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Cut and fill to get high ABP

Cut and fill to get high ABP

(OP)
Hi all,

I have a summary ground condition as below:

Stratum Depth (m) Thickness (m)
1.Top soil 0.3 0.3
2.Reddish brown clayey SAND 0.75 0.45
3.Firm gravelly CLAY with cobbles 2.20 1.45
4.Bedrock
Water table at 1m below ground.

This is a warehouse building, the structural engineer required allowable bearing pressure (ABP) = 300 kPa (I have no idea why). A previous geotechnical engineer suggested by cut and fill 0.5m with stones & sand before knowing the required ABP, now I am handling this job. We also have the MCV test is 5.3.

My question:
a.Is that possible to achieve that much ABP by cut and fill by your experience?
b.I would certainly require more test at stratum 2 & 3, which tests are most useful for these two?

All suggestions/comments are welcome!

RE: Cut and fill to get high ABP

Your information lacks some required test data. Under the circumstances this is question that you should handle with your geotechnical engineer. I'd not attempt to advise with what your are furnishing. There may be circumstances that are more critical than what is apparently implied here.

RE: Cut and fill to get high ABP

The geotechnical engineer should have qualified the allowable bearing pressure by stating the elevation to which it applies. If you have a strong layer below a soft layer, the allowable bearing pressure will obviously be higher above the strong layer than above the soft layer. You can certainly improve the bearing capacity by cutting out weaker soil and replacing it with improved soil.

RE: Cut and fill to get high ABP

I agree that there is not enough information, but just based on the soil descriptions, I don't think that you can get 300 kPa in layer 2 (I don't even consider layer 1 since I think it may need to be removed). I think that there are high chances to get 300 kPa for the bedrock. Perhaps layer 3 may work depending on how much gravel you have. But, with your water table at 1 meter you will need some dewatering to get the desirable 300 kPa anyways.

RE: Cut and fill to get high ABP

(OP)
Thank you all for your inputs.

I have checked with the structural engineer; the issue is about the ground bearing slab for a distillery. It's quite heavy load and the layers 2 & 3 may cause more unexpected differential settlements.
I am thinking of Oedometric modulus test for these 2 layers for settlement calculation. But even the settlement is acceptable, I've still concerned about differential settlement due to the thickness of these 2 layers vary significantly.

Another idea is to change the ground bearing slab to suspended slab supported by vibro concrete columns since the bedrock is not so far and keep away from dewatering pain?

Any thoughts?

RE: Cut and fill to get high ABP

absolutely the building foundation should be on the rock. but does the floor slab really have that high of a load that you need 300 kpa for bearing or that there will be a lot of settlement? Your not thinking of building the slab on fill are you?

RE: Cut and fill to get high ABP

If this requirement is for the floor slab, is this 30 kPa rather than 300 kPa? 30 kPa is still high for floor slabs...

You can preload and monitor settlements but if you really want 300kPa you may need to go to bedrock.

RE: Cut and fill to get high ABP

Seems like good conditions for drilled piers, from what little info is provided.

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