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Pouring underwater concrete: 1. For pouring underwater concrete, the conduit method is generally used. The conduit serves as the channel for pouring underwater concrete using this method; therefore, selecting an appropriate conduit is essential to ensure the smooth progress of the concrete pouring process. The diameter of the conduit is generally 25–30 cm, and it is necessary to leave sufficient clearance around the inner diameter of the framework, including the diameter of the flanges, so that the conduit can be pulled out freely. The inner wall of the conduit must be smooth with a uniform inner diameter, and flanges are welded at both ends; the joints must fit tightly together to prevent leakage when the conduit is assembled. Pre-assembly and pressure testing should be carried out before the first use. When new conduits arrive, they should be assembled in advance on a flat surface according to the length required for pouring. It is necessary to check that the conduits are straight, that the joints are tight and leak-free, and that the inside of the conduits is smooth so that balls can pass through without any obstruction. Finally, a leak test must be conducted; only if no leaks are detected can the conduits be used. II. The concrete water-stop balls or wooden ball gaskets used inside the conduit must be of appropriate size (1 cm larger than the inner diameter of the conduit), and they must be installed properly to prevent leakage of mortar. The water-stop ball should be installed about 20 cm above the water surface inside the conduit. A special valve can also be installed to replace the water-stop ball. III. On the surface of the pressure-tested conduit, mark a continuous scale in intervals of 0.5m using magnetic paint, and indicate the total length of the conduit, so as to determine the lifting height and burial depth during concrete pouring. IV. The depth to which the conduit is lowered into the borehole should be such that there is a distance of 30–40 cm between the lower end of the conduit and the bottom of the borehole, so that the wooden balls can be pushed out of the conduit during concrete pouring. V. The funnel box on the conduit should have a certain height to ensure that the top surface of the concrete in the funnel is above the water level in the hole; for cases with clean water as the shielding medium, this distance should be 3–4 cm, while it should be increased appropriately when mud is used as the shielding medium. VI. When preparing underwater concrete, the following requirements shall be met: 1. To prevent blockages in the pipes and exposure of rebar during pouring, the size of the stones used should not be too large; the maximum particle size of the coarse aggregate should be less than 1/4 of the clear distance between the rebar bars ； 2. To ensure the quality of concrete pouring, the amount of cement used per cubic meter of concrete should be no less than 350 kg, and the strength of the concrete used should be 20% higher than the requirements specified in the design. 3. To ensure sufficient fluidity of the concrete, its slump can range from 16 to 20 cm; if concrete is to be delivered using pipes with a small diameter in areas with dense rebar, the slump can be increased to 22 cm. The amount of water used during mixing must be strictly controlled, and the mixing time should be no less than 2 minutes. VII. When pouring underwater concrete, whether it is possible to successfully use the concrete to push out the water from inside the conduit during the first pour, and to properly seal the entrance of the conduit thereby creating a separation between the concrete in the conduit and the grout in the pile hole, is crucial for the success of the underwater concrete pouring process. Therefore, the following points should be taken into consideration at the start of pouring concrete: 1. At the beginning of pouring concrete, a mixture of mortar (obtained by removing the gravel from the mix) should first be poured above the water-stop ball or special valve, after which the prepared concrete should be poured into the funnel, to prevent the outlet from being blocked during the storage of the concrete. 2. Before starting the concrete pouring, a sufficient amount of concrete must be used to bury the lower part of the conduit, thereby preventing water from entering it. 3. To ensure that the conduit can be lifted by one section (1–1.5 m) after concrete pouring, and to keep the lower end of the conduit buried at a depth of at least 1 m in the concrete, at the start of concrete pouring, in addition to having an adequate amount of concrete stored in the funnel, three or four carts are also prepared with concrete in them. Once the concrete is poured from the funnel, and slurry starts to emerge from the hole, concrete from the carts is poured in promptly once the concrete in the funnel is almost depleted. 8. When pouring underwater concrete, it is necessary to keep accurate records of the hole depth and the depth to which the conduit is embedded in the concrete. IX. When the burial depth of the lower end of the conduit is around 3 meters. If concrete cannot flow down the conduit, the conduit should be lifted immediately. The lifting of the conduit must be carried out promptly and accurately; the depth at which the concrete encases the conduit should not be too great, as this may increase the difficulty of lifting. The lifting process should also not be too rapid, and after lifting, the depth of burial of the conduit should be no less than 1 meter. 10. When lifting the conduit, move the funnel at the top aside first to allow the conduit to be lifted freely. Remove one section and then reinstall the funnel to continue pouring concrete. Therefore, the height increase each time should correspond to the elevation of the funnel opening. During construction, several iron pipes with different lengths at both ends can be kept on hand to be used for adjustment when lifting the guide tube. 11. During concrete pouring, the position of the conduit must always be kept centered. When lifting the conduit, a dedicated person should hold it to prevent it from tilting, shifting, or catching on the rebar framework. If it is observed that the skeleton is rising, the lifting conduit should be stopped immediately. Lower the catheter and shake it vigorously to disengage it from the framework. 12. Concrete must be poured continuously, and it is necessary to lift and remove the upper guide pipe while pouring concrete, so as to keep the concrete in a flowing state at all times. When concrete is poured within 5 meters above the top of the pile hole, it is not necessary to lift the conduit any further; it can be removed only after reaching the desired pouring level or the surface where water emerges. When pouring concrete, it is necessary to prepare materials with an expanded coefficient; if there is a significant discrepancy between the amount of concrete available and the required pouring height, prompt action should be taken to address this issue. 13. During the pouring of underwater concrete, a dedicated person should be assigned to remove any excess water to prevent hole collapse. Once the underwater concrete has fully set, gently chisel away about 0.5 meters of the top layer (the part composed of mud and concrete) until a surface of pure concrete is exposed, after which pour the concrete for the connecting pile. 14. When pouring concrete above the filling level, the ordinary concrete pouring method can be used instead. 15. Concrete piles that have not reached 70% of the designed strength shall not bear loads, and drilling operations shall not be carried out in adjacent positions on the same pier. Unless rapid demolding is carried out as specified, the casing can generally be removed only 3 days after the concrete has been poured. 16. Records should be kept for concrete pouring. At least 3 concrete samples must be retained from the concrete poured into the borehole for compressive strength testing. Last edited by Lailai on 2009-3-15 19:40]