U.S. patent application number 12/875986 was filed with the patent office on 2011-03-03 for method and apparatus for making an expanded base pier.
This patent application is currently assigned to GEOPIER FOUNDATION COMPANY, INC.. Invention is credited to Marc Plotkin, Kord J. Wissmann.
Application Number | 20110052330 12/875986 |
Document ID | / |
Family ID | 43625188 |
Filed Date | 2011-03-03 |
United States Patent
Application |
20110052330 |
Kind Code |
A1 |
Wissmann; Kord J. ; et
al. |
March 3, 2011 |
Method and Apparatus for Making an Expanded Base Pier
Abstract
A system for constructing a support column includes a mandrel
with an upper portion and a tamper head. A feed tube extends
through the mandrel for feeding flowable material to the head. The
tamper head includes a lower enlarged chamber with a reducing
surface at an upper portion for compacting material and restricting
upward flow of aggregate. The tamper head is of a size providing an
enclosed region for allowing cementitious materials to be placed
therein. The system allows a support column including a
cementitious inclusion on top of an expanded base to be built.
Inventors: |
Wissmann; Kord J.;
(Mooresville, NC) ; Plotkin; Marc; (Huntersville,
NC) |
Assignee: |
GEOPIER FOUNDATION COMPANY,
INC.
Mooresville
NC
|
Family ID: |
43625188 |
Appl. No.: |
12/875986 |
Filed: |
September 3, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61239649 |
Sep 3, 2009 |
|
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Current U.S.
Class: |
405/233 |
Current CPC
Class: |
E02D 5/385 20130101;
E02D 5/44 20130101; E02D 3/08 20130101 |
Class at
Publication: |
405/233 |
International
Class: |
E02D 5/30 20060101
E02D005/30 |
Claims
1. A system for constructing a support column, comprising: (a) a
mandrel having an upper portion and a tamper head, and a feed tube
extending therethrough for feeding aggregate, concrete, grout, or
other flowable materials through the mandrel to the tamper head;
and (b) the tamper head defining a lower enlarged chamber having a
reducing surface at an upper portion thereof for compacting
aggregate or concrete and for restricting upward flow of aggregate
or concrete into the mandrel during compacting and the temper head
being of sufficient size for providing an enclosed region for
allowing cementitious material to be placed therein.
2. The system of claim 1, further comprising a valve mechanism
movable between an open position and a closed position for closing
off the feed tube from communication with the tamper head during
tamping operations.
3. The system of claim 1, further comprising stiffening members
secured between the reducing surface and the mandrel for providing
load support during tamping operations.
4. The system of claim 1, further comprising chains attached within
the interior of the tamper head for restricting upward flow of
material into the feed tube during downward movement of the
mandrel.
5. The system of claim 1 further comprising notches within the
interior of the tamper head for restricting upward flow of material
into the feed tube during downward movement of the mandrel.
6. The system of claim 1, further comprising a second tube
extending through the mandrel on the side of the feed tube for
allowing cementitious material to flow upward through the second
tube for inspection of the cementitious material during
pumping.
7. The system of claim 1, further comprising a hopper located at
the top of the mandrel for feeding aggregate into the feed tube of
the mandrel.
8. The system of claim 1, further comprising a closure cap on an
end of the feed tube opposite the tamper head and a concrete supply
tube connected to the feed tube.
9. The system of claim 8 further comprising an air pressure source
connected to the feed tube for evacuating concrete from the feed
tube through air pressure supplied thereto.
10. A method of constructing a support column comprising use of a
mandrel assembly having a feed tube connected to a tamper head at
an opening thereof for allowing aggregate, concrete, grout, or
other flowable material to flow into the tamper head, the method
comprising: (a) providing the tamper head of a shape with a defined
lower enlarged chamber having a reducing surface at an upper
portion thereof for compaction and for restricting upward flow of
material into the feed tube during tamping, the tamper head further
sized to provide an enclosed region for allowing cementitious
material to be placed therein; (b) driving the mandrel assembly
into a ground surface to a given depth thereby forming a cavity;
(c) lifting the mandrel assembly to release an initial charge of
aggregate or concrete from the tamper head into a bottom of the
cavity; (d) re-driving the mandrel assembly to compact the
aggregate or concrete at a bottom of the cavity and to form an
expanded base, the expanded base having a width greater than the
tamper head; and (e) withdrawing the mandrel assembly while
continuously feeding cementitious material or aggregate to be
subsequently fully or partially treated with grout through the feed
tube, thereby forming a cementitious inclusion at least partially
within the cavity, the cementitious inclusion having a width of the
cavity and being formed on top of the expanded base.
