the likely construction programme and the construction supervision team, to be engaged in managing construction. Likewise, some of these aspects were described in my Witness Statement for Construction in 2009 and I will refer to that Witness Statement where appropriate.

2.1 PRINCIPAL CHANGES SINCE 2009 ORAL HEARING

I will now summarise some of the key changes to the proposed development since the 2009 Oral Hearing.

• Horizontal alignment changed following ABP Letter, 2nd November 2009. The 2009 route (between Ch 83.91 and 89.55) entailed 2 No. micro tunnels together with extensive land based works in Rossport. Current horizontal alignment (i.e. 2010), for this area is largely confined to Sruwaddacon Bay with appropriate land based alterations to tie in to 2009 route.

The 2010 application includes a 4.2m outside diameter tunnel, 4.9km in length from Aghoos to Glengad, largely tunnelled beneath Sruwaddacon Bay.

• 9 No. Compounds 2009 reduced to 5 No. Compounds 2010.

• SC2 in Glengad greatly reduced in size.

• SC3 Aghoos extended to cater for tunnel operations with adjacent stringing area and peat storage areas.

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• Vertical alignment alterations adjacent to tunnel launch and reception areas.

• Inclusion of a 12m wide stone road in peatland areas of low environmental sensitivity. The pipeline could be constructed using a 9m wide stone road however, a 12m stone road is proposed for ease and speed of construction.

• The construction programme proposed for 2010 is 26 months in duration. The construction programme proposed for 2009 was 12 months in duration. The extended programme for the 2010 application includes construction of a 4.9km tunnel.

Alterations to material quantities will be described during my evidence. Full details on material quantities are provided in the EIS, Volume 2, Appendix R and Appendix S4.

3 PROPOSED CONSTRUCTION METHODS

I will first describe general pipeline construction methods that will be used along the proposed route. I will then discuss in more detail the proposed methods for the various sections of the pipeline route, which I have divided into 4 distinct sections, as follows: (Slide 1)

1. Glengad 2. Sruwaddacon Bay Tunnel 3. South of Sruwaddacon Bay 4. Forested area to Bellanaboy Terminal

The proposed construction methods for each of the 4 sections are summarised in Table 1, which is provided as an Appendix to this Statement. Table 1 also outlines where these construction methods are discussed in the EIS and the relevant application drawings.

The Offshore Pipeline reaches HWM at Glengad at Ch 83.38 indicating that the length of the overall pipeline to this point is 83.38km. The Onshore Pipeline application commences at this location. Therefore, the distances measured along the length of the onshore pipeline (i.e. chainages), which are used to identify specific locations commence at 83.38.

It should be noted that a description of the proposed construction methods are provided in the EIS, Volume 1, Chapter 5. As in 2009, it should be noted that some specific measures to minimise or prevent impact on sensitive habitats or areas of archaeological potential for example are described separately in the evidence to be presented later in this Oral Hearing. Method Statements will be prepared and agreed with NPWS and other relevant authorities for all proposed construction works in environmentally sensitive areas including designated conservation sites.

3.1 SPREAD TECHNIQUE

In general pipeline construction projects on land are completed using an “open cut” method. The spread technique is a standard open cut method for constructing land based pipelines and is widely used across the industry in Ireland and throughout the world. All construction work and associated activities are carried out within a fenced area that follows the length of the pipeline route. This is the “pipeline construction spread” area.

The ”pipeline construction spread” area varies in width along the route of the pipeline, but is generally 40m wide. It should be noted that the “pipeline construction spread” is always contained within the “temporary working area” as identified on the application drawings. In certain locations the “temporary working width” may be wider than the pipeline construction spread.

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A description of the Spread Technique was provided in my Witness Statement for Construction (Section 3, Spread Technique) at the Oral Hearing for the Corrib Onshore Pipeline in 2009. The technique remains unchanged in 2010.

3.2 STONE ROAD METHOD

The stone road method will be used in peatland sections of the pipeline route. A description of the Stone Road Method was also provided in my Witness Statement for Construction (Section 3, Stone Road Method) at the Oral Hearing for the Corrib Onshore Pipeline in 2009. In general this technique remains unchanged in 2010 apart from the following revisions;

• The width of the stone road at the top surface level will be 12m in areas of peatland that do not require turving.

• Turving will be carried out in one section of peatland in Aghoos, east of the Leenamore River. This section of peatland is 190m long and the width of the stone road at the top surface level will be 9m at this location.

3.3 CONSTRUCTION SITE COMPOUNDS

There are a total of 5 site compounds required for the construction of onshore pipeline. Tunnelling operations will require 2 No. compounds. These compounds are discussed in detail in Section 3.5 of my Witness Statement.

