Crack-initiated concentrated leakage is a critical loading case for embankment dams, and filters are expected to remain sufficiently collapsible to avoid sustaining an open crack or roof over a developing pipe. This paper compares candidate filter materials derived from natural soils and manufactured crushed rock. Sand Castle Test results quantify material-specific relationships between relative compaction and collapse time, and are interpreted using established collapse time reference markers. Compared with natural materials, crushed rock materials generally require less compaction to develop the potential to support a roof over a developing pipe and are more sensitive to overcompaction, such that relatively small increases in densification could lead to substantially longer collapse times and reduced collapsibility. Within this sand and gravel candidate filter dataset, excluding tailings and with non-plastic fines up to 13% passing 0·075 mm, material origin and processing provided clearer separation than fines content alone. The findings support practical compaction control and screening in filter selection.
Hans Rönnqvist (Wed,) studied this question.