PLAXIS LIQUEFACTION MODEL UBC3D-PLM - Knowledge Base

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Acceleration (m/sec^2)2.521.510.50-0.5 0 5 10 15 20 25 30 35-1-1.5-2-2.5Time (sec)Figure 3.3: Total dynamic loading time 33 seconds. 50 loading cycles. Theamplitude of acceleration equals 1.96 m/s 2 . The frequency equalas 1.5 Hz.are extracted after calibration of UBCSAND with experimental data. Theuse of them in UBC3D-PLM should always be followed from a verificationprocess with specific experimental results. The parameters are summarizedin Table 3.1. The consolidation phase is calculated with a K 0 procedure inPLAXIS. The K 0 assumed 0.5 for this case.φ p ( ◦ ) φ c ( ◦ ) KB e KG e K p G me = ne np R f N1 60 fac hard34 31 721 1031 700 0.5 0.4 0.74 10 0.7Table 3.1: Input parameters for modelling the dynamic centrifuge.The post post liquefaction factor fac post equals 0.6.3.2 Results and discussionFigure 3.4 presents the predicted acceleration during the test both in thephysical and in the numerical model. The numerical results are adequatelyaccurate at a lower depth but the residual acceleration which is mobilizedin the soil in the deeper layers does not represent the real soil behaviourobserved in the physical model. During this project the influence of theelasticity parameters on the propagation of the shear waves has also been36
checked but the results are not further improved. The residual accelerationin the soil is most likely due to rigid base used for the modelling.Figure 3.5 presents the predicted accumulation of the excess pore pressureand the comparison with the experimental result. At 13.1 meters depththe numerical prediction shows a very good agreement with the results fromthe physical model. It can be seen that initially in the experiment the dynamicloading starts a bit later from the numerical calculation but the slopesof both curves are almost identical. That means that the behaviour of theconstitutive model is very accurate for this case. The maximum effectivestress mobilized during consolidation in the experiment is higher than theprediction, however, a small deviation in the input parameters for this soilis highly likely. It can be concluded that the UBC3D-PLM can predict theonset of liquefaction with adequate accuracy for this depth.At 24.8 meters depth the onset of liquefaction is again predicted with adequateaccuracy, however, the model predicts a much more rapid evolutionof the excess pore pressure than the observed evolution during the experiment.The evolution of the excess pore pressure becomes slower after thefirst cycles and finally the onset of liquefaction is predicted in approximately10 seconds which is a very good representation of the behaviour observed inthe experiment. The maximum vertical effective stress which is predictedby PLAXIS during consolidation is slightly lower also for this depth.At 30.8 meters depth the onset of liquefaction is predicted in 10 secondswhich also represents the observed soil behaviour. However, the inaccuracyin the evolution of the excess pore pressure becomes higher for higher depth.The accumulation of excess pore pressures is overestimated in the initialcycles by the UBC3D-PLM. The final accumulated excess pore pressuresare also overestimated by PLAXIS but the onset of liquefaction is againpredicted with adequate accuracy for this case.It is concluded by the comparison of the experimental with the numericalresults that the stress densification rule plays a significant role. This leads37
Page 1: PLAXIS LIQUEFACTION MODELUBC3D-PLMA
Page 5 and 6: 3.6 Reproduced stress path in p ′
Page 7 and 8: AbstractIn this report the formulat
Page 9 and 10: Comparing with the previous version
Page 11 and 12: Figure 1.2: Projection of the yield
Page 13 and 14: ( ) mepK = KBP e A (1.9)P ref( ) ne
Page 15 and 16: The plastic potential function is f
Page 17 and 18: the secondary loading in order to e
Page 19 and 20: loading surface is used again. A ne
Page 21 and 22: The drained bulk modulus of the soi
Page 23 and 24: modelling the inherent and induced
Page 25 and 26: Table 1.1: Input Parameters for the
Page 27 and 28: whereas the P P RMAX can reveal if
Page 29 and 30: Chapter 2Validation of the UBC3D in
Page 31 and 32: Pore Pressure, u (kPa)UBC3DEx.Pore.
Page 33 and 34: first cycle of post-liquefaction be
Page 35 and 36: Shear Stress , τ (kPa)1086420-2-4-
Page 37 and 38: 1.2Excess Pore Pressures\nitial Ver
Page 39 and 40: Chapter 3Validation of theUBC3D-PLM
Page 41: Figure 3.2: The finite element mesh
Page 45 and 46: used again when the stress path exc
Page 47 and 48: EPP (kPa)EPP (kPa)EPP (kPa)Measurem
Page 49 and 50: Figure 3.8: Reproduced stress path
Page 51: S.S. Park and P.M. Byrne. Practical

PLAXIS LIQUEFACTION MODEL UBC3D-PLM - Knowledge Base

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