Apparatus to install small diameter columns of granular material in soil which includes rotating hollow shaft mandrel with external projections to aid mandrel advance into the soil and define the size of the cavity formed in the soil, the cavity being filled with granular material to form the column as the mandrel is withdrawn. The apparatus includes a storage hopper in the vicinity of its base, with the hopper sized to hold material to form more than one column, from which material is incrementally conveyed or pumped to a feed tank system which supplies granular material to the cavity along a flow path extending through the hollow shaft mandrel to produce the column. When a group of columns is required, as in a sand drain grid, the columns can be completed sequentially with reasonable continuity in the multiple column formation cycle.