SOMA HOTEL Foundation Constructors, Inc. had to solve challenge
after challenge to deliver this project
By Darren Riddle, Foundation Constructors, Inc.
The SOMA Hotel project included the addition of a ninestory
luxury hotel on a lot approximately 100 by 180 feet
in the Mission Bay District in San Francisco, Calif. The
multi-phase project enlisted Foundation Constructors, Inc. (FCI)
to install a total of 403 fourteen-inch H-piles, supplied by Nucor
Skyline, as the deep foundation solution for the project. In this
area of San Francisco, driven piles are typically the primary choice
for deep foundations due to the overall length of pile necessary to
reach competent bedrock material. Piling must be driven through
fill material placed after the 1906 earthquake and bay mud until
finally reaching competent bedrock elevation. As a result of these
existing geotechnical conditions, piles were required to be 215 feet
to 230 feet in length. In order to reach these depths, each pile needed
to be installed in three separate pieces spliced together – that
amounted to a total of 1,209 pieces of H-pile and 806 pile splices.
During the early stages of the project and prior to installing
production piles, FCI installed 20 indicator piles. Each indicator
pile was PDA tested to check the driving behavior, confirm estimated
tip elevations and finalize the full pile lengths necessary
across the site.
FCI requested a more in-depth look at the pile capacities
achieved during the indicator pile test program. Langan and
Associates and ARUP reduced the blow count requirement from
120 blows per foot to 75 blows per foot, which had a direct impact
in helping save days on the project schedule. The reduction of the
overall blows per pile also assisted in protecting FCI equipment
from unnecessary damage.
After completion of the production piles, FCI was enlisted to
design and construct a complex sheet pile shoring system. This
shoring system was successful in providing a safe and efficient
solution to the access issues the project faced during excavation
of the pile caps. FCI was able to help the entire project continue
moving forward and remain on schedule by providing this safe
access to all trades involved. Overall, the project was completed
with more than 16,000-man hours of work and no recordable safety
incidents or first aids.
Due to a demanding schedule of each phase, FCI elected to
utilize a Manitowoc 4000 with 32-inch fixed leads and a D70 hammer
for driving the H-piles. FCI used a 25-meter ABI machine to
install the sheet pile shoring system, however due to the changing
site logistics after the concrete footings were constructed, FCI was
forced to use the same Manitowoc 4000 to extract the sheet piles.
Additional equipment supporting the driving crane during pile
splices, cut-offs and cap connections were a 70-ton hydraulic crane
Rendering: Hornberger + Worstell
Photo: Fair, Jamal
64 | ISSUE 5 2020 www.piledrivers.org
/www.piledrivers.org
