Convergence (mining)

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As convergence is known in mining to be due to the rock pressure as an approximation of Hangendem and lying resulting length amount. In the coal mining industry , the bank-appropriate approach of two convergence measuring points was previously referred to as convergence.

Basics

In the mountains , there are tensions due to the pressure of the mountains, which arise from the weight of the overlying rock layers. However, these tensions are at rest when the rock is not scratched. If a cavity is now created, load redistribution occurs in the mountains surrounding the cavity. The burden of the mountains shifts to the surrounding area. If the cavity is enlarged further, the state of tension in the rock changes continuously. If the resistance of the rock is greater than the changes in tension, there is no change in the created cavity. The decisive factor here is how high the ratio of the vertical stress of the rock mass to the greatest horizontal stress is. Are formed through the cavity new voltages greater than the rock strength , the rock mass adjacent to respond to these stresses. Since these rock masses have no way of escaping into the unscratched mountains, they penetrate the cavity. This is done in such a way that the mountain bends gradually into the cavity. The cavity is compressed. These profile constrictions are known as convergence. In principle, convergences occur wherever cavities are created through driving or dismantling. The percentage shrinkage of the void volume is called volume convergence. It is given as a percentage of the initial volume. The convergences of the underground cavities have an impact above ground . This then leads to subsidence . The speed at which convergence takes place is called the rate of convergence. It mainly depends on the surrounding rock.

Types of convergence

There are several types of convergence. There is the approach convergence, the creep convergence, the apron convergence, the face convergence and the end convergence.

The convergence that occurs in stretches that have been driven in the rock is called drive convergence. The drive-up convergence is a consequence of the drive-up (installation) and is completed after about half a year. The rock strength of the lying surface and the prevailing rock pressure have an influence on the approach convergence . If a further convergence arises after the approach convergence has subsided, this is referred to as creep convergence. Creep convergences are caused by seams that are located below the bottom of the driven route.

The apron convergence is created by the additional pressure of the sub-structure of the mountain. It begins between 50 and 100 meters before the excavation face, depending on the rock on the hillside. In the case of the apron convergence, a distinction is made between the apron convergence in the mining field and the apron convergence in the extraction field. Due to the convergence of the apron, the seam is compressed and gives way to the excavation cavity.

Strut convergences arise at the offset edge or the break edge. The width of these zones is around six meters from the joint and extends to the edge of the offset field. Due to the weight of the rock strata's own weight, the strata bends and the lowest strata break into the face.

The post-convergence arises in the old man , here the mountains lie on the rubble or on the offset . The post-convergence increases up to the center of the full surface. The final convergence is the complete compression of the debris or the offset.

Convergence measurement

In order to detect changes in distance between the respective convergence points, convergence measurements are required. For this purpose, corresponding convergence measuring points must be set up in the respective convergence area, which are then checked at regular intervals. The spatial position of the convergence measurement points relative to one another and the spatial position of the convergence lines measured between the measurement points are recorded during the measurements. For documentation purposes, the measurement results are first entered in a sketch and above ground in a plan . After certain time intervals and corresponding measurements, the convergence can be determined from the difference between the measured values. During the calculation, the older one is subtracted from the newer measurement. If negative values ​​result as the difference, one speaks of convergence, in the case of positive values ​​one speaks of divergence. The quotient of the convergence or divergence ( , ) and the time difference between the measurement times and is called the convergence speed. The dimensions day, week, month, and year are preferably used as the time difference.

Convergence forecast

The convergence prediction is a mathematical-statistical method, which to predict the final convergence of degradation routes used. Both geological and operational influencing factors are taken into account in the convergence forecast. The convergence is given as a percentage of the distance traveled. Geological influencing variables are the depth, the seam thickness and the lying adjacent rock (lying key figure). Operational parameters are the route height and the seam offset.

Countermeasures

Since the layout of the deposit often means that multiple use of the mining accompanying stretches is necessary, it must be ensured that a sufficiently large cross-section of the route is maintained behind the mining front. For this reason, measures and methods are being taken which are mainly intended to counteract convergence. As an effective method, the introduction is by route accompanying dams proved from building materials. The dam will be built at the edge of the route immediately after the longwall pass. If the route cross-section is reduced due to swollen lying rock, the route cross-section is increased again by means of lowering work .

Individual evidence

  1. ↑ a b c d e f g h i j Walter Bischoff , Heinz Bramann, Westfälische Berggewerkschaftskasse Bochum: The small mining dictionary . 7th edition, Verlag Glückauf GmbH, Essen 1988, ISBN 3-7739-0501-7 .
  2. ↑ a b c Josef Stini: Tunneling Geology . The geological foundations of tunnel and tunnel construction, Springer-Verlag, Vienna 1950, pp. 131-134.
  3. ↑ a b c Helmut Prinz, Roland Strauss: Engineering Geology . 5th edited and expanded edition, Spektrum akademischer Verlag, Heidelberg 2011, ISBN 978-3-8274-2472-3 , pp. 519,520,526,531.
  4. ↑ a b c Karsten Zimmermann: Forecast and analysis of mining damage of dynamic soil movements caused by near-surface hard coal mining in the USA . Approved dissertation from the Technical University Bergakademie Freiberg, Freiberg 2011, pp. 14-16.
  5. ↑ a b Ralf E. Krupp: Brief report on the long-term safety of solution caverns in the Etzel salt dome . Burgdorf 2012, pp. 7–8.
  6. ↑ Antje Bohn: Hydrogeological analysis and modeling of solution and reaction processes in the saline and overburden on the Staßfurter Sattel . Approved dissertation from the Brandenburg Technical University Cottbus-Senftenberg, Cottbus 2013, p. 3.
  7. ↑ a b c d Helmut Kratzsch: Bergschadenkunde . 5th updated and revised edition, Papierflieger Verlag GmbH, Clausthal-Zellerfeld 2008, ISBN 3-00-001661-9 , pp. 5-100.
  8. ↑ Evaluation of Markscheider measurements . Online ( Memento from April 20, 2004 in the Internet Archive ) (PDF; 220 kB) (accessed on August 1, 2016).
  9. ↑ Stanislaw Prusek, Bergbau- Hauptinstitut (GIG) Kattowitz: Determination of the supporting force of roadside dams after longwall pass (=  Glückauf . 138th year, no. 6 ). Glückauf, Essen 2002, p. 269-273 ( online [accessed February 4, 2016]).

Remarks

  1. ↑ The direction that is perpendicular to the hanging or lying wall of a deposit is referred to as banking law . (Source: Walter Bischoff, Heinz Bramann, Westfälische Berggewerkschaftskasse Bochum: Das kleine Bergbaulexikon .)