Drilling-induced borehole-wall damage at spent fuel test-climax

Microcracks in a sample of quartz monzonite from the Spent Fuel Test-Climax were measured by means of a scanning electron microscope in order to estimate the background level of damage near the borehole-wall. It appears that the hammer-drilling operation used to create the borehole has caused some microfracturing in a region 10 to 30 mm wide around the borehole. Beyond 30 mm, the level of microfracturing cannot be distinguished from background

SEM studies of stressed and irradiated Climax Stock quartz monzonite

In an effort to find the mechanism by which gamma irradiation weakens the unconfined compressive strength of Climax Stock quartz monzonite (CSQM), sections of rock which had been irradiated and loaded to near failure were studied by scanning electron microscopy and compared to sections of rock which had been loaded but not irradiated. The quantities measured and compared were numbers and lengths of microfractures in the rock. We found that the crack parameters depended neither on irradiation treatment nor even on stress history, except in one sample which actually failed. By comparison to cracks counted in other granites by other workers, the crack statistics on CSQM are much noisier and much less indicative of stress history. CSQM is structurally more heterogeneous than the other granites, which is probably the cause of the greater noise level. 12 references, 3 figures, 5 tables

Physical and chemical changes to rock near electrically heated boreholes at Spent Fuel Test-Climax

Sections of Climax Stock quartz monzonite taken from the vicinity of two electrically heated boreholes at Spent Fuel Test-Climax (SFT-C) have been studied by scanning electron microscopy and optical microscopy for signs of changes in crack structure and in mineralogy resulting from operations at SFT-C. The crack structure, as measured by density of cracks and average crack lengths was found not to have changed as a result of heating, regardless of distance from the heater hole. However, rock near the heater borehole sampled in the north heater drift was found to be more cracked than rock near the borehole sampled in the south heater drift. Mineralogically, the post-test samples are identical to the pre-test samples. No new phases have been formed as a result of the test. 10 refs., 6 figs., 8 tabs

Low-Temperature Plasticity in Olivine: Grain Size, Strain Hardening, and the Strength of the Lithosphere

Plastic deformation of olivine at relatively low temperatures (i.e., low-temperature plasticity) likely controls the strength of the lithospheric mantle in a variety of geodynamic contexts. Unfortunately, laboratory estimates of the strength of olivine deforming by low-temperature plasticity vary considerably from study to study, limiting confidence in extrapolation to geological conditions. Here we present the results of deformation experiments on olivine single crystals and aggregates conducted in a deformation-DIA at confining pressures of 5 to 9 GPa and temperatures of 298 to 1473 K. These results demonstrate that, under conditions in which low-temperature plasticity is the dominant deformation mechanism, fine-grained samples are stronger at yield than coarse-grained samples, and the yield stress decreases with increasing temperature. All samples exhibited significant strain hardening until an approximately constant flow stress was reached. The magnitude of the increase in stress from the yield stress to the flow stress was independent of grain size and temperature. Cyclical loading experiments revealed a Bauschinger effect, wherein the initial yield strength is higher than the yield strength during subsequent cycles. Both strain hardening and the Bauschinger effect are interpreted to result from the development of back stresses associated with long-range dislocation interactions. We calibrated a constitutive model based on these observations, and extrapolation of the model to geological conditions predicts that the strength of the lithosphere at yield is low compared to previous experimental predictions but increases significantly with increasing strain. Our results resolve apparent discrepancies in recent observational estimates of the strength of the oceanic lithosphere.Support for this research was provided by Natural Environment Research Council (NERC) grant NE/M000966/1 and NSF Division of Earth Sciences grants 1255620, 1464714, and 1550112. D.E.J.A. acknowledges funding from the Royal Academy of Engineering through a research fellowship

