Downloads - Pile Driving Contractors Association

Project Spotlight
Huntingdon Place
When Toll Brothers, Inc. purchased a parcel of land
in Huntingdon Valley, Pa., it envisioned a luxury
condominium complex with picturesque views
of the adjoining creek and wooded areas. The severe sloping
of the property, however, and the fact that 75 percent
of the parcel was below the 100-year floodplain elevation,
presented design and construction challenges that would
require creativity to realize the vision that the Toll team
had created.
The first task in accomplishing the goal was to arrange
the site so that residential living could occupy the site and
not have any concerns about potential flooding. The solution
was to create a detention basin and lake area that would
have the capacity to contain storm events and still allow
enough area to provide adequate residential living space.
Doing so would require the construction of a retaining wall
around 80 percent of the site and the cut and fill of 100,000
cubic yards of material. The second task was to determine
how best to support the proposed structure, which consisted
of five total levels with the first level dedicated as an atgrade
parking level under an elevated podium slab and the
remainder of residential living space.
The owner’s design team determined that given the
poor soil conditions and the need for a grade separation wall
between the building footprint and the retention basin, a
precast segmental concrete wall would be used to support the
embankment and auger cast piles would be used to support
the structure. When original budget pricing was received
from several contractors, the estimated construction costs
far exceeded the client’s budget and nearly scrapped the
project.
One of the contractors that submitted budget pricing was
PDCA member Loftus Construction, Inc. of Cinnaminson,
N.J. When notified by Toll that the project was grossly over
budget, that construction time far exceeded the anticipated
opening date and the project was in peril of being shelved,
Loftus requested the opportunity to present value engineering
solutions.
Having been granted the time by Toll to evaluate value
engineering solutions, Loftus engaged the services of Pierce
Engineering, Inc., the pre-eminent foundation design firm in
the Delaware Valley and a PDCA member firm. The team
then sought to pinpoint critical components of the project
that were driving the costs and schedule, and how to best
minimize the impact of those components. The single largest
factor driving the cost and schedule was the poor soil conditions.
The design team’s selection of the precast concrete
wall was well suited for the soil conditions, but would require
the export of nearly 40,000 CY of material excavated for the
wall and the import of clean stone.
Loftus, after careful consideration of several options,
proposed a contractor designed steel sheet pile wall that was
tied back with a reinforced concrete deadman system. This
system was chosen for many reasons. It was cost effective
compared to other solutions due to the curving geometry of
the structure, and multiple changes in direction of the proposed
wall layout which is 1,100 feet long and 30 feet high.
Specifically, the wall was constructed of PZ27 sheets with a
coal tar epoxy coating. Double C12x30 members were used
as walers and a 1¼” grade 50, epoxy coated threadbar was
used as tiebacks to the reinforced concrete deadmen. The
deadman was situated such that bearing pile installation
could follow the sheeting without affecting the tiebacks.
The proposed system drastically reduced the overall cost
of the perimeter wall by eliminating the structural excavation
for the segmental wall and eliminating the need for a
costly wellpoint dewatering system as all of the structural
excavation was below the groundwater level. The proposed
system also reduced the cost of the earthwork package by
eliminating the export of 40,000 CY and the import of the
clean stone. An additional benefit of the value engineering
design is the elimination of staged earthwork further reduc-
• Q4 • 2008
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