Ground improvement methods for establishment of the federal road B 176 on a new elevated dump in the brown coal area of MIBRAG

摘要

The MIBRAG Company explores large new brown coal areas south of Leipzig in Germany. Large machines separate coal and soil directly at the surface up to 60 m deep. This is the reason to shift the existing B176 road up to 1 km in position on more than 5 km length. The new road is built from the existing road on natural soil conditions over a large dump with up to 60 m deep mixed sand, silt and coarse clay. This fine soil will be in loose condition when the large machines are gone. The new road on this dump is expected to settle in different ways at about 1 m in total due to the different age and thickness of the dump, the load of up to 15 m high dams and finally the rising ground water level within the next hundred years. Controlled Modulus Columns CMC are used as rigid inclusions at the border to the natural soil and as bridge foundations in different conditions in order to guarantee small settlements. The vibration free drilling technique is necessary to work in only 1m distance to the MIBRAG production technique. Considerable parts of the dump were treated by dynamic consolidation and dynamic replacement. This soil improvement method was used for dams up to 4 m height, partially in combination with a 3m thick fly ash stabilized load transfer layer. The higher dams are up to 70 m wide and 15 m high. Because of significant stability problems, 15 m deep stone columns are installed floatingly in the 60 m deep dump below the 15 m high dam with slopes of 1:2. The design and the settlements were significantly optimized by the combination of the different soil improvement techniques. The calculations were additionally based and optimized on DIN EN 4094-5 Menard pressuremeter results gained before and after the execution. Long-time measurement systems like horizontal and vertical inclinometers will control the success during the next years. First results are published in this article.