n Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese - Hydraulic resistance of segmentally lined water tunnels with regular patterned indentations - a hydraulic model investigation : technical paper

Volume 40, Issue 2
  • ISSN : 1021-2019



Experiments were carried out to determine the effect on the hydraulic resistance and hence delivery capacity of segmentally lined water tunnels if the regularly patterned indentations were left unfilled. Two separate investigations were conducted that utilized the same basic flow-circuit facility. One study utilized a 1:15 small-scale model of a reach of lined tunnel, making hydraulic head-loss measurements along its length. The head-loss over a length of smooth interior was compared with theat ove an equal length of indentated interior. The other study employed full-size models of actual indentations, which were arranged free to move against restraining forces, which were measured. These models were located in indentations in the false floor of a flume. The unit forces, when integrated over a length of tunnel, directly yielded hydraulic resistance. Data obtained with unfilled and filled indentations were compared. The results indicated that the hydraulic losses were slightly yet significantly larger for tunnels with unfilled indentations than for those without or with filled-in indentations. The small-scale model tunnel tests showed a measurable increase in head loss in the case of the indentated interior above that for the smooth interior, hence a slight reduction in discharge capacity owing to the indentation not being filled. The full-scale model flume tests indicated on average an expedited increase in overall head-loss in a tunnel of some eight per cent, hence an estimated reduction in discharge capacity of about four per cent owing to the indentations not being filled.

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