The size and shape of soil particles reflect the formation history of the grains. In turn, the macroscale behavior of the soil mass results from particle level interactions which are affected by particle shape. Sphericity, roundness, and smoothness characterize different scales associated with particle shape. New experimental data and results from published studies are gathered into two databases to explore the effects of particle shape on packing density and on the small-to-large strain mechanical properties of sandy soils. In agreement with previous studies, these data confirm that increased angularity or eccentricity produces an increase in emax and emin. Furthermore, the data show that increasing particle irregularity causes a decrease in stiffness yet heightened sensitivity to the state of stress; an increase in compressibility under zero-lateral strain loading; an increase in the critical state friction angle cs; and an increase in the intercept of the critical state line there is a weak effect on the slope . Therefore, particle shape emerges as a significant soil index property that needs to be properly characterized and documented, particularly in clean sands and gravels. The systematic assessment of particle shape will lead to a better understanding of sand behavior.

Particle Shape Effects on Packing Density, Stiffness, and Strength: Natural and Crushed Sands

Different measures have been suggested for quantifying the amount of fragmentation in randomly compacted crushable aggregates. A most effective and popular measure is to adopt variants of Hardin's [1985. Crushing of soil particles. J. Geotech. Eng. ASCE 111(10), 1177–1192] definition of relative breakage ‘ B r ’. In this paper we further develop the concept of breakage to formulate a new continuum mechanics theory for crushable granular materials based on statistical and thermomechanical principles. Analogous to the damage internal variable ‘ D ’ which is used in continuum damage mechanics (CDM), here the breakage internal variable ‘ B ’ is adopted. This internal variable represents a particular form of the relative breakage ‘ B r ’ and measures the relative distance of the current grain size distribution from the initial and ultimate distributions. Similar to ‘ D ’, ‘ B ’ varies from zero to one and describes processes of micro-fractures and the growth of surface area. However, unlike damage that is most suitable to tensioned solid-like materials, the breakage is aimed towards compressed granular matter. While damage effectively represents the opening of micro-cavities and cracks, breakage represents comminution of particles. We term the new theory continuum breakage mechanics (CBM), reflecting the analogy with CDM. A focus is given to developing fundamental concepts and postulates, and identifying the physical meaning of the various variables. In this part of the paper we limit the study to describe an ideal dissipative process that includes breakage without plasticity. Plastic strains are essential, however, in representing aspects that relate to frictional dissipation, and this is covered in Part II of this paper together with model examples.

Breakage mechanics—Part I: Theory

Computer simulations of crushable agglomerates were performed using the PFC3D computer code, which adopts the distinct element method (DEM). Agglomerates were made by bonding elementary spheres in ‘crystallo-graphic’ arrays, and by giving each sphere an existence probability of 0·8. Weibull statistics of the crushing strength of the resulting agglomerates, when tested singly between parallel platens, matches that of real silica sand grains. Triaxial tests on a cubical sample made of 389 agglomerates were then simulated. Curves of isotropic compression are shown, and the effect of loading rate on the position of the compression curves is discussed in relation to the practical question of performing DEM simulations as fast as possible without creating inertia errors. Other stress paths, including conventional ‘drained’ triaxial compression, constant mean effective stress, and constant-volume paths, were also simulated from different initial stresses along the virgin e–log p′ curve. The numerical results are...

http://www-civ.eng.cam.ac.uk/geotech_new/people/bolton/mdb_pub/129_Geotechnique_No53_Issue7_633_641.pdf

Discrete element simulation of crushable soil

Microscopic particle crushing of sand subjected to high pressure one-dimensional compression

Single-particle crushing tests have been carried out on the component minerals of a sand and the results have been compared statistically with those obtained for individually marked particles placed in triaxial samples and then subjected to isotropic consolidation and shear tests. The single-particle crushing strength was defined for breakage of asperities and for whole-particle fracture. The results were analysed and compared using particle survival probability curves. Maximum characteristic stresses were estimated for the individual particles embedded in the test specimens using a simplified analysis and then survival probabilities at these stress levels were abstracted from the curves for the single-particle tests. A statistical comparison with the observed particle breakages showed good agreement. A particle breakage factor was defined in terms of the evolution of the particle size grading curve with respect to the smallest particle size and related to the survival probability curve for the breakage o...

A probabilistic approach to sand particle crushing in the triaxial test

https://www.jstage.jst.go.jp/article/sandf1995/41/2/41_2_39/_pdf

One-dimensional compression behaviour of uniformly graded sand related to single particle crushing strength

The occurrence and formation of crushable soils is a widespread phenomenon. Warm tropical seas give rise to deep deposits of biogenic skeletal sediments in coastal shelf areas, or exposed granitic ...

Pile end-bearing capacity in crushable sands

Crushable soils when sheared in a dense state have stress paths which are similar to those for loose, hard-grained sands; however, because of their angular nature they do not liquefy as easily unde...

Adrian F.L. Hyde

Papers

Microscopic particle crushing of sand subjected to high pressure one-dimensional compression

A probabilistic approach to sand particle crushing in the triaxial test

One-dimensional compression behaviour of uniformly graded sand related to single particle crushing strength

Pile end-bearing capacity in crushable sands

Liquefaction of crushable soils