Retaining wall design

[newengland]

I'm currently trying to design a retaining wall/retaining wall system the total height of the drop I'm looking at is 15'. The back side is to be backfilled and the front side will be mostly exposed. The front side of the retaining wall will be exposed to a pond, though normally just above water height. the soil is sand, don't ask me the properties has this is just a preliminary design. the idea is either 1 tall retaining wall or 2 retaining walls with the lower one being 10' and the upper one being 5' (exposed). The owner demanding the lowest possible cost. With that being said heavy equipment cannot make it to the site, and concrete if trucked in will have to be wheel barreled to the site since low cover prevents a boom pump from being used. What is everyone’s suggestion on material, and approximate cost the wall will be about, 25' long. I was thinking about using CMU's with a poured footing using 1 wall.

 

[jdonville]

"...The owner demanding the lowest possible cost. With that being said heavy equipment cannot make it to the site..."

Why can't equipment be mobilized to the site?

Building the wall by hand (manual labor) will not likely be cost-competitive, either...

More information would help us help you.

Jeff




Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

The views or opinions expressed by me are my own and do not necessarily reflect the views or opinions of my employer.

 

[newengland]

the only real acesses to the site is an pathway about 2'wide, and overhead clearance above the house being about 2. the only othe way to get to the location is the pond. thw owner is p;aning on doing much of the manual labor between himself and his family ,since most have done or are in the construction business

 

[SlideRuleEra]

newengland - If you want to get an idea of what can be constructed from wood, by hand, take a look at the Australian document "Timber Retaining Walls for Residential Applications" at this link

http://www.hyne.com.au/downloads/dih_downloads/timberTDS/09_retaining_walls.pdf

Note that these plans limit height to just over 7.5 feet (2.4 meters), so two walls of this height would be required. Also they would need significant horizontal separation since the posts cannot be installed very deep.

With a pond at the site and sandy soil, it may be possible to install the posts by jetting with a centrifugal pump (I have done this, personally - years ago).

I'm not suggesting that you follow these plans, perhaps going over them with the Owner may give him some idea of just how much work (manual labor) this would be.

http://www.SlideRuleEra.net

 

[TDAA]

Depending on the distance and availability, concrete conveyors may be an easy way to get mud in.

 

[GabionGuy]

Have you considered gabions? These structures have been built by homeowners in North America for over 50 years.

Many a Cottager has memories of the summer that the Family built the retaining wall.

 

[newengland]

I think that the Gabion wall is best suited for the situation. Now I have a few basic questions.
1) if I want to terrace this how far apart do the walls have to be

2) is there anyway to reduce the size of the base, it looks like for a 15' wall i need a 9' width, and a 10' high wall will require a 7.5' base

 

[blueoak]

A timber crib wall may be attractive too. Caltrans has some standard drawings. The timber spec'd is a little big since it is for road conditions and needs to last with little maintenance. I am going to put in a timber crib to plant a garden (low water use). So it better be easy for me and 3 kids to do.

 

[newengland]

Timber is out of the question in this case, since they used a timber pole design to retain the stairs and after about 10 years they're rotting away.

 

[blueoak]

I have used wood (redwood or treated) in areas with a lot of wet/dry cycles that have done well. My assumption is a good drain layer between wood and the soil works well. That's a good reason to go with gabions though. I have been thinking of using concrete for the bottom level.

 

[ItsOnlyDirt]

Sounds like a classic gabion solution to me, just be sure about the global stability, especially if its near a stream/river alluvium can be a tricky material, failing that a proprietry reinforced soil with stone facing might work. Try this link its UK based but theres some useful stuff on it.

http://www.maccaferri.co.uk/

failng that I've got a Maccaferri Literature CD I could email the contents of to you if your desperate.

Cheers

 

[newengland]

I agree that a Gabion is the most realistic way to go. This is going to help not only retaning the hill that is currently on the site but also help stop the erosion from the pond. I was planing on using a flush front and a stepped back, hoping that this would reduce the size of wall needed. since the lateral distance from the front of the wall to that back of the wall can be no more the 10' the smaller the base the better, since 10' would me taking out must of the hill to place the base down

 

[ItsOnlyDirt]

How about making the base 2 gabions deep (they are usually 1m square) to reduce the volume of excavation required and tilting the gabions backwards slightly to improve sliding resistance.

 

[newengland]

so your saying make the base 2m deep ground penatration correct? I was thinking 1m ground penateration do to the water table. though 2m might be possable with pumping out the water

 

[dik]

Segmental precast, anyone... like Pisa Stone or Allan Block?

Dik

 

[blueoak]

I spoke with a friend who put in a >15' wall with an MSE backing and used a pisa stone like stuff for the facing. It was pricey, but like this job they could only get a bobcat to the site (took awhile). Without cranes and at a remote forest site they couldn't use a cheaper facing.

 

[ItsOnlyDirt]

No not 2m deep 2m thick, upto say 3m then step it back and have 1m thick for the remaining 2m. 1m penetration should be ok. Post and panel might be a good option too though. Gabions are useful though as they are free draining so you dont have to worry about presures building up at the back

 

[newengland]

just to throw out another Idea what does everyone thing of using CMU's. my conceren is that they'll crack with the freezing and thawing being on the water, any idea's?

 

[GabionGuy]

newengland

All of the technical issues you have with the gabion wall can be readily addressed by contacting Maccaferri directly.

Design assistance and site visits are provided, typically free of charge. The more detailed the information about the site, the more accurate the design. If you have specific site restrictions, they can be addressed.

Your concerns about the frost are also addressed with the gabions. Unlike most other materials used for retaining wall construction, the gabions are naturally flexible, so as the ground moves, so moves the structure.

 

[oldestguy]

OK, here comes more dust in the air

See the other thread on this subject for what works here in cold climate also.

If folks want to do manual work them selves, the crib type thing with RR ties also is in the picture. In that case, terraces are pretty much needed, probably three. Manual excavation also is less than for gabions, being limited to the tie backs.

By the way, creosoted ties, even if old, last very long.