A case of damages in the secondary lining of a multiarch tunnel is studied by field investigation and numerical analysis, which is subject to asymmetry pressure and buried at shallow depth. The study focuses on the key influencing factors inducing these damages. The numerical analysis is implemented, taking account of the possible influencing factors obtained from field investigation, in which two cases with different numerical models are utilized to discriminate the effects caused by shallow tunnel depth and asymmetric pressure on the tunnel comparatively. The numerical result demonstrates that the topography with shallow depth and asymmetry pressure has much influence on the safety of the multiarch tunnel’s structure, and the cause of damages in the multiarch tunnel structure can be analyzed by field investigation and numerical simulation, which can provide the design basis for appropriate strengthening of the damaged tunnel structure.

This paper presents a case study of damage in the concrete lining of an operational tunnel by field investigation and numerical analysis, in which the field-investigated construction deficiency is considered in the numerical model, and the implemented numerical analysis is adopted for investigating the effect of damaging in the structure of the operating tunnel induced by the construction deficiency. The numerical analysis illustrates that the construction deficiency of a cavity can influence the stress state of a tunnel structure and plays an important role in the stability of the operating tunnel, which results in significant influence on the damage in the concrete lining of the operating tunnel and must be timely treated to prevent subsequent damage in the tunnel lining. Moreover, the numerical model considering construction deficiency of a cavity around the tunnel is efficient for evaluating the effect of damaging the structure of the operating tunnel induced by this construction deficiency.

The excavation of a deep foundation pit adjacent to an existing tunnel may lead to the large deformation and induce damages in the tunnel structure. However, the influence on existing tunnel structure from nearby excavations has not been understood clearly, since it is affected by complex influencing factors of not only the geological and topographical conditions but also the construction method and positional relationship of the adjacent structures. This paper presents a numerical investigation into an existing underground rail transit line during the excavation of an adjacent deep foundation pit, in which the behavior of the existing tunnel structure from excavating the aforementioned foundation pit is clarified, and the effectiveness of the adopted three-dimensional model is confirmed by comparison between the numerically calculated and field-measured ground settlement of the monitoring point. The results demonstrate that the deformation of the existing tunnel structure is mostly induced by the excavation of the deep foundation pit. This study can provide a reference of deep excavations adjacent to existing infrastructures.

Grouting materials require not only high ultra-early-stage strength of the stone body, but also proper working performances, such as high fluidity and fast setting time, as well as good stability. Compared with the traditional pure cement grout, geopolymer grouting material has the advantages of fast setting time, high fluidity, good slurry stability, and high early strength of the slurry stone body, which is beneficial to reuse solid waste resources and can be applied to the conditions of rapid construction or repair work to a certain extent. This paper presents an experimental investigation into the performance variation of geopolymer grouting material with varied mass fractions of raw materials, and the grouting performance of geopolymer material with optimal mix proportion is also presented. The study is implemented by employing the designed experimental schemes, focused on fluidity and setting times, as well as ultra-early-stage (4 h, 8 h, 12 h, 16 h, 20 h, and 24 h) mechanical strength. The experimental result demonstrates that both ground granulated blast-furnace slag (GGBS) content and the mass ratio of activator solution to solid have influence on the working performance of geopolymers, and both GGBS content and activator concentration have influence on the mechanical strength of geopolymers. Furthermore, the variance analysis demonstrates that the fluidity of geopolymer material is dominantly affected by the mass ratio of activator solution to solid, the setting time of geopolymer material is mainly influenced by GGBS content, and the mechanical strength of geopolymer material is mainly affected by activator concentration. Moreover, the recommended mix proportion of geopolymer grouting material is proposed in this study, in which the replacement rate of GGBS is 45%; the modulus and concentration of modified sodium silicate activator are 1.5 and 75%, respectively; and the mass ratio of activator solution to solid is 1.5. In the recommended mix proportion, the geopolymer material has excellent comprehensive performance to implement grouting operation, in which the compressive and tensile strengths of the stone body reach 12.2 MPa and 0.8 MPa in 4 h, and reach 21.2 MPa and 2.1 MPa in 24 h. The fluidity is 223 mm, the initial setting and final setting times are 50 min and 57 min, the slurry stability of geopolymer material is good without liquid precipitation, in which the setting time is far less than 2 h. This work provides the experimental foundations for investigating the performance of geopolymer grouting material, which is also expected to provide reference for the further application and promotion of geopolymer materials used for grouting operations in rapid construction or repair work.

Plant fibers, characterized by their low density, renewable nature, and environmentally friendly characteristics, offer considerable potential as reinforcement materials in geopolymer composites. This review provides a critical and thorough examination of recent developments and emerging trends in plant fiber-reinforced geopolymer concrete (PFRGC). The paper commences by detailing the inherent characteristics of plant fibers and the mechanisms governing their interfacial adhesion with the geopolymer matrix, with specific emphasis on the impact of fiber surface modification on interface properties. The review offers a comprehensive investigation of the mechanical properties of plant fiber-reinforced geopolymer concrete, encompassing compressive strength, tensile strength, and toughness. Additionally, the paper examines the influence of plant fiber integration on the durability of geopolymer concrete, discussing improvements in freeze-thaw resistance, permeability, and carbonation resistance. In conclusion, this review highlights the prevailing challenges in the domain and provides insights into future developments of plant fiber-reinforced geopolymer concrete. An analysis was performed utilizing papers from 2000 to 2025 indexed in prominent databases including Web of Science, Scopus, and ScienceDirect to enhance the review. Integrating plant fibers into developing technologies, such as 3D printing of geo-polymer matrices, signifies a promising avenue for structural applications. It advocates that future research efforts should focus on enhancing fiber modification techniques, exploring novel fiber materials, and doing thorough assessments of long-term performance.

Single-layer tunnel lining using shotcrete has the significant advantages of reducing the tunnel excavation volume and saving construction materials, which has been gradually applied in tunnel construction. The high-performance concretes are generally adopted in single-layer tunnel lining for enhancing the bearing capacity of the tunnel lining, whereas the single-layer tunnel lining may still induce damages due to the adverse conditions such as shallow buried depth of the tunnel, and further study related to its application condition is thus required. This paper presents a study of the single-layer tunnel lining with shotcrete employed for supporting the large-span tunnel, in which the reinforcement ribs are also adopted in the single-layer lining for improving the lining stiffness and strength. The study is implemented using numerical simulation, focusing on the safety and performance variation of the single-layer tunnel lining influenced from the varied lining thicknesses and shallow buried depths of the tunnel. The results shows that the single-layer tunnel lining has the obvious advantage of toughness in significantly absorbing large deformation of surrounding rocks and improving the ability to resist lining cracking. The results also demonstrate that the single-layer tunnel lining with shotcrete and reinforcement ribs can safely support the large-span tunnel, in which the stability and safety of the large-span tunnel are confirmed from both the tunnel deformation and lining stresses. Moreover, the factors related to both the lining thickness and shallow buried depth of the tunnel have great influence on the single-layer tunnel lining with shotcrete and reinforcement ribs, in which the insufficient lining thickness and excessive shallow buried depth of the tunnel can induce the damages of the single-layer tunnel lining due to shotcrete stresses exceeding its strength. This study provides some references of employing the single-layer tunnel lining with shotcrete and reinforcement ribs for supporting large-span tunnel.