U.S. patent application number 16/867268 was filed with the patent office on 2020-08-20 for threaded truss foundations and related systems, methods and machines.
The applicant listed for this patent is Ojjo, Inc.. Invention is credited to Charles Almy, Tyrus Hudson, Jack West.
Application Number | 20200263723 16/867268 |
Document ID | 20200263723 / US20200263723 |
Family ID | 1000004799220 |
Filed Date | 2020-08-20 |
Patent Application | download [pdf] |
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United States Patent
Application |
20200263723 |
Kind Code |
A1 |
Hudson; Tyrus ; et
al. |
August 20, 2020 |
Threaded truss foundations and related systems, methods and
machines
Abstract
A screw anchor for a trussed foundation system to support
single-axis trackers and other structures and related methods of
driving such a screw anchor into underlying ground. A hollowed tube
of uniform diameter is open at both ends with a thread form
beginning at one end and circumscribing a portion the tube, the
thread form having a tapered lead-in. The open-ended geometry
allows a mandrel or rock drill to be inserted and operated through
the anchor during driving to expedite the driving process. The
tapered thread form provides a lead-in for driving the anchor into
a rock bore.
Inventors: |
Hudson; Tyrus; (Petaluma,
CA) ; Almy; Charles; (Berkeley, CA) ; West;
Jack; (San Rafael, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ojjo, Inc. |
San Rafael |
CA |
US |
|
|
Family ID: |
1000004799220 |
Appl. No.: |
16/867268 |
Filed: |
May 5, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16416022 |
May 17, 2019 |
10697490 |
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16867268 |
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62702879 |
Jul 24, 2018 |
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62718780 |
Aug 14, 2018 |
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62726909 |
Sep 4, 2018 |
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62733273 |
Sep 19, 2018 |
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62748083 |
Oct 19, 2018 |
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62752197 |
Oct 29, 2018 |
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62756028 |
Nov 5, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16B 19/1045 20130101;
F24S 30/425 20180501; F16B 25/00 20130101; F16B 25/0084 20130101;
F16B 25/0094 20130101; F16B 25/0026 20130101; F24S 2030/10
20180501 |
International
Class: |
F16B 25/00 20060101
F16B025/00; F16B 19/10 20060101 F16B019/10 |
Claims
1. A screw anchor formed by the steps of: forming a hollow,
open-ended tube of steel having a substantially uniform inside
diameter; attaching an external thread form beginning at a first
end of the tube and terminating at a point along the tube's length;
and attaching a driving coupler at a second, opposing, end of the
tube, wherein the external thread form has a tapered lead-in.
2. The screw anchor formed by the steps of claim 1, further
comprising the step of applying an anti-corrosion coating to the
screw anchor.
3. The screw anchor formed by the steps of claim 2, wherein the
anti-corrosion coating is a galvanizing coating.
4. A method of forming a screw anchor comprising: forming an
elongated section of tubular steel having open ends and a
substantially uniform inside diameter; attaching a driving coupler
to a first end of the elongated section; and attaching an external
thread form to the elongated section of tubular steel, beginning at
a first end and terminating at a point along the section, wherein
the external thread form has a tapered lead-in.
5. The method according to claim 4, further comprising dipping the
formed screw anchor in an anti-corrosion solution.
6. The method according to claim 5, wherein the anti-corrosion
solution is a galvanizing solution.
7. A process for forming a component for a solar foundation
comprising the steps of: forming an elongated section of metal
tube, the elongated section having a substantially uniform inside
diameter and remaining open at opposing ends; forming a driving
feature at one end of the elongated section; beginning at an
opposing end of the elongated section, forming an external thread
form that terminates at a point along the elongated section; and
imparting a tapered lead-in to the external thread form.
8. The process according to claim 7, further comprising the step of
submerging the formed foundation component in a corrosion
inhibiting solution.
9. The process according to claim 8, wherein the corrosion
inhibiting solution is a galvanizing solution.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. patent application Ser. No.
16/416,022 titled "Thread truss foundations and related systems,
methods and machines," filed May 17, 2019 which claims priority to
U.S. provisional patent application No. 62/702,879, filed Jul. 24,
2018, titled "FOUNDATION PIERS FOR AXIAL SOLAR ARRAYS AND RELATED
SYSTEMS AND METHODS," no. 62/718,780, filed Aug. 14, 2018, titled
"FOUNDATION PIERS FOR AXIAL SOLAR ARRAYS AND RELATED SYSTEMS AND
METHODS," no. 62/726,909, filed Sep. 4, 2018, titled "FOUNDATION
PIERS FOR AXIAL SOLAR ARRAYS AND RELATED SYSTEMS AND METHODS," no.
62/733,273, filed Sep. 19, 2018, titled "FOUNDATION PIERS FOR AXIAL
SOLAR ARRAYS AND RELATED SYSTEMS AND METHODS," no. 62/748,083,
filed Oct. 19, 2018, titled "FOUNDATIONS FOR AXIAL SOLAR ARRAY AND
RELATED SYSTEMS AND METHODS," no. 62/752,197, filed Oct. 29, 2018,
titled SYSTEMS, METHODS AND MACHINES FOR MANUFACTURING A FOUNDATION
PILE," and no. 62/756,028, filed Nov. 5, 2018, titled "CLOSED LOOP
FEEDBACK CONTROL FOR IMPROVED SOLAR PILE DRIVING AND RELATED
SYSTEMS, MACHINES AND CIRCUITS," the disclosures of which are
hereby incorporated by reference in its entirety.
BACKGROUND
[0002] Utility-scale solar power plants are predominantly
configured as fixed-tilt ground mounted arrays or single-axis
trackers. Fixed-tilt arrays are arranged in East-West oriented rows
of panels tilted South at an angle dictated by the latitude of the
array site--the further away from the equator, the steeper the tilt
angle. By contrast, single-axis trackers are installed in
North-South rows with the solar panels attached to a rotating axis
called a torque tube that move the panels from an East-facing
orientation to a West-facing orientation throughout the course of
each day, following the sun's progression through the sky. For
purposes of this disclosure, both fixed-tilt and single-axis
trackers are referred to collectively as axial solar arrays.
