Discrete-Element Investigation on the Progressive Failure of Cut-and-Cover Tunnel Lining with Various Section Features.

Similar to the deep-buried tunnel, the lining of the cut-and-cover tunnel (CCT) exhibits varying degrees of cracking failure during ultrahigh backfill. To explore the whole progressive failure process of a high-filled cut-and-cover tunnel lining structure from the mesodamage to the macrolocal failure and then to the overall instability during backfill, based on the discrete-element program PFC2D, we simulated the mechanical behavior and fracture characteristics of the CCTs with rectangular, circular, and arch lining section features with the backfill height. Two load-reduction measures—load-reduction material (LRM) and the interaction of LRM and concrete walls—were then further proposed, and the impact of load-reduction measures on the progressive failure of CCT lining was analyzed. The simulation results show that the various lining section features indicate differences in the distribution and value of lining stress and fracture. But the CCT lining with features of the three sections exhibits a progressive failure process from cracking to local collapse and falling and finally to overall instability as the backfill height increases. Furthermore, the LRM and concrete walls can effectively reduce the vertical stress of the lining vault and the horizontal stress of the haunch, respectively, to ensure the stability and integrity of the CCT. [ABSTRACT FROM AUTHOR]