Challenging large trench sewer construction

On the construction site of the B464 Sindelfingen-Renningen (lot 13; section 03), Rädlinger Bauunternehmen was entrusted with the construction of a sewer with storage capacity and overflow, amongst other things. A particularly challenging project that required a lot of deliberations, advance planning and scheduling. The manufactured sewer with storage capacity and overflow is a reinforced concrete pipe DN 2400 with a length of approx. 86 m. Prefabricated shafts are arranged at the ends of the pipes as inlet and outlet structures. A plastic pipe DN 400 was laid in parallel to the pipe as a discharge line. In the outlet structure, the road water flow is reduced, controlled by eddy flow limiters and fed on to the sewer.

The greatly varying soil classes from two to seven and the depth of the utility trench of 4 to 8 m under ground level and its width of 7m presented challenges when digging the excavation pit or the utility trench. For these reasons, no conventional boxes could be used for sliding rail shoring to secure the utility trench.

As an initial measure for the realisation of the challenging project, a Liebherr 984 excavator equipped with a Rädlinger rock bucket was chosen. Thus, even rock that is difficult to detach presented no problems during the digging of the excavation pit or the utility trench.

As the sliding rail shoring could not be positioned in the conventional way by pressing the steel girders and shoring plates into the earth, the shoring had to be set up outside the excavation trench using two excavators. For this, steel plates that had already been welded in the factory were attached to the sliding rail shoring supports. The sliding rail shoring (net weight approx. 16 t) was lifted with the load hook attached to the Liebherr 984. This is a Rädlinger Maschinenbau special design with a 20 t  load capacity. Along with a special chain sling, it was also used to lift the reinforced concrete pipes (net weight approx. 13 t), which were then laid using a pipe grab.

Beforehand, however, the bed of the utility trench and the pipe bedding zone were produced from concrete using GPS machine guidance on a long reach excavator. This was also used for re-filling the pipe zone and the trench.

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