Note: Descriptions are shown in the official language in which they were submitted.
OPEN-BOTTOM EXTENSIBLE SHELLS AND RELATED METHODS FOR
CONSTRUCTING A SUPPORT PIER
TECHNICAL FIELD
[0001] The present invention relates to ground or soil improvement
apparatuses and
methods.
[0002] More specifically, the present invention relates to open-end
extensible shells and
related methods for constructing a support pier.
BACKGROUND ART
100031 Buildings, walls, industrial facilities, and transportation-
related structures typically
consist of shallow foundations, such as spread footings, or deep foundations,
such as driven pilings or
drilled shafts. Shallow foundations are much less costly to construct than
deep foundations. Thus,
deep foundations are generally used only if shallow foundations cannot provide
adequate bearing
capacity to support building weight with tolerable settlements.
[0004] Recently, ground improvement techniques such as jet grouting,
soil mixing, stone
columns, and aggregate columns have been used to improve soil sufficiently to
allow for the use of
shallow foundations. Cement-based systems such as grouting or mixing methods
can carry heavy
loads but remain relatively costly. Stone columns and aggregate columns are
generally more cost
effective but can be limited by the load bearing capacity of the columns in
soft clay soil.
[0005] Additionally, it is known in the art to use metal shells for the
driving and forming of
concrete piles. One set of examples includes U.S. Patent Nos. 3,316,722 and
3,327,483 to Gibbons,
which disclose the driving of a tapered, tubular metal shell into the ground
and subsequent filling of
the shell with concrete in order to form a pile. Another example is U.S.
Patent No. 3,027,724 to Smith
which discloses the installation of' shells in the earth for subsequent
filling with concrete for the
forming of a concrete pile. A disadvantage of these prior art shells is that
their sole purpose is for
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providing a temporary form for the insertion of cementitious material for the
forming of a hardened
pile for structural load support. The prior art shells are not extensible and
thus do not exhibit
properties that allow them to engage the surrounding soil through lateral
deformations. Further,
because they relate to the use of ferrous materials, which are subject to
corrosion, their function is
complete once the concrete infill hardens. Thus, the prior art shells are not
suitable for containing less
expensive granular infill materials such as sand or aggregate, because the
prior art shells cannot
laterally contain the inserted materials during the life of the pier. The
prior art shells are also not
permeable and are thus ill-suited to drain cohesive soils.
[0006] Accordingly, it is desirable to provide improved techniques for
constructing a
shallow support pier in soil or the ground using extensible shells formed of
relatively permanent
material of a substantially non-corrosive or non-degradable nature for the
containment of compacted
aggregate therein.
BRIEF DESCRIPTION OF THE INVENTION
[0007] Extensible shells and related methods for constructing a
support pier in ground are
disclosed. An extensible shell may define an interior for holding granular
construction material and
may define an opening for receiving the granular construction material into
the interior. The shell may
be flexible such that the shell expands laterally outward when granular
construction material is
compacted in the interior of the shell.
[0008] According to one aspect, the shell may include a first end that
defines the opening.
The shell may be shaped to taper downward from the first end to an opposing
second end of the shell.
[0009] According to another aspect, the second end of the shell may
define a substantially
flat, blunt surface.
[0010] According to yet another aspect, a cross-section of the shell
may form one of a
substantially hexagonal shape and a substantially octagonal shape along a
length of the shell extending
between the first and second ends.
[0011] According to a further aspect, a cross-section of the first end
of the shell is sized
larger than a cross-section of the second end.
[0012] According to a still further aspect, the shell is comprised of
plastic.
[0013] According to another aspect, the shell may define a plurality
of apertures extending
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between an interior of the shell to an exterior of the shell.
[0014] According to yet another aspect, the shell may be either
substantially cylindrical in
shape or substantially conical in shape.
[0015] According to an additional aspect, a method may include
positioning the shell in the
ground and filling at least a portion of the interior of the shell with the
granular construction material.
The granular construction material may be compacted in the interior of the
shell to form a pier.
[0016] According to another aspect, a method may include forming a
cavity in the ground.
The cavity may be partially backfilled with aggregate construction material.
Next, the shell may be
positioned with the cavity and at least a portion of the interior of the shell
filled with granular
construction material. The granular construction material may then be
compacted in the interior of the
shell to form a pier. The compaction may be performed with a primary mandrel.
Additional
compacting may be performed with a second mandrel that has a larger cross-
sectional area than the
primary mandrel.
[0017] According to a further aspect, the extensible shell may
comprise a plurality of slots
extending between an interior of the shell to an exterior of the shell, the
slots being generally
transverse to a centerline along the length of the shell. The slots may be
discontinuous around a
circumference of the shell thereby maintaining portions of continuous material
connectivity along the
length of the shell. The slots may have a width in the range of 1/4 inch (6.35
mm) to 3/8 inch (9.53
mm) and may be spaced at a distance of 6 inches (152 mm) from one another.
[0018] According to a still further aspect, the disclosure is directed
to an extensible shell
for constructing a support pier in ground, the extensible shell defining an
interior for holding granular
construction material and said extensible shell defining a first end having a
first opening for receiving
granular construction material into the interior and a second end having a
second opening, wherein the
shell is flexible such that the shell expands laterally outward when granular
construction material is
compacted in the interior of the shell.
[0019] In another aspect, the first end defines the first opening with
the shell shaped to
taper from the first end to opposing second end of the shell, with the second
end comprising a second
opening.
[0020] In yet another aspect, a method for constructing a support pier
in ground is
disclosed, the method comprising: positioning an extensible shell into ground,
the shell defining an
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interior for holding granular construction material and defining a first
opening at a first end for
receiving granular construction material into the interior and a second
opening at a second end,
wherein the shell is flexible such that the shell expands laterally outward
when granular construction
material is compacted in the interior of the shell; filling at least a portion
of the interior of the shell
with granular construction material; and compacting the granular construction
material in the interior
of the shell to form a support pier.
