Thinking ABC on MassDOT’s Acceler-8 I-90 Bridge Replacements Project

Introduction
After a busy summer of 2021 with construction activities in the I-90 corridor in Southborough and Westborough, MA, the Acceler-8 project is in its final stage and is coming to an end. The project included replacement of eight bridge superstructures (four – twin structures) using NEXTD beams and rehabilitation of bridge substructures using Accelerated Bridge Construction (ABC) techniques under the Design Build (D/B) project delivery method to minimize the impact on one of Massachusetts’ most important highway arteries.  The bulk of the construction took place between mid-June and mid-August of 2021, executing the major milestone of replacing the eight bridges in just six weekends as follows: (1) Weekend 1 – WB Bridge over Woodland Road; (2) Weekend 2 – WB Bridge Over Cordaville Road; (3) Weekend 3 – WB Bridges over Parkerville Road and Flanders Road; (4) Weekend 4 – EB Bridge over Woodland Road; (5) Weekend 5 – EB Bridge over Cordaville Road; and (6) Weekend 6 – EB Bridges over Parkerville Road and Flanders Road. 

Backfilling behind abutments after night demolition
of superstructure at I-90 WB Bridge over Woodland Road

NEXTD Beam erection at I-90 WB Bridge over Parkerville Road

History of the Project
Even though most of the project construction took place in summer 2021, extensive coordination was needed from the beginning back in 2019. The project was initially conceived by MassDOT to be constructed in two construction seasons using the Design Bid Build project delivery (D/B/B) and it was only supposed to replace the bridges over Woodland, Cordaville and Parkerville Roads. However, a planned project at the I-90/I-495 interchange was going to conflict with the bridge superstructure replacements.  Therefore, MassDOT decided to use a single-contractor D/B management approach to accelerate the project so that it would be completed prior to the interchange project.   Additionally, the Flanders Road bridge was added to the project so that all the bridges between the interchange and Woodland Road would be complete before the interchange project began construction.  To accomplish this, MassDOT engaged CDR Maguire in summer 2019 as the owner’s Preliminary Design Consultant to do the preliminary design of the project and put together the Preliminary Structures Reports and the Base Technical Concept package that would be used later for the D/B teams to bid the project. CDR Maguire proposed using ABC techniques which were used in 2012 on MassDOT’s Fast-14 project and most recently in the Commonwealth Avenue bridge replacement project in 2018 to minimize impacts to the travelling public.  Working together with CDR Maguire, MassDOT also engaged CHA as a peer-reviewer late in summer 2019 due to their experience developing similar conceptual documents in the previously mentioned projects as well as the firm’s experience helping develop PCI’s Northeast Extreme Tee (NEXT) D Beam details and MassDOT’s Part III Prefabricated Bridge Element details. CHA’s role was to provide constructability advice and peer review for the development of the BTC with a project concept and details that not only could be achieved within the proposed weekend shutdowns, but also conformed to the details and methodologies of the MassDOT Bridge Manual and other industry standards. CHA assisted CDR Maguire with developing feasible BTC alternatives, reviewing anticipated construction milestones and shutdown periods, and contingency planning.

CDR Maguire acted as a project liaison assisting MassDOT throughout the whole project, from its project initial conception, preliminary design, and providing technical support through the procurement and selection process, final design, fabrication, construction, and final project close-out of the project in early 2022. The project was awarded in summer 2020 to the joint venture (JV) between JF White Contracting Co. in association with Gill Engineering and Tetra Tech. 

Discussion of ABC Details at Preliminary Design
Because of the high traffic volumes on I-90, MassDOT limited the Design-Builder to just 55 hours over a weekend to construct each bridge.  Therefore, Accelerated Bridge Construction (ABC) was critical to construct the bridges.  With all bridges needing to be replaced during weekend shutdowns, prefabricated bridge elements would be required. Given the short spans of the proposed bridges, the need to expedite construction, and the importance of minimizing the weight of superstructure on the existing substructures, both precast NEXT D Beams and Prefabricated Bridge Units (PBUs) were viable alternatives. CDR Maguire assumed Prefabricated Bridge Units (PBUs) for the new superstructures. Even though the final superstructure was conceived by the D/B team to use NEXT D beams, the preliminary cost estimate using PBUs yielded a final cost estimate that was very close (within 2%) to the project amount that was anticipated by MassDOT.

To leave all ABC options open and to avoid directing the D/B bidders to one option or another, MassDOT directed CDR Maguire to present an “open concept” at the Base Technical Concept stage. After concrete testing and initial structural analysis by CDR Maguire, it was determined that the existing substructures could withstand the current HL-93 loads and that rehabilitation of the abutments was feasible. 

CDR Maguire worked with CHA to present Conceptual Details at the Abutment using precast caps with rapid set concrete which provided a deck over backwall to reduce the water infiltration at the bridge seat.  In addition, for the I-90 bridge over Cordaville Road, due to its past success in previous projects in the Northeast, CHA presented the option of replacing the 3-span bridge with a single span using micropiles and constructing new abutments between the existing abutments and piers prior to the demolition of the superstructure to avoid impacting traffic on I-90 above. 

Suggested abutment details from base technical concepts plan
(CDR Maguire)

Working with MassDOT and the D/B Team
Throughout the Design-Build Process, CDR Maguire worked directly with the Design-Build team on MassDOT’s behalf to review the final design plans and calculations, construction phasing and schemes, and shop drawings to ensure that the end product would meet the requirements of the project.  Further, CDR Maguire worked with MassDOT to review RFI’s and NCR’s and provided technical support to resolve design and construction issues as they arose.  And finally, CDR Maguire provided on-site staff during construction to address any problems so that a solution could be found without impacting the ability to open I-90 to traffic within the 55-hour time frame.  Thankfully, and with credit to the entire design-build team, construction went smoothly, and all 8 bridges were constructed and opened to traffic with plenty of time to spare.

Summary
MassDOT demonstrated again with the Acceler-8 project that engaging consultants in early project stages, together with the application of the D/B management approach and ABC methodologies is a tried-and-true strategy that works and that can result in many benefits to the road users and adjacent communities. MassDOT, together with CDR Maguire and CHA, achieved this goal maximizing collaboration with the D/B team during design and minimized risks during fabrication and construction.