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Underground vaults to be evaluated before Nashua sidewalk repair

Union Leader Correspondent

February 04. 2013 10:41PM

NASHUA - Underground rooms, vaults and old coal chutes have been located beneath Main Street during recent sidewalk renovations, prompting the need for a structural evaluation so sidewalk work can resume this spring.

On Wednesday, the aldermanic Finance Committee will review a proposed contract to hire a Portsmouth firm charged with evaluating and recommending remediation efforts for the underground structures.

"We knew some of these smaller structures were in existence, but the staff wasn't aware of some of the larger structures," City Engineer Steve Dookran said on Monday, explaining a handful of the underground rooms extend about 10 to 12 feet from some of the buildings.

Dookran said some of the vaults were likely built in the early 1900s or late 1800s, adding there are not many records or documentation on the underground chutes. It is important to evaluate the structural integrity of the underground rooms and determine whether they can hold the weight of a new sidewalk, said Dookran, adding engineers must also determine what kinds of repairs may be needed to strengthen the underground vaults.

"Structural elements include several rooms located under the sidewalk, existing vaults, access points and possibly old coal chutes that have been sealed in the basement but not addressed under the sidewalk," says a request for proposals by the City of Nashua.

Several locations have been identified along Main Street where bulkheads, coal chutes, manholes or access hatches are still located in the sidewalk. While these areas have been sealed off in basements, it is unknown what might remain below the sidewalk, according to the request for proposals. Specifically, there are five downtown buildings where a portion of the structure extends under the sidewalk, including an office building at 143 Main St., the new Twill knitting and fabric store at 100 Main St., Martha's Exchange at 185 Main St., Fay's Cabinetry at 172 Main St. and Nashua Garden deli at 121 Main St.

There are several other locations along Main Street where access hatches, air intakes or exhaust ports are visible from the sidewalk area to various basements that must also be evaluated before sidewalk work can take place, according to the document on file at Nashua City Hall.

"We can still proceed with the sidewalk (renovation) work, but we will try to work around these - at least in the beginning," said Dookran, explaining it should not delay the start of spring sidewalk improvements.

Construction crews first became aware of an underground structure while installing a new foundation for a mast arm traffic signal at 143 Main St. last summer. An underground room was located, which extended under the sidewalk about 12 feet from the face of the building.

"As a result, site visits have been made to each building in the project area to examine the existing basements, locate areas of concern and document existing conditions to the extent feasible," says the request for proposals, adding an evaluation is necessary as soon as possible so that sidewalk reconstruction can continue once the weather warms.

Hoyle, Tanner and Associates Inc. of Portsmouth is being recommended for the estimated $45,000 underground structural evaluation.

"The vault evaluation project is unique and will require a specialized set of skills," says a letter from Christopher Mulleavey of the engineering firm.

His company has recent experience with evaluation and repairs to basements of historic buildings, and previously designed structural repairs in a crawl space of the Amoskeag Mill building in Manchester.

Ten blocks along Main Street in Nashua will undergo major sidewalk improvements within the next three years, a project that could cost upwards of $2 million.

In addition to improving all of the sidewalks, city workers will correct drainage problems and install new street lights, mast arm mounted traffic signals, benches, trash containers and newspaper boxes. Every tree along Main Street will be removed and then new trees will be planted with root barriers so that they do not destroy the new sidewalks.

Work began last summer in the downtown area, as members of the city's Public Works Department began installing new sidewalks along both sides of the Main Street Bridge.

It is the city's intention to repair sidewalks from the Main Street Bridge up to Water Street on the west side and up to Park Street on the east side, in addition to the path from West Pearl Street to City Hall.

Wednesday's meeting begins at 7 p.m. at Nashua City Hall.

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