MECHANISED TUNNELLING | TECHNICAL
The geological conditions along the tunnel route posed
a particular challenge in this demanding project: the soil in south-east Paris consists mainly of ‘Argiles Vertes’, a clay with swelling and clogging properties. In addition, the MTBMs were supposed to pass through layers of Cyrene marl and occasionally limestone layers at the upper edge of the tunnel cross-section. After intensive discussions with the customer,
Herrenknecht engineers and geologists recommended the use of the AVN technology. However, the machine design was specially modified and tailored to the prevailing underground conditions. In order to counteract the effects of swelling clay, for example, the overcut was increased to 45mm. This created a larger annular gap around the shield of the machine to prevent jamming of the MTBM caused by the volume increase of swelling clay. Herrenknecht also countered the adhesive properties
of the clay with special design details on the cutterheads: two of the three MTBMs used a three-spoke cutterhead (see photo p10), while the third machine has a four- spoke cutterhead. The smaller number of struts reduced the area where the clay could adhere. In addition, eight instead of six nozzles were installed in the cutting wheel to flush away the clogging clay with water pressure. The openings in the cone crusher were also designed with a larger diameter than usual. They ensure that the excavated material is sucked out in the form of a slurry. The MTBMs, which drove the microtunnels with a
limestone layer at the upper edge of the MTBM, were equipped with disc cutters in addition to the cutting bits on the outer edge of the cutting wheel. This new design not only offered an optimal solution for the complex geological conditions but also ensured consistently high- performance rates during tunnelling: an average tunnelling speed of 40mm/min–50mm/min was achieved, with peak rates in certain sections reaching up to 200mm/min. In total, the ambitious construction project required
three launch shafts and three target shafts for five sections. Due to the limited space available in the densely built-up urban area, the construction site could only be organised on public ground. To save space, the work areas were installed on several levels of the launch shaft, including the AVN’s slurry pump. Finally, the development and integration of operational
technology and information technology create new opportunities to make data accessible and transparent via the cloud. Parts of the project in Paris (and that in Canada) were covered with the Herrenknecht IoT platform
Herrenknecht.Connected. Predefined views enable continuous monitoring and interpretation of key MTBM parameters—such as sensor data—in near real-time, from any location. Solutions like MT.ON, part of the IoT platform, help to detect machine failures or deviations at an early stage and enable quick reaction and correction measures. In Paris, this led to improvements in terms of communication, transparency, planning, costs, and safety.
CONCLUSION Like many other tunnel construction projects worldwide that have been realised with TBMs, such as from
Left: AVN800 HR Cutterhead with TCI Cutters
Herrenknecht, the construction of the new rainwater tunnel in the south-east of Paris and the hard rock tunnels in Canada are proof that the geological conditions of the construction site are a decisive factor for the success of tunnel projects and contribute significantly to the success of the project. Therefore, a detailed and individual analysis of the
specific subsoil conditions is essential. A generalised approach and standard, off-the-shelf solutions are not sufficient – what is needed are tailor-made concepts that are precisely customised to the respective conditions on site. In this context, Herrenknecht focuses on geotechnical assessment at a very early stage of project planning, enabling the technical implementation of appropriate TBM solutions. The approach consistently takes geological conditions
into account from the outset, and close cooperation with the customer and their practical experience and expertise play a central role in the outcomes. Only through continuous exchange, tailor-made technical solutions can be developed and optimally implemented in the project context. Aspects such as the quality and quantity of the bentonite, the selection of suitable concrete pipes or efficient logistics have to be integrated into the planning process at an early stage and in a practical manner – a decisive factor for the successful completion of a pipejacking project in any geological conditions.
REFERENCES
● ‘Driving slurry rock tunnelling in small diameters’, T&TI, Jan 2024 ● Lang, G. & Lehmann, G. (2022) ‘Rock tunnelling in small diameters: latest trends and technologies’; NASTT No-Dig Show 2022
● Lehmann, G., Lubbers, M. & Fluck, A. (2023) ‘Slurry pipe jacking in hard rock: pushing boundaries for sustainable infrastructure’;
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