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Modern tunnel faces a multitude of complex challenges that require innovative planning approaches and advanced technologies. Dynamic loads caused by traffic or seismic activities place high demands on the stability and durability of tunnel structures. In addition, repeated stress can negatively affect the fatigue behaviour of the materials used and cause creeping damage that jeopardises the life and safety of a tunnel.
Special risks arise from cracks in the concrete, which not only affect the load-bearing capacity, but can also accelerate the corrosion of the reinforcement and allow water to enter.
In addition, the fire resistance of tunnel structures plays a crucial role: In the event of a fire, these must withstand extreme temperatures to ensure the safety of users and rescuers.
These challenges highlight the importance of using proven and innovative technologies for safe, durable and sustainable tunnelling. They form the basis for successfully implementing modern infrastructure projects and meeting the high requirements for functionality and security.
In new tunnel construction and in the renovation of existing tunnel structures, fastening systems play a central role in the load-bearing capacity and stability of the structure. They must not only withstand static and dynamic loads during the construction phase and operation, but also withstand corrosion in the long term. These requirements are particularly relevant as tunnel structures can be subjected to continuous traffic loads and mechanical vibrations. Seismic effects must also be taken into account.
The fatigue behaviour of fastening systems depends largely on the material properties, e.g. steel grade, anchoring conditions and environmental influences. Chemical systems apply the forces over a large area, which reduces stress peaks and increases fatigue resistance. This makes them particularly suitable for demanding dynamic applications. Mechanical bolt anchors are characterised by high robustness and are suitable for medium dynamic applications.
Cyclic load testing is essential to ensure that fastening systems do not lose their load-bearing capacity even after millions of load changes. Additional challenges arise from extreme environmental conditions, such as strong temperature fluctuations or aggressive chemical influences, e.g. due to a corrosive atmosphere of exhaust gas engines.
Fastening systems in tunnel construction- such as mechanical bolt anchors or chemical injection systems - are often exposed to cyclic forces. These occur due to recurring loads, for example from train, truck or metro traffic. Cyclic forces lead to vibrations and micro-movements that stress the structure and fasteners. Fatigue strength is therefore an essential requirement for fastening systems to prevent material failure such as breakage or loosening.
Chemical fasteners, such as injection systems, offer the advantage of uniform force application in the anchoring area. This makes them particularly suitable for cyclic loads such as vibrations or frequent load changes. Mechanical bolt anchors, which are fixed in the material by form-fitting or friction, score points with immediate load absorption.
Comprehensive tests and approvals are required to prove the suitability of fastening systems. General building authority approvals (abZ) from the German Institute for Building Technology (DIBt) and European Technical Assessments (ETA) ensure that products are tested with regard to load-bearing capacity, fatigue strength and corrosion resistance. For international projects, products are often evaluated according to the ICC Evaluation Service and additional certifications according to ASTM or ISO standards are required.
When renovating tunnel structures, fastening systems must be flexibly adapted to the often heterogeneous and damaged substance. Chemical fasteners are ideal for cracked or brittle material, as the anchorage does not expand. Mechanical bolt anchors, on the other hand, are the first choice when immediate load transfer is required or chemical systems are less suitable due to environmental conditions, such as extreme fire stress. Both systems contribute significantly to the stabilisation of existing structures and the integration of new supporting structures.
Systems such as cable trays, ventilation or duct systems are not only tested for fire resistance, but also for functional suitability in the event of fire. The fire resistance duration of these systems is specified for use in tunnels according to specially developed tunnel fire curves.
