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This paper describes a series of laboratory tests performed to characterize the mechanical and hydraulic properties of plastic concrete (PL-C). PL-C is used in the construction of seepage cut-off walls in dams and it comprises cement, aggregate, and water mixed with sodium bentonite. The addition of sodium bentonite causes a reduction in strength and improved ductility after failure compared with normal concrete. The mechanical properties of PL-C are studied using a series of unconfined compression tests and confined compression tests performed while simultaneously permeating water through PL-C specimens. Stress relaxation and controlled rate of loading tests are also performed to investigate the rate-sensitivity and time-dependency of plastic concrete. The test results show that the hydraulic conductivity of PL-C increases between two and three orders of magnitude during triaxial compression due to yielding, crack formation, and dilation of the cracks. Such changes in the behaviour of PL-C should be minimized during design by controlling the working strains and using erosion-resistant mixes. In addition to these findings, PL-C exhibits significant time-dependent behaviour similar to that observed for clays, and the variation of compressive strength versus confining stress is comparable to normal strength concrete. Key words: plastic concrete, stress relaxation, hydraulic conductivity, axial strain, dams. Cet article deecrit une serie d'essais en laboratoire effectues dans le but de caracteriser les proprieetesmeecaniques et hydrauliques du beton plastique (BP). Le BP est utilise; dans la construction de systemes de coupure dans les barrages. Il est constitue du ciment, de l'agregat et de l'eau melange avec de la bentonite de sodium. L'ajout de bentonite de sodium entraine une reduction de la resistance et une amelioration de la ductilite suite a la rupture, comparativement au beton standard. Les proprieetesmeecaniques du BP sont etudieees a l'aide d'essais en compression non confines et confines effectueesen meme temps que l'eau peenetre a travers les echantillons de BP. Des essais de relaxation des contraintes et de chargement a taux controle ont aussi ete effectues pour investiguer la sensibilite au taux et la dependance au temps des BP. Les resultats des essais montrent que la conductivite hydraulique du beton plastique augmente de deux a trois ordres de grandeur durant la compression triaxiale en raison de l'ecoulement, de la formation de fissures et de la dilatation dans les fissures. Ces changements dans le comportement du BP devraient etre minimises durant la conception par un controle des deformations et par l'utilisation de melanges resistants a l?eerosion. De plus, le beton plastique demontre un comportement dependant du temps de facon significative, comme ce qui est observe: pour les argiles, et la variation de la contrainte compressive versus la contrainte de confinement est comparable a la resistance normale d'un beton. Mots-cles: beton plastique, relaxation des contraintes, conductivite hydraulique, deformation axiale, barrages. [Traduit par la Redaction], Introduction Advancements in the construction of plastic concrete (PL-C) cut-off walls have enabled the construction of large zoned earthfill embankment dams on deep pervious foundations (Davidson et al. 1992; Balian [...]

The weak understanding of crack growth mechanisms in ductile soil is addressed by testing a new fracture mechanics approach. Samples are fractured using a deep-notch (3-point) bend test, with data on sample bending, crack growth, and crack mouth opening collected to assess the crack opening angle (COA), the crack tip opening angle (CTOA), and plastic energy dissipation rate ([D.sub.pl]). The test variables are clay and salinity content, with samples formed from mixtures of kaolinite and fine sand. The CTOA and [D.sub.pl] detect differences in fracture mechanics due to clay, but not salinity. The energy needed to drive crack extension, [D.sub.pl], is one order of magnitude higher for samples containing a ratio of sand to kaolinite of 75:25, as compared with 50:50. However, the CTOA due to plasticity was 0.19 and 0.24 for the same samples respectively, indicating that more strain is needed for crack growth in the specimens with more clay.