Abstract: Compared with the concrete liner pre-stressed with circumferential bonded tendons, the
tunnel liner pre-stressed with circumferential un-bonded tendons has many outstanding advantages, but
the reliability restrict its general application. Stress state variation of tendon is one of the important
parameters to evaluate the reliability of this type of liner structure. Based on the long-term monitoring
data of tendon dynamometers in Xiao Langdi pre-stressed sediment tunnels, the influences of ambient
temperature and water head on the tendon stress were analyzed. The results show that the variation of
temperature has a significant effect to the tendon stress, while the variation of water head has a little
impact. Xiao Langdi pre-stressed sediment tunnels has been safely served for more than 10 years and
experienced the highest design water head, the prestress in the tendons is stable at all times, no fracture
or relaxation of un-bonded steel strands was observed. The experience of Xiao Langdi sediment tunnels
shows that the anchorage of un-bonded tendons is reliable and a safe operation can be realized for the
tunnel concrete liner pre-stressed with circumferential un-bonded tendons.