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Wrong pore pressure and effective stress state in ABAQUS

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I want to model an anchored sheet pile wall placed in a completly saturated clay material, where

the excavation steps on the left side of the wall have to be taken into account.

I am using the keyword in ABAQUS *Model change, Remove to remove my elements, so I can

simulate the excavation steps. Unfortunately, my pore pressures seem stranges in the

model when I am using this keyword.

As a very simpel example I have tried to model two rectangular completly saturated soil

elements placed on each other with a tie constraint to tie them together (element1 is

placed on element2). The two elements have same soil parameters. As my first step I have

made a geostatic step, where the gravitation load is applied to establish equilibrium

with the initial stresses in the model. In this step ABAQUS simulate a hydrostatic pore

pressure with zero pressure at the top surface at element1 and maximal pressure at the

bottom of element2 - just as it was expected. In the next step I have used the keyword

*Model change, Remove to remove element1. Now the hydrostatic pore pressure should be

zero at the top surface at element2 and maximal at the bottom surface at element2. But

this is not the case - instead I get negativ pore pressures at the top and the bottom

surfaces in element2, when I am removing element1.

Model settings:

- dry density: 1631kg/m^3

- specific weight of water: 9820N/m^3

- void ratio: 0.652

- Gravity load: g=9,81m/s^2

- pore fluid/stress elements is used

- element1 coordinate (left upper, right upper, left under, right under):


- element1 coordinate (left upper, right upper, left under, right under):


I really hope you can help me.