SVM MIS/DEIS - 3.1.6 Construction Considerations

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Major Investment Study / Draft Environmental Impact Statement
3. Conceptual Engineering, Operations Analysis, and Costs

3.1.6 CONSTRUCTION CONSIDERATIONS

3.1.6.1 CONSTRUCTION METHODS - GENERAL CONSTRUCTION

The following section documents the assumed construction methods that served as the basis for the capital cost estimates. Preliminary engineering may necessitate changes in the proposed style and means of construction.

At-Grade Sections - The majority of at-grade track construction will be in direct proximity to active freight tracks and all construction activities will take into consideration the resulting limitations and safety precautions necessitated by this. At-grade construction within railroad right-of-way will consist of one of the following: replacement of existing, abandoned, or removed track; shifting of existing track; physical widening of roadbed with construction of new track; or a combination of these. For portions of the alignment requiring little or no heavy earthwork to place additional track, construction will be limited to light grading, followed by the placement of sub-ballast, ballast and finally the track elements. Where possible, some of these activities would be performed from an existing adjacent track.

In sections where significant earthwork is required, temporary shoring or other physical separation methods may be employed to separate freight and construction operations so that they can occur simultaneously. Where existing tracks need to be shifted to make full use of the existing roadbed, the shifting may occur prior to adjacent new construction. Embankment cutting would be performed using heavy equipment and material hauled away using trucks or rail cars.

Support structures for the Overhead Contact System (OCS) will be constructed on the outside of new SVM tracks or between two SVM tracks for those alternatives using separate tracks, depending on the final design of the OCS. For commuter rail alternatives, the support structures will be located outside the combined track area.

Aerial Sections and Fly-Overs - Aerial guideway sections (located along the King of Prussia spur), and the proposed fly-over structures will generally consist of reinforced concrete piers and longitudinal members. For the fly-overs, steel integral-pier caps with steel stringers are proposed, as these offer the lowest structural depth thereby helping to provide the required vertical clearance over freight tracks. For sections of aerial guideway, precast, prestressed concrete segmental box girders are proposed. More traditional composite steel girder or reinforced concrete I-Beam designs would also be possible. These will be analyzed further and the best option selected during preliminary engineering and final design.

The substructures would be supported by spread footings, or pile foundations based on geotechnical conditions. The piers would be formed, reinforcing steel installed, and then concrete would be placed. Most piers consist of a single column with a hammerhead pier cap. However, for the flyover structures, a portal configuration is used to span the freight tracks with columns on either side with appropriate side clearances. The steel superstructure (for flyovers) will be fabricated off-site and assembled locally by placing the pier caps on the columns and then placing and connecting the longitudinal girders and diaphragms. This will minimize disruption to the freight service for the fly-over structures. Steel members will be delivered via tractor trailers or rail cars, and lifted in place using cranes. The remaining superstructure - concrete deck forms, foundations for OCS support poles, reinforcing steel - would be installed, and concrete placed. All concrete would be delivered in trucks and pumped into the piers or deck. Optionally, precast concrete deck panels may be used and will be investigated. This would greatly reduce the time required to construct the deck slab.

The segmental concrete box girders for the aerial guideway will consist of short sections that will be precast, possibly on site, before being lifted into place, post-tensioned and connected into long continuous girders. They will be supported by concrete piers. During construction between piers, sections are supported by temporary supports.

Mechanically Stabilized Earth (MSE) retaining walls are proposed for the approaches to aerial sections and fly-overs. These will confine the width of fill and have a significantly lower cost than cantilever or gravity walls. The abutments may be of the stub type, which are supported by piles, or full length abutments extending below the existing ground surface. Due to the modular nature of the MSE walls, the impact to adjacent freight tracks during construction will be minimal, as there will be no need for forming and pouring of the walls. Also, the footing envelope will be drastically reduced thus minimizing the impact on adjacent freight tracks.

