Hello，
If in phase 1, there are two layers of soil in the model, but in phase 2, I need to replace the material of the upper soil with concrete, and at the same time, at this stage, I do not want this layer of concrete to cause any pressure on the lower soil. What should be the right thing to do ? I tried to apply a fixed displacement at the bottom of the concrete material but found that the soil at the bottom was still compressed.
And where does that machine lean on then? I guess you're not keeping it up with a helicopter?So if it's a crane keeping the plate up, why not put an upward force on the slap to lift it. If it's something underneath the concrete slap, that something will put pressure on the soil and that pressure should be modelled.
Again, not enough information. A gap won't work since gravity will just pull down your slap unless something prevents that (helicopter, crane, jack....). What is is that you want to see as the result of your PLAXIS calculation? The side friction, the support force (what support force, btw, since your concrete is unsupported).Hence, I think you should better make a service request and send this in as a support question so that you can share a bit more information.
With kind regards,
Dennis Waterman
Dear Dennis，
In fact, there is a machine that lifts the concrete so that it does not touch the soil on the bottom, but allows it to contact the soil on the side. If expressed as a formula, it would be: F(machine)=F(concrete)+F(side friction) instead of Fmachine=F(concrete)+F(side friction)+support force. So I can get the right number of side friction. My main problem is how to keep the concrete from touching the bottom soil. I have tried to add a fairly small gap between the concrete and the soil, but the grid is too small to divide.
Dear Xin Fang,
I think that makes 3 of us. I honestly don't understand what you're trying to model. You want to replace soil by concrete but you don't want the concrete to cause any pressure on the soil. So how is that physically possible, and what do you mean exactly with "no pressure". You want zero pressure as if the concrete is not there, or you don't want pressures any higher than the former soil pressures? The latter can be simply arranged by giving the concrete the same weight as the soil.If you don't want any pressures at all, I guess that means the concrete footing is on piles or so? If so, then model the piles. If not, I don't see how it's physically possible. Actually, if you don't want the concrete to give any pressure on the soil, why do you model the concrete at all? Just excavate and done.So maybe if you would explain a little bit more what you try to achieve instead of letting us guess in the dark, we can better help you.
Can you help me answer this question? I 'm very confused
Hi，
Thank you for your kind reply.
But the reality is that I need to excavate a layer of previously soil material and replace the material with concrete to simulate the construction of a prefabricated foundation. It should be noted that at this phase, it is assumed that there are suspended forces holding the foundation in place to prevent it from coming into contact with the soil below the foundation (it can come into contact with the soil on the side of the foundation). So I wonder if it is correct to add fixed constraints (x, y, z) directly to the bottom of the foundation.Or do I need to add an interface at the bottom and add constraints at the same time