Great Yarmouth Flood Alleviation Scheme | Keller United Kingdom

Great Yarmouth Flood Alleviation Scheme

Following a series of flooding incidents since the 1953 Great Storm in which numerous lives were lost Great Yarmouth‘s flood protection is being upgraded significantly. As part of this project Keller Geotechnique were awarded the sub-contract to install and test both the Preliminary Trial Anchors for Walls 91-95 and the Main Wall Permanent Anchors for Wall 91-92.

Previous Site Investigation boreholes had indicated that suitable founding strata, in this area of Great Yarmouth, was at considerable depth  (in excess of 15-20m) and of marginal quality for the anchor loads (c. 800kN Axial SWL) under consideration; even for Keller‘s patented SBMA (Single Bore Multiple Anchor) system.

  • Four Vertical Trial Anchors were installed at intervals behind Walls 91—95.
  • Drilled depths ranged from 26—31m using a 133/76 rotary-percussive water flush drilling system.
  • Trial tendon comprised 5 SBMA units each of 2 No. 18mm Dyform prestressing strands - Ultimate Tendon Test Capacity = 3040kN
  • Anchor Grout—neat CEM1 (52.5N) in a 0.45 w/c ratio.
  • Cyclic Trial Testing (to BS 8081) mobilised ultimate grout/ground bond stresses (failure) for the majority of the SBMA units allowing back calculation of working SBMA units capacities and lengths to suit the design requirement for an Axial SWL of 804kN at an average declination of 300.
  • The drilled length required to reach the founding strata plus the SBMA overall fixed length of 21.0m resulted in installation lengths of 58 to 62m from Entry Level. These are some of the longest anchors ever installed in the UK.
  • These drilled lengths were considered to be at the limit of standard practice for a fully cased and end-of-casing pressure grouted drilling system but 2 successful drilled and grouted (no tendon) probe holes were drilled by conventional crawler rig (M9) as part of the Trial Works.
  • Working anchor installation was carried out over the River Yare using 2 specially adapted CAT 315 excavators and drill masts fitted out and assembled by Keller in their Coventry Depot.
  • These rigs, in conjunction with a robust, over water working platform designed and provided by Interserve, have achieved a commendable installation rate on an extremely challenging project.
  • Installed Working Anchor requirements are summarised:
    • Axial SWL 754kN
    • Declination 27.7/32.5° alternate
    • Spacing 1.45m avg.
    • Installed Length 58.0/64.0m alternate
    • SBMA configuration 6 units each of 1 no. 15.2mm Dyform strand

System : Permanent SBMA Ground Anchors

Client: Environment Agency

Contractor: Interserve Construction Ltd.

Engineer: CH2M HILL

Year of execution:2014

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