Back Analyses of Historical Ground Subsidence Induced by the Lowering of Groundwater Table

Abstract

Numerical analyses were conducted to correlate the ground settlements observed in the central area of the Taipei Basin with the variations of the piezometric levels in the Jingmei formation. The relationship of the historic changes of the piezometric levels and the ground settlements induced by the consolidation of the Songshan formation was established by matching the results of the analyses with the observed settlements. The influence of replenishing water from rivers and infiltration of surface water into the Songshan formation was accounted for by assuming a linear distribution of water pressures with zero pressure at a level of replenishment and a pressure corresponding to the piezometric level in the Jingmei formation at the bottom of the Songshan formation. The records of the ground settlement and piezometric levels in the Jingmei formation obtained in the Beimen area were used in the analyses and the results of analyses indicated that the ground could have settled by 0.38 m before the initial reading of settlement was taken in 1950, giving a total settlement of 2.55 m, instead of 2.17 m reported in literature (Wu 1987). It has also been found that consolidation of the sandy layers contributed to more than half of the settlement.