Pit wood
Pit wood is the wood that is used in a mine . The term “pit wood” is defined by the intended use, so all types of wood and wood forms are counted as pit wood that are used in mining operations, whether in open-cast or underground mining .
history
For centuries, wood has been the most versatile and important, and in some cases even the only building material for mining . In the past, enormous amounts of wood were used in mining. Until the middle of the 19th century, oak was used almost exclusively. The reason for this was that oak was not much more expensive than fir, but it is more durable. The wood was used in all areas of underground mining. Towards the end of the 19th century, more than 1,173,000 cubic meters of wood were used annually in the Ruhr mining industry alone . In 1907, the consumption was already 2,650,000 solid meters of wood. As a result, entire forests or even entire mountain ranges were cleared to supply the mines with pit wood. In order to meet the constant need for pit wood, the forest owners were forced to plant other types of wood that grew quickly. While pure oak forests were planted around 1850 , pine forests were planted as early as 1870 . The advantage of this type of tree is that it grows faster, so that such trees could be marketed as pit wood after just 30 to 60 years. From 1930 on, friction stamps and caps made of steel were introduced in the German coal mining industry . This led to the fact that the timber construction was gradually displaced from the longwall , which ultimately also led to a reduction in the need for wood. Nevertheless, pit wood remained an important building material for mining even after the Second World War . The rising wood prices could do little to change that. Due to the mining crisis of the 1960s, the demand for pit timber sank so much that the pit timber no longer played an important role as a finishing material.
Basics
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Pit wood is still used in mining today. Even though the use of wood, especially in mines that are intended to be kept open, has decreased significantly in recent times, it is still justified today. Wood is used underground in particular for mining work in the form of supporting elements. Wood offers many advantages, it is easy to work on the spot, cheap to buy, usually easily available, comparatively flexible with respect to rock pressure and, due to its low specific weight, can be moved easily. The splittability of the wood has a great influence on its strength. Wood that can be split well can be processed well, but it has a lower buckling, bending and compressive strength than wood that is difficult to split. A special property of wood is its ability to warn of mountain movements. This characteristic of the wood manifests itself in the fact that the wood warns the miners when the crackling load increases.
On the other hand, there are disadvantages of wood as a material used in mining. Above all, the lower durability of the timber construction necessitates regular renewal in the event that a longer service life is desired. Wood (with the same dimensions) is less stable than steel or reinforced concrete . Wood is flammable and susceptible to moisture damage and fungal attack . Another wood pest is the pit wood beetle , which gets its name from the fact that it is mainly found in old pit wood. This pest spreads particularly in pit wood that has been damaged by fungus. Impregnation can delay the decay of the wood, but not completely prevent it.
Classification
Intended use
Pit wood is divided into:
- Punches and caps ( trunks ) - supporting parts
- Half-shells (halved round timber) also called half-timber - warpage and bolt
- Squared timbers, sleepers
- Crush wood for installation between expansion parts and rock
- Boards - delay and dubbing
- Logs - for pressure boxes
- Beam - shaft extension (frame)
The wood used for guide battens is also counted as pit wood. The fascines that used to be used to back up the extension when the mountains are under pressure do not count as pit wood.
Types of wood
In principle, almost all types of wood are suitable for use as pit wood, the prerequisite for use is a diameter of the log that is adapted to the intended use. The most suitable types of wood are those whose wood is very dense or, if they are less dense, very resinous. Acacia wood is the most durable, followed by oak. The hornbeam and hornbeam are also very suitable woods due to their toughness. Other hardwoods such as ash, alder, poplar and willow are, because they are too soft, less suitable for use as pit wood. Of the conifers, the pine, spruce, pine, red fir and larch are among the types of wood suitable for mining. The silver fir, the wood of which is not resinous and easy to split, is less suitable. First and foremost, softwood such as pine or spruce is suitable for pit construction. Their long-fiber wood initially deforms with a loud crack when it is subjected to a load, before it breaks. Depending on the mountain pressure , logs with a diameter of six to ten inches are used for the excavation . Hardwood such as oak can take higher loads than softwoods, but due to its short-fiber structure it is not capable of warning and breaks immediately. Beech wood is also less suitable for expansion purposes, as it has a lower load-bearing capacity and also has no warning capability. In addition, these types of wood are very expensive, so that hardwood has not been used in mining for a long time.
Basically, pit timber is divided into pit logs and pit lumber. All coniferous and hardwoods that are sawn in lengths of up to five meters are used as pit logs. These woods are either left in their original round shape, split lengthways or trimmed on one side. The woods are used with or without bark. The requirements for pit logs are summarized in DIN 21320 (pit logs, technical quality and delivery conditions). Punches, caps, billets, pillar wood, bolts and formwork timbers are made from pit logs. Pit lumber is processed wood. It is used for square timbers, track battens, driving timber, sleepers, planks and boards.
durability
The durability of pit timber varies greatly due to environmental factors. The humidity and temperature in particular have a major influence on the durability of the pit timber. It is crucial for the durability that the wood is sufficiently dry. Only when dry can rot fungi adhere to the wood and destroy the wood. At temperatures below 20 ° C, there is little rot formation. If the relative humidity is below 89 percent, the wood will not rot. Completely dry wood, but also wood that is under water, does not rot. Due to these circumstances, the lifespan of wood on soles and in stretches with moving weather is shorter than in routes with moving weather. The durability of the individual types of wood is very different. Oak wood lasts an average of seven to eight years, even in the storm. Good oak can even remain stable for up to twelve years. Fir wood lasts a maximum of four years in the downpour, often even less. Beech wood is particularly quickly attacked by rot fungi. Oak wood can be used for around 25 years in incoming winds. Pine wood has a shelf life of up to 15 years in this environment. Under particularly favorable environmental conditions, oak wood lasts up to 40 years and softwood up to 20 years. Various carpentry was even found in some of the pits in the old man , the wood of which had been in use for 300 years and was still intact.
