Discussion: Optimal design of curved bed trapezoidal canal sections

Abstract

Contribution by A. Laycock, Adrian Laycock LtdInvestigating the theoretical least-cost cross-sectional profile is a favourite academic exercise that has been explored in numerous papers. However, the practical implications of constructing curved section canals are less well documented but far more relevant. In practice the cost is rarely dependent on the theoretical minimum section, and the choice of geometry will depend on various factors, some of which are listed below. lining, which should not create discontinuity-induced internal stress. (e) Ease of placing other lining material, such as less permeable compacted soil or artificial membranes. ( f ) Whether maintenance equipment will be required to operate on the canal bed. (g) The type of sediment expected to be deposited or required to be transported. Curved bed canals are not efficient at transporting coarse sediment, although deposited material will collect in the centre of the channel making it easier to remove during maintenance. (h) Strength of rigid lining. A curved shell is inherently stronger than a section with planar sides and base. A very common cause of failure in trapezoidal lining is cracking at the base of the side slopes where a geometric discontinuity leads to intense stresses from soil pressure, soil movement or external loads. (i) Placing concrete on a long constant slope in a trapezoidal section can be problematic as tension cracks develop owing to slippage of the wet concrete. This is not a problem in large parabolic sections, in which the slope is gradually reducing with depth below the bank top.

Editorial

“…I am pleased that this issue contains a discussion by Laycock of a paper by Chahar and Basu on the optimal design of curved bed trapezoidal canal sections (Chahar and Basu, 2010). The journal welcomes discussions on papers as this is an excellent way of airing issues and exploring different aspects of a topic.…”