| 摘要 |
The block (1) consists of a separate facing panel (2) with a thrust heel (8) along the base of its rear surface (5), and two lengthwise ribs (3a, 3b) of trapezoid cross-section with their smaller ends uppermost and raised projections (16a, 16b) at their forward ends and recesses (20a, 20b) at the bottom to receive the heel. The ribs can be joined together by crosspieces (21) or made in one piece with a transverse core.
|
