Back Analysis for Hydrogeologic Parameters of Aquitard at Tianjin Railway Station

The aquitards, confined and unconfined aquifers are often dewatered together in deep excavation. The hydraulic connection among the aquifers has a great effect on the dewatering efficiency. While the conventional pumping tests scarcely focus on the hydraulic connection. The pumping test focused on the hydraulic connection between the phreatic aquifer and the confined aquifer was implemented at plaza before the station. The aquifers of pumping test are phreatic aquifer and confined aquifer. The test have 2 fully penetrating wells, 5 observation holes, 12 pore pressure gauges and 3 stress periods. The monitoring data reveal the response of the water level in each aquifer and the aquitard over all during the test. After data preprocessing, Mod flow, a ground-water flow model program, was applied to numerical simulate and back analyze the pumping tests process. The results of the numerical simulation fit well with the observed data. The estimated hydro geologic parameters for the phreatic aquifer, confined aquifer and the aquitard derived from back calculation are of high reliability. The hydro geologic parameters can be used to quantitative analysis for the hydraulic connection among the aquifers and the aquitard.