[0021] In a further aspect, the disclosure is directed to a method for
constructing a support
pier in ground, with the method comprising: forming a cavity in the ground;
partially backfilling the
cavity with an aggregate construction material; positioning an extensible
shell into the cavity, with the
shell having a first end with a first opening and a second end having a second
opening, with the shell
defining an interior for holding granular construction material and defining
an opening for receiving
the granular construction material into the interior, wherein the shell is
flexible such that the shell
expands when granular construction material is compacted in the interior of
the shell; filling at least a
portion of the interior of the shell with the granular construction material;
and compacting the granular
construction material in the interior of the shell to form a support pier.
[0022] This brief description is provided to introduce a selection of
concepts in a simplified
form that are further described below in the detailed description of the
invention. This brief
description of the invention is not intended to identify key features or
essential features of the claimed
subject matter, nor is it intended to be used to limit the scope of the
claimed subject matter. Further,
the claimed subject matter is not limited to implementations that solve any or
all disadvantages noted
in any part of this disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1A, Figure 1B, Figure 1C, Figure 1D, and Figure lE
illustrate different
views of an extensible shell in accordance with embodiments of the present
invention;
[0024] Figure 2A, Figure 2B, and Figure 2C illustrate steps in an
exemplary method of
constructing a pier in ground using an extensible shell in accordance with an
embodiment of the
present invention;
[0025] Figure 3A, Figure 3B, Figure 3C, and Figure 3D illustrate steps
in another
exemplary method of constructing a support pier in ground using an extensible
shell in accordance
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with embodiments of the present invention;
[0026] Figure 4, Figure 5, Figure 6, and Figure 7 are graphs showing
results of load tests of
support piers constructed using an extensible shell in accordance with
embodiments of the present
invention;
[0027] Figure 8 illustrates a perspective view of another embodiment
of the present
invention pertaining to a slotted shell;
[0028] Figure 9 is a graph showing results of load tests of a support
pier constructed using
an embodiment as shown in Figure 8;
[0029] Figure 10A and Figure 10B illustrate a perspective view and a
cross-sectional view
of an example of an open-end extensible shell in accordance with embodiments
of the present
invention;
[0030] Figure 11A, Figure 11B, and Figure 11C illustrate perspective
views and a cross-
sectional view of another example of an open-end extensible shell in
accordance with embodiments of
the present invention;
[0031] Figure 12A and Figure 12B show an example of a process of
installing the open-end
extensible shell into the ground;
[0032] Figure 13 shows another example of installing the open-end
extensible shell into the
ground;
[0033] Figure 14 shows a flow diagram of an example of a method of
using the open-end
extensible shell to form a support pier;
[0034] Figure 15A and Figure 15B show certain process steps of using
the open-end
extensible shell to form a pier; and
[0035] Figure 16 is a graph showing results of load tests of a support
pier constructed using
an embodiment as shown in Figure 10A, Figure 10B and/or Figure 11A, Figure
11B, Figure 11C.
DETAILED DESCRIPTION OF THE INVENTION
[0036] The present invention is directed to an extensible shell and
related methods for
constructing a support "shell pier" in ground. Particularly, an extensible
shell in accordance with
embodiments of the present invention can have an interior into which granular
construction material
can be loaded and compacted. The shell can be positioned in a cavity formed in
the ground (the cavity
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being formed through a variety of methods as described in more detail below,
including driving the
shell from grade to form the cavity). After positioning in the ground,
granular construction material
can be loaded into the interior through an opening of the shell. The granular
construction material may
be subsequently compacted. The shell can be extensible (or flexible) such that
walls of the shell
expand when the granular construction material is compacted in the interior of
the shell. Therefore,
since the shell maintains the compacted granular construction material in a
contained manner (i.e., the
material cannot expand laterally beyond the shell walls into the in-situ soil)
the ground surrounding the
shell is reinforced and improved for supporting shallow foundations and other
structures. The present
invention can be advantageous, for example, because it allows for much higher
load carrying capacity
due to its ability to limit the granular construction material from bulging
laterally outward during
loading. The shell is typically made of relatively pelinanent, substantially
non-corrosive and/or non-
degradable material such that the lateral bulging of the material is limited
for the life of the pier.
100371 Figures 1A - 1E illustrate different views of an extensible
shell 100 in accordance
with embodiments of the present invention. Figure lA depicts a perspective
view of the extensible
shell 100, which includes an enclosed end 102. The surface of the enclosed end
102 can define a
substantially flat, blunt bottom surface 104, which can be hexagonal in shape.
In the alternative, the
enclosed end 102 may have any other suitable shape or size. Further, the
bottom of the shell may be
open, or may be blunt as in the case of a cylindrical shell, may be pointed as
the bottom of a conical
shell, or may be truncated to form a blunt shape at the bottom of conical or
articulated section such as,
for example, a frustum, or frustoconical configuration. It is therefore
understood, for the purposes of
this disclosure, that the term conical includes frustoconical configurations.
The length of the shell may
range from about 0.5 m to about 20 m long; such as from about 1 m to about 10
m long. The surfaces
of the shell (inside and/or outside) may be smooth or contain a varying degree
of roughness for
interaction with surrounding surfaces.
100381 Opposing the enclosed end 102 is another end, open end 106,
which defines an
opening 108 for receiving granular construction material into an interior (not
shown in Figure 1A)
defined by the shell 100. As will be described in further detail herein below,
the open end 106 is
positioned substantial vertical to and above from the enclosed end 102 during
construction of the pier.
