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Calibration

Calibration is a comparison between measurements – one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device.

The device with the known or assigned correctness is called the standard. The second device is the unit under test, test instrument, or any of several other names for the device being calibrated. Calibration of all Geosense sensors is traceable to UKAS standards.

California Bearing Ratio (CBR)

A laboratory test that is used to determine the suitability of of a soil for use as a subbase in a pavement section.

Capillary rise

The height to which water will rise above the water table due to negative pore water pressure or capillary action of the soil. See Capillary information in the settlement analysis and stress analysis section for equations and calculations.

Capillary stresses

Pore water pressures less than atmospheric values produced by surface tension of pore water acting on the meniscus formed in void spaces between soil particles.

CE compliance

CE marking is a key indicator of a product’s compliance with EU legislation and enables the free movement of products within the European market. By affixing the CE marking on a product, a manufacturer is declaring, on his sole responsibility, conformity with all of the legal requirements to achieve CE marking and therefore ensuring validity for that product to be sold throughout the EEA, the 27 member states of the EU and European Free Trade Association countries - Iceland, Norway, Liechtenstein and Turkey. This also applies to products made in third countries which are sold in the EEA and Turkey. However, not all products must bear the CE marking. Only those product categories subject to specific directives that provide for the CE marking are required to be CE marked.

CE marking

CE marking is a mandatory conformity marking for certain products sold within the European Union since 1993. The CE marking is the manufacturer's declaration that the product meets the requirements of the applicable EC directives. Directives are agreed, adopted & accepted by the governments of the member states into national law. They are “transposed into UK Law” as Statutory Instruments which gives the Directives the same status as other laws in this country. It places responsibility with the manufacturer or importer of goods from outside the EU, whoever places the equipment on the market that the product is compliant and conforms to the relevant CE Directives.

The CE Marking Directives that are applicable to the majority of Geotechnical and Structural instruments are as follows

Directive                     Title of Directive

2004/108/EC                  Electromagnetic compatibility (EMC)

1999/5/EC                      Radio Equipment and Telecommunications Terminal Equipment (R & TTE) 

2011/65/EU                    Restriction of Hazardous Substances (RoHS)

2002/96/EC                    Waste electrical and electronic equipment (WEEE)

Compliance is demonstrated by various harmonised standards as follows

Directive                     Assessment standard

EMC                             EN 61326-1

R & TTE                        EN 61011 & ETSI

RoHS                            SI 2008 No. 37

WEEE                           SI 2006 No. 3289

The manufacturer or importer should ensure that they have a full technical file to demonstrate the conformity and make a declaration of conformity and attach the CE mark to the product. Failure to do the above means that the product is non-compliant and should not be sold within the EU.

Clay

Soil particles which are smaller than 0.002 mm (2 micron) in size.

Coarse-grained soils

Soils with more than 50% by weight of grains retained on the #200 sieve (0.075mm).

Cobbles

Soil particles between 76 mm and 305 mm in size.

Coefficient of active earth pressure

The ratio of the minimum horizontal effective stress of a soil to the vertical effective stress at a single point in a soil mass retained by a retaining wall as the wall moves away from the soil. See the link to Retaining Walls for equations and calculations.

Coefficient of compressibility

The ratio of void ratio difference to the effective pressure difference of two different loadings during primary consolidation.

Coefficient of secondary consolidation

The change in volumetric strain per a logarithmic cycle of time after primary consolidation is complete.

Coefficient of consolidation

The rate of change of volume during primary consolidation. Units: m²/s.

Coefficient of curvature

Also curvature coefficient. A measure of the shape parameter obtained from a grain size distribution curve. CD=(D30)2/D10D60.

Coefficient of earth pressure at rest

The ratio of horizontal effective stress of a soil to the vertical effective stress at a specific point in a soil mass behind a retaining wall when the wall does not move (loaded in conditions of zero horizontal strain).

Coefficient of friction

The ratio between the tangential force required to cause a body, such as a foundation surface or a retaining wall, to slide along a plane and the normal force between the body and the plane.

Coefficient of passive earth pressure

The ratio of the maximum horizontal effective stress of a soil to the vertical effective stress at a specific point in a soil mass behind a retaining wall as the wall moves toward the soil. See the link to Retaining Walls for equations and calculations.

Coefficient of secondary consolidation

Coefficient of secondary consolidation The change in volumetric strain per a logarithmic cycle of time after primary consolidation is complete.

Coefficient of uniformity

A measure of the slope of a grain size distribution curve, and therefore the uniformity of the soil. Cu=D60/D10.

Cofferdam

A temporary structure used to enclose a construction area, and prevent soil or water from entering the construction area.

Cohesive soils

Clay type soils with angles of internal friction close to zero. Cohesion is the force that holds together molecules or like particles within a substance.

Colluvial soils

Soils deposited at the base of foot-hills via gravity or erosion.

Compaction

Volume change in soils which air is expelled from the voids, but with the water content remaining constant. Compaction may occur due to vibration, and self-weight. In construction, compaction is achieved by rolling, tamping or vibrating fill soils. See link relating to Compaction for additional information, equations and calculations.

Compensation grouting

The excavation of tunnels produces settlement which can propagate to the surface and cause structural damage to those structures which lie on or near their path. The philosophy of compensation grouting is to reduce, or even prevent settlement by injecting relatively small quantities of grout between the source of the settlement, (the tunnel) and the foundations of the structures that require protection. An essential component of compensation grouting is the monitoring of movements. Precise levelling and tilt monitoring of the ground and structures overlying the tunnel are essential to keep settlement and deformations within specified limits.

Cone penetration test

A penetration test in which a cone that has a 60º point is pushed into the ground at a continuous rate. Resistance is measured by correlating the depth penetrated with the force applied.

Cone Penetration Test (CPT)

Similar to the SPT in that it is used to determine the density of subsurface soils. This test uses a metal rod or tube fitted with a special point that is equipped with sensors that measure the resistance that is required to advance the point through the soil as it is hydraulically forced into the ground.

Confined aquifer

An aquifer that is contained between two stratifications of low permeability soil or rock.

Consolidation

Volume change due to dissipation of excess pore pressure from static loads.

Consolidation (settlement)

The settlement of a foundation due to squeezing out of water from the pores as the soil comes to equilibrium with the applied loads.

Colloidal mixer

A type of grout mixer that mixes by recirculating the grout through a pump, injecting tangentially into a chamber with a very fast spinning paddle, creating a vortex. The main attributes of colloidal grout mixers are greater speed of mixing and output capacity than traditional paddle mixers.

Coulomb earth pressure theory

An earth pressure theory that includes friction between the soil and retaining structure, and assumes that failure occurs along a flat plane behind the retaining structure at an angle that is in part derived from the angle of internal friction.

Coulomb's equation

Named after Charles Augustin Coulomb, (1736-1806) An equation relating the shear strength of soil to the normal effective stress on the failure plane.

Creep

Time dependent deformations which occurs in soil at constant effective stress without changes in volume and pore water pressure.

Critical circle

In a slope stability analyses, the slip circle that corresponds to the lowest factor of safety.

Critical ground slope angle

The angle of the ground slope that corresponds to a factor of safety of 1.0 relative to the slope stability.

Critical height

The height of a slope that corresponds to a factor of safety of 1.0 relative to slope failure

Critical hydraulic gradient

The hydraulic gradient at which effective stresses becomes zero. Upward seepage.