pieu de sable

CONT: Sand drains, or piles, are used for compaction, stabilization, and draining of compressible material ... They actually are cylindrical piles of sand in the ground ... They act as wicks for water squeezed from the soil, thus accelerating settlement of the poor material by allowing pore water to drain. Holes for the sand may be drilled with an auger or driven with a pile, which is retracted.
OBS: Terms often found in plural.