| 摘要 |
PROBLEM TO BE SOLVED: To provide a small-bore propulsion machine, a method for recovering a leading pipe, and a method for inserting the leading pipe, whereby the leading pipe can be propelled at reduced propulsion resistance and high accuracy with respect to a wide range of soil qualities from sand and conglomerate layers to bedrock layers and can be easily recovered to a starting vertical shaft through buried pipes laid in place and the recovered leading pipe or a new leading pipe can be inserted for re-boring into the buried pipes laid in advance. SOLUTION: A leading pipe C and an outer cylinder A are connected together, and the leading pipe C is advanced for digging while the diameter of a cutter head 6 is increased, so as to lay buried pipes 2 in sequence. To pull back the leading pipe C, the diameter of the cutter head 6 is reduced and the connection is undone, after which the force to pull back is imparted to the leading pipe C to pull it back into a starting vertical shaft. To perform re-boring work using the leading pipe C, the cutter head 6 is inserted into the outer cylinder A and connected thereto and its diameter is increased to advance the leading pipe C for digging.
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