The Schuylkill River Bridge/Diamond
Run Viaduct Project
By I. Victor Warnquist, P.E.
Urban Engineers, Inc.
In 1998, the Pennsylvania Turnpike Commission (PTC) began
modernization of 1.8 miles of the Pennsylvania Turnpike between
Valley Forge and Norristown. The widening of the Schuylkill
River Bridge, as part of this contract, constituted a major
technical challenge for the PTC and Urban Engineers, Inc., the
Designer, Construction Manager, and Construction Inspector.
This project involved rehabilitating the existing westbound
bridge and "shoehorning" a new 1224-foot long eastbound
bridge between the existing Turnpike right-of-way and an existing
Conrail railroad bridge just 55 feet south of the Turnpike.
Additionally, foundations for the new bridge were built in a
Karst limestone area; steelwork spanned an active SEPTA commuter
rail line, the Schuylkill River and State Route 23; the Diamond
Run Creek was diverted for construction of new abutments and
piers for the Conrail Bridge; a 660' long viaduct was replaced
with fill between two bridges; and 3000 cubic yards of compaction
grouting were placed in a void under a new abutment; all while
four lanes of traffic were maintained throughout the project.
Upon completion of the project the new Schuylkill River Bridge
carries eastbound traffic and the existing improved bridge carries
westbound traffic. Two of the three new travel lanes in each
direction were opened after construction.
The PTC called this project "the most complex in the Commission's
history." The technical aspects of this project were such
that a high degree of engineering innovation and construction
resourcefulness were required.
Significant features concerning this project as constructed
by IA Construction/Tony DePaul & Sons, Inc., A Joint Venture
Abutment and Pier Design and Construction in a Complicated
This Norristown-Valley Forge locality has a unique transitional
geologic setting. Three formations of Cambrian rocks have been
altered, fractured, and deformed in the geologic history. The
final result is a complicated Karst setting characterized by
significant rock voids, boulders, sloping rocks, and numerous
As a result of geotechnical analyses, the Schuylkill River
EB west abutment and Piers 1 EB through 3 EB were founded on
30" caissons, 30' to 80' deep, with 36" sockets; the
Schuylkill River Piers 4 EB and 5 EB and the east abutment used
spread footings; the Conrail Bridge piers and east abutments,
and the west abutments on Conshohocken Road were founded on
piles; and the Conshohocken Road east abutment was supported
on 3000 CY's of compaction grouting.
EB Structural Steel Erection of Girders
On this project, EB structural steel girders on Spans 6 through
1 needed to be erected by crane and traveler over SEPTA, the
Schuylkill River, SR 23, and Fourth Street. This girder bridge
was located in a 55' slot with active PTC traffic on the north
and the Conrail Bridge, including a 13.8 KW electric service
line, to the south.
In order to erect Span 6 steelwork, the PTC allowed a weekend
outage in their special provisions. After raising Span 6 by
a crane, a platform derrick/crane combination erected 90' to
130' girders at night delivered directly to the existing bridge
EB travel lane.
Rehabilitation of the Existing Bridge (New WB)
Some of the more complex engineering and construction issues
on this project were the removal of the existing concrete deck,
originally placed in 1953; the jacking of sections of this 11-span,
1224' deck; dismantling of the existing 3' high fixed and expansion
bearings; placement of a 2.5' concrete pier stem extension;
erection of seismic isolation bearings; and jacking down of
the bridge steelwork to these new bearings.
Since this project had a $20,000 per day Incentive/Disincentive
clause the schedule was "king". Urban updated the
schedule with IA/DePaul bi-weekly and presented these results
at each succeeding bi-weekly progress meeting. If work approached
the critical path, IA/DePaul was ever aware of the situation
and worked men and equipment overtime to get work back on schedule.
The major goal at the onsite of work was to switch traffic
from Stage 2 to Stage 3 on or ahead of schedule and after work
started in Stage 3, to complete most deck pours prior to winter
1999/2000. IA/DePaul met or bettered all milestones.
This project demonstrates that the resourcefulness and management
skills of today's engineers can overcome technological challenges.
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