FEATURE ARTICLE DEEP FOUNDATIONS • JAN/FEB 2019 • 63 AUTHORS Ed O’Malley, P.E., GeoStructures, Inc., and Mike Pockoski, P.E., Geopier Foundation Company Grouted Rigid Inclusions Support Sports Complex This 161,000 sq ft (14,955 sq m), sports complex and youth training center is located at 401 Garasches Lane on what was once an industrialized area in South Wilmington, Del. The facility, called the “76ers Fieldhouse,” is the first of its kind in the tri-state area. It includes a main basketball arena, which will seat 2,500 spectators and will be the home of the Delaware Blue Coats, an NBA G-league team. The complex also features two full- sized artificial turf soccer fields — one indoor and one outdoor — and two additional full-sized basketball courts. In addition to the sports-specific amenities, the complex also includes the Nemours sports medicine clinic, Titus Sports Academy performance training center, retail space and office space. Rossetti Architects designed this arena with long roof spans, providing clearance for the Working with the design team, Desai/Nasr Structural Engineers (DNSE) and GTA Geotechnical Engineers (GTA), GeoStructures (GSI) was able to provide a fast-track design-build foundation solution for a site with very soft organic soils and large aerial loads due to grade raised fill. The ® use of Geopier rigid inclusions provided settlement control for the new sports com- plex. The displacement installation method allowed the in-place environmentally impacted soils to remain undisturbed while allowing for the design and construction of conventional shallow foundations with a slab- on-grade in lieu of piles and a structural slab. Structural and Loading Details Column loads in the one- and two- story retail, concession, locker rooms and office areas were less than 200 kips (890 kN). While floor slab loads are generally between 150 and 200 psf (7.2 and 9.6 kPa), the levelness of the floor slabs, which would support basketball courts and artificial-turf soccer fields, was very important. Therefore, delivering uniform settlement control was a critical element in making sure the slabs would perform well. indoor soccer field and unobstructed viewing in the basketball arena. To achieve the required spans, the construction consists of steel girders with insulated roof panels. Column loads for the long span roof structure were on the order of 200 to 300 kips (890 to 1,335 kN).
Transcript
FEATURE ARTICLE
DEEP FOUNDATIONS • JAN/FEB 2019 • 63
AUTHORS Ed O’Malley, P.E., GeoStructures, Inc., and Mike Pockoski, P.E., Geopier Foundation Company
Grouted Rigid Inclusions Support Sports Complex
This 161,000 sq ft (14,955 sq m), sports
complex and youth training center is
located at 401 Garasches Lane on what was
once an industrialized area in South
Wilmington, Del. The facility, called the
“76ers Fieldhouse,” is the first of its kind in
the tri-state area. It includes a main
basketball arena, which will seat 2,500
spectators and will be the home of the
Delaware Blue Coats, an NBA G-league
team. The complex also features two full-
sized artificial turf soccer fields — one
indoor and one outdoor — and two
additional full-sized basketball courts. In
addition to the sports-specific amenities,
the complex also includes the Nemours
sports medicine clinic, Titus Sports
Academy performance training center,
retail space and office space.
Rossetti Architects designed this arena with
long roof spans, providing clearance for the
Working with the design team,
Desai/Nasr Structural Engineers (DNSE)
and GTA Geotechnical Engineers (GTA),
GeoStructures (GSI) was able to provide a
fast-track design-build foundation solution
for a site with very soft organic soils and
large aerial loads due to grade raised fill. The ®use of Geopier rigid inclusions provided
settlement control for the new sports com-
plex. The displacement installation method
allowed the in-place environmentally
impacted soils to remain undisturbed while
allowing for the design and construction of
conventional shallow foundations with a slab-
on-grade in lieu of piles and a structural slab.
Structural and Loading Details
Column loads in the one- and two-
story retail, concession, locker rooms and
office areas were less than 200 kips (890 kN).
