Hydraulic Characteristics of Jingmei Formation and Dewatering for Deep Excavations in Taipei Basin

Abstract

The presence of the Jingmei Formation is a unique geological feature of the Taipei Basin. This highly permeable and waterrich stratum was responsible for many failures in underground constructions. The piezometric heads in the Jingmei Formation had to be lowered by pumping for deep excavations to be carried out safely. Discussed herein are the hydraulic characteristics of the Jingmei Formation and the experience gained in large scale dewatering schemes. Attempts have been made to establish the relationship between the progression of tides in the river and the fluctuation of the piezometric levels in the Jingmei Formation.

It has been found that, the transmissivity and storage coefficient deduced from the observed groundwater drawdown are affected by not only the pumping rate, but also the duration of pumping. Therefore, the rates required tend to be overestimated based on the results pumping tests.