The damaging mechanism and performance design of the off-wall tunnel under the dynamic and static combined cycling loading model

The underground off-wall tunnels find wide application in the civil underground projects and the national defense projects due to its merits of small backfilling workload, quick construction progress, good drainage and being damp-proof and easy to be repaired and maintained. Based on the dynamic and static combined cycling loading method and the design strategy of the structure performance, this paper adopts the combination method of similarity physical model experiment and the numerical analog calculation to conduct dynamic damaging mechanism and performance standard design research of underground off-wall tunnel. The research results show that the dynamic and static combined cycling loading method can better reflect the generation and expansion progress of the inner microcracks of rocks and concrete materials, thus it is an effective method to research into the damaging rules and stability of the underground off-wall tunnel; the plasticity displacement, strain and pressure stress changes of the monitoring point can better describe the damaging status of the underground projects; the increase of load magnitude can obviously result in the displacement of the monitoring point (vault), which may cause the first transcending damage of the tunnel, and the cycling loading will show accumulated damage with the load magnitude positively related to the degree of accumulated damage; the strain of the monitoring point will undergo sudden changes when reaching the ultimate pressure value, while the crack width parallel to the tunnel diameter is the reference to the damaging status of the underground tunnel; the experimental and numerical simulated results coincide with each other, and can well represent the performance standard of the underground tunnel, thus providing the reference for the earthquake and explosion effect, as well as the protection a design of the underground tunnel. © 2014, Journal of Chemical and Pharmaceutical Research. All rights reserved.