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When concrete starts to flow out of tremie pipe, the lifting of tremie pipe should be carried out slowly to avoid disturbance of material surrounding the end of tremie pipe. The mouth of pipe is embedded at least 1m below the concrete surface to maintain the seal.
If a tremie pipe is left in a position too long without lifting up, it would impair the quality of already-placed concrete. The fresh concrete may be placed under the portion of concrete which have set already so that it would raise the mass of already-placed concrete and induce cracks on it.