Nov. 25 update: Access pit camera, dewatering
Posted on Nov 25 2014 3:17 PM
We’re happy to report that access pit camera 2 is back online after an extended power outage. Thanks for your patience as we worked to restore power. We hope you enjoy the view as Seattle Tunnel Partners continues building the circular pit (pdf 2.5 Mb) that will allow them to access and repair, Bertha, the SR 99 tunneling machine.
In addition to doing some excavation, crews have spent the past few weeks finalizing the system of underground wells and pumps that will allow them to control groundwater in and near the pit. The system consists of 15 well points that extend between 20 and 185 feet underground. The shallower well points are there to control groundwater within the pit. The deeper well points are tasked with reducing pressure in the deep aquifer located beneath the pit. Here’s a graphic that shows the pit and the wells, which are depicted in blue.
When excavation is complete, STP crews will pour a concrete pad at the bottom. This pad, or cradle, will stabilize the pit floor and provide a resting spot for Bertha after she tunnels through the pit’s southern wall.