Heave Foundation Design

[ONENGINEER]

I am designing foundation for a truck scale with a 3 footings of each about 120 kips. The manufacturer recommends footings of 4 ft x 13 ft. The allowable soil capacity is about 850 psf (silty sand and sandy silt). How can I avoid piling.

 

[JedClampett]

You can spread the load out further, like use an 8 ft by 17 ft slab. Ask the manufacturer if that is a problem.
Alternates to driven piles are AugerCast piles, Geopiers, cast in place concrete piers, etc. Whoever gave you the 850 psf capacity should be able to suggest means of improving the capacity.

 

[dik]

Have to be careful... if it is sandy-silt, depending on water conditions and climate, it may be prone to frost heave...

Dik

 

[motorbiketocrank]

How did you come up with the 850 psf bearing capacity? That's a very low value.

 

[ONENGINEER]

I did some testing in the past (including SPT with very difficulty as well as shelby) and could reach a value of about 38 kPa for these deltaic deposits. The 850 kPa was proposed by a colleague professional who was also invloved in these soil strata.

 

[ONENGINEER]

Some testing was done in the past (including SPT with very difficulty as well as shelby) and could reach a value of about 38 kPa for these deltaic deposits. The DCPT values were also less than 10 in another SI.

The 850 kPa was proposed by a colleague professional who was also invloved in these often soft soil strata. I will be having a test pit to see the soil quality in the upper 10' using Torvane, Pocket PT and my thumb If you have more comments, I would appreciate it.

 

[kieran1]

Engineered Fill?

Kieran

 

[JedClampett]

Not to be picky (but I'm going to be), you say the allowable bearing is 850 psf in the initial post, but change it to 850kPa in your later ones. Twice.
Also, are you concerned about Heave (in your title) or is that a typo and it's supposed to be Heavy?

 

[MiketheEngineer]

I also noticed the unit switch.

Onengineeer - try again please!!

 

[ONENGINEER]

You are right about the mistakes in my comments.

The title is Heavy Foundation Design (heave was a typo)

The locally presumed bearing capacity is 850 psf (the reported 850 kPa was incorrect).

My own field testing results had shown that the bearing capacity in the soft materials was 38 kPa (equal to approx 760 psf).

Sorry for the confusions.

 

[MiketheEngineer]

One -

That is just above quicksand.....

Your are going to need some deep footings or pilings or something along those lines!!

 

[Bobber1]

A 150 lb man standing on a 3.5" long piece of 2x4 exerts a soil bearing pressure of 1.76 ksf. Just to get a feel for what you've got.

 

[aeoliantexan]

ONENGINEER,

The old mechanical truck scales used to be built on a pit - an open-topped RC box about 6 to 8 feet deep. Assuming your scale is about 65 feet by 9 feet and soil weighs 125 pcf, the excavated soil weighs 440 kips,more than your foundations,so you can have a balanced mat foundation. The walls provide beam strength, and the floor is designed as a mat spanning from wall to wall.

Be careful; it can float if the water table is high. An underdrain and sump pump may be necessary.

And the SM or ML is probably frost-susceptible. Frost can heave the pit and/or squeeze the sides in until the scale doesn't work. In cold country, I would put at least 2 inches of styrofoam under the floor and behind the walls.

 

[BigH]

I think that aeoliantexan hit the nail on the head - a "floating" foundation - can use soil anchors to tie the structure down if groundwater conditions are unfavourable.