Draft Project Impact Report - Boston Redevelopment Authority

Exeter Residences/888 Boylston
Geotechnical Impacts Monitoring Program
\\Mabos\projects\09916.00\docs\Permits\DPIR\Text\DPIR Chapter 5
Environmental.docx
The drilled shafts will be cored through the existing concrete floor slab of the garage.
No permanent construction is planned below the garage slab level. However,
isolated excavations below the slab may be required for pile cap construction, grade
beams and structural connections. These shallow excavations will likely require
localized temporary construction dewatering. Temporary shoring or earth support
that may be required at these locations will be within the footprint of the new
structure and not in the public way.
With the exception of the Prudential Center Garage, existing buildings within the
Prudential Center are supported on deep foundations which bear below the level
that may potentially be impacted by the planned construction activity. The
Boylston, Fairfield and Gloucester Apartments, the portion of the Mandarin Oriental
Boston closest to the construction work, and the Hynes Convention Center are all
supported on deep foundations extending to bedrock at depths of greater than 100 ft
below site grades. The Lord & Taylor building is supported on pressure injected
footing foundations extending to the about 20 ft below garage level. The Prudential
Center Garage is founded on wood piles or a concrete mat depending on the
location. The garage adjacent to the proposed construction is wood pile supported.
Existing foundation plans for the adjacent portion of the garage, supported on wood
piles, indicate the tops of piles (cut-off elevations) range from about El. -1 to -4 BCB.
Pile lengths vary but extend to average depths of 15 to 20 ft below the garage level
into the marine sand or clay layers. The tops of the piles are well below area
groundwater levels so are not at risk of exposure, which would result in pile
deterioration and loss of capacity.
The Lenox Hotel is located beyond the Prudential Center Garage, north of the
proposed construction and is also supported on wood pile foundations extending
into the underlying marine sand or clay at depths of about 25 ft below the basement
level of the hotel. The Lenox Hotel has one basement level with a basement floor
slab at about El. 9.5 to 10. The tops of the wood piles supporting the Lenox Hotel are
cut off at about El. 2.3 and are below area groundwater levels based on available
nearby groundwater level data.
Other structures are located at a distance that would not be impacted by the
planned foundation installation. In addition, no significant excavation, no pile
driving or permanent dewatering is planned or needed for the construction.
The objective of the design and construction of the foundation system will be to
avoid adverse impacts to adjacent buildings and other structures in close proximity
to the buildings. This will be accomplished through requirements of the design
criteria developed and selection of appropriate construction methodology. A
DRAFT - Environmental Protection 5-42