LAND: $500,000 TO $2 MILLION
could be achieved using driven 16-inch by 0.312-inch steel pipe
piles that extended to either the lower sand and gravel layer or to
the upper sand layer, if present. The owner accepted the proposed
driven steel pipe pile alternate because of the cost and time savings
to the project. The driving criteria that were developed based on the
dynamic pile test program allowed many of the piles to end within
the upper sand layer, which provided additional cost savings to the
project. The relative ease of the pile testing and documentation of
the pile installation allowed for this cost savings to be realized even
with such challenging site conditions. Considering the variability in
the site conditions, these savings may not have been as easily realized
using ACIP piles.
Another challenge to this project was the construction of the
50-foot diameter sub-pit structure, which is located about 44 feet
below the pit level and about 72 feet below the ground surface. The
foundation walls needed to retain soft, saturated clay and to be
waterproof. The secant wall consisting of 36-inch diameter piles
was initially specified; however, one challenge with this approach
was that the waterproofing installers were unable to provide a certified
product to the owner. The proposed driven temporary sheet
piling was a benefit to the project because of the installation cost,
but more importantly, it benefitted the owner as it allowed the
permanent foundation wall to be constructed using conventional
forming. Having a formed foundation wall allowed the back of the
wall to be waterproofed using conventional methods and products
that were certified by the installer.
Left: A view of the sub-pit
Above: Sub-pit excavation
An innovative construction technique that was used in the
design and construction of the driven sheet pile shoring was
the use of circular compression rings for the wales. The upper
walers consisted of rolled steel wide f lange beams and the lower
walers consist of reinforced concrete beams. The compression
rings were very efficient in resisting the lateral earth and
water pressures and maintaining an open work area within the
shoring. The piezometers installed by Gerhart Cole were used
to monitor the hydrostatic pressures behind the shoring and
to assess the performance of the dewatering system installed
by the general contractor. The monitoring was used to assess
the shoring design during the shoring construction and the
needed adjustments in the waler locations were quickly and
easily made.
In summary, RLW met the challenge of this difficult job and
used cost savings and value engineering methods in the design
and construction of the sheet pile earth shoring system and the
driven foundation pile system. Both the client and owner recognized
the cost effectiveness of replacing the ACIP piles with the
driven foundation piles and appreciated RLW’s quality of work
and their ability to meet a demanding project schedule in a safe
and productive manner. t
Ralph L. Wadsworth Construction Company, LLC won a 2017
PDCA Project of the Year Award in the Land: $500,000 to $2
Million category.
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