Chamber construction

With room and pillar means a special mining method in mining . Chamber construction, like site construction and expansion construction, is one of the mining methods with chamber-like construction. The mining method was already used in ancient Roman mining as a common method for mining minerals . Today the chamber construction is used in massive as well as in seam-like deposits . This mining method is mainly used in potash and salt mining and in iron ore mining. But chamber construction is also predominantly used in the underground mining of limestone and gypsum and in roofing slate mining. In the Bohemian mountain region, the mining method was used in lignite mining.

Basics

Pillar chamber construction in iron ore mining: the safety pillar can be seen in the foreground on the left ( Eisenberg mine , Philippstollen)

In the case of storage sites where there is water in the overburden, there must not be any subsidence at any point . The reason for this is that these subsidence lead to a fracture or crack in the overburden . Here mining methods are chosen in which parts of the deposit remain as pillars and thus support the overburden. Suitable methods here are mining methods with a chamber-like construction. The chamber construction is used for deposits with great thickness , it does not matter which incursion the deposit has. Due to the way this process is constructed, the hanging wall of mountain festivals is supported in a way that is comparable to that of a ceiling on the walls of the room. Although the chamber construction is very similar to the local construction and there are also transitions between the two methods, the chamber construction differs from this mining method in the larger dimensions of the excavation joint and the resulting excavation space (chamber).

The dismantling process

Basic construction

In this mining process, each cavity is surrounded by safety pillars. These pillars practically serve as walls, so that individual mining chambers are formed. As this systematically creates chambers with pillars in between, this process is also known as chamber pillar construction. The prerequisite for this mining process is that the rock has sufficient stability . This is necessary so that the chambers in their excavation without expansion can remain open. In addition, the pillars must have a certain strength so that the hanging wall does not collapse. If the pillars and mountain festivals are insufficiently dimensioned, daybreak can occur. The pending mineral is mined by breaking elongated chambers from the rock underground within the deposit , which are evenly distributed over the mining field. The mining direction is usually floating. The direction of prevention is either stroking or cross-cutting. The cheek- like chopping method is used. The chamber construction is particularly suitable in irregular deposits in which the minerals do not occur evenly together. The chamber construction allows high mining rates to be achieved with relatively low extraction costs. The disadvantage of chamber construction is the high degradation losses of 50 percent and sometimes even more. The open chamber ridges can also cause problems . Here, the stability can be influenced by technical and natural influences. The specific use of rock anchors improves the stability of the ridges.

Depending on the deposit, different variants of the chamber construction are used. There is the chamber construction without offset, the chamber construction with offset and the chamber break construction. Depending on the method, the supporting pillars are also dismantled. There is also a variant in which both the flexible pillars and the supporting pillars are not dismantled. The chamber construction with offset is used almost exclusively in potash mining. The introduction of backfill is necessary in potash mining, unlike in rock salt mining, for reasons of stability of the chambers. As an offset , residues from the potash factory are brought into the cleared chambers using scrapers. In the past, the offset was also introduced by hand or with a vibrating slide. In some mines in the Stassfurter Revier, the backfill was also extracted underground in the mountain mill and then brought into the dismantled chambers. In the potash mining of the southern Harz Mountains, flushing backfill was also introduced into the excavated chambers instead of the mountain backfill. If this backfill had hardened well, the pillars could then also be won. If the pillars are dismantled without shifting the chambers, the cavity created will gradually break . This type of chamber construction is then called chamber pillar fracture construction. A special type of chamber construction is the multi-storey building .

Preparatory work

Before the deposit can be dismantled by means of chamber construction, a main route network must first be created. Depending on the size of the deposit, several cross passages are driven in the deposit, starting from a striking main conveying line. To ensure that the conveyor lines are largely protected from the effects of mining, around twelve meter thick salt festivals are left standing on both sides of the conveyor lines. The individual chambers are created based on the cross passages. The individual chambers are connected to the cross-passages at the height of the route using passages. A break-in is then created at the level of the route, from which the chamber is dismantled.

