Static and dynamic elastic moduli of rock in a complex axisymmetric stressed state
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The magnitude of the ratio of the static and dynamic moduli in the sublimiting and trans-limiting strain regions depends to a significant degree on the stress-strain state.
For small strains (elastic region), the range in variation in the Est/Ed ratio for lateral pressures of less than 20 MPa falls within the limits of 0.7–1.3 (for marble) as a function of axial force. For large deformations (inelastic region), the Est/Ed ratio varies within the limits of ±0.04 as a function of the relationship between the axial and lateral pressures. The range of variation in the Est/Ed ratio increases with decreasing axial loads. This ratio increases monotonically with increasing lateral pressure.
It is shown that constancy of the amplitude of the ultrasound signal can be explained by the appearance of two effects acting in opposing directions-by a reduction in the effective diameter of the microcracks and by an increase in the damping coefficient with frequency. According to ultrasound measurements, the effective diameter of the microcracks is reduced by a factor of 1.75 in the interval of hydrostatic pressures from zero to 100 MPa.
The relationships obtained make it possible to determine the magnitude of the static modulus of rock (for example, in the zone of influence of an underground excavation) from the data of ultrasound measurements, and to estimate the behavior of rock subject to a dynamic disturbance.
KeywordsRock Mass PMMA Hydrostatic Pressure Dynamic Modulus Lateral Pressure
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