FLAC3D Theory and Background • Constitutive Models
Comparison between Mohr-Coulomb Model and Plastic-Hardening model
Note
To view this project in FLAC3D, use the menu command . The project’s main data files are shown at the end of this example.
This example compares the behavior of the Plastic-Hardening (PH) model and Mohr-Coulomb (MC) model during the triaxial compression. Both models are used in a one-zone triaxial compression test with a constant cell pressure of 100 kPa. The strength parameters (including friction angle, dilation angle, and tension limit) are the same for both models. The \(E_{50}\) stiffness of the PH model is used as Young’s modulus for the MC model and \(E^{ref}_{ur}\) is assumed to be three times the value of \(E^{ref}_{50}\). Material properties for this example are summarized in Table 1. Material parameters not listed in the table are default values.
Parameters |
PH |
MC |
\(\phi\) (degrees) |
30 |
30 |
\(c\) (kPa) |
0 |
0 |
\(\psi\) (degrees) |
10 |
10 |
\(E^{ref}_{50}\) (kPa) |
2e4 |
|
\(E\) (kPa) |
2e4 |
|
\(\nu\) |
0.2 |
0.2 |
\(E^{ref}_{ur}\) (kPa) |
6e4 |
|
\(m\) |
0.6 |
|
\(R_f\) |
0.9 |
|
\(p^{ref}\) (kPa) |
100 |
|
\(\sigma^{ini}_{1 \sim 3}\) (kPa) |
-100 |
Figure 1 shows a plot deviatoric stress versus axial strain for both PH and MC models. It is easy to verify the following from the figure:
The ultimate failure deviatoric stresses (200 kPa) are the same for both models, as expected.
For the pre-failure curve, the PH and MC models are crossing at the half of the failure stress (100 kPa), which is consistent with the concept of \(E_{50}\) stiffness.
The unloading stiffness in the MC model is the same as the loading stiffness (\(E\) in the MC model, or \(E_{50}\) in the PH model), while these stiffnesses are different in the PH model.
![../../../../../_images/modelph-comparison.png](../../../../../_images/modelph-comparison.png)
Figure 1: Comparison of PH and MC models for a triaxial compression test.
Data Files
TriaxialCompressionPlasticHardening.dat
model new
model large-strain off
;
zone create brick size 1 1 1
zone cmodel assign plastic-hardening
zone property stiffness-50-reference=2.0e4 stiffness-ur-reference=6.0e4 ...
pressure-reference=100.0 exponent=0.6
zone property friction=30.0 dilation=10.0 cohesion=0.0
zone property stress-1-effective=-100.0 stress-2-effective=-100.0 ...
stress-3-effective=-100.0
;
zone gridpoint fix velocity-z
zone face apply stress-xx=-100.0 range union position-x 0 position-x 1
zone face apply stress-yy=-100.0 range union position-y 0 position-y 1
zone initialize stress xx -100.0 yy -100.0 zz -100.0
;
fish define hhhq_
local zp_ = zone.head
local gp_ = gp.find(8)
global hhhq_ = zone.stress.xx(zp_) - zone.stress.zz(zp_)
global hhha_ = -gp.disp.z(gp_)
end
history interval 10
fish history hhhq_
fish history hhha_
;
zone gridpoint initialize velocity-z -2e-6 range position-z 1
model step 10000
zone gridpoint initialize velocity-z 1e-6 range position-z 1
model step 1000
zone gridpoint initialize velocity-z -2e-6 range position-z 1
model step 10000
zone gridpoint initialize velocity-z 1e-6 range position-z 1
model step 1000
zone gridpoint initialize velocity-z -2e-6 range position-z 1
model step 10000
zone gridpoint initialize velocity-z 1e-6 range position-z 1
model step 1000
zone gridpoint initialize velocity-z -2e-6 range position-z 1
model step 20000
;
history export '1' vs '2' table 'ph_qs_100'
table 'ph_qs_100' export 'ph_qs_100' truncate
;
model save 'ph100'
TriaxialCompressionMohrCoulomb.dat
model new
model large-strain off
;
zone create brick size 1 1 1
zone cmodel assign mohr-coulomb
zone property young=2.0e4 poisson=0.2 friction=30 dilation=10
;
zone gridpoint fix velocity-z
zone face apply stress-xx=-100.0 range union position-x 0 position-x 1
zone face apply stress-yy=-100.0 range union position-y 0 position-y 1
zone initialize stress xx -100.0 yy -100.0 zz -100.0
;
fish define hhhq_
local zp_ = zone.head
local gp_ = gp.find(8)
global hhhq_ = zone.stress.xx(zp_) - zone.stress.zz(zp_)
global hhha_ = -gp.disp.z(gp_)
end
history interval 10
fish history hhhq_
fish history hhha_
;
zone gridpoint initialize velocity-z -2e-6 range position-z 1
model step 10000
zone gridpoint initialize velocity-z 1e-6 range position-z 1
model step 1000
zone gridpoint initialize velocity-z -2e-6 range position-z 1
model step 10000
zone gridpoint initialize velocity-z 1e-6 range position-z 1
model step 1000
zone gridpoint initialize velocity-z -2e-6 range position-z 1
model step 10000
zone gridpoint initialize velocity-z 1e-6 range position-z 1
model step 1000
zone gridpoint initialize velocity-z -2e-6 range position-z 1
model step 20000
;
history export '1' vs '2' table 'mc_qs_100'
table 'mc_qs_100' export 'mc_qs_100' truncate
;
model save 'mc100'
⇐ Drained Triaxial Compression Test with Simplified Cap-Yield (CHSoil) Model | Comparison of Plastic-Hardening Model without and with Small-Strain Stiffness ⇒
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