PURPOSE: To quickly settle a large bore and depth of cylindrical structure at low cost by drilling and advancing the inside of the cylindrical structure, enlarging the bottom of and drilling the advanced portion to settle the cylindrical structure and layering and connecting the cylindrical structures. ;CONSTITUTION: One or more blocks of cylindrical structures 1 are connected together, settled in a firm hole 2 drilled by a drilling machine and further advanced about one block inside by a drilling bucket or others. The drilling machine is replaced by a bottom enlarging device 4 and the lower end of the cylindrical structure is passed therethrough and a bottom enlarging drilling arm 4a is protruded to the outer periphery direction by a spring and rotated by a kelly-bar 5 to drill sediment at the lower end of the cylindrical structure 1 with the edge 4b. The drilled sediment is dropped down to the bottom of the firm hole 2 previously drilled in excess and discharged to settle the cylindrical structure 1. On the settled cylindrical structure, the next cylindrical structure 1 is layered for connection. The drilling, advancing, bottom-enlarging, cylindrical structure 1 settling and layering processes are repeated until an intended depth is reached.;COPYRIGHT: (C)1996,JPO
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