100391 Figures 1B, 1C, 1D, and lE depict a top view, bottom view, a
side view, and a
cross-sectional side view of the extensible shell 100, respectively. As shown
in Figure 1B, the
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extensible shell 100 defines a substantially hollow interior 110 extending
between the open end 106
(with opening 108) and the enclosed end 102.
[0040] Figure 1C shows that a cross-section of the open end 106 may be
sized larger than
the bottom surface 104 of the enclosed end 102. Figure 1D shows section line A-
A arrows indicating
the direction of the cross-sectional side view of the extensible shell 100
depicted in Figure 1E.
[0041] The shape of the exterior of the shell 100 may be articulated
to form a plurality of
panels that form a hexagonal shape in cross-section as viewed from the top or
bottom of the shell.
Alternatively, the shape may be octagonal, cylindrical, conical, or any other
suitable shape.
[0042] The extensible shell 100 is often shaped to taper downward from
the open end 106
to the enclosed end 102. In one embodiment, the shell 100 tapers at a 2 degree
angle, although the
shell may taper at any other suitable angle.
[0043] The extensible shell 100 may be made of plastic, aluminum, or
any metallic or non-
metallic material of suitable extensibility, and preferably substantially non-
corrosive and/or non-
degradable material. The shell 100 may be relatively thin-walled. The
thickness of the wall of the
shell 100 may range, for example, from about 0.5 mm to about 100 mm. The
example shell 100 of
Figure 1B has a thickness of about 0.25 inches (approximately 6.35 mm),
although the shell may have
any other suitable thickness. This thickness distance is the distance that
uniformly separates the
interior 110 and the exterior of the shell. The material of the shell and its
thickness may be configured
such that the shell has suitable integrity to hold construction material in
its interior 110 and to expand
laterally at least some distance when the construction material is compacted
in the interior 110.
[0044] Figures 2A - 2C illustrate steps in an exemplary method of
constructing a pier in
ground using an extensible shell 100 in accordance with an embodiment of the
present invention. In
this example, side partial cross-section views illustrate the use of the
extensible shell 100 for
constructing a pier 200 in the ground (see Figure 2C) in accordance with an
embodiment of the present
invention. Other methods are described with reference to Figures 3A - 3D and
the Examples below.
The method of Figures 2A - 2C includes forming a pre-formed elongate vertical
cavity 202 or hole in a
ground surface 204, as shown in Figure 2A. The ground may be comprised of
primarily soft cohesive
soil such as soft clay and silt, or also loose sand, fill materials, or the
like. The cavity 202 may be
formed with a suitable drilling device having, for example, a drill head or
auger for forming a cavity or
hole, or may be formed by other methods for foiiiiing a cavity such as by
inserting and removing a
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driving mandrel to the desired pre-formed cavity depth. In some embodiments,
the cavity may not be
formed at all prior to shell insertion, such as described below with reference
to Figures 3A - 3D.
100451 After the partial cavity 202 has been formed, the extensible
shell 100 may be
positioned within the cavity 202, as shown in Figure 2B, for ultimate driving
to the desired depth.
Particularly, an extractable mandrel 206 may be used for driving the
extensible shell 100 into the
cavity 202 and ground 204. A tamper head 208 of the mandrel 206 may be
positioned against a bottom
surface 210 of the interior 110 and used to drive the shell 100 to the desired
penetration depth, as
shown in Figure 2C. The cavity 202 is at that point foitned of a size and
dimension such that the
exterior surface of the extensible shell 100 fits tightly against the walls of
the cavity 202.
100461 After the extensible shell 100 has been driven into (while
forming) the fully
enlarged cavity 202, the mandrel 206 is removed, leaving behind the shell 100
in the cavity 202 and
with the interior 110 being empty. The shell 100 may then be filled with a
granular construction
material 212, such as sand, aggregate, admixture-stabilized sand or aggregate,
recycled materials,
crushed glass, or other suitable materials as shown in Figure 2C. The granular
construction material
212 may be compacted within the shell using the mandrel 206. The compaction
increases the strength
and stiffness of the internal granular construction material 212 and pushes
the granular construction
material 212 outward against the walls of the shell 100, which pre-strains the
shell 100 and increases
the coupling of the shell 100 with the in-situ soil. Significant increases in
the load carrying capacity of
the pier 200 can be achieved as a result of the restraint offered by the shell
100.
100471 Figures 3A - 3D illustrate steps in another exemplary method of
constructing a pier
in ground using an extensible shell in accordance with an embodiment of the
present invention.
Referring to Figure 3A, an aggregate construction material 300 (e.g., sand) is
placed in the interior 110
of the shell 100 to a predetermined level above the bottom surface 210 of the
shell 100. Next, the
tamper head 208 of the extractable mandrel 206 is fitted to the interior 110
of the extensible shell 100,
and against the top of the aggregate construction material 300. The mandrel
206 may then be moved
towards the ground 204 in a direction indicated by arrow 302 for driving the
shell 100 into the ground
204. Driving may be facilitated using a small pre-fonned cavity (e.g., the
cavity 202 shown in Figure
2A), or not, depending on site conditions.
100481 Referring to Figure 3B, the mandrel 206 is shown driving the
shell 100 into the
ground 204 in the direction 302 such that the shell 100 is at a predetelmined
depth below grade. Next,
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the mandrel 206 may be removed. At Figure 3C, the shell 100 is substantially
filled with additional
aggregate construction material 304 (e.g., sand) through opening 108, and the
mandrel 206 is
positioned as shown. Next, vertical compaction force and/or vibratory energy
is applied to the mandrel
206 for compacting the materials 300 and 304. The shell 100 may be driven by
this force to a further
depth below grade. The addition of construction material 304 and subsequent
compaction can be
repeated several times until the final pier is constructed. Alternatively, the
shell may be "topped off'
with additional construction material after only one compaction cycle.
