Rock burst

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

Causes

The most common cause of rock bursts is the human intervention in the stone structure by mining. This build up in layers of rock with low modulus voltages on that break suddenly and abruptly when the deformation limit is exceeded. The rock burst in potash flag was caused by excessive pillar weakening. When used there degradation process chamber - pillar method chessboard-like chambers were excavated between which are remained approximately square pillars that abstützten the ridges. In the piers voltage lines are formed, extending concave. The material outside the line voltage curve has no load-bearing function. This effect is made ​​possible to take advantage in order to minimize the degradation losses caused by the permanent stand lasting pier. Was removed too much material from errors in the calculation and the pillars thereby weakened.

Expiration

Due to the sudden stress relief cracks in the rock, in consequence there is a dangerous material separation in the face, to the bumps and ridges. For size, type and location of the delamination location of the epicenter plays a role. In most cases, a blasting provides the initial for the stress relief. The sudden relaxations are under-and over days as well audible beats and vibrations perceptible. In a series of pillars flag most ( domino effect), as they could no longer bear the burden of the overburden. The strength of such an event depends on the size of the cavity, which is filled by the collapse of the overburden. The collapse of extensive cavities can cause very severe vibrations that can be perceived as, usually weak, earthquakes in the surrounding region.

Follow

In severe cases, a rock burst to the sudden collapse of cavities lead. No miners are that in most cases, to harm, is that in today's mining safety reasons the blasting operations are carried out in the time of shift change, when there are no miners in the mine are ( central Shooting). With the collapse of the cavities damage to materials and equipment enter. Above ground subsidence damage can be the result of a mountain shock. These range from sinkholes up to the collapse of entire buildings. Since a rock burst - except for the cause - just runs like a small earthquake, the consequences are similar.

Prevention

By using flexible expansion species such as anchors or mounting sheets in tunneling the effects of mountain shock can be countered. In so-called flexible anchors a certain play is scheduled, that is, they can absorb the sudden stress redistribution without losing their viability.

Single events

The strongest rock burst caused by mining occurred on 13 March 1989 at the potash plant marker for Völkershausen. The quake was felt up to 300 km wide, reaching the local magnitude ML = 5.6. Other examples are the rock bursts of strength 5.5 on the Richter scale in Teutschenthal on 11 September 1996 and 23 February 2008 in the district of Saarlouis ( Saar mine ) with the strength of 4