alternate to replace the ACIP piles with driven 16-inch diameter
steel pipe piles and to replace the secant wall with a temporary circular
sheet pile wall. RLW subcontracted with Gerhart Cole, Inc.
to perform the design and testing of the driven foundation piles and
the design of the 65-foot-diameter by 44-foot-deep sheet pile earth
shoring wall.
The subsurface conditions encountered as part of the geotechnical
studies prepared for this project consisted of soft to medium
stiff lean clay that extended to depths ranging from 39 to 44 feet
below the ground surface, followed by dense to very dense sand
that extended to depths ranging from approximately 59 to 64 feet.
Soft to stiff lean clay was encountered below the sand layer, followed
by dense to very dense sand and gravel that was encountered
beginning at depths ranging from 90 to 95 feet below ground.
Groundwater was reported as being at depths ranging from 7 to 10
feet below grade. As part of the design of the driven piles and sheet
pile shoring, Gerhart Cole subcontracted with Bedke Geotechnical
Field Services to advance several more cone penetration tests
(CPT) in order to further assess the subsurface conditions and
also to install vibrating wire piezometers in locations behind the
proposed sheet piling.
One challenge to this project that was identified initially
through the additional CPT soundings was how the subsurface
conditions varied across the site. The presence of the upper sand
layer was highly variable and the lower sand and gravel layer was
present throughout the site but the elevation of the top of the layer
varied significantly. The deep foundations were initially designed to
consist of 36-inch diameter ACIP piles that extended down to the
lower sand and gravel layer. Initial static pile capacity analyses performed
during the bid process suggested that the required capacity
LAND: $500,000 TO $2 MILLION
Sheet piles
A rendering of the deep foundation system
A rendering of the completed structure
90 | ISSUE 4 2017