# Calc. active earth pressue with ccx

Hello,
is it possible to calc. active earth pressue with ccx?
for example to get the Pa?

wbr dichtstoff & thnx for your help

If itâ€™s just a linearly varying pressure (like a hydrostatic pressure) then you could use the hydrostatic pressure load in PrePoMax which lets you define the pressure values at 2 different points.

Otherwise, likely only the dload.f subroutine or an approximation with multiple uniform pressure loads on surface partitions would work. Unless GraphiX offers some additional tricks.

i want to have calc. the pressure from ccx,
according to â€śangle of internal friction of soilâ€ť value.

model of retaining wall with concrete material and surrounding soil will directly account for both active and passive pressure, but another did not available is in saturated conditions.

*edited
increasing unit weight, reduction of cohesion and friction angle can be used as approximation of degree of saturations.

Active and passive pressure comes from limit state method. When using FEA, you just calculate normal state, with some safety ratios - reducing phi and c. This will be design pressure.

So i can calc. the reaction force (nomal state) with of the wall
with ccx and *MOHR COULOMB card?

Maybe i have a missing link:
If i want to calc. these issue with ccx, the model must first
have these glidding area, and with the glidding area i would get

is it possible to calc. the ground pressure with soil and ccx?
how can i influence the the propagation angle?

thnx for you help and your time

active/passive pressure or at rest is related to Mohr-Coulomb theory itself, so it does. The pressure is not by designed, itâ€™s a soil properties and geometry, loads as additional.

last figure is foundation bearing capacity and shear failure, another can be slope stability also the same.

You can calculate limit pressure and actual pressure for given BC.
limit means that you can reproduce formulas at the building codes (up to safety ratios).
Any info on this soil model is in Plaxis tutorials. It does the same basically. One thing what is still not clear for me - the problems like excavation of the soul and removing/adding soil by stages. At Plaxis it is very easy.

CalculiX seems capable to do analysis of soil excavation or any stage construction, below simple example keyword and plot results. Nonlinearity of material by Mohr-Coulomb and residual stress from previous analysis step also.

``````*MODEL CHANGE,TYPE=ELEMENT,REMOVE
Solid_part-5
``````

Hello xyont,

can you give me your example for examine?

wbr

I think that results are not correct. Iâ€™ve tried this option before. There is should be reverse arching of the pit bottom.

my example is simple elastic material, only quick test for seeking the possibility of further and advanced one.

Maybe I am wrong about that.
Here is an inp file:

Plaxis has special feature, when displacements from initial step are set to zero. Initial step means native state of soil under the gravity - it is not interesting how the soil is permanently displaced.

1 Like

When setting c=0 (phi stay 30 deg) - the wall crashes. But for some reason it works only with user material at this version: CalculiXforWin download | SourceForge.net
Not with official implementation at 2.21

``````** user material provided with calculix launcher

**     par1=Young's modulus, E
**     par2=Poisson's ratio, nu
**     par3=cohesion, c
**     par4=friction angle, phi [degrees] Cannot be set to zero
**     par5=dilation angle, psi [degrees] Cannot be set to zero

*MATERIAL,NAME=ABAQUSMCWD
*USER MATERIAL, CONSTANTS=5
3e7,0.3,0.,30.,30.

*DENSITY
1500.
``````

same thing at plaxis2d (initial stage displacements are set to zero)