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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. They can be used in either temporary or permanent applications. Typical uses for earth anchors include for supporting retaining walls and for prop protection structures.

Earth pressure

Earth pressure is the pressure that soil exerts against a structure in a sideways, mainly horizontal (lateral) direction. The common applications of lateral earth pressure theory are for the design of ground engineering structures such as retaining walls, basements, tunnels, and to determine the friction on the sides of deep foundations. To describe the pressure a soil will exert, an earth pressure coefficient, K, is used. K is a function of the soil properties and has a horizontal component Kh and a smaller vertical component Kv. Kh has a value between 0 (completely solid) and 1 (completely liquid). Horizontal earth pressure is assumed to be directly proportional to the vertical pressure at any given point in the soil profile. K can also depend on the stress history of the soil. Lateral earth pressure coefficients are broken up into three categories: at-rest, active, and passive.

Earth pressure cells

Earth Pressure Cells (often known as Total Pressure Cells) measure total stresses in soils which is the combination of effective stress and pore-water pressures. They are normally used to validate design assumptions and to give adequate warning of soil pressures in excess of those designed to be exerted by a structure.

Earthfill dams

Earth-fill dams are constructed as a simple embankment of well compacted earth. A homogeneous rolled-earth dam is entirely constructed of one type of material but may contain a drain layer to collect seep water. A zoned-earth dam has distinct parts or zones of dissimilar material, typically a locally plentiful shell with a watertight clay core. Modern zoned-earth embankments employ filter and drain zones to collect and remove seep water and preserve the integrity of the downstream shell zone.

Eccentric loading

A load imposed on a structural member at some point other than the centroid of the section and typically experienced with anchor load cell applications and is minimised by having multi sensor s within the load cell and by ensuring good quality load distribution and bearing plates are used. A load on a column or pile which is non-symmetric with respect to the central axis, therefore producing a bending moment which can be monitored by strain gauges, sister bars, inclinometer.

Effective stress

All soils are under pressure, be it under their own or an added load being applied on the soil (termed to be total stress (σ)). Due to water being present in soils, the water also puts its own load on soils. This is termed to be pore water pressure (u). Having total stress (σ) and pore water pressure (u) allows the calculation of the effective stress (σ’), which is the pressure that is on the soil particles that are in contact with each other. Total Stress – Pore water pressure = Effective Stress σ – u = σ’ Total stress (σ) Pore water pressure (u) Effective stress (σ’)

Electrolevel Sensor

The Electrolevel sensor consists of an electrolytic tilt sensor. The tilt sensor is a precision bubble-level that is sensed electrically as a resistance bridge. The bridge circuit outputs a voltage proportional to the tilt of the sensor. The effects of temperature change can be significant and have more or less been superseded by MEMS Tilt Sensors.


An embankment usually refers to an earthen structure that is used to raise the elevation of a roadway or railway above the elevation of the surrounding area. Embankments are typically built by compacting earthen materials in place, so the compaction properties of the soil (optimum water content and maximum dry density) are very important to performance. The compressibility and shear strength are also important measures of the compacted material. In addition, drainage is an important consideration to prevent the loss of shear strength due to saturation. Whether embankments are constructed on soft or hard ground is very significant. On soft soils the behaviour is dominated by the properties of the soft ground and monitoring the progress of consolidation and stability. Whereas on hard ground the main concern is arc rotation along the slip plane.

Embankment dams

General term used for earthfill dams of various types, rockfill with impervious cores or with impervious upstream concrete or asphaltic concrete facing.

Embedment strain gauge – vibrating wire

Used for measuring strain in concrete structures and is suitable for direct burial. Also used in pile tests, load bearing concrete beams and columns, tunnel segments and concrete foundations.

EMC (electro magnetic compatibility)

Electromagnetic compatibility (EMC) is the branch of electrical sciences which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects (electromagnetic interference, or EMI) that such energy may induce. EMC aims to ensure that equipment items or systems will not interfere with or prevent each other's correct operation through spurious emission and absorption of EMI. EMC is sometimes referred to as EMI Control, and in practice EMC and EMI are frequently referred to as a combined term "EMC/EMI". Instruments should be designed and special cables used to eliminate effects of EMC. See CE marking.

Engineered fill

Soils used as fill, such as retaining wall backfill, foundation support, dams, slopes, etc. that are to be placed in accordance to engineered specifications. These specifications may delineate soil grain-size, plasticity, moisture, compaction, angularity, and many other index properties depending on the application

Engineering properties

Engineering parameters of a soil such as permeability, shear strength and consolidation.