[0003] Excluding land acquisitions costs, overall project costs for
utility-scale arrays include site preparation (surveying, road
building, leveling, grid and water connections etc.), foundations,
tracker or fixed-tilt hardware, solar panels, inverters and
electrical connections (conduit, wiring, trenching, grid interface,
etc.). Many of these costs have come down over the past few years
due to ongoing innovation and economies of scale, however, one area
that has been largely ignored is foundations. Foundations provide a
uniform structural interface that couples the system to the
ground.
[0004] When installing a conventional single-axis tracker, after
the site has been prepped, plumb monopiles are driven into the
ground at regular intervals dictated by the tracker manufacturer
and/or the site plan; the tracker system components are
subsequently attached to the head of those piles. Most often, the
piles have an H-shaped profile, but they may also be C-shaped or
even box-shaped. In conventional, large-scale single-axis tracker
arrays, the procurement and construction of the foundations may
represent up to 5-10 percent of the total system cost. Despite this
relatively small share, any savings in steel and labor associated
with foundations will amount to a significant amount of money over
a large portfolio of solar projects. Also, tracker development
deals are often locked-in a year or more before the installation
costs are actually incurred, so any post-deal foundation savings
that can be realized will be on top of the profits already factored
into calculations that supported the construction of the
project.
[0005] One reason monopiles have dominated the market for
single-axis tracker foundations is their simplicity. It is
relatively easy to drive monopiles into the ground along a straight
line with existing technology. Even though their design is
inherently wasteful, their relatively low cost and predictable
performance makes them an obvious choice over more expensive
alternatives. The physics of a monopile mandates that it be
oversized because single structural members are not good at
resisting bending forces. When used to support a single-axis
tracker, the largest forces on the foundation are not from the
weight of the components, but rather the combined lateral force of
wind striking the solar panels attached to the array. This lateral
force gets translated into the monopile foundation as a bending
moment. The magnitude of the moment is much greater than the static
loading attributable to the weight of the panels and tracker
components. Therefore, when used to support single-axis trackers,
monopile foundations must be oversized and driven deeply into the
ground to stand up to lateral loads.
[0006] There are alternatives to monopiles available in the
marketplace but thus far they have not been cost competitive. For
example, in very difficult soils where costly refusals dominate,
some solar installers will use ground screws instead of H-piles. As
the name implies, a ground screw is essentially a scaled-up version
of a wood screw or self-taping metal screw, with an elongated,
hollow shaft and a tapered end terminating in a blade or point. The
screw also has a large, external thread form extending from the
tip, up the taper and even partially up the shaft to enable it to
engage with soil when screwed into the ground. Such a prior art
ground screw is shown, for example, in FIG. 1A. Ground screws like
the ground screw 10 in 1A are manufactured and sold by Krinner,
GmbH of Strasskirchen, Germany, among others. When installers
encounter rocky soils or must install over bedrock, they predrill
holes at the location of each ground screw and then drive the
screws into the pre-drilled holes, attaching above-ground
foundation hardware to the head of each screw.
[0007] When used in foundations for single-axis trackers, grounds
screws like that in FIG. 1A are typically installed in adjacent
pairs. The pairs are joined above-ground with an upside-down T
bracket that presents a monopile interface for the single-axis
tracker. This is seen, for example, in system 20 in FIG. 1B. Ft.
Meyers, Fla. based TERRASMART installs foundations like system 20
using Krinner ground screws. While this may mitigate the problem of
refusals, it does not optimize material savings and will only
pencil out where less expensive alternatives won't work. Vertical
foundations that support single-axis trackers must resist bending,
whether made from H-piles or ground screws. Referring to FIG. 2B,
when wind strikes the array, it generates a lateral force labeled
F.sub.L in the figure. The magnitude of this force is equal to
F.sub.L multiplied by the height of the pile above the point where
the foundation is pinned to the ground (e.g., does not move). This
force puts plumb foundation components into bending. Because
structural members are generally poor at resisting bending, they
must be overbuilt to withstand it.
[0008] Another proposed alternative to percussion driven H-piles
and vertical ground screws, uses a pair of ground screws driven at
acute angles to each other in an A-frame configuration. Unlike
plumb monopiles or the double-screw foundation of FIG. 1B, an
A-frame has the advantage of converting lateral loads into axial
forces of tension and compression in the legs. This is seen, for
example, in published U.S. patent application, 2018/0051915 (herein
after, "the '915 application"). FIG. 1C shows the system described
in the '915 application. In theory, such as system enables the legs
to be thinner than those used, for example, in the system of 1B,
because the legs are not subjected to bending. FIG. 2C is a force
diagram showing how lateral loads are translated in an A-frame such
as that in 1C. Lateral load F.sub.L puts tension on the windward
leg and compression on the leeward leg. System 30 is potentially an
improvement over plumb piles and parallel ground screws, however,
any system that uses standard ground screws is at a costs
disadvantage relative to other structures. Moreover, the ground
screw's closed geometry mandates a separate pre-drilling step where
direct driving is not possible. Therefore, in their current form,
and with conventional rotary driving and drilling equipment, it is
not possible for ground screws to achieve cost parity with monopile
foundations in anywhere other than in the worst soil conditions,
and even in those conditions, there is room for significant
improvement.
