Stabilisation of bank slopes that are prone to liquefaction in ecologically sensitive areas

A consequence of lignite stripping in the Lusatia mining district (East Ger many) is the backfilling of dumps that mainly consist of low-compacted fine and medium-grained sands. When the ground-water table, which had been lowe red while stripping the coal, is rising again, these dumps might be affecte d by a settlement flow due to the liquefaction of soils. Common methods for stabilisation as, for instance, blasting or vibrator-jetting deep compacti on, are not very useful in ecologically sensitive areas, where dumps have b een afforested and embankment areas of residual lakes have developed into h ighly valuable biotopes. A new so-called air-impulse method in combination with directional horizontal drilling has been developed, which does not hav e a considerably negative impact on the vegetation during compaction. The e xperience gained during the first employment of this method at the lake "Ka tja", a residual lake of lignite stripping, is presented in this paper. (C) 2001 Elsevier Science Ltd. All rights reserved.