SCHREYER AWARD: Whittier Access Project Tunnel Segment, Alaska, U.S.
Category: TransportationHATCH MOTT MACDONALDThe Whittier Access Project fulfils a long-term goal to provide highway access to the city of Whittier located on magnificent Prince William Sound in Alaska...
HATCH MOTT MACDONALD
The Whittier Access Project fulfils a long-term goal to provide highway access to the city of Whittier located on magnificent Prince William Sound in Alaska. Whittier was historically a military base, but is now a cargo port, recreational area and tourist destination.
Before this project, Whittier was separated from the nearest highway by eight kilometres of rugged mountains, lakes and glaciers. For the last 40 years residents have accessed the area by loading automobiles onto railroad cars and travelling through a four-kilometre long railroad tunnel through the mountains. During the summer over 130 trains per week travel the route, and about 30 trains do so in the winter. A better means of access was needed to meet increasing user demand and to comply with new Federal Railroad Administration guidelines for safety.
After many studies of rail, conventional roads and separate tunnels, it was decided that the best approach was to convert the existing 1940s Anton Anderson railroad tunnel into a dual use facility that can carry trains as well as automobiles. The US $80 million project was divided into three segments. The Portage segment was the western road link and included a bridge and road tunnel. The Whittier segment included the bridge and road improvements at the eastern end. Both these phases were contracted in the traditional design-bid-build process with design by CH2M Hill.
The Tunnel segment, which consisted of the modifications to the four-kilometre Anton Anderson Tunnel, staging areas, plus railway signal and tunnel control systems, represented 75 per cent of the total work. It was tendered as a design-build contract, with the contractor responsible for producing a workable tunnel operating scheme. Hatch Mott MacDonald, based in Mississauga, Ontario, was the prime consultant to the successful bidder, Kiewit Construction.
Completed last June, the project provides the first and only highway access into Whittier, enabling people to travel to and from the community seven days a week.
Trains and cars share
In considering different options for creating vehicle access to Whittier, it was not practical to build a tunnel parallel to the existing railway tunnel because of the high cost and environmental issues. At the same time, it was not possible to build a traditional highway route because of the steep mountain grades, brutal mountain weather, and visual impact on the landscape.
Instead, therefore, it was decided to recycle the existing railroad tunnel to make it have shared highway and rail use. The result is the longest highway tunnel in North America, and the first tunnel in the world to have one-way reversible traffic shared with a train. Automobiles of up to 15 feet high and 11 feet wide can pass through at the rate of 800 vehicles per hour (400 in each direction) and speeds up to 25 mph. However, trains have priority use.
Having trains and cars in the same tunnel poses a safety risk, so specially integrated controls ensure that trains and cars cannot be in the tunnel at the same time. When the tunnel is in railroad mode, the train signal system (TSS) controls the trains and locks out the operation of the tunnel control system (TCS). All highway gates are closed and the road signals turn to red. When the tunnel is in highway mode, the TCS locks out the TSS until highway vehicles clear the tunnel. In this mode, derail tracks ensure that trains can never proceed through the tunnel when cars are present.
The traffic and alarm monitoring systems are integrated with traffic control, video monitoring, and emergency response systems, and controlled from the Tunnel Control Centre constructed in the western staging area. The tunnel control system operates 19 radar units for vehicle detection, 50 cameras, train signalling, traffic metering, lighting, ventilation, tunnel doors and air quality. The system detects traffic stoppages, remote cameras pan to the area, and strobe lights and signs notify the drivers in the case of an emergency.
Constructing a parallel access tunnel for emergency egress was too costly, so instead the tunnel is designed with eight safehouses located alongside the road/track at 400 metre intervals. Each safehouse can hold 55 people and has an independent air supply.
For ventilation in the tunnel, there is a combination of six 75-h.p. jet fans for the normal operation, and four 300-h.p. portal fans for purging the tunnel of smoke in case of a fire. The fans push the air in the same direction as the traffic so that vehicles ahead of the fire would continue to the tunnel exit, and drivers behind the fire would evacuate to the safe houses.
Building in winter
The harsh climate and the need to do the construction during the winter months were a challenge. The area has winds strong enough to snap telephone poles, and in winter snow higher than a three-storey building. Temperatures dip to minus 40 degrees F. The solution was to locate staging areas away from avalanche run-out zones. The western portal building is designed for 1,000 psf avalanche impact loads (and has successfully withstood three avalanches already).
In just 40 days in the dead of an Alaskan winter, crews removed the existing tunnel invert and completely reconstructed 4,175 metres of track and roadway. The work involved only nine track outages, and freight service was not affected.
With only nine construction windows and a tunnel that was too narrow to allow two pieces of equipment to work side by side, innovative measures were required. The construction team used a special rail-mounted gantry crane, and worked around the clock during the track outages. The gantry system allowed the excavations and grading operations to proceed simultaneously with the installation of the roadway panels.
The roadway to carry both trains and automobiles consists of precast concrete panels with embedded track. Such panels are common on railway crossings in city streets, but this was the first time they had been used in a four kilometre tunnel. Crews completely removed the existing tunnel invert and reconstructed it with 1,800 precast panels.
To cope with the ice that typically formed in the tunnel during the winter and was a major maintenance and safety concern, Hatch Mott MacDonald designed a hydronic ice control system to prevent tunnel leaks from freezing on the roadway. The system consists of a prefabricated insulated corrugated steel arch panel, with a collection system behind the panel to direct water to the roadway drains. The system is fitted with an enclosed hot-water circulating heating system fed from boilers located in the portal buildings. As well, the roadway drainage system, electrical duct bank and safehouse supply air ducting were integrated into the subgrade of the narrow roadway.
Despite extremely harsh weather, including winds in excess of 190 km/h and avalanches that isolated the project for four days, the project was completed ahead of schedule. The design-build-operate construction method reduced the time needed to design and build the Tunnel Segment to 16 months. The tunnel is now in its two-year operation period before it is turned over to the State of Alaska transportation department next June.
Being located within the Chugach National Forest, near spectacular glaciers, snow-capped mountains and wildlife, the Whittier Access team took special measures to minimize its impact on the environment. Road alignments were drawn to avoid sensitive plants and salmon spawning beds. Critical views were protected, and restrictions on the levels of noise and site illumination were implemented.
The Whittier community is drawing many benefits from the vastly improved access. These include improved access to shopping, services, social and cultural opportunities, and improved economic opportunities for the town as a freight and cruise ship port. There is also a much better ability to respond quickly should there be an oil spill in Prince William Sound.
Earlier this year, the project won the 2001 OPAL Award for Outstanding Civil Engineering
Achievement from the American Society of Civil Engineers.CCE
Name of project: Whittier Access Project Tunnel Segment, Alaska, U.S.A.
Award-winning firm: Hatch Mott MacDonald, Mississauga, Calgary and Buffalo offices
Project team leaders: Frank P. Frandina, P.E., Christopher J. Tattersall, P.Eng., Patrick O’Connor, P.Eng., Alfred Bennett
Role of award-winning firm: prime consultant to design/build contractor
Client/Design-build contractor: Kiewit Construction
Owner: Alaska Dept. of Transportation & Public Facilities
Other key players: HDR Alaska (owner’s consultant), CH2M-Hill (Portage and Whittier Segments designer)