Earth anchor
An earth anchor is a device designed to support structures, most commonly used in geotechnical and construction applications. Also known as a ground anchor, percussion driven earth anchor or mechanical anchor, it may be impact driven into the ground or run in spirally, depending on its design and intended force-resistance characteristics.
Earth anchors are used in both temporary or permanent applications, including supporting retaining walls, guyed masts, and circus tents.
History
[edit]The first practical earth anchor was invented in 1912 by Albert Bishop Chance in Centralia, Missouri, in response to an ice storm that knocked down his company’s telephone poles.[1] The town of Centralia holds an annual Anchor Day Festival.[2]
Applications
[edit]
Earth anchors are typically used in civil engineering and construction projects, and have a variety of applications, including:
- Retaining walls, as part of erosion control systems.[3]
- Structural support of temporary buildings and structures,[4] such as circus tents and outdoor stages.
- Tethering marine structures, such as floating docks and pipelines.
- Supporting guyed masts, such as radio transmission towers.
- Anchoring utility poles and similar structures.
- Drainage systems, for loadlocking and restraining capability to happen simultaneously.[clarification needed][5]
- Landscape, anchoring trees, often semi-mature transplants.[6]
- General security, as in anchoring small aircraft.
- Sporting activities, such as slacklining or abseiling.
Types
[edit]Deadman
[edit]A deadman is one of the simplest ground anchors in terms of equipment needed, and is suitable for light loads or temporary installations. It is a horizontal beam, such as a log or steel girder, or concrete block placed crosswise to the load and buried in a hole in the ground. It can be constructed with as little as a tree branch, adequate rope and adequate digging.[7]
A deadman may also be placed on the surface, held in place by a number of picket stakes. This allows a greater load to be taken than a single row of pickets.
Performance
[edit]Once installed and load-locked, an earth anchor exerts effort to the soil above it, with the soil in turn providing resistance.[8] Upward soil compression created by the anchor is typically exerted in a frustum shaped cone,[9] reflecting:
- The shear angle of the soil
- The depth at which the anchor has been installed
- The load applied to the anchor
- The size of the anchor and size and angle of its lateral surfaces
When angled these lateral surfaces generate greater cone-shaped soil resistance than a simple cylinder created by purely perpendicular design.[10]
Installation
[edit]Site analysis determining soil load resistance is often required before earth anchor installation.[11] Included are depth that the anchor is to be driven, and soil strength, moisture content, and corrosivity.[12] When appropriate, test installations are done to determine optimal anchor design or conformance with project specifications.
Installation methods differ depending on soil composition and moisture.[11] Earth anchors are commonly driven into the ground using a drive rod and impact hammer. Pilot holes are required in denser soils. After an impact driven anchor has been installed, the drive rod is removed and the anchor load-locked, typically by rotating it ninety degrees. For lighter anchors a hand tool is often sufficient.
References
[edit]- ^ "Ground Anchors – The History". 30 March 2017.
- ^ "Annual Anchor Festival". Archived from the original on 2020-09-26. Retrieved 2019-07-23.
- ^ [1]Archived 2012-08-21 at the Wayback Machine Core Applications, retrieved 2012-07-09
- ^ Geotechnical Engineering Circular No. 4 retrieved 2012-07-09
- ^ [2] Archived 2012-08-21 at the Wayback Machine Platipus Anchors, retrieved 2012-07-09
- ^ Patent 2765764 Summary
- ^ "6: Rigging" (PDF). Steelworker, vol 2. US Navy. p. 6-26. NAVEDTRA No: 14251 – via GlobalSecurity.org.
- ^ "Helical Anchors - A complete guide".
- ^ "How A Mechanical Anchor Works". Archived from the original on 2012-08-21. Retrieved 2012-07-16.
- ^ "Canadian Intellectual Property Office: Patent 2175673 Summary".
- ^ a b "An Earth Anchor System: Installation and Design Guide" (PDF).
- ^ "Ground Anchor Practice in New Zealand - A Review of Applications, Design and Execution" (PDF). Archived from the original (PDF) on 2012-07-11. Retrieved 2012-07-16.
