Portland-Milwaukie Light Rail Bridge Construction, June 2011 - TriMet

June 2011Building the Portland-MilwaukieLight Rail Bridge

Project Overview6 th MAX construction project,expanding system to 60 miles7.3-mile light rail extension10 stationsUp to 25,500 weekday ridesby 20302 Park & Ride lotsUp to 400 bike spacesNew multimodal bridgeUp to 14,000 jobs2

Cable-Stayed Bridge 1,720’ long Light rail, buses and future streetcar Two 14’ bicycle and pedestrian paths Width: 75’ 6”; at towers: 110’ 6”3

Why a Cable-Stayed Bridge?3-year process to selectthe best bridge type anddesign for the areaCost-effectiveThin, efficient structurethat maximizes verticaland horizontal clearanceElegant and beautifulMinimizes impactto river habitats4

Four-Pier Cable-Stayed BridgeWest TowerEast TowerWest PierAbutmentWork starts withfoundations in the riverEast PierAbutmentFour piers – two in water Two towers: 180’Vertical clearance: 77.52’ (Columbia River Datum*) Horizontal clearance: up to 725’*All measurements are Columbia River Datum (CRD)5

River Depth• 77.52’ vertical clearance for 150’ section of main span• 65’ vertical clearance for entire span 128 years of daily water heights evaluated to select vertical clearance (1879-2007) Since last dam installation on the Willamette, Columbia, and tributaries, highest riverelevation was 28.5’ during1996 flood – ordinary high water elevation is 14.7’ Excluding 1996 flood, the highest river elevations recorded range from 16’ to 20’between November and June. Riverbed roughly 53’ below mean water elevation (avg.) at East Tower, 22’ at West6

Each towerfoundation iscreated from awork bridgeabove thecofferdam.Construction Begins July 1Crews build temporary work bridges from east and westEast: 460’ longWest: 335’ longA typical example of atemporary work bridge.East Work BridgeWest Work BridgeBarges located adjacent to future towers tofacilitate building cofferdams and work bridges In-water construction window8July 1-Oct. 31 annually

Cofferdam ExamplesCofferdam: “construction island” in the water9

Cofferdam for Building Base and TowerCOFFERDAM FRAME(IN RED)Dimensions: 71’ x 110’10

Cofferdam Construction Sequence• Install 12”-18” layer of sand onriverbed to maintain water qualityand to control turbidity11

Cofferdam Construction Sequence• Position steel sheet pile template• 20’ tall12

Cofferdam Construction Sequence• Install the sheet pile13

Cofferdam Construction Sequence• Remove fish and pump waterfrom inside the cell14

Cofferdam Construction Sequence• Install scour protection• Place 2’ to 5’ of rock materialon riverbed to stabilize sand15

Cofferdam Construction Sequence• Fill cofferdam with sand and gravel• East tower foundation:8,500 cubic yards• West tower foundation:2,200 cubic yards• West side is roughly20’ shallower thaneast side16

Drill Shafts for Tower Foundation6 drilled shafts per tower Shafts are 10’ indiameter Drilled down 150’ to 170’ Pile cap: concretecover over the6 drilled shafts Pile cap is10’ to 18’ thick Together, the shaftsand pile cap serve asthe tower foundationPile Cap and Shafts(in red)17

Oscillator will install 10’ diameter casings used for shaft construction18

Drilled Shaft Installation• 6 drilled shafts per tower – two months per tower• Drilled shafts begin October 2011 – completed in March 201219

Drilled Shaft Installation• Each shaft is 150’ to 170’ long20

Tower ConstructionTower cranePier tablePile capStarts in February 2012 – up to 5 months to build one tower 21

Temporarysupport cablesPermanentcablesCofferdam• 20 cables per tower, 10 on each side• Total length of cable is roughly 3.5 miles22

Form travelers• Form traveler: while suspended, creates area for next work segment• Construct center span closure in spring 201423

Watch live, time-lapsed videoof the constructiontrimet.org/pmbridgecams24

Opening in Fall 201525

Terminology Tower 3 – west tower Tower 4 – east tower Bent 2 – west pier Bent 5 – east pier “trestle” – work bridge “pylon” – tower