Uplift Anchors

Various types of vertical uplift resisting anchors exist:

  • Deadweight anchors
  • Propellant actuated anchors
  • Vibrated direct embedment anchors
  • Screw-in anchors
  • Driven anchors
  • Drilled anchors
  • Deadweight Anchors

    Deadweight anchors are the oldest means of anchoring. They are the cheapest type of anchorage to achieve, however, they are inefficient and unpredictable. In sloping seafloors they tend to slide down or may be easily displaced by lateral forces. They can be used in conjunction with conventional anchors to resist the lateral loads imposed but this is an inefficient and crude solution. Deadweight anchors have distinct advantages in that they are simple to construct, economical and can be made readily available. They can be used in most seabed conditions excluding steeply sloping seafloors. Their uplift resistance can be precisely predicted and their installation is relatively simple. A major disadvantage of deadweight anchors is that their holding-capacity to weight ratio is low and they become increasingly impracticable as holding capacity requirements increase.

    Propellant Actuated Anchors

    Anchorages are achieved by mechanically firing the anchoring component into the seabed. They have a wide range of holding capacity (4. 5kN to 980 kN) and are suitable for water depths of up to 180 m. Can be used in varying seabed conditions but cannot be guaranteed in rock.

    Vibrated Embedment Anchors

    The anchoring component is vibrated by mechanical means. They are intended for deep-water use (>180 m) but are limited to use in sediments.

    Screw-in Anchors

    The anchoring component is screwed into the seabed by mechanical manipulation. As a result the operation is only suited to shallow-water use and for sediment conditions.

    Driven Anchors

    These anchors are hammered into the seabed by means similar to percussion piling. Air hammers can only operate in shallow waters (<100 m) and underwater hammers can only operate in depths less than 300 m.

    Drilled Anchors

    Drilled Anchors are suitable for use in rock and coral. Drilled anchorages are achieved by drilling a hole in the rock and grouting in the anchoring component. Drilled anchors are the only assured type of anchorage in rock conditions. They can be pull-tested following deployment to confirm their load bearing capacity. They can be used in depths of over 180m but are expensive to install.