An earth anchor is a device designed to support structures, most commonly used in

geotechnical Geotechnical engineering, also known as geotechnics, is the branch of civil engineering concerned with the engineering behavior of earth materials. It uses the principles of soil mechanics and rock mechanics to solve its engineering problems. I ...

and

construction Construction are processes involved in delivering buildings, infrastructure, industrial facilities, and associated activities through to the end of their life. It typically starts with planning, financing, and design that continues until the a ...

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 wall Retaining walls are relatively rigid walls used for supporting soil laterally so that it can be retained at different levels on the two sides. Retaining walls are structures designed to restrain soil to a slope that it would not naturally keep to ...

guyed mast A guyed mast is a tall thin vertical structure that depends on guy lines (diagonal tensioned cables attached to the ground or a base) for stability. The mast itself has the compressive strength to support its own weight, but does not have the ...

s, and circus tents.

History

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. The town of Centralia holds an annual Anchor Day Festival.

Applications

Thabazimbi tower - Guy wire earth anchor - 001

Earth anchors are typically used in

civil engineering Civil engineering is a regulation and licensure in engineering, professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads ...

and

projects, and have a variety of applications, including: *

Retaining walls Retaining walls are relatively rigid walls used for supporting soil laterally so that it can be retained at different levels on the two sides. Retaining walls are structures designed to restrain soil to a slope that it would not naturally keep to ...

, as part of erosion control systems. * Structural support of temporary buildings and structures,Geotechnical Engineering Circular No. 4
retrieved 2012-07-09 such as

circus tent A circus is a company of performers who put on diverse entertainment shows that may include clowns, acrobats, trained animals, trapeze acts, musicians, dancers, hoopers, tightrope walkers, jugglers, magicians, ventriloquists, and unicycl ...

s and outdoor stages. * Tethering marine structures, such as floating docks and

pipelines A pipeline is a system of pipes for long-distance transportation of a liquid or gas, typically to a market area for consumption. The latest data from 2014 gives a total of slightly less than of pipeline in 120 countries around the world. The Un ...

. * Supporting

s, such as radio transmission towers. * Anchoring

utility pole A utility pole, commonly referred to as a transmission pole, telephone pole, telecommunication pole, power pole, hydro pole, telegraph pole, or telegraph post, is a column or post used to support overhead power lines and various other public util ...

s and similar structures. * Drainage systems, for loadlocking and restraining capability to happen simultaneously. * Landscape, anchoring trees, often semi-mature transplants. * General security, as in anchoring small aircraft. * Sporting activities, such as slacklining or

abseiling Abseiling ( ; ), also known as rappelling ( ; ), is the controlled descent of a steep slope, such as a rock face, by moving down a rope. When abseiling, the person descending controls their own movement down a static or fixed rope, in cont ...

Types

Deadman

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. 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

Once installed and load-locked, an earth anchor exerts effort to the soil above it, with the soil in turn providing resistance. Upward soil compression created by the anchor is typically exerted in a

frustum In geometry, a ; (: frusta or frustums) is the portion of a polyhedron, solid (normally a pyramid (geometry), pyramid or a cone (geometry), cone) that lies between two parallel planes cutting the solid. In the case of a pyramid, the base faces a ...

shaped cone, 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.

Installation

Site analysis Site analysis is a preliminary phase of architectural and urban design processes dedicated to the study of the climatic, geographical, historical, legal, and infrastructural context of a specific site. The result of this analytic process is a summ ...

determining soil load resistance is often required before earth anchor installation. Included are depth that the anchor is to be driven, and soil strength, moisture content, and corrosivity. 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. Earth anchors are commonly driven into the ground using a drive rod and impact hammer.

Pilot hole In construction, a pilot hole is a small hole Drilling, drilled into a piece of construction material. Its purpose may be: # to guide a larger drill to the appropriate location and ease the job of the larger drill, # allow the insertion of anothe ...

s 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

{{commonscat, Earth anchors Centralia, Missouri Geotechnical shoring structures