The Top-Down Construction Method is popular in the Taipei area for fast track procedure.  With two construction levels, the upper stories go up and the basement excavation goes down together, the construction time can be reduced.  However, the last stage of the construction will be very difficult due to the 6m~8m excavation without any shoring support.  This case study utilizes the thick PC layer to support the last stage of excavation.  It was proved that the Un-Shoring Method is an effective and economic way of underground construction.