Foundations on Peat 1

[ONENGINEER]

Could a light pole (footing pressure about 17 kPa) be founded on peat materails.

The peat is more than 6 m deep and the cloient is not in favour of a pile foundation with the high costs.

If a pad footing would be possible, what is the maximum bearing pressure that is typically assumed for peat materials? Thanks.

 

[msquared48]

I would never found any structure you want to be permanent on Peat materials. I would always either spec pile, or over-excavation and backfill.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[ukengineer58]

if he wants to eliminate piles then you'll need to test the characteristics of the soil. peat is highly compressing however your pressures are low. in an area we built recently previous development a pavement path had 300mm of settlement. so that was also lightly loaded

 

[dik]

and it consolidates nearly for ever!

 

[Ron]

Agree with others...not a good idea. Allowable bearing pressure for peat can be as low as a few hundred psf...even then you can get settlement. (Settlement and bearing capacity are two different issues)

as dik noted...can go on forever. Keep in mind that moisture contents in peat materials are commonly 200 to 400 percent...footing loads tend to squeeze that water out (reduction in void ratio), thus settlement occurs. The time to consolidation can be excrutiatingly slow...but damaging.

 

[ONENGINEER]

Thanks all for the comments. Is there any alternative solution to piles. This is a footing for a single light pole of 14 m high.

 

[BigH]

By the way - is the peat fibrous or amorphous peat? Where is the groundwater table? Do you have several feet of "desiccated" peat?

Have you thought of using preloads? One possible scenario - without using piles would be to load up 5 to 8 ft of sand in an area that would be 10 ft or so beyond the edge of your footing - let it sit for several months . . . yes, to build out primary and several cycles of secondary settlement. (note, depending on the peat, the side slopes might need to be 3H:1V or so.) Remove the preload to ground level. I would then dig out about 2 to 3 times my footing width (and say a footing width wider) and replace using the left over preload sand on which the foundation can be placed. You could also consider the use of geo-grids in the sand - but the width of excavation would need to be such that the grids would have enough tension length.

But for only a 6 m depth of peat - and assuming that you have "good" material below, why not just use helical piles that can be installed using light equipment -s houldn't be too expensive.

 

[dik]

Can you dig a big hole, put in a large 12' long x 6' dia HDG culvert that extends 4' out of the peat, backfill hole and fill with rocks and have an annual maintenance program? They do that for utility poles in the northern regions... expect it to tilt after a bit... depending on the pole height, embed it 4' to 6' in the granular stuff in the culvert.

Dik

 

[FixedEarth]

See attached.

 

[dirtsqueezer]

What is your foundation area? Possibly widen it? There is something called the 'sphere of influence' that you might be able to highten above that peat elevation with a lower psf, but if you're limited on space you might not be able to do that. No references, sorry.

 

[chicopee]

Several years ago, we build a new bridge spanning the CT River in Old Saybrook, the contract called for a new boat ramp on peat and it was build without any significant settlement. Of course, it was a significant concrete slab

 

[fattdad]

sometimes you need to find new clients.

f-d

¡papá gordo ain’t no madre flaca!