Learning Forum

[Naresh Jogi]

Hello, Can anyone show me how to calculate the foundation stiffness for soil? 

I'm using the elastic support on the embedded piles in the soil, but I do not know how to calculate the soil stiffness. I do have the geotechnical report for this job but it does not give the soil stiffness directly, I know it needs to be calculated by using some formula and the data in the geotechnical report. 

 

Thank you

[peteroznewman]

Can you copy/paste the geotechnical report into your reply?

[Naresh Jogi]

 

 

its a 52 page report, not sure how to paste it though. if you can share your email ID, I’ll try to email it to you. 

As a sample, attaching the bore test information, maybe this should help you, as it has the ‘N’ value from the SPT test. 

 

Thank you

 

 

[peteroznewman]

Please paste a page of data associated with the first sample recovered.

You can upload the 52 page report to a file sharing site such as Google Drive or OneDrive and provide a link in your reply. Make sure to create a link that anyone can use to download the report.

[Naresh Jogi]

ntg

[Naresh Jogi]

 

 

please let me know when you download it. 

 

 

[peteroznewman]

I downloaded it, thanks.

[Naresh Jogi]

any update?

[peteroznewman]

I read the report but I don't know how to estimate soil stiffness from the data in the report either.

I suggest you contact the authors of the report for the information you need.

[Naresh Jogi]

okay. thank you

 

[Naresh Jogi]

 

Hey, I contacted my client and they gave me a direct number for that soil stiffness. Thank you for that part. 

The other thing I need to know is that, As I explained before the beams are embedded in the soil and I’m using elastic stiffness as a fixed boundary condition. And apart from this I even need to include the friction between the soil and the beams in the model. How can I put this value? 

To my knowledge, we generally use frictional contact between soil and beams and input the friction value, but in this case, we omitted the soil part and just considered the beams with structure. How can I input the friction value in this case?   

The green highlighted part/structure below is embedded in the soil and has an elastic boundary condition on that particular face. 

 

 

[peteroznewman]

I haven't done any research on how friction is used in pile/soil models, but I can give you my thoughts. A coefficient of friction creates a frictional force because there is a normal force at the interface. What is the normal force that the soil makes against the pile?  However, even if there is a large normal force, the soil has a limited shear strength, so the frictional force can't be greater than the shear strength.

I don't often use Elastic Support in Ansys Mechanical, but my understanding is that it only provides a spring force normal to the surface. When the surface is a vertical cylinder, it will provide a lateral stiffness that opposes motion in the ground plane, but does it provide any stiffness in the vertical direction?  What happens when you run the model with elastic support and a Standard Earth Gravity load? How far does the structure sink into the ground?  From the weight of the structure, you can calculate the vertical stiffness.

[Naresh Jogi]

I do not know the normal force that the soil makes against the pile.

 

When I run the static simulation with the gravitational force on the structure, the entire structure displaces by 3.0" into the ground.