G — Dictionary of Quarrying Terms

GDO: abbr. General Development Order. The Town and Country Planning Development Order 1988.

ggbs: abbr. ground granulated blast-furnace slag.

gabion: A wire cage containing rock which can be used to give protection against erosion or to counteract slope instability.

galvanometer: An instrument designed to detect and indicate the magnitude of small currents.

gangue: The material of no apparent value associated with minerals in lodes or veins.

gap-graded aggregate: A material in which particular size fractions are absent.

gape: The distance across the crusher feed opening between the fixed and moving members.

gas welding: Any metal welding process in which a combination of gases are used to obtain a hot flame; the most commonly used process employs the oxy-acetylene combination.

gate valve: A stop valve which closes a pipe to the flow of fluid by means of a plate which moves in a plane at right-angles to the direction of flow. When closed, the plate seals the pipe and, when open, the full bore of the pipe is available for flow and resistance to flow is less than with other types of valve.

gear pump: A small pump consisting of a casing enclosing a driven gear wheel in mesh with a second gear wheel, the fluid being carried from the suction to the delivery side of the pump in the spaces between the teeth.

gearing: The relationship between the amounts invested in a business by its owners as equity and by others as debt.

generator: A machine, designed on the laws of electromagnetic induction, for converting mechanical to electrical energy.

geological maps: see ‘drift map’ and ‘solid map’.

geophone: An instrument used for detecting the passage of sound waves through the strata.

geophysical prospecting: The making and interpretation of certain physical measurements to obtain information on the subsurface geological structures.

geophysics: The study of the Earth’s physical characteristics by the use of instruments to determine physical properties such as relative density, electrical conductivity, magnetic susceptibility, seismic wave propagation etc.

geotechnical appraisal: an exercise conducted on a tip or excavation to determine whether movement or collapse would present a significant hazard. If so, the tip is notifiable and a geotechnical assessment is required.

geotechnical assessment: a detailed study by a geotechnical specialist of the design and construction of a tip or excavation to determine the probability of failure.

geotextile: A synthetic fabric used as a filter in groundwork.

giga-: A prefix indicating multiplication by one thousand million. abbr: G.

glacial: Formed by ice action.

glacial drift: Material transported and deposited by glaciers.

glory hole: An open-pit method of excavation in which underground drives are put in below the area to be excavated and raises are then driven into the excavation site; the raises are used as passes for the broken ore or rock which is drawn off and transported as required.

gneiss: A metamorphic rock with constituents similar to that of granite but having a foliated or banded structure.

grab dredger: A dredger, used in river and estuary operations, on which are mounted one or more grab cranes.

grab sample: A random sample taken from a stockpile or consignment when there is insufficient time or labour to take a representative sample. Taken by an experienced sampler, it can be used to obtain a good estimate of the quality of the material.

grader: A machine used for the final surfacing and repairing of haul roads. It has a blade the tilt and angle of which can be varied while the machine is in motion and its wheel cambers can also be altered.

gradient: The rise or fall per unit horizontal length of a road, railway etc. Gradient may be expressed as a ratio or as a percentage.

grading: 1 The percentage by weight of different sizes present in an aggregate, established by sieve analysis and expressed on a grading curve. 2 Shaping the ground surface, usually by means of a grader or bulldozer.

grading curve: A graphical representation of the proportions of different particle sizes in a material. There are many ways of recording the results of a sieving test, the most common being that of plotting the cumulative percentages of material passing through (or retained on) the sieves against apertures size. Particle size is usually plotted on a horizontal logarithmic scale and percentages on a vertical arithmetic scale.

granite: A coarse-grained igneous rock consisting of quartz, orthoclase felspar and mica. Relative density 2.5-2.8. Crushing strength up to 140N/mm².

granulator: A jaw crusher with a high width/gape ratio, normally used for the reduction of oversize in gravel deposits at low capacity.

graticule: The set of cross-hairs fitted into the diaphragm of a surveying instrument telescope.

gravel: Granular material in the size range 2mm to 60mm, generally arising in the form of sand and gravel deposits allied to river/ water activity.

gravel pump: A centrifugal pump with renewable impellers and linings for raising gravel and other abrasive materials. Many pumps of this type are rubber-lined.

gravimeter: An instrument used in gravity surveying to measure changes in the value of gravity over an area.

gravity: The force which attracts matter towards the centre of the Earth. The acceleration due to gravity is 9.81m/s/s at sea level.

gravity concentration: Processes for sorting granular material by forces which depend on differences in the densities, shapes and sizes of the particles.

gravity surveying: A method of geophysical prospecting using a sensitive instrument known as a gravimeter to measure small variations in the Earth’s gravitational field caused by density differences in the underlying rocks.

greywacke: A dark-coloured, poorly graded, argillaceous sandstone.

grid: 1 A fixed heavy-duty screen. See ‘grizzly’. 2 A rectangular layout of straight lines used in locating points on a plan.

grit: 1 Term which, when applied to describe dispersions of small solid particles in air or other gas, refers to those particles which are larger than 76μm. 2 Small hard fragments of mineral aggregate for application to a road surface.

gritter: 1 A machine or attachment to a lorry for applying chippings or small aggregate in a uniform layer to the surface of a road, as a surface dressing. 2 A machine for distributing small chippings, sand or salt over a road surface to counteract slipperiness caused by frost, snow etc.

gritting: The operation of spreading grit or similar material on a road surface to reduce the possibility of skidding.

grizzly: A sturdily built type of screen constructed of parallel tapered steel bars held apart by distance pieces.

ground water: Water which has penetrated from the surface and filled the pores and fissures of the strata up to the water table.

grout: Fluid or semi-fluid cement slurry for pouring into masonry joints, injection into the ground and filling the space surrounding foundation bolts.

grout box: The wood or metal box in a concrete foundation, with a metal plate at its lower end through which the foundation bolt passes.

grouted macadam: A form of road construction made of coarse aggregate into which a bituminous binder or a mortar of Portland cement and sand is poured after spreading the aggregate.

grouting: 1 The pouring of grout into masonry joints and the space surrounding foundation bolts, also its injection into fissured ground. 2 Introduction of a liquid binder into the interstices of a material.

guard: A fence or other device fitted to the moving parts of machinery to prevent injury to operators.

gunpowder: see ‘black powder’.

gypsum: Hydrated calcium sulphate, CaS0₄.2H₂O, associated with other evaporite minerals in extensive beds. Used in the manufacture of plaster-board, Portland cement, fertilizer etc.

gyradisc crusher: A gyratory crusher mechanically similar to a cone crusher but with a much lower head angle and a principal application of producing high volumes of rock fines or stone chippings with good particle shape.

gyratory crusher: A compression crusher consisting of a moving member, known as the head, in the form of an erect truncated cone rotating eccentrically within the fixed member (the outer shell), which is in the form of a frustum of an inverted cone.