L — Dictionary of Quarrying Terms

LGP: abbr. low ground pressure.

LHD: abbr.load-haul-dump. Used to describe vehicles, such as bowl scrapers, which carry out all three functions.

lake asphalt: A highly viscous natural asphalt found in well defined surface deposits.

Lang’s lay:A term applied to a steelwire rope in which the wires forming each strand and the strands themselves are twisted in the same direction.

laser-profiling: The use of an instrument emitting a laser beam to survey a face prior to blasting.

latent heat: The heat required to change the state of a substance from solid to liquid, or from liquid to gas, without change in temperature. see ‘specific heat of fusion’ and ‘specific heat of vaporization’.

laterite: Highly weathered residual soil material rich in oxides of aluminium and iron, traditionally useful for brickmaking.

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

lay: The lay of a wire rope describes the way in which the wires and strands are twisted to form the rope. see ‘Lang’s lay’ and ‘ordinary lay’.

lay shaft: A secondary shaft parallel to the main shaft of an automobile gearbox to and from which the drive is transferred by gear wheels of varying ratio.

leaching: 1 Selective removal of soluble constituents from soil or rock by the action of surface water penetrating downwards. 2 The removal of soluble salts or metals from material by the use of a suitable solvent.

leader: In linear surveying, the man holding the leading end of the tape and who is aligned by the follower.

leading: The use of a piece of lead on the end of a string dropped into the chamber of a crusher to determine the setting.

Lenz’s law: The direction of the electromotive force induced in a circuit by a changing magnetic flux is such that the direction of any current produced opposes the change producing it.

lift: In a quarry or opencast site may be used to denote the configuration of the face eg multiple lift (= several benches).

lifting tackle: Lifting blocks, ropes, chains, hooks, slings etc.

lightweight aggregates: Aggregates used in the production of lightweight concretes. Natural types include pumice and diatomite and manufactured ones furnace clinker, foamed slag, expanded slate, expanded perlite, expanded vermiculite and plastic particles.

lignite: Coal of low rank with high inherent moisture and volatile matter.

lime concrete: Concrete in which the cementing agent is burnt and ground lime.

limestone: Rock consisting predominantly of calcium carbonate.

limit switch: A safety device fitted to electrically operated lifts, travelling cranes etc which prevents them passing a certain point by cutting off the power supply.

limited liability company: A business established under the provisions of the Companies Acts in which the shareholders’ liability is limited by shares or guarantee.

limiting friction: Limiting friction occurs when the moving force and the force opposing motion are equal; any addition to the moving force will cause slipping. The limiting frictional force is proportional to the normal reaction between the contacting surfaces and is independent of the area of contact.

line voltage: The voltage between two of the power conductors of a three-phase system.

lithology: The character of a rock expressed in terms of its mineral composition, structure, grain size and arrangement of its component parts.

lithosphere: The Earth’s crust and overlying superficial deposits.

littoral deposit: A marine deposit laid down between low and high tide marks usually consisting of boulders, pebbles and coarse sand.

littoral drift: The movement of boulders, pebbles and sand along a shore belt by the action of currents and waves.

live load: All loads applied to a structure other than its own weight, eg the load applied to a bridge by the traffic moving over it.

load: 1 The power output of a generator, motor, transformer etc or the power carried by a circuit. 2 The weight supported by a structure. See ‘dead load’ and ‘live load’.

load-cells: Load-measuring elements utilizing electrical or hydraulic effects which are remotely indicated or give digital read-outs.

load factor: The ratio of the energy units used in a given time to the units used, had the maximum demand been continuous during the same time.

loading density: The mass of explosive per unit length of blasthole measured in kg/m.

loan capital: Long-term liabilities such as loans and debentures.

lock nut: A second nut screwed on to a bolt to prevent the first nut from loosening under vibration.

lock valves: Hydraulic valves which permit free flow in one direction and will allow flow in the reverse direction when a piston receives a pressure signal.

locked coil rope: A high-strength wire rope of all-steel round and shaped wires. Used for heavyduty winding and aerial ropeways.

lode: see ‘vein’.

log-washer: A long water tank set at a slope, in which one or two shafts, or logs, fitted with paddles set helically rotate. The feed is introduced at the lower end of the tank, the paddles break it up and subject it to a tumbling action; dirty water and fines are discharged at the lower end and washed aggregate at the upper end. These washers are used where there is conglomerate or a high proportion of clay among the gravel.

longitudinal waves: Waves where particles of the medium vibrate parallel to the direction of wave travel.

Los Angeles abrasion test: A test for mechanical strength in which an aggregate sample is rotated in a horizontal drum with a charge of steel spheres. The percentage of the original sample which passes a standard sieve after 500 revolutions is reported as the percentage of wear. Adopted as an European standard BS EN 1097 Part 2.

low explosive: An explosive, such as black powder, which can be fired by simple ignition. Propagation is by rapid combustion and the rate of travel of the flame front is relatively slow, producing a heaving type of explosion.

low wall: In a surface mining operation, the spoil slope where overburden is dumped into an excavated area.

Lower Palaeozoic: Early part of Palaeozoic era, ranging in time from 590 to 395 million years ago and comprising the Cambrian, Ordovician and Silurian systems.

lowerator: A machine used in an automated concrete block making plant for moving blocks from the curing zone to the stacking and packaging section.

lumen: The flux emitted within a unit solid angle of one steradian by a point source having a uniform intensity of one candela. Symbol: lm.

luminous efficacy: The ratio of the luminous flux emitted by a lamp to the power consumed by it. Symbol: K Units: lumens per watt (lm/W).

luminous flux: The quantity of light emitted by a source related to the solid angle over which the measurement is made. Unit: lumen (1m).

luminous intensity: The quantity which describes the capacity of a source or illuminated surface to emit light in a given direction. Symbol: I. Unit: candela (cd).

lux: An illumination of one lumen per square metre. Symbol: lx.