Driven Pile Retaining Wall
Driven Pile Retaining Wall
(OP)
I am looking into the preliminary design for a driven pile retaining wall, which will run between the bottom of a 35degree slope and a proposed housing development.
The slope is generally poorly cemented sands, with some clay lenses. The SI is currently pending but we hope it will pick up the clay horizon expected to be sitting at around 15m BGL.
The major problem with the site conditions is the presence of the water table which sits at the bottom of the slope. Therefore any excavations for foundation work for the houses will become inundated with groundwater.
My thought is to drive the retaining wall down to the clay layer and thus intercepting the groundwater from across the site. Therefore some management of the water is required to avoid the buildup of porewater pressures behind the retaining wall.
Has anyone got any experience of managing groundwater flow behind a driven retaining wall?? and know of any good systems?
Any help, guidence, pointers will be greatly appreciated.
The slope is generally poorly cemented sands, with some clay lenses. The SI is currently pending but we hope it will pick up the clay horizon expected to be sitting at around 15m BGL.
The major problem with the site conditions is the presence of the water table which sits at the bottom of the slope. Therefore any excavations for foundation work for the houses will become inundated with groundwater.
My thought is to drive the retaining wall down to the clay layer and thus intercepting the groundwater from across the site. Therefore some management of the water is required to avoid the buildup of porewater pressures behind the retaining wall.
Has anyone got any experience of managing groundwater flow behind a driven retaining wall?? and know of any good systems?
Any help, guidence, pointers will be greatly appreciated.





RE: Driven Pile Retaining Wall
RE: Driven Pile Retaining Wall
I am also looking at the use of a counterfort drains around my retaining wall. This is something i have very limited experience of.
Does anyone have any pointers, in terms of useful texts/papers which could get me started?
Cheers
F
RE: Driven Pile Retaining Wall
One option may be to forget about trying to cut off the ground water and address house foundation dewatering on a case-by-case basis. Although the "static" water level may be high, once an excavation is dug, the "flow rate" into the hole may be quite low - easily controlled during construction with simple diaphragm pumps, etc. Perhaps some test pits dug now will give a clue if this approach is practical for your site.
For documents on sheet piling, check this page of my website
http://www.slideruleera.net/Steel-Piling.html
www.SlideRuleEra.net
RE: Driven Pile Retaining Wall
My question is why is the retaining wall piled?
RE: Driven Pile Retaining Wall
I've worked on a few jobs where we wanted to keep ground water from moving laterally. One was a waste disposl site with nasty stuff in the water. This and others had an impervious layer to go to. The barrier was a trench filled with either ordinary local clay, or a bentonite slurry.
These worked very well, as planned, but ground surface was near level.
For this site, I'd be wary of bentonite, due to it being not significantly heavier than water, with little resistance to lateral pressures.
However, I question at this site, digging the trench and not having a slope movement toward it while trench is open. Perhaps with braced sheeting or trenching box it might be done. This may need a stability check first, with open trench in the calcs.
Will such a barrier have water then rise up and flow over the top causing "springs" and other mischief? So, before any barrier is done you had better know the natural ground water flow conditions.
Of course one could consider a sub-drain up-stream from the barrier, but that too has questions on how to do it at slope base.
RE: Driven Pile Retaining Wall
Further SI and pezo testing are pending... but should be carried out ASAP. Generally working on limited data at the moment.
All assistance is greatly appreciated.
RE: Driven Pile Retaining Wall
I've done a few jobs where drainage of moving slopes was done by methods similar to those done by California DOT.
Drains are installed by drilling into the slope at the base, installing near-horizontal perforated pipe and, if possible, sand filter surrounding. It is chancy, since the drains are perpendicular to the flow situation.
We also have augmented these by coming down vertically at the top of the slope, meeting the horizontal pipe with a sand filled hole, tapping seepage zones.
It has a lot of trial and error associated with it, but it has stopped slippage. These were clay slopes with sand seams.
RE: Driven Pile Retaining Wall
RE: Driven Pile Retaining Wall
I am intrigued by the Horizontal drainage system. Can you recommend any sources of further information?
Regards
F
RE: Driven Pile Retaining Wall
Also, with a bored pile wall, you could leave a space between the piles to allow the pressures to dissipate. Drainage can be added between the piles to carry water to the toe, and into a perforated pipe to convey the water away.
RE: Driven Pile Retaining Wall
RE: Driven Pile Retaining Wall
Use of Vacuum horizontal drains for slope stability mitigation
www.bitech.ca/pdf/brawner_book_review.pdf
www.imwa.info/bibliographie/01_1_001-106.pdf
www.highwaygeologysymposium.org/hgsindex.pdf Pakalnis
www.tkk.
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www.slopeindicator.com/pdf/application%20guide.pdf
RE: Driven Pile Retaining Wall
The main advantage is that the sytem doesn't require power. For your case, you may need a sump near the bottom to collect GW and pump it out. Another method is to do a sand or gravel-filled trench upslope from the wall that intercepts and directs it to a place where it can be pumped. A thorough stability check would be needed for this case, along with careful planning on construction sequencing.