With the concept of smart geogrid coming out, many scholars have built optical fiber into the geogrid to form a kind of smart geogrid material with self‐sensing function of structural deformation. It can not only reinforce the parts with potential safety hazards, but also have the functions of safety monitoring, intelligent prevention, and control of engineering disasters, which is of great significance for ensuring the safety of tunnel construction and improving the tunnel monitoring methods. Based on predecessors’ research on smart geogrid tensile calibration experiment and sensor method simulation and experimental verification, this paper analyzes the smart geogrid and the tunnel surrounding rock as a whole, to study the deformation coordination mechanism between the geogrid material and the tunnel surrounding rock. Referring to the relevant engineering practice case, through finite element numerical simulation, the optimal layout of smart geogrid material was explored, and the principle of discrete curvature reconstruction curve sensing of smart geogrid was optimized by simulating the working conditions of different construction methods and supporting conditions, in order to provide a theoretical basis for the application of smart geogrid material in practical tunnel engineering.

Freeze‐thaw cycle is a type of fatigue loading, and rock stress relaxation under freeze‐thaw cycles takes into account the influence of the freeze‐thaw cycle damage and deterioration. Rock stress relaxation under freeze‐thaw cycles is one of the paramount issues in tunnel and slope stability research. To accurately describe the mechanical behaviour of stress relaxation of rocks under freeze‐thaw, the software element is constructed based on the theory of fractional calculus to replace the ideal viscous element in the traditional element model. The freeze‐thaw damage degradation of viscosity coefficient is considered. A new three‐element model is established to better reflect the nonlinear stress relaxation behavior of rocks under freeze‐thaw. The freeze‐thaw and stress relaxation of rock are simulated by ABAQUS, the relevant model parameters are determined, and the stress relaxation equation of rock under freeze‐thaw cycle is obtained based on numerical simulation results. The research shows that the test results are consistent with the calculated results, indicating that the constitutive equation can better describe the stress relaxation characteristics of rocks under freeze‐thaw and provide theoretical basis for surrounding rock support in cold region.

In hard cataclastic surrounding rock with high geostress, the rock monomer strength is high and the rock is broken, and tunnel excavation in it is apt to cause large deformation, collapsing, and breaking, causing initial support crack and even intruding of the initial support deformation. The characteristics of the support system under different support parameters and shapes are analyzed, and the reasonable support section shape and support parameters are determined. The results showed that (1) under the condition of high geostress and hard cataclastic surrounding rock, the initial support deformation is large, the horizontal convergence is much larger than the settlement of arch, and the deformation duration is relatively short; (2) the distribution of pressure and stress in initial support are very uneven on the cross-section and greatly affected by the construction process; (3) in the case of large horizontal tectonic stress, the use of large curvature side wall support is beneficial to improve the quality of support and control the deformation of the structure, especially to improve the stress of concrete; (4) the closure time of the supporting system greatly influences the stress state and deformation, so it is necessary to shorten the length of the lower bench and the distance of the invert as possible so as to close the support as early as possible; (5) different location of the tunnel surrounding rock stress distribution is very uneven, the measured value is much larger than calculated value in level III based on the specification of surrounding rock; (6) under high strength and ground stress, the initial supporting stress of steel frame increases rapidly, and the measured stress is larger. This indicates that the steel frame structure bears heavy early load. Therefore, the stiffness of the steel frame should be as large as possible to meet the loading requirements.