[0009] In recognition of these and other problems, it is an object
of various embodiments of this disclosure to provide a truss or
A-frame foundation for single-axis trackers and other applications
that realizes the benefits of ground screws in a less costly, more
robust, and flexible form factor, as well as machines and methods
for installing such foundations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1A shows a conventional ground screw;
[0011] FIG. 1B shows a conventional double ground screw foundation
for single-axis trackers;
[0012] FIG. 1C shows a steeply sloped A-frame foundation for
single-axis trackers using a pair of conventional ground
screws;
[0013] FIG. 2A is a ground screw supporting a monopile
foundation;
[0014] FIG. 2B is a force diagram showing how lateral loads are
translated in a monopile foundation;
[0015] FIG. 2C is a force diagram showing how lateral loads are
translated in an A-frame foundation;
[0016] FIGS. 3A-D show the manufacturing steps for a tapered ground
screw;
[0017] FIG. 4A shows a screw anchor according to various
embodiments of the invention;
[0018] FIG. 4B is a close-up view of the threaded end of the screw
anchor of FIG. 4A;
[0019] FIG. 4C shows a screw anchor according to various other
embodiments of the invention;
[0020] FIG. 5A is a cutaway view of a screw anchor and mandrel
during driving according to various embodiments of the
invention;
[0021] FIG. 5B shows a screw anchor being driven while a mandrel is
simultaneously hammered through the center of the screw anchor;
[0022] FIG. 6A shows a pair of adjacent screw anchors driven into
underlying ground to form the base of a truss foundation according
to various embodiments of the invention;
[0023] FIG. 6B shows a completed truss foundation supporting a
portion of a single-axis tracker according to various embodiments
of the invention;
[0024] FIG. 7A shows a refusal of a screw anchor and mandrel while
driving due to hitting bedrock according to various embodiments of
the invention;
[0025] FIG. 7B shows an intermediate step of a process for in-situ
refusal mitigation according to various embodiments of the
invention;
[0026] FIG. 7C shows the screw anchor of 7B after in-situ refusal
mitigation according to various embodiments of the invention;
[0027] FIG. 7D shows the screw anchor of 7B after an alternative
in-situ refusal mitigation technique according to various
embodiments of the invention;
[0028] FIG. 8 is a partial cutaway viewing showing an augured drill
shaft according to various embodiments of the invention;
[0029] FIGS. 9A-C shows various rock drill bits usable to perform
in-situ refusal mitigation according to various embodiments of the
invention;
[0030] FIGS. 10A and B are side and front view of a piece of heavy
equipment with an attachment for installing screw anchors according
to various embodiments of the invention;
[0031] FIG. 11 is a view of a portion of an attachment for driving
a screw anchor with a rotary driver and mandrel according to
various embodiments of the invention;
[0032] FIG. 12 is an exploded view of an assembly for actuating a
mandrel through a rotary driver and screw anchor according to
various embodiments of the invention;
[0033] FIG. 13 is a portion of a screw anchor according to various
embodiments of the invention; and
[0034] FIG. 14A-C are various views of a helical nut usable with a
screw anchor according to various embodiments of the invention.
DETAILED DESCRIPTION
[0035] The following description is intended to convey a thorough
understanding of the embodiments described by providing a number of
specific embodiments and details involving A-frame foundations used
to support single-axis solar trackers. It should be appreciated,
however, that the present invention is not limited to these
specific embodiments and details, which are exemplary only. It is
further understood that one possessing ordinary skill in the art in
light of known systems and methods, would appreciate the use of the
invention for its intended purpose.
[0036] As discussed in the Background, ground screws are one
alternative to conventional monopiles (e.g., H-piles, I-piles, post
and cement, etc.). Ground screws are screw into underlying ground
with a rotary driving using a combination of downward pressure and
torque, much like driving a screw into wood. Usually, they are
driven until they are completely or almost completely buried and
then other hardware such as mounting brackets, braces, or supports
may be attached to the portion remaining above-ground to support
signs, decks, small building frames, and single-axis solar trackers
among other structures.
[0037] Like any screw, the ground screw's pointed tip serves at
least two functions: one, it allows the screw to be precisely
oriented over the insertion point and provides a lead-in to help
keep it on path and to pull the screw into the ground when driving.
Second, the point and taper increase pressure around the threads as
the screw penetrates, helping them to better grip the soil. The tip
may also displace small rocks that could impede driving. All these
benefits, however, are realized during driving. After the screw is
in the ground, the tip serves little purpose and may be less
effective than the remainder of the of the screw at resisting axial
forces due to its tapered geometry. One reason why ground screws
are seldom used in large-scale single-axis trackers is that they
are relatively difficult and expensive to manufacture compared to
H-piles and therefore cost more. A process for making a ground
screw is shown, for example, in FIGS. 3A-D.
[0038] The process starts with cutting a length of rounded hollow
pipe to a desired length. Then, one end of the pipe is inserted in
an oven or electric heater and until it reaches a supercritical
temperature. The hot end is then inserted into a shrinking machine
that closes the tip imparts a taper and point. Once that cools, a
strip of metal is formed around the pipe in a thread pattern and is
welded to the pipe's surface. After it cools, the finished screw is
galvanized to complete the manufacturing process. The two
hot-forming steps require a large amount of input energy and the
welded thread form is much more expensive than equivalent structure
formed in a cold process. Also, the intermediate hot steps preclude
the use of metal that has been pre-galvanized. Post manufacturing
galvanization is much more expensive than starting with
pre-galvanized metal.
[0039] To a large extent, the way that ground screws are installed
and used requires that this expensive, multi-step manufacturing
process. Screws need a tip to assist with driving and monopiles
must be overbuilt to withstand bending forces that are orthogonal
to the axis of the screw. The system shown in the '915 application
overcomes the latter problem by translating the lateral load into
axial forces of tension and compression, however, the magnitude of
the tensile and compressive forces increases exponentially the
steeper the legs are angled (e.g., the smaller the apex angle
between the truss legs)--a fact not recognized in that '915
application. Therefore, even though the foundation shown in 1C may
avoid bending, the large axial forces generated by the steep angles
recommended will still require the ground screws to be overbuilt
relative to A-frames oriented as less steep legs or with a larger
apex angle. Moreover, because the system is built on ground screws,
it still suffers from the inherent cost disadvantages discussed
herein.
