Abstract: Techniques are described for forming an elevated concrete slab-like supporting platform. A sand blanket is installed on the platform site and supporting piles are driven down through the sand blanket. A concrete slat is poured over the sand blanket and a moat is dug around its periphery. Water jet nozzles are positioned within the sand blanket prior to pouring of the concrete slab; and water conduits are also provided to extend from outside the sand blanket to the nozzles. After the concrete slab hardens, water is pumped through the conduits to form water jets at the nozzles which wash the sand blanket out from under the slab.