An additional 3 site compounds are required along the route of the pipeline to facilitate construction. These site compounds remain the same as described in my Witness Statement submitted to the Oral Hearing for the Corrib Onshore Pipeline in 2009. As fewer site compounds are required overall in 2010, the compound numbers have been revised in 2010 to reflect this change. The revised site compound numbers are indicated below.

Table 2 Comparison of Site Compound Details (2009 – 2010)

2010 2009 Comment

SC1 SC1 Unchanged

SC2 SC2 Decreased in size

SC3 SC7 Increased in size

SC4 SC8 Unchanged

SC5 SC9 Unchanged

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3.4 THE TUNNELLING PROCESS

A tunnelling construction method known as segment lined tunnelling will be used to construct the Sruwaddacon Bay tunnel. A description of tunnel design and construction methodology will be provided in the Witness Statement on Tunnelling Construction.

Tunnelling Compounds will be required in Aghoos (SC3) and Glengad (SC2) to facilitate tunnelling operations. The tunnelling operation will commence at a starting pit in Aghoos and proceed towards a reception pit in Glengad.

The majority of tunnelling operations will be carried out from the compound at Aghoos (Slide 2). This compound will consist of the following components;

• SC 3 - Tunnelling Compound (indicated by light blue colour in Slide 2),

• Stringing Area (indicated by dark blue colour in Slide 2),

• Peat Storage area (indicated by yellow colour in Slide 2).

The tunnelling compound and stringing area will be provided with artificial lighting for carrying out operations at night. The lighting system will consist of lanterns mounted on 8m high poles located to provide an adequate standard of lighting to facilitate the necessary construction operations both safely and effectively. The lighting system will be designed to minimise spill of lighting outside of the compound while providing adequate lighting to facilitate the undertaking of the necessary construction operations in a safe manner.

The tunnel will be excavated using a Tunnel Boring Machine (TBM). As the TBM excavates its way forward, the tunnel will be lined (from within) using concrete segments. A steel ventilation shaft will be installed within the completed segments as the tunnel progresses. Material is gradually cut away by the head of the TBM and transported back to a separation plant at the tunnelling compound using a bentonite slurry process. The bentonite slurry is also used for lubrication and cooling of the cutting head.

During each advance of the TBM, the annulus between the outside wall of the tunnel and the excavated surface of the surrounding ground will be injected with a mortar grout.

When the tunnel has been completed, the TBM will be removed from the reception pit. The gas pipeline and services will then be installed within the tunnel. Spare services including a HDPE duct, umbilical, electrical cable and fibre-optic cable will also be installed within the tunnel (see EIS, Volume 1, Section 4.3.1.1). Installation of these spare elements within the tunnel is considered to be an important contingency measure. The gas pipeline and services will then be connected to the onland sections of the onshore pipeline. Following hydrostatic testing of the onshore pipeline, the ventilation shaft will be retained, and the remainder of the tunnel will be grouted internally.

I will now consider certain aspects of the tunnelling process in more detail, in particular land based operations. Further details will be presented in the Witness Statement for Tunnelling.

3.4.1 Bentonite Slurry and Water Consumption

Bentonite slurry is used for lubrication and cooling of the cutting head and removal of cuttings. The bentonite slurry used throughout the tunnelling operation will consist of a mixture of bentonite and water (see EIS, Volume 1, Chapter 5). The bentonite slurry will be pumped directly from a header tank located in the main compound (SC3) to the head of the TBM. The bentonite slurry return line will

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transport material back from the cutting face and will be connected directly to the bentonite handling unit and separation plant. (Slide 3) This bentonite slurry mixture will need to be replenished on a continuous basis. Although the bentonite slurry will be continuously recycled and reused, it is estimated that an average of 150m3 of fresh water per day will need to be introduced into the system to compensate for losses (described further in the Witness Statement for Tunnelling). It is proposed that this water will be sourced from rainwater harvested within the tunnelling compound. Additional quantities of water will be sourced from the Terminal site which will be delivered by tanker to the compound in Aghoos when required.

Should the daily rate of tunnelling increase, then the daily water requirements will also increase. To cater for the potential increases in freshwater consumption, storage will be provided on site in storage tanks with an additional reserve in the settlement lagoon. Any additional freshwater required for construction will be delivered to the site in tankers as described above.

3.4.2 Rainwater Harvesting

In order to reduce the necessity for imported water during the tunnelling process, harvested rainwater from the tunnelling compound and stringing area will be used as much as possible. The settlement lagoon in the compound will be used as the collection area for rainwater. The harvested rainwater will be pumped from the settlement lagoon to water storage tanks located in the tunnelling compound SC3. It is estimated that approximately 50m3 per day of rainwater could be harvested from the compound area (SC3). This volume would increase to an average 80m3 per day with the addition of rainwater harvested from the stringing area.

