Early detection of crack is critical for the maintenance of reinforced concrete (RC) structures. In this study, a distributed optical fiber (DOF) sensing system with Rayleigh Optical Frequency Domain Reflectometry (OFDR) technique was deployed to a member of RC structure in a full‐scale laboratory experiment, which was subjected to a monotonic lateral load. With the aid of a high space resolution (up to 1 mm) and measurement accuracy (±1 micro strain) interrogator (OSI‐S by Semicon), continuous strain measurements inside of the RC member are elaborately implemented. The result of crack detection by the analysis of the measured tensile strain profiles is in excellent agreement with the visually observable cracks mapped during the test. This confirms the ability of the optical fiber inside of RC members to capture cracks on concrete surface. Moreover, the recognition of crack orientation and depth is accomplished by comparing strain measurements of optical fibers installed at multiple locations.

This study investigates the influence of subsequent tunnel boring machine (TBM)-driven processes on the responses of the first tunnel in twin-tunnel construction using the ultra-rapid underground pass (URUP) method. A comprehensive finite element analysis (FEA) is performed to simulate the URUP TBM tunneling, considering the non-uniform convergence caused by the TBM geometry, the tunnel face supporting pressure, and the tail-grouting pressure. The FEA model is validated by the monitoring results of the bending element of the first tunnel lining. The FEA results reveal that the grouting pressure of the second tunnel has significant influence on lining deformation of the first tunnel, while the face supporting pressure shows little effect. The relationship between the grouting pressure and the maximum bending moment of adjacent first tunnel can be fitted by linear function. A grouting pressure equals to the lateral earth pressure is able the reduce the variation of the bending element of the first tunnel during the TBM-driven process of the second tunnel. The bending element of the first tunnel shows a typical lognormal relationship with the face supporting pressure during the TBM advance of the second tunnel. A critical cover-to-depth ratio, under which the horizontal and vertical soil arching effect vanishes, can be deduced to be within the range of 0.55–0.60.

The transverse effective rigidity ratio is a key parameter when the uniform rigidity ring model is adopted to design or numerically analyse segmental lining structures commonly used on a shield‐driven tunnel. Traditionally, the transverse effective rigidity ratio η is treated as a constant, which can be evaluated through theoretical analysis and model tests. In this study, scale models were designed and tested to investigate the variation of the transverse effective rigidity ratio in the segmental linings’ flattening deformation process. The test results suggested that in the elastic stage, the transverse effective rigidity ratio fluctuated between 0.667 and 0.734 for the stagger‐jointed rings and fluctuated between 0.503 and 0.642 for the straight‐jointed rings. When segmental linings were squashed and started to crack at the circumferential joints, the transverse effective rigidity ratio decreases sharply. Then, a regression equation was obtained to fit the variation trend of η with the increase of horizontal convergence to the outer‐diameter ratio (ΔD/D_out). Finally, in a case study, the regression equation was adapted to determine the value of η of an operated shield tunnel which was once surcharged accidentally and deformed severely so as to numerically predict the prospective deformation induced by the upcoming adjacent excavation. Numerical results indicated that as the value of η decreases, the horizontal convergences of shield tunnel induced by adjacent excavation increase significantly and even more than doubled in the case study. Comparatively, through taking account of the operating tunnels’ exiting transverse deformation, the predicted deformation tends to be unfavourable.

This paper presents a method for dynamic risk assessment of operating power tunnel, on the basis of the generic procedure of risk assessment, the tunnel structural real-time monitoring system in a separate paper, and the corresponding evaluation criterion. In the proposed method, the common risk hazards during the operational period of power tunnel are firstly cataloged as three special subjects, and all the risk factors are given a risk level by two consecutive risk assessment methods and formed a basic list of risk factors. Local adjustment for the risk resources in this form will be done when the internal and external operating environment of power tunnel changes. Meanwhile, a risk assessment method, which combines the real-time monitoring data for power tunnel, periodic reports from patrol staff, and the risk evaluation criterion, are used to determine the risk level of corresponding risk factors, for some risk hazards. A cable tunnel in Shanghai Power Grid is studied as a case of this method, and the result demonstrates that it can provide some operable basis for the safety control of power cable tunnel.

Working shafts or manholes, usually made of concrete or reinforced concrete, are essential parts of the underground electrical power transmission system. However, the working shaft frequently encountered differential settlement, tilt and other damage like cracking when construction activity was carried out near the high-voltage electricity cables. This paper reported a severe damaged working shaft in South China including its settlement and cracks. Numerical simulation was also performed to reveal the evolution of structural damage with an increased differential settlement. The results show a good agreement with field observation in respect to the initiation of concrete tension damage. It is proposed that if a differential settlement higher than 5mm is observed, preventative measures are needed and the risk is conditional acceptable.