Engineering units

The term used for the conversion of instrument output such as volts, milliamps, frequency into a unit of measurement such as pressure, load, strain, tilt etc


The difference between a computed or measured value and a true or theoretically correct value. Instrument error - the combined accuracy and precision of a measuring instrument, or the difference between the actual value and the value indicated by the instrument (error). Other errors that occur within geotechnical instrumentation are:- Gross error - mistakes that make the measurement very far off of the known/accepted value. Typical causes are misreading, misrecording, computational error. Systematic error - errors due to the limitations or characteristics of the equipment such as hysteresis, non-linearity, incorrect calibration. Every instrument has an element of systematic error. Environmental error – caused by the influence of pressure, temperature, humidity, vibration etc. Correction factors can be applied such as temperature and barometric compensation to negate this error or instruments chosen which are not adversely affected by environmental factors. Observational error – where different people take readings using different techniques. Using automatic data acquisition systems eliminates this error. Sampling error – insufficient amount of monitoring points within inherent variable materials leads to sampling errors and are minimised by installing a sufficient amount of instruments at representative locations.

Excess pore pressure

That increment of pore water pressures greater than hydro-static values, produced by consolidation stresses in compressible materials or by shear strain; excess pore pressure is dissipated during consolidation.

Extensometer anchor – groutable

Extensometer anchors are located in zones of interest as far as movement are concerned and the groutable type consists of a short length of re-bar into which the inner rod and outer sleeve are attached. They are the preferred type for vertical installations although they can be used in horizontal and inclined installations. Grouting of the borehole can be done either by passing the grout tube through the reference head to the base of the borehole or by running the tube outside the head in the annulus of the borehole to the base of the borehole.

Extensometer anchor – hydraulic (Borros)

Hydraulic Borros anchors are located in zones of interest as far as movement are concerned and the hydraulic type consists of a short body which houses a hydraulic piston and 3 internal prongs. The piston is put under pressure using a surface mounted pump which forces the inner rods out from the base and into the surrounding soil. The inner rod and outer sleeve are attached to the top of the anchor body. Hydraulic anchors are used primarily in clay soils.

Extensometer anchor – packer

Extensometer anchors are located in zones of interest as far as movement are concerned and the packer type consists of an inner steel sleeve which is covered by a geotextile sock attached at both ends. A cement grout (approx. 1:1 cement to water ) is pumped into the annulus between the packer body and the geotextile sleeve which expands and as the cement grout dries it is anchored to the wall of the borehole.

Extensometer anchor – Snap-ring

Snap-Ring Anchors are quickly are used predominantly hard or competent rock and are particularly useful in upward directed boreholes although a precise borehole is required with a tolerance of ± 1mm. The anchors are pushed to the required depth on the end of setting rods and then a cord is pulled to remove the locking pin which allows two retaining rings on each anchor to snap outward and grip the borehole. Up to eight anchors can be installed, at various depths, in a 76 mm diameter borehole.

Extensometer rod sleeve – flexible

Continuous flexible outer sleeve used with the flexible rod to enable factory pre-coiling.

Extension rod

A rod to connect various instruments or parts of instrument clusters. Examples are In-place inclinometers, slip indicators, extensometers, convergence monitors

Extensometer rod – flexible

A continuous length of fibre glass rod which allows extensometers to be pre-coiled in the factory and quickly installed into the borehole.

Extensometer rod – rigid

Rigid extensometer rods are used to connect the anchor to the reference head. Usually made from stainless steel rigid rods are connected using a flush thread to allow them to move inside an outer sleeve. Available in 1, 2 and 3m lengths.

Extensometer rod sleeve – rigid

The outer sleeve of a rod extensometer allows the inner rod to be “de-bonded” to the surrounding ground and allow free movement. Normally made from rigid PVC they are connected using a flush glued push together fitting.

Extensometer – rod type

Rod type extensometers are used to measure and locate settlement, displacement and deformation in soil and rock. It consists of a reference head and one or more in-hole anchors each of which is placed at a known depth and connected to the reference head by either a rigid or flexible rod running inside a sleeve which keeps the rod de-bonded from the grout. They are usually installed within boreholes and can be manual, automatic or a combination of both with the addition of vibrating wire or liner potentiometer displacement transducers. As the soil or rock deforms the distances between the in-hole anchors change as do the distances between the individual in-hole anchors and the reference head. The magnitude, distribution, rate and acceleration of deformation can be accurately measured at the reference head.

Expansive clays

Also, Reactive Clays. Clays that are sensitive to water, causing them to swell or expand.