pad foundation on fill 4

[longisland]

I'm asked to design a pad footing of 25 ton working load capacity on a filled ground.
There's no test conducted in the borrow source(from the adjacrnt hill with no ground water detected) but the fill material seems to be stiff clay (light brown color). The compaction seems to achieve 95% MDD according to the contractor eventhough I don't have the density of the fill material. What is the typical settlment value?
Will ther be excessive settlement ?

 

[Ron]

Settlement will depend on more variables than you have accounted for. How deep is the fill material? What is the unit weight of the fill? What is the stratification just under the footing (upper 1xB)? What are the subsurface conditions? Will the fill cause settlement of soft underlying strata? Is the fill underlain by sand? What is your anticipated bearing capacity and bearing pressure? Will there be more than one footing? Is differential settlement an issue for multiple footings? If so, how much is tolerable for the construction?

Just a few things you need to consider.

 

[GeoEng]

You are flirting with disaster if the fill is very thick at all. Do not believe the contractor! Demand to see test results of the density of the fill and inspection reports from independent laboratory.

 

[longisland]

thanks for the response. My friend, a geotech engineer, gave similar advice to me. to find out the settlement, a consolidation test can be carried out. a plate loading test can be done as well. the problem is my client may not allow it. differential settlement is a concern. I'm worried about tilting of structure if the compaction is not consistent.
what other field test can be used? what about sample plasticity index? Settlement is always related to compressibility.

 

[Ron]

Listen carefully!!! Compaction is not your issue. That's easily controlled. YOU MUST KNOW WHAT THE SUBSURFACE CONDITIONS ARE! Compaction has only minor implication to settlement. If the owner is not willing to allow an appropriate investigation of the subsurface conditions, then you might be better served to walk from the job. If you don't, then I hope you have a good contract and attorney, because if something goes wrong and settlement occurs, guess who gets blamed!!?

 

[longisland]

Thanks for the reminder. I infact checked the borehole log of the initial si before I even bother considering my client's suggestion. the original ground is okay.

 

[Rowland33]

In my experience, uncontrolled fills are exactly what they purport to be, fills without the benefit of engineering control. Personally I would walk away rather than design a structure on such a fill. If the underlying soil is acceptable, go for piles but before you do, get the opinion of a geotechnical engineer in writing.

 

[IJR]

Thanks all of you guys, this is really a valuable discussion

 

[ishvaaag]

True I see piles the only reasonable solution in such site... and then geotechnical information be logically required. Don't forget negative friction charging more the upper part of the piles when the fill further settles.