Hel needed: Simulation of Direct Shear Test

PFC
1

Subject: Help required for Direct Shear Test (DST) simulation in PFC2D with moving bottom box

I am trying to simulate a Direct Shear Test (DST) in PFC2D. I have been following the built-in PFC2D direct shear example, where:

wall servo command — PFC 6.0 documentation

  • Normal stress is applied through the top wall

  • The upper shear box is moved horizontally

However, my experimental setup is different:

  • Normal loading is applied on the top plate/wall

  • The bottom shear box moves horizontally, while the top box remains fixed

I am facing difficulties modifying the example according to my experimental configuration.

My main issues are:

  1. When I try to move the lower wall/box, I get errors such as:

    • "wall2 not found"

    • or the wall reference is not recognized

  2. I am unsure how to correctly:

    • Define separate upper and lower shear boxes

    • Apply horizontal velocity only to the bottom box

    • Keep the top box fixed while maintaining normal loading

  3. I would also like guidance on how to calculate:

    • Shear load vs horizontal displacement

    • Shear stress vs displacement curve

    • Normal displacement during shearing

  4. I am using a bonded particle assembly, and I would like to know:

    • What changes are needed in wall generation or wall grouping

    • Whether I should use wall IDs, wall names, or ranges

    • The proper method for servo-controlled normal loading while the lower box moves

My current understanding is:

  • Top wall → applies vertical stress

  • Bottom box → moves in horizontal direction

  • Need to monitor reaction force and displacement during shearing

I would appreciate:

  • Example PFC2D commands/scripts

  • Suggestions on modifying the built-in DST example

  • Best practices for calculating load–displacement response in DST simulations

Thank you very much for your help.

image
image1123×455 3.36 KB

model new
model large strain on
model title ‘Testing Bonded Particle Model’

; Set the domain extent
model domain extent -0.05 0.05 -0.1 0.1 condition destroy

contact cmat default model linear method deform emod 1.0e9 kratio 0.0
contact cmat default property dp_nratio 0.5

; create walls that extend past the edges of the sample
wall create vertices -0.03,0.0 -0.03,0.0175 id 1

wall create vertices -0.03,0.0175 0.03,0.0175 id 2

wall create vertices 0.03,0 0.03,0.0175 id 3
wall group ‘top’ range id 1 3
wall create vertices -0.03,0.0 -0.03,-0.0175 id 4

wall create vertices -0.03,-0.0175 0.03,-0.0175 id 5

wall create vertices 0.03,0 0.03,-0.0175 id 6
wall group ‘bot’ range id 4 6
wall create vertices -0.05,0.0 -0.03,0.0 id 7
wall group ‘topext’ range id 7
wall create vertices 0.03,0.0 0.05,0.0 id 8
wall group ‘botext’ range id 8
;[wp_left_top = wall.find(1)]
;[wp_right_top = wall.find(3)]
;[wp_bot = wall.find(5)]
;[wp_top = wall.find(2)]
;[wp_left_bot = wall.find(4)]
;[wp_right_bot = wall.find(6)]

model random 10001
ball distribute poros 0.35 …
resolution 0.04 …
radius 75e-6 4.75e-3 …
box -0.03 0.03 -0.0175 0.0175
ball attribute density 2500 damp 0.7
measure create id 1 rad [0.9*(math.min(0.03,0.0175))]
[porosity = measure.porosity(measure.find(1))]

; program call parallel bonded
contact cmat default model linearpbond property pb_ten 30.0e3 pb_coh 20.0e3 pb_fa 10.0 fric 0.5 kn 1e11 ks 1e7 …
method deformability emod 60e9 kratio 1 …;e10
method pb_deformability emod 60e9 kratio 1
contact model linearpbond range contact type ‘ball-ball’
contact method bond gap 0.5e-4

; excerpt-nrnz-start
; set linear stiffness
contact method deform emod 60.0e7 krat 1

; set stiffness of bond material
contact method pb_deform emod 60.0e7 krat 2.0
; excerpt-nrnz-end

; set bond strengths
contact property pb_ten 53.0e5 pb_coh 56.0e5 pb_fa 10

; set some damping at the contacts
contact property dp_nratio 0.5

; set ball-ball friction to non-zero value
contact property fric 0.718 range contact type ‘ball-ball’

; Reset ball displacement
ball attribute displacement multiply 0.0

; excerpt-eire-start
; Set linear force to 0.0 and force a reset of the linear contact forces.
contact property lin_force 0.0 0.0 lin_mode 1
ball attribute force-contact multiply 0.0 moment-contact multiply 0.0
; excerpt-eire-end
model gravity 10.0
model cycle 100 calm 10
model solve cycle 1000;ratio-average 1e-1
model mechanical time-total 0.0
model save ‘sb-init-dst’

; — activate servo on top wall to apply a target force
ball attribute displacement 0.0 0.0 damp 0.7
ball property ‘fric’ 0.5
[m=100.0] ; mass
[p=m*global.gravity()] ; force
wall servo force [p] activate on range set name ‘wall2’
model history name ‘1’ mechanical age
model history name ‘2’ mechanical ratio-average
wall history name ‘11’ displacement-x name ‘wall2’
wall history name ‘12’ displacement-y name ‘wall2’
wall history name ‘21’ force-contact-y name ‘wall2’
wall history name ‘22’ force-contact-x name ‘wall4’
wall history name ‘23’ force-contact-y name ‘wall4’
model solve cycle 1000
model save ‘sb-load-dst’

; — maintain servo on top wall but superimpose an orthogonal velocity
history purge
model mechanical time-total 0.0
ball attribute displacement 0.0 0.0
wall attribute displacement 0.0 0.0
wall attribute velocity-x 0.05 range group ‘bot’
model solve time 5.0
model save ‘sb-move-dst’
program return
return

2

Again, I cannot provide free support to debug your data file. You may wish to look at the PFC2D direct-shear test example that I use in the PFC & BPM Short Course. It works with PFC2D 9.6.46. I cannot provide further support for it. You can use it as is. The project can be downloaded from the link: ShareFile

PFC2D_ShearBox.pdf (1.2 MB)