A new way for Seattle

The replacement of an earthquake-damaged 1950s viaduct with a state-of-the-art tunnel provided Seattle with a lasting traffic solution and opened up the waterfront for the city’s residents

Project Alaskan Way Viaduct Replacement

Location Seattle, Washington, USA

Client Washington State Department of Transportation (WSDOT)

Project value US$3.35bn (£2.49bn)

Expertise Tunnelling, programme and design management, risk management, construction management, project controls and reporting

In 1953 the city saw the completion of a double-decked flyover at this location. The 3.5km Alaskan Way Viaduct was never the most aesthetic addition to the waterfront, and served as something of a dividing line between the bay and the rest of the city; but it

bore a steady increase in traffic over the decades, and 50 years on it was carrying 100,000 vehicles per day, around 25% of Seattle’s through-traffic.

But everything changed in 2001 when the 6.8 magnitude Nisqually earthquake struck,

Seattle’s State Route 99 forms one of two north-south arteries servicing the city and runs past Elliott Bay to its west and the historic downtown Pioneer Square neighbourhood and industrial district to the east.

damaging the viaduct and its supporting seawall. So severely was the structure affected that examining engineers said the viaduct was within a few seconds of complete collapse.

Remediation efforts to the ageing structure, already

two-thirds of the way into its 75-year design life, cost more than $14M (£10M). Yet although the patched-up viaduct was deemed safe in the immediate term, concerns remained about its vulnerability to future quakes. Moreover, the seawall was in disrepair, and

the soil it supported around the viaduct’s foundations was subject to liquefaction.

It was clear to the city’s planners that they needed a more comprehensive solution. With the structurally compromised

viaduct providing a sense of urgency, the Washington State Department of Transportation (WSDOT), in partnership with Mott MacDonald, created the ‘Moving Forward' programme to explore a set of alternative solutions for its replacement.

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2 I Mott MacDonald I A new way for Seattle

Record-breaking solution

In 2007 WSDOT decided to replace the southern end of the viaduct, while continuing to consider options for superseding the waterfront section.

3.2kmtunnel length

17mdiameter borehole

Two options were initially considered – an alternative elevated highway and a cut and cover tunnel – but both of these were voted down by the public, potentially delaying the project.

Meanwhile, contractors sank foundations for the new side-by-side roadway up to 79 metres deep to increase stability, and provided wider lanes and shoulders.

By January 2009 the decision was made to recommend a bored tunnel to replace the waterfront section – the only option that would allow the state highway to remain open during construction.

The following year, it was settled that a 3.2km tunnel would be bored at a then record-breaking 17m in diameter, which required the construction of the world’s largest tunnel boring machine (TBM).

Once the tunnel was completed in 2019, and with traffic diverted from the viaduct down through it, contractors could dismantle the ageing flyover without shutting down this section of SR 99.

Credit: Erin Schedler Photography

Mott MacDonald’s role

Handed an already broad brief, the role increased as WSDOT’s faith grew. By the project’s completion in 2019 it included:• Programme and design

management support• Independent oversight• Risk, value engineering and

constructability review• Change control

and configuration management support

• Construction management• Project controls and reporting• Intergovernmental

agreements• Document management

and budgeting/funding management support

WSDOT appointed Mott MacDonald as Project Management Assistant Consultant (PMAC), providing programme/design management and related technical and construction management services.

To ensure maximum collaboration and coordination, the Mott MacDonald team co-located with the client, allowing it to operate in a blended team environment with the agency and other consultant personnel.

Mott MacDonald's initial major tasks included developing a Federal Highway Administration-mandated project management plan (PMP) for the project, and a PMP template suitable for use by the agency on all other WSDOT mega projects; carrying out a design review of deliverables; and developing a programme management process using best-of-breed software tools.

A big key to AWV’s success was Mott MacDonald’s KPI control packages. We established the baseline, monitored the heck out of it, and strategically retired risk money to free up funds for other uses. As a team we applied a strong and realistic Monte Carlo simulation to make the best business decisions.Joe Hedges, PE, PMP Formerly AWV Programme Administrator, WSDOT

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Tunnel alignment changes

Mott MacDonald played a key role in the selection of the tunnel’s alignment.

