In a one-dimensional consolidation test, a sustained load duration in excess of 10{sup}4 mm is rarelyused for evaluation of the coefficient of secondary compression even for very plastic clays. However,there are instances in the literature where load durations have exceeded 10{sup}5 mm. The cloggingof porous stones by migration of soil fines is conventionally prevented by interposing filter paperseparators between the porous stones and the soil specimen. The present study examines the effectof filter paper separators on the secondary compression and swelling characteristics of a bentonite-sand mixture. In long-term volume change tests, use of filter paper separators results in increaseddeformation when the soil is undergoing drained creep in consolidation tests. When the soilundergoes swelling over a long period of time, some collapse occurs due to the decay of the filterpaper separators. The observations of a long-duration drained creep test on this soil are used toexplain the reported secondary compression behavior of some natural soils. The results of the studybring out the need to develop nondegradable separators for long-duration tests to protect porousstones from clogging with soil fines.
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