Concrete Riverbank Protection 5

[dik]

We are considering a concrete slab to reinforce a riverbank. It will be approximately 2’ to 3’ thick and reinforced accordingly. It will be cast on a sloping bank that is approximately 1v:1.75h slope. Reinforcing will either be HDG or stainless steel and the slabs will be cast in sections to accommodate the slope. We are looking at uplift forces that have been estimated at 1.5m of water (head approx 5’).

Issues are draining the underside of the slab, determining if the slab should be vented, scouring at the toe of the slope, and precedence.

Is anyone aware of this type of construction to reinforce a riverbank and where it has been used successfully?

Dik

 

[SMIAH]

To secure it against undermining is indeed a major issue.
I think the best permanent method to do so is when the slope is excavated and revetted down to an inerodible material or below expected scour levels. It may be impractical or uneconomical depending on the depth of this material.

A sheetpile cutoff wall could be used or rock-filled toe trench.

It would depend on the material forming the channel bed.

I guess this kind of protection is good as rigid material is more resistant than any other type to attack by debris (and ice, if there is).

 

[dik]

SMIAH:
Riverbed and banks are highly plastic clay for a depth of approx 40'. Sheetpiling would be an easy option as would a stone toe trench. Flow velocity is 5 or 6 ft per second.

Do you know of any concrete bank reinforcement that has been existing for any length of time?

Dik

 

[Ryb01]

I would think that unless absolutely required, sheet piling and or concrete would be difficult to get approval.

What about trying a boulder revetment? Large keystones to reinforce the bottom of the slope and transition to small stones as you move up the bank. This type of reinforcement is not a static type of reinforcement and has room to give wheile still providing habitat to fisheries.

Before moving too far forward I would have a discussion with either FEMA or the Corps...pending jurisdiction.

Hope this helps.

 

[gbam]

Are you set on the use of concrete? Also your proposed slab thickness is really thick. How high will the bank be?

Your velocities you mention are not that significant. What are your scour depths?

Other good sources of bank protection include Rock Riprap, gabions and articulated concrete bocks. These would not require any type of under drain.

 

[SMIAH]

Very true.

There could be other options. As grouted rip rap or gabions combined with bioengineering revetment (e.g. woody vegetation as a component of bank protection).

As Ryb01 pointed out, concrete slab in streams is not anymore accepted here for environmental concerns. Didn't think about this issue!

 

[beej67]

Bioengineered revetment will work better than concrete anyway.

I worked on a project about 15 years ago that had these concrete precast things that looked like jacks, from the bounce-a-ball-pick-up-the-jacks kids game. They were precast, and then set into bank slopes in an interlocking fashion such that they locked with each other, but had gaps to allow vegetation to take hold, and the points of the jacks reduced boundary layer flow velocities to prevent erosion.

Here's a ConTech link to a similar product:

http://www.contech-cpi.com/ess/products/contech_hard_armor/armortec_family/a_jacks/219

..although I think they're produced by several different manufacturers, and in different sizes. I believe design criteria can be obtained from the manufacturer. Do a google image search for 'concrete jacks' and you should get some hits worth following.

I'd look that way first, because they bypass most of the major issues you're concerned with, such as reinforcement, uplift, etc. You didn't even mention constructability, but dear god I can't imagine it'd be easy/cheap to form cast in place slabs on a fluctuating river.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[beej67]

Here's a photo in a shoreline stabilization application:

http://upload.wikimedia.org/wikipedia/commons/b/b7/Concrete_jacks.jpg

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[dik]

We've looked into using graded granitic riprap (1100mm size going to 900mm in places with smaller stones); my preference would be to use limestone. This is common and better reflects the area. There are durability issues.

The client is leaning towards a concrete slab. It will require a terraced slab to accommodate the bank slope 1:1.75 (v:h). The application is critical and longevity is great. Safety factors are considerably greater than normally required, hence the thicker concrete slab. There is also a requirement of 'proven' useage and we were looking for applications where a concrete slab is used. Can anyone provide any examples where a concrete slab has been successfully used? As noted, prior useage is a key requirement.

