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BFstr (Structural) (OP)
22 Jul 09 10:13
Hi Every one,

I have to design a retaining wall which is close to a river bank. It consists of a headwall and two wings with different lenghts which wings are 45 degrees. I attached the sectional cut of head wall and a plan showing the location of wall to river bank.

I have few questions and appreciate any design guidelines. I am green at this.

1- Is this wall considered as a waterfront structure since it might see rivers water pressure or is a regular retaining wall?

2- Should I apply rivers water pressure on wall or just as being shown in drawing since is currently not in direct contact with river there is no need the water be applied to the exposed face of wall?

3- Is it better to design the wall as a gravity retaining wall since is less that 10 ft or you would design it as a cantilever retaining wall?

Has anyone had such a case before, could you please out line some sources or design steps. How do I have to deal with river?

What if the river's water level rises?


I appreciate your suggestions, guidelines and advises.
I lack any help.


Sincerely,
BFstr.     
cvg (Civil/Environmental)
22 Jul 09 12:53
generally headwalls support the ground at the end of a drainage pipe. As such, they will likely see water pressure, often to the top of the headwall or even higher. You may also have rapid drawdown where you may have full saturation of the earth to be retained. The wingwalls, apron slab and cutoff walls should be designed to reinforce and "hold up" the headwall as well as protect against erosion. I have rarely seen these designed as gravity walls. Most designs are per standard drawings. You should check with the local highway department for their standard designs which are proven to work.
dm3415 (Structural)
23 Jul 09 12:04
Be careful with using passive pressure for resiting sliding in your wall, you may lose the soil in front of the headwalls due to erosion.

CVG is right about rapid draw down too, you should have a design case with full height hydrostatic pressure.

You might also check with the full structure submerged (Density of concrete-Density of water) and with a reduced weight for sliding and overturning as well. A FEMA flood map or friendly hydrologist should give a better idea of the statistical probability of flooding at your structure, and you could design accordingly.

Looking at your sketch, a gabion gravity wall may be ideal for this situation, if the labor costs are justified.
BFstr (Structural) (OP)
23 Jul 09 15:58

 Dear dm3415 (Structural,

Thank you so much for your comment and direction.

Could please explain few below questions please:

Q1)
So please correct me, when you said "...you should have a design case with full height hydrostatic pressure. "  did you mean I have to consider a case assuming water pressure (river's water) applying on the face of the wall that is facing river with the prescience of the soil pressure on the other face of the wall at the same time?


Q2) Is above statement full structure submerged check as you mentioned? If not could please explain how I can do the full submerged check.

Q3)

May I ask where I can get a FEMA flood map? It's my first time hearing this. What usually a Structural Eng extracts from a FEMA flood map (what kind of information/data?)


Q4)

I am wondering if the location of my wall if is too close to water? Is any standard or code requirement for the distance of wall to the bank river?

Q5)

What about the footing of wall elevation is it okay? Has to be deeper in ground?

Q6) Is this wall by professional standards called a an Inland flood wall or an Inland flood wall is a different case?


I would be appreciated to hear your comments. Once thank you so much for directions.  
jgailla (Geotechnical)
24 Jul 09 12:55
BFstr,
You can get FEMA flood maps (free) online at:
http://msc.fema.gov/webapp/wcs/stores/servlet/CategoryDisplay?catalogId=10001&storeId=10001&categoryId=12001&langId=-1&userType=G&type=1

The website is difficult to navigate and get the FEMA sheets printed, but all the information is there.
If you're not in the US this will be useless.

The FEMA flood map will tell you the calculated elevation of the water during a 100-year storm(1% probability of exceedance in any given year).  You would then use this high water elevation as cvg and dm3415 have noted.

The maps are generated with typical black magic hydrology, but it is a source you can rely on.

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