Earth anchor
An earth anchor is a device that is designed to support structures and is used in geotechnical and construction applications. It can also be referred to as a ground anchor, percussion driven earth anchor or mechanical anchor.
Earth anchors can be used in either temporary or permanent applications. Typical uses for earth anchors include for supporting retaining walls and for crop protection structures.
Typical applications
Typically used within civil engineering and construction projects, earth anchors are used in a variety of applications:
- Earth anchors have had much use in the retaining of slopes. Typically, earth anchors have been used in this context to prevent deep seated failures, as well as a form of erosion control.[1]
- Another typical usage of Earth Anchors is the structural support of Temporary Buildings and Structures.[2] Such structures include circus tents and outdoor stages.
- Although unrelated to the typical boat anchor, earth anchors have also been used within marine applications. These applications include structural support for floating docks and pipelines.
- Another usage of ground anchors has been in the support of guyed structures.
- Earth anchors have also been used for general security, for example, in the anchoring of small aircraft.
- One more commonly seen usage of mechanical earth anchors is within utility systems. Earth anchors are typically used for the anchoring of utility poles.
- Some anchor systems have now been combined with drainage solutions. This allows for loadlocking and restraining capability to happen simultaneously.[3]
- Earth anchors have also had great success in the anchoring of trees. This anchoring is typically used when a semi-mature tree is transplanted to a different site. Earth anchors have popularity for being used in this area as anchoring trees by using this method removes the need for unsightly guy wires and tree stakes.[4]
Installation
Before installing an earth anchor, site analysis has to be done at the site of installation.[5] This analysis is done so that it can be determined what loading capacity is required of the earth anchors. This site analysis needs to include the depth that the earth anchor is driven into, the soil strength and the moisture content of the soil. The site analysis also needs to measure the corrosivity of the soil, so that a suitable anchor material can be picked which matches the design life of the project.[6]
Earth anchors normally have a drive rod attached. The earth anchor is driven into the ground, typically with an impact hammer. However, this installation method may differ depending on the composition of the soil that the anchor is being inserted into.[5] In more dense soils, a pilot hole is drilled into the earth. Typically, anchors are inserted into the soil and used for testing before the final anchor design is decided on. After an anchor has been installed, the drive rod is removed and the anchor is load-locked. For lighter anchors, this is typically done by a hand tool. The angle of the wings on the anchor allow for increase of frustum pressure on the soil. Normally, earth anchors are designed to rotate ninety degrees during this load-locking process.
How earth anchors work
Once load-locked, the earth anchor exerts effort to the soil above the anchor. This pressure is in a conical shape,[7] with the size and angle of this conical shape depending on factors including:
- The shear angle of the soil.
- The depth at which the earth anchor has been installed.
- The load applied to the earth anchor.
- The size of the earth anchor.
This conical compression of the soil creates resistance to any further movement of the anchor.[8] The shape of Earth Anchors are typically designed to provide as much frustum shaped pressure as possible, and this is typically achieved with the usage of large surface areas and trailing edges around the anchor.[9]
References
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