HR: 1340h
AN: H23G-1726    [Abstracts]
TI: Three-Dimensional Groundwater Modeling for Tunnel Construction in Faulted and Fractured Bedrock
AU: * Zhang, J
EM: jim_zhang@urscorp.com
AF: URS Corporation, 1333 Broadway, Suite 800, Oakland, CA 94612, United States
AU: Jaramillo, C A
EM: Carlos_Jaramillo@urscorp.com
AU: Feldsher, T B
EM: Theodore_Feldsher@urscorp.com
AB: This paper describes the 3-D groundwater flow model developed for the San Francisco Public Utilities Commission's Irvington Tunnel No. 2 Project. The tunnel will be constructed through the East Bay hills east of Fremont in Alameda County, California. The proposed tunnel is located within about 200 feet and parallel to the existing Irvington Tunnel, which was built in the 1930's. Both tunnels are approximately 3.5 miles long, and have a ground cover ranging from about 100 to 750 feet along the alignment. The geologic formations along the tunnel include cretaceous and tertiary sandstone, shale, and claystone, separated by four inactive faults and a number of minor shear zones. The faults and shear zones contain varying thicknesses of crushed, broken, sheared, and/or soil-like material. Many of these zones provided large groundwater inflows during construction of the first tunnel. The 3-D groundwater flow model was developed using finite-element modeling code FEFLOW, which is capable of simulating discrete features such as fault zones, tunnels, and mine workings. Both, the existing tunnel and the proposed tunnel were incorporated into the model. The modeling objectives were to predict the groundwater inflows to the tunnel during its construction, and to assess the potential hydrological effects of the new tunnel construction on the local groundwater system. Groundwater level variations and flow conditions were modeled during tunnel construction and during the groundwater recovery phase following tunnel lining and completion. The model was first calibrated to simulate the groundwater response reported during construction of the first tunnel in the 1930's. The calibration was carried out using the parameter optimizer PEST. The model calibration was refined using a classical calibration process, focusing on characterizing the hydraulic properties (mainly conductivity and storativity) for the key geologic features. After satisfactory model calibration, the model was used to evaluate the groundwater response during the construction of the new tunnel for several alternative tunnel excavation and lining system scenarios. The predicted groundwater recovery following tunnel completion was also evaluated. The results were used by the design team to establish the tunnel excavation method and lining system for final design. This paper will present details on the methodology of modeling tunnel construction, modeling groundwater flow in fractured zones, and model development. The model setup, calibration, and predictive simulation results are also discussed.
DE: 1829 Groundwater hydrology
DE: 1846 Model calibration (3333)
DE: 1847 Modeling
SC: Hydrology [H]
MN: 2007 Fall Meeting