Abstract: A drilling assembly (210) for in-situ cast piles has a drill stem (211) with a helical flyte (212). A drilling head (224), with teeth (225), and a belling tool (226), with retractable cutting tools (227) are mounted on, in driving engagement with, the non-circular shank (218) of a soil stabilization spear (214). The spear (214) drills a pilot hole in advance of the drilling head (224) and grout pumped down through the tubular body (215) of the spear (214) fills the cracks and fissures in the surrounding soil to stabilize the soil as the drilling assembly (210) is advanced. When the desired depth is reached, the rotation of the drilling assembly (210) is reversed and cutting tools (227) are extended to cut a "bell" or annular chamber around the hole. As the drill assembly (210) is withdrawn from the hole, grout pumped down the interior (230) of the stem (211) fills the hole to cast a pile in-situ, the increased diameter of the bottom of the pile, and the stabilized soil around it, increasing its load strength.