PurposeShield tunnel is usually used as permanent underground facilities with a design service life of 100 years, and operational safety is very important. The objective of this paper is to investigate the failure mechanism and resilience evolution of double-layer lining structures of shield tunnels and to maintain the safety of structural operation.Design/methodology/approachA macro-micro model is established based on the refinement concept, considering the influences of hand-hole weakening, multi-contact interactions and reinforcement bars. The macro model describes the stress and deformation of the soil-reinforced structure using the stratum-structure method. The micro model introduces the total strain crack model, which accurately characterizes the tensile, compressive and shear behavior of concrete, calculating the millimeter-scale crack characteristics at the interface between the double-layer lining and the concrete. The mechanical response and resilience evolution of the reinforced structure are studied.FindingsThe results show that the segmental lining joint is the weakest part of the reinforced structure. The primary failure modes include the destruction of the arch vault and left-right spandrel joints, fractures in the tension zone and crack propagation and penetration at the interface. The segmental lining and secondary lining are not perfectly connected, resulting in different internal force distribution patterns, and the secondary lining exhibits a deformation mode different from the typical elliptical type. There is a significant difference between the normal and tangential displacement distributions at the interface of the double-layer lining structure, with interface failure mainly characterized by shear slip. Reinforcement of the secondary lining can significantly enhance the resilience of the segmental lining, and the resilience recovery of the structure is more pronounced with earlier reinforcement intervention.Originality/valueThis study demonstrates notable originality and value. It develops a refined model to simulate the failure and damage of a double-layer lining structure, with millimeter-scale simulations of crack propagation at the interface of the interlayer area. A framework for evaluating the structural resilience of shield tunnels reinforced with double-layer linings is established, and the evolution of performance and structural resilience throughout the loading process and subsequent lining reinforcement was thoroughly analyzed. The findings provide valuable recommendations for the reinforcement of double-layer linings in shield tunnel projects.

To investigate the asymmetric deformation and stress characteristics of tunnels and support structures in high geostress layered fractured rock, this paper establishes two refined modeling methods: a numerical model for anchor bolt failure and a model for fractured layered surrounding rock, while considering the spatial variability of soil. The study analyzes tunnel deformation and bolt tensile-shear fracture mechanics under varying bedding angles. The results indicate that: (1) the most unfavorable stress position for tunnel structures in layered fractured rock typically occurs normal to the bedding planes; (2) the tunnel's asymmetric deformation is due to normal compressive and tangential sliding effects of geostress on the bedding planes. When the bedding angle is gently inclined, significant extrusion deformation occurs at the tunnel crown and invert; when steep, substantial tangential sliding forces cause maximum deformation at points where the bedding direction is tangent to the tunnel profile. (3) Fracture development in the surrounding rock primarily occurs normal to the foliation planes, similar to maximum displacement deformation patterns, while other areas propagate outward due to joint shear slip. (4) In layered fractured rock, failed bolts predominantly show tensile-shear fractures, influenced by bedding angle, particularly near the left shoulder to the crown and right invert. Finally, based on the deformation characteristics of layered fractured surrounding rock and the mechanical properties of anchor rod fracture, reasonable differential support optimization measures were proposed, and the simulation results were applied to the Yangjiaping Tunnel of the Chenglan Railway in China.

As common backfill materials, soil and rock mixtures (S-RMs) are widely used in high-fill slope engineering projects. The shear resistance of the interphase between the S-RM and bedrock is usually weak. To improve the stability of the slope, the bedrock can be excavated into a bench-like shape. However, the shear mechanical properties of benched interphases are complex and need to be clarified. The coupling of the finite difference method (FDM) and discrete element method (DEM) creates a powerful tool for simulating soil-rock contact. In this paper, a coupled FDM-DEM is proposed to simulate the benched interphase that considered the microstructure of an S-RM and demonstrated high computational efficiency. First, the method was validated with the results of laboratory tests. Then, the typical failure characteristics of the benched interphase were simulated and the impacts of the physical parameters of the S-RMs were discussed. According to the results, the macroscopic mechanical response of the benched interphase was closely related to the changes in the skeleton structure formed by the rock blocks and benched bedrock. Consequently, the rock block rotation, force chain distribution, crack distribution, shear stress-displacement response, and strength of the interphase underwent regular changes. Overall, the influence of the rock block proportion was more significant than the influences of the rock block shape and maximum rock block size. Therefore, to improve the stability of the high-fill slopes of S-RMs, the rock block proportion should first increase, and then the rock block shape irregularity and maximum rock block size should increase.