D — Dictionary of Quarrying Terms

DAPS: abbr. The Doncaster Assisted Private Study scheme.

dc: abbr. see ‘direct current’.

DCF: abbr. discounted cash flow.

DMS: abbr. 1 Dense-media separation. See ‘heavy-media separation’. 2 Diploma in Management Studies.

DTH: abbr. down-the-hole. See ‘down-the-hole drilling’.

DTS: abbr. dense tar surfacing.

database: A collection of itemized records held in an organized filing system commonly in a computerized form.

dash pot: A device for damping-out vibration or retarding motion in one direction. It consists of a piston fitting loosely in a cylinder of oil or other fluid.

datum: An assumed reference surface from which the measurement of reduced levels are measured.

dead load: The weight of the structure and any loads fixed to it.

deca-: A prefix meaning ten times.

deci-: A prefix meaning one tenth.

decibel (dB): Unit for comparison of intensities of sounds and of power in electrical communications circuits.

deck charge: A charge which is divided into several separate components, down a blasthole, by inert material.

declination: The angular variation, in degrees, of the magnetic compass needle, uninfluenced by local causes, from the true north and south. This varies from one locality to another and in any given locality it varies with time.

decoupling: When the explosive charge is not in full contact with the rock, so reducing the effect of the explosion.

deflection: The intentional alteration of the course of a borehole in directional drilling.

deflection wedge: A wedge-shaped tool inserted into a borehole to direct the bit along a prescribed course.

delay detonator: A detonator in which there is a designed interval of time between the application of an electric current to the detonator and its detonation.

delay element: The part of a delay detonator interposed between the fusehead and the priming charge.

delay firing: The firing of several shots in sequence, at designed intervals of time, usually by means of delay detonators, detonating relays or sequence switches.

delay interval: The nominal period between the firing of successive delay detonators in a series of shots.

delay relay: see ‘detonating relay’.

delta connection: A three-phase electrical connection in which the windings are connected in a closed ring and the supply connected to or taken from the junctions.

dense tar surfacing: A hot-process wearing course consisting of aggregate, filler and road tar, in such gradings and proportions that when hot can be spread and compacted, to provide a close-textured impervious mixture. abbr: DTS.

dense-media separation: see ‘heavy-media separation’.

density: The mass of unit volume of a substance. Units: kg/m³.

departure: The distance in metres of a point east or west of a north-south axis. May also be referred to as an easting, in which case all distances measured to the east are regarded as being positive. See ‘co-ordinates’.

depreciation: A method of charging against annual costs, over the expected life of an asset, its original total cost. This can be done by equal or decreasing increments.

depressants: see ‘regulators’.

derrick: A lifting device which takes a number of forms including: a pole, held in position by a number of guy ropes, at the top of which a hoisting rope passes over a pulley; and a three-legged framework over a borehole, used primarily to allow lengths of drill rod to be added to the drilling column.

designed mixes: Mixes for which the concrete producer is responsible for selecting the mix proportions to produce concrete with the required performance. Bituminous mixes can also be designed to meet stated parameters (void content, stability etc).

detonating fuse: A fuse containing a core of detonating explosive. It has a velocity of detonation of approximately 6,500m/s and is used extensively in quarrying and opencast blasting operations. It is manufactured in two main grades: Cordtex or Pentaflex 12 which will initiate commercial explosives but require a primer for ANFO and slurries, and the higher-powered Superflex or Pentaflex 40 which will initiate them without the use of a primer but are intended for down-the-hole use only.

detonating relay: A device used intermediately in a detonating fuse circuit to obtain a short time delay.

detonation: The action of converting the chemicals in an explosive charge to gases at high pressure, by means of a self-propagating shock wave passing through the charge.

detonation impedance: The resistance of rock to blasting.

detonator: A device for producing detonation in a high-explosive charge, and initiated by safety fuse, electrical current or shock.

detrital deposit: A sandy or gravelly deposit formed by river or sea action, consisting of materials eroded from earlier deposits.

development: Work done in a quarry to obtain access to the mineral or to facilitate the opening-out of a new working area.

deviation: 1. The wandering of a borehole from its intended course. 2 The difference between one value of a set and the average. See ‘standard deviation’.

