

ThyssenKrupp Steel (TKCSA) is building a steel plant in the lowlands at the Brazilian seashore near Sepetiba inclusive of a stock yard for coal/coke. The total stockyard area is ca. 800 m x 600 m, the coal/coke part ca. 800 m x 350 m. The entire area consists of soft soils of very low bearing capacity; the ground water level is just below the surface. The thickness of soft soil clay layers varies between ca. 15 and 20 meters, being underlayed by sands and rock. Beside the stockpiles of ca. 13 m height, the coal/coke stockyards also include runways for the so called stacker/reclaimers similar to the heavy equipment in open mining. A deep foundation and/or soft soil improvement for the stockyard had to meet different and to some extent controversial requirements in the terms of settlement, bearing behavior, general deformability/ductility, costs for construction and later maintenance and in terms of construction time. Stiff piles were risky because of their brittle behavior and at the same time huge lateral stresses in the soft soil below the stock. The optimum solution found was a foundation of the runways on geotextile encased columns (GEC) in combination with horizontal high-strength geosynthetic reinforcement over the whole area. The main idea of GEC is to create a vertical pile-similar element consisting (usually) of compacted sand and a confining high-strength high-modular geotextile encasement providing bearing capacity and reducing compressibility. The high-strength horizontal geosynthetic reinforcement increases the overall stability of the system and reduces lateral pressures and horizontal displacements of the sensitive runways. Project-specific conditions in terms of geotechnical situation, loads, geometries and specific requirements to be met are described. The most important design concepts and results are shortly explained and the final optimized solution presented.