July/August 2023 - 79
The Bruce Museum in
Greenwich, Connecticut
FEATURE ARTICLE
An Active Soil Nail Wall Underpinning Solution
The Bruce Museum is an art, science
and natural history museum in Greenwich,
Connecticut. The museum was
originally built as a private residence in
1853, and has undergone several renovations,
the most recent dating to 1992.
The current renovation is part of a $60
million capital expansion plan for the
" New Bruce. " The renovation includes a
43,000 sf (4,000 m2), three-story addition
that will more than double the size of the
museum, adding space for new exhibitions,
education and community
spaces. The proposed bottom of the
foundations for the renovation sit up to
16 ft (5 m) below the Bruce Museum's
existing shallow foundations.
Project/Geotechnical
Challenges
To excavate and install foundations up
to 16 ft (5 m) below the existing foundations,
traditional underpinning was
proposed by the geotechnical engineer
of record. Eastern Excavation - retained
by the owner to perform earthwork
and excavation support - retained
Geoscience Testing and Research (GTR)
to design the temporary underpinning
system. Based on the underpinning
height, the team considered the feasibility
of traditional underpinning
and deemed
it hazardous and too
complex to construct at
the site. Several options
were discussed with the
geotechnical engineer of
record and the project
engineers and architects
for an alternative to
traditional underpinning. GTR proposed
an " active " soil nail wall
underpinning design to accommodate
the construction sequencing, variable
rock surface and to carry the permanent
wall load.
According to the 2015 " Soils and
Foundation Investigation Report " and
results from drill probes, the depth to
AUTHORS Jonathan Ernst, P.E., and Les Chernauskas, P.E., Geosciences Testing and Research
DEEP FOUNDATIONS * JULY/AUG 2023 * 79
competent bedrock was variable across
the site, ranging from approximately
3-16 ft (1-5 m) below existing grade. In
addition to this variability, sloping bedrock
was anticipated beneath the
traditional underpinning, posing issues
Based on the underpinning height,
the team considered the feasibility of
traditional underpinning and deemed
it unnecessarily hazardous and too
complex to construct at the site.
with sliding. Excavation would require
removal of bedrock beneath the upper
underpinning tier and the existing
foundations whereby excessive vibrations
due to excavation activities could
cause movement and instability.
Based on the required cut heights,
the traditional underpinning approach
would create the need for an anchor
July/August 2023
Table of Contents for the Digital Edition of July/August 2023
TOC
July/August 2023 - Intro
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