Freezing process

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Freezer

The freezing process is a process that is used to produce artificially frozen bodies of soil. In mining , the method is in the drilling of wells used. The process is also called the freezer shaft process and shafts that are produced using this process are called freezer shafts in mining.

history

As early as the winter of 1853, French engineers were using the properties of naturally frozen ground to create a mine shaft in the water-bearing soft rock. Artificial cold was first used in shaft sinking in Great Britain (Wales) in 1862. Here, however, the bottom of the shaft was frozen in sections. In Germany, the process was developed in 1883 by the German engineer Friedrich Hermann Poetsch and tried out for the first time. In the same year Poetsch had this process patented and successfully applied it for the first time at the Archibald mine near Schneidlingen . This procedure then established itself internationally. Many shafts in the hard coal mining of the Ruhr area , in which the overlying overburden had to be penetrated, were created in this way. Until the middle of the 20th century, the process was limited to the construction of shafts, with a few exceptions. Since the behavior of frozen soils has been researched, this method is now also used in other areas.

Basics

In mining, the penetration of aquifers is preparing the drilling of wells major problems. The occurrence of so-called floating sand layers is associated with great difficulties due to the lack of stability of such layers. In the 19th century in particular, it was a great challenge for miners to cut through such layers. But also in tunnel construction it happens that water-bearing loose mountain layers have to be crossed. The freezing of the loose rock layers is particularly suitable for larger disturbances in the soil. However, the process is too costly for simple seals or supports. If loose layers of rock or sand are frozen, they become solid and impermeable to water. Frozen soil is chemically neutral, malleable and almost as solid as lean concrete .

Procedure

First of all, around the planned property, e.g. B. a shaft to be sunk, drilled holes at short intervals of about one meter. The holes are created at a distance of two to three meters from the perimeter of the excavation. The water-bearing layers are drilled into the water-retaining mountains. Pipes are installed in the drilled holes that are closed at the bottom. A downpipe, also known as a freezer pipe, is hung into each of these outer pipes. These downpipes are open at the bottom. After all pipes have been installed, the pipes are connected to a refrigeration machine and then a coolant is applied to them. The coolant reaches the bottom of the borehole via the downpipe and rises again in the outer annulus. During this process, heat is extracted from the surrounding mountains and a body of frost is created. In its protection, the shaft is then sunk like in a stable mountain. As the sinking work progresses, a watertight shaft lining is installed in the shaft tube. The brine process is used for cooling . Shock freezing with nitrogen is used to generate very low temperatures . The process does not pollute the groundwater or the soil . Apart from a few soft pipes, no further residue remains in the soil after thawing. Therefore, after applying the procedure, there are no hindrances for later construction work. Applications are also known which promote the freezing process by blowing cold air; Tunnel construction by Brunkebergsåsen / Stockholm 1884 and tunnel construction using the freeze construction method under the East River.

Stability of the frozen body

The strength of the frost wall and the compressive strength of the mountain determine the stability of the frozen body. The stability of the frozen body is determined on the basis of soil samples using uniaxial or triaxial pressure tests. The compressive strength of the frozen body increases with decreasing temperature. Frozen, pure quartz sand achieves the highest strength, the coarser the grain, the higher the strength of the sand. The strength of frozen clay is only half that of quartz sand. The required strength of the frost wall can be determined on the basis of the determined values ​​of the soil samples. The values ​​that are determined on the basis of the uniaxial compression tests are, however, not precise enough to determine an economic dimensioning of the frozen body at great depths . The three-axial pressure tests bring more precise values ​​here. The thickness of the frost wall is then ultimately determined depending on the compressive strength of the frozen body. By re-freezing, the frost body can be strengthened throughout its life. If there are larger cavities in the ground to be frozen and filled with water, the success of the freezing process can be seriously impaired. In these cases, the cavities can be strengthened by cementing beforehand. As a result, the mountains contain less water and freeze faster. In addition, such measures strengthen fragile rock.

