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NORTH BLYTH BIOMASS PROJECT THE · PDF fileTHE PROPOSED NORTH BLYTH BIOMASS POWER ... The sequence of works presented in this method statement is ... reinforced plastic outfall pipe

Aug 21, 2018

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  • NORTH BLYTH BIOMASS PROJECT THE PROPOSED NORTH BLYTH BIOMASS POWER STATION ORDER

    APFP Regulation: 5(2)(a)

    Document Title: Preliminary Outline Method Statement Outfall Structure (Appendix 4.3 of Environmental Statement) Date: February 2012 Author: Fairhurst Ltd Document Number: 6.2.9

    Document Ref: 02377-001225 Issue: 02

  • Revision History Document Title: Preliminary Outline Method Statement Outfall Structure (Appendix 4.3 of Environmental Statement) Revision Date Author

    01 February 2012 Fairhurst Ltd

    Document Ref: 02377-001225 Issue: 02

  • Preliminary Outline Method Statement Outfall Structure

    February 2012

    RES North Blyth Renewable Energy Plant D/I/D/81354/103

    Document Ref: 02377-001225 Issue: 02

  • North Blyth Renewable Energy Plant D/I/D/81354/103

    CONTROL SHEET

    CLIENT: RES

    PROJECT TITLE: North Blyth Renewable Energy Plant

    REPORT TITLE: Preliminary Outline Method Statement Outfall Structure

    PROJECT REFERENCE: 81354 Issue and Approval Schedule:

    ISSUE 1

    DRAFT Name Signature Date

    Prepared by A Lowes

    Reviewed by D Ladkin

    Approved by D Ladkin

    Revision Record:

    Issue Date Status Description By Chk App

    2 04/04/11 Information Minor Amendments AJL DL DL

    3 25/07/11 Information Minor Amendments ABSW AJL AJL

    4 26/07/11 Information Drawing Amended & Minor Text Amendments

    5 7/09/11 Information Minor Amendments

    6 2/02/12 Information Minor Amendments LT AJL AJL

    This report has been prepared in accordance with procedure OP/P02 of Fairhursts Quality Assurance System.

    Document Ref: 02377-001225 Issue: 02

  • North Blyth Renewable Energy Plant D/I/D/81354/103

    CONTENTS 1.0 INTRODUCTION ......................................................................................................... 1 2.0 LOCATION OF WORKS ............................................................................................. 1 3.0 FORM OF STRUCTURE ............................................................................................ 1 4.0 EXPECTED GEOTECHNICAL AND HYDROLOGICAL CONDITIONS ..................... 1 5.0 TECHNICAL CONSTRAINTS .................................................................................... 1 6.0 SEQUENCE OF CONSTRUCTION ............................................................................ 2 APPENDIX A DRAWINGS

    Document Ref: 02377-001225 Issue: 02

  • North Blyth Renewable Energy Plant D/I/D/81354/103

    Page 1 February 2012

    1.0 INTRODUCTION As part of the proposal to develop a Biomass Power Station at Battleship Wharf, Port of Blyth, it will be necessary to construct a cooling water system with an outfall to the North Sea. It will be located approximately 770m from Mean Low Water or 1050m from the site boundary as shown on Drawing 81354/SK007, Appendix A.

    This preliminary outline method statement discusses the potential methods and sequence of construction for this structure based upon outline design information supplied by SKM, available geotechnical and hydrological information for the area and constraints imposed by undertaking works in an offshore location. For directional drilling, advice was taken from specialist contractors LMR Drilling, Profile Drilling Services and AMS No-Dig as part of the preparation of this method statement and report D/I/D/81354/503 Cooling Water Options Study.

    This method statement has been prepared to discuss the technical procedures and sequence of works for the installation of the cooling water outfall. Health, safety and environmental requirements, design and construction quality assurance procedures, regulatory liaison and liaison with third parties are not included in this method statement.

    2.0 LOCATION OF WORKS The outfall structure will be located approximately 770m from Mean Low Water or 1050m from the site boundary at grid reference 432025 east, 583375 west. At low water the depth to the sea bed is approximately 8m.

    3.0 FORM OF STRUCTURE A preliminary arrangement of the likely form of the structure is shown drawings 81354/SK004 and 81354/SK008, Appendix A. To prevent oscillation in the currents and to allow access for maintenance, the outfall head will be secured to the seabed by a concrete slab secured to the rock by either rock bolts or anchors. This is the most likely method of construction.

