+44 (0)1359 270457

Support

Go to MGS website

A axis

Inclinometer

A axis = the direction of the anticipated movement.

A+ = the orientation of the casing groove into which the leading wheel of the inclinometer probe is located on the first run of a set of readings. This is also the orientation of the primary sensor.

A- = the orientation of the casing groove into which the leading wheel of the inclinometer probe is located on the second run of a set of readings. This is also the orientation of the primary sensor.

B+ = the orientation of the secondary sensor during the first run of a set of readings.

B- = the orientation of the secondary sensor during the second run of a set of readings.

Abutment plate

Used with anchor load cells. A thick steel plate (at least the same thickness as the load distribution plate and 20mm larger in diameter than the load cell) which sits between the load cell and/or load cell distribution plate and the wall where the anchor is being installed. This is normally produced locally to suit site requirements.

ABS (Acrylonitrile butadiene styrene)

The plastic most preferred for the manufacture of inclinometer casing. The most important mechanical properties of ABS are its ability to maintain consistency of dimensions during processing. In addition it is resistant to wear from the inclinometer probe wheels, which means that data integrity is maximised.

Access tubing

A tube which is installed within ground or a structure to allow access to a remote measurement point. Typical examples are:- • Inclinometer casing (with internal keyways) • Extensometer tubing (with external magnetic or inductive targets) Typically they have flush connections to allow the targets to move along the outside.

Accuracy

The accuracy of a measurement is the degree of closeness of the measurement of a quantity to that quantity's actual (true) value. It is measured for instruments by means of calibration against another instrument whose accuracy is ideally verified and traceable to an acceptable international standard e.g. UKAS. Within the geotechnical and structural monitoring industry it is standard practice to define accuracy by both Linearity and Polynomial factors, the latter of which is determined mathematically by a least squares regression analysis.

Typically accuracy is expressed in one of the following ways

  1. ± number - means that the measured value is within ± number of the true value
  2. ± percentage - means that the measured value is within ± % of the true value
  3. ± % full scale - means that the measured value is within ± % FS of the full scale

Active earth pressure

The minimum value of earth pressure which exists when a soil mass is permitted to yield sufficiently to cause its internal shearing resistance along a potential failure surface to be completely mobilised.

Active (Rankine) zone

The area behind a retaining structure that is above the failure plane.

Adhesion

The shear resistance between soil and a structure (e.g. steel, concrete or timber piles; along a retaining wall).

Air entry value

Term used for filter types particularly associated with piezometers. There are two types HAE (High air entry) and LAE (Low air entry). This often causes confusion as the HAE actually means “high RESISTANCE to air entry” and LAE means “low RESISTANCE to air entry”.

HAE filters are normally ceramic with a 1 micron pore size and are used in low permeability media. Since the surface tension of the water in the very fine pores of the filter prevents entry of air it is important that they are saturated before installation. All Geosense HAE piezometers are shipped pre-saturated with a special sheath to prevent them drying out.

LAE filters are typically used in non-cohesive and highly permeable media. Whilst they do not need to be saturated prior to installation, it is good practice to do so.

Anchor - ground

Ground anchor is a collective term for strand and bar anchors. The type of anchor depends on whether it is for rock or soil, for temporary or permanent use, whether or not it is tensioned and whether or not permanent corrosion protection is required.

Typical examples of ground anchors are:

  • Strand - a type of ground anchor used for a wide variety of geotechnical applications including but not limited to temporary and permanent applications such as tunnels, excavations, retaining walls and buried structures. They are made from multiple wire strands of varying diameter and quantity corresponding to various load capacities. They can be stressed or unstressed.

  • Bar - (often known as rod) anchors are a type of ground anchor which can be used as soil nails, rock bolts, micro piles, tie-down and tie-backs for a wide variety of geotechnical applications including but not limited to temporary and permanent applications such as tunnels, excavations, retaining walls and buried structures. They are made from solid, hollow or thread bar of varying grades, diameter corresponding to various loads. They can be pre-stressed.

