Centrally located in a Boston neighborhood, Roslindale’s Robert Street Bridge functioned as a commuting lifeline, carrying the MBTA’s Needham Line across Robert Street. Built in 1898 and rehabilitated in 1985, the bridge served the public well beyond its intended lifespan. Inspection reports confirmed the structure was approaching the end of its useful life. To maintain its infrastructure’s state of good repair and provide safe, efficient transportation for transit riders, the Massachusetts Bay Transportation Authority (MBTA) decided to replace the bridge. Minimizing impacts to the public was paramount—major rail service and roadway disruptions were not an option. Partnering with the MBTA’s construction management team and Canton, Massachusetts-based contractor Barletta Heavy Division, VHB‘s structural design team stepped up to the challenge and delivered this critical project ahead of schedule. They created an innovative solution using Accelerated Bridge Construction (ABC) techniques to limit shutdowns on a busy corridor and keep the Roslindale community moving.
The Robert Street Bridge’s location in the heart of the bustling Roslindale neighborhood made this an exceptionally demanding project from an engineering standpoint. The bridge replacement had the potential to make substantial economic and social impacts on the community by disrupting access to local businesses already struggling during the COVID-19 pandemic, as well as by inconveniencing the traveling public. Adding further complexity to the project, the corner of Roslindale Village’s rail station platform was only two feet away from the rear of one of the bridge’s abutments and any impacts to the platform could have necessitated a full replacement of the entire station, which the project budget did not support. The project team had to manage these constraints within the limits of a rigorous 18-month construction schedule.
Presented with the additional challenge of constructing the bridge in such a way that did not preclude a future track through the corridor, VHB’s structural engineers resourcefully laid the groundwork for later expansion by increasing the capacity of the new bridge foundations to accommodate a potential twin-bridge superstructure without increasing project cost. This future-ready design will facilitate any possible upgrades to the bridge within the rail right-of-way with minimal disruption to the existing track and roadway.
The contract envisioned the Robert Street Bridge replacement requiring two weekend rail shutdowns, which would allow installation of the proposed substructure in the first weekend and the installation of the superstructure in the second weekend. Working closely with the MBTA and the contractor, VHB’s engineers designed a highly creative solution for replacing the vital century-old bridge with just one weekend of interruption to rail traffic and without impacting the station platform. In just 48 hours—with no allowance for delays—the project team demolished the original bridge, rolled the new bridge into position, and reconstructed the tracks. By reducing the amount of rail shutdown time by 50 percent, the project team was able to move the project forward 21 days ahead of schedule.
Though the project was delivered through the traditional Design-Bid-Build process, VHB, Barletta Heavy Division, and the MBTA formed a tight-knit partnership that proved instrumental to the project’s success within trying parameters. The MBTA’s Chief of Capital Delivery Katie Choe hailed the “combination of mutual respect, strong relationships, and technical expertise among the team members.”
A Creative Design
With the Robert Street Bridge situated in a densely populated urban neighborhood, the project team prioritized safely replacing the structure with the least possible impact on the community. To meet this objective, VHB and the MBTA construction management team collaborated to employ ABC techniques for the project. The new bridge superstructure was assembled adjacent to the existing bridge and mounted above the roadway on temporary supports, allowing both the commuter rail and the roadway below to operate normally.
While the MBTA has successfully used this ABC technique in the past, it was the project’s foundation construction and planning for future rail expansion that made the Robert Street Bridge Replacement project unique. With the rear of the bridge’s east abutment only two feet from the corner of the rail station platform and station repairs or replacement not in the budget, VHB’s engineers had to creatively determine an alternative that would not cause any impacts to the platform. Their well-considered foundation design comprised micropiles and drilled shafts to keep the station platform intact and minimize disruptions to MBTA revenue service.
Using 10 micropiles installed through and in front of the east abutment’s existing granite blocks, topped by a precast concrete pile cap, the proposed foundation layout enabled support of the new bridge without any impact to the platform. The micropiles were positioned outside of the limits of the existing superstructure, which allowed the bridge to remain open during the work. Sliding bearings would be set on the retrofitted abutment, and a new formlined concrete face poured. Barletta Heavy Division and the MBTA had successfully employed this construction approach for the replacement of another bridge and testing of the abutment’s granite blocks confirmed its feasibility. To accommodate the large horizontal forces of the railroad VHB’s engineers proposed deep foundations consisting of a precast pile cap supported by two six-foot-diameter drilled shafts at the west abutment. The shafts and abutment cap would be installed behind the existing abutment and fixed bearings placed at the abutment.
In considering the design and detailing of the proposed bridge foundations, the VHB team investigated the geometry of a potential future second bridge and its relation to the existing abutments. Decades ago, the Needham Line carried two tracks, but the Roslindale Village Station platform now sits over the former second track’s alignment. The proposed bridge’s single-span through-girder structure and modern horizontal track clearance envelopes required that the bridge be significantly wider than the existing three-span bridge. Any future second bridge’s track alignment would therefore need to be located well off the previous track alignment. The engineers designed a forward-thinking solution: a substructure with the flexibility to be modified to accommodate a second adjacent superstructure. VHB designed the micropiles and drilled shafts for both the proposed condition and a future second track condition to facilitate any future expansion of the rail corridor.
Planning Pays Off
Staging the construction over four phases from summer 2020 through summer 2021, the project team was able to complete the majority of the work without impacting either the road or the railway. Ultimately, they not only prevented structural impact to the station platform, but also enabled rail service to continue during installation of the adjacent micropile foundations. Pedestrian access to the station remained uninterrupted throughout the duration of the project. Construction required three weekend road closures, occasional lane shifts and one-way traffic, and pedestrian detours across Robert Street.
Bridge superstructure installation over one weekend shutdown
The project team worked diligently to ensure that the one rail service shutdown weekend of June 4, 2021, was a success and trains were able to run on time for the Monday morning rush. Preparations for the weekend shutdown of commuter rail traffic required extensive planning, coordination with subconsultants and suppliers, and public engagement well in advance of the disruption. Over the shutdown weekend, the existing bridge was demolished. Then using two large-capacity self-propelled modular transporters (SPMTs), the new bridge was lifted and moved into place. Careful organization went into this engineering feat, including a detailed hour-by-hour schedule for the weekend and direct coordination with the transit operator Keolis to include time to test trains before the line could reopen by 5 a.m. Monday morning.
Delivering for Stakeholders
Due to its proximity to downtown Roslindale, the Robert Street Bridge Replacement project became a point of local interest. Going above and beyond the task of replacing a bridge, the project team made sure the project fit within the context of the community while contributing to the identity of the downtown Roslindale Village area. The project team diligently involved Roslindale residents by holding interactive public meetings to increase understanding and maximize the project’s value as a gateway to Roslindale’s bustling downtown. Planning for the safety of anticipated local spectators during construction activities such as erecting the steel and moving the bridge into place, the team created designated spaces where they could watch the transformation. The team successfully kept the onlookers safe while completing the work, fostering the public’s positive engagement with the project.
“We were met with a fair number of challenges with the replacement of the Robert Street Bridge,” said VHB’s Highway and Structures Director, Robert Penfield, PE. “Our team worked hard to develop a thoughtful, future-proof design, while pragmatically applying ABC techniques, to provide the MBTA a truly cost-effective solution that minimized impacts to the traveling public and the community.” By carefully and creatively considering each obstacle in this complex and context-sensitive project, VHB’s engineers helped deliver a bridge replacement project that met the needs of the MBTA, the Roslindale community, and transit riders and will continue to do so for years to come.
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