在软弱围岩中开挖隧道，各断面变形值差异很大，这给预留变形量的确定造成很大困难；按预留变形量加工的钢架，难以与随时变化的断面形式及设计要求的轴线相吻合。就预留变形量不定的情况下，可能出现的问题提出了解决的方法。

 In soft ground tunneling, the deformation of each crosssection differs very much, which causes great difficulties to the determination of the preset deformation. The steel arches manufactured based on the preset deformation are difficult to coincide with the varying crosssections and designed axis lines of the tunnels. In the paper, the problems that are subject to occurring under the condition of uncertain preset deformation are presented and solutions are recommended.