Devonian: A period of the Palaeozoic era spanning the time from 395 to 360 million years ago.

diamond drilling: A method of rotary drilling in rock, usually for exploratory purposes, using hollow diamond-crowned bits to obtain a core for examination.

diamond saw: A circular or reciprocating saw with a diamondbonded cutting edge used to cut concrete, stone, slate and other hard materials.

diaphragm: The fitting in the telescope of a surveying instrument which carries the graticule.

diaphragm pump: A reciprocating pump in which a flexible diaphragm set between two non-return valves is clamped at its edge and at its centre is moved to and fro through a short stroke.

diecasting: Casting of metals or plastics in permanent moulds, made of non-deforming metal, which can be used repeatedly for producing large numbers of castings.

diesel engine: An internal combustion engine running on a light fuel oil which is pumped into the cylinders and ignited solely by the high compression in the cylinders; no electrical spark is required. The operating cycle was invented by Rudolf Diesel (1858-1913), a German engineer.

differential gear: A gear permitting relative rotation of two shafts driven by a third. The two driven shafts are independent but the sum of their rotation rates is constant.

differential pulley block: Lifting tackle consisting of two chain wheels of different diameters turning together on the same shaft and over which an endless chain passes. The chain wheel is rotated by a hanging loop and this shortens a second loop which supports the pulley to which the load is attached. A large mechanical advantage is obtained and the chain cannot run back.

diggability: A reference to the excavation characteristics of the rock to be dug.

dimension stone: Stone cut to regular shapes and sizes for use in the construction industry.

diode: A valve with only two electrodes - an anode and a cathode.

diorite: A coarse-grained plutonic igneous rock with a high content of plagioclase feldspar. Very tough and used as concrete aggregate and road metal.

dip: The inclination of the strata to the horizontal. See ‘apparent dip’ and ‘full dip’.

direct initiation: A method of blasting in which the primer cartridge is placed at the end of the explosive charge nearest the entrance to the blasthole and the detonator is placed at the outer end of the primer cartridge.

direct-on-line starting: Starting in which the full supply voltage is connected directly to the motor.

discharge valve: A valve for controlling the rate of flow from a pipe or a tank.

discounted cash flow: A method of financial assessment of a project in which the initial expenditure and estimated future profits are discounted (reduced) year by year either (a) by the estimated interest rate of borrowing to give the Net Present Value of the project over its estimated useful life , or (b) by such a discount rate that the NPV is zero over the useful life of the project.

discrimination: Means by which protective devices operate circuitbreakers to disconnect faulty apparatus from the system but leave sound electrical equipment to continue to function.

displacement: 1 The volume swept by a piston moving through its full stroke in a cylinder. 2 The weight of water displaced by a floating vessel or by a submerged solid.

displacement pump: Any pump with a pulsing action, produced by compressed air, steam or a plunger.

dolerite: A medium-grained basic igneous rock occurring as intrusions, eg dykes and sills. A typical dolerite contains plagioclase, augite and ilmenite. Used in road making and as concrete aggregate.

dolomite: A mineral composed of calcium magnesium carbonate or a rock consisting predominantly of that mineral.

dome: A structure in which the strata dip outwards on all sides.

double-cage motor: A type of squirrel-cage motor having a rotor with two separate cages, a high-resistance cage occupying slots on the periphery of the rotor and a low-resistance cage set deeper in the rotor. Such motors provide improved starting characteristics compared with single-cage motors of similar rating.

double-roll crusher: see ‘roll crushers’.

