Techniques and Performance of Post-Prestressed Tunnel Liner

Abstract

This research examined a new type of tunnel liner–concrete liner postprestressed with double-looped unbonded tendons. The performance of the liner was investigated by full-scale model tests and field instrumentations conducted for the Xiao Langdi sediment tunnel, which is the first water convey tunnel constructed using this method in the world. There are many remarkable advantages of this new type of tunnel liner over liner postprestressed with uncoated tendons, including its more uniform stress distribution due to the significant reduction of friction losses; its lower construction cost through deletion of corrugated metal ducts, reducing 50% of the total number of anchor heads and 30% of the strands required; its shortened construction cycle due to the simplicity of tensioning and boxout backfilling; and its improved structural integrity from reduction of about 50% of boxouts. The subject tunnels have been in use for more than three years to date and indicated that a postprestressed tunel liner is a desirable solution for water conveyance tunnels with a high antiseepage requirement but poor geological conditions. The technique can also be used in other structures, such as cylindrical concrete tanks and hydroelectrical power tunnels.