Offshore Construction

LBM UHPC offshore construction abilities to enhance infrastructure.

Monopile wind turbine designs are still the most widely used standard foundation design in many coastal areas. Jackets, Gravity base, Tripods, and Tri-piles systems are also used depending on requirements and need. UHPC grout is used in all foundation techniques.

LBM UHPC Grouting material is used for the connection between monopile and transition pieces. Monopiles have been deployed with even larger turbines in even deeper waters. Today monopile systems are in production with a weight of 1200 tons, a diameter of 9 meters, and a length of 81 meters. Such systems are rammed approx. 40 meters deep into the seabed.

Transition pieces

Using LBM UHPC Grouting material for offshore grouting of a transition piece to a monopile makes it simple to adjust the tower vertically in the event of indignation in the monopile. More than 2000 transition pieces have now been successfully cast worldwide with UHPC Grouting materials. Transition pieces can have a weight of up to 350 tons.

The next generation of LBM UHPC Grouting materials is currently under development.

LBM UHPC Grouting benefits for transition pieces:

  •    Extremely high strength

  •    Excellent fatigue properties

  •    Minimal to no shrinkage

  •    Extreme bond between UHPC Grouting material and steel

  •    Fast setting development

  •    Very high inner cohesion

  •    No mixing with saltwater

  •    Very low hydration heat

  •    No corrosion

 Working steps:

  •    Monopiles are driven into the seabed

  •    The transition piece are installed – lifted – leveled

  •    Mixing and pumping of LBM UHPC Grouting material offshore in the annulus between transition piece and pile for connection

  •    Erection of the turbine

Technical description of the UHPC grouted connection (Transition piece):

  • The height of the grouted connection is 1,5x monopile outside diameter

  •  The standard LBM UHPC Grout has a compressive strength of 210 MPa / 30500 PSI

  • The grouting is done underwater, which means 100% humidity

  • The thickness of the gap is 70 – 125 mm

  • The connection is without shear keys

Tripile
A tripile foundation consists of three steel piles driven into the seabed after which a three-legged transition piece structure is slid into the three piles. The overlaps between piles and transition pieces are grouted with LBM UHPC. The UHPC connections evenly distribute the forces from the three-legged transition piece to the piles.

Tripod
A tripod support structure/foundation is secured in place by driving three piles into the seabed through a sleeve in each of the three corners. LBM UHPC is pumped into the annuli between pile and sleeve to ensure a strong and durable connection.

Jacket
Jacket foundations are secured to the seabed by four piles placed in a sleeve in each corner and driven into the seabed. Jackets are generally considered to be better than monopiles for seabeds where the substrate is poor or in deeper water. So here UHPC grouting can be used in the “transition piece” and in the lower foundation.

Gravity foundations
Are well suited for rocky sea beds. The complete foundation system can be manufactured on land and then pulled into position with a ship and then sunk. Depending on the design, the entire foundation piece can be made from UHPC. LBM UHPC Grouting will be perfect for slip casting the entire foundation.

The future innovative designs include:

 – Suction caissons mono-tower
 – Application of screw piles
 – Floating structures 
      Spars
      Semi-submersible
      Barge
      Tension-leg platform

Spars
First systems are already being tested. In the near future, a wind farm with spar systems is being built off the coast of Scotland. These systems can reach total lengths of over 90 meters, with about 75 meters of them underwater. The entire underwater area can be made of UHPC.
LBM UHPC grouting materials are particularly well suited for this type of foundation, which gives them extremely high strength and saltwater resistance. There is no corrosion, so the pendulum foundations made of LBM UHPC are almost free of maintenance.

Semi-submersible
Similar to the Spars, the whole underwater construction can be made of LBM UHPC.

Barge
Barge systems are actually classic pontoon systems. There is now UHPC available which in addition to its high strength also swims without the large cavities inside the barge that must be generated.

The main arguments for floating systems are:

  • Access to useful areas that are in deep water yet often near shore.
  • Potential for standard equipment
  • Easier installation

One of the future key aspects is the build-up of scale and speed in production in order to achieve cost reduction.

LBM UHPC Grout

LBM UHPC Grouting is a pumpable UHPC grouting material specially developed for any offshore grouting jobs like offshore foundation or offshore corrosion protection.

Benefits:

  • Extremely low shrinkage
  • Strong bondage to any metal construction
  • Absolute saltwater resistantance
  • Low hydration heat
  • Extreme high strength development
  • Fast curing
  • Fast strength gain
  • Easy and simple to pump
  • Pumping of several hundred meters possible

Gravity based structures (GBS)

LBM UHPC grouting materials are pumpable and developed for offshore gravity-based structures and have been used widely in connection with the structural strengthening of offshore platforms. The LBM UHPC gravity-based structures are an interesting concept for shallow water oil and gas development.

LBM UHPC concrete gravity-based structure can be used as an LNG terminal to be oriented to shelter the carriers from dominant sea directions. Fixed to the seabed they offer a stable platform for storage and regasification of LNG.

 Advantages

  • Build onshore site
  • Ease of transportation
  • Low weight construction by using LBM UHPC
  • International requirements Compressive strength min. 40 MPa and water/cement ratio 0,45 – 0,4
  • UHPC Compressive strength min. 130 MPa and water/cement ratio of 0,2

LBM UHPC grouting materials have been used offshore in connection with:

  •    Strengthening of intact tubular members

  •    Reinforcement of joints

  •    Repair of damaged members

  •    Pile-sleeve connections

  •    Strengthening of double skin sections

  •    Platform designs

  •    Underwater operation

  •    Caisson construction

LBM UHPC grouting material was used as grout material instead of the intended conventional grout. In the above-selected cases, the design strength of the members was re-established due to the extreme effect offered by high strength materials and at the same time, the solutions were economically attractive.

LBM UHPC grouting materials are suitable for casting both above and below water. Due to the viscous consistency of the mixed materials, there is no risk of washing out cementitious particles or mixing with water when cast below sea level.

LBM UHPC grouting materials for offshore have been developed having very low shrinkage so that the grout and surrounding steel remains in physical contact after curing. These products have been developed to show limited heat development during the hardening process eliminating the risk of thermal cracking.

Structurally, the LBM UHPC is extremely robust and requires no to extremely low maintenance for a 100+ year lifetime. Building it does not require sophisticated technical know-how.

"It is only impossible if you have not tried it"

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