Ground Anchors

Ground anchors consist of a steel bar or tendon installed in a drill hole (typically 6 inches in diameter or less). Grout (a mixture of cement and water) is then pumped into the bottom of the drill hole until the drill hole is filled.  Ground anchor can also be constructed using helical pile systems and mechanical anchor systems.

Ground anchors go by many names such as rock anchors, tiedown anchors, tieback anchors, soil anchors, earth anchors, foundation anchors and micropiles. Regardless of the specific term used, ground anchors transfer load from a structure into the ground.  Although these terms are sometimes used interchangeably, the appropriate term often depends upon the context and the type of ground conditions. 

Rock anchors generally refer to any anchor drilled in rock and can be used in rockfall mitigation systems and in foundation systems.

  • Rockfall hazards are mitigated by securing unstable rock with rock anchors. Rock slopes or a rock face exposed from excavating may require rock anchors to maintain localized face stability or to mitigate the risk of larger rock wedge failures. 
  • Rock anchors may also be used as the foundation system of structures such as new communication towers or to augment the foundation of existing towers required as part of an overall structural retrofit. Rock anchor installation for tower foundations can require limited access drilling equipment and often occurs on remote mountain summits. 

Tiedown anchors refer to anchors used to resist the uplift of buoyant forces present in structures submerged below the groundwater table.  Buried storage tanks, pipelines, buildings with basements, even swimming pools, must all be designed to resist buoyant forces if the groundwater table submerges enough of the structure such that the buoyant force exceeds the weight of the structure.

Tiedown anchors can also be used in dams to increase the resistance to sliding or overturning failure.

Tieback anchors commonly refer to anchors used in earth retention systems and landslide mitigation systems.

Soil anchors or earth anchors often refer to anchors used in a soil nail and shotcrete earth retention system, but can also be any anchor that is founded in and achieves its capacity in soil. 

Micropiles refer to anchors used in a foundation application.  Micropiles may be in tension or compression, but its use implies there is at least a compression load.

Ground anchors may be post-tensioned (also termed pre-tensioned).  If ground anchors are not post-tensioned they are termed passive anchors.  Post-tensioned anchors are placed in tension using a hydraulic hollow ram and then locked off at a prescribed load.

Post-tensioned anchors reduce the deflection of the engineered system once under service load.  Post-tensioning:

  1. Elastically deforms the anchor, reducing elastic deformation once under service load.
  2. Allows inelastic ‘seating’ deformations within the engineered system and between the engineered system and the ground to occur, minimizing additional inelastic deformations once under service load.
  3. Provides lateral load counter to lateral earth loads in earth retention systems thereby reducing the net horizontal deflection.
  4. In rockfall and landslide mitigation systems post-tensioning increases the interface friction between rock joints or in any potential failure plane of a landslide mass. This increases the restive force to wedge failure and sliding failure and thereby increases the stability of the system.

Design and successful construction of ground anchor systems requires knowledge and understanding of the specific application and project location, and understanding the ground conditions and site access constraints, including overhead and underground utilities.  Selection of the appropriate equipment and drilling means and methods integral to success. 

Geo Craft Builders has expertise, developed over 20 years and includes projects of all sizes and access constraints in both urbanized areas and the most remote mountain summits.  If you would like more information about ground anchor systems, or have any questions regarding feasibility, constructability or pricing reach out to us at Geocraft Builders today. We look forward to working with you.

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