PROJECT - HYDROPOWER CONVERSION | ROCK TUNNELLING
CONSTRUCTION Porr Tunnelbau is undertaking the main construction work on the project, under the Lot 2 civils package won in 2023 at approximately €98 million, or about a third of the overall budget. tunnelling on which began in early 2024, a little over half a year after it was greenlit for funding by the owner, EnBW. Excavation expects to open up about 450,000m3
of tunnels and caverns. The tunnel system has a total length of 5.2km and will include shafts excavated by raise-boring, said Porr. More than one million tonnes of mostly rock is to be excavated on the project. The works are split into five different sites:
● 1) Main Access Tunnel and Powerhouse Cavern; ● 2) Schutterstollen Supply/Mucking out Adit; ● 3) Outlet Structure; ● 4) Murg Transfer Tunnel; and, ● 5) Schwarzenbach Conveyance Tunnel.
Construction Sites 1-3 commence from the downstream ends of the project and excavate into the hill to establish the various tunnels and caverns. Construction Site 4 is at the upper end of the project,
relatively near Schwarzenbach dam and reservoir but the tunnel in these works will not be involved with those waters. Instead, as noted, it will transfer water from another reservoir - Kirschbaumwasen - via a dedicated tunnel down to the powerhouse. Construction Site 5 is also at the upper end of the
project, closer to the Schwarzenbach dam and reservoir. The tunnel will convey water from that reservoir down to the powerhouse cavern, via its own dedicated tunnel.
CONSTRUCTION PROGRESS EnBW reports that excavation started first in April 2024 on Construction Site 2, the Schutterstollen Supply/Mucking Out Adit. In June, blasting began on Construction Site 1, for the Main Access Tunnel works. By late autumn both tunnels were completed. At the end of the Access Tunnel, excavation then got
underway for the other major part of the Construction Site 1’s works - the Powerhouse Cavern. The cavern has dimension of 123m x 20m x 42m (L x W x H). Excavations have been underway on the cavern October 2024, with mucking out via the Construction Site 2 short tunnel route. Preparatory works by then had also started at
Construction Site 5, the Schwarzenbach Conveyance Tunnel, to establish the portal area. By January 2025 excavation of the Schwarzenbach conveyance tunnel was underway. Over the winter, in the vault of the powerhouse
cavern, Porr Spezialtiefbau installed lines of permanent anchors into rock to support the travelling crane rails, needed both during construction and over the operational life of the hydro plant. There were 50No four-strand permanent anchors used, with double corrosion protection, a 3m-long grout body length. They are 18m long and were drilled, uncased, at 27° incline. A Klemm 806 GS rig was used, adapted for the inclined drilling, and used clean water rather than compressed air for the hammer drill. The crane was lifted into place in February, said Porr. Also by February 2025, the project was halfway through excavation, said EnBW.
HYDRO HISTORY AT FORBACH
Built a little over 100-years ago, the Rudolph Fettweis power plant complex, in Forbach, comprises four separate power plant systems as well as a dam, surface powerhouse, and tunnels. The power plants were built over two stages, 1914-18 and 1922-26, respectively. The network of plants began with two (including Murg) in the first stage and then a further two (Raumuzach, Schwarzenbach) were added in the second stage. The key dam in the hydro scheme is the
Schwarzenbach Dam, which serves as the upper reservoir to two turbines in the Forbach power complex, almost 360m below, beside the river. Water flows down through tunnels and pipelines to the plant. EnBW said the reservoir has been drained three times - in 1935, 1952 and 1997 - for repair and maintenance work on the dam. The powerhouse also has five turbines fed by the
Murg waters. In total, all seven turbines have an installed capacity of 65MW for power generation.
The next stage of life for the Forbach power site will not see the surface powerhouse in a key role. A new, underground, powerhouse is to be built, tapping the same Murg and Schwarzenbach waters. The new hydraulic arrangement and equipment are to add a further 12MW of installed capacity to the Forbach site. New storage caverns are also to be added as the
Forbach site switches to have key capability in pumped storage. The caverns will act as a ‘lower reservoir’ to the Schwarzenbach ‘upper reservoir’, for pumped storage operations - with a 57MW pump-turbine. In May 2023, at the time of EnBW’s final financial decision to investment in the project, following receipt of planning approval, EnBW’s chief operator officer, for sustainable generation infrastructure, Georg Stamatelopoulos, said in a statement: “EnBW has a clear generation strategy focused on the accelerated expansion of renewables and achieving climate neutrality by 2035. To accomplish this, we require additional dispatchable capacity and storage reservoirs that can quickly deliver electricity on demand and ensure stable grid operation.”
June 2025 | 13
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