Mountain pressure

In mining and tunneling, rock pressure is an invisible tension that occurs around an underground cavity or in unscratched rock. The mountain pressure is one of the triggers for mountain hits .

Mountain pressure theories

Several theories about the distribution of the rock pressure and the accumulation of compressive stresses in the rock were already developed in the 19th century. In 1879 Ritter developed a theory about the vertical pressure when the depth is neglected. This theory was further developed by other engineers such as Friedrich Engesser (1882) and Forchheimer (1882). In 1913 Bierbaumer developed the theory of vertical pressure taking into account the depth. In 1920, Suquet's remarks were added. The mountain pressure theory by Terzaghi from 1946, which is also known as the silo pressure theory, is very widespread. In total, more than 20 rock pressure theories have been developed, some of which are similar. Two theories have prevailed in hard coal mining, the Spackeler vault theory and Lehmann's trough theory.

Basics

Every body exerts a certain pressure on the ground due to its weight; this is no different with mountain masses. At a depth of 800 meters, this pressure reaches a strength of around 20 megapascals . This corresponds to about 200 . The pressure of the mountain body creates a vertical mountain tension, which, due to the structure of the mountain body, also has a lateral effect. Since the particles that make up the mountain cannot expand laterally, the mountain pressure acts on all sides. The actual rock pressure at a certain depth is difficult to calculate. This is due to the inhomogeneity of the mountain body; The pressure can only be calculated more precisely in the case of very flexible rock. Because of the different effects, a distinction is made between pressures in unscratched and scratched mountains. ${\ displaystyle kg / cm ^ {2}}$

Uncarved mountains

Uncarved rock is in a state of tension that is caused by the weight of the overlying rock layers. The vertical pressure that is created there is called the overlay pressure. This overburden pressure depends on the rock density and depth . The pressure in the unscratched mountain acts both downwards and to the side, the vertical pressure being just as great as the horizontal pressure. This pressure equilibrium is disturbed in the vicinity of mine workings.

Scattered mountains

While the rock pressure can be limited to the two pressures horizontal pressure and superposition pressure in the case of unscratched rock, this is not possible in the case of scratched rock. By creating a mining cavity, the existing equilibrium in the rock is destroyed, thereby changing the stress distribution in the rock. The rock pressure is composed of a number of individual forces of different directions and sizes. The Austrian university professor Ladislaus von Rabcewicz divided the mountain pressure into several forces that burden the expansion , which he attributed to different causes. The loosening of the mountains as a result of mining activities creates a pressure that is known as pure ridge pressure or also as loosening pressure . The real rock pressure is the pressure caused by the tectonics. The real rock pressure is a relief process in the rock. During this relief process, the stress peaks in the rock caused by the created cavities are balanced. As a result, the forces are distributed to other areas of the mountain body. The loosening pressure arises from fissures in the mountains and is mainly expressed in the ridge area. Another form of printing is swelling pressure, which is created by preventing the sole lifting . In the vicinity of mine workings, vertical pressure usually predominates. This is made up of the overlay pressure and the additional pressure, also known as the overlay pressure. The vertical pressure can be a multiple of the overlay pressure.

Effects

Depending on the size and direction, the rock pressure has different effects on the scratched rock. Mild or fragile rock layers break off under the pressure of the mountains. Loose heaped up or cohesive masses in a lying position inflate and press into the existing cavity. If there are such masses in the hanging wall , they sink. Due to the distribution of the rock pressure and the structure of the rock layers, only a small part of the pressure is on the expansion . The expansion therefore only has to bear the weight of the lower rock layers. The effects on mining are heavily dependent on the shape of the cross-section. Trapezoidal and rectangular cross-sections are very unfavorable shapes. With these cross-sections, the impacts are exposed to high pressure loads. Considerable tensile stresses occur in the area of the roof and the base. With other cross-sectional shapes, such as. B. the semicircular cross-section, the tensile stresses are weakened in the roof. The most favorable cross-sectional shapes are those that have a greater height than width. Particularly favorable conditions with regard to the loads in the ridge area have teardrop-shaped cross-sections.

Individual evidence

↑ ^a ^b ^c ^d ^e ^f 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 Jürgen Anton Schmitt: Stress deformation behavior of the rock when driving with tunnel boring machines with shield. (Dissertation) ingenieur-bauwesen.de (accessed December 5, 2011; PDF; 5.9 MB)
↑ ^a ^b Helmut Kratzsch: Bergschadenkunde . Ed .: Deutscher Markscheider-Verein eV 5th edition. Bochum 1997, ISBN 3-00-001661-9 .
^ ^A ^b ^c ^d ^e Carl Hellmut Fritzsche: Textbook of mining science. Second volume, 10th edition, Springer Verlag, Berlin / Göttingen / Heidelberg 1962.
↑ ^a ^b Ladislaus von Rabcewicz. Rock pressure and tunneling. Unchanged reprint 1993, Springer Verlag Wien GmbH, Vienna 1993, ISBN 978-3-7091-2325-6 .
^ Wulf Schubert: Mountain pressure and tunnel construction from the perspective of Rabcewicz 1944 . In: Felsbau . tape 12 , no. 5 . VGE, Essen 1994, p. 303–306 ( online.tugraz.at [PDF; 669 kB ; accessed on September 29, 2014]).
^ Franz Rziha: Textbook of the entire art of tunneling. Second volume, published by Ernst & Korn, Berlin 1872.
^ Association for Mining Interests in the Upper Mining District Dortmund: 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.

[Quelle1-1] ↑ ^a ^b ^c ^d ^e ^f Walter Bischoff , Heinz Bramann, Westfälische Berggewerkschaftskasse Bochum: The small mining dictionary. 7th edition, Verlag Glückauf GmbH, Essen 1988, ISBN 3-7739-0501-7 .

[Quelle2-2] Jürgen Anton Schmitt: Stress deformation behavior of the rock when driving with tunnel boring machines with shield. (Dissertation) ingenieur-bauwesen.de (accessed December 5, 2011; PDF; 5.9 MB)

[Quelle3-3] Helmut Kratzsch: Bergschadenkunde . Ed .: Deutscher Markscheider-Verein eV 5th edition. Bochum 1997, ISBN 3-00-001661-9 .

[Quelle4-4] A ^b ^c ^d ^e Carl Hellmut Fritzsche: Textbook of mining science. Second volume, 10th edition, Springer Verlag, Berlin / Göttingen / Heidelberg 1962.

[Quelle5-5] Ladislaus von Rabcewicz. Rock pressure and tunneling. Unchanged reprint 1993, Springer Verlag Wien GmbH, Vienna 1993, ISBN 978-3-7091-2325-6 .

[Quelle6-6] Wulf Schubert: Mountain pressure and tunnel construction from the perspective of Rabcewicz 1944 . In: Felsbau . tape 12 , no. 5 . VGE, Essen 1994, p. 303–306 ( online.tugraz.at [PDF; 669 kB ; accessed on September 29, 2014]).

[Quelle7-7] Franz Rziha: Textbook of the entire art of tunneling. Second volume, published by Ernst & Korn, Berlin 1872.

[Quelle8-8] Association for Mining Interests in the Upper Mining District Dortmund: 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.