岩石の力学的性質におよぼす繰返し荷重の影響 (第1報)

抄録

Some physical properties of Sanjome andesite and Aoishi sandy-tuff are measured before and after apply-ing repeated compressive or tensile load with mean stress of 35% and stress amplitude of 30% of static compre-ssive or tensile strength respectively, until 10₆cycles, and the difference of physical properties and the effects of the number of stress cycle on some mechanical properties are investigated.
For both rocks, the changes of specific gravity and porosity are relatively small, within the limit of accuracy of measurement, and it could be said that there is no influence of repeated compressive load on both properties, but from the shape of stress-strain curve of andesite there is a tendency of increasing of volume of clos-ing cracks with increasing the number of stress cycle.
Uniaxial compressive and tensile strengths remain constant after applying repeated load. This agrees with the suggestion that the fatigue failure of rock under repeated loading is a stochastic process.
There is no remarkable change of-the static stress-strain curve of both rocks by applying repeated tensile load, on the other hand, by applying repeated compressive load and in the range of small strain, static tangent Young's modulus of andesite decreases and Poisson's ratio increases from the early stage of repetition of load.
The distinct change ofP-wave velocity measured at the same direction as the loading direction in rock is not observed after applying repeated tensile load. When repeated compressive load is applied, the velocity in Aoishi sandytuff remains constant, while the velocity in Sanjome andesite increases.