[0040] The inventors of this invention have proposed a foundation
system, particularly well-suited for axial solar arrays (e.g.,
single axis trackers and fixed-tilt ground mounted arrays), that
uses a pair of adjacent angled supports configured as a moderately
angled A-frame (below 72.5 degrees) instead of a single vertical
pile. The system is known commercially as EARTH TRUSS. FIG. 4A
shows the base EARTH TRUSS component, screw anchor 200. Screw
anchor 200 consists a section of elongated pipe having a
substantially uniform diameter along its length that is open at
both ends. These are important distinctions over conventional
ground screws. The bottom or below-ground end of screw anchor 200
has an external thread form beginning proximate the lower end that
increases in diameter as it extends up the pipe until it levels out
to a uniform diameter for several more rotations. This is seen in
greater detail in 4B, which shows only threaded portion 210 of
anchor 200. As is discussed in greater detail herein, the
significance of the tapered lead in may come in during driving as
well as when doing in-situ refusal mitigation. The other end of
exemplary anchor 200 in 4A has a connection portion 220, which in
this example, is shown as a coupling. Connecting portion 220 has
features that engage with the chuck of a rotary driver to enable
screw anchor 200 to be driven. Connecting portion 220 also has at
least one coupling feature to enable screw anchor 200 to be
connected to other components that extend along substantially the
same axis to make a two-piece leg.
[0041] It should be appreciated that in various embodiments, riving
features may instead be stamped into the upper end of screw anchor
200 rather than part of a separate attached element. Moreover, a
combination of camming and friction or other suitable mechanical
technique may enable screw anchor 200 to be rotated into the ground
without any driving features built into the upper end. In such
embodiments, a separate connecting portion may be used or coupling
elements may be built into other components above screw anchor
200.
[0042] FIG. 4C shows screw anchor 250 according to various other
embodiment of the invention. Screw anchor 250 differs from screw
anchor 200 in that the it has a slight taper to the tip rather than
having a tapered lead in on the external thread form. Although this
may be more expensive to manufacture than screw anchor 200, as long
as the opening at the tapered end is sufficiently large, it may
enjoy all of the other benefits of anchor 200 as discussed herein.
Other embodiments may utilize both a slightly tapered tip and
thread form with a tapered lead-in.
[0043] In various embodiments, a screw anchor such anchor 200 or
anchor 250 will be rotated into the ground using a rotary driver or
other like device. The rotary driver may rotate the screw anchor
from the top or may be partially or fully inserted into the pile to
rotate it partially from within. Because the various screw anchors
disclosed herein are open at both ends, and as discussed in greater
detail herein, it is possible, and may be desirable to insert
another tool into the shaft of the pile from above during driving
to clear a path ahead of the pile, to increase soil pressure around
the thread form, and even to excavate a cavity in solid rock to
receive the pile.
[0044] Turning to FIGS. 5A and B, various embodiments of the
invention take advantage of the open geometry of the screw anchor
to insert tools into it during driving. In various embodiments,
these tools may provide some of the benefits of a tip on a
conventional ground screw and yet due to the hollow body, do not
need to remain in the ground after the screw anchor is installed.
To that end, FIG. 5A is a partial cutaway view showing a portion of
exemplary screw anchor 200 with mandrel 300 extending through its
center. Mandrel 300 is an elongated member, preferably of high
strength steel and with a smaller outside diameter than the inside
diameter of screw anchor 200. In various embodiments, mandrel 300
may have a detachable tip 310 that is profiled for the specific
soil conditions present and to facilitate tip replacement without
discarding the entire mandrel. Mandrel 300 may be actuated to apply
downward pressure as screw anchor 200 is simultaneously rotated
around it. Alternatively, mandrel 300 may apply a hammering
force.
[0045] In various embodiments, the open geometry of screw anchor
200 makes it possible for tools such as a mandrel to be
independently operated within anchor 200 and to be removed after
driving is complete, leaving only those component required to
resist axial forces in the ground. As seen in FIGS. 5A and B,
during installation mandrel 300 may be inserted into the top end of
screw anchor 200, slid all the way down its length until it reaches
the opposing, below-ground end and actuated to push or hammer
against the underlying ground. In various embodiments, and as
discussed in greater detail herein, mandrel 300 may be connected to
a separate driver that is aligned on an axis overlapping with an
axis through the center of mass of screw anchor 200. Mandrel 300
may travel with screw anchor 200 as it is rotated in to prevent
soil from plugging into the center of screw anchor 200.
Alternatively, mandrel 300 may push downward ahead of the screw
anchor to help clear a path and create soil tension around external
thread form 210. This may be true whether the mandrel exerts stead
downward pressure, is reciprocated, or is hammered into the
underlying soil.
[0046] Reciprocating, hammering or simply pushing down with the
mandrel may also allow it to displace and/or break up smaller rocks
that are in the driving path. Without such action, rocks and other
obstructions may cause a refusal and/or damage screw anchor 200. In
the field of solar pile driving, a refusal occurs when additional
driving force fails to result in further embedment. Usually, this
indicates that the pile has struck a rock, cementious soil or, in
the extreme case, solid bedrock. By reciprocating, hammering or
pushing down with the mandrel, it functions as a chisel that can
crumble small rocks, buried objects and pockets of dense or
cementious soil. This is shown and discussed in greater detail, in
the context of FIGS. 7A-D.
