Cracking in fibre reinforced concrete jacketed-pipes for long-distance tunnels in rock

This study investigates the cracking mechanism of reinforced concrete pipes during long-distance pipe jacking in rock strata and evaluates the potential of fibre reinforced concrete pipes (FRCPs) as a crack-mitigation measure. Field crack surveys were conducted in three non-pressure tunnels of the Guanjingkou Water Conservancy Project, and three-dimensional finite-element models were established to reproduce typical pipe-rock interaction modes. The field investigation showed that longitudinal cracks were dominant, accounting for approximately 87.1%–89.7% of the detected cracks. Numerical results indicated that pipe cracking was governed by the coupled effect of pipe deflection angle ( χ ) and jacking force (JF), and the upward deflection mode represented the most unfavorable condition. Compared with ordinary reinforced concrete pipes, basalt-polypropylene fibre reinforced concrete (B/PPFRC) pipe showed increases of more than 20% in the JF corresponding to initial cracking P cr and 0.3 mm crack width P 0.3 under the simulated conditions. In addition, four prototype FRCPs with different fibre configurations, including one B/PPFRC pipe, were installed in No. 7 non-pressure tunnel (NPT), and no visible cracking was observed during the monitoring period. These field observations provide preliminary qualitative evidence supporting the practical feasibility of FRCPs under the investigated construction conditions and are qualitatively consistent with the numerical prediction that fibre reinforcement can improve crack resistance. Nevertheless, because only one prototype adopted the B/PPFRC mixture considered in the numerical analysis, larger-scale field applications are still required to validate its long-term crack-control performance.