A number of 1/5 scale normal concrete (NC), reinforced concrete (RC), Engineered cementitious composites (ECC) and reinforced ECC (R/ECC) tunnel lining specimens were tested under vertical loading applied at the mid-top of the crown and the mechanical behaviours were analysed. Four lining FE models were established and compared in detail with the test data. Subsequently, numerical analysis of NC lining strengthening methods for different damage levels was performed. The NC linings exhibiting different damage levels were strengthened by either RC arch, ECC arch, R/ECC arch, steel plate and carbon fibre reinforced polymer (CFRP) sheet. The mechanical behaviour of the retrofitted NC linings was analysed, and the strengthening effects were thoroughly evaluated. The results showed that the load-bearing capacity and ductility of NC linings retrofitted by R/ECC arch were better than NC linings strengthened by ECC arch or RC arch. The steel plate and CFRP sheet retrofitted NC linings resulted in lower load-carrying capacities compared with linings strengthened by arches. For the plate strengthening methods, when the damage level of the strengthened NC lining is lower, more pronounced strengthening effects could be attained compared with the highly damaged linings.

The presence of symmetric and asymmetric voids directly affects the mechanical behaviors of tunnel linings and further induces tunnel diseases among influence factors. In this paper, 1:5-scale model tests were carried out to study the mechanical behaviors of reinforced concrete (RC) linings considering the voids located at the crown and at the spandrel. Based on the experimental results and concrete plastic damage (CDP) model, the effects of void (i.e., location and size), subgrade stiffness, and lining size on bearing capacity of RC lining were investigated using numerical simulation. The results of model test and parametric analysis showed that the existence of voids significantly affected the mechanical behavior of the lining during inelastic deformation period. The lining with a larger void size corresponded to low bearing capacity and larger deformation around the void, thus increasing the damage possibility of linings. The influence of voids on the bearing capacity of linings varied with the void location, load direction (especially under horizontal symmetrical loads), and subgrade stiffness. High soil stiffness corresponded to a great influence of the void size on the lining bearing capacity. In addition, the lining strength increased inconsistently with the increase of model size. On the basis of parameter sensitivity analysis, the Levenberg–Marquardt (L-M) optimization algorithm and Logistic model were used to establish the equation of lining bearing capacity loss rate considering the void effect.

Engineered cementitious composites (ECC) have higher ultimate tensile strains than normal concrete. The mechanical properties of ECC strongly depend on raw materials and the mix proportions. The uniform design test method and alternating conditional expectation, which is a nonparametric regression analysis method, were used to design the ECC mix proportion. According to the regression analysis, the optimized W/B, S/B, and F/B ranges could be obtained as 0.35–0.42, 0.25–0.3, and 0.02, respectively. The tested proportions for validation were randomly adopted within the range of W/B, S/B, and F/B. The uniaxial compression, tension, and four‐point bending tests were conducted to verify the material behaviour of the designed ECC. Results showed that all the specimens had large ultimate tensile strains and high fracture energy capacities, and strain hardening was also observed. The fibers were found to be uniformly distributed in the specimens by using a scanning electron microscope. This paper may provide theoretical and practical guidance for the ECC and other cement‐based material mix proportion design.