Draft Project Impact Report - Boston Redevelopment Authority

Exeter Residences/888 Boylston
Foundation Construction Methodology
\\Mabos\projects\09916.00\docs\Permits\DPIR\Text\DPIR Chapter 5
Environmental.docx
subject area on surrounding lots. Specifically, the Project must capture into a
suitably designed system a volume of rainfall equivalent to not less than 1-inch
across the portions of the lot occupied by the Project. A system to capture and
infiltrate rainwater will be installed. Considering site constraints the infiltration
system will be installed along Exeter Street outside of the existing below grade
garage at the Prudential Center as described in Chapter 6, Infrastructure Systems.
The Project will not result in any negative impacts to groundwater levels.
Extensive groundwater monitoring programs have been undertaken during previous
construction activities within the Prudential Center. Analysis of the data collected
indicates that groundwater levels outside the Prudential Center are not impacted by
temporary, localized dewatering within the garage. Furthermore, groundwater
levels recharged rapidly (within 24 hours) once temporary dewatering was
terminated in specific work areas.
The new buildings will be supported on deep foundations extending through the soft
compressible marine clay soils to bedrock at depths of 125 to 150 ft. Drilled, high
capacity foundation elements are planned. Either large diameter (approximately 3 to
6 ft) drilled shafts /caissons or small diameter (less than 12 inches) will be used. The
construction methodology used for foundation installation provides continuous
support of the drilled hole at all times either by use of a steel casing as the drilling is
advanced, or by use of bentonite slurry to prevent caving and loss of ground until
concrete is placed to construct the foundation element. No temporary or permanent
dewatering is needed for the drilled shaft or drilled pile installation. However, some
localized temporary construction dewatering may be required for other construction
activity at the site due to the shallow groundwater levels described above.
The non-displacement, drilled-in deep foundations have been selected to result in
negligible ground movement and vibration during installation. These types of
foundations have been installed successfully at other locations within the Prudential
Center, including for support of 111 Huntington tower and the Mandarin Oriental
Boston, without impact to abutting structures. In addition, a preconstruction survey
of existing surrounding buildings will be prepared. Furthermore, this type of
installation creates less noise than traditional pile driving.
The foundations will consist of discrete concrete elements that do not require
dewatering for installation and do not create a barrier to groundwater flow.
Therefore there is no impact to groundwater levels from the foundation construction
activity. No basement levels below the current garage are planned. Therefore, there
is no potential for impacts or change to the current groundwater conditions from the
planned permanent construction.
DRAFT - Environmental Protection 5-41