Cast-in-Place Concrete Pile Retaining Wall - Site Limitations 2

[JrStructuralEng]

I have a retaining wall that is ~2ft from the property line and approximately 7ft high. The contractor had gone ahead and installed piles prior to our involvement. The retaining wall is holding back about 6.5ft of sandy till.

We would typically use buttresses with piles set back from the retaining wall 4-5ft for overturning and span the retaining wall horizontally. However, because of the site limitations(and that the neighbour won't allow for us to tamper with his property or use steel tiebacks) does anyone have any other suggestions?

I thought about using a quasi-footing that cantilevered at the base out 2ft in order to allow for passive overturning resistance due to the weight of the backfill resting on the footing. We will include a few butresses but centerline offset will only be 1'10" which won't allow for much overturning resistance. Does anyone know of any good literature for determining that capacity of each piles resistance to overturning? or have any other ideas.

Thanks,
JrEng

 

[MiketheEngineer]

Could you use something like a Versalok wall??

 

[PSlem]

Try Peck, Hansen and Thornburn for pile supported cantilever wall design. I have designed some with very little heel and a row of helical tension piles.

 

[JrStructuralEng]

versalok walls that are non-reinforced (i.e. don't use geotextile) are only good up to 4ft. I did think of that but we can't go dig up the neighbours yard to run geo sheets back.

Any other ideas, i will check peck,hansen, thornburn. THanks pslem

 

[MiketheEngineer]

Neighbor really is being a jerk!!!

 

[escrowe]

Here's a product I've always wanted to see in action.
Redi-Rock makes massive block retaining walls.
This one can be constructed to 10 feet without reinforcement.

http://www.redirock.com/engineering.../?value=B60&connector=0&degree=34&condition=C

If they use it, be sure to post some pictures... : ]

 

[DRC1]

Properly designed, a sigle row of piles can retain easily up to 12 feet and under good conditions 16 feet. depending on how the piles were driven you may be able to use the lateral resistance of the driveen piles.

 

[JrStructuralEng]

Yes, they were drilled piles. The piles are 12" dia x 15ft deep only. They are in a sandy till.

I am looking at getting some lateral resistance from the drilled piles but I don't have any good literature on lateral resistance of piles. To date I have only used coupled piles for overturning.

 

[escrowe]

You might consider setting up a lateral load test
to support your design. We've run them using a crane or
large truck winch, steel cable, load cell, and a transit.
You can test multiple piles...

 

[DRC1]

Not knowing the site conditions, I would say 15 ft deep drilled in piers are a pretty good bet to support a 6.5 ft retained height. Rather than run a lateral load test, have a geotech compute the capacity. It should require only a couple of hours and will be significantly less expensive.

 

[escrowe]

Not knowing the site conditions, I would say 15 ft deep drilled in piers are a pretty good bet to support a 6.5 ft retained height. Rather than run a lateral load test, have a geotech compute the capacity. It should require only a couple of hours and will be significantly less expensive.

Why expect the certified work of a PE to be less expensive than a simple field test?

I strongly suspect that any reputable geo signing on
for this work will insist on at least two SPT/CPT borings,
possibly supporting lab test, and an LPILE analysis.
And the owner should expect a signed sealed report transmitting the recommendations.

And the geo engineer might STILL recommend a lateral load test for piles,
the installation of which he did not observe.

Consider that by accepting this work,
the PE is taking significant responsibility for the wall design and performance.

 

[DRC1]

Why would you need 2 borings, lab tests and an L-pile analysis for a 6.5 foot wall? There is probably some knowledge of the subsurface conditions or if a boring is needed, two 20 foot borings should not cost more than $2,000. If the contractor is on site, a test pit may surfice. A lateral load test is not a simple test, requires a reaction frame, a lot of setup, data reduction and just the civil portion can run $25,000 easily. Engineering is not cheap either. Further, I have never heard of doing a lateral load test for a retaining wall, only foundation piles.
I still say this is something that should easily be computed by hand or with software like Civiltech.

 

[escrowe]

Geo engineers don't get no respect. Seriously.

A 'civil engineer' might be able to stamp someone else's drawings based on his own review,
but work in the subsurface is a different animal. Geo engineers are (with good reason!) very reluctant to provide
any recommendtions (especially for design) based on someone else's data. No thanks.
For my part, I would insist on generating my own field and laboratory data.

In my own practice I've run lateral tests on piles supporting floating piers (for example),
a dozen piles at a time, for a total cost of $3,000 to $5,000 with the analysis and report,
and made money doing so. The lateral load test is relatively simple,
beacuse the loads are much lower than foe an axial compression test, a single load cell is required,
and deflections are measured directly. I just charge crew time...

As for the means of analysis, there are many. However, I believe that an engineer's time and advice
are his stock and trade.
Clients sometimes forget that the value of an expert's involvement is not measured in hours or minutes.
That can lead to situations like the one under discussion.

 

[BoydZander]

PSlem, you refered to a text book above. Could you provide the ISDN number? I'm very interested in design examples of conventional cantilever retaining walls supported on piles.

PSslem quote: "Try Peck, Hansen and Thornburn for pile supported cantilever wall design. I have designed some with very little heel and a row of helical tension piles.
"

Thanks

Boyd

 

[muuddfun]

Just because a wall is only 6 or 7 feet tall has nothing to do with how addequate piles to 15 feet would be without know for sure what is down there. I am currently working on just such a wall, and at first we were only able to get hand augers down to 6 feet, and found some nast stuff, so I gave a very low bearing capacity after looking at the lab data, which everyone was not happy about. Sufficient to say we were then able to get money and permission to do a real investigation, and the stuff goes to 20 feet deep. So we probably will end up with driven piles 30 feet long for a wall 6 feet tall, and 250 feet long. The piling probably will cost $70,000 alone for just the deep foundation. So don't assume anything.

 

[BigH]

Where are you exactly? You say you have sandy till - any history in the area of SPT N values? Till plain? - You might want to check (and I know I'll get hit on for suggesting a reference from the 60s) Golder and Seychuk who wrote a paper on soldier pile walls based on their work on the Toronto subway. You can check this out - I would think as indicated earlier that for only a 6.5 ft high wall ('ell, this is only 2 m - shorter than King James) - a 5 m embed into the ground would likely be sufficient to act as a cantilever. Site "load tests" are a good idea - but you might not have enough room to work - given the attitude of the neighbour.