DFI Magazine September/October 2020 - 20

Installing a deeper, steeply angled tieback

Construction Coordination
The management and coordination during several stages of
construction was logistically complex because of several
operations taking place simultaneously at the site each day,
including tieback installation and testing, excavation, deepfoundation installation, and basement and core construction. Up
to four ACIP and drilled-shaft rigs with support cranes and other
equipment were installing deep foundations, while three tieback
rigs worked their way around the perimeter. As many as seven field
inspectors were on site observing the geotechnical aspects of the
foundation and shoring installation and testing.

Conclusions
Chase Center design and construction was successful despite time
constraints and complicated site conditions because of the
collaboration and commitment of the entire project team. Even
through challenges, the project team's innovation through
partnership allowed the on-schedule completion of the state-ofthe-art facility. Site challenges included:
* Developing foundations to provide adequate compression
and tension support, especially where bedrock is shallow and
the arena core loads would be high. A combination of
large-diameter drilled shafts and ACIP piles was used for
foundation support.
* Overcoming poor soils with a support-of-excavation system
involving a laterally restrained CDSM cutoff wall along the
entire perimeter. The perimeter shoring system included
tiebacks in the fill, Bay Mud, and deeper dense sand of the
Colma Formation and bedrock.
20 * DEEP FOUNDATIONS * SEPT/OCT 2020

* Overcoming groundwater intrusion issues. The CDSM cutoff
wall also cut off groundwater into the excavation. The CDSM
panels extended into the low permeability Bay Mud to cut off
groundwater.
* Overcoming the low bearing capacity of Bay Mud at the bottom
of excavation. A stabilized working platform was constructed to
support deep foundation equipment and to resist hydrostatic
seepage during construction.

Acknowledgements
Langan Engineering and Environmental Services was the
geotechnical engineer. Malcolm Drilling served as the foundation
contractor, and Condon-Johnson & Associates, as the shoring
designer and contractor. Mortenson-Clark Joint Venture was the
general contractor.

Lori A. Simpson, P.E., G.E., is a senior principal at Langan Engineering and
Environmental Services. She has over 30 years of experience in her field.
Simpson is a trustee of DFI, and has published papers on deep foundations,
ground response monitoring and ground improvement.
Serena T. Jang, P.E., G.E., is a senior associate at Langan Engineering and
Environmental Services. She has over 22 years of experience in design and
construction in geotechnical engineering in the San Francisco Bay Area.
Matthew C. Pepin, P.E., is a project engineer at Langan Engineering and
Environmental Services, with 9 years of experience in geotechnical engineering
on projects throughout the United States.

DFI Magazine September/October 2020

Table of Contents for the Digital Edition of DFI Magazine September/October 2020