Mechanics of Cohesive-frictional Materials最新文献

It has been found that the experimental results on frictional and cohesive materials such as cemented sands and unsaturated soils obtained under constant mean effective principal stress (σ_m=const.) in three-dimensional (3D) stress can be consistently arranged on the concept of the Extended Spatially Mobilized Plane (the extended-SMP), which is modified from the original SMP by introducing cohesion parameter σ₀(=c cot ϕ). Consequently, an elastoplastic model for frictional and cohesive materials is developed from the extended-SMP and the t_ij-sand model for frictional materials by taking the effect of cohesion (σ₀) into consideration. The model covers both Von Mises type model for metals (σ₀→∞) and t_ij-sand model for granular materials (σ₀=0) at two extremes. In this paper, the derivation of the proposed model, the physical meaning and determination of seven model parameters, the comparison of the model predictions with the results of triaxial compression, triaxial extension and true triaxial tests on cemented sands, and the relationship among the proposed model, the plastic theory of Mises type for metals and an elastoplastic model for granular materials, are presented. Copyright © 1999 John Wiley & Sons, Ltd.

Most historic cases of liquefaction have been found to occur in alluvial (water) deposited silty sands. Currently, the effect of non-plastic fines (particles smaller than No. 200 sieve) on the liquefaction behaviour of sands is viewed to be either negligible or its presence actually inhibits liquefaction. Undrained triaxial compression test results performed on silty sands clearly indicate a direct correlation between the quantity of finer, non-plastic constituents and the liquefaction potential of granular soils. Increasing the fines content increases the liquefaction potential, even though the density increases. Complete static liquefaction occurs at low confining pressures. As confining pressures increase, the liquefaction potential decreases resulting in increased stability. Thus, silty sands exhibit a ‘reverse’ pattern of soil behaviour with confining pressure. Drained tests indicate both a large contractive volume change and a suppressed friction angle at low confining pressures, and this explains the undrained behaviour. It is hypothesized that the mechanism underlying this behaviour is related to the formation of a particle structure between the large and small grains which creates a highly compressible soil fabric. This ‘reverse’ behaviour pattern makes predictions of static liquefaction of silty sands difficult. However, simple modifications to the Single Hardening Model yield surface formulation enables predictions of this behaviour pattern. Copyright © 1999 John Wiley & Sons, Ltd.

A viscoelastic fictitious crack model has been applied in this paper to the analysis of large-scale in situ sea ice tests. By matching the experimental response, a stress-separation curve has been derived for the in situ response of sea ice. The importance of including time dependent deformations in sea ice fracture models is illustrated. The limitations of the fictitious crack model in reproducing the ‘stick-slip’ crack growth typically observed in sea ice are revealed. Copyright © 1999 John Wiley & Sons, Ltd.

A homogenization technique is applied to develop a new interface or joint element for the finite element analysis of media having discrete or instantaneous discontinuities such as rock masses including a finite number of joints, soil–structure and soil–reinforcement interface, localised shear cracks, etc. The joint or crack is treated as an inclusion in the media. Using an average rule, the influence to the joint is smeared into a small region of the adjacent intact material. The constitutive model in the region is defined in terms of constitutive properties of both the intact media and the joint as well as the geometry of the homogenized domain. The proposed element has been implemented in a finite element program and its performance has been compared with that of standard continuum finite elements. The results of numerical analysis are virtually insensitive to the thickness of the homogenized region, which is the main advantage of this technique over other conventional joint elements. Copyright © 1999 John Wiley & Sons, Ltd.

In this paper, a length scale included in multiphase materials such as saturated and partially saturated porous media is discussed, where the viscous terms are introduced naturally by the fluid mass balance equations. The discussion is limited to the dynamic case. The characteristic stability equation is given in explicit form for one-dimensional wave propagation. It is shown that for axial waves a wave number domain exists for which the material model is dispersive when softening behaviour occurs for solid skeleton and that an internal length scale can be derived, while for ideal shear propagation this is not the case. Numerical examples are given to corroborate the validity of the expressions derived. Copyright © 1999 John Wiley & Sons, Ltd.

The stress–strain behaviour of granular materials can be modelled with hypoplastic constitutive relations. A hypoplastic model is briefly introduced for the axially symmetric case, and a procedure for the determination of its parameters is described in detail. It is shown, for several sands and one gravel, that all parameters of the hypoplastic model are closely related to the granulometric properties of grain assemblies. Recalculations of some element tests are presented in order to verify the proposed procedure. Copyright © 1999 John Wiley & Sons, Ltd.