A method and apparatus are provided for forming an in situ subterranean soil cement structure wherein a soil processing tool incorporates a novel cyclonic mixing region. The cyclonic mixing region is formed by deflecting a jetstream which initially moves away from a hollow Kelly and, after being deflected, the jetstream is redirected into a direction flowing towards the hollow Kelly. A contoured flight is provided having an exterior contoured surface extending upwardly from a central section of the contoured flight and bends through an angle greater than 110° in order to deflect a jetstream which is directed outwardly from the hollow Kelly back towards the hollow Kelly. By preventing any of the high pressure jetstreams from impacting the side wall of the hole, higher jetstream velocities and pressures may be utilized. Two or more jetstreams may also be utilized to direct their jetstreams around a central horizontal axis to provide the cyclonic mixing region. A preferred embodiment is designed for use in clay subsoil typically found in the Gulf Coast region of the United States. This preferred embodiment utilizes a support structure strengthening the tool and also utilizes a flat bottom with cutting teeth extending downwardly below the flat bottom surface of the tool.