Note: Descriptions are shown in the official language in which they were submitted.
ADJUSTABLE CAP FOR COLUMN FOUNDATION
[0001] This application claims priority of US provisional patent
application 62/723,091
filed August 27, 2018, and is incorporated herein by reference.
Technical Field
[0002] The present patent application relates to electrical power
transmission and to
foundation installation and construction for supporting towers and other
structures.
Background
[0003] Electrical power transmission lines are an important part of an
electrical power
grid infrastructure. Commonly, a tower is erected to support a transmission
line. Some
towers have a single central foundation support and use guy cables to
stabilize the tower
structure. These foundations support a downward load only. Other towers have
multiple
legs connected to foundation supports. These towers support the load of the
downward
weight of the tower, while also anchoring the tower when wind forces would
cause one
leg to want to lift or when the transmission lines terminate and/or change
direction. In this
latter type of tower, guy cables are not required.
[0004] The foundations for electrical power transmission line towers are
typically
directly built on the bedrock to ensure the desired stability when the bedrock
is readily
accessible (less than 5 meters deep). As illustrated in Figure 1, this can
involve the
excavation of very large pit for each leg's foundation. The pit can extend
down to the
bedrock on which a foundation is built that extends up to ground level to
support the leg
of the tower. Rainfall and groundwater can fill the pits while installing the
foundations and
the environment is disturbed by the excavation. In cold climates, such
foundation work
must be done while protecting concrete from the cold while it sets. When
conditions are
difficult, the installation of a single tower for a 735 kV AC transmission
tower as shown in
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Figure 1 can involve a cost of about $250,000 and to up to $500,000 when
conditions are
challenging (Canadian funds).
[0005] In many cases, the structure of the electrical transmission tower is
based on
angle iron members. The connection of each tower leg at the foundation
typically involves
connecting the leg to the foundation using strapping or other members that
hold the legs
down under tension so that wind forces cannot lift the legs.
[0006] Applicant has installed in Quebec foundations for electrical
transmission towers
of a different nature than that illustrated in Figure 1. These foundations, as
illustrated in
Figure 2, avoid excavation down to the bedrock and instead rely on drilling a
large
borehole of about between 30 cm to 60 cm in diameter that extend through 2 m
to 5 m of
earth (i.e. the overburden layer 2) to reach the bedrock and then about 1 m to
2 m into
the bedrock 3 for stabilization. These boreholes can be fitted with a sleeve
12 and are
filled with a cement material 20 that then provide rigid support columns
providing an
above-ground support 16 for the tower leg.
[0007] Applicant has also proposed in US patent application publication
2017/0321388, published on November 9, 2017 a foundation and a method of
installing
a foundation that uses the borehole approach, but with tension anchors that
stabilize the
column. In some cases, the borehole does not need to penetrate the bedrock to
any
significant depth.
Summary
[0008] Applicant has found that it is a challenge to connect a tower leg to
a column-
type foundation. One issue is that the connection of the tower leg to the base
(i.e. the top
or cap of the column-type foundation) involves creating the attachment on
site. Another
issue is that the ability to drill a borehole with exact precision in position
so that the center
of the column-type support is centered with the tower leg is very difficult.
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[0009] Applicant proposed herein to provide a position adjustable cap for a
column-
type foundation. Such a cap can provide a base mounting for a leg of a tower
that is
solidly connected to the column while being adjustable during installation in
a number of
axes. Such a cap can be adjusted to be in the precise position desired so that
it can
provide an integral attachment strap or member having one or more connection
surfaces
for connection to the leg of the tower.
[0010] The cap can be connected to the column using a central bar or bolt
anchored
in the column. Alternatives to using a central bar or bolt are possible,
however, they are
more complicated. For example, it is possible to use a plurality of bars or
bolts extending
down and anchored into the column. While potentially stronger, this can be
more
complicated to adjust in position. Alternatively, the cap can be attached to
the main
column using fasteners extending perpendicular to the lengthwise axis of the
column to
be supported by the casing or sleeve of the column (in the case that the
column has a
casing) or by the body of the column.
[0011] The cap can be fixed in its adjusted relative position with respect
to the column
by using a sellable filling material such as cement, concrete, epoxy, resin,
etc. to hold a
position fixed prior to the setting of the material. The cap can provide a
sealed casing for
the settable filling material and the casing can be adjusted in the desired
position using
an external support or by using members that are part of the casing. A
compliant seal can
be used at the bottom of a cylindrical casing to provide sufficient tolerance
for adjustment
in position. Set screws can be used as members that are part of the casing to
position the
casing with respect to the column.
