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Wrong pore pressure and effective stress state in ABAQUS


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.


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