Concrete tunnel linings can either be precast segmental linings, shotcrete or poured in place. In the past tunnel contractors have been faced with the arduous task of correctly pacing wire mesh or rebar reinforcement in tunnel linings. It is now common practice to reinforce the linings with fibers or a combination of fibers and rebar. Fibers have been in use for over 25 years as a reinforcing method in linings since they offer a more efficient and cost effective production as well as higher durability and fewer precast panel rejections. The performance characteristics of quality assured steel and macro fibers, now make it possible for tunnel linings to be manufactured entirely from fiber reinforced concrete.
Fiber reinforced tunnel segments can be designed through the use of ITA Technical Guidance notes for Precast Fibre Reinforced Concrete Segments or ACI 544.7R-16 Report on Design and Construction of Fiber-Reinforced Precast Concrete Tunnel Segments.
- Steel and macro concrete fibers are designed to improve the flexural toughness and energy absorption of the concrete.
- Increased ductility in tension and compression.
- Increased impact resistance.
- High resistance against spalling during shipment and jacking of tunnel segments which leads to improved joints between segments.
- Provides superior crack width control.
- Offers three dimensional homogenous reinforcement, which is always positioned properly.
- Reduce fire explosive spalling with Fibermesh® 150F.
- The use of fiber reinforced concrete simplifies the construction process and accelerates the speed of execution.
- Cost-savings due to elimination of the cage production, storage and installation and enhances flexibility in case, for example, of project modifications.
- Products tested and proven independently to ASTM and European Standards.
- Reduces water migration and porosity
REINFORCING THE STRUCTURE
The shape of the tunnel segments lead to complex traditional reinforcement arrangement which can be replaced in full or minimized with the Enduro® synthetic or Novocon® steel fiber reinforced concrete. It is important to maintain the structural integrity of the concrete segment by limiting the concrete cracking, mainly in curing, transportation and assembly steps. Enduro® and Novocon® steel fiber three dimensional reinforcement defends the segment against the impact loads and point loads from the TBM rams. Another advantage, with the use of Enduro® and Novocon®, fiber reinforced in tunnel segments is the removal of cathodic protection due to fact that the fiber are dispersed in the concrete matrix and the lack of contact between the fibers does not allow the onset of current. Furthermore, the use of Fibermesh® 150F reinforced concrete increases the fire protection performance of the material, limiting the spalling.
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