Stations and Platforms - All but two stations are at-grade and do not require complicated or unusual construction methods. Station platforms will likely be pre-cast modular sections to be placed on piled foundations on site. The construction of underpasses with ramps and elevator shafts to these will require deep excavation involving shoring techniques. At stations with underpasses, pumping and de-watering may be necessary.

Pedestrian overpasses will be erected by building support piers and abutments on either side of the tracks. The main span will be fabricated off-site and lifted into place using a crane, thus minimizing construction activity above freight tracks.

The complexity of station construction and proximity to existing freight tracks varies from station to station. Typically, the station platform and access structures are located at least one track width away from an existing or active freight track so that station construction can occur without a direct impact to, or service interruption of, adjacent freight tracks. Temporary barriers and flagging protection will be provided as necessary.

For the two elevated stations, platform construction will be incorporated into the elevated guideway construction. Through the station section, the super structure and supporting pier caps will be wider, with additional columns as needed to support the platforms. At locations of elevator shafts and stairway entrances, additional supports will be constructed to bridge the discontinuity in the girders.

3.1.6.2 CONSTRUCTION METHODS - SPECIAL CONSTRUCTION

Norristown River Bridges - West of Norristown, crossing two channels of the Schuylkill River separated by Barbadoes Island, the existing river bridges need to be expanded for some of the alternatives. The bridge closest to Norristown will be expanded with one additional track on the south side. The bridge between Barbadoes Island and the southern bank will be augmented with a new double track bridge that will lead into a fly-over structure over the NS mainline tracks. The new bridges will require the construction of new pier foundations, which are to be placed in line with the existing piers to minimize any restriction to river flow. The piers will be supported by deep foundations. To construct the new foundations and piers, a temporary causeway will be constructed in a way that water flow is maintained. Methods of performing work from the existing adjacent railroad bridge may also be considered. A cofferdam would need to be constructed around each pier location. Sheet piles for the cofferdam and load-bearing piles for the pier foundation would be driven via equipment on the causeway, or from the existing bridge. The cofferdam will need to be dewatered and riverbed material removed to the required depth of the pier footing. Pumped water and other material will need to be placed in a settling tank or basin before water is discharged. A reinforced concrete footing would then be constructed. Forms for the pier columns would be constructed on top of this footing with a reinforcing cage. Ready-mix concrete would be placed by pumping. After the pier columns have been constructed, pier caps would be formed, reinforced, and concrete placed. Following this, longitudinal steel girders will be lifted into place using cranes. Stay in place forms will be installed and the concrete deck placed. OCS structure supports will also be incorporated with the deck pour. Finally, track elements will be placed. Depending on the final construction staging and access plan, the majority of the work may be done from a temporary causeway, which would provide the most unobstructed work conditions, largely independent from freight activities on the existing bridge. However, if the use of the existing bridge is determined to be feasible and advantageous for some or a large portion of the work, this method may be employed. The new structure crossing over the southern channel diverges from the existing structure, however, so that it is very likely that a causeway will be necessary here.

Bridge Over PA Turnpike - The SVM alignment in the King of Prussia area requires the crossing of the Pennsylvania Turnpike approximately 3700 ft east of the Valley Forge Interchange (#24). The alignment crosses the Turnpike at a skew of 35 degrees. This, coupled with a widened section of roadway which includes an exit lane, results in a span of 205 feet. In order to construct a single span railroad bridge for the length required, a truss structure is recommended. A single span is necessary to comply with the Turnpike Commission's requirement that there be no center support in the median of the highway.

The following construction sequence is proposed. The bridge abutments will be constructed on both sides of the turnpike. The bottom chords of the truss will be lifted into place and secured. To support these and the remaining truss members during construction, a temporary queen truss will be installed under the bottom chords. A work platform and safety netting will be constructed on this truss to allow for the construction of the permanent truss without interruption to highway operation below. Once the permanent truss is completed, the queen truss will be removed. The primary impact to turnpike operation would occur during the placement of the bottom chords, and during the construction and dismantling of the queen truss.

