Cutting tool adapter and method of underpinning structures using cutting tool adapter for soil mixing

A method of underpinning an existing structure, comprising:

• creating an approach pit in an area adjacent to soil below the existing structure;
• inserting a mechanical cutting tool into the approach pit, the mechanical cutting tool including at least a drum and plurality of cutting blades attached thereto;
• rotating the mechanical cutting tool to a substantially horizontal position, rotating the mechanical cutting tool including rotating the drum and plurality of cutting blades;
• cutting and dislodging soil below the existing structure by rotating the drum and plurality of cutting blades relative to a remaining portion of the cutting tool, wherein the cutting and dislodging soil further includes contacting a bottom surface of the existing structure with the cutting tool to remove soil in contact with the bottom surface of the existing structure;
• introducing an additive to the soil below the existing structure;
• using the mechanical cutting tool, mixing the soil and the additive in an area below the existing structure;
• and
• allowing the mixed soil and additive to harden forming an underpinning structure below the existing structure.