Variation in Anisotropy with Dehydration in Layered Sandstone
Anisotropy in rock could significantly affect the stability and safety of rock engineering by differing physical and mechanical properties of rock in different directions. Another major factor for physical and mechanical properties of rock is moisture state, however, whether anisotropy can be altered by it remains unclear. This study investigated variation in anisotropy (by conduct-ing ultrasonic tests) with moisture state (measured by nuclear magnetic resonance) in layered sandstones, and interpreted the phenomenon from the perspective of linking dehydration with pore structure of rock. The results show that (1) sandstone with more obvious bedding bears stronger anisotropy, the P-wave velocity in the perpendicular direction is much lower than that in the parallel direction. (2) The anisotropy index fluctuates around 1 with dehydration of sandstone without obvious bedding, while the anisotropy in sandstone with obvious bedding was significantly enhanced be dehydration. (3) During dehydration bulk water escaped firstly then capillary water and bound water. (4) Dehydration is controlled by the bedding structure. The different dehydration rates of pore water in different directions inevitably lead to heterogeneity in moisture state that change the anisotropy of the rock, which is reflected by the non-synchronous changes in P-wave velocities in different directions.