# Pore pressure curve - consolidation **URL:** \ **Category:** FLAC3D\ **Created:** [January 24, 2025, 5:30am UTC](https://forum.itascainternational.com/t/pore-pressure-curve-consolidation/1913 "2025-01-24T05:30:07Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![sowmyaramanis](https://avatars.discourse-cdn.com/v4/letter/s/839c29/32.png) [@sowmyaramanis](https://forum.itascainternational.com/u/sowmyaramanis)\ **Post date:** [January 24, 2025, 5:30am UTC](https://forum.itascainternational.com/t/pore-pressure-curve-consolidation/1913/1 "2025-01-24T05:30:07Z")
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. ![image](https://canada1.discourse-cdn.com/flex031/uploads/itasca/original/2X/3/38c5ccf72b4bfac5dfcef95f25fb95eeb9d690e6.png) ![image](https://canada1.discourse-cdn.com/flex031/uploads/itasca/original/2X/3/3b2d613dd7bf4f394ca3095b2e5644905851eb9a.png) ![image](https://canada1.discourse-cdn.com/flex031/uploads/itasca/original/2X/6/6264b2480aa613ded2eaebda41e39372a391eba3.png) Thanks in advance. ---
**Author:** ![cheng](https://avatars.discourse-cdn.com/v4/letter/c/ecccb3/32.png) [@cheng](https://forum.itascainternational.com/u/cheng)\ **Post date:** [January 24, 2025, 8:58pm UTC](https://forum.itascainternational.com/t/pore-pressure-curve-consolidation/1913/2 "2025-01-24T20:58:17Z")
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? ---
**Author:** ![sowmyaramanis](https://avatars.discourse-cdn.com/v4/letter/s/839c29/32.png) [@sowmyaramanis](https://forum.itascainternational.com/u/sowmyaramanis)\ **Post date:** [January 26, 2025, 3:57am UTC](https://forum.itascainternational.com/t/pore-pressure-curve-consolidation/1913/3 "2025-01-26T03:57:54Z")
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. ![image](https://canada1.discourse-cdn.com/flex031/uploads/itasca/original/2X/8/878dcf9cdd781c5e99271f300afc515881d98357.png) 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. ---
**Author:** ![cheng](https://avatars.discourse-cdn.com/v4/letter/c/ecccb3/32.png) [@cheng](https://forum.itascainternational.com/u/cheng)\ **Post date:** [January 27, 2025, 8:22pm UTC](https://forum.itascainternational.com/t/pore-pressure-curve-consolidation/1913/4 "2025-01-27T20:22:26Z")
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): ![a](https://canada1.discourse-cdn.com/flex031/uploads/itasca/original/2X/0/0411198cc06251ad8c1dfee52138cca56a1e785a.png) ---
**Author:** ![cheng](https://avatars.discourse-cdn.com/v4/letter/c/ecccb3/32.png) [@cheng](https://forum.itascainternational.com/u/cheng)\ **Post date:** [January 28, 2025, 3:43pm UTC](https://forum.itascainternational.com/t/pore-pressure-curve-consolidation/1913/5 "2025-01-28T15:43:42Z")
If running to the end, the plot looks ![b](https://canada1.discourse-cdn.com/flex031/uploads/itasca/original/2X/8/832e98f175b974d01a0b72eeccd577bdd089790d.png) It is absolutely numerically reasonable. ---
**Author:** ![sowmyaramanis](https://avatars.discourse-cdn.com/v4/letter/s/839c29/32.png) [@sowmyaramanis](https://forum.itascainternational.com/u/sowmyaramanis)\ **Post date:** [February 11, 2025, 3:56pm UTC](https://forum.itascainternational.com/t/pore-pressure-curve-consolidation/1913/6 "2025-02-11T15:56:38Z")
Hello cheng. For the above problem, if I have to apply an incremental loading(i.e. 20 kPa for first 2 hrs, then 40 kPa for the next 4 hrs and 60 kPa for the next 8 hrs), how should the code be writtern? I could not find any example code for the incremental loading for the consolidation. Can you help me with this? ---
**Author:** ![cheng](https://avatars.discourse-cdn.com/v4/letter/c/ecccb3/32.png) [@cheng](https://forum.itascainternational.com/u/cheng)\ **Post date:** [February 11, 2025, 10:38pm UTC](https://forum.itascainternational.com/t/pore-pressure-curve-consolidation/1913/7 "2025-02-11T22:38:56Z")
You can use the command “zone face apply stress-normal xx” on the same faces at different times, each time it will overwrite the previous apply. ---
