Underwater concrete pouring is the construction method of pouring concrete mixture directly to the designated underwater part. In hydraulic engineering, it is often used to build cofferdam, cut-off wall, bank protection, underwater building repair, etc.

There are six main pouring methods.

(1) The most commonly used method of underwater concrete pouring by conduit method is rigid conduit or flexible conduit. The former is to transport and pour mixtures from rigid conduit to underwater warehouse surface by the weight of mixtures; the latter is to transport and pour mixtures from flexible conduit to underwater warehouse surface, and to control the falling speed of mixtures by the pressure of environmental water bunker hose.

(2) Pumping method uses concrete pump to put concrete mixture into underwater pouring silo surface along conveyor pipe and pouring pipe, which is basically the same as pipe method.

(3) The concrete mixtures are packed in closed containers which are easy to be opened by open-bottom container method. When pouring, the containers are gently placed under water and unloaded directly at the bottom of the pouring site.

(4) Pre-filling aggregate grouting method is to pre-fill aggregate in underwater formwork. Concrete is formed by grouting pipe pressurizing or self-flowing pouring cementing material, filling aggregate voids and cementing.

(5) The concrete mixtures are packed into bags by the method of overlapping bags, and then sink under water, overlapping seams between layers to form underwater concrete structures. The bags are made of hemp bags or synthetic fibers, with a coarser texture and improved water-soluble film bags. The melting time is slightly longer than the hardening time of concrete.

(6) The pouring method pours concrete mixture on the cast-in concrete, pushes the underwater concrete forward and diffuses gradually by tamping or natural flow.