Skew blocks shall tightly abut to arch-springing beam. Arch or vault shall be built after completion of bricking-up(s) (if any) behind skew blocks.

• 拱脚砖应紧靠拱脚梁砌筑。当拱脚砖后面有砌体时，应在该砌体砌完后，才可砌筑拱或拱顶。