Problem with tensile strenght assignment in FLAC 8.0

FLAC
1

Hi all,

I’m setting up a thermo-mechanical analysis in FLAC 8.0 for the study of a slope.
I’ve ran a first elastic solve (VT_j_el.sav) considering an unbalanced force of 0.01N.
Now it’s time for the rheological model uploading in which I consider a tensile strenght (ten) differentiated between a certain value for the rock mass (i.e., 2.2E5) and a value of 5E3 for some gridpoints (reported in the code as JOINT n).
Here it is the code:

;------------RESTORE ELASTIC SOLVE
restore D:\Flac\ventotene\termico\VT_j_el.sav

;------------INIZIAL. DISPL. & VELOCITIES
initial xdisp 0 ydisp 0
initial xvel 0 yvel 0

;------------------------UPLOAD RHEOLOGICAL MODEL
;------------ROCK MATRIX
m mohr reg 100 100
prop den 1750 bu 2E8 sh 5.75E8 coh 8.66E5 ten 2.2E5 fri 29 dil 0.0 reg 100 100

;------------JOINTS
;------------J3
m mohr i 224 j 172 354
prop den 1750 bu 2E8 sh 8E6 coh 4.8E3 ten 5E3 fri 44 dil 0.0 i 224 j 172 354

;------------J2
m mohr i 203 j 172 406
prop den 1750 bu 2E8 sh 8E6 coh 4.8E3 ten 5E3 fri 44 dil 0.0 i 203 j 172 406

;------------J1
m mohr i 191 j 172 406
prop den 1750 bu 2E8 sh 8E6 coh 4.8E3 ten 5E3 fri 44 dil 0.0 i 191 j 172 406

;------------------------ELASTO-PLASTIC SOLVE
;------------NO THERMAL TIME
set mech on thermal off

;------------GRID DEFORMATION OK
set large

;------------UNB. FORCE SETTING (0.05N)
solve force 0.05 sratio 0

;------------SAVE
save D:\Flac\ventotene\termico\VT_j_ep.sav

During the solve cycle, the distribution of displacements is completely anomalous. In addition, it appears that the tensile strength values of the joints are also attributed to a band in the middle of the model and some other areas:

Cattura
Cattura1225×972 114 KB

Cattura2
Cattura21224×980 96.9 KB

Cattura3
Cattura31227×980 94 KB

The same result is shown once the solve is completed.
Does anyone have an idea what the problem might be?

2

You may create a plasticity plot to check the plasticity state, please note in FLAC, once the tension limit is reached, the tensile strength will be set to zero. Also, to get a better results, at least 2-3 zones should be used to represent the joints instead of only 1 zone in your model.

3

Thank you for the response!

Here it is the plasticity plot:

Immagine 2024-06-26 102939
Immagine 2024-06-26 102939805×574 51.4 KB

The points are yield in past.
How is it possibile a concentration of yielded points in the middle of the domain (the alignment of yielded points on the right) ? It doesn’t make sense.

4

Same is also after implementing the zones referred to the joints (no more 1 zone per joint but 2):

IMG-20240627-WA0012
IMG-20240627-WA0012897×562 69.7 KB

This is the implemented code:

;------------RESTORE ELASTIC SOLVE

restore D:\Flac\ventotene\termico\VT_j_el.sav

;------------INIZIAL. DISPL. & VELOCITIES
ini xdisp 0
ini ydisp 0
ini xvel 0
ini yvel 0

;------------------------UPLOAD RHEOLOGICAL MODEL
;------------ROCK MATRIX
m mohr reg 100 100
prop den 1750 bu 2E8 sh 5.75E8 coh 8.66E5 ten 2.2E5 fri 29 dil 0.0 reg 100 100

;------------JOINTS
;------------J3
m mohr i 223 224 j 172 354
prop den 1750 bu 2E8 sh 8E6 coh 4.8E3 ten 5E3 fri 44 dil 0.0 i 223 224 j 172 354

;------------J2
m mohr i 202 203 j 172 406
prop den 1750 bu 2E8 sh 8E6 coh 4.8E3 ten 5E3 fri 44 dil 0.0 i 202 203 j 172 406

;------------J1
m mohr i 190 191 j 172 406
prop den 1750 bu 2E8 sh 8E6 coh 4.8E3 ten 5E3 fri 44 dil 0.0 i 190 191 j 172 406

;------------------------ELASTO-PLASTIC SOLVE
;------------NO THERMAL TIME
set mech on thermal off

;------------GRID DEFORMATION OK
set large

;------------UNB. FORCE SETTING (0.05N)
solve force 0.05 sratio 0

;------------SAVE
save D:\Flac\ventotene\termico\VT_j_ep.sav

5

Please send your datafiles to flacsupport@itascacg.com, we can take a look.

6

I just sent the e-mail. Thanks!