Compaction bands due to grain crushing in porous rocks: A theoretical approach based on breakage mechanics

Abstract

[1] Grain crushing and pore collapse are the principal micromechanisms controlling the physics of compaction bands in porous rocks. Several constitutive models have been previously used to predict the formation and propagation of these bands. However, they do not account directly for the physical processes of grain crushing and pore collapse. The parameters of these previous models were mostly tuned to match the predictions of compaction localization; this was usually done without validating whether the assigned parameters agree with the full constitutive behavior of the material. In this study a micromechanics-based constitutive model capable of tracking the evolving grain size distribution due to grain crushing is formulated and used for a theoretical analysis of compaction band formation in porous rocks. Linkage of the internal variables to grain crushing enables us to capture both the material behavior and the evolving grain size distribution. On this basis, we show that the model correctly predicts the formation and orientation of compaction bands experimentally observed in typical high-porosity sandstones. Furthermore, the connections between the internal variables and their underlying micromechanisms allow us to illustrate the significance of the grain size distribution and pore collapse on the formation of compaction bands.

Propagation energies inferred from deformation bands in sandstone

“…The comparable values of J I for both types of compaction bands indicate that grain crushing and the associated increase in plastic normal strain was approximately compensated by the smaller widths of pure compaction bands, implying a comparable tendency to propagate through the host sandstone. This finding may be relevant to theoretical investigations of compaction localization that are based on grain fragmentation (Das et al 2011) which utilize the material properties such as grain size and shape, stress state, and deformation mechanism within the compaction bands (i.e. fragmentation or pore collapse).…”

Theoretical breakage mechanics and experimental assessment of stresses surrounding piles penetrating into dense silica sand

“…The same theory has been applied to confined comminution problems found in saturated and unsaturated geomechanics, geophysics, geology and mineral processing engineering (see Nguyen & Einav, 2009Das et al, 2011;Rubin & Einav, 2011;Buscarnera & Einav, 2012;Zhang et al, 2013).…”

“…Following observations of intense grain breakage during calibration chamber model pile penetration in sand (Yang et al, 2010), Zhang et al (2013) reported a theoretical investigation into its potential effects that applied the breakage mechanics theory proposed by Einav (2007aEinav ( , 2007bEinav ( , 2007cEinav ( , 2007d) and developed by Nguyen & Einav (2009, Rubin & Einav (2011), Das et al (2011) and Buscarnera & Einav (2012). A simple breakage model led to predictions that Zhang et al (2013) compared with internal deformation patterns and end-bearing capacities measured in model pile tests by Kuwajima et al (2009), as well as evolving grain size distributions (GSDs) from the model tests reported by Yang et al (2010).…”

The end-bearing capacity of piles penetrating into crushable soils

“…However, the model was derived based on thermodynamics, and depends on an additional stress conjugated to the breakage flow, the breakage energy E B : In this sense the model is associated with a dissipative E B -p-q stress space. However, ø has physical meaning linked to local pore collapse, and increases with the quantity of internal pores within the grains (see discussion by Das et al (2011)). …”