Emir José Macari

Implicit integration of elastoplastic constitutive models for frictional materials with highly non-linear hardening functions

Constitutive relations in elastoplasticity may be formulated in a variety of ways, and different update algorithms may be employed to solve the resulting equations. Several implicit integration schemes, although some not widely used, have been suggested in the last years. Among them, the closest point projection method (CPPM) has proven to be an effective and robust integration scheme. In order to gain maximum control of the stress projection, a two-level CPPM iteration scheme is proposed. The hardening variables are fixed during the stress projection onto consequently fixed yield surfaces, and after the stress projection, new values of the hardening variables are calculated defining new yield surfaces. The update of the hardening parameters which, in general, may be highly nonlinear functions, may be determined by a combination of a Picard Iteration (PI) on the hardening variables and an adaptative order inverse interpolation (AOII) on the difference of subsequent iterations of the hardening variables. The integration scheme has been implemented in a general constitutive driver which has been formulated independent of the selected constitutive model and easily linked to finite element codes. A third stress invariant dependent, cone–cap elastoplastic constitutive model, referred to as the MRS–Lade, with a highly non-linear hardening function has been used to show the applicability of the proposed iteration scheme. Error analyses and accuracy assessment are presented along with some representative test results.

Internal Erosion and Rehabilitation of an Earth-Rock Dam

This paper describes an earth-rock dam whose filters’ characteristics did not comply with the design criterion. In addition, the degree of compaction and the water content in the impervious core consisted of highly plastic residual clay. Although Terzaghi’s filter design criterion was used, the as-built grain size distribution did not comply with such criterion. Several problems arose right after the first filling of the dam, including the following: (1) water leak at a rate of 200 L/s was observed along the downstream slope, in the vicinity of the outlet pipeline; the dark color of the observed water implied that the core material was being eroded; (2) two sinkholes near the crest (20 m apart) were observed along the outlet axis, one on the upstream and the other on the downstream slopes; right after the occurrence of these two sinkholes, the water leakage decreases significantly, noticing a plugged effect of the material that falls down through the sinkholes. To avoid piping, a notch was installed on th...

Constitutive modeling of unsaturated soil behavior under axisymmetric stress states using a stress/suction-controlled cubical test cell

Abstract Two elasto-plastic critical state-based formulations for modeling the constitutive behavior of an unsaturated soil are presented and briefly discussed. Computational constitutive drivers were implemented to allow for the numerical simulation of suction-controlled conventional triaxial tests. Simulations were obtained from explicit and implicit integration techniques. The algorithms support numerical analyses in a deviatoric stress plane by using a mixed control constitutive driver in conjunction with a generalized cam-clay model, within a constant-suction scheme. The results from a series of suction-controlled conventional triaxial tests conducted on several identically prepared, 10-cm side, cubical specimens of compacted silty sand, using a recently developed stress/suction-controlled cubical testing device, were used for validation of the models and the enhanced features proposed in the present work. Matric suction states in the specimens were induced and maintained constant during testing by using the axis-translation technique.

Selection and Calibration of Soil Constitutive Model Paramaters Using Genetic Algorithms

This paper presents the results of a study that uses an innovative numerical method called the genetic algorithm for material parameter optimization in constitutive modeling. A genetic algorithm based hybrid method of obtaining material parameters is used to optimize material parameters of a disturbed state concept based constitutive model. The genetic algorithm and the new fitness function were found to be capable of optimizing material parameters of complex constitutive models.