PROBLEM TO BE SOLVED: To provide a vacuum grout injection method which can inject grout without causing separation and clogging of the grout during filling and which can inject grout in every corner of a sheath pipe without causing an insufficient charge of the grout so as to improve durability of a PC structure.SOLUTION: A vacuum grout injection method comprises: a vacuum step of reducing the pressure inside a sheath pipe S2 to a predetermined vacuum pressure by a vacuum pump 2 communicating with the sheath pipe S2; an injection step of injecting grout by negative pressure and a head difference by vacuum from a grout chamber 3 communicating with the sheath pipe S2 to the inside of the sheath pipe S2, after the work of the vacuum step; and a press fitting step of pressing the grout into the sheath pipe by a press fitting pump 4 communicating with the sheath pipe S2 after the injection flow rate of the grout comes to a predetermined flow rate or lower in the injection step.SELECTED DRAWING: Figure 1
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