DYNAMIC PROPERTIES OF WEATHERED SEDIMENTARY SOFT ROCKS

抄録

The mechanical properties, in particular, the dynamic deformation properties of sedimentary soft rocks which were artificially weathered through dry-wet and freeze-thaw sequence are determined by cyclic triaxial tests and ultrasonic pulse tests in the laboratory. First, the relations among unconfined compressive strength q_u, Young's modulus E by uniaxial compression tests, and shear wave velocity V_s by ultrasonic pulse tests are investigated, and it is shown that probable values of q_u and E of weathered soft rocks can be estimated from V_s. Also, it is concluded from cyclic triaxial tests that (1) the greater the extent of weathering, the larger becomes the dependency on confining pressure of shear modulus G_o at very small strain, (2) relations between shear modulus ratio G/G_o and shear strain amplitude γ depend on the extent of weathering, namely the degree of degradation of G/G_o with γ of heavily weathered specimens is smaller than that of fresh samples. However, if γ is normalized with respect to the reference strain γ_r, G/G_o versus γ/γ_r relations are uniquely expressed irrespective of the degree of weathering, (3) moreover, material damping h versus γ/γ_r relations are also uniquely defined, (4) relations between V_s and γ_r are given as linear on log-log scaled paper, and the larger the shear wave velocity V_s, the smaller becomes the reference strain γ_r. While this relation slightly depends on kind of materials and magnitude of confining pressure, the probable values of γ_r which have a significant influence on the strain dependency of G and h may be estimated from V_s.