Lubrication can effectively reduce necessary thrust for over-cutting if a discrete layer of the lubricant is maintained between the pipe and the excavated soil. The lubricant must be designed to form a layer in the surrounding soil, be pressurized to overcome underground water pressure and stabilize the over-cutting area. The lubricant should fill the complete over-cutting area to minimize surface settlement. However, it has been clarified that for a commercial lubricant to be effective, the ingredients such as sodium and potassium should be eliminated. As a result, for a lubricant not to lose its function as a support against the overburdening pressure of an over-cutting area (hereinafter referred to as tail void) and to enable a reduction in thrust, it is necessary to develop a better quality lubricant that can overcome these problems as soon as possible. From this perspective, a lubricating material comprised of a mixture of surfactant and fly ash was developed. This report focuses attention on minimizing soil deformation. In particular, to stabilize the layer in tail void between the pipe and the excavated soil and to examine the characteristics of material attributes to avoid reduction in thrust, a variety of experiments were performed using both traditional lubricating materials and a new material mixed with fly ash.