Baker River Cable Stay Bridge, 1998

Mt. Baker Ranger District, Mt. Baker-Snoqualmie National Forest, WA


Satellite view of bridge location. (resolution insufficient to see bridge) View Larger Map
   
Baker River Bridge in March of 1999.

USE:  Pedestrian/equestrian

SPAN:  240' w/45' approach ramp

TRAVEL WIDTH:  6'

TOWERS:  38' tall, 14" x 14" ASTM A847 tube

ANCHORS:  Sahale earth anchors (one side) and twin 1 3/8" rock bolts (one side)

CABLE STAYS:  1", 1.125", 1.250", & 2" ASTM A 586 Bridge Strand

Baker River Bridge, 1998  
Main span assembly showing two skylines and carriage.

 

The Baker River Cable Stay Bridge is at the end of the Baker Lake Road, off the North Cascade Highway in Washington.  It is the northernmost trailhead link of the 14 mile long Baker Lake Trail, an historic prospecting and lumbering route through old growth forest east of the Mt. Baker volcano.  The bridge crosses the Wild and Scenic upper Baker River; a region subject to periodic violent flooding that has negated numerous previous attempts at bridging since 1900.  The simple lines and low visual impact of this bridge perfectly complement the expanse of active river channel, towering old growth forest, and surrounding snow capped, craggy peaks.

Located 1/2 mile upstream from the trailhead, the Baker River Bridge site is not accessible to conventional construction equipment.  The hydraulic permit for the project allowed movement of an excavator up the river channel for the purpose of excavating the footings, and for a small mobile crane to assist with erection of the towers, but operation of equipment from within the ordinary high water mark of the river was not permitted.  Concrete for the abutments and anchors was delivered to the site via helicopter, and for ease of construction the bridge was designed to have maximum component weight of 4000 pounds and length under 40'.

To reduce concrete volume (and expense) earth anchors were used on one side of the bridge and rock anchors in freight car sized boulders were used on the other.  One anchor rock required through-bolting, which was achieved by tunneling under it for access.

Assembly of the main span was accomplished using two aerial skylines.  Deck, railing, and rigging hardware were moved over the trail to the bridge site.  Photos on this page show skyline carriage with the bridge under construction, and Bridge Specialist Keith Monohan testing rock anchors with a 60-ton jack.

1998 Construction: Skyline and Carriage

 

Keith Monohan testing 14' long rock anchors with 60-ton hydraulic through-jack.
Testing Rock Anchors with 60 Ton Jack