The TransMed and GreenStream pipeline project, currently under construction, will transport gas from Algeria and Libya to Europe, via Sicily. As part of the project, a new gas pipeline was required to be installed using microtunnelling equipment in the Sicilian town of Nicosia.
To maximise the accuracy of the drive it was decided to utilise VMT’s SLS-Microtunnelling LT as the navigation system for the Herrenknecht manufactured machine. The contractor for the works – Ing. La Falce SRL – is a new customer for VMT.
All three drives for the project utilised VMT guidance systems, with the third drive recently breaking through on 16 September 2021. The first drive commenced on 1 May 2021, with breakthrough successfully completed just 27 days later on 28 May 2021. The second drive commenced on 14 June 2021, breaking through on 22 July 2021.
The drive profile of the 1.6 m diameter pipeline had a challenging vertical curve of radius 2,000 m, with Drives 1 and 2 having steep inclines at the reception end (+249 mm/m on Drive 1, +213 mm/m on Drive 2). Tunnelling was made particularly difficult by the high inclination and hard rock surface.
An environment of hard rock – sometimes combined with other materials – sees that tunnelling machines operate under high pressure and high contact force. Steep inclinations cause the squeezing of the pipes between two forces: while attempting to push pipes up from the start shaft, the weight of gravity presses them back down. This combination of conditions generated micro-stresses in different parts of the pipe string which were occasionally released. The resulting vibrations caused drastic and uneven back-and-forth movement of the pipe string, with the jackhammer-like movements increasing with each meter of the drives. To address the conditions, reinforcement was made on the TCA bracket. Although the VMT system still faced significant vibrations, the stability of the system was greatly improved, and excavation was able to continue as planned.
In addition, advance surveying works were required to get a proper location of the pipe axis in elevation. Here, additional preparation and accurate flow during the surveys contributed to the successful system performance.
Drive 3 presented its own challenges, demonstrating the variability that can often be experienced in underground conditions. Whereas the underground material of the first half of the drive consisted mostly of quartz – an abrasive material which can grind on the cutting wheel – the second half of the drive mostly consisted of clay, causing the periodic stalling of the machine.
Congratulations to our customer, partners and project engineers involved in the successful completion of these challenging routes.
At a Glance Fact Sheet:
The Hüller Bach, a stream which flows through Herne in North Rhine-Westphalia, Germany, is the largest tributary of the Emscher River in the Ruhr area. For years the stream has effectively functioned as an above-ground sewer, with underground canalisation not possible due to the region’s coal mining activities.
As part of a project to protect both the Hüller Bach and Emscher River from wastewater discharges, under the designation of the Emscher conversion project, the sewerage system in and around Herne is undergoing a transformation. A cease in underground coal mining has brought with it the opportunity to move sewerage below the earth’s surface, with the construction of a new 2.6 km sewer pipe string running underground and parallel to the stream.
Since 1992, the Emschergenossenschaft has been planning and implementing the Emscher Reconstruction project in close coordination with the surrounding municipalities, in which almost €5.5 billion will be invested over a period of about 30 years. Sonntag Baugesellschaft mbH & Co. KG, the contractor appointed to undertake the recent microtunnelling works, elected to work with VMT as long-time partner and guidance specialist. A Herrenknecht AVN1600 machine, enlarged to OD2160, was utilised for the project, supported by VMT’s navigation systems SLS-Microtunnelling LT and TUnIS Navigation MTLaserTotalstation.
Excellent collaboration between VMT and Centerline – who undertook the surveying for the project – contributed to the quick and successful completion of the excavation.
Three Successful Curved Drives
The new sewer sections were to be installed in three drives. Drive 1, covering a length of 350 m with a minimum curve radius 480 m, was completed in December 2020. Drive 2, completed between February and April 2021, had a length of 900 m with a minimum curve radius of 450 m. Drive 3 had a length of 700 m with a minimum curve radius of 450 m. This final drive was completed between April and May 2021.
Drive 1 utilised the standard SLS-Microtunnelling LT navigation system. This system is designed with a laser target unit, with a tunnel laser mounted in the start shaft of the drive and an active target unit placed in the machine. Data from the laser target continuously determines the exact position of the machine and displays any deviations from the desired alignment immediately on the monitor at the operator’s position. According to Sonntag Baugesellschaft, Drive 1 was described as ‘a winding 350 m long drive’ which ‘broke through the target seal with pinpoint accuracy’.
For the two longer drives with tighter curves, the contractor utilised TUnIS Navigation MTLaserTotalstation, VMT’s latest incarnation of its laser-based guidance systems. In addition to the long distance and tight curvature of the latter drives, further challenges arose as a result of drilling restrictions on site. Usually, installation of the VMT system hardware takes place with the drilling and tightening of screws, allowing an easy workflow and flexibility in case of line-of-sight problems. For this project, however, drilling was not allowed in the tunnel as the inner surface of the pipe string needed to remain unaltered: as a result, sight distances needed to be precisely calculated in advance. In order to securely mount VMT hardware without the use of standard screws, tension rings were used during installation.
TUnIS Navigation MTLaserTotalstation allows precise and efficient navigation of curved and long-distance drives. The expert system is based on the principle of invariance, where the horizontal and vertical position of the machine is determined by a laser total station in conjunction with several reference and target prisms and an electronic target unit inside the machine. The laser total station is permanently installed in the pipe string. An inclination sensor integrated in the electronic target unit measures pitch and roll of the machine. The system is drift and refraction-independent and requires 50% less control measurements than the gyro-based all-rounder system. This equates to less interruption of tunnelling, shorter downtimes, and significantly increased tunnelling performance.
With the main pipe string successfully completed, the project will end later in 2021 with the connection of the lateral sewer connections. This includes the connections at the Herne-Königsgrube pumping station, Herne-Hordeler Heide and the connection of the Herne-Röhlinghausen pumping station to the new sewer of the Emschergenossenschaft.
At a Glance Fact Sheet: