Analysis of the failure mode and softening behaviour of sands in true triaxial tests

Abstract

This paper presents a theoretical analysis and a numerical study of the failure mode in sands based on a hypoplastic description of the material. A bifurcation analysis is performed to study the failure mode in sands under true triaxial stress conditions at the material response level. It is shown that either uniform failure or localized failure can occur, depending on the intermediate principal stress. Uniform bifurcation occurs in tests along stress paths with a lower Lode angle, including the stress path for a conventional triaxial compression test. Localized failure occurs in tests along stress paths with a higher Lode angle, including stress paths for biaxial compression and triaxial extension tests. Specimen responses under laboratory conditions are then studied numerically by 3D FE simulations of biaxial compression, triaxial compression, and triaxial extension tests. The effects of initial imperfection from a homogeneous state are taken into account by introducing a frequency distribution of the initial void ratio. This permits the softening behaviour and shear localization in sand specimens to be analysed for different degrees of initial heterogeneity.

A composite particle model for non-spherical particles in DEM simulations

“…The numerical model presented in this paper can reasonably mimic the configuration of true triaxial compression apparatus. As noted by Huang et al [39], this approach can effectively control the specimen to deform uniformly and thus lead to realistic averaged stressstrain-dilation relationships. The particle properties, such as particle size distribution and contact stiffness are listed in Table 3.…”

A study of mechanical behavior of rock-fill materials with reference to particle crushing

“…Recent experimental and theoretical studies [29,30] demonstrated that uniform critical state may be achieved in a granular sample in trithe characteristic mean stress, it is reasonable to assume that failure friction angle for loose sand is a good approximation of the critical friction angle. Then these results indicate that the critical friction angle is constant for mean stress less than a characteristic value, which marks the starting of substantial particle crushing.…”

“…Critical state under 3-dimensional stress condition is difficult to obtain. In shear tests along stress paths with a Lode angle other than that for triaxial compression, localization in the sample is almost inevitable to occur [30] . This has been the major hindrance for the measurement of critical states.…”

Scale dependence of shear strength for a coarse granular soil using a superimposition-nest type of direct shear apparatus

“…Failures of soil primarily encompass two types, i.e., the tension and shear failures. In a few situations, the cracks in the soil mass caused by the tensile stresses may be of practical importance; while in the stability analysis for most engineering problems, only the resistance against shearing is taken into consideration (Huang et al 2007;Lade 2002). The shear resistance of soil governs the stability of a natural soil slope or a filling structure such as the earth dam, embankment or breakwater, and even the formation and evolution of a landslide (Li et al 2013;Liu et al 2006;Oyanguren et al 2008;Xu et al 2011).…”