締固めた凝灰岩の特異な透水性について

The permeability tests were performed on compacted tuff using triaxial cells and the unique properties of permeability were confirmed in succession with last year.
The coefficient of permeability k was decreased usually with increment of consolidation pressure esc σ3c'. But k of some specimen was increased with increment of σ3c' and k of some specimen was decreased with application of buck pressure ub. Moreover, percolated water of some specimen became muddy. Piping test was performed using perforated plate at flowout side. From this test, the risk of piping is not observed in case that hydraulic gradient is equeal or smaller than 10.