Safety evaluation of in-service sulfate corrosion tunnel considering time effect and free surface evaporation effect

The safety evaluation of tunnel linings after a sulfate attack is an important basis for ensuring the safety of tunnel service time. However, the existing tunnel safety evaluation methods are not specific enough regarding the service time, and the corresponding sulfate corrosion indoor test that does not consider the single-sided corrosion factor. Therefore, in order to evaluate the disease characteristics of the tunnel lining after sulfate attack, a lining safety evaluation method has been proposed with considering the time effect and free surface evaporation effect based on the micro-element-layering method. The key parameters of the safety evaluation model were solved through 420 days of indoor corrosion tests and numerical simulations. Moreover, compared with the test results, the variation law of the lining safety coefficient in the position of the arch foot corrosion and arch foot-waist corrosion was further studied. The results show that: the evaporation sulfate corrosion model of the free surface can accurately reveal the strength degradation mechanism of the tunnel lining, in addition to the temporal and spatial evolution law of the sulfate ions. Moreover, the prediction results of effective strength in the process of safety evaluation were in good agreement with the experimental results. In the stage of tunnel lining corrosion, the decrease in the safety factor of the arch foot corrosion and arch foot-waist corrosion section was slow and then fast within the operation time. The service life of the tunnel depends on the corrosion of the most dangerous parts. The increase in the corrosion area will not reduce the service life of the tunnel.