Improvement of durability
Various methods are used to improve the durability of the pit timber. All methods aim to remove moisture from the wood. In the case of conifers in particular, removing the bark has a positive effect on the drying out of the wood. Removing the bark removes a natural source of putrefaction. Methods of wood preservation include external charring, preservative paints, and leaching or steaming. Impregnation of the wood began as early as the 18th century. In the first method, developed as early as 1705, the wood was immersed in a solution of mercury chloride. In the years that followed, around 200 different processes were developed, which often only achieved minimal shelf life extensions. The means used only worked in the surface area of the wood. The chemicals used were often very toxic and therefore posed a major problem. As a result, the miners were poisoned very often. The sap portions of the wood were removed when watering or boiling. With this method, however, the wood inside was not reached with thicker woods. When leaching with cold water, hydrochloric acid was added to the leaching water. With this method, however, all wood pores remain open and the wood fibers are not completely protected. Another method is to bathe the woods in brine . Woods that are impregnated with brine often become very brittle. The use of unslaked lime can also be used to extend the durability of the wood. The wood is covered with unslaked lime and gradually doused with water until the lime is slaked. This makes the wood harder and more resistant to rot. Other chemical means for impregnation were vitriolic mine water , chlorine barium, chlorine zinc, zinc chloride, iron and copper vitriol, borax, sulfur barium and water glass. A well-known method is the Hasselmann method. In this case, the wood was boiled in a closed kettle and treated with chemicals such as clay, quick lime and iron vitriol under pressure. However, all water-soluble agents cannot prevent the decay of the wood, only delay it.
Timber industry
So that the pit can be supplied quickly and adequately with pit wood, there must be a storage facility at the respective mine. Appropriate logistics are essential because of the long journeys. The wood yard must be large enough to allow four months to be kept in store for the daily need for pit wood. Due to the risk of fire from the stored wood, the wood yard must be a sufficiently large distance from the shafts and the main buildings. The wood coming from the supplier is first unloaded and stacked in the wood yard, as clear as possible, and sorted by length and thickness. So that the wood does not warp, it must be stored in the lumberyard protected from rain and sun. In the past, the timber was unloaded, transported and stacked manually in the lumber yard, today the work is usually carried out by machine. Various mobile cranes are used to carry out the work. Bundling of timber is also possible with special stacking vehicles. So that the wood can be conveyed into the pit , the wood is loaded onto stake wagons. Every mining area keeps the wood it needs in stock for one day.
Dendrochronology
The previously almost exclusive use of wood in mining offers mining archeology a reliable method for dating old mine workings using dendrochronology .
Individual evidence
- ^ A b c Walter Bischoff , Heinz Bramann, Westfälische Berggewerkschaftskasse Bochum: The small mining dictionary. 7th edition, Verlag Glückauf GmbH, Essen, 1988, ISBN 3-7739-0501-7
- ↑ a b c d e f g h i j Carl Hellmut Fritzsche: Textbook of mining science. Second volume, 10th edition, Springer Verlag, Berlin / Göttingen / Heidelberg 1962.
- ↑ a b c d e f g h i j k l m G. Meier: Wood in old mining. Online (accessed on November 21, 2011; PDF; 980 kB).
- ^ A b c Association for Mining Interests in the Upper Mining District Dortmund (ed.): The development of the Lower Rhine-Westphalian hard coal mining in the second half of the 19th century. Julius Springer's publishing bookstore, Berlin 1902.
- ↑ a b c d Historical change in forest use in the Ruhr area in Swiss Journal of Forestry , Volume 155 8/04 Online ( Memento of the original from May 27, 2014 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (accessed on November 21, 2011; PDF; 2.8 MB).
- ↑ Ernst-Ulrich Reuther: Introduction to mining. 1st edition, Verlag Glückauf GmbH, Essen, 1982, ISBN 3-7739-0390-1 .
- ↑ William Jicinsky, mountain and Hüttenmännischer club Mähr Ostrau (ed.): Catechism of the pit preservation for mine and mine Steiger supervisory bodies. Commissioned by Prokisch's Buchhandlung, Mähr-Ostrau 1876.
- ↑ Pit wood beetle . Online ( Memento of the original from April 20, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (accessed on November 23, 2011; PDF; 161 kB).
- ↑ a b c Albert Serlo: Guide to mining science. First volume, published by Julius Springer, Berlin 1869.
- ^ A b Gustav Köhler: Textbook of mining history. 2nd edition, published by Wilhelm Engelmann, Leipzig 1887.
- ^ Wilhelm Leo: Textbook of mining science. Printed and published by G Basse, Quedlinburg 1861.
- ↑ Directory of Mining Standards. Online ( Memento of the original from March 7, 2010 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (accessed on November 23, 2011; PDF; 272 kB).
