Foundation on fill
Foundation on fill
(OP)
Hello all.
I need to design spead foudation with width of 2.5m,
laying in fill of fine sand with depth of 4m, on top of 20m
depth of peat.
The soil is improved using geotextile.
My question is: What are typical characteristic of soils
for sand and peat should be used for calculation of bearing
capacity and settlement of foudation.
Thank you for your comments.
I need to design spead foudation with width of 2.5m,
laying in fill of fine sand with depth of 4m, on top of 20m
depth of peat.
The soil is improved using geotextile.
My question is: What are typical characteristic of soils
for sand and peat should be used for calculation of bearing
capacity and settlement of foudation.
Thank you for your comments.





RE: Foundation on fill
This is tricky and should be handled with care. An experienced geotechnical engineer should be approached - without question. I might assume you are in Canada, if so - and you need some contacts, please advise.
Some initial thoughts:
Properties of the peat, of course, is the nature of the peat - whether fibrous or amorphous. What is the compression characteristics - i.e., primary and especially secondary. Peat will have significant secondary settlements. What are the strength parameters.
What is the nature of the fill - old/new? Was it an engineered fill or just loose fill placed and dozed as the occasions warranted??
If you are planning to add any more areal fills to raise grade - this will create muchas problemas. These fills - if done at the time of the construction - will lead to further significant primary and secondary settlements. I would, even suggest that a rigid raft fdn might be a better choice in that the structural behaviour would be more uniform - tilting, maybe, but scant to little differential between bearing walls/adjacent footings.
I was involved in a project in Burnaby, BC, Canada where some 2.5m of fill was placed atop 25ft of peat and 25ft of soft clay. The building was on piles and they used wood piles for a later expansion. As the expansion was in a traffic area, a problem was encountered in that the fill would settle leaving the butt ends of the wood piles peering up proud to the ground. They would cut off the butts to "ground level". Then, a year later, same thing - again they would cut off the butts. They did this for several cycles. So - you see, settlement ongoes.
Consideration might be given to preloading. The more the better although you will have to watch for edge instability. Plus, though, you need time.
Hope these early thoughts have been of some use to you. Check out some of the other threads given at this site regarding peat. There are some good comments in them too.
Best regards and Good Luck.
RE: Foundation on fill
I am from Vietnam and I am working at a project for building a new factory.
The designer of the project made foundation solution for this building site.
They improve soil using geogrid/geotextile, place 4m thk. compacted sandy fill on top.
For major foundations they use piles, for foundation of pipe-rack, and minor structure
they use spread foundation with the less width up to 2.5m, laying in the fill layer.
They require that the sandy fill compact to the bearing pressure of 5 ton/sq.m for
bearing the foundations. I am not satified with their solution and want to prove that the
solution is unfit. (I have not soil data yet, but looking for typical soil characteristic
for a quick judgement).
Thanks.
RE: Foundation on fill
RE: Foundation on fill
Probably no shortage of peat in your area.
On a project involving capping a pond/wetland, I ued a geogrid material, placed 2-foot medium/coarse (USCS) sand and another geogrid material and more sand, covered by general fill (mixture of sand, silt, clay). Was very stable. Contact a vendor of geogrid materials and follow Geotechnical recommendations. It can be done. Good source of published properties of sand - Bearing Capacity of Soils and Settlement of Soils, both Army Corps of Engineers publications.
Good luck, please keep us posted on what you use and results!
RE: Foundation on fill
RE: Foundation on fill
RE: Foundation on fill