Concrete Water Channel Design

[Kowycz]

I am currently trying to design a concrete water channel for a headworks building. I was just wondering what the best approach for this situation was. Initially I thought designing the channel much like that of a retaining wall would be the best approach. However I came across the PCA's publication on Rectangular Concrete Tanks and thought it might prove useful as well. However since it isn't a tank but by theoretical purposes an infinitely long retaining wall loaded on both sides I feel like my first approach was correct.

The fluid is wastewater and the channel wall is fairly short and narrow.

Width = 5'-0"
Height = 7'-0"
Desired Conc. Thickness = 8"

 

[theonlynamenottaken]

I agree with your retaining wall approach. Watchout for bouyancy issues - depending on the groundwater, likelihood of flooding and the permanency of water within the channel.

 

[JedClampett]

Design it as a cantilever retaining wall. Design for the soil case seperately, then the liquid case. I'd strongly suggest a 12 inch wall. It will be too hard to waterstop the joints for 8 inches thick . Make the base slab thicker (~2") than the walls to account for the addtional cover requirements for the bottom bars, if the slab is poured on grade.
Check the corners using the PCA tables for the maximum aspect ratios available. Add corner bars if necessary. We usually end up doubling them up. For long distances between movement joints, make sure horizontal steel ratio is at least .0052.

 

[theonlynamenottaken]

On crunching some basic numbers after that last post I see that using your provided dimensions the bouyancy and the dead load are almost equal (assuming empty channel). Perhaps that won't be an issue...

 

[Ltwine]

Structural design of open channel is not as challenge as getting information on hydraulic parameters. Talk & listen to the project hydraulist, if there is one.

Watch out for uplift, freeze & thaw, if there is such potential.

 

[JedClampett]

Ltwine, I would skip that step and design for water to the top of wall. In the lifetime of a headworks, it's almost a certainty that the screens will get fouled and water will back up until it overflows the walls. It's not pretty (or pretty smelling), but it happens.

 

[Ltwine]

I am thinking about turbulent flow, potentiall wear/tear, chemicals... As I have mentioned, structural design is simple, but not quite as simple to get full info for the material it carries.

 

[Ltwine]

Also, if there is chance to backup, the free board need to be increased. A new (first time) designer need to get as much info as he can as he has no past experience to back him up.

 

[cvg]

try the following design manual

Publication Number: EM 1110-2-2007
Title: Engineering and Design -Structural Design of Concrete Lined Flood Control Channels

http://140.194.76.129/publications/eng-manuals/em1110-2-2007/toc.htm

 

[Kowycz]

Thank you for the help and input everyone, it is greatly appreciated.

It appears for this particular application that the channel empty governed in the overall design.