Asking for recommendation for foundation design
Asking for recommendation for foundation design
(OP)
I have a warehouse design project. The geotechnical report produced the following result:
1. Net allowable bearing capacity = 40Kpa, 2.0m depth, foundation width is 3.0m or less
2. Idealized geotechnical parameters
Depth Description N-value Es(Mpa) C(kpa) unit weight(kn/m3)
0-2.0m Soft Elastic Silt N-value=4 Es(Mpa)=2 C(kpa)=6 12
2-3.0m Medium Stiff Elastic Silt N-value=9 Es(Mpa)=10 C(kpa)=25 12
3-13.50m Soft Elastic Silt N-value=3-4 Es(Mpa)=2 C(kpa)=6 12
13.5-22.0m Medium Stiff Elastic Silt N-value=7-9 Es(Mpa)=10 C(kpa)=25 16
22-24m Stiff Elastic Silt N-value=18-33 Es(Mpa)=30 C(kpa)=80 18
24-30m Hard Elastic Silt Refusal Es(Mpa)=40 C(kpa)=200 20
3. Ground water table at 6.25m
I've always read of silt being a problematic soil and belongs to the category of soils vulnerable to potential failure.
Thank you for your inputs.
1. Net allowable bearing capacity = 40Kpa, 2.0m depth, foundation width is 3.0m or less
2. Idealized geotechnical parameters
Depth Description N-value Es(Mpa) C(kpa) unit weight(kn/m3)
0-2.0m Soft Elastic Silt N-value=4 Es(Mpa)=2 C(kpa)=6 12
2-3.0m Medium Stiff Elastic Silt N-value=9 Es(Mpa)=10 C(kpa)=25 12
3-13.50m Soft Elastic Silt N-value=3-4 Es(Mpa)=2 C(kpa)=6 12
13.5-22.0m Medium Stiff Elastic Silt N-value=7-9 Es(Mpa)=10 C(kpa)=25 16
22-24m Stiff Elastic Silt N-value=18-33 Es(Mpa)=30 C(kpa)=80 18
24-30m Hard Elastic Silt Refusal Es(Mpa)=40 C(kpa)=200 20
3. Ground water table at 6.25m
I've always read of silt being a problematic soil and belongs to the category of soils vulnerable to potential failure.
Thank you for your inputs.





RE: Asking for recommendation for foundation design
RE: Asking for recommendation for foundation design
RE: Asking for recommendation for foundation design
Dik
RE: Asking for recommendation for foundation design
Okiryu....the silt from 3 to 13.5m is soft, not medium stiff. That layer is below 13.5m.
Since your building is a warehouse, I assume the footprint is relatively large. I agree with hokie66 that piles would be the better option and due to the soft materials in the upper strata, driven piles would be better than augered concrete piles as you would likely have difficulty with controlling the pile diameter in the upper 15m of soil. The piles could support caps and grade beams or a mat.
RE: Asking for recommendation for foundation design
3-13.50m Soft Elastic Silt N-value=3-4 Es(Mpa)=2 C(kpa)=6
With that low modulus, I expect that settlements are large (larger than the typically maximum allowable of 25 mm/1 inch). I agree with hokie and you about considering piles unless the geotech is very confident about settlements are okay with that soil conditions. Does the report talks about expected settlements? But even if settlements are okay, the shear strength is also very low, so if you have the footing at 2m, the stresses at say 3 m (top of the soft silt) for the size of your footing, may be about 35 kPa. This is larger than the qu of that layer (12 kPa). So, I would also be concern about a bearing capacity failure.
Also, based on the recommended bearing capacity and the size of the footing appears that the loads are not high (less than 500 kN??). I want to believe that the geotechnical report already considered settlements and bearing capacity associated with the recommended allowable bearing capacity/allowable bearing pressure.
RE: Asking for recommendation for foundation design
Dik
RE: Asking for recommendation for foundation design
RE: Asking for recommendation for foundation design
Dik
RE: Asking for recommendation for foundation design
Dik