| 摘要 |
PROBLEM TO BE SOLVED: To provide a longer and lightweight long U-shaped ditch capable of being easily executed without casing any crack or breaking in the central part of the longer ditch. SOLUTION: A long concrete ditch V is constituted of two times as long as a regular ditch, four recesses 30 and 30 are provided in side walls 2 of the ditch, both sides of them include square recess-shapes 31 and 32, sword tip- shapes 33 and 34 are symmetrically provided in the central part by making an X-Y line of the central part as a boundary line. The long concrete ditch is equipped with regular cover hanging sections 5 and 5.
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