    4.0 EXPECTED GEOTECHNICAL AND HYDROLOGICAL CONDITIONS It is expected that the geotechnical sequence on the sea bed will be thin sediment consisting of silt and sand overlying the Middle Coal Measures bedrock. It is expected that the sediments will be less than 1m thick and the rock type at rockhead will be sandstone.

    At lowest astronomical tide there will be approximately 8m of water over the location of the outfall. As such, taking into account the variation of water depth between Lowest Astronomical Tide and Mean High Water Springs, the water depth at this location will be 8m to 13m.

    5.0 TECHNICAL CONSTRAINTS To construct the intake the following technical challenges must be considered in the design of the temporary and permanent works and construction methodology.

    1. Construction of the outfall structure in 8m to 13m of water in currents.

    2. Utilising divers due to significant technical difficulties with forming a cofferdam in this area.

    3. Minimising the complexity of the works to be undertaken by divers.

    Document Ref: 02377-001225 Issue: 02

  • North Blyth Renewable Energy Plant D/I/D/81354/103

    Page 2 February 2012

    6.0 SEQUENCE OF CONSTRUCTION The sequence of construction outlined below is based upon minimising the tasks requiring the use of divers. Where possible prefabrication and carrying out operations from a jack up rig stationed over the outfall location has been included in the sequence of work.

    The works are to be coordinated with the construction of the outfall pipeline. The sequence of work is depicted on Drawing 81354/SK004, Appendix A. An indicative plan of the outfall structure steel template is shown on Drawing 81354/SK008, Appendix A. The sequence of works presented in this method statement is considered to be a worst case with respect to environmental impact.

    1. The exact specification of the jack up barge that will be used to carry out the works is not known at the time of writing, however a typical barge, used on similar sized projects, would be 15-18m square with four spud legs. The legs would be up to 25-35m in length and 760 - 1200mm diameter.

    2. Operational details cannot be confirmed at this stage however it is likely that the barge will only be required in one location and will be on site for two to three weeks.

    3. The spud legs will be lowered at the turn in tides to ensure that there is minimal disturbance of sediments and so that any sediments disturbed will fall back to the bed in the immediate vicinity of the legs.

    4. The directional drill head is recovered as it emerges from the sea floor. The glass reinforced plastic outfall pipe is drawn back through the liner and locked in position with the outfall end raised above the sea floor.

    5. Sediment is removed from the sea floor in the area where the outfall template is to be located. Sediments will be removed by a suction dredger or an air blower, controlled by a diver. Any collected sediment will be disposed of at a licensed facility and will not be discharged back to the sea floor.

    6. Rock anchors or bolts to secure the outfall template are fixed into the rock either from a jack up rig or by divers.

    7. A prefabricated steel template designed to act as formwork for the concrete infill and as the holding down bolt template for the diffuser head is lowered onto the rock anchors and secured by divers.

    8. Where the rock surface is irregular such that there are gaps between the rock and the underside of the template, the gaps shall be closed by placing concrete filled bagwork in them.

    9. Marine specification concrete shall be placed within the template using underwater concreting techniques including low pressure pumps and hose nozzle systems. Losses are expected to be minimal and at worst would create a haze around the nozzle.

    10. During its curing period the concrete will be protected by hessian mats, placed over the concrete, and secured to the sea bed. Setting of the concrete is expected within 1-2 hours, hardening within 12 hours, with full strength being reached within 28 days. The hessian mats will be removed after the initial set of the concrete, expected to be within 2 days of casting.

    Document Ref: 02377-001225 Issue: 02

  • North Blyth Renewable Energy Plant D/I/D/81354/103

    Page 3 February 2012

    11. After the concrete has cured sufficiently the end of the outfall pipe shall be trimmed as necessary and the diffuser heads fitted onto the cast in holding down bolts.

    12. Install marker pile at the location of the outfall which meets the requirements of marine navigation regulations. The marker pile will be set into a cored hole into the bedrock and the annulus between the side of the cored hole and the pile will be concreted with marine grade concrete with anti segregation admixtures. Lighting requirements will be specified by Trinity House.

    Details of the final equipment to be used and timescale for construction of the outfall will be determined during detailed engineering design for the works.

    Document Ref: 02377-001225 Issue: 02

  • North Blyth Renewable Energy Plant D/I/D/81354/103

    February 2011

    APPENDIX A DRAWINGS

    Document Ref: 02377-001225 Issue: 02

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