double-toggle jaw crusher: A jaw crusher in which the motion of the eccentric shaft is transmitted through the pitman to a toggle joint, formed by two toggle plates hinged together, at its lower end. The opposite end of one plate is hinged on the back plate and the opposite end of the other at the load point, ie the jawstock. The effort applied at the common hinge point causes the obtuse angle between the plates to increase and considerable force is produced at the jawstock.

down-the-hole drill: A percussive drill in which the percussive mechanism (hammer) is located immediately behind the drill bit.

down throw: The amount, measured vertically, of downward displacement of beds caused by a fault.

drag bit: A rotary bit which has two or more cutting blades or wings with hardfaced cutting edges.

dragline: An excavator the bucket of which is suspended by means of a wire rope from the end of a long light boom or jib. The bucket is filled by dragging it towards the machine. Draglines usually dig below the level on which they stand and a good operator can cast the spoil considerably beyond the end of the jib. See ‘walking dragline’.

draw-bar pull: The tractive effort exerted by a tractor or a locomotive which is transmitted through draw-bars to the vehicles towed behind it.

dredge: A barge or pontoon carrying digging buckets or suction pump, used for excavating alluvial deposits below water.

dressed stone: Stone which has been ‘squared’ and smoothed on the face.

drift: 1 Superficial deposits such as alluvium, boulder clay, glacial gravel, peat etc. 2 An inclined tunnel from the surface to the mineral deposit being developed.

drift map: A geological map showing all superficial deposits, ie a true picture of the ground as it exists.

drifter: A heavy percussive drill requiring some form of rigid mounting.

drill boom: An adjustable arm projecting from the drill carriage to carry a drill and hold it in selected positions.

drill carriage: A vehicle on which one or more drill booms are mounted to permit the drills to be brought easily to their work and be removed before blasting.

drill cradle: The metal channel on which a heavy drill is fed forward as drilling proceeds.

drill head: The assembly which applies the drilling pressure and rotation to the drill rods.

drill rig: Any means of supporting a rock-drill at work.

drill steel: see ‘rod’ and ‘stem’.

drill string: The string of tools commonly used in rope drilling, namely: rope, socket, sinker bar, sliding jars, drill stem and drill bit.

drilling column: The column of drill rods to the end of which the core barrel and/or bit is attached.

drop-balling: Rock breakage by dropping a heavy weight on a cable suspended from a crane or excavator jib or simply by dropping a ball from a shovel bucket.

drum-mix plant: A form of continuous asphalt plant in which the heated aggregate and bitumen are mixed in a rotating horizontal drum.

dryer: A means of heating aggregate before mixing with bitumen. It may take the form of a long drum (a continuous dryer) or a batch heater.

drying shrinkage: Contraction which takes place in concrete as hydration occurs and in some aggregates which shrink on drying out.

drystone: Quarried and processed stone which is unbound with bitumen or cement.

duct: A brick or concrete trench or a protective pipe along which cables or pipes pass through the ground.

dumper: An off-highway self-propelled wheeled machine, having an open body, which transports and dumps or spreads material. Loading is performed by means external to the dumper.

dumptruck: An on-site tipping vehicle of up to 200 tonnes carrying capacity used for the transport of excavated mineral or overburden.

dumpy level: A type of levelling instrument in which the telescope is rigidly connected at right-angles to the vertical spindle, so that its axis is horizontal.

dust: A term which, when used to describe dispersions of small solid particles in air or other gases, refers to those particles which are smaller than 76 micrometers. In construction work, the term generally applies to -3mm rock product after crushing.

dust collectors: see ‘settlement chambers’, ‘cyclone dust separators’, ‘venturi scrubbers’, ‘spray scrubbers’, ‘fabric filters’ and ‘electrostatic precipitators’.

dyke: A more or less perpendicular wall-like igneous mass intruded into other rocks.

dynamite: A general term relating to explosives in which the principal constituent, nitroglycerine, is contained within an absorbent substance.