11. The method of claim 10 wherein the tamper head is filled with
the initial charge of aggregate or concrete before driving.
12. The method of claim 10 wherein the cementitious material is one
selected from the group consisting of concrete, grout, or aggregate
that is subsequently fully or partially treated with grout.
13. The method of claim 10, further comprising providing a valve
mechanism movable between an open position and a closed position at
the opening between the feed tube and the tamper head, for
restricting the passage from flow connection into the tamper head,
and moving the closure member to an open position for introducing
cementitious material into the tamper head, and into a closed
position during downward compaction.
14. The method of claim 10, further comprising introducing
cementitious material into the enclosed region.
15. The method of claim 10, further comprising introducing a pipe
through the feed tube and tamper head after formation of the
expanded base, placing aggregate during the withdrawing step to
partially surround the pipe, and introducing cementitious material
into the pipe following aggregate placement to treat the
aggregate.
16. The method of claim 10, further comprising chains attached
within the interior of the tamper head for restricting upward flow
of material into the feed tube during downward movement of the
mandrel.
17. The method of claim 10, further comprising notches within the
interior of the tamper head for restricting upward flow of material
into the feed tube during downward movement of the mandrel.
18. The method of claim 10, further comprising providing the
mandrel with a second tube adjacent the feed tube to allow for the
inspection of cementitious material during pumping.
19. The method of claim 10, further comprising a hopper located at
the top of the mandrel for feeding aggregate into the feed tube of
the mandrel.
20. The method of claim 10, further comprising a closure cap on an
end of the feed tube opposite the tamper head and a concrete supply
tube connected to the feed tube.
21. The method of claim 20 further comprising an air pressure
source connected to the feed tube for evacuating concrete from the
feed tube through air pressure supplied thereto.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to and claims the priority of
U.S. Provisional Patent Application Ser. No. 61/239,649, filed Sep.
3, 2009; the disclosure of which is incorporated by reference in
its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to construction of a
structural support column. More specifically, the present invention
relates to a method and apparatus for building an expanded base
pier to bypass weak soils and transfer structural loads to
underlying strong soils.
BACKGROUND OF INVENTION
[0003] Heavy or settlement-sensitive facilities that are located in
areas containing soft or weak soils are often supported on deep
foundations, consisting of driven piles or drilled concrete
columns. The deep foundations are designed to transfer the
structure loads through the soft soils to more competent soil
strata.
[0004] In recent years, aggregate columns have been increasingly
used to support structures located in areas containing soft soils.
The columns are designed to reinforce and strengthen the soft layer
and minimize resulting settlements. The columns are constructed
using a variety of methods including the drilling and tamping
method described in U.S. Pat. Nos. 5,249,892 and 6,354,766; the
driven mandrel method described in U.S. Pat. No. 6,425,713; the
tamper head driven mandrel method described in U.S. Pat. No.
7,226,246; and the driven tapered mandrel method described in U.S.
Pat. No. 7,326,004; the disclosures of which are incorporated by
reference in their entirety.
[0005] The short aggregate column method (U.S. Pat. Nos. 5,249,892
and 6,354,766), which includes drilling or excavating a cavity, is
an effective foundation solution when installed in cohesive soils
where the sidewall stability of the hole is easily maintained. The
method generally consists of: a) drilling a generally cylindrical
cavity or hole in the foundation soil (typically around 30 inches);
b) compacting the soil at the bottom of the cavity; c) installing a
relatively thin lift of aggregate into the cavity (typically around
12-18 inches); d) tamping the aggregate lift with a specially
designed beveled tamper head; and e) repeating the process to form
an aggregate column generally extending to the ground surface.
Fundamental to the process is the application of sufficient energy
to the beveled tamper head such that the process builds up lateral
stresses within the matrix soil up along the sides of the cavity
during the sequential tamping. This lateral stress build up is
important because it decreases the compressibility of the matrix
soils and allows applied loads to be efficiently transferred to the
matrix soils during column loading.
[0006] The tamper head driven mandrel method (U.S. Pat. No.
7,226,246) is a displacement form of the short aggregate column
method. This method generally consists of driving a hollow pipe
(mandrel) into the ground without the need for drilling. The pipe
is fitted with a tamper head at the bottom which has a greater
diameter than the pipe and which has a flat bottom and beveled
sides. The mandrel is driven to the design bottom of column
elevation, filled with aggregate and then lifted, allowing the
aggregate to flow out of the pipe and into the cavity created by
withdrawing the mandrel. The tamper head is then driven back down
into the aggregate to compact the aggregate. The flat bottom shape
of the tamper head compacts the aggregate; the beveled sides force
the aggregate into the sidewalls of the hole thereby increasing the
lateral stresses in the surrounding ground.
