March/April 2024 - 93

concrete structure and filling the
basins with water were used to remove
most of the anticipated settlement
prior to constructing these gradesensitive
elements. A program of settlement
monitoring was implemented
to verify when sufficient settlement
had occurred.
IPS/EQ Design
The nominal 100 ft (30 m) diameter
IPS/EQ exterior shaft was designed as a
series of 4 ft (1.2 m) diameter secant piles
to provide temporary excavation
support. The shaft was to be excavated
without dewatering to limit the potential
for redirecting existing offsite groundwater
contamination plumes. Calculations
also indicated that IPS/EQ
construction dewatering could cause
offsite settlement of compressible silt
and clay that could damage buried
utilities, pavements, and structures. A
32 ft (10 m) thick non-reinforced tremie
seal was needed to resist the short-term
uplift loads from " average " measured
groundwater elevations. After the tremie
seal gained strength, the interior of the
shaft could be dewatered to allow
construction of an interior wall and base
slab, which were structurally tied to the
exterior lining. The interior wall
provided additional structural rigidity to
protect against collapse from seismically
induced lateral spreading loads induced
by a passive earth pressure wedge from
the liquefiable soil and the overlying
unliquefied soil crust. The interior wall,
base slab, interior structures and abovegrade
screening facilities also provided
uplift protection against the larger
extreme long-term uplift loads, which
were based on extreme high groundwater
over the life of the facility.
Geotechnical Restrictions on
Temporary Excavations
Large diameter pipes and a deep
regulator structure are located within a
few feet of the property lines and
settlement-sensitive existing facilities.
The interior wall, base slab, interior structures and
above-grade screening facilities also provided uplift
protection against the larger extreme long-term uplift
loads, which were based on extreme high groundwater
over the life of the facility.
Excavations within the 12-22 ft
(3.6-6.7 m) depth range adjacent to these
locations had to account for potential
dewatering-induced consolidation
settlement and construction vibrationinduced
settlement. A minimum
groundwater embedment barrier was
installed below grade at these locations
and dewatering wells, or well-points,
were specified inside the barrier to limit
dewatering-related consolidation settlement.
Specified limits on vibrations at
the property line were to protect against
vibration-induced settlement.
To reduce the risk of delay costs
from encountering undocumented
obstruct ions, vactor truck preclearance
was required for treatment
site excavations abutting the property
lines or where sheet piles were
proposed by the cont ractor for
temporary excavation support.
Construction Monitoring
To ver i fy compl iance wi th the
specifications, determine when water
preloads could be removed and verify
design, the following monitoring was
performed at the plant site:
* Settlement of approximately 50
points along the property lines and
at select nearby facilities of interest,
including existing in-street utilities.
This monitoring was to protect offsite
facilities from settlement due to
on-site vibrations (e.g., vibratory
sheet pile driving, concrete chipping,
fill and backfill compaction) and
dewatering-induced consolidation.
This monitoring was also required
by local government-issued permits.
* Deflection of approximately 30
points (at multiple depths for deeper
excavations) along temporary
shoring for the 60 and 96 in
(1,520 and 2,440 mm) effluent and
influent pipelines and the regulator,
primarily to satisfy permitting
requirements.
* Settlement of 30 structural monitoring
points set on the slabs of the
process building, IPS/EQ basin ring
beam and regulator; these were for
the geotechnical designers to
determine when and how much
final grades would need to be
adjusted and to determine when the
water preload in the process
building could be removed.
* Settlement of eight vibrating wire
plates installed beneath the structural
slab of the process building.
* Continued reading of the multilevel
strain gages installed in three
test rigid inclusions that were incorporated
as production elements.
* Groundwater elevations at seven
standpipe piezometers and two trilevel
vibrating wire piezometers.
* Vibration monitoring full-time
during vibration-causing work
combined with periodic settlement
monitoring at three neighboring
buildings.
Adjacent critical structures were also
monitored for settlement during sheet
pile installation for the conveyance and
outfall.
DEEP FOUNDATIONS * MAR/APR 2024 * 93
March/April 2024

Table of Contents for the Digital Edition of March/April 2024
