Though perhaps not as dramatic as the completion of excavation and final lining in 2012, the first quarter of 2013 has marked significant progress on the tunnel’s retaining walls, facade walls, and electrical substations, as well as the finishing touches on the seven cross passages between bores 3 & 4.
The two-foot pedestrian walkway on the tunnel’s south wall has been completed, as well as vaults, under drains and utility installation.
Work on roadway paving began in mid-March and will continue for approximately four to six weeks. The roadway is paved in layers – beginning with the aggregate, or sub-base to facilitate drainage of the tunnel’s naturally occurring groundwater. A layer of lean concrete is then applied to add structural stability, followed by the paving of the concrete roadway. When the three layers have been installed, the roadway will be about two-and-a-half feet thick.
The yellow in the graphic shows the tunnel’s final lining, which was installed in late 2012, and is designed to provide structural support for the tunnel.
Though the completion of roadway paving will mark an important milestone for the project, there is still extensive work to be done to install and test the fire safety, lighting, traffic, and communications systems before the tunnel can be opened to traffic.
Please stay tuned to the project website in the months ahead for updates on this critical work.
The final cast-in-place concrete lining was installed over a waterproof lining, which prevents groundwater seepage. A dense rebar (or reinforced steel) "cage" was built over the waterproof membrane for earthquake resistance. A series of 69 concrete pours – moving from west to east - installed the cast-in-place final lining in 15 meter (49-foot) segments. The final lining is relatively thin – approximately 15 inches in depth. In the event of an earthquake, the final lining is designed to deflect earthquake energy and the rebar cage will allow the tunnel structure to remain intact.
The seven cross passages, or safety paths, between bores three and four, which will serve as safety passages for motorists in the event of a serious incident.