[0007] The driven tapered mandrel method (U.S. Pat. No. 7,326,004)
is another means of creating an aggregate column with a
displacement mandrel. In this case, the shape of the mandrel is a
truncated cone, larger at the top than at the bottom, with a taper
angle of about 1 to about 5 degrees from vertical. The mandrel is
driven into the ground, causing the matrix soil to displace
downwardly and laterally during driving. After reaching the design
bottom of the column elevation, the mandrel is withdrawn, leaving a
cone shaped cavity in the ground. The conical shape of the mandrel
allows for temporarily stabilizing of the sidewalls of the hole
such that aggregate may be introduced into the cavity from the
ground surface. After placing a lift of aggregate, the mandrel is
re-driven downward into the aggregate to compact the aggregate and
force it sideways into the sidewalls of the hole. Sometimes, a
larger mandrel is used to compact the aggregate near the top of the
column.
[0008] U.S. Pat. No. 7,604,437 is related to a mandrel for making
aggregate support columns wherein flow restrictors are provided to
prevent upward movement of aggregate through the mandrel during
driving of the mandrel. The mandrel contemplated in this art
relates to formation of an aggregate support column such as
described in U.S. Pat. Nos. 6,425,713 and 7,226,246 discussed
above.
[0009] U.S. Pat. Nos. 4,992,002 and 6,773,208 relate to methods for
casting a partially reinforced concrete pier in the ground. One
method involves the use of an elongate mandrel with a cupped foot
having a larger cross-sectional area than the mandrel, wherein
flowable grout that is placed in the mandrel flows through openings
located near the bottom of the mandrel into the space between the
mandrel and the foot. The other method involves the installation of
an elongate hollow tubular casing that is then filled with fluid
concrete that is allowed to set while the casing remains in the
ground. Each of these references is merely to concrete hardened
inclusions and does not allow for the additional stability and
strength provided by a pier that has an expanded base.
[0010] In the area of soil improvement, it is often desirable to
install a stiff inclusion into the ground to transfer loads through
a soft or weak soil layer. Although these soil layers may also be
treated by non-cementitious aggregate columns, non-cementitious
columns are typically confining-stress dependent (i.e., they rely
on the strength of the sidewall soils to prevent bulging).
Occasionally, it is desirable to utilize cementitious inclusions to
bypass weak soils and transfer loads to underlying strong soils.
The object of the present invention is to efficiently form a strong
and stiff expanded base (either cementitious or non-cementitious)
at the bottom of the column and to provide an efficient means for
the introduction of grout, concrete, post-grouted aggregate, or
other cementitious material through the upper portions of the
column to form a cementitious inclusion.
BRIEF DESCRIPTION OF INVENTION
[0011] The present invention relates to a system for constructing a
support column. A mandrel has an upper portion and a tamper head. A
feed tube extends through the mandrel for feeding aggregate,
concrete, grout, or other flowable materials to the tamper head.
The tamper head includes a lower enlarged chamber with a reducing
surface at an upper portion thereof for compacting aggregate or
concrete and restricting upward flow of aggregate or concrete. The
tamper head is of a size providing an enclosed region for allowing
cementitious materials to be placed therein.
[0012] A method of constructing such support columns with the
system is also disclosed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The invention will be better understood from the following
detailed description made with reference to the drawings,
wherein:
[0014] FIG. 1 is a side cross-section view of a first embodiment of
a mandrel;
[0015] FIG. 2 is a side cross-section view of a second embodiment
of the mandrel with a valve;
[0016] FIG. 3 is a side cross-section view of a third embodiment of
the mandrel with internal upward flow restrictors;
[0017] FIG. 4 is a side cross-section view of a fourth embodiment
of the mandrel with a grout return pipe;
[0018] FIG. 5 illustrates a method of constructing a pier with the
mandrel of FIG. 1;
[0019] FIG. 6 illustrates an alternate method of constructing a
pier with one embodiment of the mandrel of the invention;
[0020] FIG. 7 is a side cross-section view of an alternative
embodiment of the mandrel using a closed top system to allow air
pressure to build;
[0021] FIG. 8 is a more detailed view of the operation of a closed
top system including use of an external air source; and
[0022] FIG. 9 is a graph showing results of load tests performed on
columns made according to Example I as compared to reference
piers.