While floor slab loads are generally
between 150 and 200 psf (7.2 and 9.6 kPa),
the levelness of the floor slabs, which
would support basketball courts and
artificial-turf soccer fields, was very
important. Therefore, delivering uniform
settlement control was a critical element in
making sure the slabs would perform well.
indoor soccer field and unobstructed
viewing in the basketball arena. To achieve
the required spans, the construction
consists of steel girders with insulated roof
panels. Column loads for the long span
roof structure were on the order of 200 to
300 kips (890 to 1,335 kN).
support mechanism provided by the
ground improvement system, which
facilitated optimizing the pier layout and
thickness of the slab.
During final design, uplift loading was
identified. Moderate uplift loads can be
controlled on rigid inclusion projects by
either increasing the footing dimensions to
counteract the uplift loading or by adding
uplift rods within the rigid inclusions that
are then cast into the footings. Working
with the structural engineer, both tech-
niques were used to simplify the design
and decrease the construction costs.
ConstructionA total of 1,500 rigid inclusion elements
with a nominal diameter of 20 in (508 mm)
were installed to depths of about 35 ft
(10.7 m) to support the grade-raise fill and
new structure and to resist the uplift
loading. The rigid inclusions consist of
cement grout and AASHTO #57 stone,
which is a clean, open-graded blend with a
maximum aggregate size of 1.5 in (38 mm).
A Geopier rigid inclusion is constructed
from the bottom up by inserting into the
ground to the required depth a hollow
mandrel charged with a cement grout
/stone mix. Depending on the soil
conditions, the mandrel is raised upward a
maximum of about 4 ft (1.2 m) to allow the
stone/grout mixture to fill the void space
left by the mandrel. Then, the mandrel is
pushed back downward about 2 ft (0.6 m)
to compact the 4 ft (1.2 m) height of stone
into a 2 ft (0.6 m) height of compacted lift.
The pile driving machine that installs the
64 • DEEP FOUNDATIONS • JAN/FEB 2019 DEEP FOUNDATIONS • JAN/FEB 2019 • 65
During the geotechnical exploration, GTA
identified several unique soil conditions
that would affect the project delivery. The
geotechnical investigation revealed that
soil conditions consisted of 4 to 19 ft (1.2 to
5.8 m) of loose, poorly graded, silty sand,
sandy silt and lean clay fill, which
contained varying amounts of concrete
rubble, bricks, glass, wood and slag.
Underlying the fill was a 5 to 15 ft (1.5 to
4.6 m) layer of very soft-to-soft organic silt
and elastic silt with SPT N-values ranging
from weight of hammer (WHO) to
4 blows/ft (blows/0.3 m). Below this soft
layer was an 8 to 15 ft (2.4 to 4.6 m) thick
Geology and Subsurface Conditions
Artist rendering of the 76ers Fieldhouse
The results of laboratory testing indi-
cated that the organic silts (OH) had liquid
limit moisture contents (w ) ranging from LL
104% to 130%, natural moisture contents
(w ) ) c about 96% and dry unit weights (ᵞ of dry
The presence of the very soft-to-soft
organic layer increased the complexity of
the project dramatically, primarily due to
the project’s grading requirements, which
required 2 to 8 ft (0.6 to 2.4 m) of grade-
raise fill placement across the building pad.
layer of medium dense-to-dense sand
with SPT N-values ranging from 13 to
64 blows/ft. Below the alluvial sands were
relatively stiff clays of the Potomac
Formation. Groundwater was encountered
at depths ranging from 2 to 10 ft (0.6 to
3 m) below the existing ground surface.
Generalized subsurface profile
Considering the complexity of the
project, the rigid inclusion system was
recommended to the building’s owner,
Harris Blitzer Sports & Entertainment in
partnership with The Buccini/Pollin
Because of the complex stratigraphy at the
project site, environmentally impacted fill
soils and groundwater contamination, any
foundation method selected would need to
consider the impact of the installation
methodology on the generation of
contaminated spoils as well as protection of
the groundwater.
