| 摘要 |
<p>PROBLEM TO BE SOLVED: To facilitate manufacture, convenience of handling such as transportation and storage and facilitate simplified laying work and further enhance strength and stability of a structure after laying. SOLUTION: Protruded portions 3, 4 spaced apart in a longitudinal axis direction are formed on a top face 29 of an approximately rectangularly shaped main body 2 and protruded portions 5, 6 are formed on a bottom face 2b. A first recessed portion is formed between the protruded portions 3, 4 and a second recessed portion is formed between the protruded portions 5, 6. When lengths of the first and second recessed portions in the longitudinal axis direction are respectively represented by Lr1 , Lr2 and lengths of the protruded portions 3, 4, 5, 6 in the longitudinal axis direction are respectively represented by Lp1 , Lp2 , Lp3 , Lp4 and thickness of portions of the main body 2 corresponding to the first and second recessed portions is represented by (T), then formulas Lr1 >=Lp3 +Lp4 +T, Lr2 >=Lp1 +Lr2 +T hold.</p> |