Anchor - instrument

A mechanism to connect a measuring point on or in a substrate to an instrument. Typical examples of instrument anchors are:- • Groutable anchor for rod extensometers - used with grout to establish a connection between the end of a rod and the borehole wall • Hydraulic Borros anchor for rod extensometers - used to mechanically connect rod to borehole wall • Packer anchor for rod extensometers – used to create a grouted connection at a specific point within a borehole. • Mechanical Borros anchor – used to connect a deep datum to the substrata • Boltable anchor – to allow connection of an instrument to the substrate to be monitored using bolts and inserts • Bondable anchor – to allow connection of an instrument to the substrate to be monitored using epoxy resin

Anchor load cell - hydraulic (Bourdon gauge)

Used for the measurement and control of tensile loads particularly for ground anchors, tendons, and rock bolts. It consists of a sensitive pressure pad formed by joining two stiff steel discs at their periphery. The void inside the cell is filled with de-aired fluid. When load is applied to the cell the pressure of the inside liquid changes. The changes in pressure correspond directly to the load applied and are measured in Kg using a simple Bourdon gauge.

Anchor load cell - hydraulic (vibrating wire)

Used for the measurement and control of tensile loads particularly for ground anchors, tendons and rock bolts. It consists of a sensitive pressure pad formed by joining two stiff steel discs at their periphery. The void inside the cell is filled with de-aired fluid. When load is applied to the cell the pressure of the inside liquid changes. The changes in pressure correspond directly to the load applied and are measured by a vibrating wire pressure transducer.

Anchor load cell - strain gauge

Used for the measurement and control of tensile loads particularly for ground anchors, tendons and rock bolts. It consists of a hollow cylinder of high strength steel and a series of electrical resistance strain gauges connected around the periphery as a Wheatstone Bridge and provides a single mV/V signal output.

Anchor load cell – vibrating wire

Used for the measurement and control of tensile loads particularly for ground anchors, tendons and rock bolts. Load is measured using multiple vibrating wire strain gauges mounted around the periphery of the cell body. This arrangement can be used to identify any eccentric loading.

Angle of internal friction

For a given soil, the angle on the graph of the shear stress and normal effective stresses at which shear failure occurs.

Angle of repose

The maximum angle, just before failure, of a slope composed of granular material.

Angle of shearing resistance

The ratio of effective shear and normal stresses mobilized at any state prior to failure.

Angle of slip plane

The angle referred to horizontal of a plane or other surface along which a discontinuous slip or rupture may occur.

Aquifer

A stratum of soil with relatively high permeability; a water-bearing stratum of rock or soil.

Arc second

An arc second or a second of arc or is one sixtieth (1⁄60) of one arc minute. Since one degree is defined as one three hundred and sixtieth (1⁄360) of a rotation, one minute of arc is 1⁄21,600 of a rotation.

Unit

Value  

In radians 

Degree

1/360 circle

17.4532925mrad

Arcminute            

1/60 degree

290.8882087µra

Arcsecond

1/60 arcminute 

 4.8481368 µrad

Artesian

A condition that exists when the water table piezometric surface lies above the ground level.

ATEX

European directive (ATEX 95 equipment directive 94/9/EC) for equipment and protective systems intended for use in potentially explosive atmospheres including pumps for landfill and remediation.

Automatic data acquisition

A system designed to regularly record data from instruments independent of operator input, often used in remote environments. A data logger controls and logs the sensor readings and can respond to pre-set alarm trigger levels through on-board software.

Typical components could include:

  • Central processing unit (CPU) – to which all the components are linked
  • Interface Modules: Certain types of sensors require additional interfaces. For example, vibrating wire sensors require a dedicated interface, which is connected between the CPU and the instrument.
  • Multiplexers: A relay mechanism controlled by the CPU to switch between multiple sensors so that they can be monitored by a single CPU.
  • Power Supplies: A power supply provides regulated power to the logger and sensors. Power is drawn from a battery that is charged either from an AC supply or a solar panel.
  • Communication: Remote or local connection to the CPU to program or download data including GSM, GPRS, radio and cable.