Room and pillar
With chamber construction means a special mining methods in mining. The chamber construction as part of the Örterbau and Weitungsbau to the degradation process with chamber-like design. The mining method was used in ancient Roman mining as a common method for extraction of minerals. Today, the chamber construction comes in both massive and in flözartigen deposits used. Mainly this mining method is used in potash and salt mining and iron ore mining. But the underground mining of limestone and gypsum, and the roofing slate predominantly chamber construction is applied. In Bohemia mining district with the removal procedure was used in the lignite mining.
In deposits where water is present in the cover, it may come at any point in a lowering. The reason for this is that these reductions lead to breakage or cracks in the overburden. This reduction method can be adopted in which stand as pillars parts of the deposit and thus support the overburden. Suitable methods are here mining method with chamber-like design. The chamber construction is used in reservoirs with large thickness, it is irrelevant that has dip the deposit. Due to the construction of this process the hanging wall of strongholds is comparable supported as a ceiling of the room walls. Although the chamber construction is very similar to the Örterbau and there are also transitions between the two methods, the chamber construction differs from this degradation process due to the large dimensions of the working face and thereby forming degradation room (chamber).
The degradation process
In this mining method, each cavity is around surrounded by security pillars. These pillars serve practically as walls, so that individual stopes are formed. Since this systematic chambers between standing pillars are created, this type of procedure as a room-and. Prerequisite for this degradation process is a sufficient stability of the ground. This is necessary so that the chambers can remain open at their excavation without dismantling. In addition, the pillar must have a certain thickness, so that the hanging wall not falls. Too weak sized pillars and strongholds may occur days break. The upcoming mineral is mined by underground within the deposit elongated chambers from the rock breaks, which are evenly distributed over the mining field. The working direction is floating in the rule. The Verhiebrichtung is either striking out or querschlägig. [ NOTE 1] As the first Verhiebart like Verhieb is applied. The chamber construction is particularly useful in irregular deposits in which the minerals do not occur uniformly continuous. Through the chamber construction high degradation efficiency can be achieved simultaneously with relatively low extraction costs. A disadvantage of the chamber construction, the high degradation losses of 50 percent and sometimes more. Problems can also prepare the open chamber ridges. This can be affected by technical and inherent influences the stability. The targeted use of rock anchors the stability of the ridges is improved.
Depending on the deposit different variants of the chamber construction are applied. There is the chamber construction without displacement, the chamber construction with offset and the Kammerbruchbau. The supporting pillars with reduced depending on the method. There is also a variant in which both the resilient pillars and the pillars are not degraded. The chamber construction with offset is used almost exclusively in potash mining. The introduction of offset is in the potash mining, unlike the rock salt mining, from reasons of formality rod chambers required. As an offset of potash residues are introduced by means of scrapers in the evacuated chambers. Previously, the offset by hand or with the jig was placed. In some mines in the coalfield Staßfurter the offset and underground was recovered in the mountains mill and then placed in the mined chambers. In the potash of the southern Harz also backfilling was introduced into the mined chambers instead of the Mountain Ever set. If this offset was well cured, then you could also win in the pillars. If the pillar mined without the offset of the chambers, the cavity produced is gradually broken. This type of chamber construction is then called Kammerpfeilerbruchbau. A special type of chamber construction is the stratigraphic.
Before the deposit can be mined by means of chamber construction, first a main route network must be created. Starting from a trending main gallery several crosscuts are, depending on the size of the deposit, ascended into the deposit. Thus, the conveyor sections are largely protected from the effects of mining, conveyor lines are on both sides of about twelve meters thick salt festivals left. Based on the cross-cuts, the individual chambers are created. The individual chambers are connected in line Height above blows with the crossways. An intrusion is then created in segment height, starting from which the chamber is reduced.
The degradation of the chambers
The Verhieb of the chambers can be done in two ways, from above or from below into strossenartiger construction firstenbauartiger construction.
The strossenartige Verhieb is applied to irregular ground conditions and steep dip. In this construction, the sole is made from above in strossenartig Verhieb. The height of the chamber may be any in the process. Once the overburden no longer has sufficient capacity in one chamber, the reduction in the corresponding chamber is stopped and taken a new chamber by means of a float in attack. The strossenartige construction has the advantage that the miners have greater security against rock falls. This is first of all the fact that they do not have to work under overhanging portions of the deposit. Moreover, in this construction, the ridges can be secured with rock bolts. The disadvantage, however, is that the miners further and further away from the roof and thus an observation of the mountain is very difficult. This affects in particular by the negative, as in the progressive degeneration decreases the strength and sustainability of ridges.
When Enver First chop the chambers are created from the bottom up, this is done by continuous attack of the ridges. The Hauer always have the deposit over and stand on the incoming recovered debris. Through the constant work out the mineral composition, the mountain can not fracturing. Thus the overburden has sufficient stability and the dangers of over-hanging impacts are reduced to a minimum. For this reason, the first female bat is preferred for chamber construction.
Size of the stope
The size of the stopes is dependent on the size of the deposit and the viability of the mountain. The chambers, depending on the deposit, a length of up to 200 meters and a width of 20 meters. The amount is usually between nine and eleven meters. However, there have been ascended and chambers with a height of up to 50 meters. The largest stopes occur in rock salt and roofing slate mining. In the Hungarian rock salt mining a stope reached a height of 147 meters and a width of 47 meters. Problems can always occur when the chambers are too large dimensioned. This happens especially if in addition the stability of the ground is overestimated and the safety distance from the overburden is chosen too low. Here, for example, when potash mining due to the water-bearing layers come to rock bursts or for day break. The penetration of alkali- containing waters, the so-called lye breakthrough, it can come to the flooding of the mine.
Dimensions of the pillars
As the pillar chamber construction work at the rock mechanical support elements, they must be strongly dimensioned according to their vertical load. Too weak dimensions of the pillars has a negative effect on the stability and sustainability of the pillars. The pillar shall be so placed that the parties and chambers each line up exactly. Only in this way it is ensured that the festivities and float result in a fixed supporting structure. For the dimensioning and for the distance of the piers certain empirical rules were still in use in the 20th century. To provide adequate stable pillar, pillar here starches were used by eight meters. Today it is the vertical load on the pillar with knowledge of the depths pressure and a load factor determined by calculation. For the exact dimensions of the pillars, various methods were both computational and laboratory testing procedures developed. In addition to the load factor, certain factors such as the pillar width pillar thinness, the ratio of width to pillar pillar length and depth to determine the dimensions of pillars are required.
Due to the expansion of the individual chambers in the chamber construction is usually a mechanization of production and the promotion of the mined mineral is possible. The extraction is carried out in many cases still by drilling and blasting. Drilling of blast holes by means of Drilling Vehicle. The leached mineral is then loaded by loading machines on trucks and transported to aboveground. When loading machines LHDs are used. In large stopes and shovels are used. But here mechanization through the use of continuous miners is possible. When converting from conventional production on extraction by means of the continuous miner mining methods must be adapted accordingly.