Permanent ground anchors are pre-stressed cement-grouted tendons used in soils or rock to restrain and control the displacements of structural elements such as walls or slabs. A ground anchor is essentially a vertical or lateral load-carrying element, developing a resisting force by stressing the soil around the anchorage length.
The screw anchor is a deep foundation member consisting of a steel shaft with helical plates welded to the shaft. They can be used to resist compression loads and are used as piles too. The use of anchors is widespread for both temporary and permanent work.
Typical anchor applications are to hold down slabs subjected to hydrostatic uplift, to increase the stability of a dam, or connected with guy wire to resist overturning of towers. Anchors are used because they are an economical way to provide resistance to vertical loads and are frequently far less expensive to install than the corresponding weight of concrete or to replace or rebuild the structure.
Screw anchors are installed into the soil using mechanical rotational force, and extensions are added to advance the assembly to achieve the desired tension or compressive force desired . Once installed, the anchor has bearing capacity in both tension and compression. For over 70 years, screw anchors have been used by the utility industry for power pole guying, transmission tower foundation underpinning and pipeline supports. Today, the general construction industry is discovering and using screw anchors for a much wider variety of applications including screw pile foundations