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So far, the trenchless laying method has largely been used in conjunction with pipelines made of plastic. At the same time, it is also technically feasible to lay ductile cast pipes by means of the horizontal flushing bore method. Several kilometres of pipelines made of ductile cast-iron were laid by FlowTex on behalf of the Städtische Werke Krefeld AG for the City of Krefeld's water supply. Standard boring units with maximum tensile forces of 50 and 80 kN were employed for installing the inner-urban lines with diameters of DN 100, DN 150 or DN 200. For part-sections between 100 and 180 m, in each case the pilot bore was undertaken from the starting pit, the expansions carried out from the rear and the cast line drawn in during the final expansion stage. The length of the part-section in question depends on the local conditions as well as the nature of the soil. The entire route was investigated via geo-radar before boring work with the FlowTex method began. The prerequisite for installing ductile cast pipes by means of the horizontal flushing bore method is a tension-proof connection of the cast pipes. For the construction measures in Krefeld, Tyton-Sit and TKF sleeve joints from Thyssen Guss AG were selected. The cast pipes were connected within the pit. For this purpose, the 6 m long part-sections were gradually lowered into the pit, connected with Sit rings, welded with heat-shrinkable sleeves and drawn in one by one. The starting pits for drawing in the pipes must be geared in terms of length to the dimensions of the pipe part-sections and, as a consequence, are somewhat larger than conventional pits. The tensile forces that occur during the drawing-in process mainly act on the expansion head, which is directly attached to the rod. Through the sliding action and the buoyant effect, resulting from the bore suspension, the pipeline is drawn in without any friction worth mentioning. For laying ductile cast pipes with an internal diameter of 300 mm outside the city area, a more powerful boring system with a tensile force of 100 kN was used. Here, an expansion of the borehole to 580 mm was necessary. For the pilot bore, expansion and drawing in of the product pipe, 4 working days were required for the section.
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