Abstract
During shearing in geological environments, frictional processes, including the wear of sliding rock surfaces, control the nature of the slip events. Multiple studies focusing on natural samples have investigated the frictional behaviour of a large suite of geological materials. However, due to the varied and heterogeneous nature of geomaterials, the individual controls of material properties on friction and wear remain unconstrained. Here, we use variably porous synthetic glass samples (8, 19 and 30% porosity) to explore the frictional behaviour and development of wear in geomaterials at low normal stresses (≤1 MPa). We propose that porosity provides an inherent roughness to material which wear and abrasion cannot smooth, allowing material at the pore margins to interact with the slip surface. This results in an increase in measured friction coefficient from <0.4 for 8% porosity, to <0.55 for 19% porosity and 0.6–0.8 for 30% porosity for the slip rates evaluated. For a given porosity, wear rate reduces with slip rate due to less asperity interaction time. At higher slip rates, samples also exhibit slip weakening behaviour, either due to evolution of the slipping zone or by the activation of temperature-dependent microphysical processes. However, heating rate and peak temperature may be reduced by rapid wear rates as frictional heating and wear compete. The higher wear rates and reduced heating rates of porous rocks during slip may delay the onset of thermally triggered dynamic weakening mechanisms such as flash heating, frictional melting and thermal pressurisation. Hence porosity, and the resultant friction coefficient, work, heating rate and wear rate, of materials can influence the dynamics of slip during such events as shallow crustal faulting or mass movements.
Highlights
A spectrum of geohazards and anthropogenic processes are associated with shear, rupture and slip on faults or other slip surfaces
During rotary shear experiments at different slip rate and normal stress conditions the shear resistance of variably porous synthetic rock analogues varied, and the friction coefficient, wear rate and frictional heating differed
The lowest porosity samples (8%) evolved from initial peak friction and wear rates to steady state in the shortest slip distance whereas the 30% porosity samples took longer to reach steady state, and, in many cases, the interpreted steady state areas were punctuated by multiple shear stress peaks occurring throughout the test, a phenomenon that was less commonly observed at lower porosity
Summary
A spectrum of geohazards and anthropogenic processes are associated with shear, rupture and slip on faults or other slip surfaces. Geomaterials vary greatly in their mineralogy and texture, which range from sedimentary and volcaniclastic rocks formed by the Frictional Behaviour of Porous Geomaterials deposition, compaction and cementation of grains or fragments during lithification (Lewis, 1984), to igneous rocks formed through cooling with variable degrees of crystallisation and vitrification, causing a range of textures with diverse glass, crystal and bubble contents (e.g., Le Bas and Streckeisen, 1991), and metamorphic rocks formed through recrystallisation (e.g., Schumacher, 1999) This textural and chemical variety leads to differing mechanical properties of rocks as each of the constituent phases have different strength and fracture toughness, dictating the rocks’ mechanical response to slip and comminution (Spray, 1992; Spray, 2010). It is the pairing of comminution with the production and conduction of frictional heat away from the slip interface, determined by the nature of the material, that acts to dissipate the energy of slip events (e.g., Lavallée and Kendrick, 2020 and references therein)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
