为分析软弱黄土隧道的变形规律，以西宁过境高速大有山黄土隧道为依托，采用精密水准仪和收敛计对隧道地表下沉、拱顶下沉和水平收敛进行了系统现场测试。结果表明：软弱黄土隧道拱顶下沉远大于水平收敛，变形时间长，变形量大，累计拱顶下沉值最大为950.6 mm。在临界埋深范围，围岩变形比深埋、浅埋时都大，且变形量离散性高；围岩变形速率在二衬施作时较大，软弱黄土隧道中作为围岩-支护系统稳定性判据的变形速率宜适当提高；围岩变形随时间变化符合指数函数规律，可利用指数函数预测围岩的最终变形；软弱黄土隧道变形分为急剧变形、持续增长和缓慢增长3个阶段，最终趋于稳定。隧道断面的初次开挖对地表变形影响显著，隧道轴线沉降最大，并沿横向逐渐减小。软弱黄土隧道预留变形量在不同位置处不宜统一设置，西宁地区软弱黄土Ⅴ级围岩建议拱顶预留700～800 mm，边墙预留300～350 mm，拱顶与边墙之间以曲线过渡。

To analyze the deformation of the tunnel in weak loess, the surface settlement, crown settlement and horizontal convergence are in-situ monitored in the Dayoushan loess tunnel by using precision level and convergence gauges. The results show that the magnitude of crown settlement is much larger than that of the horizontal convergence. The deformation sustains for a longer time and the steady maximum crown settlement is 950.6 mm. The deformation of surrounding rock is larger when the buried depth of the tunnel is at the critical depth. The deformation rate of surrounding rock is larger at the stage of secondary lining construction. The deformation rate, which acts as the stability criterion for the surrounding rock-supporting system in the weak loess tunnel, should be raised moderately. The deformation of the surrounding rock follows an exponential law; and the exponential function can be used to predict the final deformation of surrounding rock. The deformation of weak loess tunnel can be divided into three stages: rapid deformation stage, sustained growth stage and slow growth stage; and finally, it tends to steady. The tunnel excavation significantly influences the surface deformation; and the maximum settlement of surface occurs along the central axis of tunnel; and the settlement gradually decreases with the increase of the distance from central axis transverse. The deformation allowance of weak loess tunnel should not be unified at different locations. For the weak loess tunnel in Xining area, the reserved deformation of grade Ⅴsurrounding rock is suggested to be 700-800 mm for the crown, and 300-350 mm for the side wall. The crown and side wall of tunnel should be connected by smooth curve.