[0049] In an embodiment of the present invention, a second mandrel 212
may be used to
compact the upper portion of the material 304 in the direction 302, as shown
in Figure 3D. The second
mandrel 212 may have a larger cross-sectional area than the primary mandrel
206 to provide increased
confinement during compaction.
[0050] In an embodiment of the present invention, the shell 100 may
define apertures 218
that extend between the interior 110 and an exterior of the shell 100 to the
in-situ soil (see Figures 1A
and 2C). The apertures 218 may provide for drainage of excess pore water
pressure that may exist in
the in-situ soil to drain into the interior 110 of the shell 100. Increases in
pore water pressure typically
decreases the strength of the soil and is one of the reasons that prior art
piers are limited in their load
carrying capacity in saturated cohesive soil such as clay, silt, or the like.
The apertures 218 envisioned
herein allow the excess pore water pressure in the soil to dissipate into the
pier 200 after insertion.
This allows the in-situ soil to quickly gain strength with time, a phenomena
not enjoyed by concrete,
steel piles, or grout elements (i.e., "hardened" elements). The drainage of
excess pore water pressures
allows additional settlement of the soil that may occur as a result of pore
water pressure dissipation
prior to the application of foundation loads.
[0051] Other embodiments may not define apertures, or may provide one
or more apertures
218 on only one side of the shell 100. Alternatively, the apertures 218 may be
defined in the shell 100
such that they are positioned along a portion of the length of the shell 100,
are positioned along the full
length of the shell 100, or may be positioned asymmetrically in various
configurations. The sizes and
placements of the apertures 218 can vary according to the size of the shell
100, the conditions of the
ground (e.g., where higher water pressure is known to exist), and other
relevant factors. The apertures
218 may range in size from about 0.5 mm to about 50 mm; such as from about 1
mm to about 25 mm.
In another embodiment, the top of the shell 100 may be enclosed and connected
to vacuum pressure to
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further increase and accelerate drainage of excess water pressure in the
surrounding soil through the
apertures 218.
[0052] The mandrel 206 may be constructed of sufficient strength,
stiffness, and geometry
to adequately support the shell 100 during driving and to be able to be
retracted from the shell 100
after driving. In one embodiment, the shape of the exterior of mandrel 206 is
substantially similar to
the shape of the interior 110 defined by the shell 100. In another embodiment,
the mandrel 206 is
comprised primarily of steel. Other materials are also envisioned including,
but not limited to,
aluminum, hard composite materials, and the like.
[0053] The mandrel 206 may be driven by a piling machine or other
suitable equipment and
technique that may apply static crowd pressure, hammering, or vibration
sufficient to drive the mandrel
206 and extensible shell 100 into the surface of ground 204. In one
embodiment, the machine may be
comprised of an articulating, diesel, pile-driving hammer that drives the
mandrel 206 using high
energy impact forces. The hammer may be mounted on leads suspended from a
crane. In another
embodiment, the hammer may be a sheet pile vibrator mounted on a rig capable
of supplying a
downward static force. In another embodiment, the shell 100 may be placed in a
pre-formed cavity
200 and constructed without the use of an extractable mandrel. Standard
methods of driving mandrels
into the ground are known in the art and therefore, can be used for driving.
[0054] The following Examples illustrate further aspects of the
invention.
Example I
[0055] As an example, piers were constructed using extensible shells
in accordance with
embodiments of the present invention at a test site in Iowa. Load tests were
conducted on the piers
using a conventional process. The extensible shells used in the tests and the
methods of their use
consisted essentially of that described above and shown in the attached
Figures. In this test, extensible
shells formed from LEXAN polycarbonate plastic were installed at a test site
characterized by soft
clay soil. This testing was designed to compare the load versus deflection
characteristics of an
extensible shell in accordance with the present invention to aggregate piers
constructed using a driven
tapered pipe. Two comparison aggregate piers (of fine and coarse aggregate)
were constructed to a
depth of 12 feet below the ground surface.
[0056] In this test, the extensible shell was formed by bending sheets
of the plastic to form
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a tapered shape having a hexagonal cross-section and that tapered downward
from an outside diameter
of 24 inches (610 mm) at the top of the shell to a diameter of 18 inches (460
mm) at the bottom of the
shell. A panel of the shells overlapped, and this portion was both glued and
bolted together. The
length of the extensible shell was 9.5 feet (2.9 m). In this embodiment,
apertures were formed in the
extensible shell by perforating the sides of the shell with 3 mm to 7 mm
diameter "weep" holes spaced
apart from each another. The bottom portion of the shell was capped with a
steel shoe to facilitate
driving. LEXAN polycarbonate plastic has a tensile strength of
approximately16 MPa (2300 psi) at
11 percent elongation and a Young's modulus of 540 MPa (78,000 psi). The
extractable mandrel used
in this test was attached to a high frequency hammer, which is often
associated with driving sheet
piles. The hammer is capable of providing both downward force and vibratory
energy for driving the
shell into the ground and for compacting aggregate construction material in
the shell.
[0057] In this example, the extensible shell was driven into the
ground without pre-drilling
of the cavity or hole. Particularly, in this test, the two shells were
installed by orientating each shell in
a vertical direction, placing approximately 4 feet (1.2 m) of sand at the base
of the shell, and then
driving the shell into the ground surface with an extractable mandrel with
exterior dimensions similar
to those of the interior of the shell. The shell was driven to a depth of
approximately 8.5 feet (2.6 m)
below grade. The mandrel was removed and the shells were filled with sand. The
extractable mandrel
was then re-lowered within the shells and vertical compaction force in
combination with vibratory
energy was applied to both compact the sand to drive the shell to a depth of 9
feet (2.7 m) below grade.
