FLAC3D Theory and Background • Constitutive Models

# Isotropic Consolidation Test with Modified Cam-Clay Model

Note

The project file for this example is available to be viewed/run in FLAC3D. The project’s main data file is shown at the end of this example.

This simple one-zone example exercises the modified Cam-Clay model for a normally consolidated material subjected to several load-unload excursions in an isotropic compression test. Following sentence doesn’t make sense. The initial stresses is at isotropic stress so that \(\sigma_{xx}\) = \(\sigma_{yy}\) = \(\sigma_{zz}\) = -5 kPa. The material properties include the following:

maximum shear modulus (\(G_{max}\)) |
10 MPa |

shear modulus (\(G\)) |
250 kPa |

ratio-critical state (\(M\)) |
1.02 |

slope of normal consolidation line (\(\lambda\)) |
0.2 |

slope of elastic swelling line (\(\kappa\)) |
0.05 |

pressure reference (\(p_1\)) |
1 kPa |

specific volume reference (\(v_{\lambda}\)) |
3.32 |

pressure consolidation (\(p_{c0}\)) |
-5 kPa |

The sample is assumed normally isotropic consolidation with \(OCR\) = 1, so the initial mean effective pressure and the preconsolidation pressure are the same. Their values are specified using a simple FISH function:

```
fish define camclay_ini_p
loop foreach local p_z zone.list
local mean_p = -(zone.stress.xx(p_z) + zone.stress.yy(p_z) ...
+ zone.stress.zz(p_z))/3.0 - z.pp(p_z)
zone.prop(p_z,'pressure-effective') = mean_p
zone.prop(p_z,'pressure-preconsolidation') = mean_p
endloop
end
```

The results are shown in Figure 1, 2, and 3. Figure 1 plots the mean effective pressure history. Figure 2 plots the relation \(v\) vs. \(\ln p\), which shows the normal consolidation line and elastic swelling lines. In this example, the shear modulus is explicitly specified as an input parameter; it is thus assumed constant, while the bulk modulus is changing with the mean effective pressure. The bulk and shear modulus histories are plotted in Figure 3.

Data File

**IsotropicConsolidationModifiedCamClay.dat**

```
;------------------------------------------------------------
; Isotropic compression test on Modified-Cam-clay sample (drained)
;------------------------------------------------------------
model new
model large-strain off
fish automatic-create off
model title "Isotropic compression test for normally consolidated soil"
zone create brick size 1 1 1
zone cmodel assign modified-cam-clay
; --- boundary and initial conditions ---
zone gridpoint fix velocity
zone initialize stress xx -5. yy -5. zz -5.
; --- model properties ---
zone property shear 250. bulk-maximum 10000.
zone property ratio-critical-state 1.02 lambda 0.2 kappa 0.05
zone property pressure-reference 1. specific-volume-reference 3.32
;
program call 'fishfunctions'
[camclay_ini_p]
; --- histories ---
history interval 20
fish history G
fish history K
fish history p
fish history lnp
fish history v
zone history displacement-z position 0 0 1
; --- test ---
[loadingunloading]
model save 'camiso'
```

⇐ Isotropic Consolidation Test with Double-Yield Model | Triaxial Compression Test with Hoek-Brown Model ⇒

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