City of Cambridge planning staff is recommending full replacement of a crumbling, century-old retaining wall that has forced closure of the sidewalk on Blair Road leading down from Dickson Hill.
The decision comes after members of the municipal heritage advisory committee sought additional background information during an October meeting, along with a full review of options, including "lifecycle costs."
The wall has been the subject of damaging water run off for decades and "former residents of the area have even suggested it has been struck at least twice since the 1960s by cars as a result of treacherous winter ice conditions."
The city hired a heritage mason specialist and engineer from WSP who conducted a site visit of the 45 Blair Road retaining wall on November 8.
The engineer found the cement-based mortar used to repair the wall, which has a 1908 date mark carved into the mortar, prevented proper drainage leading to an accelerated wall decay.
Extensive organic growth has penetrated through the full thickness of the wall, which is regularly exposed to freeze-thaw cycles and higher moisture levels.
The project team met with two mason contractors who did not recommend proceeding with a wall repair option.
The repair option, while possible, wasn't considered viable since the entire wall requires repair work and any sections not addressed now will require work in the near future.
"Taking the repair route will end up having the highest total project cost as the deep repointing required is highly technical work requiring specialized tools and methods," they concluded.
They instead recommend replacement of the wall with a new cast-in-place retaining wall on caissons complete with new stone facing.
The estimated initial construction cost is $1,563,000.
The option would require major maintenance work in approximately 40 years for a total lifecycle cost of $1,624,000.
"This option is the most balanced of the options as it provides a structurally sound retaining wall while maintaining the heritage look of the original wall with a similar new stone facing," reads the staff report.
Since the wall is within the Dickson Hill Heritage Conservation District and is considered a heritage attribute, demolition or work on the wall must be done in accordance with the HCD plan, including approval from council.
Following MHAC approval, expected later this week, council will have the final say on the project.
