Vibration model test and seismic performance evaluation of polypropylene fiber reinforced concrete lining of mountainside tunnels in Loess Plateau

Abstract Currently, tunnels are key infrastructure projects for traversing the Loess Plateau and ensuring rail connectivity. However, seismic damage surveys indicate that tunnels built along mountainsides in the Loess region suffer severe damage during earthquakes due to their low structural damping and inadequate seismic performance assessments. Therefore, this manuscript is to develop a new method for evaluating the seismic performance of mountain-adjacent tunnels under the coupled effect of earthquake and slope deformation in loess region. This method proposes a concrete mix design for polypropylene-fiber-reinforced concrete (PFRC) tunnel structures built along mountainsides in the Loess Plateau. Through shake-table model tests evaluating the seismic performance of such structures, the study analyzed their seismic performance and the underlying mechanisms. The tests revealed that concrete strength first increased and then decreased as the fiber content increased; the optimal concrete strength was achieved at a fiber content of 0.9%, representing a 15% improvement over ordinary concrete. The PGA amplification factor for the slope increased nonlinearly with elevation, with a quadratic amplification phenomenon observed at the slope crest. The seismic response of bending moments of the PFRC tunnel lining at the arch, invert arch, and left and right side walls were reduced by 8.9%, 8.5%, 15.2% and 12.4%, respectively, than that of ordinary concrete. This indicates that incorporating fibers into tunnel lining can form a highly damping composite structure, yielding good seismic performance due to the continuous energy dissipation from fiber friction, crack opening and closing, etc. Meanwhile, compared to traditional lining structures, the fiber-reinforced concrete lining has advantages such as simple construction technology, excellent environmental adaptability, and low maintenance costs, which can solve the seismic problem of mountain-adjacent tunnels in loess areas.