Rock socket grouting for Narec's Offshore Anemometry Hub (2013)

The metmast is installed three nautical miles off the coast of Blyth, Northumberland as part of the 99MW Blyth Offshore Wind Demonstration Site.

The 60-metre tall tripod foundation was designed to be secured to the sea floor using a typical pile sleeve connection, along with a grouted rock socket connection at each of its three legs, due to the rocky sea bed.

The grouting operations took place in two stages: The tripod was placed and the 16.5-meter deep rock socket was drilled through the tripod’s pile sleeve. FoundOcean mixed a grout that contained a special retarder to slow the curing rate. The retarder was added via a metered dosing system built into FoundOcean’s mixer. The grout mix was pumped into the socket via a flexible umbilical connected to a Stinger with assistance from an ROV. Immediately following this, the 24-meter long pile was lowered through the sleeve into the grout-filled rock socket. The remaining two rock socket connections followed the same procedure.

Once the rock socket connections were established, FoundOcean injected ordinary Portland cement (OPC) grout into the annuli between the piles and the tripod sleeves via connectors located 21.5m above sea level.

Grouting operations were completed within 12 hours over a weather window lasting six days.

At a Glance

  • Industry    Renewables
  • Region    North Sea
  • Services    Foundation grouting
  • Project year    2013
  • Operator    Narec
  • Contractor    SeaRoc
  • Water depth    37m
  • Cement type    CEM1 Type 52.5 and BASF Pozzolith 100XR
  • Total cement    188 tonnes
  • Mixer type    Recirculating Jet Mixer
  • Grout specification    60 MPa
  • Mixing rate    Up to 25 m3/hr

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