retaining walls 1

[nza]

I am looking at putting in a retaining wall in a cut section. There are gas and telephone utility lines behind the proposed wall location at about 6' off at one point. My walls are only 6' high and have a length of about 950'. I have determined either soldier piles and lagging or soil nailing should be used. Any comments on which is more economical, practical, better to use in this situation? The soil is silty fine to medium sand with trace to little gravel from about 25' and under that is lean clay. Bedrock is at about 37' below ground. There are boulders in some locations at 12' below existing ground. For both options, what is a preliminary guess at the pile length/soil nail embedment? any suggestions would be appreciated. thank you

 

[DaveVikingPE]

What kind of surcharge loads will be imposed on the retaining wall? Maybe you can use cantilevered sheet piling and save yourself a few headaches.

 

[ishvaaag]

I have made a run of muropant (for sheet pile without tie aback) for 34 deg -maximum some codes allow- and a procedure by Teng gives for no load at the horizontal surface a required embedment of 1.36 m, for a total length of 3.16 m. This must be the strict embedment and it is usual to take 1.20 times that embedment or 1.63 m. Also, no account of water presence effect on pressure has been made so ensuring very good drainage would be fundamental.

There are other freely downloadable sheets in the Mathcad Collaboratory for walls and for tied-aback sheet-pile, water effects included.

 

[duke12]

THANK YOU FOR THE SUGGESTIONS. Sheet piling is now being loked at as well.
What is the "Mathcad Collaboratory" that was mentioned? Is it available thru this site?

 

[ishvaaag]

It is a site for Mathcad users, with which you can make books with alive formulas and more. Better than Excel for what I use such things.

http://collab.mathsoft.com/~mathcad2000

open civil engineering folder and you have there engineering procedures for free download...yey you will need a Mathcad program or runtime, both sold to use.

I name it when some of the procedures I posted there may be helpful to someone looking for something here.

My sheets require (most) Mathcad 2000 Pro or later.

 

[ERWS]

Your most economical wall at 6' would be a gravity syatem.
It would have a 3 to 4' footprint and would cost far less than sheet pile or soil nailing. Look at Gabions or Modular Block MSE systems.

 

[emmgjld]

The use of a gravity wall, either a reinforced concrete or a MSE (the modular block of ERWS) would be my choice. Either has pros and cons, assuming the surcharge loads ar not too large. I am trying to figure out why sheeting or a soldier piled wall is required, unless the soil bearing capacity is very low.

The reinforced concrete wall is very straight forward to design and build. The disadvantages include; potential of unsightly cracking and deflection/distortion which is usually more visual than affecting the longterm performance.

The MSE options is actually many options, which can be adjusted to the actual circumstances. MSE walls can withstand a lot of movement while still functioning.

 

[duke12]

From what I understand, MSE walls and reinforced concrete walls are being omitted because it will require a lot of excavation. On this particular site, there is no room for that as utilities are in the way. We would like to avoid relocation of utilities if possible. The height of the wall is a max of 6', however the effective height is about 15' due to the soil sloping up behind the wall. The sheet piling was ruled out because of the boulder found at 12' under at one point. We are not sure how large the boulder is and how many we might encounter when driving sheets.(with hp piles can put a tip on & go thru the boulder) The soil is considered to have low bearing capacity. And a sheet pile embedded only 12' will not be able to withstand the lateral loading. I guess the question was not well enough detailed. Thank you for the very helpful suggestions. (formerly known as nza)

 

[Jim6758]

While some MSE walls may require some excavation, modular block walls do not. Modular block can be used with a geogrid of relatively short length. As another responder pointed out, they can withstand a good deal of movement and still look good.

 

[Hogrider]

This is a question for ishvaaag's (Structural) reply posted Jan 31, 2002.

I am not familiar with sheet pile design but I have a question regarding your comment and
statement regarding "34 deg -maximum some codes allow". Is this based on the soil type stated in the initial question?
Who's codes apply?

Background - I am a Civil Engineer with the Federal Government and am working on a sheet pile design that
will act as a cutoff wall and retaining wall. My project will be in the river so I have alluvium material (pit-run) for the embedment of the piles. FOr this type of material, I am assuming a 37 degree internal friction. If there is a code out there that I need to be aware of? Your reply would be greatly appreciated.

Thank you

 

[ishvaaag]

From somewhere I have taken it... may be some bridge general or particular specifications of here. In any case, the "prequalified" values in the standing NBE AE-88 spanish code for loads are

Angle of inner friction for...

natural soils

compact sand gravel 30 deg
soft sand gravel 30 deg
clay 20 deg

back-fills

"vegetal" earth 25 deg
cohesionless 30 deg
crushed rock 40 deg

sexagesimal.

I don't think so to take 37 deg for something that has such angle of inner friction may be in definitive criticable if the applicable code or specification does not forbids so.

In any case, I think that precisely is the fear of submerged or saturated soils lubricating the ground what may be exacting any of the conservative evaluations of the angle of inner friction.

Now I list for you the angles of inner friction listed for the submerged parts in figures of the book on sheet piles

Cálculo Práctico de Pantallas de Tablestacas
ARBED-BELVAL
Columetal-Luxembourg
G. Colling
Madrid 1971

first a table

Sand and gravel 30 to 40 deg
Clayey Sand 25 to 35 deg
Clay 10 to 25 deg

now the angles of inner friction in embedded part in figures, deg

30, 30, 30, 30, 30, 30, 30

it is clearly a normalization but also an opinion on what one that works in the field thinks has to pass to pupils.

Also look table 5.5.5.B in AASHTO, gives delta friction at interface...that even if being less than the angle of inner friction out of natural behaviour, sometimes is allowed to go as high as the angle of inner friction itself: the highest delta listed is 35 deg and most are around 20...also suggesting angles of inner friction of around 30 typically for poorly characterized soils.

So my advice is only going high in angle on inner friction and the interface if the values standing at the worse likely situation (for some sites, the soil being submerged) are well characterized by test.

Yet if in the code you use you don't see anything contrary it is logical to assume to use the warranted value is allowed.

 

[Hogrider]

Thanks for your response. I'll research the internal friction angle more. My case will be submerged soil.

Share with me what you know about ice loadings on sheet pile and retaining walls. My site is near a roller dam where ice can form behind the dam. The only thing I found so far is a study from the 1940's for expansion of ice of varying thicknesses. Is there anything else out there?

 

[ishvaaag]

Bridge Substructure and Foundation Design
petros P. Xanthakos
Prentice Hall

has something on the ice loads, you can see what by looking the index for ice.

Particularly for the static loads on piers (such the ice forcing its separation) it says 4 to 5 kips per linear foot are expected be conservative since measured in lakes. Finnish seem go content on 5 kips/ ft.