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 (IA/DePaul) included:

Abutment and Pier Design and Construction in a Complicated Karst Setting
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 faults.

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.

Schedule
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.