To avoid the damage of surrounding rock

pre-stressed anchor cables are installed in high side-wall and cavern intersection area to control the large deformation of surrounding rock. However

research is seldom performed on estimating the pre-load of cables in underground powerhouse with high geo-stress and low strength-stress ratio in the previous literature. Jinping-I hydro-power station is recognised as a typical high geo-stress underground powerhouse. Its cavern exhibits remarkable time-dependent deformation during excavation

which may result in the continuous increase of the inner force of the anchor cable and bars

even the strength failure. To determine an appropriate pre-load

a procedure is proposed for calculating the time-dependent released load of surrounding rock

based on their deformation characteristics. At the same time

a formula is deduced to calculate the pre-load factor of pre-stressed anchor cable. This established formula considers the influences of geo-stress

anchorage force and installation time on the pre-load factor. Comparing the actual values with the theoretical values of pre-load factor of Jinping-I underground powerhouse

the result indicates that the established calculation formula for the pre-load factor is reasonable and can be referenced in practical underground engineering.