The mandrel was then extracted and the upper portion of the shell was then
filled with crushed stone to
a depth of 0.5 ft (0.2 m) below grade. A concrete cap was then poured above
the crushed stone fill to
facilitate load testing.
[0058] Radial cracks were observed to extend outward from the edge of
the shell pier.
These cracks form drainage galleries that are the result of high radial
stresses and low tangential
stresses created in the ground during pier installation. Drainage was afforded
by the perforations in the
shell and allowed soil water to drain into the sand and aggregate filled
piers.
[0059] The shell piers were load tested using a hydraulic jack pushing
against a test frame.
Figure 4 is a graph showing results of the load test compared with aggregate
piers constructed using a
similarly shaped mandrel. As shown in Figure 4, at a top of pier deflection of
one inch, the piers
constructed without shells supported a load of 15,000 pounds to 20,000 pounds
(67 kN to 89 kN). The
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shell piers constructed in this embodiment of the invention supported a load
of 310 kN to 360 kN
(70,000 to 80,000 pounds) at a top of pier deflection of one inch. The load
carrying capacity of the
shell piers constructed in accordance with the present invention provided a
3.5 to 5.3 fold improvement
when compared to aggregate piers constructed without extensible shells.
Example II
100601 In other testing, extensible shells were formed from high-
density polyethylene
polymer ("HDPE") and installed at the test site as described in Example I.
This testing program was
designed to compare the load versus deflection characteristics of this
embodiment of the present
invention to aggregate piers constructed using a driven tapered pipe as
described in Example I. A total
of six shell piers were installed as part of this example.
[0061] In this test, the extensible shell was formed by a rotomolding
process. The shells
defined a tapered shape having a hexagonal cross-section and that tapered
downward from an outside
diameter of 585 mm (23 inches) at the top of the shell to a diameter of 460 mm
(18 inches) at the
bottom of the shell. The bottom of the extensible shell was integrally
constructed as part of the shell
walls as a result of the rotomolding process. The mandrel in this embodiment
was attached to the same
hammer as described in Example I.
[0062] The installation process in this Example was somewhat different
from that in
Example I and included pre-drilling a 30 inch (0.76 m) diameter cavity to a
depth of 2 feet (0.61 m) to
3 feet (0.9 m) below the ground surface (rather than driving the shell
initially from top grade). The
shell was then placed vertically in the pre-drilled cavity. The extractable
mandrel was then inserted
into the shell, and the shell was driven to a depth 11 feet (3.4 m) to 12 feet
(3.7 m) below grade. The
extensible shell was then filled with aggregate construction material and
compacted in four lifts; with
each lift about 7.4 cubic feet (0.2 cubic meters) in volume. The aggregate
consisted of sand in five of
the piers and consisted of crushed stone in one of the piers. Each lift was
compacted with the
downward pressure and vibratory energy of the extractable mandrel.
[0063] After placement and compaction of sand within the extensible
shells, the top of the
shells were situated at about 2 feet (0.61 m) to 3 feet (0.9 m) below the
ground surface. Crushed stone
was then placed and compacted above the extensible shell to a depth of 1 foot
(0.3 m) below the
ground surface. A concrete cap was then poured above the crushed stone fill to
facilitate load testing.
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100641 The shell piers were load tested using a hydraulic jack pushing
against a test frame.
Figure 5 is a graph showing results of the load test compared with the
aggregate piers described in
Example I. As shown in Figure 5, at a top of pier deflection of one inch, the
piers constructed without
shells supported a load of 15,000 pounds to 20,000 pounds (67 kN to 89 kN).
The shell piers
constructed in this embodiment of the invention supported loads ranging from
62,000 pounds (275 kN)
to 71,000 pounds (315 kN) at the top of pier deflections of one inch. The load
carrying capacity of the
shell piers constructed in accordance with this embodiment of the present
invention provided a 3.1 to
4.7 fold improvement when compared to aggregate piers constructed without
extensible shells.
Example III
[0065] In another test, an extensible shell of the same embodiment
described in Example II
was installed at the test site as described in Example I. This testing program
was designed to compare
the load versus deflection characteristics of this embodiment of the invention
to aggregate piers
constructed using a driven tapered pipe as described in Example I. The
mandrel, hammer, and
extensible shell used for testing were the same as used in Example II.
[0066] In this embodiment of the present invention, the installation
process included pre-
drilling a 30 inch (0.76 m) diameter cavity to a depth of 3 feet (0.9 m) below
the ground surface. The
extractable mandrel was then inserted into the pre-drilled cavity, to create a
cavity with a total depth of
feet (1.5 m) below the ground surface. This cavity was then backfilled to the
ground surface with
sand. The extensible shell was then driven vertically through the sand filled
cavity with the extractable
mandrel to a depth of 9 feet (2.7 m) below the ground surface, so that the top
of the shell was situated 6
inches above the ground surface. The extensible shell was then filled with
sand in four lifts, with each
lift about 7.4 cubic feet (0.2 cubic meters) in volume. Each lift was
compacted with the downward
pressure and vibratory energy of the mandrel. A concrete cap encompassing the
top of the shell was
then cast over the shell to facilitate load testing.
[0067] The shell pier was load tested using a hydraulic jack pushing
against a test frame.
Figure 6 is a graph showing results of the load test compared with the
aggregate piers described in
Example I. As shown in Figure 6, at a top of pier deflection of one inch, the
piers constructed without
shells supported a load of 15,000 pounds to 20,000 pounds (67 kN to 89 kN).
