A DN 1000 system using the pilot PIPE-jacking method
great pipe, great performance
Andreas Engel, Berliner Wasserbetriebe (BWB), Marco Knauer, Frisch & Faust Tiefbau GmbH, Hans-Joachim Risto, Steinzeug-Keramo GmbH
In 2012, Berliner Wasserbetriebe (BWB, Berlin’s Municipal Water Utilities) put the construction of a 60-meter-long wastewater sewer of the DN 1000 standard size in Bitterfelder Straße in Berlin-Marzahn out to public tender. The special aspect of this construction project was that the sewer was to be tunnelled beneath three sets of tracks of an operating section of Deutsche Bahn AG’s railway system, meaning that it would have to be installed using the trenchless method.
The experience counts
Frisch & Faust Tiefbau GmbH, a Berlin-based company with plenty of experience in trenchless sewer construction, completed this project using the pilot pipe-jacking technology with a BM 500 machine supplied by Bohrtec GmbH, in Alsdorf – with great success. This was the very first time that this method employing jacking pipes made of vitrified clay in the large DN 1000 standard size has been used on this scale; the sand and gravel subsoil, however, and the low groundwater table provided ideal conditions for the deployment of this technology. The decision in favor of vitrified-clay jacking pipes was made for three excellent reasons:
- No additional protective pipes under the tracks required for the dynamic loads made by rail traffic
- Pipe-jacking technology a tried-and-tested construction method
- Extremely long operational lifetime
Railway construction regulations now include DN 1400 sizes
At the time BWB was planning the project (2012), vitrified-clay pipe systems of the DN 1000 standard size had not yet been given official approval by adoption into the so-called “Eisenbahnspezifische Bauregellisten” (EBRL, lists of railway-specific construction regulations) issued by Eisenbahnbundesamt (EBA, the German Federal Railways office). This is the reason why the necessary approval procedures at Deutsche Bahn sometimes took a long time to complete.
Since May 2013, things have been a lot simpler: today it’s possible to use vitrified-clay pipe systems with diameters up to DN 1400 in the load-distribution ranges involved in rail traffic. This is defined in “EBRL E A Section 1, Ser. No. 3.1.4 in conjunction with Annex E I.”
The approval procedures for future projects of this kind have now been made much simpler and faster.
Right on target
The starting shaft was secured by a soldier pile wall (Berlin-type shaft lining), while the target shaft was created using a sink shaft made of ferroconcrete with a diameter of 3.20 meters. The jacking operations themselves all went smoothly, with all pilot and steel pipes and the reamer being retrieved from the target shaft. The construction was completed by installing the final manhole in the starting shaft and making the internal fittings in the two manholes according to BWB specifications.
The pilot pipe is jacked forward to displace the subsoil. The pilot head is equipped with a target board that is accurately monitored by a height- and direction-adjustable theodolite. The pilot head can be turned to ensure that the correct jacking direction is adhered to. In the event that the pilot head comes up against an obstacle that cannot be displaced, the operator can retract the pilot rod and stop the jacking process in a controlled manner.
Phase 2 starts as soon as the pilot drill breaks through into the target shaft. This involves the attachment of a retrievable steel pipe with an external diameter of 419 mm to the pilot drill, feeding the displaced soil back to the starting shaft by means of an auger. If in this second phase an undisplaceable obstacle is encountered, it’s possible to withdraw the robust steel pipe sections, refilling the cavity at the same time.
A DA 1280 reamer carrying a hydraulic motor to power the auger is coupled with the retrievable DA 419 steel pipe. The auger now runs in the reverse direction, expelling the displaced subsoil into the target shaft. The vitrified-clay pipes are attached to the reamer and jacked forward in the direction of the target shaft.
In the event that the DA 1280 reamer comes up against an obstacle, it has three openings that can be used, e.g., to access the heading face and to attempt to remove the obstructing material manually.
Client and planning: Berliner Wasserbetriebe (BWB) | Construction: Frisch & Faust Tiefbau GmbH, Berlin