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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]

This paper presents a systematical numerical investigation into the lining performance of a tunnel with cavities around surrounding rocks, focusing on the influences of cavity size and multicavity distribution. The study demonstrates that the cavities around surrounding rocks have much influence on tunnel stability and may induce damages in tunnel structures, in which cavity width has a more severe effect on the stress state of tunnel structures than cavity depth. Moreover, the numerical investigation also illustrates that the nonadjacent distribution of multicavities has more serious influence on tunnel structures than that from adjacent distribution of multicavities as well as that from a single cavity. [ABSTRACT FROM AUTHOR]

There were several damaging behaviors observed in a highway tunnel under construction, caused by the large deformation of rock mass. For this reason, a laboratory test to analyse the mineral composition was implemented, which aims to figure out the cause of the large deformation when tunneling in carbonaceous slate stratum. The laboratory test shows the reactivity of clay minerals with water is one of the important reasons lead to large deformation. Especially, field test was adopted to evaluate the structural stability and safety, affected by large deformation resulted from carbonaceous slate stratum. Displacement of primary lining, internal force of steel arch, pressure between primary lining with rock mass, internal force of secondary lining and seepage pressure of tunnel bottom were monitored and presented during tunneling. The results demonstrate that the mechanical response and stress state of the tunnel reflect the influence of the large deformation. For primary lining, large and asymmetrical deformation, which may result in the failure of steel arch, shows high risk in safety. Moreover, according to the calculated criterion of bearing capacity, once the secondary lining starts to bear pressure from rock mass, unsafety and minor safety reservation of the secondary lining were obtained in two regions of this structure. The result in this paper can provide valuable guidance for the subsequent construction and the similar engineering projects located in this area. [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]