When the design and build procurement was prepared and the externally-produced 30% design submitted, the tunnel route would have run beneath Seattle’s historic Pioneer Square. Having reviewed this, the consultants recommended moving the start of the alignment to the west towards a route that was adjacent to the existing

viaduct. Critically, this pulled its zone of influence away from seismically vulnerable buildings, something that was taken on board and accepted.

Harry Jarnagan PE CCP was Mott MacDonald's Alaskan Way programme manager. “The design consultant that the state had employed recommended that the tunnel

start pretty much in the middle of Pioneer Square, which is an historic district and the area of first European settlement within Seattle,” he says.

“These buildings were old and not seismically reinforced,” says Jarnagan. “They were masonry buildings and when you look at the prospect of sinking a tunnel

Tunnel north portal

SR 99 tunnel

New Alaskan way

Tunnel south portal

South end viaduct replacement

boring machine underground, in the southern part of the alignment it would be operating near the surface for the first several feet and that would create disturbance at ground level.

“We knew that those structures could not bear it, so we recommended moving the starting point of the TBM

as far away from Pioneer Square as we possibly could to the west and not far off the waterfront.”

This alignment significantly reduced the risk and cost of starting TBM tunnelling in poor fill soils and debris associated with historic infilling of Puget Sound and waterfront development.

Mott MacDonald also supported the evaluation of contractor proposals leading to the execution of a design-build contract for the bored tunnel scope in early January 2011.

The new tunnel takes State Route 99 (SR99) under central Seattle.

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Digital rigourThe programme was broken up into separate projects, with Mott MacDonald delivering an extensive reconfiguration of the entire management database system to accommodate an entirely new programme structure.

It instituted industry best practices in change control that were not previously in place on the scheme. This brought significant improvement in the management of cost, schedule and physical configuration, while also enabling the team to tell the story of project development to any oversight committee or legislative decision maker that investigated or asked questions.

Jarnagan says: “We instituted change control rigour in two different ways. The first was a configuration control effort that dealt with the physical scope of the project – if there were any changes to things like vertical or horizontal match or assignment we would package those up for management approval so that everybody maintained awareness of the new configuration.

“The second part of our change management effort was at the programme level, with what we called the trend programme. Issues that had a cost or schedule aspect were put in the trend programme and also brought to management for attention.”

The team used a number of cutting edge approaches to deliver on the most successful of projects for the citizens of Washington State, a project that achieved all of its traffic capacity, seismic resiliency, and environmental sustainability goals, despite the numerous challenges along the way.Dave Sowers, PE Former deputy programme administrator for the Alaskan Way Viaduct Replacement Programme

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Positive outcomes for the client and communityThis is an exemplar project in many ways, not least because of the carefully thought through benefits for the local community.

Dave Sowers, PE, was WSDOT Deputy Programme Administrator for the Alaskan Way Viaduct Replacement Programme.

“In any big project like this, we talk to and engage the local stakeholders early on,” he says. “We looked really closely at the alignment of the existing viaduct. Because of its size and location along the waterfront, it cut off the

businesses in the downtown core and in Pioneer Square.

“For those businesses, the location of the tunnel was a huge advantage over an elevated structure. During construction the existing viaduct remained open, so it was 'business as usual’ while we built the tunnel. Afterwards, when the viaduct came down, those businesses and the community benefited greatly.

“Without the old 1950s viaduct, the experience on the waterfront will be significantly transformed. Business and residents downtown will benefit from significantly less noise, less air pollution, and the absence of the visual impact of the viaduct,” he adds.

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2013

2012

2011201020092008

20072006

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2001 2023

2022

20212020

2019

2018

201720

16201520

14

Tunnel

TBMViad

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Holgate to King

Electric lin

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SR99 demolition, decomm

issioning

relocatio

n (2008-09)

(stage 2,3,4) (2009-14)

and surface street 2018-21

Viaduc

t column st

abilisatio

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near

Yesle

r Way (

2007-08)

Street Connections (2021-22)

(2018-19)

Project (2014-17)

widening (2012)Alaskan Way North Access

SR99 connections

South Access – Surface

completes

SR99 Tunnel main

contract (2011-19)

(drilled shafts) (2014)

South Access (S. Dearborn

Street o�-ramp) (2016-17)

New Alaskan Way

(2019-22)

South Access

Programme timeline

Miscellaneous projectsSR99 TunnelSouth-end replacement

Key

Credit: erinschedlerphoto.com

Milepost 31 drives community engagementHelping to embed the rationale for a scheme of such major works within the local community was a community outreach project called Milepost 31.