[0047] Turning to FIGS. 6A and B, these figures show two stages of
installation of a pair of adjacent screw anchors and a truss
foundation for a single-axis tracker using such screw anchors
according to various exemplary embodiments of the invention. In 6A,
screw anchors 200 have been driven into the ground adjacent one
another and inclined inward at acute angles (e.g., less than
90-degrees). In various embodiments, and as shown here, they may be
driven until almost entirely embedded, so that only the end portion
remains above ground. As shown in FIGS. 5A and B, anchors 200 may
be driven through the unique process described herein whereby screw
anchor 200 is rotated into the underlying soil at the desired angle
with a combination of torque and downward pressure by a rotary
driver, while, at the same, time, a mandrel or other tool is
actuated through the screw anchor to assist driving. Once both
screw anchors 200 reach their respective target depths,
above-ground components are attached.
[0048] In the example of 6A and B, upper legs 225 are inserted over
connecting portions 220 to substantially extend the main axis of
each screw anchor 200 toward the bearing housing. Free ends of each
upper leg 225 are joined together to form a unitary A-framed-shaped
truss by adapter 230. In various embodiments, and as shown here,
adapter 230 may have a pair of symmetric connecting portions that
extend down and away from the adapter to match the spacing and
angle of upper legs 225. A bearing assembly, such as assembly 240
is attached to the top of adapter 230 and torque tube 245 rotatably
captured within bearing 242.
[0049] Turning now to FIGS. 7A-D, these figures show various
driving scenarios with a screw anchor and system for driving a
screw anchor according to various exemplary embodiments of the
invention. Starting with 7A, in this figure screw anchor 200 is
driven into the supporting soil underlying the anchor. In various
embodiments, and as discussed and shown herein, this is
accomplished with a rotary driver or screw driving machine. At
substantially the same time, mandrel 300 is actuated through screw
anchor 200 to press down, hammer and/or reciprocate against the
soil as anchor 200 travels along its path. In various embodiments,
and as shown in the figure, mandrel tip 310 may project out of the
below-ground end of screw anchor 200 as it is driven. In some
embodiments, it may stay at substantially the same position
relative to the lower end of anchor 200, traveling down with anchor
200 to displace soil and increase soil pressure around the anchor's
threads. In other embodiments, mandrel tip 310 may exert downward
pressure independent of the pile. If the rotary driver encounters
excessive driving resistance as indicated, for example, by a
reduction or stoppage in downward travel or excessive resistance
against the rotary driver or both, mandrel 300 may be partially
retracted so that tip 310 no longer projects out of the anchor to
allow dirt to plug in the end, thereby relieving the soil pressure
retarding driving. This reduction in pressure may reduce resistance
to the rotary driver. It is important when screwing a pile or
ground screw into the ground that the pile continues moving forward
so that it doesn't auger or core the hole, which will reduce the
pile's resistance to axial forces.
[0050] At some point while driving, mandrel tip 310 in 7A
encounters solid bedrock resulting in a refusal. In various
embodiments, a unique in-situ refusal mitigation process begins
that was previously impossible in the prior art with conventional
ground screw or with H-piles. The refusal condition may in various
embodiments be detected by an operator or by an automated feedback
loop sensing the failure of the mandrel or anchor to penetrate any
further. In various embodiments, the operator will remove the
mandrel from anchor 200 and replace it with a rock drill such as
drill 400. In some embodiments, the rock drill may be a different
attachment to the same driver actuating the mandrel. In other
embodiments, the rock drill may be a different machine, requiring
the mandrel driver to be pivoted or otherwise moved out of the way
to make room for the rock drill. Once out, mandrel 300 is replaced
with a drill shaft 400 and rock drill bit 410. These components are
inserted into the top end of anchor 200 and passed through it until
reaching the bedrock below. In various embodiment, the same driver
used to actuate the mandrel is used to actuate the rock drill. The
rock drill may consist of a down-the-hole hammer and bit that uses
compressed air to hammer the bit inside of anchor 200.
Alternatively, the rock drill may be a top hammer whereby hammering
action is applied to shaft 400 and this force is directly
translated to rock bit 410.
[0051] As is known in the art, rock drills typically use
pressurized air to generate the hammering action and to blow the
crushed rock spoils out of the way. The specific action of the rock
drill (e.g., hammering, rotating) will in part be dictated by the
type of drill bit used. For example, a button bit typically employs
hammering action alone whereas other types of bits may rely on a
combination of hammering and rotary cutting.
[0052] In various embodiments the rock drill will continue its
action until a cavity has been formed in the rock having the
desired depth. This depth may be the minimum depth required to
secure the screw anchor or the original target depth. In either
case, once the cavity is crated, the rock drill is removed, or
least partially withdrawn from anchor 200 so as not to project
below it and the rotary driver is engaged to drive the anchor into
the newly formed cavity. In various embodiments, the tapered
lead-in on the threads will increase the likelihood that the
application of torque and downward pressure on anchor 200 will
guide it into the cavity. In some embodiments, screw anchor 200 may
be driven all the way to the bottom of the cavity, such as shown in
7C. This will depend on the size of the bore relative to the
outside diameter of the anchor, how clean and free of spoils the
cavity is, and the geometry and dimensions of the thread form. In
other embodiments, anchor 200 may not be able to be fully driven to
the bottom of the cavity. This may be a consequence of the blind
underground conditions (e.g., cleanliness of the borehole, density
of soil above the borehole) or the dimensions of drill bit 410 or
threads. In either case, it may only be possible to drive a portion
of anchor 200 into the cavity. In some cases, driving anchor 200 as
deeply as possible may provide sufficient engagement between the
anchor threads and the wall of the cavity without additional steps.
This could, in various embodiments, be confirmed by pulling up on
anchor 200 with the rotary driver or another tool with a fixed
force. In other cases, if sufficient engagement between the threads
and the wall of the cavity is not achieved, additional steps may be
required.