3.4.3 The Separation Process and Tunnel Arisings

Excavated materials from tunnelling (tunnel arisings) will be separated from the bentonite slurry mixture at the separation plant (See Slide 3).

The separation plant will remove various fractions of excavated materials from the bentonite slurry by passing the fluid through a combination of shakers, sieves and cyclones. The separation plant will be located on an area of hard standing which will have a separate drainage system from which all run-off will be collected and pumped to a used bentonite storage tank.

The tunnel arisings material (maximum aggregate size approximately 40mm) will have re-use potential and it is proposed to re-use a proportion of the material excavated by the TBM on the project (see EIS, Volume 2, Appendix S4). The three main constituents of the arisings will be rock cuttings/stone, sands and gravels, and silts/clays.

It has been calculated that the quantity of material arising from the tunnelling works from Aghoos to Glengad is approximately 68,000m3. The tunnelling works will generate approximately 13.8m3 of spoil material per meter tunnelled (based on tunnel diameter of 4.2m). The tunnelling works will progress at an average rate of approximately 11m per day (this rate could be higher or lower on a daily basis depending on the material encountered at the tunnel face). Therefore, the quantity of tunnelling spoil arising from the works is expected to be an average of 150m3 per day.

Based on the geophysical and geotechnical information gathered to-date it is calculated that 20% of the tunnelling materials generated will be rock and stone cuttings with the remainder primarily sands and gravels. Finally, it is calculated that 15% of the sand and gravels will be silty material.

A minimum of 35% of these materials can be reused during construction of the Corrib Onshore Pipeline. Silts and clays have limited reuse potential and it is planned to take this material off site for disposal at an EPA Licensed facility.

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The tunnel arisings will be temporarily stored within the tunnelling compound in a dedicated storage area. The storage area for tunnel arisings will be bunded and will have a separate drainage system installed which will direct run off into a sump from where it will be pumped to the used bentonite storage tank. Run off from the tunnel arisings storage area will be reused in the tunnelling process if possible. Should the rate of tunnelling increase above 11m per day, the daily volume of excavated materials will also increase. To cater for such an increase in tunnelling progress, a dedicated temporary stockpiling area will also be available in the stringing area. Any excess tunnel arisings which cannot be accommodated in the dedicated storage area at the main tunnelling compound will be transferred to the temporary stockpiling area in the stringing area where it will be stored for re-use on the project or exported off site. This area will have a suitable drainage system and bunding as required.

Tunnel arisings will be stockpiled to a height of 2m – 3m.

3.4.4 Grouting

During each advance of the TBM, the annulus between the outside wall of the tunnel and the excavated surface of the surrounding ground will be injected with a mortar grout. The grouting material will be prepared in a dedicated area at the tunnelling compound in Aghoos, with a separate drainage system, adjacent to the starting pit. Grouting material will be transported in a mobile container to the TBM using the tunnel railway system.

A grouting material will also be used to fill void space within the tunnel. This procedure is described in the Witness Statement for Tunnelling.

3.5 SITE COMPOUNDS ASSOCIATED WITH THE TUNNELLING PROCESS

I will now describe the construction of the site compounds associated with the tunnelling process.

3.5.1 Tunnelling Compound and Peat Storage Area - Aghoos

The majority of tunnelling operations will be carried out from the compound at Aghoos and it is estimated that this compound will be in place for approximately 26 months.

A peat storage area will be located within the temporary working area to facilitate the construction and reinstatement of the tunnelling compound and stringing area. It is estimated that approximately 27,000m3 of peat can be stored in this area. Peat will be stockpiled to a height of 1m in the temporary peat storage area.

The peat storage area will include bog mat access roads and v-ditches to intercept and collect surface water run off and direct it to the surface water management system within the main compound area. Culverts will be installed where necessary.

A description of the site set up and construction of the Aghoos tunnelling compound can be found in the EIS, Volume 1, Section 5.5.3.

I will now present a series of stills from a high level animation which summarises the construction phases of the Tunnelling Compound, Stringing Area and Temporary Peat Storage Area.

These stills are not a definitive sequence of construction activities but are presented to assist in understanding the key activities. A full animation will be presented later in the Oral Hearing.

• Slide 4 - Initially a set down area and site entrance will be established.

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• Slide 5 - Following this approximately 2,500m of 3m high steel palisade fencing will be erected around the perimeter of the site, using temporary bog mats where appropriate. The fencing will be fastened to bogmats for support and stability as necessary. In defined areas visual and acoustic mitigation screening will be placed on the palisade security fence as it is being erected.

Temporary culverts will also be installed for existing field ditches as required.

• Slide 6 – The temporary peat storage area will be established and suitable surface water management systems put in place.

