Yade

Capillary model

Asked by Amiya Prakash Das

Hi

I am trying to model isotropic compression behavior of unsaturated soils. But when i am trying to simulate this behavior using capillary model i am getting higher void ratios even at higher matric suction (i.e. my yield stress is higher for lower matric suction). So, i am not able to realize whether the capillary model is getting invoked or not. And, moreover is there any way i can bench mark my code with some existing code or simulation.

Best
Amiya

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Solved by:
Jérôme Duriez
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Amiya Prakash Das (amiya0703) said : 		#1

# generate loose packing
from yade import pack, qt, plot

#some parameters:
young_modulus=5e6
friction = 0.5
angle = atan(friction)
local_damping = 0.01
viscous_normal = 0.021
viscous_shear = 0.8*viscous_normal
lowercorner = Vector3(0,0,0)
uppercorner = Vector3(.05,.05,.05)
key ='_triax_base_',

#creating a material (FrictMat):
O.materials.append(FrictMat(young=young_modulus,poisson=0.5,frictionAngle=angle,density=2600,label='spheres'))

#SphereMat=O.materials[id_SphereMat]
O.materials.append(FrictMat(young=young_modulus,poisson=0.5,frictionAngle=0,density=0,label='walls'))

#generate boundary:
walls=aabbWalls([lowercorner,uppercorner],thickness=0,material='walls')
wallIds=O.bodies.append(walls)

#generate particles:
sp=pack.SpherePack()

sp.makeCloud(lowercorner,uppercorner,.002,rRelFuzz=.3)
O.bodies.append([sphere(c,r,material='spheres') for c,r in sp])

triax=TriaxialStressController(thickness = 0,
          stressMask = 7,
          internalCompaction=False, # If true the confining pressure is generated by growing particles
                 goal1=-1e06,
                               goal2=-1e06,
                               goal3=-1e06,
                               max_vel=0.01,

)

#define engines:

O.engines=[
  ForceResetter(),
  InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_Box_Aabb()]),
  InteractionLoop(
   [Ig2_Sphere_Sphere_ScGeom(),Ig2_Box_Sphere_ScGeom()],
   [Ip2_FrictMat_FrictMat_CapillaryPhys()], #for linear model only
   [Law2_ScGeom_FrictPhys_CundallStrack()], #for linear model only
  ),
  Law2_ScGeom_CapillaryPhys_Capillarity(capillaryPressure=10000),#for linear model only
  GlobalStiffnessTimeStepper(active=1,timeStepUpdateInterval=100,timestepSafetyCoefficient=0.8),
                triax,
  NewtonIntegrator(damping=local_damping),
                PyRunner(command='addPlotData()',iterPeriod=100)
]

def addPlotData():
   plot.addData(
      i=O.iter,
      s11=-triax.stress(triax.wall_right_id)[0],s22=-triax.stress(triax.wall_top_id)[1],s33=-triax.stress(triax.wall_front_id)[2],
      e11=-triax.strain[0],e22=-triax.strain[1],e33=-triax.strain[2], poro=utils.porosity(), stress=-triax.meanStress,
               )

#set time step and run simulation:
O.dt=0.5*PWaveTimeStep()

plot.plots={'i ':('s11','s22','s33'),' i':('e11','e22','e33'), 'stress':('poro')}

#show the plot
plot.plot()

#save the plot
plot.saveDataTxt('Porosity.txt',vars=('i','s11','s22','s33','e11','e22','e33','poro','stress'))

from yade import qt
qt.View()
print('Press PLAY button')

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Best Jérôme Duriez (jduriez) said : 		#2

Hi,

To be sure the capillary model is invoked, I think the best is just to pick random interactions with O.interactions.nth(..) or the Inspector of the GUI (see "Inspect" button), and check if there is some capillary force, or not.

Regarding science itself and as a general remark (maybe not related to your goals), you may note that the mechanical consequences of partial saturation in the pendular regime may differ to what people usually have in mind from experiments with much higher saturation.

For instance, YADE capillary simulations typically should show a decrease of the apparent cohesion with increasing suction, contrary to what is classically stated (strength increases with suction). It just depends on what saturation regime you're looking at, literature experiments that actually consider the pendular regime confirm the strength decrease with suction in this regime (before a change in trends and an increase for higher saturations), see e.g. Pierrat et al., Powder Technology, 99(3), 1998

Jerome

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Amiya Prakash Das (amiya0703) said : 		#3

Thanks Jerome...i totally agree with the point you made.

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Amiya Prakash Das (amiya0703) said : 		#4

Thanks Jérôme Duriez, that solved my question.