A series of triaxial tests was carried outunder coupled cyclic-seepage loads for Tianjin coastal soft clay

and thevariation of permeability in different loading stages was analyzedsystematically. Combined with SEM and MIP

the evolution mechanism ofpermeability was elaborated. The results showed that under the couplingcyclic-seepage loads

the permeability of soft clay present three variationstages. With seepage loads increasing

the permeability increased initially andthen decreased

but just reverse for increase of critical dynamic stress ratio.The evolution of permeability was caused by the adjustment of micro-features ofpore shape

size

and distribution: for initial vibration

large compression ofsuper large pores (>2.5 μm) between particles occurred and pore shape variedlittle

leading to the linear reduction of permeability; at the medium loadingstage

the large particles were broken

and the newly formed small particleswere densely filled between the large particles

inducing a large number of “compactand zigzag” small pores (0.05 μm <<0.1μm)

which led to the slow decrease of permeability; at later loading stage

thestructure was compact and stable

and permeability was basically unchanged. Forthe unstable deformation

the “strips” like macropores were re-formed betweenthe particle clusters (aggregates)

and the permeability increased. The resultscan provide a theoretical basis for the determination of the permeability inthe fluid-solid coupling analysis.