• Slide 7 - Earthworks will commence with the construction of the main stone access road to the

site and will expand around the perimeter of the main compound. A peat handling area will be constructed at the location where the access road meets the compound. This area is approximately 2,500m2 in size and will be used to transfer the excavated peat from site dumpers to road-going tipper lorries. A wheelwash system will be set up in this area and trucks leaving the site will be cleaned before they exit onto the public road.

A 3m high non-transparent noise barrier fence will be installed around the perimeter of the compound and inside the palisade fencing. This barrier will be designed to mitigate the potential noise emissions from the works in the compound. It will also serve to visually screen the works.

Additional acoustic measures are currently being assessed. This assessment will continue during the final design stages and the selection of a preferred Contractor for executing the tunnel construction. Any additional acoustic measures identified during this process will be incorporated into the works.

A surface water management system will be installed as the stone road progresses which will include V-ditches along the access road, a swale and a settlement lagoon located at a low elevation at the north west corner of the site. Further details on surface water management are described in the Witness Statement on Hydrology.

During excavations the surface layer of peat including vegetation will be removed and stored at the designated peat storage area on site for use in future reinstatement activities. Below this layer, peat to a depth of up to 1.0m above mineral soil will be excavated and removed off site to the Srahmore Peat Deposition site.

Stone will be delivered to site and placed over the excavated peat surface. The access road will be constructed progressively in this way, with machinery always working from on top of the stone structure.

• Slide 8 - The tunnelling compound will be built in the same manner as the access road. A drainage system will be installed as the construction of the compound progresses.

• Slide 9 - The remaining elements of the compound will then be put in place. This will include the starting pit and ramp which will be excavated once sufficient working space has been provided within the compound area. The starting pit will be approximately 8m long x 10m wide x 12m deep. The ramp for accessing the pit will be approximately 75m long x 5m wide and increase in depth from 0m to 10m below ground level. Construction of the starting pit and ramp will entail the installation of sheet piles (and bracing where necessary), excavation of stone, installation of soil anchors and the placement of reinforced concrete base and side walls. A sealing body, located next to the launch pit (to the west) will also be constructed. The sealing pit will be backfilled with a low strength mortar.

The surface of the tunnelling compound will be finished with 100mm of surface dressing (tarmacadam). The surface dressing will provide a clean low permeable surface facilitating rainwater harvesting and contributing to general site tidiness.

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3.5.2 Stringing Area – Aghoos

The pipeline stringing area will be constructed adjacent to the Aghoos Tunnelling Compound and will be used for welding sections of pipe and preparing associated services for installation within the completed tunnel. The pipe lengths will initially be positioned on wooden skids. Subsequently the pipe lengths will be carefully aligned and welded into continuous strings of predetermined length, to facilitate insertion into the completed tunnel. It is estimated that the stringing area will be in place for approximately 21 months.

Slide 10 - Once tunnelling operations are underway the stringing area will be constructed in the same manner as the tunnelling compound. It is proposed to combine tunnel arisings with quarry stone to complete the construction of this area.

The stringing area will include a surface water treatment system consisting of v-ditches and linear drainage channels which will be linked to the system in the tunnelling compound. A second settlement pond system, similar to the system at the compound will also be constructed.

The stringing area will include a stone access road from the L1202 and noise barrier fencing around its perimeter.

A temporary stockpiling area for tunnel arisings will be provided in the stringing area, if required.

3.5.3 Tunnelling Compound - Glengad

The tunnelling compound (SC 2) at Glengad will include a reception pit to receive the TBM during the latter stage of the tunnelling process. The tunnelling compound in Glangad will be in place for approximately 12 months. Overnight working is not envisaged at the compound in Glengad. Part of this compound will be located within the boundaries of the Glenamoy Bog Complex (cSAC).

The reception pit will consist of a sheet-piled excavation with a concrete base anchored with soil anchors. A sealing body, located next to the reception pit (to the east) will consist of a second sheet-piled excavation similar in size to the reception pit, which will be backfilled with a low strength mortar.

A description of the site set up and construction of the tunnelling compound at Glengad can also be found in the EIS, Volume 1, Section 5.5.3 and is summarised below.

• A temporary access road and site compound will be required. These will be constructed using material recovered from the excavation of the LVI dished area, and they will be surfaced with stone capping material from a local quarry.

• Topsoil will be stripped from the area of the compound and stockpiled for use during reinstatement. Sheet piles for the reception pit will then be installed over a period of approximately 2 weeks. Once these have been installed, the pit will be excavated. Materials excavated will be stockpiled locally, stored separately from topsoil.

• Soil anchors will be installed in the base of the reception pit. The base of the pit will then be lined with concrete. The sealing body will be constructed and filled with low strength mortar as previously described. The sealing body will allow the smooth transition/entrance of the TBM into the reception pit and will seal the annular space at the end of the tunnel.

• As tunnelling nears completion, the TBM will pass through the sealing body to emerge at the reception pit where it will be dismantled and removed over a period of approximately one month. Due to the large size of the TBM, a crane will be required at this site.

