Mechanical properties of Nugget sandstone

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Abstract
The mechanical properties of Nugget sandstone have been determined from a number of independent measurements at pressures up to 30 kbar. Pressure- volume, strength, uniaxial stress, and uniaxial strain tests yield the failure surface and effective moduli as a function of stress state, i.e., mean pressure and shear stress. Acoustic velocity determinations provide the effective moduli for low-amplitude dynamic waves. At atmospheric pressure the initial effective bulk modulus in tests with applied differential stresses (~40 kbar) differs from that determined hydrostatically (23 kbar). This and a large pressure derivative of the shear modulus at low pressure are believed to be due to an abundance of cracks with low aspect ratios. The initial effective shear modulus of about 55 kbar increases rapidly with the closing of cracks. At 1 kbar confining pressure, a shear modulus of about l20 kbar is determined in both uniaxial stress and uniaxial strain experiments. The rock has an ultimate strength comparable to granite (1.2 kbar unconfined) and exhibits brittle behavior at failure to the highest mean pressure studied (14 kbar). Failure is preceded by dilatant behavior. (auth)

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