The pier constructed in
this embodiment of the present invention supported a load of 57,500 pounds
(255 kN) with a top of
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pier deflection of one inch. The load carrying capacity of the shell pier
constructed in accordance with
this embodiment of the present invention provided a 2.9 to 3.8 fold
improvement when compared to
aggregate piers constructed without extensible shells.
Example IV
[0068] In yet another test, an embodiment of the present invention was
installed at a project
site characterized by 3 feet (0.9 m) of loose sand soil over 7 feet (2.1 m) of
soft clay soil over dense
sand soil. The embodiment of the present invention at the project site was
used to support structural
loads, such as those associated with building foundations and heavily loaded
floor slabs. The mandrel,
hammer, and extensible shell used for testing were the same as used in
Examples II and HI.
[0069] In this embodiment of the present invention, the installation
process included pre-
drilling a 30 inch (0.76 m) diameter pre-drill to a depth of 3 feet (0.9 m)
below the ground surface.
Approximately 7.4 cubic feet (0.2 cubic meters) of sand was then placed in the
pre-drilled cavity. This
resulted in the pre-drilled cavity being about half-full.
[0070] The extensible shell was then placed vertically in the
partially backfilled pre-drilled
cavity. The extractable mandrel was then inserted into the shell, and the
shell was driven to a depth
12.5 feet (3.8 m) below grade. The extensible shell was then filled with sand
in four lifts; with each
lift about 7.4 cubic feet (0.2 cubic meters) in volume. Each lift was
compacted with the downward
pressure and vibratory energy of the mandrel.
[0071] After placement and compaction of sand within the extensible
shell, a lift of crushed
stone about 4.9 cubic feet (0.14 cubic meters) in volume was placed and
compacted within the
extensible shell. Crushed stone was then placed and compacted above the
extensible shell until the
crushed stone backfill was level with the ground surface.
[0072] At one shell location, a 30 inch (0.76 m) diameter concrete cap
was placed over the
shell to facilitate load testing. At a second shell location, a 6 foot (1.8 m)
wide by 6 foot (1.8 m) wide
concrete cap was placed over the shell to facilitate loading and to measure
the load deflection
characteristics of the composite of native matrix soil and extensible shell
(to simulate a floor slab).
[0073] The shell piers were load tested using a hydraulic jack pushing
against a test frame,
with the results of the load testing being shown in Figure 7. The shell pier
tested with the 30 inch
diameter concrete cap supported a load of 35,500 pounds (158 kN) at a
deflection of 0.4 inches (10
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mm). The shell pier tested with a 6 foot wide by 6 foot wide concrete cap
supported a load of 104,700
pounds (467 kN) at a deflection of 0.4 inches (10 mm).
Slotted Shell Embodiment
[0074] With reference to Figure 8, an alternative embodiment of the
present invention is
shown and which includes an extensible shell 800 with one or more slits or
slots 812 that extend
between an interior of the shell to an exterior of the shell. The slots 812
may be placed over the entire
length of the shell 800 or only partially located along the length and have
varying spacing, such as, for
example, slots being spaced every 6 inches (152 mm) starting generally 1.5
foot (0.46 m) from the top
and bottom.. The slots 812 may be of varying widths, such as, for example, 1/4
inch (6.35 mm) to 3/8
inch (9.53 mm) wide. The slots 812 typically run generally transverse to a
centerline along the length
of the shell and may form a minor or major part of the circumference of the
shell 800. In one
embodiment, such as shown in Figure 8, the slots 812 are discontinuous around
the circumference
leaving three spines 814 to maintain portions of continuous material
connectivity along the length of
the shell 800. The shell 800 of this embodiment may be of any suitable size or
shape as described
above with reference to shell 100.
[0075] As an example, a slotted extensible shell of this embodiment
was installed at a test
site in Iowa to compare the load versus deflection characteristics of this
embodiment of the extensible
shell to aggregate piers constructed using a driven tapered pipe. The test
site was characterized by soft
clay soil and the two comparison aggregate piers (of fine and coarse
aggregate) were constructed to a
depth of 12 feet below the ground surface.
[0076] For this test of the extensible shell, the shell was fottned
from High Density
Polyethylene polymer and was formed by the rotomolding process. The shell
formed a tapered shape
that was hexagonal in cross section and tapered downward from an outside
diameter of 23 inches (585
mm) at the top of the shell to a diameter of 18 inches (460 mm) at the bottom
of the shell. The bottom
of this embodiment of the extensible shell was integrally constructed as part
of the shell walls as a
result of the rotomolding process. In this embodiment of the invention
(similar to that shown in Figure
8), 1/4 inch (6.35 mm) wide slots were cut in a circumferential orientation
around the extensible shell.
The extensible shell was left as a single continuous piece, by not removing
material from three of the
six corners or spines. The extractable mandrel used in this test was attached
to a high frequency
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hammer, which is often associated with driving sheet piles. The hammer is
capable of providing both
downward force and vibratory energy for driving the shell into the ground and
for compacting
aggregate construction material in the shell.
100771 In this example, the installation process included a 30 inch
(0.76 m) diameter pre-
drill to a depth of 1.5 feet (0.46 m) below the ground surface. The shell was
then placed vertically in
the pre-drilled hole and then the shell was driven with an extractable mandrel
with exterior dimensions
similar to those of the interior of the shell. The shell was driven to a depth
of 11 feet (3.4 m) below
grade. The mandrel was removed and the extensible shell was then filled with
aggregate in four lifts;
with each lift about 7.4 cubic feet (0.2 cubic meters) in volume. Each lift
was compacted with the
downward pressure and vibratory energy of the extractable mandrel.
[0078] After placement and compaction of aggregate within the
extensible shell, the top of
the shell was situated at about 1.5 feet (0.46 m) below the ground surface.