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3.5.4 Reinstatement

A description of the reinstatement of the site compounds associated with tunnelling is provided in the EIS, Volume 1, Chapter 5, Section 5.5.4. I will briefly describe the process.

Aghoos

• Demobilisation of the site including removal of construction plant and machinery and equipment associated with the tunnelling process.

• Backfilling of the starting pit and ramp with tunnel arisings. Sheet piles and concrete sidewalls will be cut to a depth of 1m below finished ground level.

• Removal of surface dressing from the compound and the stringing area. A road planer will excavate and gather the tarmacadam, which will be removed off site to an authorised facility. This material can be recycled.

• The top 300 – 600mm of stone will be removed from the tunnelling compound and stringing area and filled with peat from the temporary peat storage area.

• The access road will be maintained to the surface water settlement lagoon area(s) up until the end of the reinstatement works. At this stage the surface water treatment system will no longer be required.

• Removal of noise barrier fencing in line with final reinstatement.

• When peat reinstatement works are complete the bog mats will be removed from the temporary peat storage area.

• Perimeter fencing and associated bog mats will then be removed.

Glengad

• Demobilisation of the site including removal of construction plant and machinery and equipment associated with the tunnelling process.

• Backfilling of the reception pit with stockpiled subsoil. Sheet piles will be cut to a depth of 1m below finished ground level.

• Placement of remaining stockpiled subsoil, followed by topsoil will complete the reinstatement of the area.

• Removal of perimeter fencing.

• The area will be allowed to revegetate naturally.

3.6 TUNNELLING CONTINGENCY – INTERVENTION PIT

It is considered highly unlikely that an intervention pit will be required during the tunnelling operation as an access hatch at the TBM face can be used should manual intervention be required at the TBM. All envisaged operations, including the removal of any obstacles, can take place from within the tunnel.

However, in response to a third party submission, a more detailed methodology of a possible intervention pit construction has been examined for this Oral Hearing.

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The pit would measure 15m long x 12m wide. A jack-up barge and shallow draft vessels would provide marine support. The pit would be formed using driven sheet piles on all four sides. A vibro-piling rig, situated on the jack-up barge would be used for pile driving. The pit would not be water tight (i.e. not a cofferdam) and would be constructed with single skin sheet piling to all four sides. The sheet piling would be braced internally for stability. Scour protection measures could be installed following advice from appropriate environmental specialists.

A long reach excavator would be positioned on the jack-up barge to allow excavation within the completed intervention pit. Excavated material from the surface layer of the sea bed, would be placed within the estuary, adjacent to the intervention pit, following appropriate environmental specialist advice. The lower layers of excavated material would be transported by barge, to the Aghoos compound for temporary storage.

The excavation process would continue until the TBM has been exposed. Following completion of any remedial works, the intervention pit would be backfilled with the original material, previously stored in Aghoos. Finally the sheet piling would be removed on completion of backfilling.

The intervention pit operation would entail an 8 week (approximately) marine construction programme. The programme would also entail onland mobilisation and demobilisation however, these activities would not require access to the Bay.

Finally, I again reiterate, that the construction methodology outlined here is in response to a third party submission and not a construction activity that is likely to be undertaken.

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4 BREAKDOWN OF THE ONSHORE PIPELINE DEVELOPMENT

I will now address the four identified sections of the onshore pipeline route in terms of pipeline construction methodology, commencing with Section 1.

4.1 SECTION 1 – GLENGAD - CHAINAGE 83.38 – 83.88

SLIDE 11 – Section 1

This section of the onshore pipeline extends from the HWM at Glengad to site compound (SC2) at the western end of the proposed Sruwaddacon Bay tunnel. This section of the onshore pipeline generally remains the same as I described in 2009 apart from the fact that site compound SC2 has reduced in size and the vertical alignment of the onshore pipeline has changed as it approaches SC2 due to the Sruwaddacon Bay tunnel.

4.2 SECTION 2 – SRUWADDACON BAY TUNNEL - CHAINAGE 83.88 – 88.77


The Sruwaddacon Bay tunnel extends from starting pit L2 at SC3 (Ch 88.77) to reception pit L1 at SC2 (Ch 83.88). Between these two points, construction will generally take place below the bed of Sruwaddacon Bay. This section of the works will be constructed using the tunnelling technique method described in the Witness Statement on Tunnelling Construction. The proposed tunnel will be approximately 4.9km long (4.6km beneath the Bay) with an outside diameter of approximately 4.2m.

The surface based elements of the tunnelling operation have already been described. A temporary shore access in Aghoos has also been included in the development proposal to allow access to the foreshore if there is a need for marine access.

The realignment of the pipeline route at the land based tunnelling compounds compared with the 2009 pipeline route alignment is shown in Slide 13 and 14.

