Peitou depot is the most important maintenance works of Taipei Rapid Transit Systems with an area of forty acres. A clay layer of low strength and high compressibility with a thickness of 15~50 meters is beneath the ground surface. To raise its ground level, an earthfill with a thickness of 1.5~5.2 meters was placed over the clay layer. Vertical drains were installed in the same period of time. After completion of the earthfill in November 1990, the largest settlement within the area has reached 1.9 meters and continues to increase at acurrent rate of 1.0~2.7 mm/month.