A Major Milestone in the Expansion of the A44

The Holstein Tunnel is a key structure in the construction of the new A44 federal highway between the Sontra-West and Sontra-Mitte interchanges. With a length of approximately 1,664 meters, it is one of the larger tunnel structures in the project and is part of the German Unity Transport Project (VDE) No. 15. Principal is DEGES (Deutsche Einheit Fernstraßenplanungs- und -bau GmbH), a a corporation specializing in highway planning and construction that was established after Germany’s reunification.

The tunnel will be constructed with two separate tubes, one for each direction of travel (Kassel and Eisenach). Each tunnel tube will have two 3.50-meter-wide lanes and three lay-bys. To ensure tunnel safety, seven cross-passages will be installed to connect the two tubes to each other.

The construction contract was awarded in the spring of 2024 to a joint venture (ARGE) following a Europe-wide tender. This joint venture consists of BeMo Tunneling GmbH / Subterra GmbH for construction engineering and Josef Rädlinger Bauunternehmen GmbH / Stutz GmbH for earthworks. Building Information Modeling (BIM) is being used for the first time in a tunnel project during construction.

Preparatory earthworks began at the end of 2024, including extensive ground stabilization measures in the area of the future tunnel portals. The mixed binder VARILITH TF 1 (30% lime / 70% cement) from the Dyckerhoff plant in Deuna was used for this purpose. The official start of tunneling work finally took place on March 20, 2025, with a symbolic blast.

The geological conditions in the area of the Holstein Tunnel are considered challenging. In addition to solid rock layers, there are also heavily weathered and soft strata that require additional safety measures—such as pipe shields. A total of approximately 450,000 tons of rock must be excavated and removed. Despite the difficult conditions, a total of 16 months is estimated for the tunnel excavation; according to schedule, it would therefore be completed in August 2026.

Overview of the DEGES Project Section highway 44 (Graphic: DEGES – Public Meeting, Dec. 2024)

Two mobile ready-mixed concrete batching plants from BeMo Tunneling were set up about 1 km south of the tunnel portal for concrete production. One plant is used to produce shotcrete, while the second is for the inner lining concrete. A total of approximately 250,000 m³ of concrete is produced on the construction site, comprising 125,000 m³ of shotcrete and 125,000 m³ of inner lining concrete.

Use of local binders from Dyckerhoff in Deuna
The shotcrete of strength class C 25/30 serves as a 20–30 cm thick support layer to stabilize the rock during tunneling and the construction of the inner lining. The inner linings are constructed with a thickness of 40–80 cm using concrete of strength class C 30/37. A continuous waterproofing membrane is installed between the shotcrete and the inner lining to prevent the ingress of rock water throughout the entire service life.

As early as February 2025, comprehensive tests and mixing trials were conducted at the construction site to determine the optimal mix design for the shotcrete. These tests showed that Dyckerhoff PZ Dreifach SB sprayed cement (CEM I 52.5 R sb) from Deuna exhibits very good workability and performs excellently with standard accelerators—even at outdoor temperatures around freezing.

The Deuna cement plant supplies the following products for various applications:

• Spray cement: Dyckerhoff PZ Dreifach SB – CEM I 52,5 R (sb)
• Interior shell cement: Dyckerhoff Comfort Doppel – CEM II/A-S 42,5 R
• Mixing binderVARILITH TF 1 – 30 % lime / 70 % cement
• Standard limestone powder  as an inactive additive

The tunnel floor is constructed using concrete of strength class C 30/37. This is followed by the traffic surface structure for load class BK 100 (> 32 million equivalent 10-ton axle passages) in accordance with the Guidelines for the Standardization of Traffic Surface Superstructures (Richtlinien für die Standardisierung des Oberbaus von Verkehrsflächen – RStO 12). The structure is organized as follows:

• 70 cm frost protection layer,
• 22 cm asphalt base layer,
• 9 cm asphalt binder layer and
• 3 cm mastic asphalt surface.

This creates a durable, high-performance traffic area.

Further extensive construction work planned
In addition to the tunnel, three bridge structures and several retaining structures will be built as part of this construction phase. The project also includes extensive earthwork for the highway route’s junction areas. Large portions of the embankments and parking facilities at the Sontra-Mitte interchange will be constructed using recycled tunnel excavation material.

Structural work is scheduled to be completed by 2028. This will be followed by the installation of operational and traffic control systems, with the road scheduled to open to traffic in 2030.

As part of the entire DEGES section of the BAB 44, a total of 7 tunnel structures with a combined length of 5.8 kilometers and 8 viaducts with a total length of 2.5 kilometers will be constructed over a distance of 29.4 kilometers. The project closes one of the last remaining gaps in the German highway network between the A7 near Kassel and the A4 near Wommen, thereby representing an important component of the “German Unity Transportation Projects.” It also significantly relieves traffic on the regional road network, particularly on the existing through-traffic routes along the main arteries. The Boyneburg tunnel, a project for which Dyckerhoff supplied various cements and concretes as well as soil-improvement binders in 2020/21, is also part of this overall construction project.

Photos: Dyckerhoff

For further information, please contact:
Iris Weise-Rosch, Tel.: +49 611 676-1187
marketing@dyckerhoff.com