[0053] To that end, drill shaft 400 and bit 410 may be withdrawn
from driven anchor 200 and a coupler or other device such as
coupler 430 may be dropped down anchor 200 until it reaches the
bottom of the cavity. In various embodiments, coupler 430 may be a
piece of rebar or other rigid material that is small enough to fit
within anchor 200 but long enough to extend from the bottom of the
cavity into anchor 200. The purpose of coupler 430 is to connect
anchor 200 to the underlying rock. One or more centralizers 435 or
other like devices may be used to maintain coupler 430's
orientation within the center of anchor 200 as well as in the
cavity. After coupler 430 is placed, a volume of pressurized grout,
epoxy or other suitable material 440 may be injected via the
above-ground end of anchor 200, filling the cavity completely and
surrounding coupler 430 and the portion of anchor 200 containing
the coupler. Once material 440 sets, anchor 200 will be firmly
coupled to the bedrock.
[0054] FIG. 8 shows an augered drill shaft usable with various
embodiments of the invention. Depending on the type of bit used and
whether a top hammer or bottom hammer is used, it may be necessary
and/or desirable to use mechanical energy to remove spoils
generated by the drill from the shaft of anchor 200. To that end,
drill shaft 402 includes a series of helical threads circumscribing
some, most or all of its length. These threads will tend to move
material up and out of the inside of anchor 200 when the shaft is
rotated in the correct direction (clockwise in the exemplary shaft
402 shown in the Figure). Also shown is male threaded portion 405
at the base of shaft 402 for attaching different drill bits. It
should be appreciated that threaded portion 405 is exemplary only
and meant merely to signify that tips may be removed from shaft 405
without needing to discard the entire shaft. In other embodiments,
a female opening, a pin connection, conical threads, or other known
fastening mechanisms or their functional equivalents may be used
instead.
[0055] Turning now to FIGS. 9A-C, these figures show several
different drill bits that may be used with various embodiments of
the invention. The first bit, bit 410A is a cross bit or cross rock
bit. It consists of four raised chisel-type blades oriented in a
cross pattern. This type of bit is typically made of steel with the
blades coated with titanium or made from hardened steel or carbide.
The bit may be hammered and rotated to chisel and scrape through
rock while the spoils are evacuated via the space between the four
blades. FIG. 9B shows tri-cone roller bit 410B. The tri-cone roller
bit has three rotating cone-shaped wheels covered in steel or
carbide cutting teeth that are attached to a stationary head via a
bearing connection. As the drill is rotated, these cones roll along
the bottom of the bore hole in a circular pattern chipping away at
the underlying rock. Downward pressure on the bit facilitates the
cutting. Such bits are commonly used in water, gas and oil
exploration and extraction. Spoils are drawn up an annulus in the
center of the bit with compressed air or fluid. The last bit shown
in 9C is percussion-type hammer bit 410C. Hammer bits are not sharp
and do not use cutting as their primary boring mechanism. Rather, a
series of hardened carbide buttons are embedded in the face of the
bit. During rotation, a shank beats against an anvil or strike
surface inside the bit head causing the buttons to pulverize any
rock they come into contact with while rotation and compressed air
sweeps the debris out of the way and into debris channels so that
the next impact will again strike virgin rock. Any of the bits
shown in FIGS. 9A-C, or any other commercially available or as of
yet undeveloped bits may be used with the various embodiments of
the invention.
[0056] In certain situations where drilling is required, it may be
desirable to drill a cavity that has a slightly larger outside
diameter than the base pile. For example, to create a cavity that
is wide enough to at least partially accept the threaded end 210 of
screw anchor 200. To that end, bit 410C in FIG. 9C is one type of
bit capable of drilling a larger diameter hole than the casing it
is inserted in. This technique is often employed in drill-and-case
applications where the diameter of the bore needs to be larger than
the diameter of the casing to allow spoils to be ejected around the
outer diameter of the pipe among other reasons. Bit 410C
accomplishes this with one or more deployable wings, labeled "W" in
the figure, that expand the cutting diameter of the bit once the
bit is free of the anchor. When bit 410C is initially inserted into
the end screw anchor 200, the one or more wings are recessed to be
flush with the outside surface of the bit. This can be done
mechanically or by an operator compressing them as the bit is
inserted into the anchor. When the bit emerges from the other end,
and the wings are no longer compressed by the inner surface of the
anchor, so they expand to their relaxed position, either under
spring action or via another deployment mechanism, thereby
increasing the cutting diameter of the bit. In various embodiments,
additional carbide buttons may be formed on the cutting surface of
the wings (e.g., the surface that is normal to the direction of
drilling). In various embodiments, if the wings are spring loaded,
the resistance from the rock will tend to keep them out, that is,
at the expanded orientation. Once the desired depth has been
achieved and the bit and shaft are drawn back into the bottom end
of the anchor, pressure against the back of the one or more wings
from the anchor opening will push them back to the recessed
position, reducing the outside diameter of the bit, allowing it to
be drawn up and out of the anchor. It should be appreciated that
there are various other bits available for undercut drilling,
including ones that are intentionally offset so that once they
begin to rotate they sweep around a larger diameter circle.
[0057] Contrary to the cementious and/or rocky soils that lead to
refusals, some soils may be so loosely structured that they provide
very little resistance to driving, but at the same time, lack the
ability to resist axial forces of tension and compressions. In such
soils, threaded screw anchor 200 alone may need more orthogonal
surface area to provide the required resistance. To that end, FIGS.
14A-C show a helical nut according to various embodiments of the
invention that may be usable with a screw anchor such as screw
anchor 200 in FIG. 13 to increase the anchors ability to resist
axial forces in such soils. Starting with 14A and B, these figures
show helical nut 270 according to various exemplary embodiments. As
shown, helical nut 270 consists of main body portion 272 and helix
274. As seen in the cutaway view of 14B, the inside of main body
portion 272 is threaded. In various embodiments, the depth and
pitch of these threads will match the pitch and depth of external
threads 210 on anchor 200. This will enable helical nut 270 to be
spun onto anchor 200 until the tapered lead-in of the thread form
projects further than the female thread depth in helical nut 270.
