By Elton Elperin, Chair of the Muddy River Restoration Project Technical Advisory Committee
Thanks to Senator Will Brownsberger for forwarding to the MMOC bridge inspection reports for:
- Agassiz Road Bridge
- Boylston St. Bridge
- Boylston St. Culvert / Bridge
- Brookline Ave. Bridge
- Fen Bridge
- Longwood Ave. Bridge
- Netherlands Road Bridge
- River Road Culvert / Ramp
I chose to read the Boylston St. Bridge report first, because several of us have noticed its deterioration. It is the only bridge designed by H.H. Richardson, and Olmsted wrote:
“The Boylston St. Bridge will be the most conspicuous object in all the scheme… It will dominate everything and will be seen from Charles River to Parker Hill. People will rest and linger on it and look at it more closely than anything else on the Bay.”
Each report uses the same standardized forms, breaking the inspection into the broad categories of Deck, Superstructure, and Substructure. The condition rating scale runs from 0-Failed Structure, to 9-Excellent.
Deterioration of the Arch
Deterioration of the Arch/Arch Ring is detailed, citing “efflorescence, stalactite, minor spalling, and cracking throughout the red brick arch” and “brick deterioration throughout the face of bricks up to 2″ deep.” A crack that extends up from the granite abutment through the brick arch is described as being 2″ wide just above the granite.
- The report includes a striking photograph (Photo 10) of that crack.
- The condition rating is 5-Fair – “All primary structural elements are sound but may have minor section loss, cracking, spalling or scour.”
- The Category of Deficiency is M-P:
M – “Deficiencies which are minor in nature, do not affect the structural integrity.”
P – “Prioritize…repairs made when funds and/or manpower is available.”
The report does not include a narrative that would answer questions like:
- Is water penetration causing efflorescence, brick deterioration, etc?
- If so, where is it penetrating, and what must be done to prevent it?
- Is the water causing damage behind the visible surfaces?
- What is causing the movement that is cracking the arch?
- How much cracking can the bridge tolerate?
- How can it be prevented?
Deterioration of the Deck
A visit to the bridge reveals continuous and widespread mortar loss, vertically and horizontally, at the parapet (or guardrail) walls that flank the sidewalks. Many of the red granite cap stones that form the top of the parapets have lost mortar that secures them to the wall, and in some locations are entirely missing mortar where they abut other cap stones. One or two cap stones appear to have shifted off-center of the wall below, implying that their mortar bond with the wall is broken. At those places, their joints with adjacent cap stones have also broken, creating gaps approximately twice the width of the original joint.
At one point the face of the parapet is broken (photo #13), with one section a few inches closer to the curb than the adjacent section. However, the river-facing side of the parapet is unbroken, indicating that stones on the sidewalk face have shifted away from the interior of the wall. It appears that the break in the wall has grown larger since the photo was taken in November, 2023.
All the missing mortar joints create pathways for water into the interior of the parapet, the spandrel walls, and the arch itself. When that water freezes in winter, it expands and breaks bonds between stones.
The report lists the condition of the parapet walls as 6 (”Satisfactory. Structural elements show some minor deterioration”). Again, the Category of Deficiency is M-P.
What I have described above is not “minor deterioration.”
The report (item 58.11) states: “There are random voids throughout the granite parapets.”
I’m not sure what “random voids” refers to. Perhaps where mortar is entirely missing between cap stones?
The report does not adequately convey the abysmal condition of the parapet walls, nor does it speak to any relationship between that condition and the deterioration, noted by the report, of the arch and spandrel walls below. The Category of Deficiency of M-P lacks any urgency.
The road is currently being re-surfaced. Does that include any system (e.g. a membrane) to prevent water penetration of the arch below? The report’s statement about the roadway (Item 58.1 – Wearing Surface) is simply: “There is minor wheel rutting in the bituminous wearing surface.”
The deficiencies in this report should inform our writing/editing of an RFP for the survey.
Images: Massachusetts Department of Transportation Structures Inspection Field Report, November 2, 2023. Photo at top [Photo 5]: “South arch ring west half typical brick deterioration and efflorescence.
