When it comes to meeting the world’s urgent need for clean, reliable power, engineers are literally going to great depths. Across Europe and Asia, vast underground caverns, inclined tunnels, and high-pressure shafts are being carved out to house the next generation of pumped storage and hydropower projects. These projects combine state-of-the-art tunnelling technology with innovative construction partnerships – pushing technical boundaries while ensuring energy systems are ready for a renewable-powered future.
The stories unfolding in Austria’s Tyrol, China’s Hunan Province, and Germany’s Baden-Württemberg may be thousands of kilometres apart, but they are bound by a common mission: to make large-scale, sustainable energy storage and generation possible, even in the most challenging environments.
Partnership in the Alps
In Innsbruck this spring, Austrian construction firm SWIETELSKY marked another major milestone in its tunnelling legacy. On 21 March 2025, the company signed an alliance contract with Tiroler Wasserkraft AG (TIWAG) and partners for the main construction lot of the new Imst-Haiming power plant – an ambitious hydroelectric project with a total value of €450 million.
The scope of the work includes: a 14km headrace tunnel with a surge tank and underwater tunnel; a vast cavern with access and drainage tunnels; and the creation of an underwater basin. The facility will harness alpine water power to produce clean energy for decades to come.
Peter Krammer, CEO of Swietelsky AG, describes it as much more than another contract win: “Together with our alliance partners, we are creating lasting value for the future by providing clean energy solutions. This is about enabling a more sustainable future for all.”
The alliance model is key to this vision. Building on previous successes in projects such as Kühtai, Tauernmoos, and Kaunertal, SWIETELSKY has once again chosen a collaborative contracting approach. By involving Implenia Österreich GmbH and Ing. Hans Bodner Bau GesmbH & Co KG from the earliest planning stages, the team has optimised designs and smoothed potential bottlenecks before breaking ground.
The approach – known as early contractor involvement – focuses on cooperation, fair risk sharing, 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 projects 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.