4.3 SECTION 3 – SECTION SOUTH OF SRUWADDACON BAY - CHAINAGE 88.77 – 89.54


In order to best explain the proposed construction methods in Section 3, I have divided it into four areas as I did in 2009.

Access to this section of the works will be via the public road to the south (L1202). Access will also be gained using the adjacent temporary working areas.

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4.3.1 Chainage 88.77 – 89.21

The proposed construction method for the section between the Starting Pit and the Leenamore River Estuary is the stone road method for peatland construction incorporating the spread technique, as I previously described.

4.3.2 Chainages 89.21 – 89.26 Leenamore River Inlet

The topography from Ch 89.15 to 89.35 is more steeply sloping than adjacent areas as this area forms a small valley through which the Leenamore River flows to Sruwaddacon Bay. The temporary working area at the Leenamore River Inlet crossing is generally 85m wide but as this section borders the temporary working area for SC3 and the stringing area, the temporary working area is wider to accommodate the works associated with these facilities.

This crossing will involve the installation of two concrete coated pipeline strings within the river inlet (the gas pipeline and a duct for accompanying services). The crossing will be constructed using open cut methods, which are established methods for such crossings. The pipeline route crosses the Leenamore River Inlet at a point on the foreshore where the river meets Sruwaddacon Bay. The inlet is approximately 40m wide at this point. The inlet is a tidal area. This crossing will involve the following steps:

• Preparation of concrete coated pipeline strings in the stringing area in Aghoos in advance of the works;

• Stone road to be installed from stringing area to the Leenamore River inlet; • Larger cobbles (stones) within the river inlet to which epifauna & flora are attached will be

preserved by relocating by hand to a similar height in the intertidal zone on the shore away from the works area for the duration of the construction works. These will then be reinstated on completion of the construction;

• Assessment of the upper layers of the inter-tidal area; • Removal of sections of salt marsh as turves and placing these temporarily at similar locations

on the foreshore nearby. The upper layer of the foreshore (approximately 300mm) will also be moved temporarily to one side;

• A temporary sand bag dam structure will be placed across the river inlet on the northern side of the pipeline route;

• Stream flow from the Leenamore River will be over-pumped from a location upstream of the works and discharged to the estuary downstream of the sand bag dam structure. Alternatively, a flume pipe arrangement will be used;

• A temporary access bridge will be installed for general crossing of the Leenamore Inlet; • Excavation of the trench will then commence using two long reach excavators located at

opposite sides of the river inlet; • Excavated material will be loaded into dumpers and transferred to the stringing area in

Aghoos for storage; • The excavated material will be stored in a dedicated area within the stringing area. This area

will have a separate drainage system and bunding; • A bedding layer of 150mm of pea gravel will be placed in the base of the open trench and

pipeline strings will then be installed using side boom crawler tractors; • The pipeline will be covered with pea gravel and then backfilled with the excavated material

stored in the stringing area. Precast concrete slabs will be placed 0.5m above the pipeline during this process;

• Reinstatement of the area including upper layer of inter-tidal area, cobbles/stones and salt marsh turves;

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It is anticipated that once the contractor is fully mobilised, works to construct the actual stream crossing will take less than 1 week to complete. Work will be completed during favourable weather and tidal conditions.

4.3.3 Chainages 89.26 – 89.35

As I described in 2009, this section of the pipeline route is through wet grassland. In this area, the spread technique will be used for construction.

4.3.4 Chainages 89.35 – 89.54

This section of the pipeline (approximately 190m) is gently sloping / flat and consists of recovering eroded blanket bog. The proposed construction method for this area is the stone road method with turving. It is proposed to limit the width of the stone road to 9m in this section. No excavated peat apart from turves will be stored within the temporary working area. Turves will be monitored during storage and there will be minimal delay between construction and reinstatement of this section of the route.

The pipeline construction spread will be 40m wide at this location. It is estimated that this section will take 3 - 6 months to complete, and every effort will be made to complete in a 3 month period.

4.4 SECTION 4 – FORESTED AREA TO BELLANABOY GAS TERMINAL - CHAINAGES 89.54 – 91.72


As I described in 2009, this section of the pipeline consists of coniferous forestry that was planted in an area of blanket peat. The proposed construction method for this area is the stone road method as previously outlined in 2009. It is proposed to increase the width of the stone road from 9m to 12m in this section.

This section of the pipeline route includes a road crossing (RDX 1) as shown in Slide 8. This road crossing will be carried out using standard open cut techniques as previously described in the Witness Statement for Construction (Section 3.9, Road/Track Crossings) at the Oral Hearing for the Corrib Onshore Pipeline in 2009.