Innovative Solution to Geotechnical Challenges
The fast-track construction schedule
did not allow for the time required for
traditional surcharge preloading methods
to be utilized. In addition, the variable
uncontrolled fill and soft, compressible soil
would not support the high column loads
required by the long-span construction of
the facility. The designers provided specific
recommendations for different foundation
alternatives: pipe piles, precast concrete
piles, timber piles, auger cast-in-place
piles, rammed aggregate piers and
controlled modulus columns.
about 47 lb/cu ft (7.4 kN/cu m). Based on
the presence of this highly-compressible
layer, it was determined that about 18 to
24 in (46 to 61 cm) of settlement would
occur due to the compression of the soft
soils when subjected to the applied loading
imposed by the grade-raise fill. GTA
estimated that the total settlement would
occur between 4 and 10 years without the
use of vertical drains.
The thick, highly-compressible organic
layer posed significant settlement risks to
the structure. Grade-raise fill would yield
an unacceptable magnitude of site
compression (settlement) and delay
periods, while the structural loads would
result in unacceptable compression of the
organic layer. Additionally, the proximity of
the substantial roof loads directly adjacent
to the relatively light facility and locker
room loads created differential settlement
hurdles that required careful consideration.
Traditional rammed aggregate pier
(RAP) solutions were considered and
quickly excluded as the high loads and
thick, soft organic soils required a stiffer
pier element to span the soft organic soil
strata. The pile solutions would support
the loads but would require the inclusion
of structurally reinforced grade beams and
slabs to mitigate the long-term impacts of
the organic layer. This rigid inclusion
Group, and its contractor, BPGS Con-
struction (BPGS). The rigid inclusions are
installed using a displacement process that
does not generate spoils and could provide
a structural capacity to handle the project’s
geotechnical challenges, including:
penetration of difficult fill, immediate and
future compression of the soft organic soils,
contamination in the groundwater and
cross-contamination of the subsurface
strata, and caving potential of the soft soils
during construction.
The composition of the existing fill was
undocumented and variable but could be
improved through ground improvement to
provide adequate support for the high
bearing pressure spread footings. However,
the very soft organic layer required a high
stiffness element to mitigate the potential
for long-term creep due to organic decay.
system provides the same long-term
settlement performance as the RAP system
but allows the use of conventional shallow
foundations and slabs-on-grade. The thick
structural slab and heavily reinforced grade
beams and pile caps required by the other
piling options added cost in addition to
design and construction complexity.
Rigid Inclusion Design Strategy
GSI worked with DNSE, the project
structural engineer, to provide a system
that would support the column and wall
footings as well as the slab-on-grade. The
slab design was especially challenging, as
the grade-raise fill induces substantial
compression and creep within the organic
layer that could eventually lead to minimal
support of the floor slab between rigid
inclusion elements. A soil-structure
interaction (SSI) analysis was required of
the support provided by the rigid
inclusions and the load transfer layer above
the rigid inclusions as well as the slab being
supported. A finite element analysis was
performed to evaluate the nonuniform
Installation of the grouted impact piers
Typical grouted impact pier element for footings supported on engineered fill
support mechanism provided by the
ground improvement system, which
facilitated optimizing the pier layout and
thickness of the slab.
During final design, uplift loading was
identified. Moderate uplift loads can be
controlled on rigid inclusion projects by
either increasing the footing dimensions to
counteract the uplift loading or by adding
uplift rods within the rigid inclusions that
are then cast into the footings. Working
with the structural engineer, both tech-
niques were used to simplify the design
and decrease the construction costs.
ConstructionA total of 1,500 rigid inclusion elements
with a nominal diameter of 20 in (508 mm)
were installed to depths of about 35 ft
(10.7 m) to support the grade-raise fill and
new structure and to resist the uplift
loading. The rigid inclusions consist of
cement grout and AASHTO #57 stone,
which is a clean, open-graded blend with a
maximum aggregate size of 1.5 in (38 mm).
