Page 50

2015SummerShotcreteEMag

Goin’ Underground In-Service Performance of Macrosynthetic Fiber-Reinforced Tunnel Linings By Ralf Winterberg and Axel G. Nitschke T(MSFRS) for tunnel linings and provides an of reinforcement in the Australian underground-support in both mining and civil tunnel applications. It has for instance become the standard formhis article introduces macrosynthetic fiber-reinforced concrete (MSFRC) and shotcrete overview of state-of-the-art design and testing mining industry, where 2014 literally marked the methodologies that currently exist. In addition to end of steel fiber use in shotcrete,1 and has been the structural load bearing capacity of fiber- used for over 80% of permanent tunnel linings in reinforced linings, design considerations with recent tunnel construction in Norway. Similarly, regard to long-term performance are presented, macrosynthetic fibers are becoming a standard which is getting more and more into the focus of solution for initial (or primary) tunnel linings in project owners, as well as their designers and the United States. Recent examples are the Devil’s consultants. Actual projects and recent research Slide Tunnel and Caldecott Fourth Bore Tunnel in are presented with this regard, together with best California and the Anacostia River Tunnel Inter- practice design principles, including crack width shaft Connector Tunnel in Washington, DC. In control, corrosion and durability, and sustainment addition, an increasing number of tunnels are of performance with age. adopting shotcrete permanent linings using mac- rosynthetic fibers. Examples include the A3 Hind- Introduction head tunnel near Guildford in the United Kingdom MSFRC and MSFRS have reached maturity as and the North Strathfield Rail Underpass in Sydney, an engineering process and is widely used in all Australia.2,3 A recent example of a MSFRC cast- forms of tunnel linings. The technology is now in-place permanent tunnel lining in the United States commonplace for temporary and permanent ground is the Euclid Creek Tunnel in Cleveland, OH.4 Macrosynthetic fibers have the same approxi- mate size as steel fibers, but are not to be mistaken with monofilament microsynthetic fibers, which serve a completely different purpose, as these are nonstructural fibers. Macrosynthetic fibers have typical lengths between 0.8 and 2.6 in. (20 and 65 mm) and typical equivalent diameters of 0.016 to 0.039 in. (0.4 to 1.0 mm). Due to their flexi- bility, they are much easier to handle, pump, and shoot than steel fibers, which are more prone to formation of blockages and wear and tear of pumping lines. The tensile strength and the Young’s modulus are typically around 45 to 100 ksi (300 to 700 MPa) and 725 to 2000 ksi (5 to 14 GPa), respectively. The base material of macrosynthetic fibers is usually polypropylene. Typical dosages for shotcrete primary ground support and initial tunnel linings are in the range Fig. 1: EPC DucTil 57 Macrosynthetic Fiber of 5 to 10 lb/yd3 (3 to 6 kg/m3). Typical dose 48 Shotcrete • Summer 2015


2015SummerShotcreteEMag
To see the actual publication please follow the link above