Mat foundation on expansive soils - preferred software?
Mat foundation on expansive soils - preferred software?
(OP)
I'm trying to determine if any commonly available FEM foundation software design packages such as RAM Concept, STAAD Foundation (or other) are capable of modelling large mat foundations subject to edge lift and center lift conditions? I have access to both RAM and STAAD here at the office, but I don't see where either explicitly accepts edge moisture variation distance or soil heave input values. I'm curious how others are modelling these soil loading conditions; any suggestions would be appreciated.
RE: Mat foundation on expansive soils - preferred software?
I would then apply loads (upward loading) to account for edge lift / center lift.
Is there any reason why you could not apply upward loading to simulate the lift conditions and combined those loads in the appropriate load combinations?
RE: Mat foundation on expansive soils - preferred software?
I don't think the edge lift condition is that straight-forward. The soil bearing pressure should be parabolic, highest at the perimeter and decreasing to a more uniform value near the center. It seems like it would be more complex than simply applying a uniform upward-acting load to some area of the slab perimeter. That's why I'm curious how others are tackling the problem.
RE: Mat foundation on expansive soils - preferred software?
Would you be interested in your program doing this type of calculation automatically.... Or, are you just interested in being able to apply this type of uplift load manually into the program. The 2nd option seems pretty easy, I would think every foundation program out there would allow you to do something like this. It's just another type of load.
The first option, however, is interesting to me conceptually. What would this type of calculation involve? From an engineering calc standpoint I can look that up. But, I'm wondering from a program interface standpoint. For the computer to run these numbers automatically what would it need to know about the foundation and soil. My tendency is to think that it would too complex of an issue to handle easily. Involving not just soil properties, but also geometry of the foundation (and above grade structure), maybe even drainage issues for the soil and site.
RE: Mat foundation on expansive soils - preferred software?
For edge lift, I had a lengthy conversation with a geotech before developing the model. While this might appear to be a simple load condition, it is far from it. The swell pressure is not uniform, but is tied to the ability of the soil to expand with changes in moisture content. A stiff foundation would confine or "push back" against the soil, limiting its expansion and resulting in high exerted soil pressure. A flexible foundation would bend upward, allowing the soil to reach its full volume-change potential which results in low swell pressure. So the swell pressure and foundation stiffness are related (deflection inversely related to swell pressure), and this is not captured in the simplified loading described in the OP. It represents a theoretical "worst case" assuming the soil expansion is limited to a value resulting in maximum swell pressure, but does not capture the real-world behavior or bearing pressure. The model just sees it as an uplift load that is trying to pick the mat up, instead of the soil pressure increasing below the foundation. Therefore the service load bearing pressure and the edge deflections are fictitious numbers. The model value is limited to providing worst-case design values for concrete reinforcement.
It's not a perfect solution, so I'm still interested to know if there's a better way to approach the problem.
RE: Mat foundation on expansive soils - preferred software?
RE: Mat foundation on expansive soils - preferred software?
RE: Mat foundation on expansive soils - preferred software?