Abstract: To investigate the deterioration of metro tunnel lining support structures in harsh environments, freezethaw and salt solution erosion are selected to examine the durability of tunnel lining support structures based on typical climatic conditions and corrosive environments during the service of a metro tunnel in western China. An indoor sulfate freezethaw erosion test is designed considering the autumn and winter temperatures in Lanzhou as well as the ion concentration of sulfate in groundwater. The effect of different amounts of fly ash and basalt fiber on the mass loss rate, dynamic elastic modulus, and compressive strength corrosion resistance coefficient of lining support shotcrete under freezethaw and sulfate is then studied. Finally, the compressive strength attenuation model considering the content of fly ash and basalt fiber is established based on the test results. The findings are as follows: (1) The optimum contents of fly ash and basalt fiber are 20% and 0.1% respectively. (2) The freezethaw cycle causes the concrete mass loss rate to increase first, then decrease, and finally increase; the mass loss rate of lining support shotcrete decreases with an increase in fly ash and basalt fiber content; when the contents of fly ash and basalt fiber reach 30% and 0.15%, respectively, the reducing effect on the concrete mass loss rate is no longer in force. (3) The relative dynamic elastic modulus and compressive strength corrosion resistance coefficient of shotcrete increase with the number of freezethaw cycles, with a small loss at first and then increases rapidly.

Key words: metro tunnel, lining support structure, shotcrete, sulfate attack, freezethaw cycle, durability