pond 4 of the WISMUT in Freital
WISMUT GmbH, Chemnitz
Heitkamp Erd- und Straßenbau
September 15 to June 19
In the period from 1954 to the end of the GDR in 1990, the mining company SDAG Wismut was the world’s third largest producer of uranium. After the end of the ore mining and the Saxon uranium production, several tunnels, opencast mines, dumps and tailings ponds remained as contaminated sites with a total area of approx. 37 km². The radioactive processing residues were usually fed into so-called industrial sedimentation plants (IAA). In order to prevent the spread of radioactive particles from the unsecured surface of the pond, it was decided to rehabilitate the property and this was commissioned by Wismut GmbH.
The rehabilitation concept for pond 4 of the IAA Freital included an impermeable cover. The aim of this remediation was to encapsulate the residues and reduce the radiation exposure of the environment. The situation on site was very demanding due to the low bearing capacity and very heterogeneous soil conditions. The final renovation concept was to install a multi-layer waterproofing system. In order to be able to install the mineral layers on soft subsoil, the system additionally comprised of a separating and filter layer made of nonwoven material as well as two reinforcement layers of geogrid arranged at right angles to each other. In the outer, load-bearing area, the separation and filter layer, the two reinforcement layers and the anchoring of the reinforcement in anchoring trenches were arranged. In the central covering area, the system was supplemented by 5 m long vertical drains in a grid of 1.5 m. The central area of the sludge pond had an extremely low load-bearing capacity, which is why an additional drainage layer, installed in layers in the pre-head installation, increase the bearing capacity and load distribution and enable the installation of the sealing and recultivation layers. After the sludge pond was sealed, a new rainwater retention basin was constructed, which will serve as flood protection in the future.
Since sludge ponds are formed as a result of various ore processing techniques, project-specific solutions are required to seal and encapsulate the contaminated sites. The use of geosynthetics has proven to be a reliable solution in various projects due to its high adaptability. The simultaneous effect of the drainage layer and the installed vertical drains shortens the consolidation and thus the construction time. Geosynthetics enable the superstructure to be covered with shear-resistant loose soil and the subsequent installation and compaction of the sealing clay layer. In the concrete example, the spread of contaminated dusts and the release of radioactive radiation is prevented and a recultivated, stable surface is created.