[0012] The way in which the cap held in position using a settable filling
material is
connected to the column can take different forms as described above. When a
central
bolt or bar is used, the connection between the cap and the bar can allow for
setting the
height of the cap while allowing for adjustment in a plane perpendicular to
the lengthwise
axis of the column, while allowing for adjustment of the cap in other
directions using the
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positioning of the casing relative to the column. The settable filling
material can then
solidify the positioning of the cap.
[0013] Alternatively to using a settable filling material, the adjusted
relative position
can be set using adjustable members such as a nut and bolt or using strapping
that can
be secured at a desired variable position.
[0014] While the adjustable cap represents mechanical components and
methods of
installation related to only a small portion of the foundation, Applicant
believes that it
represents a key element in providing for efficient and reliable electrical
power
transmission. Transmission lines fail when a single tower fails. Towers are
thus typically
overdesigned to handle the most extreme conditions. This means that the
foundations for
the towers are also overdesigned. The extent of the foundation preparation
when such
work involves excavation leads to environmental damage in addition to
significant costs.
When borehole column type foundations are used, a cap that is solidly
connected to the
column is important and the process of drilling does not allow for precision
positioning of
the resulting base or cap to the placed at the top of the column.
Brief Description of the Drawings
[0015] Embodiments will be better understood by way of the following
detailed
description of certain embodiments with reference to the appended drawings, in
which:
[0016] Figure 1 is a schematic illustration of a conventional installation
of a four-legged
electrical power line transmission tower showing excavated pits, exposed
bedrock,
foundations mounted on the bedrock for supporting each leg at ground level;
[0017] Figure 2 is a side sectional view of a borehole column type
foundation in which
the column is planted into the bedrock to provide a foundation support at the
ground
surface;
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[0018] Figure 3 is a side sectional view of a borehole column type
foundation column
having an adjustable cap for connecting to an angle-iron type leg of a tower
according to
one embodiment;
[0019] Figure 4 is a flow chart describing the installation steps for the
embodiment of
Figure 3;
[0020] Figure 5 is an oblique, partly-break-away view of the embodiment of
Figure 3;
[0021] Figure 6 is a side sectional view of a borehole column type
foundation column
installed at an angle with respect to the vertical and having an adjustable
cap connected
to an angle-iron type leg of a tower according to one embodiment;
[0022] Figure 7 is a plan view of a cap according to the embodiment of
Figures 3 and
4;
[0023] Figure 8 is a plan view of a cap according to an embodiment in which
three
tension anchors are connected to the cap for stabilizing the column;
[0024] Figure 9 is sectional side view of the anchor attachment of the
embodiment of
Figure 8;
[0025] Figure 10 is a schematic illustration of a four-legged tower mounted
to borehole
column type foundations of the type illustrated in Figure 3, 5 and 7;
[0026] Figures 11A-11B are schematic illustrations of a borehole column
type
foundation column having an adjustable cap for connecting to an angle-iron
type leg of a
tower according to one embodiment;
[0027] Figures 12A-12B are schematic illustrations of a four-legged tower
mounted to
borehole column type foundations of the type illustrated in Figures 11A-11B,
and details
thereof;
[0028] Figures 13A-13F are schematic illustrations of a method of
installing a borehole
column type foundation of they type illustrated in Figures 11A-11B;
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[0029] Figure 14 is a schematic illustration of a borehole column type
foundation
column having an adjustable cap for connecting to an angle-iron type leg of a
tower
according to one embodiment;
[0030] Figure 15 is a schematic illustration of a four-legged tower mounted
to borehole
column type foundations of the type illustrated in Figure 14; and
[0031] Figures 16A-16D are schematic illustrations of a four-legged tower
mounted to
borehole column type foundations including tension members, and details
thereof.
Detailed Description
[0032] In general, the present disclosure relates to electrical power
transmission
towers, borehole column type foundations for the towers, and adjustable caps
for use in
the foundations. The disclosure also relates to methods of installing the
foundations,
caps, and towers. As discussed above, the systems and methods disclosed herein
may
have advantages over the prior art and may in particular provide for efficient
and reliable
electrical power transmission.