DETAILED DESCRIPTION OF THE INVENTION
[0023] With reference to the attached figures, various embodiments
of a new and novel mandrel for forming an expanded base pier, as
part of a hardened inclusion, is provided.
[0024] FIG. 1 illustrates an embodiment of a base mandrel
contemplated herein. In this embodiment, a tamper head (2) is
formed as a unitary structure attached to one end of a feed tube or
pipe (4) to form the mandrel assembly (1). The feed pipe (4) can
typically be 4'' to 12'' in diameter and has an upper end (not
shown) opposite the tamper head (2) in which aggregate, concrete,
grout, and other flowable material can be fed. The tamper head (2)
typically comprises an enlarged lower chamber (3), typically 10''
to 24'' in diameter. The reducing surface (5) from the lower
chamber walls to the feed pipe walls serves the function as a
compaction plate for compacting aggregate or concrete as described
hereinbelow, as well as serving as an upward flow restrictor while
the initial aggregate is being driven such that the aggregate or
concrete forms a "plug" within the chamber (3) and does not flow
back up into the feed pipe (4). The lower chamber (3) at the bottom
of the head allows for formation of a densified bottom expanded
base and provides an enclosed area for the placement of grout or
concrete. Stiffeners (6) can also be placed between the feed pipe
(4) and lower chamber (3) to assist in load transfer during
driving.
[0025] FIG. 2 illustrates an embodiment of a base mandrel similar
to FIG. 1, but includes a special valve mechanism (7) that may be
used to further block the flow of aggregate or concrete from the
lower chamber (3) into the feed pipe (4). The valve mechanism (7)
seats against the reducing surface (5) of the feed pipe (4) and
physically restricts the flow of aggregate, or concrete, back up
into the feed pipe during downward driving (as opposed to the
"plug" formed as described above with reference to FIG. 1). When
the feed pipe (4) is lifted, the valve mechanism (7) opens to allow
the downward flow of grout, concrete, or other flowable material
through the feed pipe (4) and into the lower chamber (3). The valve
mechanism (7) may be manipulated by a pipe extending to the top of
the mandrel or by a mechanism that pins the valve mechanism (7) to
the sidewalls of the feed pipe (4).
[0026] The purpose of the valve mechanism (7) envisioned with
reference to FIG. 2 is to allow subsequent compaction of the bottom
aggregate or concrete expanded base initially placed and formed.
For instance, the mandrel would first be driven in the ground with
the lower chamber (3) charged with aggregate or concrete. The feed
pipe (4) would then be lifted, and the valve mechanism (7) would
open. Grout or concrete would then be added through the feed pipe
(4). The mandrel assembly (1) would then be driven back down,
thereby allowing for further compaction of the aggregate or
concrete at the bottom to form an expanded base.
[0027] FIG. 3 illustrates another variation of the embodiment of
FIG. 1. More specifically, chain links (8) are attached within the
tamper head (2) so that upon tamping, the chain links (8) move
inward to constrict the aggregate or concrete in the lower chamber
(3) and restrict aggregate or concrete from flowing upward into the
feed tube (4). It is also envisioned that internal notches may be
provided in lieu of chains in order to provide non-mechanical (or
passive) upward flow restriction.
[0028] FIG. 4 illustrates a further embodiment of a mandrel similar
to that shown in FIG. 1 but which includes a special provision for
ensuring grout placement. Instead of having a single chute feed
pipe or tube (4) as shown in FIG. 1, the embodiment contemplated
with reference to FIG. 4 has a feed pipe including a primary feed
pipe (4) and a grout return pipe (9) that is used to ensure that a
continuous column of grout is installed. Positive flow of grout
from the top of the grout return pipe (9) demonstrates that the
mandrel is full of grout before or during mandrel extraction
(lifting) operations.
[0029] A method of use is shown with reference to FIG. 5, which
shows an installation sequence with the base mandrel depicted in
FIG. 1. Step A shows placing a mound (10) of the aggregate on the
ground surface. Step B shows driving the mandrel assembly (1)
through the mound (10) of aggregate (to form an initial charge of
aggregate) and to the final driving elevation. During the driving
process, the aggregate in the lower chamber (3) forms a plug (11)
in the neck of the feed pipe (4) at the bottom of the tamper head
(2). Step C shows lifting of the mandrel assembly (1) wherein the
aggregate plug (11) or initial charge remains in place at the
bottom of the hole (it is understood that the initial charge may
also be added after driving of a closed tamper head, such as with a
sacrificial cap covering the bottom opening of the tamper head).