This section of the pipeline route also includes 2 stream crossings located at Ch 90.09 and 90.66. Both of these stream crossings will be constructed using open cut methods as previously described in the Witness Statement for Construction (Section 3.10, Stream Crossings) at the Oral Hearing for the Corrib Onshore Pipeline in 2009.

4.5 LANDFALL VALVE INSTALLATION (LVI) - CHAINAGE 83.44 - 83.49

The location of the LVI extends from Ch 83.44 to 83.49. The LVI construction will be the same design as described in my Witness Statement in 2009.

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4.6 CATHODIC PROTECTION SYSTEM

A cathodic protection system is used for protection of the pipeline. Details of the proposed pipeline protection system will be addressed in the Witness Statement presented by Dr. Steve Paterson. Construction will be completed in compliance with the design layout.

4.7 PRECOMMISSIONING

4.7.1 Hydrostatic Testing

Hydrostatic testing will be undertaken in two stages;

• Hydrostatic testing of the LVI,

• Hydrostatic testing of the onshore pipeline.

Hydrostatic Testing of LVI

It is planned to construct the LVI in 2011, subject to the necessary planning approvals. The completed LVI will be subject to 100% ultrasonic testing (UT) examination of all welded joints prior to commencement of backfilling. Hydrostatic testing of the LVI will be completed to 504bar. The test water, which will be free from chemicals or inhibitors, will be brought to site by truck from the Terminal and on completion of testing, disposed off site to a licensed waste water treatment facility.

Hydrostatic Testing of the Onshore Pipeline

On completion of pipe laying on land, and pipe insertion within the tunnel, a programme of tie-in welds will be completed. A test head will be welded to the onshore pipeline directly downstream (landside) of the LVI. The onshore pipeline termination at the Terminal site entails completing a welded joint of the onshore pipeline to a previously constructed gate valve, situated in the Terminal site. The completed onshore pipeline, will be filled with water, sourced from the Terminal settlement ponds. No chemicals or inhibitors will be added to the water. Hydrostatic testing of the onshore pipeline will be completed to 504bar. On completion of the hydrostatic testing, the onshore pipeline will be pigged, with a series of pigging runs, concluding with an intelligent pig run. A temporary pig receiver will be installed at Glengad for this purpose.

On successful completion of the testing and pigging operations, the pipeline will be dewatered. The water used shall be tested to ensure lack of contaminants prior to disposal. It is proposed that hydrostatic test water be disposed of at sea via the water outfall pipeline, which terminates in a diffuser on the sea bed approximately 2km north of Erris Head.

After the pigging operations and inspections have been completed, the temporary pig trap will be removed from the LVI compound. The onshore pipeline will be connected (welded) to the LVI. The welded connection will be subject to UT examination. Nitrogen will then be introduced to the entire onshore pipeline from the offshore pipeline, via the LVI.

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4.8 COMMISSIONING

Commissioning of the pipeline entails the introduction of hydrocarbon gas. Hydrocarbon gas from the field will be introduced slowly to the onshore pipeline, via the offshore pipeline and LVI. The displaced nitrogren will be vented at the Terminal. Venting will continue until nitrogen has been expelled from the onshore pipeline. The commissioning of the onshore pipeline will be completed when the hydrocarbon gas flow at the Terminal is deemed free of nitrogen.

4.9 POTENTIAL MODIFICATIONS TO THE ONSHORE PIPELINE

4.9.1 Additional Protection of Services

In June 2010, protestor activity at Glengad Beach had potential to damage the previously laid gas pipeline and services. Protection of the umbilicals by way of the insertion of concrete protective slabs over the umbilicals has already been proposed in the vicinity of road and water course crossings. In light of the above threat to the umbilicals, the Board may consider it appropriate to insert a modification to the proposed development to require the insertion of same for the remaining length of the pipeline outside of the tunnel (amounting to an additional length of approximately 2.3km).

Precast concrete slabs, 1.2m wide and 150mm deep, can be placed over the umbilicals and services. The precast concrete slabs would extend from downstream of the LVI to the Terminal site boundary, excluding the tunnelled section between L2 and L1. The precast concrete slabs will be installed a minimum of 900mm below finished ground level.

The volume of precast concrete slabs required is 414m3. The slabs will replace approximately 343m3 of stone from the stone road areas.

The overall project programme would not be extended should this measure be implemented.

4.10 CONSTRUCTION MANAGEMENT

A description of the construction management of the Corrib Onshore Pipeline was provided in my Witness Statement (Section 3.13, Construction Management) submitted to the Oral Hearing in 2009. This description identified some of the key roles and responsibilities and key documents required for the successful management of the construction phase of the development. This description is still applicable to the current application. Tunnelling Engineers will also be included in the project team.

4.11 PROGRAMME

It is envisaged that construction activities can be completed in 26 months, given favourable construction conditions. It is anticipated that construction will largely take place in 2011 – 2013, subject to receipt of the necessary approvals. The phasing of construction will be finalised when timing for commencement is confirmed.

