Preparation method of low-shear-strength grouting material for shield excavation gap

The invention discloses a preparation method of a low-shear-strength grouting material for a shield excavation gap. The preparation method comprises the following steps: selecting a grouting material; preliminarily designing multiple groups of grouting materials with different water cement ratios and multiple groups of grouting materials with different swelling-water ratios; manufacturing a plurality of groups of grouting material test pieces; testing the shear strength of each group of test pieces to obtain the optimal water-cement ratio and the optimal swelling-water ratio of the grouting material; adding bentonite and water into a stirrer according to the optimal swelling-water ratio, conducting stirring, fully and uniformly conducting mixing, conducting standing, and fully conducting swelling; measuring water glass with required baume degree, adding the water glass into expanded bentonite slurry, and uniformly conducting stirring; and adding cement powder, and continuously conducting stirring uniformly to