Phoenixville Tunnel Rehabilitation - The existing railroad tunnel under Fillmore Street in Phoenixville has experienced rockfalls from portions of the arch and has been removed from service. Fillmore Street above has been signed to restrict truck traffic. Rehabilitation is required prior to returning the tunnel to service to carry a single track of the SVM.

Work elements for the tunnel will include investigation to determine the extent of unstable rock, trimming of rock surfaces, stabilization of roof arch with rock bolts, installation of a drainage medium to handle drainage coming through the roof and walls, and lining with micro silica steel fiber reinforced concrete. The portals will also require reconstruction. Longitudinal drainage and lighting for safety and maintenance will be installed.

This description assumes that a single new track would be constructed offset from the centerline, allowing a track access roadway to be constructed on the opposite side. Adequate overhead clearances for traction power components will be obtained by rock trimming, and lowering of the existing track profile.

Pressure grouting of the foundation zone of Fillmore Street above may allow truck restrictions to be removed after rehabilitation of the tunnel itself. Consideration will be given to enclosure of storm water and the diversion of surface runoff in the area above the tunnel in order to reduce the destructive influence of infiltration.

None of the work adjacent to and inside the tunnel will be subject to any maintenance of traffic restrictions, as this section of alignment is currently abandoned.

Ivy Ridge Connection - A new connection between the abandoned portion of the R6 Cynwyd Line, and the active R6 Norristown line will be constructed west of the Ivy Ridge station. The two lines are apart by approximately 150 feet horizontally and 30 feet vertically. The new double track connection will be approximately 800 feet long with a maximum grade of 5 percent for light rail alternatives, and approximately 1800 feet long with a maximum grade of 3 percent for commuter rail alternatives. Necessary site preparation including clearing and utility work will commence first. This may involve changes to PECO's transmission towers and lines. Following this, a new connecting shelf will need to be cut into the existing slope. This will require the construction of retaining walls. The type of retaining walls and method of construction will be determined following more detailed design and based on a geotechnical investigation. Temporary or stay-in place shoring may be used to retain the slope during construction. Soil stabilization and vegetation measures will also be used to ensure long term stability. After completion of the primary earthwork, drainage facilities, electrification structure foundations, sub-ballast, ballast, and track elements will be constructed. The critical area of this work is at the point where the connecting tracks meet the existing R6 Norristown tracks. Trackwork and adjacent earth and structural work in this area will require careful staging and coordination to maintain service on the R6 during construction. One of the existing two tracks may have to be taken out of service for a short period.

Pottstown Cut Widening - The Pottstown Cut widening involves the removal of an existing gravity retaining wall and four overhead bridges carrying local streets, and the construction of a new retaining wall and new overhead bridges accommodating a wider right-of-way. The new wall will be constructed approximately 10 feet outside of the existing wall. To remove and later reconstruct the bridges, a temporary shield may be constructed under them so that freight traffic can be maintained during construction. The physical widening work will be done away from the existing tracks. Stay-in place or temporary shoring will be placed behind the existing walls. The intermediate fill will be excavated, and the existing wall disassembled away from the track. Following the excavation and wall removal to the required depth, new bridge abutments and a new retaining wall will be constructed. The overhead bridge demolition and reconstruction will be done in stages so that access across the railroad tracks is maintained. The new overhead bridges will be thru-girder bridges, or bridge types with shallow deck girders to avoid severe changes to the existing roadway profile. (Three of the four existing bridges are of thru-girder type). The bridge approaches will also require reconstruction. Once all structural work is complete, the existing tracks will be shifted slightly to accommodate the construction of a new track on the south side. The tracks will be reassigned with freight using the new southern track and the middle track, and the SVM using the existing (shifted) northern track. This will require existing freight tracks on the approaches to be cut and thrown to the new track configuration. Electrification structures will be erected. These may be of the portal type spanning the cut, or single-track cantilever supports over the northern SVM track. Electrification elements will be incorporated into the new overhead bridges.

