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BFstr (Structural) (OP)
22 Jul 09 21:58
BFstr (Structural)      
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 22:01
BFstr (Structural) (OP)
22 Jul 09 22:25

Dear cvg (Civil/Environme)
Thanks for your reply but still I am unclue if I need to apply the water pressure on the face of wall that facing the river. Also is it a flood wall or is considered a regular retaining wall? Should I include the flood level of river on wall?
I don't know where I get the information of state? do you have any link. Project is in OH.

Thanks.
msquared48 (Structural)
22 Jul 09 22:56
What is the 100 year flood elevation?  

What measures are you going to employ to prevent scouring at the toe of the wall which could lead to a rotational failure?  You might want to place the bottom of the footing deeper down depending on the stream velocity at flood stage.

I would look at the dry condition, and the maximum flood condition, designing the wall to be stable under both circumstances.

Another thought... Any chance, being in Ohio, of the outfall icing up in the winter, causing a back pressure and hydraulic head lateral thrust to the wall from the pipe itself (if the pipe is cast into the wall).  If the connection is a slip connection or freeezing is not an issue, please ignore the comment.

Mike McCann
MMC Engineering

BlastResistant (Structural)
23 Jul 09 2:52
You need a civil engineer to provide a hydrologic analysis to determine the 100 yr flood elevation and corresponding flows. Then you will know if the water is in contact in the wall during a "worst case scenario." The hydrologic analysis will also provide stream flow velocities which you can convert into forces acting on the wingwalls. Then you need to have a civil engineer take that hydrologic analysis and use the data to do a hydraulic analysis using computer software such as HEC-RAS. The results of the hydraulic analysis will determine the streambed section along the length of the retaining wall after taking into account scour analyses so you can properly determine the design depth of your footing to ensure it does not fail due to scour. Then you just design it like a regular retaining wall. If the water level rises above the stream bed and contacts the actual wall, it will be resisted by the soil pressure from behind the wall (under static loading conditions). Under a 100 yr stream flow velocity, you will have to determine if the upstream water pressure on the wingwall is greater than the resisting soil pressure behind the wall and design your footings appropriately. Maybe the water doesn't even rise high enough to contact the wall! You won't know unless you get a hydrologic analysis.

Good luck.
aayjaber (Structural)
23 Jul 09 3:55
Why a 100 years? Is a 100 years long enough to be assured that the wall went wash off in a big specially with a foundation higher that the water level?
4321g (Structural)
23 Jul 09 4:25
Hi

i would like to comment as follows:

1. first carry out geotechnical investigation to establish the soil profile and seepage pattern.
2. Conservatively,apply hydrstatic pressure on the wall facing the river side and provide drainage pass under the wall to avoid piping effect.
3. For economic reason is better to used cantilever wall unless noted othewise.

Bye
rowingengineer (Structural)
23 Jul 09 5:02
aayjaber,
Flood events are defined by the probability that a certain amount of water is possible any one year. For example, the infamous "100-year flood" is in fact the level of water with a 1-percent chance (1 in 100) occurring any one year. The amount of water actually varies from river to river. In fact, that amount can vary along a river. The use of "n year flood" is technical jargon that has caused endless problems with the public. The term does not mean that a flood occurs every n years, but that it has a chance of 1/n of occurring any one year. Water volume increases as the probability decreases. The table below shows how this might affect you:

Flood Probabilities for any one year  
"Year" Probability Percent Flows
500 0.002 00.2% Extreme
100 0.010 01.0% Heavy to extreme
50 0.020 02.0% Moderate
25 0.040 04.0% Light to moderate
10 0.100 10.0% Light
5 0.200 20.0% Mild

 

When in doubt, just take the next small step.
 

BFstr (Structural) (OP)
23 Jul 09 16:15
Dear 4321g (Structural),

Hello,
Thank you so much for your comment. I just wanted to ask in your second comment " 2. Conservatively,apply hydrstatic pressure on the wall facing the river side and provide drainage pass under the wall to avoid piping effect. "

Do I apply the hydrostatic pressure on the river side of wall at the same time that I am applying the soil pressure on the opposite face of wall or the hydrostatic pressure has to be applied on wall without application of the soil pressure on the other side?

Second, could you please what should I ask (what information)from soil companies to include in their geotech report? They ask me what information I need from them, could you list the items that I need from the soilreport for structural design of this wall, please?

Once again thank you so very much.
Regards,
BFstr.

 
csd72 (Structural)
24 Jul 09 3:22
Being this close to the river will effect allowable bearing capacities - check with the geotech.
civilperson (Structural)
24 Jul 09 7:14
Soil pressure and water pressure on the face oppose each other but the soil may be saturated and then the water pressures are opposite and close to equal.
4321g (Structural)
28 Jul 09 11:51
Hi,

Sorry for the delay, i was carried way with something.
Below are the explanation for you questions:

. The information required includes borehole log, which will give you the sequence of the soil types,friction angle,unit weight and water level beneath the groung surface.
. based on the soil type beneath the wall footing, evaluate the seepage pattern and its effect and provide drainage if required.
. Based on wall elevation it shows that the bank side consist of natural grade and backfill- so the loading consist of passive earth pressure, hydrostatic pressure relative to the water level and surcharge load.
And on river side- the load consist of active pressure which is at half the wall height and hydrostatic pressure over full wall height.

You can then design against all possible failure pattent and stength.

Note: if you don't know how to determine the seepage, ask the geotechnical engineer for that.

Bye  

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