To provide a working method which is inexpensive, has a water sealing performance, can correspond by purifying contaminated soil in a wall position, does not permeate a contaminated substance even if ground water containing the contaminated substance penetrates the wall and has an earthquake-proof performance.

A shielding wall is provided by a mud water drilling and solidifying method without a vertical joint and including continuous groove drilling - continuous wall creation in order to enhance the water sealing performance. Since the shielding wall washes to reuse soil in the site, the soil is introduced into a classification washing plant by carrying out the mud water drilling, and classification and washing are carried out. A mud water solidification material, an insolubilization material and further natural cohesive soil are loaded into reusable soil after classification and washing, and kneaded. In keeping with the progress of the mud water drilling, the soil is mixed and agitated with the mud water in a drilling completed groove in a horizontal direction from the rear of about 20 m to be back-filled, and the mud water is solidified. Mud water solidification work is carried out continuously so as not to generate the vertical joint. At this time, a neutral solidification material is used so that the solidification material does not react with the insolubilization material. The shielding wall to be made by solidifying the mud water suppresses a uniaxial compression strength to secure a deformation follow-up property.