**Author:** ![sowmyaramanis](https://avatars.discourse-cdn.com/v4/letter/s/839c29/32.png) [@sowmyaramanis](https://forum.itascainternational.com/u/sowmyaramanis)\ **Post date:** [February 13, 2025, 3:06am UTC](https://forum.itascainternational.com/t/pore-pressure-curve-consolidation/1913/8 "2025-02-13T03:06:59Z")
zone face apply stress-normal 20e3 range position-y 10 model solve time-total 7200 zone face apply stress-normal 40e3 range position-y 10 model solve time-total 21600 zone face apply stress-normal 60e3 range position-y 10 model solve time-total 36000 zone face apply stress-normal 80e3 range position-y 10 model solve time-total 43200 Is this how you meant? ---
**Author:** ![sowmyaramanis](https://avatars.discourse-cdn.com/v4/letter/s/839c29/32.png) [@sowmyaramanis](https://forum.itascainternational.com/u/sowmyaramanis)\ **Post date:** [February 22, 2025, 5:06am UTC](https://forum.itascainternational.com/t/pore-pressure-curve-consolidation/1913/9 "2025-02-22T05:06:22Z")
Is there any examples available in FLAC3D were the incremental load is applied similar to the one I mentioned above? ---
**Author:** ![dblanksma](https://avatars.discourse-cdn.com/v4/letter/d/858c86/32.png) [@dblanksma](https://forum.itascainternational.com/u/dblanksma)\ **Post date:** [February 24, 2025, 4:00pm UTC](https://forum.itascainternational.com/t/pore-pressure-curve-consolidation/1913/10 "2025-02-24T16:00:26Z")
@sowmyaramanis, The **zone face apply** commands you posted earlier are fine. Here’s a good example that does sequential loading. [Pile-Supported Highway Embankment — Itasca Software 9.3 documentation](https://docs.itascacg.com/itasca930/flac3d/zone/test2d/ExampleApplications/FromFLAC/14HighwayEmbankment/HighwayEmbankment.html?node4259). ---
**Author:** ![sowmyaramanis](https://avatars.discourse-cdn.com/v4/letter/s/839c29/32.png) [@sowmyaramanis](https://forum.itascainternational.com/u/sowmyaramanis)\ **Post date:** [February 27, 2025, 5:18pm UTC](https://forum.itascainternational.com/t/pore-pressure-curve-consolidation/1913/11 "2025-02-27T17:18:11Z")
I am working on a consolidation analysis of soft soil improved by deep mixing columns. The load is incremented step wise i.e, I have applied 20 kPa for 1 day, 40 kPa for the next 1 day, 60kPa for the next 3 days and finally 80 kPa for the next 6 days. The problem is the time it takes to run the code. Its been 2 days but even the first load solving itself haven’t completed yet. I have attached the code as well here. Kindly let me know what modification can be done in the code or how can the code be improvised further to speed up the simulation. Thanks in advance. Dat file: model new model large-strain off model title ‘horpibuksul2012’ model configure fluid zone create cylinder point 0 (0,0,0) point 1 (0.15,0,0) point 2 (0,0.0375,0) point 3 (0,0,0.15) size 4 1 4 group ‘sand\_bottom’ zone create cylinder point 0 (0,0.0375,0) point 1 (0.15,0.0375,0) point 2 (0,0.2375,0) point 3 (0,0.0375,0.15) size 4 4 4 group ‘soil’ zone create cylinder point 0 (0,0.2375,0) point 1 (0.15,0.2375,0) point 2 (0,0.275,0) point 3 (0,0.2375,0.15) size 4 1 4 group ‘sand\_top’ zone group ‘column’ range cylinder end-1 (0 0.0375 0) end-2 (0 0.2375 0) radius 0.025 zone property density 17000 range group ‘soil’ zone property density 14000 range group ‘column’ zone property density 18500 range group ‘sand\_bottom’ zone property density 18500 range group ‘sand\_top’ ; — mechanical model — zone cmodel assign m-c range group ‘column’ zone property young 120e6 poisson 0.3 cohesion 600e3 friction 25 range group ‘column’ zone cmodel assign s-s range group ‘soil’ zone property cohesion 1e3 friction 21 k-m 0.0095 l-m 0.095 poisson 0.3 range group ‘soil’ zone property stress-1-eff -20e3 stress-2-eff -10e3 stress-3-eff -10e3 zone cmodel assign m-c range group ‘sand\_bottom’ zone property young 52e6 poisson 0.3 cohesion 1e3 friction 37 range group ‘sand\_bottom’ zone cmodel assign m-c range group ‘sand\_top’ zone property young 13e6 poisson 0.3 cohesion 1e3 friction 37 range group ‘sand\_top’ 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” zone initialize