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Plasticity Theory: Nonlinear Deformation of Soils
Published in M.S. Rahman, M.B. Can Ülker, Modeling and Computing for Geotechnical Engineering, 2018
where σm is the mean stress, σ¯=J2 $ \bar{\sigma } = \sqrt {J_{2} } $ and instead of the friction angle, f, we now use a so called “dilation angle”, φd as measured in direct shear tests for granular materials that exhibit the tendency to increase in volume under shearing, also called dilatancy. The dilation angle is, in general, smaller than the friction angle for soils. As we can see, isotropic hardening directly affects the stress‐strain relationship through the elasto‐plastic matrix.
Earthquake effects and seismic slope analysis
Published in Robin Chowdhury, Phil Flentje, Gautam Bhattacharya, Geotechnical Slope Analysis, 2009
Robin Chowdhury, Phil Flentje, Gautam Bhattacharya
As stated above, for saturated cohesionless soils, decrease in shear strength is associated with significant increase in pore water pressure caused by cyclic loading. The pattern of strength decrease depends on the type of soil. Saturated, relatively loose cohesionless soils may be prone to liquefaction, as the pore water pressure during cyclic loading continues to increase. Dense soils exhibit dilatant behaviour and, therefore, are not prone to liquefaction. The factors which influence the likelihood of a soil undergoing liquefaction include the initial void ratio, the confining stresses and the type of ground motion. In a laboratory test, the fast-fluctuating ground motion would be represented by a certain level of applied deviator stress with an equivalent number of cycles corresponding to the particular ground motion.
Application of Biot’s dynamic equation to seismic liquefaction problem
Published in J.-F. Thimus, Y. Abousleiman, A.H.-D. Cheng, O. Coussy, E. Detournay, Poromechanics, 2020
T. Shiomi, S. Tsukuni, O.C. Zienkiewicz
To simulate cyclic behaviour of granular material dilatancy behaviour must be considered. We choose the densification model, which is originated by Zienkiewicz et al (1978). The model defines the quantity of dilatancy as function of history of shear strain and stress ratio. In this model cyclic movement causes only an accumulated plastic volumetric strain, i.e. excess pore pressure, and no reversal mechanism exists. But excess pore pressure can dissipate due to flow of the water in porous media governed by Biot’s governing equation.
Stabilised jarofix waste material for road construction
Published in International Journal of Pavement Engineering, 2021
A. K. Sinha, Vasant G. Havanagi, J. T. Shahu
Dilatancy is a fundamental aspect of soil behaviour and is described by the tendency of soil to change volume during shearing (Houslby, 1991). The ratio of vertical to horizontal displacements indicates the rate of dilation of compacted jarofix mixes at which volumetric expansion occurs with continuing shearing. The point of peak shear strength is usually associated with the maximum rate of dilation (− δy/δx) or compression (+ δy/δx). Angle of dilation (ψ) is the maximum slope at the peak stress and can be determined by Equation (4) (Jewell, 1989; Cox, 2008): For example, the peak dilation angle for 100% MDD jarofix specimens at a normal stress of 25 kPa was estimated as
Study of dilatancy behaviors of calcareous soils in a triaxial test
Published in Marine Georesources & Geotechnology, 2019
Xing Wang, Chang-Qi Zhu, Xin-Zhi Wang, Yue Qin
Dilatancy is a general property of geotechnical materials, and it is a key factor in investigating the deformation of sand, broken stone, and other granular materials by force. Dilatancy is defined as the volumetric deformation of soil under the action of shear stress; dilatation occurs in the case of a volume increase, whereas contraction (or negative dilatation) occurs in the case of a volume decrease (Qian and Yin 1996; Zhang 2000). This concept was first proposed by Reynolds (1885). Subsequently, Casagrande (1936, 1938) used tests to analyze the influence of frictional angle on soil deformation. He developed the concept of critical void ratio based on the dilatancy of sand, and thus, formally introduced dilatancy into the field of soil mechanics. In the last 20 years, dilatancy has been studied using theoretical analysis, experimental studies, and numerical simulations (Shamoto, Zhang, and Goto 1997; Wan and Guo 1999; Li and Dafalias 2000; Liu and Matsuoka 2003; Yang and Li 2004; Been and Jefferies 2004; Powrie et al. 2005; Lee et al. 2008; Wang and Zhao 2011; Xiao et al. 2014; Xiao et al. 2016; Xiao et al. 2017a). However, most of these studies have focused on the dilatancy of terrestrial soil such as siliceous sand and coarse-grained soil. Relatively few studies have been done on the dilatancy of calcareous soil (Sun and Wang 2004; Sun and Luo 2006; Hassanlourad, Salehzadeh, and Shahnazari 2008; Zhang, Jiang, and Wang 2009; Shahnazari et al. 2014; Shahnazari, Rezvani, and Tutunchian 2015; Xiao et al. 2017b).
Discrete element modelling of the influence of inherent anisotropy on the shear behaviour of granular soils
Published in European Journal of Environmental and Civil Engineering, 2018
Xiaoqiang Gu, Weiyi Li, Jiangu Qian, Kai Xu
For granular materials, the dilatancy or the volume change during the shearing is a very important characteristic. Figure 8 shows the evolution of the volumetric strain with axial strain for different specimens to illustrate the effect of inherent anisotropy. As seen in Figure 8, all the specimens contract first and then begin to dilate. Generally, the maximum volume contraction increases and the axial strain at which the specimen starts to dilate decreases as the bedding angle increases in each group, as shown in Figure 9. It is interesting to note that the trends in Figures 7 and 9 are quite similar. Meanwhile, it seems that as the degree of fabric anisotropy ac increases, the difference of volumetric behaviour at different bedding angles in each group increases. In each group, the volumetric strains at large axial strain (e.g. 15%) are quite different for specimens with different bedding angles, indicating the void ratio may be different at the critical state for different bedding angles. Above results convincingly indicates that both the principal directions of inherent anisotropy and the degree of inherent anisotropy play important roles on deformation characteristics of granular soils.