| 摘要 |
The method involves providing a shaped hub and outer shell between which the concrete is poured. It involves axial movement of the hub (1) and a rake (50) and complete closure of the hub by an obturator head (15) and vertical partitions (21,22). The shell is held closed by guides (A-C) which are retained in alignment by a vertical post (43) actuated for controlled movement.
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