Taking the undercut trial section of Tianfu Square tunnel on line 1 of Chengdu Metro as case history, the authors present comparison and contrast of tunnel construction in sandpebble ground by means of CD method with that by means of bench method so as to accumulate experience for the future largescale design and construction of Chengdu Metro by means of undercutting method and to provide reference for tunnels in similar geological conditions constructed by means of shallow undercutting method.