The project includes the drilling of 6 deep boreholes (up to 900 m depth) as part of the Geotechnical studies for the base tunnels. Also, a specific study was conducted for the tunnel ventilation system.
This is the first high-speed railway line to be built in the United States. The most notable technical challenges are those relating to the seismic design of the tunnels and structures. In particular, the crossing of active fault lines – both underground and on surface – is a unique feature, as is the design of a tunnel to support groundwater pressures of over 25 bar. The tunnels are being designed with enlarged diameters in order to adapt to potential alignment shifts caused by fault displacements linked to seismic events. Different tunnel construction methods have been considered: tunnel boring machines, sequential methods, and cut-and-cover. One of the station design options requires a significant open excavation down to 60 m deep.