Step D shows re-driving the mandrel assembly (1) one or more times
to compact the aggregate at the bottom of the hole and to form an
expanded base (12). Grout or concrete (13) may then be pumped
through the feed pipe as shown. Step E shows placing grout or
concrete (13) from the element up from the bottom while removing
the mandrel. When the grout return pipe (9) as shown in FIG. 4 is
used in conjunction with Step E of the construction process shown
in FIG. 5, grout continuity within the mandrel shaft is determined
if grout continues to flow out of the grout return pipe (9) during
extraction. The finished support column comprises an expanded base
with a cementitious inclusion located thereon.
[0030] An alternative method of use can also be shown with
reference to FIG. 5. Step A consists of filling the lower chamber
(3) of the tamper head (2) with concrete (13). This may be achieved
by driving the tamper head (2) through a mound (10) of concrete
(13) as shown on FIG. 5 or by pumping concrete (13) through the
feed tube (4) while the tamper head (2) is resting on the ground
surface. In this case, the ground surface seals the concrete (13)
from flowing out of the bottom of the lower chamber (3). As shown
in FIG. 5, the tamper head (2) is then driven to design elevation
with the concrete (13) at the bottom of the tamper head (2) forming
a plug at the bottom of the assembly mandrel (1). The valve
mechanism (7) shown in FIG. 2 or the chain links (8) shown in FIG.
3 may be used within the tamper head (2) to facilitate plugging.
Step C shows the retraction (lifting) of the assembly (2) to allow
the concrete to flow out of the bottom of the tamper head (2). Step
D shows the placement of concrete (13) through the feed pipe (4)
and the subsequent or simultaneous lowering of the mandrel assembly
(1) onto the previously placed concrete (13) to force the concrete
(13) outward thus forming an expanded base (12). Step E shows the
simultaneous placement of grout or concrete (13) through the feed
tube (4) while extracting the mandrel assembly (1) to the ground
surface. This technique forms an expanded base pier comprised of
concrete (13) at the expanded base (12) and concrete (13) within
the pier shaft (or inclusion) on top of the expanded base (12).
[0031] The benefits of the system contemplated herein are the
efficient formation of an expanded base (12) that allows load to be
transferred to the bottom of the pier and the very quick and
efficient formation of the grouted inclusion by rapidly raising the
mandrel while placing grout or concrete (13). While the method
sequence of FIG. 5 depicts the use of the base mandrel shown in
FIG. 1, it is envisioned that the method could principally be used
with any of the mandrels shown in FIGS. 1-4.
[0032] FIG. 6 shows an alternative construction sequence where
Steps A through C are as described above. In Step D, the mandrel
assembly (1) is lowered to compact the aggregate and a secondary
disposable pipe (14) is inserted into the mandrel assembly (1) to
rest on the expanded base (12). In Step E the mandrel assembly (1)
is raised and additional aggregate (15) is allowed to fill the
annular space between the disposable pipe (14) and the sidewall of
the cavity (16). The aggregate (15) placed in this step is not
compacted. In Step F the disposable pipe (14) is then used as a
conduit to place grout into the inclusion by filling the voids in
the loose aggregate (15) around the disposable pipe (14).
Typically, the disposable pipe (14) is not removed but can be cut
at ground level or just below ground level and made part of the
permanent inclusion. A hopper (17) can be used to place the
aggregate (15) within the feed pipe (4).
[0033] FIG. 7 illustrates a further embodiment of a mandrel similar
to that shown in FIG. 1 but which includes a closed system for the
placement of concrete, grout, or other flowable materials. The
mandrel of this embodiment includes an external feed tube (18) that
enters the mandrel feed tube (4) near the top of the mandrel to
allow for the passage of a flowable material (19). The external
feed tube (18) is used to pump concrete, grout, or other flowable
materials into the primary feed tube (4). The top of the mandrel is
sealed with a top plate (21) making this a closed system. An air
pressure gage (20) may optionally be installed to measure the
internal air pressure within the mandrel and allow for the use of a
pressure release valve (22) to facilitate removal of excess
internal pressure during pumping. The mandrel system of FIG. 7 may
be used in conjunction with the construction sequences shown in
FIG. 5.
[0034] FIG. 8 illustrates yet another embodiment of the mandrel
similar to that shown in FIG. 7. In this embodiment, an air source,
such as compressor (24), may optionally be used to apply elevated
air pressure to trapped air (23) within the mandrel feed pipe (4)
to evacuate concrete (13) from the mandrel.
