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1

Influence of soil fabrics and stress state on the undrained instability of overconsolidated binary granular assemblies

Mahmoudi Y., Taiba A. C., Hazout L., Baille W., Belkhatir M.

Studia Geotechnica et Mechanica

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2018

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Vol. 40, nr 2

96--116

EN

The instability of saturated granular soils in field conditions generates drastic collapse in terms of runoff deformation because of its failing to sustain naturally applied loading conditions such as earthquakes, wave actions and vibrations. The objective of this laboratory investigation is to study the effects of the depositional methods, overconsolidation ratio (OCR) and confining pressure on the undrained instability shear strength of medium dense (Dr = 52%) sand-silt mixtures under static loading conditions. For this purpose, a series of undrained monotonic triaxial tests were carried out on reconstituted saturated silty sand samples with fines content ranging from 0% to 40%. Three confining pressures were used (P’c = 100, 200 and 300 kPa) in this research. The sand-silt mixture samples were prepared using two depositional methods, dry funnel pluviation (DFP) and wet deposition (WD), and subjected to two OCRs (1 and 2). The obtained instability lines and friction angles indicate that the funnel pluviated samples exhibit strain hardening compared to the wet deposited samples and that normally consolidated and overconsolidated wet deposited clean sandy samples were very sensitive to static liquefaction. The test results also indicate that the instability friction angle increases with the increase in the OCR expressing soil dilative character tendency increase. The instability friction angle decreases with the increase in the fines content for DFP and the inverse tendency was observed in the case of WD.

2

Drained Against Undrained Behaviour of Sand

Sawicki A., Świdziński W.

Archives of Hydro-Engineering and Environmental Mechanics

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2007

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Vol. 54, nr 3

207-222

EN

The incremental constitutive equations describing the pre-failure deformations of sand are presented. These equations were calibrated on the basis of extensive experimental data, obtained from investigations performed in a triaxial apparatus. Incremental equations were calibrated separately for initially contractive and dilative soil samples. Then, they were applied to predict the undrained behaviour of saturated soil samples. In the case of contractive soils, the constitutive equations describe the effective stress paths leading to the static liquefaction. In the case of dilative soils, the effective stress path is different, as the mean effective stress initially decreases, and after passing the instability line, it starts to increase, asymptotically reaching the failure envelope. Theoretical predictions of undrained behaviour are supported by experimental data. The original feature of this paper is that one can predict the undrained behaviour of saturated granular soils on the basis of stress-strain characteristics of the same soil but dry or tested in drained conditions.

3

A Study on Pre-Failure Deformations of Granular Soils

Sawicki A.

Archives of Hydro-Engineering and Environmental Mechanics

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2007

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Vol. 54, nr 3

183-206

EN

A simple model describing pre-failure deformations of granular soils is derived on the basis of a wide range of experimental data. The model is defined by two incremental equations describing the volumetric and deviatoric strains. Functions appearing in governing equations were determined from experiments performed in the triaxial apparatus, with additional measurements of lateral strains for some simple stress paths. These functions are different for loading and unloading, and have different shapes for contractive and dilative soil samples. The instability line is built into the structure of the model. The incremental equations were applied to predict the soil behaviour during anisotropic compression, including determination of the K0-line. Some basic statistical characteristics of the initial density index of investigated soils and deformations during isotropic compression are presented.