How do you model soil and soil/structure interaction with s/w ?

[JoeH78]

hi all,

How is the correct way of modelling soil behaviour and soil structure interaction under external static, seismic, impulse or completely arbitrary loading with nowadays computer.

Regards,

 

[bookowski]

I'm assuming that s/w means shear wall? From my experience it is not common to include soil-structure interaction in overall building models. Although technically feasible now it hasn't caught on. I think it would take some code requirement that forces the analysis or else no one will want to take that leap and be playing on an uneven field with the guys that aren't including it. I think it is more common to include it in isolated parts of models - for example running nonlinear soil models for foundation element modeled separately from the overall building.

 

[kingnero]

s/w = shear wall? I'd rather say solidworks? maybe software (you're talking about computers)?

please explain!

 

[JoeH78]

Sorry for not being not verbose here (s/w = software )

I agree that soil structure interaction is not common task, I'm even bit a dubious that it'll produce practically reliable results.

My main point of interest was actually how the soil can be modelled when designing retaining walls, machine foundations etc... what type of loading the soil will produce or what will be real behaviour of soil under cycle loading for heavy machine foundation?

I'm looking for how the softwares can be used for accurately estimate the soil behaviour, instead of doing the hand calculation,e.g. location of critical circle for slope stability, how the softwares(with tetras, hexas) can be benefited?

Thanks for commenting,

 

[FixedEarth]

With soils, the properties vary in both horizontal and vetical direction. So the accuracy in a software is often much more refined than the soils values we can get in the lab.

The computer software often only take soil properties in vertical direction, specially the stress and settlement software. For slopes, you can define more accurately what the field conditions.

The main point is to have an idea or a back of the envelope calculation estimate before you model the program- this only comes with experience. Sometimes, I see others solving for non-existing problems. This is unwarranted exercise even if you have powerful software. For example, earlier this week, I saw a report that mentioned undocumented fill was present next to a structure that will soon get an addition. The addition area is attached to the existing building. How can this be, when the soils under the building is same as that next to it. There are no distress signs on the existing structure so the adjacent area must have been compacted at the same time as the original structure. This is confirmed by the medium dense consistency of the adjacent soils.

There are many such examples in tiebacks, laterally loaded foundations and machine foundations. It is better that we learn from case studies and current publications so that we may better define the most critical design concerns. Once we setup the problem, solving it by a calculator or a spreadsheet is often sufficient. As my statics teacher used to stay, set up the equations and solving it is just Algebra.

 

[JoeH78]

Sorry for the tardy reponse,

Basically we should rely on what we gained from our exprience and do hand calculation as how we have been taught on college. But didn't we sustain our experience with some numerical results, which I believe why we have been paid for.

Does that mean also, having the powerful methods such as finite element doesn't do any good for estimating the load produced by soil?

Regards,

 

[yakpol]

Complex soil structure interaction tasks typically are handled using specialized software like FLAC, Abacus or Plaxis. These programs have extensive collection of soil models,handle construction sequence and capable to analyse for all soft of loads. But they are mostly domain of geotechnical/tunnel engineers, very few structural engineers use them (cost+time+training). Using structural analysis software with equivalent soil springs, pile elements (if available) and derived from analysis above soil pressures is the most common way to handle s/s interaction by structural engineer.