Title: An experimental study on the use of polypropylene macrofibers in precast segments for hydraulic and metro tunnel lining
Author(s): Conforti, A.; Trabucchi, I.; Tiberti, G.; Plizzari, G.A.; Caratelli, A; Meda, A.; Moro, S.; Hunger, M.
Publication: Symposium Paper
Appears on pages(s): 185-194
Keywords: Fiber reinforced concrete; Polypropylene macrofibers; Point load test; Precast tunnel segments; TBM thrust jack phase.
There is a growing interest in the scientific community on the structural applicability of
polypropylene macrofibers without or in combination with conventional reinforcement as
spread reinforcement for precast tunnel segmental linings. Polypropylene macrofibers could
be used in precast tunnel segments as shear reinforcement and for withstanding splitting and
spalling tensile stresses which occur under and between Tunnel Boring Machine (TBM) rams,
respectively. Fibers could also simplify and speed up the tunnel element production process.
In this context, the present study investigates the possibility of using polypropylene
macrofiber reinforcement in precast tunnel segments for both hydraulic and metro tunnel
linings. Four full-scale segments (two counter-key segments of a hydraulic tunnel and two
trapezoidal shaped segments of a metro tunnel) were experimentally evaluated under point
load test. The latter simulate the TBM actions on segments during the excavation process
(TBM thrust jack phase), which is generally the most critical temporary loading condition for
segments. Two reinforcement solutions were studied: a typical conventional reinforcement
(reference samples) and a combination of polypropylene macrofibers and conventional
reinforcement (hybrid solution). Polypropylene macrofibers were observed to be very
effective in combination with conventional reinforcement, underlining the fibers ability in
controlling both splitting and spalling phenomena.