We will revisit the revetment use. Similar to large riprap.

Your response is greatly appreciated.

 

[cvg]

If you aren't already, you should have a hydrologist on your team. some of what you have posted seems like you are not getting advice from an expert in channel design. 2 - 3 feet thick is very thick for a concrete bank lining, even with seepage uplift. concrete bank lining has been done before but the real key to any bank lining is constructing an adequate toe down to prevent undermining. Soil cement (if you can get good aggregate from the river) or RCC (if you import the aggregate) has been used successfully for bank lining. 1100 mm riprap sounds very large for 5 - 6 feet/second. However, I don't recommend riprap on such a steep slope. Stainless steel reinforcement seems excessive to me. Check out the corps of engineers, they have a good design manual which in available online.

 

[francesca]

"Concrete Jacks" were developed by the South African Council for Scientific Research (CSIR) and we call them doloses, after oxtail bones.

http://en.wikipedia.org/wiki/Dolos

 

[dik]

I've only heard of the 'jacks' being used for shoreline stabilisation, and not for channel flow. Can they be used for both?

cvg:
the slab is a small area, several hundred metres on either side of the river where there is some turbulence and currents caused by an abutment and hydraulic structure. We have hydrologists as well as geotechnical people involved.

 

[SMIAH]

You say that Riverbed and banks are highly plastic clay. Could you solve the problem by flatten the slope to something more suitable for this kind of material (e.g. 3:1)?

Like cvg mentionned, 1100 mm riprap sounds very large for 5 - 6 feet/seconds. Without any ice concern (?)

 

[dik]

CVG:


SMIAH:
It's not possible to modify the slope and the river typically has 2' of ice in the winter and large ice chunks and ice dams in spring. My experience with the clays is that a slope of 2-1/2 or 3 is most stable.

The river also sometimes carries large trees as part of the load.

I have reviewed calculations by others (not officially, but included as part of the project data; prior to receiving them, I didn't know you could calculate riprap sizes. They use the Isbash approach and SEBJ guidelines) for the size of the riprap, the numbers are correct for the loading assumed based in the calculations. I understand that smaller 2' to 3' riprap has been moved by the flow conditions.

Dik

 

[SMIAH]

5-6 fps results in rip rap of D50 = 110 mm with Isbach.

Maybe the 1100 mm rip rap D50 is based on the ice thickness (e.g. 2x thickness of 4').

It has to be placed "by hand" on such a slope (i think).

 

[dik]

by crane... guys in this area aren't that strong <G>

Dik

 

[SMIAH]

Meant to say:

Riprap stones should be hand-placed or very carefully dumped so that smaller stones fill the voids between larger ones.

Thats usually for slopes steeper than 1.5:1.

I guess that you already know this anyway.

 

[beej67]

Francesca -

Thanks! Didn't know that.


Dik -

If you're still looking for a concrete river bank design example, there's always the Los Angeles River.

http://en.wikipedia.org/wiki/Los_Angeles_River

(recall the car race from Greece, the chase scene from Terminator 2, etc)

I don't know what sort of pavement section they had, nor what soils they had, but I'm sure you could call California DOT and ask.



Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[dik]

beej67:
Thanks, is the waterway completely concrete lined or just the bank area?

Dik

 

[beej67]

Most if it is completely concrete. Some stretches have an earth bottom, and vegetation has grown up in those over time. I've never been to LA for an extended period of time and do most of my engineering in the Gulf Coast states, so I don't really know much about it. Google could probably tell you quite a bit.

As others have mentioned, you can't do this sort of thing anymore in the States because it's very harmful to the environment. Not sure where your project is, but the sorts of federal approvals you'll need if you're in the US can be quite difficult to obtain.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com