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The results of a study with undrained cyclic triaxial and direct simple shear (DSS) tests on high-quality undisturbed samples obtained from large blocks of a soft marine Norwegian clay are presented. Several tests with different average shear stresses, shear stress amplitudes, loading frequencies, and sample geometries have been performed on block samples taken from different depths. In tests with small average shear stresses, failure occurred due to large shear strain amplitudes, while large permanent shear strains were observed in tests with higher average shear stresses. Diagrams quantifying the undrained cyclic strength, permanent shear strain, shear strain amplitude, and permanent pore-water pressure dependent on average shear stress, shear stress amplitude, and number of cycles have been developed based on the test results. The undrained cyclic strength was found strongly dependent on loading frequency. Block samples from shallower depth showed a somewhat higher undrained cyclic strength. No influence of the height-to-diameter ratio of the samples (h/d = 1 and 2 were compared) could be found. A qualitative comparison of the test results with data for standard tube samples is provided. Key words: soft marine clay, block samples, undrained cyclic triaxial tests, undrained cyclic direct simple shear (DSS) tests. Les resultats d'une etude d'essais triaxiaux non draines cycliques et d'essais cycliques non draines en cisaillement simple direct (CSD) sur des echantillons de bonne qualite non remanies provenant de blocs d'argile molle norvegienne sont presentes. Plusieurs essais avec differentes moyennes et amplitudes de contraintes de cisaillement, frequences de chargement et geometries ont ete executes sur des echantillons en bloc de differentes profondeurs. Pour les essais de faible contrainte moyenne de cisaillement, la rupture est due aux amplitudes elevees de deplacement en cisaillement, tandis que des deplacements en cisaillement permanents eleves ont ete observes pour les essais de contrainte moyenne de cisaillement elevee. Des diagrammes quantifiant les resistances cycliques non drainees, les deplacements en cisaillement permanents, l'amplitude de deplacement en cisaillement et la pression interstitielle permanente, selon la contrainte moyenne de cisaillement, l'amplitude de la contrainte de cisaillement et le nombre de cycles ont ete developpes base sur les resultats de ces essais. Il est demontre que les resistances cycliques non drainees dependent de la frequence de chargement. Des echantillons moins profonds demontrent des resistances cycliques non drainees un peu plus elevees. Aucune influence du ratio hauteur/diametre des echantillons (h/d = 1 et 2 ont ete compares) n'a ete observee. Une comparaison qualitative des resultats des essais avec des echantillons en tube standards est presentee. [Traduit par la Redaction] Mots-cles : argile marine molle, echantillons en bloc, essais triaxiaux cycliques non draines, essais cycliques non draines en cisaillement simple direct (CSD)., Introduction The foundation design of offshore installations (gravity platforms, piled installations, suction anchors, wind turbines) or structures along the coast (harbours, breakwaters, storm-surge barriers) is governed by the bearing capacity [...]

The present paper discusses the application of a high-cycle accumulation (HCA) model originally developed for sand for the prediction of permanent deformations in an unbound granular material (UGM) used for base and subbase layers in pavements. Cyclic triaxial tests on precompacted samples of an UGM have been performed in order to validate and calibrate the model. The stress amplitude, the initial density, and the average stress were varied. The test results are compared to those of air-pluviated samples of sand (subgrade material). Some significant differences in the behavior of both materials under cyclic loading are outlined. It is demonstrated that the functions describing the intensity of accumulation can be maintained for an UGM with different material constants, but that the flow rule must be generalized in order to describe the anisotropy. Recalculations of the laboratory tests show a good prediction of the modified HCA model. DOI: 10.1061/(ASCE)GT.1943-5606.0000275 CE Database subject headings: Pavements; Granular media; Deformations; Triaxial tests; Predictions. Author keywords: Payements; Unbound granular material (UGM); Permanent deformations; High-cycle accumulation model; Cyclic triaxial tests.

The paper presents a study of the influence of grain-size distribution curve on the small strain shear modulus [G.sub.max] of quartz sand with subangular grain shape. The results of 163 resonant column tests on 25 different grain-size distribution curves are presented. It is demonstrated for a constant void ratio that while [G.sub.max] is not influenced by variations in the mean grain-size [d.sub.50] in the investigated range, it significantly decreases with increasing coefficient of uniformity [C.sub.u]=[d.sub.60]/[d.sub.10] of the grain-size distribution curve. Well-known empirical formulas (e.g., Hardin's equation with its commonly used constants) may strongly overestimate the stiffness of well-graded soils. Based on the RC test results, correlations of the constants of Hardin's equation with [C.sub.u] have been developed. The predictions using Hardin's equation and these correlations are in good accordance with the test data. Correlations of the frequently used shear modulus coefficient [K.sub.2,max] with [C.sub.u] and empirical equations formulated in terms of relative density, are also given in the paper. A comparison of the predictions by the proposed empirical formulas with [G.sub.max]-data from the literature and a micromechanical explanation of the experimental results are provided. Correction factors for an application of the laboratory data to in situ conditions are also discussed. DOI: 10.1061/(ASCE)GT.1943-5606.0000096 CE Database subject headings: Shear modulus; Sand; Coefficients; Grain size; Strain.

Cyclic stresses due to passing wheels impose an accumulation of permanent strains in layers of unbound granular materials (UGMs) of flexible pavements. The hollow cylinder triaxial test would be the most appropriate test to simulate the in situ stress conditions but it is difficult to perform on UGMs due to their large maximum grain size. The simpler axisymmetric cyclic triaxial test does not consider the shear stress components. It can be performed with a constant confining pressure (CCP) or a variable confining pressure (VCP). CCP and VCP tests are commonly assumed to deliver similar residual and resilient strains as long as the average stress is the same. Thus, the simpler CCP test is mostly used in pavement engineering. However, this assumption is based on limited test data in the literature and may not be on the safe side. The present paper documents a comparative study of CCP and VCP tests on UGM. The study is mainly dedicated to the permanent deformations. The results show that only for some special stress paths do both types of tests deliver similar permanent axial or volumetric strains. For some other stress paths the CCP tests may underestimate the permanent axial strain in comparison to the corresponding VCP test. DOI: 10.1061/(ASCE)TE.1943-5436.0000009 CE Database subject headings: Flexible pavements; Cyclic loads; Triaxial tests; Granular materials.