Deformation properties of rock particle assemblages in oedometric compression (1D) and in centrifuge modelling (2D)

I Soud

Dans les comptes rendus d’articles de la conférence: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: FUNDAMENTALS - IX Physical & Numerical Modelling

ABSTRACT: The results of five centrifuge tests on models of rock particle assemblages with unsupported slopes are presentedin thispaper. The effects of compactness and submergence on the deformability of centrifugemodelswereexplored.Acomparativestudywasperformed between the vertical deformations of the centrifuge models (2D) and the verticaldeformations observed during oedometer tests (1D), conducted on rock particle assemblages from the same source andwith the same gradation, while considering theeffect ofcompactness. This comparison shows that for agiven relativedensity, the centrifuge models experience higher vertical deformations than those of the oedometer specimens. The ratiobetween the vertical deformation of the top of the centrifuge models and that obtained during the oedometer tests at agiven relative density decreases withincreasingrelative density. Finally, the particle breakage amount is found to be higherin samples excavated formthe centrifuge models comparedto that obtained from an oedometer-testedspecimen.R•SUM•Les r†sultatsde cinq essais encentrifugeusesur des mod‡les d'assemblages desparticules de roche avec des pentesnon support†essont pr†sent†s danscet article.Les effets de la compacit† et de la submersion sur la d†formabilit† desmod‡les en centrifugeuses sont explor†s.Une †tude comparative est r†alis†e entre les d†formations verticales desmod‡les en centrifugeuse (2D) et les d†formations verticales observ†es au cours des essais …dom†triques (1D), qui sontr†alis†es sur des assemblages des particules de roche dela m—me source et avec la m—me granulom†trie, tout enconsid†rant l–effet de la compacit†. Cette comparaison montre que pour une densit† donn†e, les mod‡les en centrifugeusesubissent des d†formations verticales sup†rieures ƒ celles des †chantillons …dom†triques. La valeur du rapport entre lad†formation verticale des sommets des mod‡les en centrifugeuse et celle obtenue au cours des essais …dom†triques ƒune densit† relative donn†e diminue avec l'augmentation de la densit† relative. Enfin, laquantit† de lafragmentation desparticules est plus †lev†e dans les †chantillons excav†s des mod‡les encentrifugeuseen comparaisonavec celleobtenued'un †chantillon…dom†trique.1INTRODUCTIONIt is known that if a cohesionless fill is placed in layers onan area, which is large relative to the fill depth, asconstruction continues, the fill will undergo simple one-dimensional compression atanapproximately constantstress ratio. The situationis more complex in rockfill damswhere the lack of restraint at the slopes induces morecomplex stress paths during construction. This involveschanges in the magnitude of stress ratio and rotation ofdirection of principal stresses. Therefore, it is important toexplore the validity of the simplified method that dependson the oedometer testing to predict or to estimate thevertical deformations of the central part of rockfill damswhile considering the effect of compactness, which is avery important parameter concerning the mechanicalresponse of rockfill materials.Charles(1976)derivedtypical stress paths from finiteelement analyses for three types of rockfill embankment. Itwas concluded thata great variety of stress paths occurswithin the different embankmentsduring construction andreservoir impoundmentand therefore, attempts to deriveappropriate stress-strain parameters for the soil by detailedstress path testing(LambeandWhitman, 1969)will be verydifficult. Moreover,it was found thatlarge rotations of thedirection of maximum principal stress occur, the greatestrotations occurring at the rockfill slopes. No standardlaboratory tests can simulate this behaviour.On other hand, geotechnical centrifuge technologyoffers a very powerful and sophisticated tool to understandtheoverall mechanical response of geotechnical materialsin many kinds of structures and it has many advantagesover the other alternatives. The basic principle of thecentrifuge modeling is to test a model with a scale 1/N of aprototype in the increased field of gravity of a geotechnicalcentrifuge. Gravity is increased by the same geometricfactor N compared to the normal earth–s gravity field (called1 g), which produces a centrifugal gravity field whosemagnitude is Ng and wherein the scaled model behavesinan identical manner to the prototype. Hence, geotechnicalcentrifuge technology offers the ability to reproduce the realstress-strain behavior of soils by accelerating small-scalemodels with similar geometries comparing to those of thetarget prototypes, which is considered as a very importantadvantage of this technology.Therefore, the purpose of this paper is, firstly, to designand to test centrifuge models of rock particle assemblageswith unsupported slopes and, secondly, to perform acomparisonstudy between the vertical deformationsinduced during oedometer tests (1D) and the vertical

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