The dismantling of the chambers

The Verhieb of the chambers can be done in two ways, from above or from below strossenartiger construction in firstenbauartiger construction.

The stroke-like method is used in irregular mountain conditions and steep slopes. With this type of construction, the sole is slashed from above like a stroke. With this method, the height of the chamber can be arbitrary. As soon as the overburden in a chamber no longer has sufficient load-bearing capacity, mining in the corresponding chamber is stopped and a new chamber is started by means of a levitation. The stroke-like construction has the advantage that the miners have greater security against falling stones. This is primarily because they do not have to work under overhanging parts of the deposit. In addition, with this construction method, the roof can be secured with rock bolts. The disadvantage, however, is that the miners move further and further away from the roof, making observation of the mountains very difficult. This has a negative effect in particular because the strength or load-bearing capacity of the roof decreases as degradation progresses .

When chopping the ridge, the chambers are created from bottom to top, this is done by constantly attacking the ridge. The tusks always have the deposit above them and stand on top of the recovered heap . By constantly working out the mineral mass, the mountains cannot crack. This means that the overburden has sufficient stability and the dangers of overhanging impacts are reduced to a minimum. For this reason, roofing is preferred when building chambers.

Size of the extraction chamber

Simulated mining chamber with Unimog from the Bülten-Adenstedt mine in the German Mining Museum in Bochum

The size of the extraction chambers depends on the size of the deposit and the load-bearing capacity of the rock. The chambers have a length of up to 200 meters and a width of 20 meters, depending on the deposit. The height is usually between nine and eleven meters. However, chambers with a height of up to 50 meters have also been excavated. The largest mining chambers are created in rock salt and roofing slate mining. In the Hungarian rock salt mining, a mining chamber reached a height of 147 meters and a width of 47 meters. Problems can always arise if the chambers are dimensioned too large. This happens especially when the stability of the rock is overestimated and the safety distance to the overburden is too small. In potash mining, for example, the water-bearing surface layers can lead to rockfalls or breakouts. By intrusion of alkali-containing water, the so-called liquor breakdown, it can for flooding view of the mine.

Dimensioning of the pillars

Since the pillars function as rock-mechanical load-bearing elements in chamber construction, they have to be dimensioned according to their vertical load. Insufficient dimensioning of the pillars has a negative effect on the stability and load-bearing capacity of the pillars. The pillars must be attached in such a way that the fortresses and chambers are exactly one above the other. This is the only way to ensure that the fixed and floating structures result in a solid structure. For the dimensioning and spacing of the pillars, certain empirical rules were still in use in the 20th century. In order to get enough stable pillars, pillars with a thickness of eight meters were used. Today, the vertical load on the pillars can be determined by calculation with knowledge of the sink pressure and a load factor. Various methods, both computational and laboratory testing, have been developed for the exact dimensioning of the pillars. In addition to the load factor, certain influencing factors such as the pier width, the slenderness of the pier, the ratio of pier width to pier length and the depth are required to determine the pier dimensions.

mechanization

Due to the expansion of the individual chambers, mechanization of the extraction and extraction of the mined mineral is usually possible in chamber construction. The extraction is often still carried out by drilling and blasting . The blast holes are drilled using a drill carriage . The extracted mineral is then loaded onto trucks using loading machines and transported over the surface. Vehicle loaders are used as loading machines. Backhoe excavators are also used in large excavation chambers. But here, too, mechanization is possible through the use of continuous miners . When converting from conventional extraction to extraction using continuous miners, the mining process must be adapted accordingly.