stress-yy -20e3 zone initialize stress-xx -10e3 zone initialize stress-zz -10e3 ; — fluid flow model — zone fluid cmodel assign anisotropic zone fluid property perm-xx 3e-11 perm-yy 1e-11 perm-zz 3e-11 range group ‘soil’ zone fluid property perm-xx 3e-9 perm-yy 1e-9 perm-zz 3e-9 range group ‘column’ zone fluid property perm-xx 5.83e-10 perm-yy 5.83e-10 perm-zz 5.83e-10 range group ‘sand\_bottom’ zone fluid property perm-xx 5.83e-10 perm-yy 5.83e-10 perm-zz 5.83e-10 range group ‘sand\_top’ zone gridpoint initialize fluid-modulus 9e8 ; — pore pressure fixed at zero at the surface — zone gridpoint fix pore-pressure 0 range position-y 0.275 model fluid active off zone fluid fastflow on model solve convergence 1 ; — turn on fluid flow model — model fluid active on zone gridpoint initialize velocity (0,0,0) zone gridpoint initialize displacement (0,0,0) ; — set mechanical limits — model mechanical substep 1 model mechanical follower on model fluid substep 1 ; — histories — model history name ‘time’ fluid time-total zone history name ‘disp1’ displacement-y position (0.04,0.275,0.08) zone history name ‘disp2’ displacement-y position (0.08,0.275,0.02) zone history name ‘pp1’ pore-pressure position (0.05,0.057,0.05) zone history name ‘pp2’ pore-pressure position (0.1,0.057,0.1) zone history name ‘pp3’ pore-pressure position (0.05,0.087,0.05) zone history name ‘pp4’ pore-pressure position (0.1,0.087,0.1) zone history name ‘pp5’ pore-pressure position (0.05,0.210,0.05) zone history name ‘pp6’ pore-pressure position (0.1,0.210,0.1) zone history name ‘stress1’ stress-yy position (0,0.2375,0) zone history name ‘stress2’ stress-yy position (0.092,0.2375,0.092) model fluid timestep fix 4e-3 model fluid list ;incremental loading zone face apply stress-normal -20e3 range position-y 0.275 model solve fluid time 86400 ; Run for 1 day (86400 seconds) zone face apply stress-normal -40e3 range position-y 0.275 model solve fluid time 86400 ; Run for 1 more day zone face apply stress-normal -60e3 range position-y 0.275 model solve fluid time 259200 ; Run for 3 days zone face apply stress-normal -80e3 range position-y 0.275 model solve fluid time 518400 ; Run for 8 days ---
**Author:** ![Kasra](https://avatars.discourse-cdn.com/v4/letter/k/e95f7d/32.png) [@Kasra](https://forum.itascainternational.com/u/Kasra)\ **Post date:** [April 30, 2025, 3:58pm UTC](https://forum.itascainternational.com/t/pore-pressure-curve-consolidation/1913/13 "2025-04-30T15:58:36Z")
@cheng My model should be placed under 10 m of the sea water level. In other words, I am going to model the seabed and pondering about fluid boundary condition on the top (Z=-10), on the bottom (Z=-50) and sides X=30 and X=-30 and Y=-30 and Y=30. I want to analyse my problem using the couple mode. Please guide me about fluid boundaries. Thanks so much. ---
**Author:** ![cheng](https://avatars.discourse-cdn.com/v4/letter/c/ecccb3/32.png) [@cheng](https://forum.itascainternational.com/u/cheng)\ **Post date:** [April 30, 2025, 4:09pm UTC](https://forum.itascainternational.com/t/pore-pressure-curve-consolidation/1913/14 "2025-04-30T16:09:28Z")
You need to fix or apply the pore pressure at the seabed surface > zone gridpoint fix pore-pressure … **or** > zone face apply pore-pressure … **AND** the static water pressure needs to be applied: > zone face apply stress-normal [value] gradient (0,0,-g) [range of seabed surface] ---
**Author:** ![Kasra](https://avatars.discourse-cdn.com/v4/letter/k/e95f7d/32.png) [@Kasra](https://forum.itascainternational.com/u/Kasra)\ **Post date:** [April 30, 2025, 11:26pm UTC](https://forum.itascainternational.com/t/pore-pressure-curve-consolidation/1913/15 "2025-04-30T23:26:49Z")
@cheng Thanks. And for other boundaries? Side boundaries and the lower horizontal boundary? Do they need to be fixed ? About fixing pp on the top boundary, even after that, the pore pressure change due to the condolidation. Just, the surface pore pressure remains without change becuse we have fixed the pore pressure for the face and not zone .