The aggregate backfill was
then leveled with the top of the shell, and a concrete cap was then poured
above the shell to facilitate
load testing.
[0079] The slotted shell pier was load tested using a hydraulic jack
pushing against a test
frame. Figure 9 is a graph showing results of the load test compared with the
aggregate piers described
above. As shown in Figure 9, at a top of pier deflection of one inch, the
piers constructed without
slotted shells supported a load of 15,000 pounds to 20,000 pounds (67 kN to 89
kN). The pier
constructed in this embodiment of the invention supported a load of 77,500
pounds (345 kN) at a top
of pier deflection of one inch. The load carrying capacity of the pier
constructed in accordance with
this embodiment of the invention provided a 3.9 to 5.2 fold improvement when
compared to aggregate
piers constructed without extensible shells.
Open-End Embodiment
[0080] With reference to Figures 10A through 15B, an alternative
embodiment of the
present invention is shown and which includes an open-end extensible shell
that can be used to form
piers. Namely, Figure 10A shows a perspective view of an example of an open-
end extensible shell
1000. Figure 10B shows a cross-sectional view of open-end extensible shell
1000 taken along line A-A
for Figure 10A. In this example, open-end extensible shell 1000 is a hollow
tubular member that has a
first open end 1010 and a second open end 1012. Open-end extensible shell 1000
can be used in any
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orientation with respect to driving into the ground. However, for illustration
purposes, first open end
1010 is hereafter referred to as advancing open end 1010, wherein advancing
open end 1010 means the
bottom end of open-end extensible shell 1000 that is advanced into the ground
first. Further, second
open end 1012 is hereafter referred to as trailing open end 1012, wherein
trailing open end 1012 means
the top end of open-end extensible shell 1000 that is mated to driving
equipment, such as a mandrel.
[0081] Open-end extensible shell 1000 can be any length and any width
or diameter.
Without limitation, the length of open-end extensible shell 1000 can be from
about 3.05 m (5 ft) to
about 6.1 m (20 ft) in one example, or can be about 3.05 m (10 ft) in another
example. Without
limitation, the width or diameter of open-end extensible shell 1000 can be
from about 61 cm (24 in) to
about 46 cm (18 in) in one example, or can be about 51.8 cm (20.4 in) in
another example. In one
example, open-end extensible shell 1000 can be formed of plastic, such as high-
density polyethylene
polymer (HDPE) plastic. In another example, open-end extensible shell 1000 can
be formed of metal,
such as steel or aluminum.
[0082] Open-end extensible shell 1000 is not limited to a straight
tubular shape. For
example, Figures 11A, 11B, and 11C illustrate various views of an example of
an open-end extensible
shell 100 that has a hexagon-shaped cross-section and a tapered tip; namely,
advancing open end 1010
is tapered. Namely, Figures 11A and 11B show perspective views of the
advancing open end 1010-
portion of open-end extensible shell 100, which is hexagonal and includes a
taper 1020. Figure 11C
shows a cross-sectional view of open-end extensible shell 1000 taken along
line B-B for Figure 11B.
In one example, the width or diameter of open-end extensible shell 100 is
tapered from about 51.8 cm
(20.4 in) to about 46 cm (18.1 in).
[0083] Figures 12A and 12B show an example of a process of installing
open-end
extensible shell 1000 into the ground (e.g., ground 1205). In this example, a
closed pipe mandrel 1210
that has a shoulder collar 1215 is used to drive open-end extensible shell
1000 into ground 1205.
Closed pipe mandrel 1210 is inserted into open-end extensible shell 1000 until
shoulder collar 1215
contacts trailing open end 1012 of open-end extensible shell 1000. In this
way, driving force is
transferred from closed pipe mandrel 1210 to open-end extensible shell 1000.
In Figures 12A and
12B, the advancing end of closed pipe mandrel 1210 extends beyond advancing
open end 1010 of
open-end extensible shell 1000. In one example, the end of closed pipe mandrel
1210 extends about
1.5 m (5 ft) beyond advancing open end 1010 of open-end extensible shell 1000.
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[0084] However, the position of shoulder collar 1215 can be adjustable
along the length of
closed pipe mandrel 1210. Namely, shoulder collar 1215 can be adjustable such
that a range of depths
and relative positions of open-end extensible shell 1000 and closed pipe
mandrel 1210 can be achieved
without the need to change mandrels. For example, Figure 13 shows the position
of shoulder collar
1215 set such that the advancing end of closed pipe mandrel 1210 substantially
aligns with advancing
open end 1010 of open-end extensible shell 1000.
[0085] Figure 14 shows a flow diagram of an example of a method 1400
of using open-end
extensible shell 1000 to form a support pier. Method 1400 may include, but is
not limited to, the
following steps.
[0086] At a step 1410, open-end extensible shell 1000 is driven into
the ground using a
mandrel. For example and referring again to Figures 12A and 12B, open-end
extensible shell 1000 is
driven into ground 1205 using closed pipe mandrel 1210.
[0087] At a step 1415, the mandrel (e.g., closed pipe mandrel 1210) is
withdrawn from
open-end extensible shell 1000, leaving open-end extensible shell 1000 in the
ground. For example,
Figure 15A shows open-end extensible shell 1000 in ground 1205 after closed
pipe mandrel 1210 is
withdrawn, creating a shell cavity 1220. Namely, shell cavity 1220 is a
portion of ground 1205 that is
void of material.
[0088] At a step 1420, shell cavity 1220 is backfilled with sand,
aggregate, cementitious
grout, and/or any other material. For example, Figure 15B shows shell cavity
1220 of open-end
extensible shell 1000 backfilled with a volume of material 1225.
