Hydrogeological properties of the Hawkesbury Sandstone in the Sydney Region

Geotechnical and hydrogeological data obtained from investigations for the design of tunnels in Sydney have created a large database that describes the hydrogeological properties of the Sydney Hawkesbury Sandstone, providing an insight into its hydraulic behaviour. Investigations for the Epping to Chatswood Rail Line and another tunnel project in Sydney included drilling of over 150 boreholes and execution of over 450 packer (water pressure) tests within these boreholes. For the Epping to Chatswood Rail Line, a 48-hour pumping test was conducted at two separate locations and acoustic borehole imaging was conducted in 20 boreholes to provide information on subsurface defect characteristics, essential to understanding hydraulic behaviour. This paper presents the results of a statistical analysis of packer test results and borehole imaging data, a comparison to pumping test results, and compares measured groundwater inflow rates from the tunnels with estimates from numerical modelling. Data analyses show the depth-dependence of the hydraulic conductivity of the Hawkesbury Sandstone, show a relationship between hydraulic conductivity and defect distribution, and demonstrate the requirement to address scale effects when using packer test results to assess groundwater inflow to underground excavations.