Hydrogeological parameters for dewatering design in deep excavation within a gravelly cobble site

This study aims to determine realistic hydrogeological parameters of gravelly cobble deposits used for designing dewatering systems of deep excavations in the Taichung metropolitan area. A hydrogeological investigation, including geological surveys, in-situ pumping tests, slug-in tests, and laboratory permeability tests on the matrix, was conducted at a large-scale deep excavation site to explore the influence of different tests on regional hydrogeological parameters and the correlation between regional and local hydraulic characteristics. The results indicate that the dewatering range during deep excavation is located in the unconfined aquifer of gravel deposits with a high cobble content and a highly permeable sandy matrix. The regional hydraulic conductivities revealed by the pumping tests, involving different discharge controls and data analysis, were similar, ranging from 2.0×10 −2 cm/s to 3.6×10 −2 cm/s. The difference between local hydraulic conductivities of the matrix obtained through laboratory permeability tests and regional hydraulic conductivities obtained through pumping tests was within one order of magnitude, indicating that the permeability characteristics of gravelly cobble deposits are primarily determined by the matrix. Moreover, the verification validated the rationality and applicability of the evaluation procedure of the hydrogeological parameters considering different budget of hydrogeological survey, indicating that the procedure can be utilized in designing dewatering systems for the deep excavation of aquifers with similar hydrogeological characteristics.