A kinematic hardening constitutive model for natural clays with loss of structure

Abstract

A rate-independent constitutive model for natural clays is presented, formulated within the framework of kinematic hardening with elements of bounding surface plasticity. The modelling framework is intended to include effects of damage to structure caused by irrecoverable plastic strains caused by sampling, laboratory testing, or geotechnical loading. The incorporation of a structure measure allows the size of the bounding surface to decay with plastic deformations. This model can be seen as a logical extension from the Cam-clay model. The steady fall of stiffness with strain towards the Cam-clay value is controlled by a particular interpolation function. This ensures a smooth degree of approach between a kinematically hardening bubble (which is the boundary of the elastic region) and the bounding surface during their relative translation with stress history. The model describes the essential phenomena of pre-failure behaviour of natural clays: stiffness variation with strain, volumetric change accompanying distortion, peak strength at small strains. Illustrative numerical results for common geotechnical experiments on a low-sensitivity Swedish clay demonstrate the potential of the proposed model.

Compaction Bands and Oedometric Testing in Cemented Soils

“…Several optimization strategies, either formal (e.g. Rouainia and Wood, 2000) or informal, may be employed to obtain a good match to a series of selected results, but ample test databases are not always available and it is therefore desirable to have calibration procedures as straightforward as possible. Of the plastic functions that are employed to build the model (plastic potential, yield and hardening functions) some are easier to calibrate than others.…”

Comparison of Predictive Capabilities of Selected Elasto-Plastic and Hypoplastic Models for Structured Clays

“…The structure-related parameters k, A, and s f /s ep f were calibrated by direct evaluation of experimental data on natural Pisa clay. The approach used for their calibra- Rouainia and Muir Wood (2000). When compared with the SMCC model, the kinematic hardening model takes into account non-linearity of soil behaviour inside the state boundary surface, small-strain stiŠness anisotropy, non-circular cross section of the yield locus in the octahedral plane and fabric anisotropy, which is included through rotated shape of the SBS.…”

“…This model requires the same number of soil parameters with equivalent physical interpretation as the hypoplastic model of interest. Second, predictions by hypoplasticity are compared with predictions by advanced elasto-plastic models based on kinematic hardening approach (Baudet and Stallebrass, 2004;Rouainia and Muir Wood, 2000). These models require larger number of material constants, but they provide more realistic predictions of non-linear soil behaviour than the basic elasto-plastic critical state models.…”

Simplifying calibration of bonded elasto-plastic models

“…Taking a different perspective, a number of researchers have successfully extended elasto-plastic models for soils of the critical state tradition to represent artificially cemented clays [5] and silts [6]. This approach is directly inspired by a long line of constitutive models originally developed for naturally structured soils and soft rocks ( [7], [8] , [9], [10]) Despite all those developments it is fair to say that simplified, elastic perfectly plastic models (with either a Mohr-Coulomb or Tresca failure criterion) still dominate numerical applications (e.g. [11], [12]).…”