MINE SURVEYING. to protect against dangers such as opening old workings that might be flooded or contain gas.

Transcription

1 surveyor takes angular and linear measurements of particular parts of the earth s surface; a mine surveyor also works underground. The surveyor keeps a record of the results of the survey and uses them to make calculations to enable him to draw maps and plans of the survey area on a reduced scale. The maps and plans are used to facilitate the methodical planning of the layout of a mine. Surveyors have not always worked in coal mining. fter the Coal Mines ct of 1887, mine owners were obliged to have accurate maps and plans of their mine. Having up-to-date and exact surveys was necessary for a number of reasons. The plans included faults, seams, strata, roadways, ventilation plans, depths of shafts and so on. Therefore, the surveyor had an important role to play in planning any future development of the mine, including ensuring that the mine never strayed out of its boundaries into someone else s land. The provision of accurate underground maps also prevented the haphazard, or unscientific, search for coal, therefore saving the mine money. Steel measuring tapes were used to measure distances. Furthermore, a surveyor had an important role to play in ensuring the safety of men underground. n accurate map could help to protect against dangers such as opening old workings that might be flooded or contain gas. Images of some of the equipment that a mine surveyor used at the beginning of the twentieth century are pictured here. Each piece of equipment was used at a different stage in the survey process. The basic items used in many different surveying operations were chains, tripods, staves, and steel tapes. Surveyors also used instruments such as dials, levels, and theodolites. Many similar instruments are still used today. Surveyor s chains Surveyor s chains were used to measure horizontal distances; steel measuring tapes were sometimes used as well. The chain used in mining was called the Gunter Chain. It was 66 feet long (approx. 20m) surveying chain and divided up into 100 links. 80 chains were equivalent to a mile (or approx. 1.6km). long the length of the chain, every ten links, there were brass tallies suspended from the join in-between two links. Each tally was identified by the number of prongs it had. The middle tally, at 50 links, was round. The tallies either side of the central one had four prongs, then three, two and one. In

2 Each brass tally has two values this way, a surveyor could use the tallies to measure from either end of the chain. The tripod tripod is a three-legged stand used to provide a stable, adjustable platform for scientific instruments. They are still used to this day. Turn of the century tripods had legs in one piece, or with several extendable sections. The legs were spread out at different angles whilst the instrument platform remained stable. Tripods often had a plumb-line hanging from the middle of the base (or a hole to allow instrument plumb-lines to fall through). plumb-bob was a brass pear shape with a steel tip that was suspended from the plumb-line, and was used to ensure that the tripod was centred. brass plumb -bob tripod s a result, the tripod was used on uneven ground, such as the floor of a roadway, to provide a stable base for a piece of surveying equipment. Survey stations Survey stations provided a fixed location from which a measurement could be taken. temporary survey station consisted of a chalk mark or a circle on the wall or pavement of a roadway. nail in a wooden plug in a hole chiselled into the ceiling formed a permanent survey station. Theodolites or dials would be set up at one station, and a miner s lamp suspended from another station would be used as a target. Each permanent survey station was given a reference number and the angles and distances between stations were measured and recorded. permanent survey station in the roof of chalk mark at the end of a chain or tape was called a sight point, and was used like a survey station.

3 Surveying with the miner s dial The miner s dial was used to measure horizontal and vertical angles. It had a magnetic compass needle pivoted on a circular dial face from which measurements were read. To perform a basic survey of the route of a roadway a surveyor took the following steps: 1. The dial was placed at station B making sure that it was horizontal (using the spirit level on the face) and the needle had settled. The miner s dial, c lamp was held at station in the centre of the shaft. The sights of the dial (the vanes attached to the side of the face) were rotated until the hairs, set in the vanes, cut the light. 3. The bearing was then read off and noted. The distance between stations was measured with a chain. 4. The lamp was then placed at station C in the centre of the road, and the bearing from B to C taken, then C to D, D to E and finally E to F. Surveyors were not always able to use the magnetic needle dial if there were steel girders or any iron-ore present underground. These metals have a natural attraction, and affect the reading given by the needle. If steel rails were the only obstacles they were lifted out of place and the bearing of the first line ( to B) was taken. This line was then used as the base bearing for the rest of the survey. Surveying a path with a dial Level, c1900

4 Levelling stave Levelling Levelling was used to measure the difference in height between two points from a fixed horizontal line. This fixed line was called a datum. Levelling allowed the surveyor to plot contour lines on plans and to calculate the gradient of roadways to be driven from one seam to another. This ensured that roadways were laid out at the proper gradient and haulage and pumping machinery positioned correctly. The instrument used to take levelling measurements was called a level. It consisted of a telescope mounted on an adjustable base, and it was positioned on a tripod. It had a pair of spirit levels, one along the telescope and one across, used to ensure the level was set up horizontally. Once the instrument was in place it was fixed in position by tightening a set of screws. To use a level, a surveyor looked through the telescope and read the vertical height of the target using the cross hairs visible through the lens to focus. The target was a levelling stave, which is a telescopic wooden staff, in three sections, with a set of numbers and figures painted onto the front. The surveyor would read the height from the line of sight to the station using these instruments. Traverse Surveying t the turn of the century the theodolite was primarily used for checking main road surveys and for levelling, rather than for general surveys. It was the most complex piece of a surveyor s equipment, consisting of a telescope mounted on a base and equipped with spirit levels and horizontal and vertical protractors called circles. It took a more accurate sight than could be achieved with a dial. The theodolite was centred and levelled at a fixed station. The surveyor then sighted the target station using the Theodolite, c1900 telescope. Once the objective had been sighted the telescope was locked into position. The surveyor then read the angle off the protractors (circles) placed to the side of the telescope. This was repeated with a second target station. The angle at the middle of the three stations could then be calculated using mathematical rules.

5 B D Booking and mapping the survey Throughout the survey, the surveyor would record and sketch all the measurements taken. This was known as booking the survey. The results of the survey were then taken back to an office and used to draw maps and plans. The surveyor used another set of precision equipment to do this, including large sets of drawing tools, the parallel ruler and mathematical instruments such as the plotting protractor. E F C Some of the drawing tools used C to map a survey, c1900 : Parallel ruler B: Drawing pen C: Pricker D: Compasses E: Bow pen F: Pencil holder G: Compasses G