[0089] At a step 1425, the mandrel (e.g., closed pipe mandrel 1210) is
reinserted into open-
end extensible shell 1000. Then, material 1225 is packed to below advancing
open end 1010 of open-
end extensible shell 1000. For example, Figure 15B shows a "bulb" of material
1225 is folmed in
ground 1205 below advancing open end 1010 of open-end extensible shell 1000.
[0090] At a step 1430, the mandrel (e.g., closed pipe mandrel 1210) is
withdrawn from
open-end extensible shell 1000, again as shown in Figure 15A.
[0091] At a step 1435, the remaining portion of shell cavity 1220 is
backfilled with material
1225 (e.g., sand, aggregate, cementitious grout, and/or any other material).
[0092] At a step 1440, the mandrel (e.g., closed pipe mandrel 1210) is
reinserted into open-
end extensible shell 1000. Then, material 1225 is packed into shell cavity
1220 of open-end extensible
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shell 1000.
100931 At a step 1445, the mandrel (e.g., closed pipe mandrel 1210) is
withdrawn from
open-end extensible shell 1000, again as shown in Figure 15A.
100941 At a decision step 1450, it is detemiined whether the
construction of the support pier
is complete. If the construction of the support pier is complete, then method
1400 ends. However, if
the construction of the support pier is not complete, then method 1400 returns
to 1435.
[0095] A benefit of using open-end extensible shell 1000 and method
1400 is that it
provides increased stiffness for the shell support layer and increased overall
length of the extensible
shell system in the upper zone (open-end extensible shell 1000 plus "bulb"
depth).
Example V
[0096] As an example, support piers were constructed using extensible
shells in accordance
with embodiments of the present invention at a test site in Iowa. Load tests
were conducted on the
piers using a conventional process. The extensible shells used in the tests
and the methods of their use
consisted essentially of that described above and shown in Figures 10A through
15B. In this test,
extensible shells formed of high-density polyethylene polymer (HDPE) plastic
were installed at a test
site characterized by soft clay soil. This testing was designed to compare the
load versus deflection
characteristics of an extensible shell in accordance with the present
invention to aggregate piers
constructed with a driven tapered pipe. Two comparison aggregate piers were
constructed to a depth
of 12 feet below the ground surface.
[0097] In this test, the extensible shell was formed by a rotomolding
process. The shells
defined a tapered shape having a hexagonal cross-section (e.g., as shown in
Figures 11A, 11B, 11C)
and that tapered downward from an outside diameter of 518 mm (20.4inches) at
the top of the shell to a
diameter of 460 mm (18.1 inches) at the bottom of the shell. In this
embodiment of the invention the
extensible shell has a total length of 3.05 m (10 feet), and both the top and
the bottom ends of the shell
are open such that and extractable tapered mandrel commonly used for
constructing aggregate piers
could fully pass through the extensible shell.
[0098] The extractable mandrel used in this test was attached to a
high frequency hammer,
which is often associated with driving sheet piles. The hammer is capable of
providing both
downward force and vibratory energy for driving the shell into the ground and
for compacting
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aggregate construction material in the shell. The "open bottom" extensible
shell pier and the aggregate
pier were constructed with a similar mandrel and high frequency hammer.
[0099] In this example, a 61 cm (24 in) diameter and 61 cm (24 in)
deep pre-drill hole was
formed at the ground surface prior to driving the extensible shell. The
purpose of the pre-drill is to
facilitate the placement of a concrete cap for the load test. The extensible
shell, and Tapered Mandrel
were then driven into the ground such that the tip of the tapered mandrel was
at a depth of about 5.2 m
(17 ft) below the ground surface, the bottom of the extensible shell was at a
depth of about 3.65 m (12
ft) below the ground surface, and the top of the shell was at a depth of about
61 cm (24 in) below the
ground surface.
[00100] The tapered mandrel used in this example is hollow such that such that
the mandrel
can be filled with aggregate, and allowed to flow out the bottom of the
mandrel. An aggregate pier is
constructed with this mandrel by raising and lowering the mandrel pre-
determined distances to
construct the aggregate pier. In this example, an aggregate pier was
constructed below and within the
extensible shell using a similar process.
[00101] The open bottom extensible shell piers were load tested using a
hydraulic jack
pushing against a test frame. Figure 16 is a graph showing results of the load
test compared with
aggregate piers constructed using an embodiment as shown in Figures 10A, 10B
and/or Figures 11A,
11B, 11C. As shown in Figure 16, at a top of pier deflection of one inch, the
piers constructed without
shells supported a load of 67 kN to 89 kN (15,000 pounds to 20,000 pounds).
The piers constructed in
this embodiment of the invention supported a load of 188 kN (42,300 pounds) at
a top of pier
deflection of one inch. The load carrying capacity of the piers constructed in
accordance with the
present invention provided a 2.1 to 2.8 fold improvement when compared to
aggregate piers
constructed without extensible shells.
[00102] The foregoing detailed description of embodiments refers to the
accompanying
drawings, which illustrate specific embodiments of the invention. Other
embodiments having different
structures and operations do not depart from the scope of the invention. The
term "the invention" or
the like is used with reference to certain specific examples of the many
alternative aspects or
embodiments of the applicant's invention set forth in this specification, and
neither its use not its
absence is intended to limit the scope of the applicant's invention or the
scope of the claims.
Moreover, although the term "step" may be used herein to connote different
aspects of methods
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employed, the term should not be interpreted as implying any particular order
among or between
various steps herein disclosed unless and except when the order of individual
steps is explicitly
described. This specification is divided into sections for the convenience of
the reader only. Headings
should not be construed as limiting of the scope of the invention. It will be
understood that various
details of the invention may be changed without departing from the scope of
the invention.
Furthermore, the foregoing description is for the purpose of illustration
only, and not for the purpose of
limitation.
21
