PURPOSE:To more securely inject grout in correspondence to the properties of the ground, when injection is shifted from flash setting to slow setting, by shifting injection to slow setting while injecting grout in the period of the shift. CONSTITUTION:A flash setting grout G is injected through an injection pipe 1, and a packer or primary injection is formed around the injection pipe 1. Next, a shifting period grout Gm is injected to complement the flash setting grout G. Then, a slow setting grout Gl is injected to carry out permeation injection. After completion of this injection, the injection pipe 1 is stepped up, and while injection is shifted to a grout of short gel time, step-up is carried out, and in the position the same injection work is repeated.
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