Settlement flow

Settlement flow is a phenomenon that can occur in loose soils such as sand in the slopes of dumps and spoil heaps when the groundwater rises and the soil gradually becomes saturated with water. The soil is softened and has a pulpy consistency, since the adhesion of the soil particles to one another is greatly reduced by static buoyancy and the water, which acts like a lubricant.

Emergence

Such floors can begin to flow even with small triggers. There is a risk that huge masses of earth will suddenly liquefy and slide off at high speed. This can be triggered by the weight of the floor alone, without any external influences.

Three criteria are essential for the development of settlement flow:

• Storage density
• Grain shape and distribution
• Water content

Since, of these factors, only the storage density can be changed with reasonable effort, soil compaction measures can be carried out in the endangered slope areas.

If the settlement flows, there is a danger to life through burial. If the embankment slides into a lake, larger tidal waves can be triggered.

Settlement flow can also occur in mining when old opencast mines are abandoned. A settlement flow can be triggered by the rising groundwater level or active flooding of the remaining hole.

The necessary rise in groundwater is the result of the cessation of groundwater elevation or active flooding of the remaining hole. The problem is widespread in the former opencast mines of the Lusatian Lake District, but is by no means limited to this region.

Countermeasures

In order to reduce the risk of settlement flow, the slope edges are flattened during the mining rehabilitation. Alternatively, the soil can be compacted. This is possible, for example, with vibratory compaction, but also with explosive charges.

"Hidden dams" have proven to be a good means of securing against settlement flow. These support bodies are created on endangered embankments parallel to the bank by compacting them by vibrating or blasting the subsoil without being visible in the landscape. They can be 50 to 150 m wide.

Possible incidents

• The Aberfan disaster is explained by settlement flow.
• After the landslide in Nachterstedt in 2009 , when parts of the village slid into Lake Concordia , settlement flow was discussed as the cause, but not confirmed.

See also

• List of landslides in mining
• Soil liquefaction

literature

• Lausitzer- und Mitteldeutsche Bergbauverwaltungsgesellschaft mbH (LMBV): Safe Design of Sump Edge Areas at Risk of Settlement Flow , Berlin, 1996.
• Claudia Hanke: Securing embankments on residual lakes - problem definition and analysis of the engineering-biological solution methods , diploma thesis, University of Leipzig, 2000 . (PDF file; 4.09 MB)
• Order on heaps and remaining holes of October 2, 1980 (HaldeRLAno) , GDR Law Gazette 1980 I p. 301 .
• Daniel Schueler: A stochastic approach to the settlement forecast of open pit rock soils , diploma thesis, Weimar, 2001 . (PDF file; 1.09 MB)

Web links

• Article in the construction dictionary online
• LMBV glossary
• Mining in Saxony (Section 1.1) (PDF file; 1.1 MB)
• Stability analysis of embankments at risk of settlement flow with initial entry attempts (PDF file; 1.20 MB)

Individual evidence

1. ↑ Archived copy ( memento of the original from July 30, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (P. 10) (PDF file, 4.2 MB) 
2. ↑ especially page 9 and bibliography
3. ↑ § 9 of the HaldeRLAno stipulates that the height of the individual slopes of the stockpiles may not be greater than 10 m and the inclination of permanent individual embankments over 5 to 10 m embankment height not steeper than 1: 2. The settlement flow is explicitly mentioned in § 16. This provision continues to apply in accordance with the Unification Agreement.