The L9 line of the Barcelona underground has some segments in which the steel reinforment has been partially or totally replaced by steel fibres. Testing , Numerical Modelling and other analysis are available in peer-reviewed journals related to tunelling and civil engineering.

What is the reinforcement for? Is it just for handling / building stresses? In use, the segments should normally be solely in compression.

Add "plastic" fibres for fire resistance.

Thank you for your answers

First of all, I reviewed almost all materials regarding the design of TBM segments available online. I am very comfortable with the design process of segments with conventional reinforcement, but the contractor is not willing to use conventional reinforcement, even partially. I think using both of them in the design does not make sense to me, because you need to think of both conventional reinforcement and steel fiber simultaneously in the design. This makes the design more complicated and difficult. Therefore, in this sense, using just conventional reinforcement or steel fiber is more logical. As much as I understand from literature review, there are many researches completed or undergoing and I concluded that there are not certain rules for segment design with only steel fiber and more research needed to be done to make sure the use of only steel fiber for segments. Some researchers conclude that yes ok it is fine to use steel fiber only, while some others put research findings conflicting with this. I confused at that point.

Secondly, conventional reinforcement usually is included in the design to withstand the design loads such us rock loads, grouting pressures, self weight, etc… After determination of the reinforcement, it is also checked if reinforcement is adequate to eliminate the tension crack due to TBM thrust. Currently, handling / building stresses are of secondary importance for the design. I also know that use of steel fiber is more effective for handling / building stresses than conventional reinforcement.

Now, question is this: in case of use of just steel fiber, how can I check segments resist the design loads and TBM thrust. Is there any design procedure available and recognized by the construction community?

I would appreciate any answers.

Pl.see the link:http://www.tunnel-online.info/en/artikel/tunnel_2011-01_Steel-fibre-reinforced_segmental_linings_State-of-the-art_and_completed_1076896.html

Thank you Professor, This material is exactly what I am lookıng for. I appreciate your help.

Finally, we came up with an agreement with the contractor such that I will reinforce the segments conventionally, and then they will pre-cast the segments in the factory. They will also pre-cast the segments with the concrete included steel fiber at different rates such as 35kg/m3, 40kg/m3, 45kg/m3, 50kg/m3 for an experiment. Afterwards, they will test the samples under the loads that I obtained from the FEM analysis (the loads that I also used in conventional design). If one of the tests gives satisfactory results, then associated mix is going to be used in the tunnel for lining. I will post the experimental results here for your knowledge so that you can make use of them for your works as well.

The construction of test panels at each of the 4 steel fiber amounts followed by

core drilling and standard compression test may be of use.

Also construction of beams that are loaded at the third points for each

of the 4 steel fiber amounts you listed.

The other important factor is that you have not indicated the geology

of the area that is going to be tunnel bored, nor the

earthquake history of the area to be bored through.

in the 1960s part of London Underground's 12'-2 1/2" I.D. Victoria Line tunnels through London Clay behind a TBM were built using 6" thick "flexible concrete" (knuckle-jointed) segments with no reinforcement at all. The lining supported the ground, and the ground supported the lining.

You could test full sized panels at the Federal Center in Lakewood Colorado.

The test machine can exert up to 5,000,000 lbs of force in either tension

or compression, or you could build a jig to do the testing of the

curved segments in bending.

They test concrete core samples from concrete dams that are 2 feet to

three feet in diameter.

If you really want to know, test the full sized segments.

They tested the connections between the space shuttle and its external

tanks and rocket boosters.