Shaft custody
In the mining industry, shaft storage is the permanent, maintenance-free and effective closure of a discarded shaft . Shaft repositories are considered permanent if they lock the shaft securely for at least 100 years.
Basics
Shafts that are no longer required represent a great potential risk, especially if the shaft openings are not secured. For example, in July 2012 a three-year-old child fell as part of a kindergarten excursion into a 25 m deep ventilation shaft of an old coal mine near Osterwald and could only be rescued with minor injuries because his teacher jumped after and held the child above water until the fire brigade arrived . In the past, thrown shafts were only filled with rubble or rubbish and temporarily covered. Over the years, the filling column was under the influence of mine water softened and sagged, the makeshift weight saver broke and it came to Schachtverbruch . Experts assume that there are over a thousand old shafts in the Ruhr area alone that are not adequately secured. Based on the experiences of various Schachtverbrüchen standards were for the custody of the 1970s seigeren and tonnlägigen developed wells.
planning
All technical measures are preceded by detailed planning. First, the actual condition of the shaft to be kept is examined. Adjacent cavities and pits are included in the planning of the manhole storage measures . Depending on the mined mineral, the distances to the shaft to be included are between ten and fifty meters. The planning engineers get an initial overview of the manhole based on technical documents about the manhole installations and mine- separating cracks . An important aspect for the filling materials used is the knowledge of the amount and the composition of the pit water; hydrological studies provide important information. Further knowledge about the structure of the shaft is provided by maneuvers and camera inspections of the shaft. During the drives, the rock can be checked by means of boreholes, and further measurements can also be carried out in the shaft. The knowledge about the situation at the surface will also flow into the planning. This is particularly important so that the thrown shaft does not pose any dangers to the public. Based on the planning, the corresponding safekeeping goals are derived and the corresponding safekeeping measures are determined from them.
execution
The type of storage of day shafts depends on the local geotechnical and mining conditions. Depending on the local conditions and storage goals, day shafts are either fully or partially filled. As a rule, manholes are completely backfilled, partial backfills are only used if it is necessary to discharge the mine gas or the mine water. If deeper sections of the manhole are no longer accessible, partial backfilling is also appropriate.
In the case of filling goods, a distinction is made between load-bearing filling goods, sealing filling goods and filling goods that fill cavities. Load-bearing filling material is stable in position, it has cavity-filling properties and can dissipate the forces that occur well. Gravel and concrete are used as the load-bearing filling material . Sealing filling material prevents the exchange of substances, clay , asphalt or bitumen are suitable for this. Filling material that fills void spaces is not always positionally stable, so it is only used to completely fill shaft voids. Suitable materials are gravel , sand, salt, dam building material or crushed stone.
There are three methods of introducing the backfill:
- Free falling
- Introduction via pipelines
- Introduction with discontinuous processes
When the backfill material is brought in by falling freely, the manhole installations in the manhole can cause so-called bridging . In order to prevent this, all manhole installations that could hinder the free fall of the product are removed in advance.
Bringing in via pipelines is much more gentle on the shaft construction than falling freely. It is mostly used when there are concerns about free falling due to the existing fixtures. When introducing the product via pipelines, lines with a sufficiently large diameter are used in accordance with the grain size of the product.
When introducing with discontinuous processes, the filling material is brought in by means of the existing shaft conveyor system. A feed bucket or a conveyor vessel with bottom emptying is used for this. This process also gently introduces the contents.
Problems
When backfilling with ordinary concrete made of cement and gravel, the individual components can separate from a fall height of 30 meters and more. The aggregates separate from the liquid concrete and fall into the shaft faster than the cement paste. As a result, the filling material no longer has the required mixture when it hits the bottom of the shaft. Free fall in the shaft is also not always guaranteed, especially at great depths . Often times the filling material touches the shaft wall and is swirled during the fall. The filling material also sticks to built-in components, protrusions and the shaft wall. This leads to narrowing of the free shaft cross-section. This can mean that the backfill column is not continuous and that cavities form in the backfill column. These cavities can fill up with mine gas over time. Unwanted water inflows cause further problems; depending on the amount of water, it can impair the strength of the backfill material.
