Rock Anisotropy and the Theory of Stress Measurements

Any undisturbed rock mass is subject to natural stresses inclu ding gravitational stresses due to the mass of the overburden and possibly tectonic stresses due to the straining of the earth's crust and remanent stresses due to past tectonism. Knowledge of the in situ stress field must be integrated into any rock engineering design along with general rock mass characteristics such as de for mability, strength, permeability and time dependent behavior. For example, the choice of optimum orientation and shape of deep underground caverns or complex underground works will be controlled by the orientation and the magnitude of the in situ stress @ield if it is necessary to minimize stress concentration problems. Long term variation of the in situ stress field may also help to evaluate the potential hazard of earthquake occurences. The magnitude and orientation of the stress field ata point within a rock mass can be measured but there is no known method by which the state of stress at a point can be accurately determined by instruments located remotely. In general, measurements are made inside boreholes, on outcrops or on the internal surfaces of under ground cavities. Most of the measuring techniques intentionally disturb the state of stress in the rock and then measure consequent strains and displacements. Measured strains or displacements are then related to the stresses through assumptions of material behavior. A common procedure is to assume that the rock mass is linearly elastic, isotropic, continuous and homogeneous.

Texte du rabat

Any undisturbed rock mass is subject to natural stresses inclu­ ding gravitational stresses due to the mass of the overburden and possibly tectonic stresses due to the straining of the earth's crust and remanent stresses due to past tectonism. Knowledge of the in situ stress field must be integrated into any rock engineering design along with general rock mass characteristics such as de for­ mability, strength, permeability and time dependent behavior. For example, the choice of optimum orientation and shape of deep underground caverns or complex underground works will be controlled by the orientation and the magnitude of the in situ stress @ield if it is necessary to minimize stress concentration problems. Long term variation of the in situ stress field may also help to evaluate the potential hazard of earthquake occurences. The magnitude and orientation of the stress field ata point within a rock mass can be measured but there is no known method by which the state of stress at a point can be accurately determined by instruments located remotely. In general, measurements are made inside boreholes, on outcrops or on the internal surfaces of under­ ground cavities. Most of the measuring techniques intentionally disturb the state of stress in the rock and then measure consequent strains and displacements. Measured strains or displacements are then related to the stresses through assumptions of material behavior. A common procedure is to assume that the rock mass is linearly elastic, isotropic, continuous and homogeneous.

Contenu
1: Introduction.- 2: Deformability of Anisotropic Rocks.- 2.1 Introduction.- 2.2 Constitutive Relations.- 2.3 Testing of Anisotropic Rocks.- 3: Strength of Anisotropic Rocks.- 3.1 Introduction.- 3.2 Experimental Observations.- 3.3 Analytical Models.- 4: Elastic Equilibrium of an Anisotropic Homogeneous Body Bounded Internally by a Cylindrical Surface of Arbitrary Cross Section.- 4.1 Introduction.- 4.2 Geometry and Definition of the Problem.- 4.3 Formulation of the Problem.- 4.4 Special Case of Anisotropy: A Plane of Elastic Symmetry Perpendicular to the Hole Axis.- 4.5 Plane Strain and Plane Stress Formulations.- 4.6 Particular Solution for an Infinite Cylinder with a Circular Cross Section.- 5: Elastic Equilibrium of an Anisotropic Homogeneous Body Bounded Internally by an Isotropic Inclusion of Circular Cross Section.- 5.1 Introduction.- 5.2 Geometry and Definition of the Problem.- 5.3 Formulation of Problem (A).- 5.4 Formulation of Problem (B).- 5.5 Condition of Continuity.- 5.6 Closed Form Solutions.- 5.7 Remarks.- 5.8 Numerical Examples.- 6: Influence of Rock Anisotropy on Stress Measurements by Overcoring Techniques.- 6.1 Introduction.- 6.2 In Situ Determination of Stress by Relief Techniques.- 6.3 Information Obtained from Measuring Techniques.- 6.4 General Formulas for Overcoring and Undercoring Techniques.- 6.5 General Results for Overcoring in Anisotropic Media.- 7: Summary and Conclusions.- References.- Appendix 2.1.- Appendix 4.1.- Appendix 4.2.- Appendix 4.3.- Appendix 4.4.- Appendix 4.5.- Appendix 4.6.- Appendix 4.7.- Appendix 4.8.- Appendix 5.1.- Appendix 5.2.- Appendix 5.3.- Appendix 5.4.- Appendix 6.1.- Appendix 6.2: Program Berni 1.- Appendix 6.3: Program Berni 2.- Appendix 6.4: Program Berni 3.- Appendix 6.5: Program listings.