| 摘要 |
In a pilot head 20 to be used in a ground drilling machine, the injection ports 22A for injecting digging liquid are directed rearward and angularly separated from the axis of rotation N by an obtuse angle theta1 (168E). With this arrangement, when digging a leading hole D from a starting pit, the flow rate of digging liquid flowing from the front end of the leading hole D toward the starting pit can be increased to efficiently deliver soil produced by the digging operation to remarkably improve the soil removing efficiency.
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