[0035] The following examples illustrate further aspects of the
invention.
Example I
[0036] As an example, an embodiment of the system of the present
invention was used to install a support column, also described
herein as an Expanded Base Pier ("EBP"), at a test site in Iowa.
The test site was characterized by 4 feet of sandy lean clay
underlain by sand. This testing program was designed to compare the
load versus deflection characteristics of this embodiment of the
EBP to reference piers constructed in successive lifts, such as a
pier constructed by the tamper head driven mandrel method. The
reference piers of this example had a nominal diameter of 20 inches
and an installed length of 23 feet. One reference pier was
constructed of aggregate only to a diameter of 20 inches. Another
reference pier was constructed with a grout additive, commonly
referred to as grouted pier, to a diameter of 14 inches.
[0037] In this embodiment of the invention, the EBP was formed by
filling the extractable mandrel (FIG. 1) with a combination of open
graded aggregate and fluid grout. The mandrel had a lower chamber
(3) outside diameter of 14 inches and a feed pipe outside diameter
of 12 inches. The mandrel of this embodiment was connected at its
open end (opposite the tamper head) to an open hopper for filling.
The full mandrel was then advanced to a depth of 23 feet below the
ground surface. The mandrel assembly was then raised 3 feet and
lowered 3 feet a total of 3 times to form a bottom expanded base.
Each raising and lowering of the mandrel is referred to as a
"stroke." The mandrel was then raised 3 feet, lowered 2 feet, and
then slowly extracted to the ground surface allowing a column of
grout and aggregate to be placed in the cavity created during
mandrel installation. The EBP was constructed with a base diameter
of 20 inches, and a shaft diameter of 14 inches. Once the mandrel
was fully extracted, a 1 inch diameter reinforcing steel rod was
inserted the full length of the EBP. A concrete cap was then poured
above the EBP to facilitate load testing.
[0038] The extractable mandrel of this embodiment 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.
[0039] The reference pier and the EBP were load tested using a
hydraulic jack pushing against a test frame. FIG. 9 shows the
results of the load test compared with the reference piers. At a
top of pier deflection of 0.5 inches, the reference pier with
aggregate supported a load of about 23,300 pounds, the reference
pier with grout supported a load of about 50,000 pounds, and the
EBP supported a load of about 70,300 pounds. At a top of pier
deflection of 1 inch, the reference pier with aggregate supported a
load of about 38,800 pounds, the reference pier with grout
supported a load of about 62,700 pounds, and the EBP supported a
load of about 97,000 pounds. The load carrying capacity of the pier
constructed in accordance with this embodiment of the present
invention showed a 2.5 to 3 fold improvement when compared to a
reference pier with aggregate, and a 1.4 to 1.5 fold improvement
when compared to a reference pier with grout. The difference in the
behavior relative to the grouted pier is caused by the formation of
the bottom expanded base during the construction of the EBP.
Example II
[0040] As another example, the system of another embodiment of the
present invention was used to install five EBP elements at a test
site in Virginia. The test site is characterized by hard clay.
Prior to installation of the EBP, 30 inch diameter drill holes were
excavated to a depth of 8 feet below the ground surface. The voids
were then loosely backfilled with sand. The EBP elements of this
example were formed within the backfilled holes.
[0041] In this embodiment of the invention, the EBP was formed by
filling the mandrel described in FIG. 7 with concrete. The mandrel
of this embodiment featured a "closed top" as opposed to the "open
hopper" configuration as described with reference to Example I. The
full mandrel was then advanced to a depth of 8 feet below the
ground surface. The mandrel was then raised 3 feet, and then
lowered 2 feet for three repetitions to create the expanded base. A
process of raising the mandrel 3 feet, and then lowering 1 foot was
then used to complete the full length of the pier. Once the
concrete had cured, each of the piers was excavated and the pier
base and shaft diameters were measured.
[0042] The lower chamber in this embodiment had a nominal 12 inch
diameter outer dimension. The excavated and measured piers had an
average nominal diameter of 18 inches. Expanded bases at the
bottoms of the piers exceeded 24 inches demonstrating the
effectiveness of this construction technique.
[0043] The mandrel in this embodiment was attached to a similar
hammer as in the embodiment of Example I.
[0044] 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 nor its absence is intended to limit the scope of
the applicant's invention or the scope of the claims. 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. The definitions are intended as a part of
the description 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.
* * * * *