PURPOSE: To apply an earth pressure system shielding method even to the gravel ground under high water pressure by blending water and macromolecule polymer system silicate at a given proportion to make a mud-adding material, and injecting the mud-adding material into a working face side of a shielding machine.

CONSTITUTION: A mud-adding material is made to have viscosity of about 150-250cps to the viscous ground by blending an about 5-10kg main material of inorganic system nacromolecule polymer silicate powder to 1000l water, and viscosity of about 250-850cps for the sand ground by blending the about 10-50kg same main material to 1000l water. Then the mud-adding material of a planed quantity is pressure-injected in a chamber C of a shielding machine B and a working face side, and the working face is cut and also earth and sand are taken in the chamber C. This excludes water among soil grains with the mud-adding material, and fills gaps among the soil grains with the mud- adding material, enabling the application of a shielding method even to the sand ground under high water pressure.