To provide a sealing method for civil engineering work, which is easily carried out only with a low cost, for preventing water leakage and sand leakage from a gap between an earth retaining wall and an existing underground structure even if slight displacement such as an uplift occurs in the existing underground structure due to excavation etc. of the ground.

The sealing method for the civil engineering work, is composed of: a bag body setting step of setting bag bodies in the gap between a secondary earth retaining wall fixed to the earth retaining wall and the existing underground structure; and a self-hardening liquid resin injection step of injecting a self-hardening liquid resin 100 having an elasticity after hardening, into each bag body 50 at an injection pressure not smaller than an external water pressure that is a water pressure applied to the gap from the ground.