Initial situation

The specific characteristics of the former Koschen opencast mining pit, which has been partially landfilled, in combination with the rising water levels posed the danger that the inner slopes might slide and collapse. In order to be able to end mine monitoring of the excavation and make the former mine pit available for after-use, the embankments had to be rendered safe for the public.

Approach

The area of the lakeside open pit slopes of the interior landfill of the former opencast mine pit were secured against sliding and collapsing by using the vibration-pressure process to compact a 20 to 60 meter wide, 16 to 44 meter deep, and 4,520 meter long supporting body. This was followed by the stabilisation, also using the vibration-pressure process, of the lakeside pit slope surface, and its final hydro-mechanical shaping. These measures were based on detailed plans for the open pit slopes, which had been drawn up by a recognised LMBV expert.
Progress and geotechnical monitoring of the project allowed it to be continuously adapted according to the geotechnical conditions so that compaction could be optimised.

Result

This project, involving the vibration pressure process compaction of some 13 million m³ of landfill, has resulted in the landfill open pit slopes embankments of the future Geierswalder See Lake having been made permanently secure against settlement sliding, and creating the preconditions that have allowed subsequent work, forming a compensating profile to resist wind wave abrasion.