nto the mine ceiling from which is threaded a plumbline. The spad is an underground survey station similar to the use of stakes in marking survey points on the surface. A pointer spad, or sight spad, is a station that allows a mine foreman to visually align entries or breaks from the main spad.Span- The horizontal distance between the side supports or solid abutments along sides of a roadway.
Specific gravity- The weight of a substance compared with the weight of an equal volume of pure water at 4 degrees Celsius.
Split
- Any division or branch of the ventilating current. Also, the workings ventilated by one branch. Also, to divide a pillar by driving one or more roads through it.
Squeeze- The settling, without breaking, of the roof and the gradual upheaval of the floor of a mine due to the weight of the overlying strata.
Steeply inclined- Said of deposits and coal seams with a dip of from 0.7 to 1 rad (40 degrees to 60 degrees).
Stemming- The noncombustible material used on top or in front of a charge or explosive.
Strike- The direction of the line of intersection of a bed or vein with the horizontal plane. The strike of a bed is the direction of a straight line that connects two points of equal elevation on the bed.
Stripping ratio�C The unit amount of overburden that must be removed to gain access to a similar unit amount of coal or mineral material.
Stump- Any small pillar.
Subbituminous�C Coal of a rank intermediate between lignite and bituminous.
Subsidence�C The gradual sinking, or sometimes abrupt collapse, of the rock and soil layers into an underground mine. Structures and surface features above the subsidence area can be affected.
Sump- The bottom of a shaft, or any other place in a mine, that is used as a collecting point for drainage water.
Sumping- To force the cutter bar of a machine into or under the coal. Also called a sumping cut, or sumping in.
Support- The all-important function of keeping the mine workings open. As a verb, it refers to this function; as a noun it refers to all the equipment and materials--timber, roof bolts, concrete, steel, etc.--that are used to carry out this function.
Surface mine�C A mine in which the coal lies near the surface and can be extracted by removing the covering layers of rock and soil.
Suspension- Weaker strata hanging from stronger, overlying strata by means of roof bolts.
Syncline- A fold in rock in which the strata dip inward from both sides toward the axis. The opposite of anticline.
T
Tailgate- A subsidiary gate road t
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