Mechanics of granular-frictional-visco-plastic fluids in civil and mining engineering

The shear stress generated in mine backfill slurries and fresh concrete contains both velocity gradient dependent and frictional terms, categorised as frictional viscous plastic fluids. This paper discusses application of the developed analytical solution for flow rate as a function of pressure and pressure gradient in discs, pipes and cones for such frictional Bingham-Herschel-Bulkley fluids. This paper discusses application of this continuum fluid model to industrial materials like mine and mineral slurries, backfills and fresh concrete tests

Experimental investigation on the effect of wear flat inclination on the cutting response of a blunt tool in rock cutting

A vast majority of experimental researches focuses on the cutting action of a sharp cutter, while there has been limited experimental work devoted to the study of the contact process at the wear flat-rock interface. The specific objective of this study is to determine the effect of the wear flat inclination angle ( β ) with respect to the cutter velocity vector ( vv ) on both the contact stress ( σ ) and friction coefficient ( μ ) mobilized at the wear flat-rock interface. An extensive and comprehensive set of cutting experiments was carried out on thirteen different sedimentary quarry rock samples using a state-of-the-art rock cutting equipment. A unique cutter holder was purposely designed and manufactured along with a precise experimental protocol implemented in order to change the back rake angle and therefore the inclination β by steps of 0.10∘ . The experimental observations confirm the existence of three regimes of frictional contact (identified as elastic, elasto-plastic and plastic) for all rock samples. Further, the results suggest that the scaled contact stress is predominantly controlled by a dimensionless number η=E∗tanβq with E∗ the plane strain elastic modulus and q the rock strength

On the initial non-linearity of compressive stress-strain curves for intact rock

The unconfined compression load-displacement curves for rock samples were described. A series of uniaxial compression tests was performed to implement and compare two different methods of deformation measurements. Stress-strain plots corresponding to these different methods were compared with numerical results. Results concluded the nonlinear effects of the interfaces between the loading platen and the sample or sample and the indenter

An application of linearised dimensional analysis to rock cutting

Three linearized predictive models are presented: one from the sandstone and marble data; one from the sandstone data; and one from the marble data. These three models allow modifications as the experimental program progresses. Further, these models are shown to be useful for predicting the machine reaction forces under a variety of test conditions

An analytical model for the indentation of rocks by blunt tools

A methodology based on the cavity expansion model is developed to analyze the indentation of rocks by a class of blunt indenters. The analysis covers the particular self-similar case of indentation by blunt wedges or cones. As an example, the main results for the indentation of rocks by a spherical tool are presented and the analytical solution is compared with experimental results obtained by indenting a sphere in Harcourt granite

Numerical analysis of Rayleigh-Plesset equation for cavitating water jets

High-pressure water jets are used to cut and drill into rocks by generating cavitating water bubbles in the jet which collapse on the surface of the rock target material. The dynamics of submerged bubbles depends strongly on the surrounding pressure, temperature and liquid surface tension. The Rayleigh-Plesset (RF) equation governs the dynamic growth and collapse of a bubble under various pressure and temperature conditions. A numerical finite difference model is established for simulating the process of growth, collapse and rebound of a cavitation bubble travelling along the flow through a nozzle producing a cavitating water jet. A variable time-step technique is applied to solve the highly non-linear second-order differential equation. This technique, which emerged after testing four finite difference schemes (Euler, central, modified Euler and Runge-Kutta-Fehiberg (RKF)), successfully solves the Rayleigh-Plesset (RP) equation for wide ranges of pressure variation and bubble initial sizes and saves considerable computing time. Inputs for this model are the pressure and velocity data obtained from a CFD (computational fluid dynamics) analysis of the jet. Copyright (c) 2007 John Wiley & Sons, Ltd

Flow analysis, transportation, and deposition of frictional viscoplastic slurries and pastes in civil and mining engineering

Backfilling and injection of granular materials into mining induced voids, separated beddings, and cracks, as either diluted slurry or concrete paste, is widely used to control coal mine subsidence. As a viable environmental solution, mine waste and rejected materials from underground coal seams are used in both backfilling and injection mine operations. During longwall mining, the grout slurry is pumped into the separated beds of the fractured rock mass through a pipeline connected to a central vertical borehole, which is drilled deep into the interburden rock strata above the coal seam. Either as dilute slurry or thick paste or cake, the fill material normally needs to travel a significant distance in a long pipeline. A blockage can occur in the pipeline when the slurry velocity falls below a certain critical threshold value, indicating a material phase change from cohesive-viscous to cohesive-frictional. In a previous study of radial flow through disks, complete analytical solutions of the required pump pressure versus fluid volume rate were presented for such slurries, categorized as frictional Bingham-Herschel-Bulkley fluids. This paper is an extension to the theory of fluid mechanics to this type of flow in uniform circular pipes. General analytical solutions were developed for complex fluids in velocity and pressure gradients and velocity and pressure as a function of pipe length, from which special and familiar equations for simpler fluids are derivable by mathematical reduction of the general equations. This study differs from the previous research in consideration of the variable shear parameters rather than fixed values, inclusion of total nonlinear behavior, and implementation of a friction function to mimic behavior of the depositing and consolidating stiff slurry, which can cause a significant pressure rise as a result of the increased shear resistance