Gentle installation of gas service pipe using the keyhole in Ingolstadt/Germany

23.10.18 - A large number of supply and disposal lines run underground, making the installation of new lines more and more difficult. So what shall be done if a subsequent property service connection to an existing supply line becomes necessary? Installation in open construction usually involves a great deal of effort: a trench must be dug, the pipe laid and the trench then filled back again. Apart from the long time needed for the execution of this work, it also means a considerable interference with the traffic infrastructure and the destruction of many a well maintained front garden or paved yard. Not so with the trenchless installation technology, in which time-consuming excavation and restoration work is no longer necessary and valuable surfaces are preserved.


In April of this year, the most gentle of all trenchless techniques was used in Irgertsheim, a district of Ingolstadt: the minimally invasive keyhole method for installing pipes through a low-stress circular excavation pit (keyhole). Here a house owner wanted to replace his old oil-fired heating system with a modern gas heating system and thus be retrofitted to the existing gas mainline, which is laid in the street in front of his house. The perfect job for the steerable GRUNDOPITKS50 which was especially developed for this innovative technique. This was also recognised by the Ingolstadt public utility company, on whose behalf TUR Saugbaggerdienst GmbH, supported by a team from TRACTO-TECHNIK, installed the gas service pipe from out of a keyhole over a length of 8 m directly into the cellar of the residential building. This reduced the amount of work to a total of one working day and the front garden remained completely intact. In order to convince themselves of the advantages of this innovative and multiply awarded method, this construction measure served the public utilities Ingolstadt also for demonstration purposes.


To produce the keyhole, a circular asphalt core with a diameter of only 65 cm was cut out of the road surface with the GRUNDOCORE core drill unit. The core was carefully lifted out and put aside so that it could be inserted into the asphalt again after completion of the construction work. A suction excavator was then used. "In contrast to a conventional excavator, the soil is vacuumed cleanly and quickly, and other pipes in the keyhole area are not damaged," explains Uwe Richter, owner of TUR Saugbaggerdienst, the principle of the suction excavator. "Larger stones are also sucked up and extracted from the keyhole. Once the suction excavator had produced the desired depth of the keyhole, the GRUNDOPITKS50 drilling rig was installed, aligned for drilling and fixed inside the keyhole.


In Irgertsheim, the experts from TRACTO-TECHNIK encountered special challenges in the form of intersecting supply lines in the pavement area, the foundation of an old garden wall and a rainwater pipe ND 100 directly in front of the house wall. "Usually we establish the keyhole and drill the hole from there. But here the borehole almost had the same depth as the intersecting lines; therefore, for safety reasons, the parties involved decided to create two search slots. These helped us to prevent damage of the lines while drilling," Philipp Schumacher, product manager at TRACTO-TECHNIK, explains the special situation on site. "We bored through the foundation with the drill head without any problems." The two survey slots were also produced with the suction excavator.


The bore was steered by the GRUNDOPITKS50 from the ground surface. First, a pilot bore was drilled down to the basement of the residential building. The length of the specially designed pilot pipes is adapted to the drill rig diameter. They are automatically fed, in compliance with the drilling progress, via a magazine loaded from the surface and then pieced together inside the drill rig. Since the GRUNDOPITKS50 can raise a torque of up to 1200 Nm and a pulling / thrust force of 50 kN, the method can be used in almost any soils.

Thanks to the two survey slots, the bore was guided, with visual contact to the bore head, between the existing lines without any problems. The outer wall of the basement was also broken through with the bore head at the intended spot. Once in the basement, the drill head was replaced by a core drill. In reverse operation of the GRUNDOPITKS50, it drilled through the house wall from the inside out and thus achieved the desired diameter of ND 100; in the following step, the pilot bore was expanded to ND 85 with the backreamer. For this purpose, the coring unit was pushed back into the basement in a forward motion. In the next step, the backreamer was connected to the pilot pipe rod string. At the end of the backreamer, the first protective pipe ND 63 was installed in preparation of the product pipe ND 32. Since there was no connection of tensile strength between the backreamer and the protective tube, a steel cable was attached to the end of the backreamer, passed through the protective tube and braced at the end with a special device. By continuously moving the backreamer back towards the keyhole, it was possible to assemble the protective pipe bit by bit in the basement and draw it into the ground. On arrival of the backreamer in the keyhole, the experts from TRACTO-TECHNIK removed the drill rig from the keyhole. Finally, the product line could be inserted in the protective pipeline.


A special fitting was used to connect the property service connection pipe to the main gas pipe line. The advantage of this fitting was that the main pipe for the connection did not have to be shut down. The fitting was first welded onto the main pipe line, then the property service gas connection pipe was adjoined by an employee of the Municipal Utilities Ingolstadt. After a successful pressure and leak test of the connecting pipe, the main pipe inside the fitting was drilled open under pressure, thus establishing a passage between the two pipes. In addition, this fitting contained a flow monitor, which is mandated by the Municipal Utilities Ingolstadt for property service gas connection pipes. All the work necessary for the assembly of the fitting was carried out from the surface with the help of special tools from TRACTO-TECHNIK. Thanks to a house lead-in for gas lines, a special design for the trenchless installation of lines, sealing of the basement wall from the outside was not required. The assembly was carried out completely from the within..


After the connections were made both inside the keyhole and in the basement, the keyhole was backfilled in layers. Compaction was carried out with a small pneumatic backfill rammer. In addition, the frost protection layer was restored with gravel and the last 5 cm up to the bottom edge of the asphalt layer were filled with stone chippings. This serves as a bearing for the annular asphalt core, which was then cemented into the road surface. The bonding used here was a special very low-viscosity, frost and salt-resistant mortar which was poured into the gap of the cutting edge between asphalt and core, leaving a space of approx. 3 cm to the upper rim. Due to its flow properties, the mortar crept under the re-inserted annular asphalt core and the adjacent asphalt and oozed into possible break-outs under the roadway, thus creating a full-surface contact between the asphalt and the road bed. The remaining raw edges were finally filled up with a two-component cold bitumen and sanded. Thus, the driving surface was restored without differences in elevation within the area of the building measure.

The innovative keyhole technology cannot only be used for the subsequent connection to existing cables in the immediate vicinity of the first keyhole in Ingolstadt, a second one was built to replace a defective tapping bridge of the water connection pipe. Here, the work was also carried out quickly and to the satisfaction of all. One aspect that Uwe Richter will always remember in connection with this construction project: "The owner of the house was so grateful that we did not damage his front garden or destroy his rainwater sewer when installing the pipe line. In the course of the property service gas connection line installation, nobody suffered restrictions of any kind: there were no excavated soil mounds and therefore virtually no dirt on the doorstep. With a total working time of approx. one day for both keyholes, the project was done in a flash.”


Within the bounds of extended services we offer utilities and network operators a special introductory package for the innovative keyhole technology on attractive conditions.
The package ‘house connection technology’ includes:
  • Provision, transport and set-up of the trenchless equipment
  • Execution of the bores and installation of the pipes
  • Connection to the main line using special tools
  • Briefing and debriefing as well as documentation
  • Provision of personnel
  • Jobsite analysis and lecture on the method
The client is only responsible for approval, preliminary exploration, civil engineering works sand provision of materials. We take care of everything else.

If you are interested, contact our sales team.



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