EXPERIMENTAL ROCK DEFORMATION OF CAMBRIAN-ORDOVICIAN CARBONATES FROM THE VALLEY AND RIDGE OF THE APPALACHIANS

In attempt to determine broad stratigraphic trends in brittle strength, of the Paleozoic section in the Valley and Ridge province of Appalachian, this study looked at the experimental compressive strength at brittle failure of several carbonate formations from the Cambrian to Ordovician section in Rockbridge County, Virginia. A total of 38 cores were taken from samples gathered in the field and tested, utilizing an ADR 2000 triaxial press from ELE International. The cores were deformed at failure, under conditions of axial stress (σ₁) values from 85 to 460 MPa and confining pressure (σ₃ = σ₃), ranging from 5 to 80 MPa. Dry samples were deformed at room temperature with no pore-fluid pressure, and at rapid strain rates such that discrete fractures were developed. Fracture orientation relative to σ₁ was measured. Using a best-fit for all calculated shear and normal stresses, and assuming a Coulomb failure criterion, the angle of the friction, φ, and cohesive shear strength, S_o, were determined for each formation. Preliminary results show a variation of cohesive shear strength, S_o, from between 10-29 MPa and an angle of the friction, φ, from between 36-54 deg. Dolostones of the Lower Cambrian Elbrook and Lower Ordovician Beekmantown Fms. in general had higher S_o and φ than limestones of the Middle Ordovician Lincolnshire and Edinburg Fms.