September/October 2021 - 95

* Phase 2: DPP deep foundations from
4 to 10 ft (1.2 to 3 m) away from the
brick façade walls in the city sidewalk
to support the falsework,
structural steel and exoskeleton that
would provide lateral support for the
walls during hotel construction
* Phase 3: ACP deep foundation support
for the new hotel with less than
0.5 in (12.7 mm) total settlement
tolerance
* Phase 4: Cantilever soldier beam and
wood lagging shoring for the elevator
and fire water tank excavation inside
the new hotel
Geotechnical Investigation
and Challenges
The site's subsurface soil profile
consisted of undocumented fill with
poorly graded gravel with sand and silt
with occasional brick, wood and metal
debris to depths of about 10 to 12 ft (3 to
3.6 m). Soil beneath the fill at depths
from 10 to 50 ft (3 to 15.2 m) was
identified as " recent " alluvium with
interbedded, soft to medium-stiff silt
(ML) and lean clay (CL). Soil at depths
from 50 to 55 ft (15.2 to 16.7 m) consists
of " recent " alluvium with loose to
medium dense, poorly graded sand and
silty sand with fines content ranging
from approximately 10 to 40%. Soil at
depths below 55 ft (16.7 m) consists of
" older " alluvium with dense to very
dense, poorly graded gravel (GP) with
sand and poorly graded sand (SP) with
variable amounts of fine gravel. This
layer is the bearing layer for most deep
foundation systems in downtown
Sacramento. During Sacramento River
crest periods in 2017, depth to groundwater
was measured by the geotechnical
engineering firm at approximately 11 ft
(3.3 m) below street level.
The geotechnical engineering firm
did not have access to the interior core
area of the new hotel and was forced to
make geotechnical interpretations
based on adjacent deep foundations
and site work at Golden 1 Center, and
two closely arranged sets of mud-rotary
borings, cone penetration tests (CPT),
and dilatometer tests at the north and
south end of the site. The borings and
CPT showed that the depth to dense
gravel varied from about 45 ft (13.7 m)
on the south side to about 70 ft (21.3 m)
on the north side, with a sloping depth
estimated using the adjacent site
micro-pile drill logs. Subsequently, the
geotechnical report soil cross section
proved to be generally accurate for the
depth of the dense gravel layer.
Geocon's geotechnical investigation
report provided the data and critical
information needed to design the three
different pile systems for this project.
The report figures showing a cross
section of the site were useful when
preparing the deep foundation bid for
the project. The best feature of the
geotechnical report was a coordinated
CPT and dilatometer test (DMT) at each
of the two borings, which provided
reliable soil properties to prepare deep
foundation design calculations.
The boring samples confirmed soil
types with fines content to compare
with the CPT and DMT results. This data
allowed for estimating pile capacity
more accurately, which increased confidence
and allowed for the relocation of
planned piles when new discoveries
occurred during demolition.
Construction With
Design Revisions
The geocontractor's engineering team
prepared submittal sets of drawings
and calculations for HP, DPP, ACP and
cantilever soldier beam shoring based
on the known soil conditions and
interpretations of existing foundation
conditions. Depending on conditions
revealed during the demolition phases,
the geocontractor was ready to design
adjusted pile solutions to maintain
schedule during an active project site.
Each deep foundation system used on
this project had full-scale bearing and
tension load tests to confirm design
capacity calculations.
During demolition of the old hotel
slab and exposure of the existing façade
foundation, davisREED exposed several
different existing foundations and active
utility conditions. Farrell promptly redesigned
theHP foundations so that demolition
could continue, and construction
of the façade walls' temporary exoskeleton
support could begin. Exposed ground
conditions, old foundations and belowground
obstructions required the HP
locations to be field adjusted from 4 to
16 in (102 to 406 mm) horizontally. A
total of 25 HPs were installed with a 2 in
(51 mm) steel shaft and an 8-10-12-14 in
Helical pile installation to directly support façade walls
DEEP FOUNDATIONS * SEPT/OCT 2021 * 95
September/October 2021

Table of Contents for the Digital Edition of September/October 2021