This quintuple award-winning information centre in Seattle’s Pioneer Square neighbourhood was developed by Mott MacDonald subcontract and facilities manager Jennifer Carlson. Its positive impact on the neighbourhood is elegantly captured in film by client WSDOT in the screenshot (left).

“We had an environmental commitment to the federal

government to benefit local businesses and continuing to create interest in Pioneer Square during the construction programme, so we created this information centre,” says Jarnagan.

“I was fortunate to have Jennifer Carlson on my team who was an incredible ball of energy and had a degree in interior design. She came up with the design of

it, helped procure the exhibits and led the way for a team of people. When it opened it was a small museum that not only talked about the project but the history of Seattle and what this programme was going to do.”

Mott MacDonald was a big part of the AWV success because they had an extremely high degree of competency. Together with WSDOT we all applied our best resources for the success of the partnership and the programme.Joe Hedges, PE, PMP Formerly AWV Programme Administrator, WSDOT

Cost controlThe programme's costs were kept under control despite the team facing a series of challenges.

It’s hardly news that major public sector construction schemes have a propensity to overshoot the budget.However, even though the project was hit with a setback due to TBM ‘Bertha’ stopping for mechanical

repair, the impact on budget was comparatively negligible.

“The full programme, once we selected the machine-driven bored tunnel, was about $3.1bn and at the end it was $3.3bn,” says Jarnagan.

The Alaskan Way Viaduct Replacement team of WSDOT and Mott McDonald staff pushed the limits of what was possible not just from a technical perspective, in delivering the world’s largest bored tunnel, but what was also possible in innovative programme management and project delivery.Dave Sowers, PE Former deputy programme administrator for the Alaskan Way Viaduct Replacement Programme

“That represented about a 5% increase, which is pretty good considering what happened (such as the TBM stoppage).

"Cost increases of 30% are not uncommon in big public works; well we blew that away. It was

an intense effort to control costs and schedule. I had a team of cost engineers that searched for money that could be de-committed and redeployed elsewhere – we were very stingy with programme money, as the results show.”

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Commitment fulfilment

The Alaskan Way project featured several third party agreements – including with the Port and City of Seattle and with native American tribes – and Mott MacDonald created a commitment tracking system so that the team could ensure they followed through on all of the promises made.

“For each agreement we extracted all the commitment statements, put them into a database and tracked the progress made to satisfying each,” says Jarnagan. “It proactively helped our relationship with our stakeholders and showed we were on top of our commitments.

We inserted the same formal rigour that we had for change control and risk. It very quickly got to the point where commitments were no longer a worry and we are now using a GIS evolved version of this commitment tracking system on another project.”

With SR 99 successfully rerouted from the elevated highway and all of Mott MacDonald’s contractual commitments fulfilled, the new tunnel opened in 2019 with Seattle’s citizens invited to take the first official journey on foot through the realigned structure, with a fun run that began at the portal.

Significant portions of the scope of the Alaskan Way Viaduct Replacement programme, to include the bored tunnel, used a design-build delivery method. While this is a proven and effective delivery method, many of the programme’s diverse stakeholders had little experience or knowledge of design-build, which proved a hurdle for WSDOT to overcome.

The WSDOT staff administering, reviewing design, and overseeing AWVRP construction were all seasoned and had

Design-build delivery

worked on multiple design-build projects, and the tunnel contract provided an opportunity for education in the design-build process to colleagues working for the city and county.

Unfortunately, other agencies needed time to understand the many nuances of design-build — such as quality assurance/quality control (QA/QC) responsibility — and this led to minor delays in design development and reviews. In the end, design-build delivery charted the best course for a successful project, while protecting all parties.

Opening opportunities with connected thinking.

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