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Peter I. Kattan - One of the best experts on this subject based on the ideXlab platform.
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Chapter 11 – Symmetrization of the Effective Stress tensor
Advances in Damage Mechanics, 2006Co-Authors: George Z. Voyiadjis, Peter I. KattanAbstract:Publisher Summary The aim of this chapter is to provide a solid mathematical basis for symmetrization methods of the Effective Stress tensor, and justification for their use and validity. The Effective Stress tensor is examined within the framework of continuum damage mechanics. For a general state of deformation and damage, it is seen that the Effective Stress tensor is usually not symmetric. Therefore, its symmetrization is necessary for a continuum theory to be valid. There are three types of symmetrization methods: explicit symmetrization, square root symmetrization, and implicit symmetrization. These three symmetrization methods are compared, and certain recommendations are made regarding their suitability. This chapter concludes that the explicit method produces higher damage effect values, thus resulting in higher Effective Stresses than the other two methods. The implicit method produces the lowest symmetrized Stress values. All three symmetrization methods display qualitatively the same variation of the damage effect tensor. Only the explicit and implicit symmetrization methods depict more accurately the physics of the material damage behavior.
Chuangbing Zhou - One of the best experts on this subject based on the ideXlab platform.
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Effective Stress Principle for Partially Saturated Rock Fractures
Rock Mechanics and Rock Engineering, 2015Co-Authors: Yuan Chen, Chuangbing ZhouAbstract:Soils and rocks are commonly characterized as a porous or fractured medium, with liquid and gaseous fluids occupying and moving in the void space. The presence of water in the void space remarkably influences the deformation behaviors, mechanical properties and Stress states of soils and rocks. It has been well recognized that the induced volume change, deformation and shear strength decrease of soils and rocks do not depend on the total Stress applied, but on the Effective Stress defined at the saturated state due to the difference between the total Stress and the fluid pressure in the pore space. The deformation of soils and rocks further alters the pore or fracture network and induces a nonnegligible variation in hydraulic properties (Kirby 1991; Chen et al. 2007; Li et al. 2014a). Therefore, the concept of Effective Stress plays a dominant role in understanding the coupled hydromechanical behaviors of soils and fractured rocks. Von Terzaghi (1923) pioneered the principle of Effective Stress for saturated soils, in which the Effective Stress was defined as the difference between the total Stress and the pore water pressure: r0 1⁄4 r uw ð1Þ where r denotes the total Stress, uw the pore water pressure, and r0 the Effective Stress. The pores and voids of an unsaturated soil, however, are only partially occupied by water, with the rest being occupied by air, which leads to a different Stress state in the soils. A modification of Terzaghi’s Effective Stress principle is therefore required for unsaturated soils. Bishop (1959) proposed the principle of Effective Stress for unsaturated soils by introducing an Effective Stress parameter into Eq. (1): r0 1⁄4 r ua ð Þ v uw ua ð Þ ð2Þ
David J. Lowe - One of the best experts on this subject based on the ideXlab platform.
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Rainfall threshold for initiating Effective Stress decrease and failure in weathered tephra slopes
Landslides, 2020Co-Authors: Max Oke Kluger, M. Ehsan Jorat, Vicki G. Moon, Stefan Kreiter, Willem P. Lange, Tobias Mörz, Thomas Robertson, David J. LoweAbstract:Rainfall is one of the most important triggers of slope failure. Weathered pyroclastic (tephra) deposits are especially vulnerable to slope failure because they commonly form slopes of high porosity and high clay content. Empirically derived thresholds for the triggering of landslides are commonly based on rainfall conditions and have been widely applied in volcanic soils. However, so far only few researchers utilized pore water pressure in the slope as additional variable for the threshold calibration. Here, we derived a new rainfall threshold for initiating the decrease in Effective Stress in the slope by analyzing a long-term record of rainfall and piezometer data from a slide-prone coastal area in northern New Zealand that consists of clayey, halloysitic tephra deposits. The level of Effective Stress decrease increased with rainfall intensity and duration. We observed highest Effective Stress decrease of up to 36% during rainfall events that triggered landslides in our study area. The Effective Stress threshold exhibits a satisfactory predictive capability. The probability of correctly predicting a decrease in Effective Stress is 53%. The Effective Stress threshold contributes towards the implementation of the decrease in Effective Stress into rainfall thresholds for the occurrence of landslides.
Tom Schanz - One of the best experts on this subject based on the ideXlab platform.
