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Practical estimates of rock mass strength

The validity of the cubic law for laminar flow of fluids through open fractures consisting of parallel planar plates has been established by others over a wide range of conditions with apertures ranging down to a minimum of 0.2 µm. The law may be given in simplified form by Q/Δh = C(2b)3, where Q is the flow rate, Δh is the difference in hydraulic head, C is a constant that depends on the flow geometry and fluid properties, and 2b is the fracture aperture. The validity of this law for flow in a closed fracture where the surfaces are in contact and the aperture is being decreased under stress has been investigated at room temperature by using homogeneous samples of granite, basalt, and marble. Tension fractures were artificially induced, and the laboratory setup used radial as well as straight flow geometries. Apertures ranged from 250 down to 4µm, which was the minimum size that could be attained under a normal stress of 20 MPa. The cubic law was found to be valid whether the fracture surfaces were held open or were being closed under stress, and the results are not dependent on rock type. Permeability was uniquely defined by fracture aperture and was independent of the stress history used in these investigations. The effects of deviations from the ideal parallel plate concept only cause an apparent reduction in flow and may be incorporated into the cubic law by replacing C by C/ƒ. The factor ƒ varied from 1.04 to 1.65 in these investigations. The model of a fracture that is being closed under normal stress is visualized as being controlled by the strength of the asperities that are in contact. These contact areas are able to withstand significant stresses while maintaining space for fluids to continue to flow as the fracture aperture decreases. The controlling factor is the magnitude of the aperture, and since flow depends on (2b)3, a slight change in aperture evidently can easily dominate any other change in the geometry of the flow field. Thus one does not see any noticeable shift in the correlations of our experimental results in passing from a condition where the fracture surfaces were held open to one where the surfaces were being closed under stress.

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VALIDITY OF CUBIC LAW FOR FLUID FLOW IN A DEFORMABLE ROCK FRACTURE - eScholarship

Evaluating Fractured Reservoirs Reservoir Management Detecting And Predicting Fracture Occurrence and Intensity Analysis Of Anisotropic Reservoirs Analysis Procedures in Fractured Reservoirs Appendix A: List of Documented Fractured Reservoirs Appendix B: Procedures Checklist Appendix C: Averaging Techniques

Geologic Analysis of Naturally Fractured Reservoirs

Scaling in fracture systems has become an active field of research in the last 25 years motivated by practical applications in hazardous waste disposal, hy- drocarbon reservoir management, and earthquake haz- ard assessment. Relevant publications are therefore spread widely through the literature. Although it is rec- ognized that some fracture systems are best described by scale-limited laws (lognormal, exponential), it is now recognized that power laws and fractal geometry provide widely applicable descriptive tools for fracture system characterization. A key argument for power law and fractal scaling is the absence of characteristic length scales in the fracture growth process. All power law and fractal characteristics in nature must have upper and lower bounds. This topic has been largely neglected, but recent studies emphasize the importance of layering on all scales in limiting the scaling characteristics of natural fracture systems. The determination of power law expo- nents and fractal dimensions from observations, al- though outwardly simple, is problematic, and uncritical use of analysis techniques has resulted in inaccurate and even meaningless exponents. We review these tech- niques and suggest guidelines for the accurate and ob- jective estimation of exponents and fractal dimensions. Syntheses of length, displacement, aperture power law exponents, and fractal dimensions are found, after crit- ical appraisal of published studies, to show a wide vari- ation, frequently spanning the theoretically possible range. Extrapolations from one dimension to two and from two dimensions to three are found to be nontrivial, and simple laws must be used with caution. Directions for future research include improved techniques for gathering data sets over great scale ranges and more rigorous application of existing analysis methods. More data are needed on joints and veins to illuminate the differences between different fracture modes. The phys- ical causes of power law scaling and variation in expo- nents and fractal dimensions are still poorly understood.

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Scaling of fracture systems in geological media

A review of techniques, advances and outstanding issues in numerical modelling for rock mechanics and rock engineering

Draft ISRM suggested method for the complete stress-strain curve for intact rock in uniaxial compression

Numerical methods in rock mechanics

Estimation of discontinuity spacing and trace length using scanline surveys

Keywords: Caracterisation ; Resistance ; Deformation ; Analyse ; Dimensionnement ; Essais sur pieux ; Excavation ; Revetement ; Auscultation ; Realisations existantes Reference Record created on 2004-09-07, modified on 2016-08-08

Comprehensive rock engineering

Preface Units and Symbols Part A: Illustrative Worked Examples - Questions and Answers Introduction Geological setting Stress In situ rock stress Strain and the theory of elasticity Intact rock: deformability, strength and failure Fractures and hemispherical projection Rock masses: deformability, strength, failure and Permeability Anisotropy and inhomogeneity Testing techniques Rock mass classification Rock dynamics and time dependency Rock mechanics interactions and rock engineering systems Excavation principles Rock reinforcement and rock support Foundations and slopes - instability mechanisms Design of surface excavations Underground excavation instability mechanisms Design of underground excavations Part B: Questions Only The questions in Part A are repeated here without the answers for those who wish to attempt the questions without the answers being visible Questions 1.1-1.5: Introduction. Questions 2.1-2.10: Geological setting. Questions 3.1-3.10: Stress. Questions 4.1-4.10: In situ rock stress. Questions 5.1-5.10: Strain and the theory of elasticity. Questions 6.1-6.10: Intact rock. Questions 7.1-7.10: Fractures and hemispherical projection. Questions 8.1-8.10: Rock masses. Questions 9.1-9.10: Permeability. Questions 10.1-10.10: Anisotropy and inhomogeneity. Questions 11.1-11.10: Testing techniques. Questions 12.1-12.10: Rock mass classification. Questions 13.1-13.10: Rock dynamics and time dependency. Questions 14.1-14.10: Rock mechanics interactions and rock engineering systems. Questions 15.1-15.10: Excavation principles. Questions 16.1-16.10: Rock reinforcement and rock support. Questions 17.1-17.10: Foundations and slopes - instability mechanisms. Questions 18.1-18.10: Design of surface excavations. Questions 19.1-19.10: Underground excavation instability mechanism. Questions 20.1-20.10: Design of underground excavations. Appendix 1. 3-D stress cube model Appendix 2. Hemispherical projection sheet Appendix 3. Rock mass classification tables: RMR and Q References Index

John A. Hudson

Papers

Draft ISRM suggested method for the complete stress-strain curve for intact rock in uniaxial compression

Numerical methods in rock mechanics

Estimation of discontinuity spacing and trace length using scanline surveys

Comprehensive rock engineering

Engineering Rock Mechanics: An Introduction to the Principles