Abstract: Three types of Wudang group schist with different macroscopic characteristics were selected to make the standard cylindrical test specimens possessing different schistosity angles. Firstly, P-wave velocity of the specimens were tested after dried and soaked to investigate the velocity anisotropy of Wudang group schist in different water bearing states. Then, combined with mineral composition and microstructure characteristics of three kinds of schist obtained by polarizing microscope and scanning electron microscopy, he wave velocity anisotropy affected by internal and external factors were further investigated. The results indicate that the major minerals of Wudang group schist are hard granular quartz, feldspar and soft muscovite. The higher content of hard mineral or the smaller porosity of schist, the larger P-wave velocity and vice versa. The P-wave velocity of dry samples shows significant anisotropy. As the angle between the direction of wave propagation and foliation decreases, the wave velocity increases gradually. Wave velocity in different directions can be predicted by the formula expressed as wave velocity circle. The wave velocity anisotropy is essentially caused by the directional and the interval distribution of micro fissures, of which the degree k can be evaluated indirectly through the orientation coefficient of muscovite. There is a linear positive correlation between and , and the upper limit of the p-wave anisotropy of the Wudang group schist is 2.90. Due to the increase of the equivalent volume modulus of schist after the pores filled by water, the P-wave velocity of the soaking sample is generally increased. And the increasing effect of velocity depends greatly on the porosity and distribution of micro fissures, leading to the difference of P-wave velocity among different kinds of schists and a inverse correlation between the anisotropy degree of wave velocity for the same kind of schist and the soaking time.

Key words: schist, P-wave velocity, anisotropy, microstructure, mechanism