Directional response of a reconstituted fine-grained soil—Part I: experimental investigation

Abstract

SUMMARYThis paper discusses the results of a large experimental program designed to investigate in a systematic manner the main features of the incremental response of fine-grained soils. The results are obtained from triaxial stress probing experiments carried out on a French silty clay (Beaucaire Marl). All the tests have been performed on reconstituted specimens, normally consolidated to an initial state which is either isotropic or anisotropic. In the interpretation of the experimental results, extensive use is made of the concept of strain response envelope. The response envelopes obtained for different stress increment magnitudes are remarkably consistent with each other and indicate an inelastic and irreversible material response, i.e. a strong dependence on the stress increment direction, also at relatively small strain levels. A companion paper (Int. J. Numer. Anal. Meth. Geomech., this issue, 2006) assesses the performance of some advanced constitutive models in reproducing the behaviour of reconstituted Beaucaire Marl as observed in this experimental program.

State boundary surface of a hypoplastic model for clays

“…An inverse procedure with constantT and fixed length stress increments R Dr , constituting in the strain space incremental strain response envelopes, was applied experimentally by Royis and Doanh [30] for sand and Costanzo et al [6] for clays. These results were followed by numerical investigations using DEM with rigid spheres [3] and used for evaluation of predictive capabilities of different constitutive models [23,33].…”

Directional response of a reconstituted fine-grained soil—Part II: performance of different constitutive models

“…Therefore, the observed shape of the experimental REs might be affected to some extent by the unavoidable scatter always present in experimental measurements. Second, the occurrence of small amounts of viscous strains may affect both size and shape of the measured response envelopes, even if to a limited extent, see Costanzo et al (2006). Interpreting the observed response in light of rate-independent constitutive theories might therefore lead to an underestimation of soil stiffness for some probe directions and to an overestimation of soil stiffness for other probe directions, as thoroughly discussed in the companion paper (Costanzo et al, 2006).…”

“…The stress-probing tests were performed on reconstituted material, consolidated in a large consolidometer up to a nominal vertical effective stress of 75 kPa. Full details of the experimental procedures employed in the testing program are given by Costanzo et al (2006).…”

“…In trying to compare the performances of the different models, the experimental data of Costanzo et al (2006) have been considered as portraying the actual mechanical response of the soil. However, two main points should be stressed in this respect.…”

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SUMMARYIn this paper, the performance of different advanced constitutive models for soils is evaluated with respect to the experimentally observed behavior of a soft reconstituted clay subject to a wide range of loading directions, see Costanzo et al (2006). The models considered include a three-surface kinematic hardening elastoplastic model (Stallebrass, 1990)

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