DFI Magazine November/December 2020 - 82

Otherwise, the fine sandier material would
have become suspended and acted similar
to an aggregate, resulting in an increase in
cutoff wall strength, while the clay material
would have also become suspended. That,
in turn, would have resulted in a longer
cure period to achieve the specified
unconfined compressive strength and
maximum hydraulic conductivity that
were needed. The contractor worked with
onsite professional geologists who logged
the trench during excavation to determine
the soil conditions of each area and
appropriately adjust the mix.
Forgen used its batch plant, which has
technology for real-time data monitoring
and batch downloads, as well as calibrated
scales to ensure mix consistency between
each batch. The rural project location meant
limited staging locations for the large batch
plant and real estate for import trucks. This
also lengthened the pumping distance from
the batch plant to the trench. The
contractor worked with pump professionals
to determine where to set up in-line booster
pumps that allowed pumping of SCCB
slurry for up to 4,000 ft (1,220 m).

Construction
Levee improvements included over
200,000 cu yd (152,910 cu m) of levee
excavation and placement, 211,245 sq ft
(19,625 sq m) of SB cutoff wall, and
191,968 sq ft (17,834 sq m) of SCCB cutoff
wall that was constructed with a very
limited work pad over and around the
following obstacles:
* Multiple high-pressure gas lines
ranging in size from 2 in to 20 in (5 cm
to 51 cm) that ranged in depth from
approximately 3 ft to 40 ft (0.9 m to
12.2 m) below grade. The cutoff wall
either went above the PG&E lines or
was excavated and protected in place.
* Under the Rio Linda Boulevard Bridge,
which had a clearance of 15 ft to 17 ft
(4.6 m to 5.2 m).
* Over a 66 in (167.6 cm) Sacramento
Regional County Sanitation District
(SRCSD) sewer line that had to be
monitored in real time for deflection.

82 * DEEP FOUNDATIONS * NOV/DEC 2020

Pretrenching for SCCB cutoff wall below bridge

* Around AT&T fiber optic lines
approximately 3 ft (0.91 m) below
grade.
* Around a 24 in (61 cm) Storm Water
RCP pipe approximately 11 ft (3.4 m)
below grade.
* Through the heavily traveled
Sacramento Bike Trail.
* Around an active 30 in (76.2 cm) city
potable water line that was
approximately 5 ft (1.5 m) below grade
and was a critical water source locally.
* Through Norwood Avenue, a heavily
traveled road that services many
homes, businesses and schools and that
could only be limited to a single-lane
closure during construction.

SB cutoff walls were implemented in
areas of the project that did not contain
utility conflicts or road crossings. SCCB
cutoff walls were instead constructed when
cutoff walls were designed to be installed
on the waterside toe and in areas with
utility conflicts and road crossings. All site
conflicts discussed above remained in
service and were protected in place during
all construction activities.

Excavating Around Utilities
Excavating around protect-in-place utilities
was a significant challenge that the
contractor addressed with zero utility
strikes or outages. The approach for each
conflict included the same procedure and
started with calling Underground Service
Alert (USA) to mark out the utilities and
DFI Magazine November/December 2020

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