Improved Design Method for Pre-stressed Water Tunnels

The final design of the pumped-storage project Feldsee features a complex lining and pre-stress grouting concept, rendering the method presented by Seeber insufficient for an accurate determination of the system behaviour in all stages of construction and operation. A calculation procedure based on the matrix stiffness method has been implemented, allowing incorporation of multistage pre-stressing injections at different locations of a lining being composed of several layers with different mechanical properties. Based on the design obtained by applying the above method, another question of maximum allowable non-symmetric displacement of the pre-cast concrete segment arose. A parametric study has been used to determine the boundaries of asymmetric displacements throughout the pre-stressing procedure, allowing establishment of threshold values for the monitoring conducted during the pre-stressing injections.