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

geotechnical Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. It uses the principles of soil mechanics and rock mechanics for the solution of its respective engineering problems. It al ...

and

construction Construction is a general term meaning the art and science to form objects, systems, or organizations,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and ...

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 ...

s, guyed masts, 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 professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads, bridges, canals, dams, airports, sewa ...

and

projects, and have a variety of applications, including: * Retaining walls, 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 tents and outdoor stages. * Tethering marine structures, such as floating docks and pipelines. * Supporting guyed masts, such as radio transmission towers. * Anchoring

utility pole A utility pole is a column or post typically made out of wood used to support overhead power lines and various other public utilities, such as electrical cable, fiber optic cable, and related equipment such as transformers and street lights. I ...

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 A light aircraft is an aircraft that has a maximum gross takeoff weight of or less.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 308. Aviation Supplies & Academics, 1997. Light aircraft are used as utility aircraft c ...

. * 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 the rope, in contrast to low ...

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 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 sum ...

determining soil

load resistance The input impedance of an electrical network is the measure of the opposition to current ( impedance), both static ( resistance) and dynamic ( reactance), into the load network that is ''external'' to the electrical source. The input admittance (the ...

is often required before earth anchor installation. Included are depth that the anchor is to be driven, and soil strength, moisture content, and

corrosivity Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

. 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 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

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