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Prediction of Effective Stress in partially saturated sand–kaolin mixtures
Geomechanics for Energy and the Environment, 2018Co-Authors: G. Heibrock, Diethard König, Maria Datcheva, A. Pourzargar, J. Alabdullah, Tom SchanzAbstract:Abstract This paper addresses the applicability of the Effective Stress principle in partially saturated soils by proposing a definition of the Effective Stress parameter. The definition of the Effective Stress parameter is based on a model for the soil–water retention relationship (SWCC model) considering the soil saturation as a sum of a term representing the water stored in the bimodal soil–pore system and a term accounting the water adsorbed on the solid surface. The validation of the proposed Effective Stress parameter is done by conducting conventional triaxial and uniaxial tensile tests on partially saturated samples of artificial compacted sand–kaolin mixtures and by analyzing the results. It is shown that the proposed Effective Stress parameter is applicable for sandy to non-swelling clayey soils and it can explain the shear strength of the soil in a wide range of suctions. However, the experimental results showed significant difference in measured and predicted tensile strength for the soils with higher clay contents. This discrepancy may be attributed to soil structure effects and to the different processes determining shear strength and tensile strength, indicating the need of further research in this case.
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Effective Stress in clays of various mineralogy
Vadose Zone Journal, 2014Co-Authors: Wiebke Baille, Snehasis Tripathy, Tom SchanzAbstract:Effective Stress changes during the drying process were determined for three clays. Suction Stress decreased, remain nearly constant, and increased with increasing suction for kaolinite and illite clays but decreased monotonically for montmorillonite clay. Decreasing suction Stress caused an increase in Effective Stress. Considerable suction Stress occurred at very high suction for the illite and montmorillonite clays. The Effective Stress in clays possessing a significant proportion of one of the clay minerals kaolinite, illite, or montmorillonite was determined based on the suction Stress characteristic curves (SSCCs) of the clays. The SSCCs were determined based on the drying soil-water characteristic curves of the clays for a suction range of 0.03 to about 219.0 MPa. One-dimensional compressibility behavior of initially saturated clays was also studied by loading clay specimens up to a maximum vertical Stress of 21.0 MPa. The Effective Stress–void ratio responses of the clays during the drying process were compared with their saturated counterparts. The shapes of SSCCs and the magnitudes of minimum and maximum suction Stress were strongly dependent on the mineralogy and the properties of the clays. For the clays with kaolinite and illite as the dominant clay minerals, the suction Stress decreased, remained nearly constant, and then increased with an increase in the applied suction, whereas it decreased monotonically with increasing suction for the montmorillonite clay. A decrease in the suction Stress caused an increase in the Effective Stress, which in turn reduced the volume of the clays. For applied suctions smaller than the air-entry value of any clay, equal magnitudes of suction Stress and Effective Stress produced a similar volume change of the clay. The study clearly showed that suction changes beyond the air-entry value are less Effective in producing volume changes in unsaturated soils, primarily because of a decrease in the Effective Stress due to an increase in the suction Stress.
Nasser Khalili - One of the best experts on this subject based on the ideXlab platform.
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Principle of Effective Stress in Variably Saturated Porous Media
Vadose Zone Journal, 2014Co-Authors: Nasser Khalili, Ehsan Nikooee, S. Majid HassanizadehAbstract:In 1961, in the wake of emerging geotechnical problems under unsaturated conditions, the British Royal Society held a conference on the Effective Stress principle. Much of the debate stemmed from pressing needs to go beyond [Terzaghi’s (1923][1], [1936)][2] Effective Stress for saturated porous
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Effective Stress in Unsaturated Soils: Review with New Evidence
International Journal of Geomechanics, 2004Co-Authors: Nasser Khalili, F. Geiser, G. E. BlightAbstract:The application of the Effective Stress principle to unsaturated soils is critically reviewed, and the reasons underlying the difficulties in previous investigations of the Effective Stress in unsaturated soils are highlighted. The validity of the relationship proposed by Khalili and Khabbaz in 1998 for the determination of the Effective Stress parameter, χ, is examined using an extensive array of experimental data. It is shown that quantitative predictions of shear strength and volume change in unsaturated soils can be made using the Effective Stress concept. The uniqueness of the critical state line in the deviatoric Stress–Effective mean Stress plane for saturated as well as unsaturated soils is investigated, and the incremental form of the Effective Stress parameter is derived.
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Application of Effective Stress Concept to Unsaturated Soils
1999Co-Authors: Nasser Khalili, M H KhabbazAbstract:The application of the Effective Stress concept to unsaturated soils is critically reviewed. The validity and the appropriateness of the relationship proposed by Khalili and Khabbaz (1996, 1998) for the determination of the Effective Stress parameter χ are examined using both shear strength and volumetric change data. Extremely good agreement is obtained between the measured and predicted values in all cases. It is shown that quantitative predictions of shear strength and deformation in unsaturated soils can be made using the Effective Stress concept. The model parameters will be exactly the same as those used in saturated soils, except for a single parameter which can be determined in any soil physics laboratory. This is in contrast to the current models of unsaturated soils which require extensive laboratory testing.
