September/October 2021 - 110

Project requirements for the five
water tanks included improving the
loose sand to a safety factor of at least
1.1 against liquefaction. The loose sand
primarily comprised a layer located
between an elevation of -0.5 m and -7 m
(-1.6 ft and -2.3 ft). Cone penetrometer
testing (CPT) before and after RI
installation evaluated the densification
requirements and confirmed the soil
densification needed to mitigate liquefaction.
Based on the results of these
evaluations, the RI were designed and
installed to improve the loose sands in
accordance with the design intent.
Prior to commencing design, SBM
performed a series of CPT soundings
and flat-plate dilatometer tests across
the area of the proposed tanks to
supplement existing geotechnical
information. These tests provided the
basis for DDP RI capacity evaluation,
determinat ion of pert inent soi l
compressibility and overconsolidation
properties to develop an accurate soil
profile under the water tanks. SBM
utilized its 30 ton (27,215 kg) CPT
crawler unit to facilitate CPT soundings
through dense soil strata.
Sacrificial endplate attachment to DeWaal tool
two-dimensional plane strain and
three-dimensional models. A 3D finite
element settlement model predicted
maximum settlement of 6.3 in (16 cm),
which was within the allowable total
tank settlement limit. Settlements at
the bottom of the RI were computed to
be approximately 5 in (12.7 cm), with an
additional 1.3 in (3.3 cm) of settlement
occurring in the deeper soils.
SBM retained Shea Brothers Engineering
and GEI Consultants to engineer
the rigid inclusions for the five
water tanks. The RI were designed to
mitigate liquefaction and control
settlements to within allowable ranges.
The full-displacement piles were used
in lieu of dynamic compaction or vibrocompaction
methods to densify the upper
sands and lessen liquefaction risks.
Installed rigid inclusions for a Predio 1 tank
To conf i rm tha t the g round
improvement design would meet
project settlement criteria, SBM's team
prepared several finite element models,
including single cell axisymmetric,
110 * DEEP FOUNDATIONS * SEPT/OCT 2021
SBM employed three drill rigs in a
systematic, design-build approach that
offered production efficiencies and
expedi ted complet ion under an
ambitious schedule. A concrete mix
wa s de s i gned by SBM to be s t
accommodate the patented drilled
displacement pile system, as well as
site-specific corrosive soil conditions.
The two additional rings of rigid
inclusions were installed outside of the
tank footprint areas to extend the zone
of liquefaction mitigation, and provide a
nonliquefiable confinement zone
around the tanks. SBM determined that
the tension and shear stresses induced
in the RI during a seismic event
required the use of #6 grade 60 center
bars to a depth of approximately 12 ft
(3.66 m) to provide adequate structural
capacity.
Automated Monitoring
All aspects of the drilling process and
concrete placement were observed and
recorded by the Shea Brothers Mexico
Automated Monitoring Equipment
(AME) in real time. Upon completion of
each pile, the rig automatically transmitted
installation data to project
managers and quality control professionals.
The recorded pile/RI information
and drilling/ concreting parameters
provided a comprehensive record of the
installation process and detailed Quality
Control documentation.
September/October 2021

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