A Geopier rigid inclusion is constructed
from the bottom up by inserting into the
ground to the required depth a hollow
mandrel charged with a cement grout
/stone mix. Depending on the soil
conditions, the mandrel is raised upward a
maximum of about 4 ft (1.2 m) to allow the
stone/grout mixture to fill the void space
left by the mandrel. Then, the mandrel is
pushed back downward about 2 ft (0.6 m)
to compact the 4 ft (1.2 m) height of stone
into a 2 ft (0.6 m) height of compacted lift.
The pile driving machine that installs the
64 • DEEP FOUNDATIONS • JAN/FEB 2019 DEEP FOUNDATIONS • JAN/FEB 2019 • 65
During the geotechnical exploration, GTA
identified several unique soil conditions
that would affect the project delivery. The
geotechnical investigation revealed that
soil conditions consisted of 4 to 19 ft (1.2 to
5.8 m) of loose, poorly graded, silty sand,
sandy silt and lean clay fill, which
contained varying amounts of concrete
rubble, bricks, glass, wood and slag.
Underlying the fill was a 5 to 15 ft (1.5 to
4.6 m) layer of very soft-to-soft organic silt
and elastic silt with SPT N-values ranging
from weight of hammer (WHO) to
4 blows/ft (blows/0.3 m). Below this soft
layer was an 8 to 15 ft (2.4 to 4.6 m) thick
Geology and Subsurface Conditions
Artist rendering of the 76ers Fieldhouse
The results of laboratory testing indi-
cated that the organic silts (OH) had liquid
limit moisture contents (w ) ranging from LL
104% to 130%, natural moisture contents
(w ) ) c about 96% and dry unit weights (ᵞ of dry
The presence of the very soft-to-soft
organic layer increased the complexity of
the project dramatically, primarily due to
the project’s grading requirements, which
required 2 to 8 ft (0.6 to 2.4 m) of grade-
raise fill placement across the building pad.
layer of medium dense-to-dense sand
with SPT N-values ranging from 13 to
64 blows/ft. Below the alluvial sands were
relatively stiff clays of the Potomac
Formation. Groundwater was encountered
at depths ranging from 2 to 10 ft (0.6 to
3 m) below the existing ground surface.
Generalized subsurface profile
Considering the complexity of the
project, the rigid inclusion system was
recommended to the building’s owner,
Harris Blitzer Sports & Entertainment in
partnership with The Buccini/Pollin
Because of the complex stratigraphy at the
project site, environmentally impacted fill
soils and groundwater contamination, any
foundation method selected would need to
consider the impact of the installation
methodology on the generation of
contaminated spoils as well as protection of
the groundwater.
Innovative Solution to Geotechnical Challenges
The fast-track construction schedule
did not allow for the time required for
traditional surcharge preloading methods
to be utilized. In addition, the variable
uncontrolled fill and soft, compressible soil
would not support the high column loads
required by the long-span construction of
the facility. The designers provided specific
recommendations for different foundation
alternatives: pipe piles, precast concrete
piles, timber piles, auger cast-in-place
piles, rammed aggregate piers and
controlled modulus columns.
about 47 lb/cu ft (7.4 kN/cu m). Based on
the presence of this highly-compressible
layer, it was determined that about 18 to
24 in (46 to 61 cm) of settlement would
occur due to the compression of the soft
soils when subjected to the applied loading
imposed by the grade-raise fill. GTA
estimated that the total settlement would
occur between 4 and 10 years without the
use of vertical drains.
The thick, highly-compressible organic
layer posed significant settlement risks to
the structure. Grade-raise fill would yield
an unacceptable magnitude of site
compression (settlement) and delay
periods, while the structural loads would
result in unacceptable compression of the
organic layer. Additionally, the proximity of
the substantial roof loads directly adjacent
to the relatively light facility and locker
room loads created differential settlement
hurdles that required careful consideration.