When anchor 200 is driven into underlying ground with helical nut
270 attached, clockwise rotation of the anchor will reinforce
rather than loosen the connection between nut 270 and threaded
portion 210. The outside diameter of helix 274 can substantially
increase the amount of orthogonal surface area, creating a column
or cone of resistance to pull-out and making it very difficult to
further compress anchor 200 after it's driven.
[0058] FIG. 14C shows another embodiment of a helical nut usable
with a screw anchor according to various exemplary embodiments of
the invention. Nut 280 of 14C consist of threaded retaining nut 282
and separate helix 280. In various embodiments, helix 280 has a
pitch that matches the pitch of the threads on threaded portion 210
and a center opening slightly larger than the outside diameter of
anchor 200 so that helix 280 can be threaded up anchor 200 to a
desired location. Then, threaded retaining nut 282, which
preferably has threads substantially matching those of helical nut
272, that is, threads that are the same pitch and depth of threaded
portion 210 so that retaining nut 282 can also be threaded onto
threaded portion 210 to press helix 285 against the external
threads at the desired location and to capture it there. Driving
the resulting helical screw anchor may be performed in the same
manner as described herein.
[0059] Up to this point, the disclosure has focused on screw
anchors and techniques for driving the screw anchor. The remainder
of this disclosure will focus on exemplary machines and methods of
operating machines to drive screw anchors into supporting ground
while actuating a mandrel or rock drill through the screw anchor
according to various embodiments of the invention. It should be
appreciated that machines shown in these figures are exemplary only
and should be considered in terms of their functionality with
respect to driving screw anchors rather than their physical
attributes as shown in the drawings. Different physical embodiments
are possible while retaining the spirit and scope of the various
embodiments of the invention.
[0060] Turning to FIGS. 10A and 1B, these figures show side and
front views respectively of exemplary machine 600 for driving screw
anchors according to various embodiments of the invention. As
shown, machine 600 includes a main body 605 riding on a tracked
chassis 610. It should be appreciated that machine 600 could
instead have tires, a combination of tires and tracks, one or more
floating pontoons, rails or other known means. As shown, machine
600 has an attachment, attachment 500, mounted to the end of
articulating arm 620. In various embodiments, articulating arm 620
is part of the base machine and can move through an arc of
approximately 90 degrees from a stowed position where the arm is
substantially perpendicular to the ground to an in-use position
where the arm is substantially parallel to the ground. In various
embodiments, the end of articulating arm 620 is also able to rotate
through a range of angles about its axis (e.g., .+-.35-degrees from
vertical) so that screw anchors may be driven into the ground at
non-plumb angles. This also decouples the screw anchor driving axis
from the orientation of the machine by allowing it to compensate
for uneven terrain in at least the East-West direction.
Alternatively, a rotator may be located at the end of arm 620 so
that the entire arm does not have to rotate in order to rotate
attachment 500. In various embodiments, the end of articulating arm
620 supports driving attachment 500 with a main axis that may be
substantially perpendicular to articulating arm 620. Therefore,
when arm 620 is in the stowed position, attachment 500 will be
substantially parallel to the ground, minimizing its height,
whereas when arm 620 is in the in-use position, driving attachment
500 will be substantially perpendicular to the ground.
[0061] As shown in the example of FIGS. 10A/10B, attachment 500
includes frame 510 that functions as a scaffold to support rotary
or screw driver 550 and mandrel driver 520, and that provides a
common axis for them to move along. In various embodiments, frame
510 includes a pair of parallel side members 510A/B that are
interconnected by cross members. This configuration is exemplary
only. Various trussed and/or reinforced supports, beams and cross
members may be used to provide the requisite rigidity and strength.
Frame 510 may also include one or more tracks that the mandrel
driver and rotary driver travel on to limit their movement to axial
movement only. The one or more tracks may be located between
parallel side member 510A/B, or, alternatively, as shown in the
figures, may be attached to the side members 510A/B. In still
further alternatives, mandrel driver 520 and rotary driver 550 may
travel on wheels inside recesses formed in parallel side members
510A/B. The specific mechanism used to limit movement to a single
axis along attachment 500 is a design choice.
[0062] In various embodiments, one or more linked drive chains and
corresponding motor assemblies may be used to move mandrel driver
520 and rotary driver 550 along the one or more tracks. In various
embodiments, they may move independent of one another. In other
embodiments, they may move together. In still further embodiments,
both modes may be possible. For example, when driving, rotary
driver 550 will apply torque while a motor driving chain 515 will
generate downforce that is translated to the anchor via rotary
driver 550. Therefore, from the perspective of the screw anchor the
rotary driver is applying torque and axial force even the source of
the axial force may be a motor driving the chain. Similarly,
mandrel driver 520 may applying a hammering action to mandrel 300
however, axial downforce may also come from the motor driving chain
515, which in turn, pull mandrel driver 520 downwards. This force,
however, is translated through the mandrel driver to the mandrel so
from the perspective of the mandrel both of these axial forces
(hammering and downward pressure) are coming from the mandrel
driver.
[0063] In various embodiments, rotary driver 550 may be powered by
electric current or by hydraulic actuation in a manner known in the
art. Similarly, mandrel driver 520 may be powered by compressed
air, electric current or by hydraulic actuation. Mandrel driver 520
may be a hydraulic drifter or other suitable device for generating
downforce and/or hammering force. In various embodiments, and as
shown in the figures, mandrel driver 520 and rotary driver 550 may
be oriented concentrically on the frame in the direction of the one
or more tracks so that the shaft of mandrel 300 can pass through
rotary driver 550 and move up and down within driver 550 while it
is rotating a screw anchor into the ground. In this manner, tip 310
of mandrel 300 may operate ahead of screw anchor 200, projecting
out of its bottom (below-ground) opening, to clear a path for and
ahead of screw anchor 200. This may also allow mandrel 300 to be
dropped down through rotary driver once it is decoupled from driver
520 for repair and/or replacement without completely disassembling
attachment 500.
