Life after Bertha: Focus shifts from mining to other tunnel work

Bertha, the SR 99 tunneling machine, has completed her 9,270-foot journey beneath Seattle. Although tunnel boring has come to end, crews have significant work to do before the tunnel can open to traffic in 2019.
 
Construction of the SR 99 tunnel can be broken down into five activities: 
 
  1. Mining (completed in April 2017)
  2. Disassembly and removal of the tunneling machine
  3. Interior roadway construction
  4. Installation of mechanical, electrical and plumbing systems
  5. Testing and commissioning
 

Disassembly and removal of the tunneling machine

The sooner Bertha is removed from the disassembly pit, the sooner crews can continue work on the northernmost section of the tunnel. STP will disassemble the machine by cutting it into pieces. The pieces will be removed from the pit by crane and placed on trucks. Due to roadway restrictions, each truckload will weigh no more than 20 tons.
 
Some pieces of the machine may be reused on other tunneling projects, while others will be recycled. Because the machine is so large, removing it will likely take several months.
 
Overhead view of the disassembly pit
 

The tunneling machine will be cut into pieces and removed from the disassembly pit near Seattle Center.

Interior roadway construction

Construction of the double-deck highway inside the tunnel began in 2016. Crews build the roadway in stages, as shown in the graphic below. 

The 6 steps in building a road inside a circular tunnel

As of spring 2017, the southbound roadway deck stretched past Pike Place Market, beyond the tunnel’s halfway point.
 

Installation of mechanical, electrical and plumbing systems

A complex set of interconnected systems will ensure the tunnel is safe and functional. Each of these systems must be installed by crews along the length of the tunnel. This includes mechanical systems, such as ventilation, fire detection and suppression, security and lighting. 
 
This work is already underway, and will be one of the last items completed by STP before the tunnel opens to traffic.
 
Tunnel rendering shows the digital signs on the tunnel celing that will show speed limits
 
The interior of the tunnel will include 35 variable message signs, 66 lane control signs and a public address system.
 

Testing and commissioning

Before the tunnel can open to traffic, crews must verify that all of its systems are working properly. This is done through a thorough testing and commissioning process.
 
The process includes design reviews, system demonstrations, performance verification, and operator and maintenance training. For example, the tunnel ventilation system must be tested to ensure its many elements are working properly. The operators in charge of running the system also must be trained to respond to incidents, such as a vehicle fire, that would require them to put the system to use. 
 
The commissioning team will work its way through a long checklist between now and the day the tunnel opens. In all, they will verify the functionality of more than 8,500 components, both individually and as part of the tunnel’s integrated network of systems. 
 
Cross-section of the tunnel showing the escape routes
Emergency exits doors will be installed approximately every 650 feet within the tunnel. Beyond these doors is an exit corridor that leads to the surface.