Schleußner, HP & Mühlig, K 2025, 'Innovative technologies in the remediation of landscapes left behind 
by the former lignite mining industry in eastern Germany', in S Knutsson, AB Fourie & M Tibbett (eds), Mine Closure 2025: Proceedings of the 18th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1-10, https://doi.org/10.36487/ACG_repo/2515_70
(https://papers.acg.uwa.edu.au/p/2515_70_Schleussner/)
Abstract: Abstract
Over the last few decades, attractive lake landscapes have been created in Lusatia and Central Germany from old open cast mines of the former lignite mining industry. The main player in this transformation process in eastern Germany is Lausitzer und Mitteldeutsche Bergbau-Verwaltungsgesellschaft (LMBV).
A large proportion of the open cast mine dumps in LMBV's area of responsibility consist of loose sands that are sensitive to liquefaction. With increasing groundwater rebound after the end of mining, spontaneous liquefaction events were occurring, especially after 2009. It was due to the structural collapse in the watersaturated soil. One of the largest geotechnical events of this kind affected approximately 160 ha of dump area.
At present, approximately 31,500 ha of dump areas are affected by closures or restrictions on use.
The remediation of these areas poses a major challenge due to the risks to people and materials. For this reason, remediation work is currently focusing on securing extensive dump areas against soil liquefaction. This requires geotechnically efficient, economical methods that are geared towards minimising the impact on protected assets. 
The technologies presented below involve the optimisation of established remediation technologies such as gentle blasting compaction (GBC). GBC is used to compact the loosely stored dump sands by means of relatively small quantities of charge ignited in boreholes. By using low-weight, all-terrain technology, large dump areas can be efficiently secured. Important data such as the position and depth of the blastholes, charge quantity, time of blasting and vibration velocities are recorded and can be visualised and retrieved. In preparation for a quantitative proof of compaction, freeze samples were taken after dump ground freezing down to great depths. These samples are used to determine the material and relevant parameters for earth stability calculations.
Terrain depressions are low-lying dump areas with groundwater levels close to the surface, and thus an increased risk of soil liquefaction. An alternative to using earthworks techniques for backfilling of terrain depressions is by use of a throwing belt. Therefore tests are currently being carried out to determine optimum operating conditions.
Furthermore, unconventional materials such as perlite were tested for filling terrain depressions. This material has a low weight which minimises stresses in the soil and forms a sufficient load-bearing surface. For this reason, perlite is intended for use as a foundation layer in future conventional backfilling.

Keywords: lignite mining, groundwater rebound, open cast mines, soil liquefaction, gentle blasting compaction, soil freezing, throwing belt, perlite, filling terrain depressions