Traditional rammed aggregate pier
(RAP) solutions were considered and
quickly excluded as the high loads and
thick, soft organic soils required a stiffer
pier element to span the soft organic soil
strata. The pile solutions would support
the loads but would require the inclusion
of structurally reinforced grade beams and
slabs to mitigate the long-term impacts of
the organic layer. This rigid inclusion
Group, and its contractor, BPGS Con-
struction (BPGS). The rigid inclusions are
installed using a displacement process that
does not generate spoils and could provide
a structural capacity to handle the project’s
geotechnical challenges, including:
penetration of difficult fill, immediate and
future compression of the soft organic soils,
contamination in the groundwater and
cross-contamination of the subsurface
strata, and caving potential of the soft soils
during construction.
The composition of the existing fill was
undocumented and variable but could be
improved through ground improvement to
provide adequate support for the high
bearing pressure spread footings. However,
the very soft organic layer required a high
stiffness element to mitigate the potential
for long-term creep due to organic decay.
system provides the same long-term
settlement performance as the RAP system
but allows the use of conventional shallow
foundations and slabs-on-grade. The thick
structural slab and heavily reinforced grade
beams and pile caps required by the other
piling options added cost in addition to
design and construction complexity.
Rigid Inclusion Design Strategy
GSI worked with DNSE, the project
structural engineer, to provide a system
that would support the column and wall
footings as well as the slab-on-grade. The
slab design was especially challenging, as
the grade-raise fill induces substantial
compression and creep within the organic
layer that could eventually lead to minimal
support of the floor slab between rigid
inclusion elements. A soil-structure
interaction (SSI) analysis was required of
the support provided by the rigid
inclusions and the load transfer layer above
the rigid inclusions as well as the slab being
supported. A finite element analysis was
performed to evaluate the nonuniform
Installation of the grouted impact piers
Typical grouted impact pier element for footings supported on engineered fill
66 • DEEP FOUNDATIONS • JAN/FEB 2019
piers has approximately 30,000 lb
(134 kN) of crowd force to compact the
stone downward and out radially.
By applying lateral pressure to the soil
deposit, the pier develops additional skin
friction and bond with the surrounding soil
matrix, which helps to increase its capacity
when compared to a conventional rigid
inclusion system. The ultimate result is a
rigid element that can support the load
imposed by the grade-raise fill as well as the
new building’s applied loading and can
provide long-term settlement control. The
rigid inclusions were designed using a
composite aggregate/grout unconfined
compressive strength of 2,000 psi
(13.8 MPa) to provide a working axial
capacity of 120 kips (535 kN), which was
verified in the field by the load testing of a
nonproduction element.
ConclusionThe use of the composite aggregate/grout
rigid inclusions saved time on the construc-
tion schedule and resulted in a cost savings
compared to an alternative system con-
sisting of a deep foundation and structural
slab. Ultimately, a cost savings of $600,000
was realized on the project. This rigid inclusion
system provided multiple benefits to the project:
• The risk of bulging in the soft organic
soils was mitigated and the system
provided long-term settlement control.
• A low permeability material (grouted
stone) was used to mitigate the risk of
groundwater cross-contamination.
• The displacement and tremie method
reduced the risk of caving in the soft
soils during construction, allowed for
the construction of elements beneath
the groundwater table and eliminated
spoils on this contaminated site.
• Uplift elements provided uplift control
and saved money versus constructing
oversized spread footings.
• A conventional slab-on-grade was
constructed eliminating the need for a
thick structural slab.
Ed O’Malley, P.E., is vice president of engineering for
GeoStructures. He specializes in assisting customers
solve various engineering challenges by utilizing
many different shallow and deep foundation systems.
Mike Pockoski, P.E., is the area manager of the
eastern division for Geopier Foundation Company.
He works with a strong network of specialty ®geotechnical contractors to deliver the Geopier