Safekeeping in case of shaft breaches
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The safekeeping of daily shafts that have already been broken in is often much more difficult than the safekeeping of non-broken shafts. Special security measures are taken here. Different shaped concrete seals have also proven particularly useful. These seals are used as storage bodies in shafts in the solid rock zone. In many cases, various measures are also used side by side. In the case of a sagged loose filler mass column, there is the possibility of partially stabilizing the sagged loose filler mass column or a cohesive partial filling of the shaft is used.
The following methods are available for manhole covers:
- Attachment of a cover plate with a single pile foundation
- Attaching a cover plate with external reinforcement
- Attaching a cover plate in which the existing and still intact shaft extension serves as a foundation
- Attaching a cover plate in which the surrounding overburden serves as a foundation (in the case of rock overburden)
Which manhole covers are used depends on the damage to the manhole lining and the rock surrounding the manhole.
Closing measures
To ensure safe subsequent use, further measures are taken after the shaft has been backfilled. Depending on the safekeeping concept, the other measures range from covering the shaft column and marking the safe shaft to discharging the mine gas and defining security zones and control periods. In certain cases it is even necessary that the filling column has to be supplemented after a certain settlement.
Day manholes are usually covered with a reinforced concrete slab after filling. The shaft extension is used as an abutment for this plate if it is sufficiently stable. This stability must be examined locally and verified by calculation. If a shaft has been filled with hydraulically binding, non-washable and stable material (cohesive filling material), the shaft plate is not required. In manholes where the manhole head is already deformed, the manhole lining can no longer be used as an abutment. In such shafts, special concrete foundations are used, which are placed outside the unsafe area.
After backfilling, all manholes must be checked by a qualified person after a certain period of time to see whether the backfill column has sagged or whether harmful gases are escaping. Shafts where there is a risk of outgassing are provided with devices that enable the mine gas to be discharged safely. A safety zone is established around such shafts to ward off health hazards and explosions.
The location of the former shaft must be permanently marked. Suitable plates are used for this, on which the name of the manhole, the clear width of the manhole disc, the position of the manhole center and the permissible load on the manhole cover are indicated.
Individual evidence
- ^ A b Günter Meier: custody principles in old mining. Online (PDF; 143 kB). (last accessed on April 30, 2015)
- ↑ Body heat of the teacher saved three-year-olds
- ↑ Dieter D. Genske: Engineering geology basics and application. Springer Verlag, Berlin Heidelberg 2006, ISBN 978-3-540-25756-1 , p. 457.
- ↑ Axel Preuße, Jörg Krämer, Anton Sroka: Technical assessment of consequential loads of hard coal mining. Mining 12/2007 Online ( Memento from February 21, 2014 in the Internet Archive ) (PDF; 1.8 MB) (last accessed April 30, 2015).
- ↑ Guidelines of the Arnsberg District Government, Dept. Mining and Energy in North Rhine-Westphalia, for the safekeeping of day shafts from December 5, 2007 online (last accessed on April 30, 2015).
- ↑ a b c Guide for the safekeeping of day shafts in Thuringia . Online ( Memento from April 20, 2014 in the Internet Archive ) (PDF; 616 kB) (last accessed April 30, 2015).
- ↑ R & B Industrieanlageverwertung GmbH, 46238 Bottrop, DE: Method for filling deep shafts. Patent No. DE10236795B4 January 29, 2009 Online (last accessed April 30, 2015).
- ↑ Melanie Niese. Dealing with mining damage in the southern Ruhr area. Dissertation at the Faculty of Geosciences of the Ruhr University Bochum, Bielefeld 2010.
- ↑ Special procedure for safekeeping . Online ( Memento of February 3, 2013 in the Internet Archive ) (PDF; 63 kB) (accessed via Archive org. On April 30, 2015).