Pore pressure curve - consolidation

Hello all. I am a beginner in FLAC3D and am working on the consolidation of a unit cell model.
when I trying to plot the pore pressure against time, as soon as I activate the fluid i.e. model fluid active on, the pore pressure is expected to decrease. But in my case it is increasing initially to a certain value and then starts to decrease.
I am unaware, what’s wrong with my code or the inputs I have given.
I have also attached my code and the pore pressure variation. Kindly let me know where and what is wrong.



Thanks in advance.

To receive quicker and more convenient assistance, could you please share the actual scripts (so they can be copied and pasted to reproduce the issue) rather than a picture of the scripts?

Sure.

Datafile1:
model new
model large-strain off
model title ‘Instantaneous pore pressures generated under an applied load’
model configure fluid
zone create cylinder point 0 (0,0,0) point 1 (1.275,0,0) point 2 (0,10,0) point 3 (0,0,1.275) size 5 10 5
; — mechanical model —
zone cmodel assign elastic
zone property young 3e6 poisson 0.3
zone face skin
zone face apply velocity-z 0 range group ‘bottom’
zone face apply velocity-x 0 range group ‘west’
zone face apply velocity-x 0 range group ‘east’
zone face apply velocity-z 0 range group ‘east’
zone face apply velocity (0,0,0) range group “south”
; — apply load slowly —
fish define ramp
ramp = math.min(1,global.step/1000)
end
zone face apply stress-normal = -0.3e6 fish ramp …
range position-y 10
; — fluid flow model —
zone fluid cmodel assign isotropic
zone gridpoint initialize fluid-modulus 9e8
; — pore pressure fixed at zero at the surface —
zone gridpoint fix pore-pressure 0 range position-y 10
; — settings —
model fluid active off
; — timing —
[global t0 = time.clock/100]
model solve convergence 1
[(time.clock/100)-t0]
model save ‘SE_INST_6’
program return

Datafile2:
model restore ‘SE_INST_6’
; — turn on fluid flow model —
zone fluid property permeability 1e-12
model fluid active on
zone gridpoint initialize velocity (0,0,0)
zone gridpoint initialize displacement (0,0,0)
; — set mechanical limits —
model mechanical substep 100
model mechanical follower on
model fluid substep 10
; — histories —
model history fluid time-total
zone history pore-pressure position (0,0,0)
zone history pore-pressure position (0,0,1.275)

zone history displacement-y position (0,10,0)
zone history displacement-y position (0,10,1.275)
; — solve to 3,000,000 sec —
[global t0 = time.clock/100]
model solve fluid time-total 3.0e8 or mechanical convergence 10
[(time.clock/100)-t0]
model save ‘SE_END_6’
program return

The obtained pore pressure curve is below.

I am unsure why the pore pressure is being constant and then increasing initially. Ideally it is supposed to decrease right?
Where and what do I have to modify in the code to set my problem right?

Thanks in advance.

The reason is that you used a logarithmic scale on the x-axis. If we use a normal time scale, we will observe reasonable results (I did not run it completely):

If running to the end, the plot looks

It is absolutely numerically reasonable.