Good morning,

repeating what was written in the post:

and thanking @JS for his answer, I try to explain me better for my problem (rereading what I wrote I think it's not clear).

Below a model with I'm analyzing. There are two concentrated forces (one force's value=450000N) and soil seabed reaction modeled as Hydrostatyc pressure (applied on the external and internal walls of the structure):

One concentrated force have to be in balance with the soil reaction, so the value of the soil reaction has been achieved in this way. Considering one half of the wall (surface area 16911136 mm²)

450000=[(Hydrostatic_Soil_Pressure_on_External_Wall*16911136 mm²)/2]+[(Hydrostatic_Soil_Pressure_on_Internal_Wall*16911136 mm²)/2]

where: Hydrostatic_Soil_Pressure_on_External_Wall = Hydrostatic_Soil_Pressure_on_Internal_Wall=Hydrostatic_Presure

so: 450000 = 2*[(Hydrostatic_Presure*16911136 mm²)/2] → 450000 = (Hydrostatic_Presure*16911136mm²)

Hydrostatic_Presure≈0,02661MPa

Now for apply the pressure I set n. 4 set of surfaces (n. 2 for external wall and n. 2 for internal wall):

And the Hydrostatic pressure was set in this way (vertical axis is Z as per previous figures):

(Magnitude 1 is set because the step is linear perturbation and the value of 0,02661MPa was applied as coefficient whe load cases were set as scale factor):

The Zero pressure height is 22,05 mm is because the upper end of the wall has that z coordinate

And the Reference pressure height is -2582,05 mm because the bottom end of the wall is height 2582,05 mm but downward the z=0 coordinate

I performed n. 4 analysys:

HYDROSTATIC_PRESSURE_TEST_1 → pressure applied on one half wall:

HYDROSTATIC_PRESSURE_TEST_2 → pressure applied on on entire internal and external walls:

HYDROSTATIC_PRESSURE_TEST_3 → only concentrated forces are applied:

HYDROSTATIC_PRESSURE_TEST_4 → the structure is full loaded:

Below results where is clear that, only when hydrostatic pressure and concentrated forces act together, Boundary Conditions and external resultant loads are not in balance (Boundary Conditions are per previuous figures):

The procedure was replicated not with linear perturbation step, but with n. 4 models with static general step and results are the same.

My question is, what's my mistake?

Thank you in advance to whoever answers.