New user, in need of guidance trying to figure out what model is best for the analysis of fill under a building over deep, soft soils.
Does the SS model calculate only primary consolidation and the SSC only secondary creep settlement as a result of loading onto the soft soils?
OR
Does the SSC calculate both?
Another question sorry,
I'm having issues with the SSC model running a consolidation analysis for staged construction, wherein in the first phase I am applying a fill load, allowing 14 days for construction and in the second phase an applied building load for a time period of 3650 days, to understand longterm settlement over 10 years.
the first phase works fine and I get a realistic output, however, the second phase shows high deformation at the corner of the fill and large positive deformation at the top of the model. See below, do you know why this might be? I've looked over the model geometry and this is ok, and my parameters seem to be appropriate. Perhaps the time step is defined incorrectly? or boundary not defined?
Also, if I was to run a plastic analysis, instead of consolidation, does the output represent the maximum deformation of the soil independent of time ie what may occur over a very long period (100s of years).
Really appreciate the help here.
Well, first of all, if you apply a load in phase with a time interval, the load is applied linear in time. So in your case the building load is gradually applied over a period of 10 years. I'm not sure that is really what you intended? Hence, you may want to insert a phase to model the application of the building load in what is more or less the construction time of the building, and then leave everything for 10 years to just consolidate and creep.Since you apply the load in 10 years, you probably never reach consolidated state as you keep developping excess pore pressures by the continuous increasing load. Hence, the soil behaves pretty much undrained and the so if you push it down in the middle, it heaves on the sides.
Third of all, your boundary conditions are way to close to your applied building load. The influence zone of an applied load on undrained soil is up to 3 times the width of the area where the load is applied. Hence, the left and right boundary should be at least a distance of 3 times the width of the load from the load....Now the upheave is very concentrated in the narrow area between load and boundary condition, and therefore heaves unrealistically much.
Best regards,
Dennis Waterman
did you have any advice on the last part of the above question?
"Also, if I was to run a plastic analysis, instead of consolidation, does the output represent the maximum deformation of the soil independent of time ie what may occur over a very long period (100s of years).?"
Sorry, I forgot
Well, no, because also in a plastic calculation there is creep. So if would already make a difference whether you would specify a plastic phase of 100 days or 100 years, the latter would give a lot more deformation.Creep is something that is always there, whether there are pore pressures or not and whether there is consolidation or not. There will always be creep though it will go slower and slower in time. But there is no asymptotic value or so that would give it a maximum: at infinite time there is infinite settlement - or at least according to the Soft Soil Creep model there is. In reality at some point probably creep would really stop when the soil reaches it's minimum void ratio, but that is not taken into account by the Soft Soil Creep model
Thanks again Dennis,
For the purpose of my calculation, I think the soft-soil-creep model, coupled with a Plastic analysis is appropriate. ie determining appropriate building loads on a 30m deep profile of soft soils such that settlement will not result in significant damage to the infrastructure.