Mountain range

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As a rock burst sudden stress redistribution are in a compact, brittle rock called.

Causes and process

The most common cause of rockfalls is human intervention in the rock structure through mining . As a result, tensions build up in rock layers with a low modulus of elasticity , which are suddenly and abruptly reduced when the deformation limit is exceeded. The sudden reduction in stress causes cracks in the rock, which in turn lead to dangerous material detachment in the face , at the joints and the roof . The location of the epicenter plays a role in the size, type and location of the detachments . In most cases, an explosion provides the initial step for the stress relief. The sudden relaxation is perceptible above and below the surface as clearly audible blows and shocks. The severity of such an event depends on the size of the cavity that is filled by the collapse of the overburden. The collapse of extensive cavities can cause very strong vibrations that can be perceived as (usually weak) earthquakes in the surrounding region .

consequences

In severe cases, a rockfall can lead to the sudden collapse of cavities. The fact that in most cases no miners are harmed is due to the fact that in today's mining, for safety reasons, the blasting is carried out during the shift change when there are no miners in the pit ( centralized shooting ). The collapse of the cavities causes damage to material and equipment. Over days, mountain damage can be the result of a mountain impact. These range from sinkholes to the collapse of entire buildings. Since a rock attack - except for the cause - happens just like a light earthquake, the consequences are similar.

Prevention

The effects of rockfalls can be countered by using flexible types of construction such as anchors or installation arches in tunnel construction . A certain amount of play is planned for so-called flexible anchors, which means that they can absorb the sudden stress redistribution without losing their load-bearing capacity.

Single events

The strongest rockfall caused by mining so far occurred on March 13, 1989 in the Merkers potash works near Völkershausen . The quake could be felt up to 300 km and reached the local magnitude M L = 5.6. Further examples are the rock blows with a strength of 5.5 on the Richter scale in Teutschenthal on September 11, 1996 and on February 23, 2008 in the Saarlouis district ( Saar mine ) with a strength of 4.

The rockfall in the Merkers potash works was caused by excessive pier weakening. In Merkers several pillars burst ( domino effect ) when they could no longer bear the weight of the overburden. When applied there degradation process chamber pillar working chambers were a chessboard ascended between which approximately square pillars remained standing, the abstützten the ridges. Tension lines that are concave form in the pillars. The material outside of the stress line has no supporting function. This effect was used to minimize the mining losses due to the permanent pillars. Too much material was removed due to errors in the calculation and the pillars were weakened too much.

literature

Individual evidence

  1. ↑ Dangerous tension in the depths. Geoscientists analyze rockfalls in Saar mining. Deutschlandradio, February 26, 2008, accessed on August 10, 2014 .
  2. ↑ Bernhard Mackowiak: Why the ground collapses in the Saarland. In: world. February 8, 2008, accessed August 10, 2014 .