18^th Street Tunnel - Alternative 5ET requires construction of a tunnel under 18^th Street between the City Branch and Suburban Station. The tunnel would be constructed by cut-and-cover methods. Utilities in the street would be relocated prior to construction or protected in place during construction. Shoring would be placed on each side of the street and the roadway reinstated using a temporary deck. Underpinning of adjacent structures may be required. The excavation would take place under the decking to the invert of the tunnel. The tunnel box would be constructed of reinforced concrete. The tunnel box would be backfilled and the permanent road reinstated.

Tunneling under the Vine Street Expressway will require additional techniques to minimize any potential effects to the expressway structures. These techniques may involve underpinning and grouting. It may be feasible to take a portion of the expressway out of service a lane at a time to advance the tunnel from the roadway surface.

3.1.6.3 CONSTRUCTION IMPACTS

Construction of the Schuylkill Valley Metro in the NS segment will impact the freight operation. Both light rail and commuter rail have the potential of significantly impacting the continuous use of existing NS tracks during construction. In the case of light rail this is due to more intense work adjacent to the freight track for right-of-way widening, new track construction and electrification, which could temporarily require putting one existing track out of service. Additionally, in many areas freight tracks need to be shifted or a section of new freight track tied in at each end resulting in impacts and requiring well planned staging of work. In the case of commuter rail, and in particular electric commuter rail, the majority of the impacts will result from construction on or above the existing tracks as a result of the signal system replacement and the construction of overhead catenary. Impacts from construction adjacent to the existing tracks would be less than for light rail due to less new track construction and right-of-way widening.

The construction of three fly-overs for light rail and one for the Route 100 (NHSL) extension also has a high potential to impact freight operations. The design developed for these structures would allow for significant portions of this work to be performed adjacent to the freight tracks or off-site to reduce these impacts. Other direct and indirect impacts to the freight operator would result from the reconstruction of overhead bridges and the rehabilitation or widening of undergrade bridges, and from the replacement of grade crossings.

Construction on those sections comprising the existing R6 Regional Rail lines may interfere with the existing services on those lines. For most of the alternatives, this construction is limited primarily to station upgrades and improvements similar to work currently being performed at many SEPTA stations without major service interruptions. Work to restore the abandoned track on the Cynwyd line should have only a limited impact on the active track. For commuter rail Alternatives 1D and 1E that include the wide gauge light rail shuttle from Ivy Ridge to Center City (via Cynwyd), requiring a change in track gauge, as well as a change in power supply from 12 kV AC to 600V DC, more severe impacts to the Cynwyd line service would be experienced during construction, including the potential of service interruption for a period of time. For all light rail alternatives, Alternative 6, and commuter rail Alternative 2D, the connection west of Ivy Ridge from the Cynwyd line to the Norristown line would likely impact the R6 Norristown service for certain periods during its construction and may require service interruptions. The construction of a third track (for freight use) through the Norristown Transportation Center (NTC) for all light rail alternatives would have an impact on the operation of the NTC with respect to pedestrian flow between the R6 station and the NTC, as well as on movements of buses through the bus terminal area.

The construction of light rail track and trolley wire in city streets will impact traffic flow and operation on those streets and have spillover effects onto cross streets and other parallel streets absorbing some of this impact. These impacts apply to Alternatives 1D, 1E, 5E, and 5ET, all of which include street running. The construction of a new tunnel under 18^th Street being considered for Alternative 5ET will have major construction impacts to traffic on and access to 18^th Street with the spill-over impacts to cross streets and parallel streets. The functionality and access to buildings on 18^th Street would be impacted. The rerouting of a major sewer could cause traffic impacts on other streets. Additionally, the construction of the tunnel would likely impact the Vine Street Expressway (I-676) operation and could affect the operation of the Center City Commuter Tunnel during construction into Suburban Station.

The need to replace or modify existing undergrade and overhead bridges as well as upgrade grade crossings in areas west of Norristown could affect the operation of several major highways and smaller roads crossing the right-of-way.

Construction in nearly all areas will have impacts to utilities, especially fiber-optic cable relocation and PECO transmission line tower relocations. This will require close coordination with the utility companies. In most cases new facilities would be constructed and then tied in before the existing utilities are removed, thereby limiting utility service interruptions.