Abstract
Results are reported from a series of hydraulic tests designed to capture the response of soils subjected to simultaneous axial compression and upward seepage flow. An internally stable soil could be characterized by the development of heave at very high hydraulic pressures, while an unstable soil suffered from suffusion at relatively smaller hydraulic pressures. At the onset of seepage failure, the local porosity of critical zone in soil increased, while hydraulic gradients and associated effective stresses decreased. During static tests, seepage induced heave and composite heave-piping failures evolved in dense uniform fine gravels and sands, respectively, and suffusion in gap-graded sand-gravel mixtures. Under cyclic loading, the uniform soils reproduced similar hydraulic responses albeit at relatively smaller applied hydraulic pressures and larger local hydraulic gradients than static tests. The gap-graded soil exhibited premature suffusion that became excessive at higher cyclic frequencies. Cyclic loading induced agitation and transient pore pressure deteriorated the stable constriction network of soil, thereby allowing residual fines to escape from pore spaces and causing internal instability. The instability potential of tested soils could be quantified by comparing the pre- and post-test particle size distribution analyses. Results are compared with the assessments of various existing criteria for internal stability and recommendations are made for possible practical implications.
Keyword(s)
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