| Underground construction


and efficiency. The hope is that the sense of shared ownership fostered now will translate into a more seamless construction process in the years ahead.


Engineering on the edge While SWIETELSKY and partners are mapping their


way through Tyrolean bedrock, a very different tunnelling story has just been written in China – this one almost defying gravity.


On 6 June, engineers at the Pingjiang Pumped


Storage Power Station achieved a world first: the full breakthrough of a diversion inclined shaft excavated using CRCHI’s “Tianyue” tunnel boring machine (TBM). The numbers alone tell an interesting story – an 87m-long, 900-tonne TBM boring through hard rock on a 50-degree slope, while dynamically adjusting its diameter from 6.5m to 8m. Inclined shafts of this steepness are notoriously difficult and dangerous to construct. Conventional methods are slow, labour-intensive, and risky. But “Tianyue” moves three times faster, excavating and lining the tunnel in one continuous operation. The No. 1 diversion shaft, stretching 1337.9m, has a “wider-top, narrower-bottom” profile: 8m wide at the upper section to reduce flow velocity and prevent cavitation, tapering to 6.5m at the lower high-pressure zone to cut steel usage by over 30% and avoid deep excavation hazards. Central to this success is a triple-gripping hydraulic


interlock system – three grippers anchored to the shaft wall in a triangular matrix. As the TBM advances, the grippers alternate their hold every 1.5m, providing secure footing “like caterpillar feet gripping the ground” even on the steep incline. But perhaps the most interesting feature is its adjustable-diameter technology. Engineers devised an expandable shield and cutting wheel system, along with a lifting and diameter-changing device, allowing the TBM to switch diameters mid-tunnel without replacing equipment. The result: major cost savings, shorter construction timelines, and valuable lessons for future steep-slope tunnelling worldwide.


Modernising a classic While China’s TBM is blazing a trail for future projects,


in Germany, engineers are revitalising a piece of hydropower history. The Rudolf-Fettweis-Werk (RFW) in Forbach has been supplying electricity since the 1920s. Now, PORR Tunnelbau and EnBW Energie Baden-Württemberg AG are converting it into a high- performance pumped storage power plant to help stabilise the modern renewable-heavy grid. Work began in early 2024 and is progressing at pace. By mid-May, tunnelling had begun on the Murgwerk access tunnel – an essential artery in the sprawling upgrade. The project also saw the completion of the crane runway beam and the breakthrough of the energy discharge tunnel to the cavern. Meanwhile, at the Schwarzenbach plant, engineers


are drilling a 350m-deep shaft. The pilot bore – just 35cm in diameter – was completed in less than two weeks, using precision instruments to guide its path to the shaft foot cavern. Next comes widening the shaft to 3.1m using an 11-tonne reamer. Inside the cavern itself, progress is equally rapid.


Blasting is on schedule, with the dome and first two benches fully excavated and work advancing on the


third. All of this keeps the 2027 operational target in sight – when the upgraded RFW will provide critical storage capacity, storing surplus renewable energy when supply is high and releasing it back into the grid during demand peaks.


A connected vision: tunnels as engines


of transition Although they differ in geography, scale, and method, these three projects tell a unified story. Hydropower and pumped storage remain essential tools in the renewable energy toolkit – not just for generating electricity, but for balancing the grid as wind and solar expand. In Tyrol, the Imst-Haiming project shows how


collaborative contracting can bring complex alpine engineering to life. In Hunan, the “Tianyue” TBM proves that some of the steepest geological challenges can be met with precision-built, adaptable machinery. And in the Black Forest, the RFW conversion demonstrates that older infrastructure can be repurposed to meet modern demands. What they also reveal is the role of tunnelling as a kind of invisible backbone for the energy transition. Most of the public will never see the kilometres of rock removed, the vast caverns hollowed out, or the steep shafts drilled at improbable angles. Yet these hidden works are what make it possible to store solar power generated at midday for use at night, or to channel alpine water to turbines with minimal environmental disruption. The commitment behind such feats is as impressive as the engineering itself. For SWIETELSKY’s team, that means years of careful planning and tight cooperation. For CRCHI’s “Tianyue” developers, it meant designing a machine capable of holding itself against gravity while reshaping its own dimensions mid-job. For PORR and EnBW, it’s about balancing heritage with high-tech upgrades. As the deadlines approach – whether 2027 in Germany or earlier in China – the payoff will be measured not just in megawatts delivered, but in the resilience of the energy systems these projects support.


Above: CRCHI’s “Tianyue” tunnel boring machine broke through the diversion shaft at Pingjiang pumped storage project in China


Bottom: The pilot borehole at the Rudolf-Fettweis-Werk project is made using precise measuring instruments and serves to prepare for the subsequent widening of the shaft © PORR


www.waterpowermagazine.com | September 2025 | 31


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