Pore Pressures and Strains After Repeated Loading of Saturated Clay

Abstract

Repeated and sustained loading tests on undrained samples of normally consolidated lacustrine clay are used to prove the existence of a relationship between pore water pressures and axial strains.The behavior of the clay is studied by investigating the pore pressure and strain responses under repeated loading, and comparing them with the responses from the more usual sustained loading. Samples under repeated loading fail at a stress below the compressive strength of the material as obtained from a standard strength test.It has been shown that, for a repeated stress level below a critical value a non failure equilibrium state is reached, closed stress-strain hysteresis loops occur and the soil behavior is essentially elastic. For a repeated stress above the critical value, the effective stress failure envelope is reached and each loading cycle leads to further nonrecoverable deformations and ultimate failure.The pore pressures and axial strains produced by loading may be divided into recoverable and nonrecoverable components; both components of pore water pressure are linearly related to the axial strain provided the sample is not close to failure and there is a gradual increase in axial strains and pore pre~sures with time. This relationship is explained by a simple mechanistic picture.The pore pressures due to the application of a shear stress may be considered as a combination of an elastic recoverable component, due to the elastic response of the soil grain structure, and a plastic nonrecoverable component due to a partial collapse of the grain structure with subsequent transfer of stresses from the failed grain contacts to the pore water. There are coresponding axial strains occurring due to the elastic response of the soil grain structure and the partial collapse of the structure.Experimental proof of the pore pressure versus strain relationship is presented by means of a series of loading tests on normally consolidated lacustrine silty clay samples tested under undrained triaxial conditions. Des essais non draines de changernent a charge constante ou alternee sont utilises pour demontrer l'existence d'une relation entre pressions interstitielles et deformations axiales.Le comporternent de l'argile est etudie, par observation des variations de pressions interstitielles et des deformations sous I'infiuence de charges alternees et par comparaison de ces variations avec celles qui :;e produisent dans les essais classiques ii charge constante, Les echantillons soumis a des charges alternees atteignent la rupture pour une contrainte inferieure it la resistance en compression du rnateriau telle qu'obtenue a partir d'essais standards.II a cte etabli que, pour un niveau de contrainte alternee 'inferieur it une valeur critique, un etat d'equilibre stable est atteint auquel correspondent des courbes effort-deformation en forme de boucles d'hysrerisis ferrnees et un cornporternent essentiellernent elastique du sol. Pour une contrainte alternee superieure a la valeur critique, I'enveloppe de rupture en contraintes effe...

Coarse-fine mixtures subjected to repetitive Ko loading: Effects of fines fraction, particle shape, and size ratio

“…for i ≥ 0 and m > 0 (8) where e 1 is the void ratio measured after 1 st cycle, and the terminal void ratio e T corresponds to the asymptotic void ratio as the number of cycles reaches infinite i→∞. The model parameter N * captures the number of cycles where the half of the asymptotic contraction (e o -e T )/2 occurs and m is a fitting constant.…”

“…Previous studies have explored the long-term effect of repetitive mechanical loads on pure coarse or pure fine sediments [8][9][10][11][12][13]. However, soils are granular materials consisting of a broad range of grain sizes; therefore, the role of fines as a minor component in coarse-fine mixtures should be considered for the long-term performance of geosystems [14][15][16][17].…”

“…describes the terminal void ratio e T for three sands-fines mixtures versus initial void ratio e o [Eq (8)…”

Recent Advances in Seismic Soil Liquefaction Engineering

“…Except the theoretically-based attempts (e.g. Wilson and Greenwood 1974;Hyde and Brown 1976) proposed in the mid-1970s for the prediction of plastic deformation of plastic fine-grained subgrade soils under repeated loading, Hyodo et al (1994) presented one of the few remarkable effort. Hyodo et al (1994) attempted to correlate cyclically-induced shear strains with residual axial strains.…”

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