EVALUATION OF FEM ENGINEERING PARAMETERS FROM INSITU TESTS

mahyarov · 11-12-2012, 09:02 PM

The purpose of this study was to take a critical look at insitu test methods (SPT, CPT, DMT, and PMT) as a means for developing finite element constitutive model input parameters. The first part of the research examined insitu test derived parameters with laboratory triaxial tests at three sites: Saunder's Creek, Archer Landfill, and SW Recreation Center. The triaxial tests on these sands were used to develop baseline input parameters. These parameters were verified by simulating the triaxial tests using two finite element codes. From these comparisons, the following conclusions were drawn: (1) FEM simulations of triaxial test stress-strain curves produced excellent results; (2) The hardening models (PLAXIS - Hardening Soil and PlasFEM - Sandler Dimaggio) simulated the nonlinear behavior better than the Mohr-Coulomb or Drucker-Prager models; (3) In general, E sub 50 triaxial test modulus values agreed with those estimated from DMT and PMT unloading tests; and (4) FEM simulations of field PMT curves using triaxial test based parameters were unsuccessful. The second phase of this study was to predict the deformations of a cantilevered sheet pile wall (unloading case), and the deformations of a 2-m diameter shallow footing (loading case). Conventional analysis methods were compared with FEM using insitu test derived input parameters. Conclusions were: (1) Conventional analyses (CWALSHT) under-predicted wall deformations unconservatively, while wall deflections were accurately predicted using the Hardening Soil Model with input parameters estimated from SPT correlations and "curved matched" PMT values; (2) Fundamentally, the stress history of a soil profile, i.e., OCR or preconsolidation pressure, must be known for any settlement prediction either using conventional or finite element methods; (3) Of the conventional methods for estimating settlements (CSANDSET), only the SPT based D'Appolonia, and Peck and Bazaraa methods provided reasonable estimates of the observed settlement; (4) The conventional DMT method, which correlates OCR values, slightly overestimated measured settlements; (5) None of the insitu test derived input parameters (SPT, CPT, DMT, and PMT) coupled with FEM Mohr-Coulomb or Hardening Soil models, accurately predicted the shallow footing settlements.

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