Tunnel Technologies
- NATM - New Austrian Tunneling Method (Austria)
- TBM - Tunnel Boring Machine (Germany)
The New Austrian Tunneling Method (NATM) is a highly efficient tunneling technology, distinct from the Tunnel Boring Machine (TBM) method. Unlike TBM, which requires large, specialized machinery, the NATM utilizes more conventional equipment. The excavation begins with a special excavator equipped with a flexible head (dredging shovel) to start forming the tunnel profile (cross-section).
The excavation process varies depending on the material being excavated (stone or hard soil). Typically, we dig between 2 to 4 meters inside, after which we begin installing the tunnel reinforcement as per the project specifications. To speed up the process, specialists may employ micro-explosions to make excavation easier. Following the excavation, sprayed concrete is applied to reinforce the tunnel vault.
This process is performed section by section: excavation, reinforcement installation, and sprayed concrete application. During the reinforcement phase, the reinforcement is anchored to the surrounding soil or rock, ensuring stability. Excavated material is transported out by wheel loaders and trucks.
Safety is always our top priority. Ventilation systems are installed throughout the tunnel to maintain air quality, and designated "safety stations" equipped with oxygen tanks are placed to ensure the safety of workers during emergency situations.
The NATM is faster, more cost-effective, and more economical compared to the TBM method. One of the significant advantages of NATM is its adaptability to curves in the tunnel route. In contrast, with TBM, if a curve is required, the machine may experience difficulties, potentially causing stoppages if the operator makes a slight error.
The cost of a TBM can range up to $50 million USD or more, depending on the diameter, and transporting a TBM—often 12-15 meters in diameter and up to 35-50 meters long—can be highly challenging, especially when broken down into sections. Furthermore, TBMs typically create a circular tunnel cross-section, which is less efficient for certain uses. For road or railway tunnels, up to 20-25% of the tunnel’s cross-section must be refilled.
In contrast, the NATM produces an egg-shaped tunnel with a flat curve at the base, making it more efficient and cost-effective for infrastructure projects. This shape allows for better utilization of space and fewer materials required for refilling.