[0064] With continued reference to FIGS. 10A and 10B, exemplary
machine 600 has a main body portion 605 housing the machine's
petrol engine or electric motor, a fuel tank or power cell, a
hydraulic system, counterweights if necessary, and a control
interface, sitting on tracked chassis 610. Machine 600 may also
have an air compressor and air lines for supplying pressurized air
to an air hammer or other equipment, a power take-off for
mechanically transferring power to external devices, an electrical
connection for providing electric power to attachment 500, and one
or more hydraulic interfaces for communicating hydraulic fluid to
attachment 500, mandrel driver 520, and/or rotary driver 550. In
the example of FIGS. 10A/B, articulating arm 620 projects away from
one end of the machine (e.g., front or rear), functioning as an
attachment support. In other embodiments, it may project from
either side. In still further embodiments, arm 620 may be mounted
on a rotatable turret that can rotate completely around a vertical
axis over tracked chassis 610 to any radial orientation. Dotted
lines in FIG. 10B on either side of attachment 500 show how it can
rotate about a rotation point to drive screw anchors into the
ground at angles.
[0065] FIG. 11 is a close-up view of mandrel driver 520 and rotary
driver 550. For ease of illustration, the attachment and machine
have been intentionally omitted. In the exemplary configuration
shown here, mandrel 300 is attached to mandrel driver 520 via pin
connection 521. As noted herein, in various embodiments, this may
enable simplified removal of the mandrel 300 by removing the pin
and allowing mandrel 300 to drop through rotary driver 550 under
the force of gravity. In various embodiments, one or more bearings
such as bearing 552 are located above and below rotary driver 550
to limit the motion of the mandrel 300 and prevent it from damaging
rotary driver 550. Rotary driver 550 may have a rotating head such
as head 555, chuck, or other device for transferring torque and
downward pressure to screw anchor 200. The partial cutaway at the
bottom of FIG. 11 shows that the fitment of mandrel 300 within
screw anchor 200. In this exemplary figure, movement of rotary
driver 550 and mandrel driver 520 are facilitated via a chain and
drive motor moving the chain. In various embodiments, rotary driver
550 is fixed to chain 515, while mandrel driver 520 is attached but
able to be decoupled from chain 515 for independent movement or to
stay in place. It should be appreciated that instead of a chain two
or more hydraulic actuators may be used to push and pull rotary
driver 550 along its axis of travel and to make mandrel driver 520
travel with it or independent of it. The specific manner in which
downforce is generated and the way that rotary driver 550 and
mandrel driver 520 travel along their axis is a design choice.
[0066] As discussed herein, the ability to actuate tools through
the screw anchor while driving is a major advantage relative to
conventional ground screws. This is possible because both ends of
the screw anchor are open. Having the ends open is accomplished
with fewer rather than more manufacturing steps, allowing a less
expensive and energy intensive manufacturing process. The tools can
mimic the functionality and benefits of the ground screw tip, all
of which are realized during driving, while providing better pull
out and compressive resistance per unit of length because the tip
is removed after driving. To accomplish this, depending on how
torque is imparted to the screw anchor, it may be necessary for the
mandrel to pass directly through the rotary driver. FIG. 12 shows
one assembly for accomplishing this, however, it should be
appreciated that there are many possible ways of doing so.
[0067] FIG. 12 is a partial exploded view of a drive train and gear
assembly stack that allows mandrel 300 to actuate within rotary
driver 550 without affecting its operation according to various
embodiments of the invention. As shown, at its top end, output gear
551 is mechanically coupled to the output shaft of an electric or
hydraulic motor. It may be directly coupled to the output or
coupled via a transmission or other reduction gear assembly (not
shown) to provide greater mechanical advantage. Output gear 551 is
synchronized to two-part drive gear 552 consisting of driven
portion 553 and driving portion 554. In various embodiments,
driving portion 554 is splined to interface with splines in sun
gear 576 that is the center of planetary gear assembly 575.
Planetary gear assembly 575 consists of ring gear 571 on the inside
of housing 570 that retains planetary gears 577 orbiting sun gear
576. As drive gear 551 rotates driven portion 553 of the drive
gear, driving portion 554 rotates sun gear 576 in place. Sun gear
576 drives planetary gears 577, in this case, four planetary gears,
to rotate within ring gear 571. Planetary carrier 580 is attached
to the center of each planetary gear 577 with a bearing to generate
output power for the rotary driver. Planetary carrier 580 includes
splined hub 581 that mates with splined driving head 582. A chuck
or drive plate such as drive plate 554 in FIG. 11 or driving chuck
555 in FIG. 12 is connected to splined driving head 582 to transfer
torque to the head of a screw anchor. Though now shown, one or more
bearing collars may be positioned at the point where mandrel 300
enters and exists housing 570 of rotary driver 550 to limit its
motion to the axial motion without affecting the rotary driver's
motion.
[0068] The embodiments of the present inventions are not to be
limited in scope by the specific embodiments described herein.
Indeed, various modifications of the embodiments of the present
inventions, in addition to those described herein, will be apparent
to those of ordinary skill in the art from the foregoing
description and accompanying drawings. Thus, such modifications are
intended to fall within the scope of the following appended claims.
Further, although some of the embodiments of the present invention
have been described herein in the context of a particular
implementation in a particular environment for a particular
purpose, those of ordinary skill in the art will recognize that its
usefulness is not limited thereto and that the embodiments of the
present inventions can be beneficially implemented in any number of
environments for any number of purposes. Accordingly, the claims
set forth below should be construed in view of the full breath and
spirit of the embodiments of the present inventions as disclosed
herein.
* * * * *