Background

Disused quarries are a direct consequence of surface mining. Normally abandoned quarries are left to flood with ground or surface water and are redesigned as lakes. The abandoned quarry lake Scheibe, located near Hoyerswerda, in Saxony, Germany was created this way. Lake Scheibe will be used as a local recreation destination in the future, however nature conservation will be a priority at the eastern part of the lake. The northern bank of the lake had been subject to increased erosion since 2003. In the course of the erosion process the northern beach and the embankment support of the natural landmark “Landmarke Eiche” were in danger. Between 2006 and 2007 significant changes in the embankment profile, and a considerable regression of the shoreline occurred. This led to the formation of a 130 m long basin and the formation of a cliff measuring up to 2.8 m in height in some sections. Additionally, the bank slope inclination declined to 1V to 6H below the water level. In this way the foot of the embankment shifted by up to 50 m. Due to advancing erosion and scour formation, the stability of the revetment of the “Landmarke Eiche”was at risk. For this reason a suitable protection of the affected area against further wave induced erosion was necessary, however the existing homogenous sands, which have a distinct tendency to flow, complicated this.

Solution

The placement of an erosion-proof support in the riparian zone and the wave run-up area as a stabilisation measure was considered. The limited access to the area would only allow the use of light to medium sized construction vehicles, which would have made the delivery of mass materials impossible. On the other hand, this necessitated the use of the locally available sand as a construction material.
As an efficient, technically simple to implement and cost-efficient solution, the use of geotextile sand containers was planned by the engineering firm G.U.B. Ingenieur AG.
The execution of the project called for a multi-layer shoring of the riparian zone with 1 m³ sand containers to form a support structure, this support also needed to function as a dam. This was solved by the use of light machinery and the back-out installation method. A particular challenge posed was the guarantee of a durability of the fabric containers in the acidic waters (since the lake water had a pH level of 2-4). This requirement was met by the use of a suitable (polypropylene) material.
After construction had been finished a survey of the front and rear edges of the support as well as an appraisal of the bank was carried out by an expert on behalf of the Saxon Upper Mining Authority. It was noted that the bank protected by the geotextile sand containers was built according to the computerized structural integrity analysis. The completion according to the detailed planning and calculations as well as the availability of a appropriate geotextile material contributed to the success of this project. ´

Site:Burg bei Hoyerswerda
Awarding authority: LMBV Lausitzer and Mitteldeutsche Bergbau-Verwaltungsgesellschaft mbH
Planning: G.U.B. Ingenieur AG, Dresden
Office Construction: NADEBOR Tief- und Landeskulturbau GmbH, Krauschwitz Building time: 2008
Product: Geotextile sand container
(SoilTain®) out of nonwoven fabric (PP)