Wastewater disposal

›› AKP Renningen
›› Beinberg tunnel
›› Ebersbach sewer auguring

General sewage plan (AKP)

Client: Renningen City Council
Period of execution: 2006/2007

The most recent complete general sewer system plan was prepared in 1990, and had to be newly defined because of the increasing density of structural development and sealing off of existing urban areas, as well as within the scope of planned long-term urban development.

The current general sewage plan involves the entire sewer system of the city of Renningen, including the Malmsheim district, the entire area of the Renningen sewage works and the development of new residential areas. The objective of the redevelopment was the optimum utilisation of the sewerage system, which was hydraulically overloaded.

In view of the complex sewerage system, simulation models for the calculation of the sewer network were developed, making it possible to capture the various load and overload conditions realistically, using computer models, and the effect of special structures (stormwater overflow tanks, weirs, restriction means, storage facilities, etc.). Because of the complex regional structure, a model for calculating the contaminant load was selected to provide evidence of stormwater treatment methods and as part of applications for permits from the competent environmental authority.

The primary focus of the redevelopment effort was on heavily overloaded sections or those which were known to have caused damage as a result of flooding in the past. This primarily involves the following sections needing to be redeveloped: Industriestraße and Rutesheimer Straße, along with Lehenbühlstraße. Other areas urgently requiring redevelopment are the following: Hindenburgstr. and Kronenstr., Siemensstr. and Hinterriedstr., and also Bühlstr., Kasernenstr. and Heidestr. in Malmsheim.


Specialised civil engineering

Client: Bad Liebenzell City Council
Period of execution: 2000/2006

Because of its location in Water Protection Zone 2, the sewer system in the Beinberg district requires to be totally redesigned and restructured. Since seepage or infiltration is no longer permitted in this location, the present combined system needs to be replaced with a separation system. Any surface water run-off from undeveloped areas and rooftop surfaces needs to be disposed of by seepage on site, and wastewater is to be fed through a canal having a length of 2.5 km into the Bad Liebenzell sewer system.

The canal gradient involves inclines exceeding 50%, because the run involves having to traverse a park that has been existing for several decades, which makes it impossible to build a canal with a continuous open design. Special attention also needs to be paid to the fact that it would have to run through the water source area for feeding the mineral springs in Bad Liebenzell, as well as its location within the water protection zone. These are certainly factors to be considered in the planning and during the construction period, at the same time taking care to interfere as little as possible with civic activities, particularly in the centre of Bad Liebenzell.

Following extensive investigations of the sub-surface with regard to the hydraulic permeability of the soils accompanied by large-scale surveying, a drainage design was prepared to allow for the separation and proper discharge of wastewater and stormwater. The stormwater is discharged via multiple small-scale drainage systems using four water distribution troughs to balance the load. Due to the prevailing gradient, the wastewater had to be routed mostly across private land.

Keeping in mind the environmental sensitivity of the area, the wastewater is to be conveyed in ductile cast iron piping, since this replicates the characteristics of both rigid and flexible pipe systems. The long runs of wastewater ducts with steep gradients produce high flow velocities, the inherent energy of which is neutralised in stilling ponds. Prior to completion, the stilling pond is utilised as a press pit. Starting from this point, the gradient route of the canal is advanced "mining style" using a Herrenknecht AVN 1200 microtunnelling machine. This project involves tunnelling with the steepest gradient worldwide.


Tunnelling in Ebersbach for the Stuttgart to Munich railway line

Client: Ebersbach City Council
Period of execution: 2006
Distance: 23.5 m

Based upon the general sewer system plan, a new 1400 m diameter sewer line for improving drainage conditions in the municipal districts north of the railway line had to be erected. In this context, the sewer line had to pass below the double track railway line from Stuttgart to Ulm, as well as a track to industrial terminals. Due to the low cover (approx. 1.75 m) above the pipe apex and the geological conditions in the subsoil, the installation of reinforced small auxiliary bridges within the vicinity of the railway line was necessary to ensure the safety of railway operations.

The tunnelling for the pipeline using a face-trace tunnelling machine was monitored by daily settlement measurements using a fine levelling technique within the vicinity of the railway line. By grouting the annular space with a suspension of bentonite, it was possible to stabilise the subsoil in the vicinity of the railway line. After connecting the new wastewater duct to the existing sewer network north and south of the railway line, two new DN 200/100 water lines of ductile cast iron piping and additional conduit piping were inserted into the old duct fixtures by means of skids. These new feed and disposal lines will provide a long-term solution and an efficient connection between the sewer lines of the neighbourhoods north and south of the railway line.

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