Robertson Tunnel

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Info
Robertson Tunnel

Robertson Tunnel is named mid-platform in the Washington Park station
Line	westside MAX Blue Line
Location	Tualatin Mountains, Portland, Oregon, USA 45°30′38″N 122°43′01″W / 45.510661, -122.716869Coordinates: 45°30′38″N 122°43′01″W / 45.510661, -122.716869
Status	in service
System	MAX Light Rail
Start	Goose Hollow 45°31′09″N 122°41′59″W / 45.519087, -122.699749
End	Sunset Hills Mortuary 45°30′23″N 122°45′14″W / 45.506324, -122.753833
No. of stations	1
Operation
Opened	September 12, 1998
Owner	TriMet
Character	passenger commuter
Technical
Line length	18 mi (29 km)
Track length	3.1 mi (5.0 km)
No. of tracks	double track
Gauge	1,435 mm (4 ft 8½ in)^[1]
Electrified	overhead 750 Vdc^[2]
Operating speed	55 mph (90 km/h)
Highest elevation	450 ft
Lowest elevation	250 ft^{[citation needed]}

The Robertson Tunnel is a tunnel through the west hills of Portland, Oregon, U.S. for the TriMet public transit MAX Light Rail system. The tunnel is 3.1 miles (5.0 km) long and consists of twin 21 foot (6.4 m) diameter tunnels. There is one station within the tunnel at Washington Park, the second deepest such station in the world. The tunnel has won several worldwide engineering and environmental awards.^[3] It was placed into service September 12, 1998.^[4]

The tunnels pass through basalt up to 16 million years old. Due to variations in the rock composition, the tunnel curves mildly side to side and up and down to follow the best rock construction conditions.^[5] The tunnels vary from 80 to 300 feet (24–91 m) below the surface. A core sample taken during construction is on display with a timeline of local geologic history.^[6] The east tunnel entrance is near Vista Bridge at the edge of the Goose Hollow neighborhood at the foot of Washington Park. The west entrance is along U.S. Route 26 just west of the Finley-Sunset Hills cemetery, about a mile east of the junction with Oregon Route 217.^[7]

1 Name
2 History
3 Route
4 See also
5 References
6 External links

[edit] Name

William D. Robertson 1947–1997 commemorative plaque displayed at Washington Park station platform

Core sample and geologic time display in the Robertson Tunnel

The tunnel is named for William D. Robertson who served on the TriMet board of directors and was its president at the time of his death.

[edit] History

Originally, it was expected that the westside MAX line would be adjacent to the Sunset Highway, despite the six percent average grade. Reliability, weather conditions, public opinion, and environmental concerns led to choosing to tunnel through the Tualatin Mountains instead.

Construction began in the summer of 1993 at the west end employing the conventional mining technique of drilling and blasting due to the loose mixture of materials. More than 75 tons of explosives were used and mining progressed about a mile into the hill. East end construction began in August of 1994 with a customized tunnel boring machine. About a thousand workers from 230 construction firms were involved in the 18 mile westside MAX line, including those who built the tunnel and installed the reinforced concrete liner, tracks and wiring. One worker was killed while operating equipment.^[7]

Tunnel construction continued 24 hours a day, six days per week. The north tunnelers met after 16 months on December 29, 1995, and the boring machine began the south tunnel in April 1996. The south tunnel took only four months before the tunneling teams met on August 15, 1996.^[7]

To complete the west end at the cemetery, 14 bodies were relocated.^[7]

The original estimate for the tunnel was $103.7 million, but the final price tag came to $184 million, largely due to challenges posed by unexpected loose layers of silt and gravel, and crumbling basalt which prevented the boring machine from working effectively.^[7]

[edit] Route

east end of the tunnel goes under Washington Park

west end of the tunnel just below Finley-Sunset Memorial Park

just outside the west end of the tunnel facing Beaverton

The tunnel generally follows, but remains north of U.S. Route 26, diverging the most (1/3 mi, 500 m) in the Oregon Zoo area.

The elevation at the west end is higher than the east but there is very little perceptible slope except for several gentle, short grades which exist presumably to follow the easiest-to-bore rock stratum.

During construction, the east portal was west of Canyon Road, below City of Portland Reservoir 4. After completion, the road was raised and an overpass placed over the track. This effectively extends the tunnel about 430 ft (130 m) so it emerges on the east side of Canyon Road.

Beginning at the east end (traveling westward), under Canyon Road the tunnel turns SSW (202°)^[8] for about 300 m (1000 ft) where it turns WSW (236°) under the large field east of the Elephant House. 1200 m (4000 ft) later it is directly under and follows SW Kingston Road at a point 250 m (800 ft) north of the zoo's elephant exhibit. For the next 250 m, it arcs until almost directly westward (263°) and straightens for 300 m (1000 ft) to arrive at the Washington Park station.

After the station, it passes under the south side of the World Forestry Center's main building and turns 4° northward (267°) and continues for its longest straight stretch of 900 m (3000 ft). At the point it passes under SW Skyline Road 150 m (500 ft) north of the Sylvan Bridge, it turns slightly southward (253°) and—300 m (1000 ft) later—goes under the Finley-Sunset Hills building and water feature. For the remaining 500 m (1700 ft), it turns right in a long gradual arc exactly paralleling Sunset Hwy. The arc continues at the same rate after the west portals, and is due west (270°) about 500 m (1700 ft) past the portals.