Bellevue Tunnel Portal

Light Rail Station

The East Link extension adds 14 miles and 10 stations to Sound Transit’s light rail system, carrying commuters between Bellevue and Seattle.

South Portal Park

This is a conceptual drawing of the south portal site, where the light rail enters the Bellevue Downtown Tunnel.

South Portal Sound Wall

This was the actual south portal site, cleared, graded, and ready for excavation. A 20 foot sound wall has been built around the entire site.

Placing AMTS on Sound Wall

GEO deployed an AMTS on the sound wall to monitor the 850 linear-foot soil nail wall leading to the tunnel portal.

AMTS and Solar Panel

The AMTS had clear line of sight to the monitoring prisms installed on wall. Solar power was required initially.

Monitoring and Control Prisms

Monitoring prisms (red) were placed on the wall. Control prisms (green) were placed at stable locations outside the zone of influence to correct for changes in the position of the AMTS itself.

Prisms on Head Wall

Three prisms are visible on the head wall. The painted marks were guides for placement of the pipe arch canopy.

Pipe arch in place

In this photo, the pipe arch canopy was now in place. Pipes were about 70 feet long.

Monitoring Tunnels - Bellevue Tunnel

A few days later, mining began. A GEO logger ( circled ) one of many that were installed, was already collecting measurements from strain gauges installed on lattice girders. More about this in another article.