Individual evidence

^ 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 Ernst-Ulrich Reuther: Introduction to mining . 1st edition, Verlag Glückauf GmbH, Essen, 1982, ISBN 3-7739-0390-1 .
^ ^A ^b Gerd Weisgerber : Basics of a systematic mining science for prehistory and early history and antiquity . In: Association of Friends of Mining in Graubünden. (Ed.): Berg-Knappe. No. 59, January 1992, pp. 7-9
↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v Carl Hellmut Fritzsche: Textbook of mining studies. Second volume, 10th edition, Springer Verlag, Berlin / Göttingen / Heidelberg 1962
↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p F. Heise, F. Herbst: Textbook of mining science with special consideration of hard coal mining. First volume, published by Julius Springer, Berlin 1908
↑ ^a ^b ^c Norbert Deisenroth: 150 years of potash mining in Germany . In: Hessischer Landesverband eV in the Bund Deutscher Bergmanns-, Hütten- und Knappenvereine eV (Hrsg.): Tackling box. No. 8, ISSN 1867-0458 , February 2011, pp. 14-18
^ Förderverein Rammelsberger Bergbaumuseum Goslar eV (Hrsg.): Ore mining in the Rammelsberg. Self-published by the Förderverein, Druck Papierflieger Clausthal-Zellerfeld, Goslar 2009
^ Franz Adolf Fürer: Salt mining and salt research. Printed and published by Friedrich Vieweg and Son, Braunschweig 1900
↑ ^a ^b ^c Axel Hausdorf: Numerical studies on the stability of chamber ridges in salt mining with special attention to system anchoring with elasto - plastic - strengthening anchor characteristics and different anchor preload values . Approved dissertation, Bergakademie Freiberg, Freiberg 2006, pp. 6–29
↑ ^a ^b Eric Drüppel: Development of a concept for the cutting extraction in rock salt. Approved dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, Aachen 2010, pp. 34–35

Remarks

↑ The direction that runs horizontally across the longitudinal axis of the deposit is referred to as cross-cutting . (Source: Förderverein Rammelsberger Bergbaumuseum Goslar eV (Ed.): Ore mining in Rammelsberg. )

[Quelle_1-1] Walter Bischoff , Heinz Bramann, Westfälische Berggewerkschaftskasse Bochum: The small mining dictionary . 7th edition, Verlag Glückauf GmbH, Essen 1988, ISBN 3-7739-0501-7 .

[Quelle_4-2] Ernst-Ulrich Reuther: Introduction to mining . 1st edition, Verlag Glückauf GmbH, Essen, 1982, ISBN 3-7739-0390-1 .

[Quelle_5-3] A ^b Gerd Weisgerber : Basics of a systematic mining science for prehistory and early history and antiquity . In: Association of Friends of Mining in Graubünden. (Ed.): Berg-Knappe. No. 59, January 1992, pp. 7-9

[Quelle_2-4] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v Carl Hellmut Fritzsche: Textbook of mining studies. Second volume, 10th edition, Springer Verlag, Berlin / Göttingen / Heidelberg 1962

[Quelle_3-5] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p F. Heise, F. Herbst: Textbook of mining science with special consideration of hard coal mining. First volume, published by Julius Springer, Berlin 1908

[Quelle_6-6] Norbert Deisenroth: 150 years of potash mining in Germany . In: Hessischer Landesverband eV in the Bund Deutscher Bergmanns-, Hütten- und Knappenvereine eV (Hrsg.): Tackling box. No. 8, ISSN 1867-0458 , February 2011, pp. 14-18

[Quelle_10-8] Förderverein Rammelsberger Bergbaumuseum Goslar eV (Hrsg.): Ore mining in the Rammelsberg. Self-published by the Förderverein, Druck Papierflieger Clausthal-Zellerfeld, Goslar 2009

[Quelle_8-9] Franz Adolf Fürer: Salt mining and salt research. Printed and published by Friedrich Vieweg and Son, Braunschweig 1900

[Quelle_9-10] Axel Hausdorf: Numerical studies on the stability of chamber ridges in salt mining with special attention to system anchoring with elasto - plastic - strengthening anchor characteristics and different anchor preload values . Approved dissertation, Bergakademie Freiberg, Freiberg 2006, pp. 6–29

[Quelle_7-11] Eric Drüppel: Development of a concept for the cutting extraction in rock salt. Approved dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, Aachen 2010, pp. 34–35

[Anm._Förderv.-7] The direction that runs horizontally across the longitudinal axis of the deposit is referred to as cross-cutting . (Source: Förderverein Rammelsberger Bergbaumuseum Goslar eV (Ed.): Ore mining in Rammelsberg. )