After thawing

It should be noted that after thawing, the frozen soil changes its properties. In particular, the load-bearing capacity and the change in volume are important. After thawing, the load-bearing capacity drops, especially in the case of bog or peat soils. With these soils, the load-bearing capacity is based solely on the frost. In clay or silty clay it comes after defrosting to subsidence . Since the volume of the bottom increases when it freezes, there is a decrease in volume when it is thawed. Whether the soil will regain the same volume as it was before freezing depends on several factors. In particular, the behavior of the water in the ground during the freezing process has an influence on the volume after thawing. If the soil absorbs additional water during the freezing process, the frost body expands more intensely. This in turn leads to a greater decrease in volume after thawing.

commitment

In addition to its use in shaft sinking, the method is also used outside of mining in tunneling and foundation engineering. In tunnel construction, the freezing process is used to freeze ridge and secure the advance. The process is also used to create starting shafts and to create cross passages between two tunnel tubes . It is also used to create lead-in and start-up seals for shield drives and pipe grouting. In foundation construction, the method is used to stabilize foundations and walls and to enclose building pits. It is also used for sealing and underpinning sheet piling. In Hamburg, the procedure was used when building the City-S-Bahn to relocate a Stammsiel .

literature

in order of appearance

  • The freezing process . In: Zentralblatt der Bauverwaltung . No. 2, January 6, 1915 ( digitized version [accessed March 3, 2013]).
  • Karl Dolezalek The railway tunnel. A guide to tunnel construction . Urban & Schwarzenberg, Berlin and Vienna 1919, there page 53 f. and page 172 ff.
  • Dietrich Hoffmann: Eight decades of freezing processes according to Poetsch. A contribution to the history of shaft sinking in difficult cases . Glückauf Publishing House, Essen 1962.
  • Günter Pinzke: The sinking of the first potash shaft using the “Poetsch'en freeze shaft method” . In: Bull and Griffin. Sheets on cultural and regional history in Mecklenburg-Western Pomerania , vol. 20 (2010), pp. 62–74, here p. 64 ( PDF ).

Individual evidence

  1. ↑ a b c d H. L. Jessberger: The creep behavior of frozen loose rock in connection with the structural application of the freezing process . In: RHEOLOGICA ACTA . Volume 4, No. 2 , p. 123-133 , doi : 10.1007 / BF01984708 .
  2. ^ Walter Bischoff , Heinz Bramann: The small mining dictionary . Ed .: Westfälische Berggewerkschaftskasse Bochum. 7th edition. Verlag Glückauf GmbH, Essen 1988, ISBN 3-7739-0501-7 .
  3. ↑ a b c d e f g h i Anton Sres: Theoretical and experimental investigations on artificial soil freezing in flowing groundwater . Zurich 2009 ( PDF 4.9MB [accessed on March 3, 2013] Dissertation, ETH No. 18278).
  4. ↑ a b c Ernst-Ulrich Reuther: Introduction to mining . 1st edition. Glückauf, Essen 1982, ISBN 3-7739-0390-1 .
  5. ↑ Günter Pinzke: The sinking of the first potash shaft according to the "Poetsch'en frozen pit method" . In: Publications on mining in Mecklenburg . ( PDF 1.9MB [accessed March 3, 2013]).
  6. ^ A b Albert Serlo: Guide to mining science . Fourth edition. First volume. Springer, Berlin 1884.
  7. ↑ a b c d e f Carl Hellmut Fritzsche: Textbook of mining science . 10th edition. Second volume. Springer, Berlin / Göttingen / Heidelberg 1962.
  8. ↑ a b Siegfried Nagelsdiek: glaciations in urban civil engineering . Ed .: Strabag . ( PDF 3.2MB [accessed March 3, 2013]).
  9. ^ W. Cauer: Application of the freezing process in Stockholm. , in: Zentralblatt der Bauverwaltung 1885, p. 587 and 1886, page 38.
  10. ^ American Scientific 1906
  11. ↑ Bernd Braun: Laying a sewer using the freezing process . In: Our company . Works magazine for the companies of the Deilmann Haniel Group. No. 3, April 1969 ( PDF 4.5MB [accessed March 3, 2013]).