The Inden Residual Lake and the Federal Autobahn A44n – Geotechnical Requirements to Be Met by Large-Scale Structures in the Rhenish Lignite Mining Area

The geotechnical requirements of two major structures in the Rhenish lignite mining area will be discussed – the Inden residual lake and the federal autobahn A44n.

According to current planning, the Inden residual lake is going to be the first of three large residual lakes to be filled from about 2030 onwards when coal extraction at the Inden opencast mine comes to an end. However, the construction of the lakes’ final slopes will start as soon as 2014. Compared to the existing man-made lakes in the Rhenish lignite mining area, with the largest being the 100-hectare large Blausteinsee, the area of the Inden residual lake will cover approximately 1,100 hectares and thus become the largest lake in North-Rhine Westphalia. Consequently, geotechnical aspects such as material distribution in the slopes have to be considered carefully and overall stability of single slopes as well as the slope system has to be ensured. Furthermore, the influence of waves, erosion and earthquakes on the overall stability will be discussed. A focus will be on additional loads caused by earthquakes that play an important role due to the fact that the Lower Rhine Embayment is one of the most active earthquake areas in Germany.

The second project presented here is the construction of the federal autobahn A44n. The A61 between the Jackerath and Wanlo interchanges will be decommissioned due to the progress made by the Garzweiler opencast mine. By then, the new autobahn A44n has to be commissioned in order to replace the above-mentioned A61 and the former autobahn A44 that had to make way for mining in 2006. More than 7 km of the new A44n including several bridges will be located on dumped soil with a thickness of up to 190 m. Geotechnical aspects including settlement forecasts and field measurements will be presented. Furthermore, this paper outlines measures to offset settlements including a so-called precautionary gradient as well as material distribution beneath the autobahn. Finally, soil improvement measures beneath a bridge with a clear span of over 100 m will be discussed.