Effect of gamma irradiation on the strength of Climax stock quartz monzonite

A laboratory study was made of the effects of a massive dose of {gamma} irradiation upon the mechanical properties of Climax stock quartz monzonite. Twenty-nine cylinders of rocks were tested using the Brazilian method and 26 strain gauged cylinders were tested to failure in uniaxial compression. One-half the cylinders in each group were subjected to a {gamma} ray dose of 13.2 MGy (1.32 x 10{sup 9} rads), or six times the maximum five-year dose to rock at the Spent Fuel Test-Climax, Nevada Test Site. The irradiation treatment lowered the ultimate compressional strength and lowered Young`s modulus under uniaxial loads greater than 20 MPa. The treatment did not measurable affect the elastic behavior of the rock in compression, nor did it affect the Brazilian tensile strength. These trends suggest that the {gamma} irradiation lowered the threshold stress at which microfractures begin to form. The irradiation has apparently not directly induced microfracturing in the rock, so a direct degrading effect on thermal and fluid transport properties is not expected

Capabilities for measuring physical and chemical properties of rocks at high pressure

The Experimental Geophysics Group of the Earth Sciences Department at Lawrence Livermore National Laboratory (LLNL) has experimental equipment that measures a variety of physical properties and phase equilibria and kinetics on rocks and minerals at extreme pressures (to 500 GPa) and temperatures (from 10 to 2800 K). These experimental capabilities are described in this report in terms of published results, photographs, and schematic diagrams

Drilling-induced borehole-wall damage at spent fuel test-climax

Microcracks in a sample of quartz monzonite from the Spent Fuel Test-Climax were measured by means of a scanning electron microscope in order to estimate the background level of damage near the borehole-wall. It appears that the hammer-drilling operation used to create the borehole has caused some microfracturing in a region 10 to 30 mm wide around the borehole. Beyond 30 mm, the level of microfracturing cannot be distinguished from background

Can the multianvil apparatus really be used for high-pressure deformation experiments?

Past claims of the suitability of the MA-8 multianvil press as a deformation apparatus may have been overstated. On the basis of measurements of final octahedron size and of guide block displacement as a function of time, using the 10/5, 14/8, and 18/11 assemblies (octahedron edge length in mm/truncation edge length in mm) with MgO octahedra and pyrophyllite gasketing, it appears that at run conditions of interest to most researchers there is no appreciable time-dependent creep of gaskets and octahedra. All inelastic deformation occurs at rather low pressures: below about 10 GPa for the 10/5, 7 GPa for the 14/8, and 6 GPa for the 18/11 assemblies, with substantial uncertainties in these pressures. Above these limits all deformation of the pressure medium is elastic. Pressure stepping as a means of increasing the inelastic deformation rate of a sample is probably ineffective. Displacement measured at the guide blocks, previously believed to indicate deformation of the gaskets and octahedron, appears now to be unrelated to creep of these components. The calibrations have not been exhaustive and there is considerable scatter in some of the size measurements, so the above conclusions are not unequivocal. The calibrations do not exclude the possibility of deformation of a few tens of microns after the attainment of high pressure. Efforts to impose permanent shape change to samples at high pressure and temperature simply by relying on long run durations must be viewed with skepticism. There may be possibilities for deformation in the multianvil apparatus if materials of contrasting elastic modulus are used to differentially load a sample during pressure stepping

SEM studies of stressed and irradiated Climax Stock quartz monzonite

In an effort to find the mechanism by which gamma irradiation weakens the unconfined compressive strength of Climax Stock quartz monzonite (CSQM), sections of rock which had been irradiated and loaded to near failure were studied by scanning electron microscopy and compared to sections of rock which had been loaded but not irradiated. The quantities measured and compared were numbers and lengths of microfractures in the rock. We found that the crack parameters depended neither on irradiation treatment nor even on stress history, except in one sample which actually failed. By comparison to cracks counted in other granites by other workers, the crack statistics on CSQM are much noisier and much less indicative of stress history. CSQM is structurally more heterogeneous than the other granites, which is probably the cause of the greater noise level. 12 references, 3 figures, 5 tables