Normal working hours will be between the hours of 7.00am to 7.00pm Monday and Friday and 7.00am to 4.00pm on Saturdays. Tunnelling operations will need to be undertaken on a continuous 24 hour, 7 days per week basis.

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The current 26 month construction programme includes a continuous 15 month tunnel drilling period. The proposed 24 hour drilling operation provides an opportunity to expedite the tunnelling works and consequently minimise the duration of the construction impacts on the local community and local environment. A reduced daily tunnelling operation could extend the project by a potential 15 - 20 months and in particular require the retention of the Aghoos Compound and operation for an extended period.

Sunday working (apart from tunnelling operations) will be avoided but may be necessary on some occasions. If working outside of normal hours is required, discussions will be held with Mayo County Council before operations begin and adequate notice will be given to the local community.

4.12 CONCLUSION

In summary, my Witness Statement covered the onshore pipeline construction and outlined the following:

• The Spread Technique to be used in Section 1: Glengad, between the LVI and the tunnel reception pit;

• The construction of site compounds including Stringing Area / Temporary Peat Storage Area; • The segment lined tunnel method to be used in Section 2: Sruwaddacon Bay Tunnel; • The Stone Road method to be used in peatland areas in Section 3: South of Sruwaddacon Bay

and in Section 4: Forested area to Bellanaboy Terminal; • The proposed pipeline testing and commissioning operations.

Little has changed since 2009 in respect of the proposed land based pipeline construction methodologies in Glengad, South of Sruwaddacon Bay and the forested area to Bellanaboy Gas Terminal. The well tested spread technique, together with the stone road approach, is again proposed for pipeline construction in these areas. As stated in 2009, these construction techniques are totally suitable for pipeline construction in these areas.

The proposed tunnel is a suitable trenchless technique for pipelaying in Sruwaddacon Bay. The desire to minimise disturbance to the Bay, requires the use of a trenchless technique and the scale is such that conventional pipe jacking could not be used. The tunnel process, whilst challenging, is widely and successfully used throughout the world, on a regular basis.. The presence of a rail system, in the completed tunnel greatly facilitates the insertion of the gas pipeline and associated services.

I am satisfied that the Corrib Onshore Gas Pipeline can be constructed using the methodologies, as outlined in my Brief of Evidence and as outlined in the EIS.

Inspector, this concludes my Brief of Evidence.

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Appendix A: Summary of Proposed Construction Methods

Table 1: Proposed Construction Methods along the Pipeline Route.

Location / Chainage Proposed Construction Method

Description in EIS

83.38 – 83.88 (Section 1 - Glengad) 83.44 – 83.49 Landfall Valve Installation

Spread technique Spread technique and general civil and mechanical construction.

Section 5.4 Dg0604

83.88 – 88.77 (Section 2 – Sruwaddacon Bay Tunnel)

83.88 – 83.91 Tunnelling construction compound SC2 and access pit L1 88.73 – 88.95 Tunnelling construction compound SC3 and access pit L2 88.95 – 300m South East Pipeline Stringing area

Segment Lining tunnelling method. Area to be prepared for Tunnelling construction equipment (reception site) Area to be prepared for Tunnelling construction equipment (Starting Pit) Area to be prepared for pipeline stringing

Section 5.5 Dg0401 Dg0402 Dg0403 Dg0404

88.77 – 89.21 (Section 3 – Section south of Sruwaddacon Bay)

Stone road method Section 5.4.5 Dg0601


Open cut with salt marsh turving. Spread technique

Section 5.4.9 Dg0604


Stone road method with turving where possible



Stone Road Method with Turving


89.54 – 91.72 (Section 4 – Forested area to Gas Terminal)

Stone road method. Section 5.4.5 Dg0601

Corrib Onshore Pipeline

Pipeline Construction

By Eamon Kelly

(An Bord Pleanála Application Reference No.: PL16.GA0004)

Proposed Construction Plan

Corrib Onshore Pipeline Oral Hearing: Pipeline Construction 1

Tunnel Compound, Stringing Area and Temporary Peat Storage Area in Aghoos


Tunnel Construction (Figure 5.7, Chapter 5, Onshore Pipeline EIS)


Set down area and site entrance


Palisade fencing with visual and acoustic screening


Temporary Peat Storage Area and surface water management system


Construct stone access road, peat handling area, wheel wash and SWM system


Complete construction of the tunnelling compound



Installation of tunnelling elements within compound

Construction of pipeline stringing area


Section 1


Section 2


Realignment of pipeline route at Site Compound in Glengad


Realignment of pipeline route at Site Compound in Aghoos


Section 3


Section 4


corrib onshore pipeline brief of evidence - construction by eamon · pdf file ·...

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