New method for true-triaxial rock testing

Two new and related true-triaxial apparatus are described that make use of conventional triaxial pressure vessels in combination with specially configured, high-pressure hydraulic jacks inside these vessels. The development combines advantages not found in existing facilities, including a compact design, pore-pressure and flow-through capabilities, the ability to attain high principal stresses and principal stress differences, direct access to parts of the sample, and provisions to go to relatively large deformations without developing serious stress field inhomogeneities

Analysis of steady state creep of southeastern New Mexico bedded salt

Steady state creep rates have been obtained from a large suite of existing experimental creep data relating to bedded rock salt from the Salado formation of S.E. New Mexico. Experimental conditions covered an intermediate temperature range from 22/sup 0/C to 200/sup 0/C, and shear stresses from 1000 psi (7 MPa) to 6000 psi (31 MPa). An expression, based on a single diffusion controlled dislocation climb mechanism, has been found to fit the observed dependence of steady state creep rate on shear stress and temperature, yielding an activation energy of 12 kcal/mole (50 kJ/mole) and a stress exponent of 4.9. Multiple regression analysis revealed a dependence on stratigraphy, but no statistically significant dependence on pressure of specimen size. No consistent dilatancy or compaction associated with steady state creep was found, although some individual specimens dilated or compacted during creep. The steady state creep data were found to agree very well with creep data for both bedded and dome salt from a variety of other locations

Quasi-static rock mechanics data for rocksalt from three Strategic Petroleum Reserve domes

Triaxial compression and extension experiments have been run on rocksalt samples from three Strategic Petroleum Reserve (SPR) domes. Seventeen quasi-static tests were loaded at mean stress rates of .66 to 1.04 psi/sec (4.5 to 7.2 kPa/sec), confining pressures of 14.5 to 2000 psi (0.1 to 13.8 MPa) and temperatures of 22 to 100/sup 0/C. Eleven of the test specimens were from Bryan Mound, Texas, and three each were from Bayou Choctaw, Louisiana, and West Hackberry, Louisiana. In general, the resulting mechanical data from the three domes are similar, and they are consistent with previously published data. Ultimate sample strengths are directly related to confining pressure (least principal stress) and indirectly related to temperature, while ductility increases with both pressure and temperature

Micro-gas Hypothesis for Behaviors of Rocks under Loading

I propose a micro-gas hypothesis for the mechanism of mechanical and physical behaviors of intact rocks under loading in this paper. The rock behaviors include elastic deformation, brittle cracking, strain hardening, strain softening, ductile deformation, plastic deformation, creep, as well as change from brittle to ductile under confining pressures. The hypothesis is based on the observation that natural gas can be present in micro-voids, micro-pores, lattice boundaries and interfaces of intact rocks and their minerals with various porosities. The coupled interaction between the micro-gas and the rock mineral solids can determine the individual behaviors of intact rocks under loading