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This paper presents a case study of local repair to damaged concrete lining in an operational tunnel, in which a local repairing countermeasure is proposed and adopted in practical implementation. The countermeasure consisted of grouting cavities with cement slurry and installing a ribbed ring reinforcement in the damaged part of the concrete lining. The field investigation and numerical analysis demonstrate the concrete lining damage is primarily induced by the field-observed construction deficiency of small-size cavities around surrounding rocks. The implemented treatment work demonstrates that the employed countermeasure is capable of local repair of the damaged concrete lining induced by the aforementioned construction deficiency of small-size cavities around surrounding rocks, which can provide the design basis for similar treatment work. [ABSTRACT FROM AUTHOR]

• The damage cause of ground surface and tunnel lining during tunneling is studied. • The tunnel damages during tunneling in silty clay can be reasonably simulated. • The field monitored softening soil body has much influence on tunnel damages. This paper presents a case study of investigating the cause of tunnel damages during tunneling in silty clay, in which the damages are existed in both ground surface and tunnel lining. The study is implemented by field investigation and numerical back analysis to determine the cause of tunnel damages, in which the field observed funnel-shaped surface subsidence of ground and surrounding soil moving to the tunnel are considered as softening soil body from ground surface until surrounding rocks in the numerical model, and the material parameters of the field monitored softening soil body are respectively taken as 0.8 times and 0.6 times of the original ones. This work confirms that the field observed tunnel damages during tunneling in silty clay can be numerically simulated, which is significantly influenced by the field monitored softening soil body from ground surface until surrounding rocks. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The cracks caused by fracture of concrete lining have adverse impacts on the tunnel structure, considering the influences of serviceability and durability. In this paper, a particular case study of a newly built tunnel structure is presented for a certain amount of longitudinal cracks, focusing on the inducement of cracking and effect of concrete fracture. An integrated field investigation is implemented to characterize the spatial distribution of longitudinal cracks and detailed site situations, and the temperature difference of concrete within the lining is as inducement according to a series of reliable experiments. To further understanding of the lining structure performance influenced by fracture behaviors, two groups of numerical models based on finite element software are simulated for reinforced concrete and concrete cross sections, respectively. Among the numerical models, a simplified crack model is applied for damaged lining structure, considering the realistic width and depth of cracks. Ultimately, different safety factors are adopted not only for verifying the stability of cracks but also for getting the differences of structural safety under maintenance work. Situations of crack are in accordance with the real conditions in situ, besides the maintenance work is proved as essential and effective methods in this damaged tunnel. [ABSTRACT FROM AUTHOR]

Abstract A case of damaging behavior in the concrete lining of an operational railway tunnel is studied and presented in this paper. The study focuses on the influence of tunnel structure damaging due to field observed construction deficiency of cavities around surrounding rocks, which is evaluated by means of field observation and numerical analysis. This work demonstrates that the construction deficiency of cavities around surrounding rocks plays an important role in the stability of tunnel structure, which can vary the stress state distribution of tunnel structure even with damaging behavior. Moreover, the implemented numerical analysis also demonstrates that the damaging behavior of tunnel structure induced by the field investigated cavities can be numerically simulated with taking account of the aforementioned cavities in the numerical model, which provides the design basis for appropriately strengthening the damaged tunnel structure. Highlights • A case study of damaging behavior in an operational tunnel structure is presented. • The assumed lightweight elastic material can be adopted for modeling the cavity. • Construction deficiency of cavity has much influence for tunnel structure stability. [ABSTRACT FROM AUTHOR]