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E320 Future Wye Technical Memorandum
MEMORANDUM
Sound Transit East Link I South Bellevue to OTC
E320 Future Wye Technical Memorandum
Date:
November 8ü, 2013
To:
DeWittJensen
From:
Jerry Dorn, Kent Ferguson, Bryan Williams
CC:
Jim Schettler
Re:
Concept for future lssaquah Wye Connection
Summary
The Prelíminary Engineering documents included provisions for a future wye connection near l-90 that could
serve a line extension to lssaquah thet would have required significant design and construction in the East Link
package. The
H-J-H scope was modifíed
to instead provide
a feasible concept for the
future lssaquah wye
connection while minimizing design and construction work to the current East Link Project.
Scope of Work
o
r
o
Develop concept for future wye connection in sufficient detail to show concept is feasible and will not
preclude a future connection.
Develop conceptual track layout and column locations.
Prepare Technical Memorandum to identifo a feasible concept, the assumptions for layout, and the
identification of future construction work required.
o
Basis
o
Deliverables wíll include E320 Future Wye Technical Memorandum.
for Concept
East Link connection will be isolated from the future lssaquah line through use of rail and structure
expansion joints.
o
Details will include a feasible concept for future wye connection to current structure without significant
interruptions to service.
o
Replacement of plinths to remove track superelevation and addition of special track work is acceptable
future work, therefore main line service will be out for extended periods of time. lt is assumed that for
the majority of the outages, single track operations will be possible.
o
Construction of new straddle bents and demolition of current columns or bents is an acceptable level of
future impacts.
o
Perform preliminary design of wye only in sufficient detail for proof of concept.
East Link I South Bellevue
to Overlake Transit Center
Page
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1
sT002434
E320 Future Wye Technical Memorandum
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The structural analysis global modelwill be developed based on the no wye connection option only, it is
assumed that the future design will create the future global model based on future layout details. A
concept for modeling is discussed in the memorandum.
.
o
o
LzO' spans or less assumed for wye,
Design and layout is not optimized, a single feasible concept is provided.
Relocation of existing ramps, existing facilitíes and existing utilities is feasible
Relocation these items
will only be investigated to determine feasibility.
o
o
Current final design and details will only include the option without the wye.
Plan sheets are not required, engineering sketches only will be prepared.
Concept Description
Track
The current track alignment where the future wye would be connected consists of a 806.09' and 82L.94' radius
curves on a vertical tangent profile. The design concept for the future connection is the turnouts would be
placed within the body of the horizontal curve on the radial or divergent side of the turnouts. The proposed #10
turnout radius is 806.09', matching the minimum radius of the mainline curves. At the time the turnouts are
installed the track superelevation of 3"would need to be removed.
The future wye would consist of a three leg wye with double track on each leg so a full range of two direction
movement can be accomplished to the west and east. To make the wye connection in the future, each leg of
the wye would have a speed consistent with the turnouts The superelevation would need to be removed to
make the switch which will reduce operating speed through the connection to 20 miles per hour. The
alignment of the lssaquah Extension as it crosses the slough was not determined, it was assumed to run parallel
to the exist¡ng 190 highway.
Structure
Additional deck width and tub girders will be needed where the wye connects. This can be accomplished by
framing tubs parallel to the current tubs and connecting at the slab level and diaphragms. The future slab and
diaphragm connection will drill and dowel into the current contract structure. lf slab continuity is required in
the future due to special trackwork, a link slab will be used. To support the additional superstructure, additional
cap crossbeam and columns will be required. The added columns will be placed outside the current structure
and the new cap beam will be built around the current cap beam. The future cap beam would be post
tensioned to pick up the load from the current pier cap. This makes the future wye extension integral with the
current design. The current columns can either be used in the future layout or removed in the future after the
connected column and cap are constructed and post tensioned. Exact details will be determined in the future.
Seismic
The future wye connection and the continuous rail for the lssaquah Extension will create add extra stiffness in
the seismic and temperature load distribution that will affect the current adjacent East Link aerial guideway. ln
order to minímize the stiffness effects, the future lssaquah Extension would contain an expansion joínt on the
wye legs so the wye connectíon to East Link is isolated from the future lssaquah Extension. The columns and
cap beam that are added wíth the future wye connection would be designed to resist their share of the seismic
and temperature loads so the current lateral design of East Link would not be affected.
East Link I South Bellevue to Overlake Transit Center
Page 2 of 5
sT002435
E320 Future Wye Technical Memorandum
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GlobalModeling
The current design has a global model of the structure that includes the rail, superstructure, columns and
foundations. The model is used to determine vertical and lateral loads on the structure and to evaluate rail
structure interaction. A similar model would be created in the future that would include the current structures
and future lssaquah Extension structures and rail. The stiffness of the future structures and rail expansion
joints would be used to limit the forces to the current structure. The results of the future model would be
compared to the current model results to determine if the future structure causes overload of the current
structure. The future structure would be modified if necessary to limit loads on current structure.
Future Design and Detail Work
Some of the future design and details that will need to be advanced to final design when the lssaquah Extension
is advanced are summarized in the following bullets:
o
o
¡
o
¡
o
o
.
o
o
o
o
o
o
o
.
o
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lssaquah Extension alignment and profile
Structure concept and span layout over the slough
Environmental impacts and mitigation
WYe laYout oPtimization
Turnout details
Superstructure framing plan
Column locations
Cap beam details for extension of cap beam around current cap beam
Slab and Diaphragm connection to current structure
Geotechnicalinvestigations
Seismic analysis of global seismic resísting system including current and future structure
Column and foundation design based on future seismic models
Continuous rail analysis and rail expansion joint locations
Roadway ramp clearances and sight distances
Utility conflicts
Systems layout; routing of conduits will typically be on the deck
OCS pole locations; poles will be added on the future structure and cantilevered over to the current
structure as required.
Drainage
Future Construction Work and lnterruption to Service
The elimination of track superelevation and the addition of switches in the track will require modification of
current plinths. This work could be staged so the majority of the work would be completed while operation
continues on the adjacent track. There will be periods of time when a switch is added and rail connections made
that w¡ll require shut down on both tracks, but it would be possible to complete this work duríng non-revenue
service.
For the structure, drilled shafts and columns could be constructed outside the current structure while operation
continues. There will be interruptions to service when heavy lifting occurs such as setting tub girders, when
there are closure pours between structures such as diaphragms and decks, and when there is a change in the
load path such as demolition of an existing column.
East Link I South Bellevue to Overlake Transit Center
Page 3 of 5
sr002436
E320 Future Wye Technical Memorandum
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