Deep drilling and induced seismicity experiments at several locations worldwide indicate that, in general, the brittle crust in intraplate regions is critically stressed, pore pressures are close to hydrostatic, and in situ bulk permeability is ∼10 −17 to 10 −16 m 2 . This high permeability, three or four orders of magnitude higher than that measured on core samples, appears to be maintained by critically stressed faults and greatly facilitates fluid movement through the brittle crust. We demonstrate that such high permeabilities can maintain approximately hydrostatic fluid pressures at depths comparable to the thickness of the seismogenic crust. This leads to the counterintuitive result that faulting keeps intraplate crust inherently strong by preventing pore pressures greater than hydrostatic from persisting at depth.

How faulting keeps the crust strong

Biocementation is a recently developed new branch in geotechnical engineering that deals with the application of microbiological activity to improve the engineering properties of soils. One of the most commonly adopted processes to achieve soil biocementation is through microbially induced calcite precipitation (MICP). This technique utilizes the metabolic pathways of bacteria to form calcite (CaCO3) that binds the soil particles together, leading to increased soil strength and stiffness. This paper presents a review of the use of MICP for soil improvement and discusses the treatment process including the primary components involved and major affecting factors. Envisioned applications, potential advantages and limitations of MICP for soil improvement are also presented and discussed. Finally, the primary challenges that lay ahead for the future research (i.e. treatment optimization, upscaling for in situ implementation and self-healing of biotreated soils) are briefly discussed.

State-of-the-Art Review of Biocementation by Microbially Induced Calcite Precipitation (MICP) for Soil Stabilization

The distinct element analysis for hydraulic fracturing in hard rock considering fluid viscosity and particle size distribution

Numerical methods for hydraulic fracture propagation: a review of recent trends

Humanity already possesses the fundamental scientific, technical, and industrial know-how to solve the carbon and climate problem for the next half-century. A portfolio of technologies now exists to meet the world's energy needs over the next 50 years and limit atmospheric CO2 to a trajectory that avoids a doubling of the preindustrial concentration. Every element in this portfolio has passed beyond the laboratory bench and demonstration project; many are already implemented somewhere at full industrial scale. Although no element is a credible candidate for doing the entire job (or even half the job) by itself, the portfolio as a whole is large enough that not every element has to be used.

“Stabilization wedges: Solving the climate problem for the next 50 years with current technologies” from science magazine (2004)

SUMMARY

Tool-rock interaction processes can be classified as indentation or cutting depending on the direction of motion of the tool with respect to the rock surface. The modes of failure induced in the rock by an indenting or a cutting tool can be ductile and/or brittle. The ductile mode is associated with the development of a damage zone, whereas the brittle mode involves the growth of macrocracks. This is the first part of a series of two papers concerned with an analysis of the cutting and the indentation processes based on using the discrete element method. In this paper, numerical simulations of the cutting process are conducted to reproduce the transition from a ductile to a brittle failure mode with increasing depth of cut, which is observed in experiments. The numerical results provide evidence that the critical depth of cut d *  controlling the failure mode transition is related to the characteristic length l = (KIc ∕ σc)2 with KIc denoting the material toughness and σc its unconfined compressive strength. The nature of frictional contact between the cutter face and the rock in the ductile failure mode is also examined. It is shown that the inclination of the total cutting force is controlled by a multi-directional flow mechanism ahead of the cutter that is related to the formation of a wedge of failed material, intermittently adhering to the cutter. As a result, the inclination of the total cutting force varies with the rake angle of the cutter and cannot be considered an intrinsic measure of the interfacial friction between the cutter and the rock. Copyright © 2012 John Wiley & Sons, Ltd.

Discrete element modeling of tool-rock interaction I: rock cutting

Indentation and cutting experiments in rocks reveal that the action of a tool can induce either ductile and/or brittle failure, with the ductile mode associated with damage of the rock and/or plastic flow, and the brittle mode with the propagation of cracks. In normal indentation, the development of a damaged zone precedes the initiation of tensile cracks; in cutting, the failure mechanism switches from a ductile to a brittle mode as the depth of cut is increased beyond a threshold value. In this paper, we first argue that these observations can be accounted for by introducing an intrinsic length scale lm ∼ ( KIc ∕ σc )2 in the rock description (with KIc denoting the toughness and σc the compressive strength). Next, we report the results of numerical simulation of indentation and cutting tests with the discrete element method. After showing that the internal length scale lm can be modified by the ratio of the shear to normal bond strength, we illustrate by numerical simulations that the selection of the f...

Intrinsic Length Scales in Tool-Rock Interaction

Applicability of the Forchheimer Equation for Non-Darcy Flow in Porous Media

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.

An Analytical Model for the Indentation of Rocks by Blunt Tools

The paper reports results of a numerical analysis of the wedge indentation problem. The main objective of this research is to investigate the influence of the lateral confining stress on the development of the plastic zone under the indenter and on the initiation of tensile fractures. Numerical analysis indicates that the location of maximum tensile stress (interpreted as the point of crack initiation) moves away from the indentation axis as the lateral confinement increases. It is found that a small increase in the confining stress from zero induces a large increase in the inclination of this point on the indentation axis. However, the confinement does not reduce significantly the maximum tensile stress and it hardly influences the indentation pressure. These numerical results shed some light on the mechanism of formation of lateral or sub-horizontal tensile cracks observed in the indentation experiments.

Haiying Huang

Papers

Discrete element modeling of tool-rock interaction I: rock cutting

Intrinsic Length Scales in Tool-Rock Interaction

Applicability of the Forchheimer Equation for Non-Darcy Flow in Porous Media

An Analytical Model for the Indentation of Rocks by Blunt Tools

Normal Wedge Indentation in Rocks with Lateral Confinement