[0033] In the embodiment of Figure 3, there is shown a borehole column type
foundation in which a column 12 is embedded into bedrock 3 and set in its
borehole using
sealant 15. The column 12 illustrated is of the type that has a hollow casing
filled with
concrete or cement 14, such as 30 megapascal (MPa) cement (preferably the
settable
material should be able to withstand more than 25 MPa and in some cases up to
40 MPa
for a transmission tower application, however, this resistance to pressure can
vary from
the needs of the column foundation). The sealant 15 can be the same material
as the
filler 14 for the column and the column 12 can have apertures (not shown) for
the cement
14 to pass through the column 12.
[0034] In some cases, the column 12 can comprise an H- or an I-beam (or
other rigid
member) that is set in a settable material such as cement or concrete 14. In
such cases,
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it can be desirable to weld or attach bar 18 to the I-beam. In some
embodiments, the
column casing and sealant 16 can be replaced by the concrete surrounding the I-
beam.
[0035] The column 12 in Figure 3 is anchored in the bedrock 3 and rises up
through
the overburden layer 2. This involves drilling into the bedrock 3. Applicant
uses a drill rig
attached to a stable support and capable of drilling a borehole in a
relatively straight line
through soft ground and through any rocks or boulders in the overburden layer
2. The
column 12 can alternatively be set on the bedrock (rather than in it) and
stabilized using
side anchors as described in Applicant's US patent application publication
2017/0321388,
published on November 9, 2017.
[0036] A cap 16 can cover the top of the column 12. The cap 16 can be
solidly
connected to the column 12 as the leg of the tower (or other structure to be
supported)
can apply not only downward forces but also upward forces as the wind acts on
the tower.
The cap 16 can be given most of its strength through its connection to the bar
18 that is
embedded in the column material 14. The bar 18 can be textured like rebar so
as to hold
well in the material 14.
[0037] In the embodiment of Figure 3, the adjustable position of the cap 16
with
respect to the column 12 come from an adjustable connection between the
central bar 18
and the cap 16 that is locked in place using a settable material 36 filling a
casing 35 that
can seal against the column 12 using a seal 24. The settable material 36
provides load
resistance in at least compression, while the bar 18 provides a solid
connection in tension
as well. While not shown in Figure 3, the cement 15 (or other suitable
settable material)
can extend between the column 12 and the overburden layer 2, namely it can
fill a space
between the borehole and the column 12.
[0038] The setting of the material 14 can take a few days in the case of
cement. It will
be understood that a holder (not shown) can be used to hold the bar 18 in
place during
setting or curing of the material 14. The precision of the final position of
the bar 18 is very
difficult to ensure during this process.
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[0039] The upper end of the bar 18 can be threaded so that nuts 20 and 30
can be
adjustably positioned thereon. An aperture 22 in the cap 16 allows the cap 16
to be
positioned laterally within a range of movement. The cap 16 is sandwiched
between
plates 22 and 28 that have central holes fitting over the bar 18. The double
nuts 20 and
30 allow for adjusting height and locking the position when the nuts are
turned to
compress against each other. In this way, the cap can be attached to the
column 12 with
an adjustable height and horizontal position. The cap 16 can be rotated about
its vertical
axis so as to position the leg support members 38 and 40 as desired. The exact
leveling
and position can also be set using screws 32 (three can be provided as shown
in Figures
7 and 8).
[0040] While three threaded screws 32 can be used that are turned to adjust
their
position, it will be appreciated that other adjustable length members can be
used in a
similar manner to provide the position adjustment between the casing 35 and
the top of
the column 12.
[0041] It will be appreciated that the embodiment of Figure 3 allows for a
limited
displacement of the cap 16 within a plane perpendicular to the lengthwise
direction of the
column 12, while allowing for rotation about the lengthwise direction of the
column 12 as
well as some adjustment in orientation of the top surface of the cap 16 using
the set
screws 32. In total this gives the embodiment of Figure 3 six degrees of
freedom including
the ability to adjust its height using rod 18. It will be appreciated that as
few as two degrees
of freedom can be practical, although three or more will typically be
provided.
[0042] Once the cap 16 is correctly positioned, a filling hole 34 in the
cap 16 is used
to fill the chamber defined by the cap 16 and its casing 35 and seal 24. The
filling material
can be a sealant material or cement providing suitable load resistance
properties. The
seal 24 can be an 0-ring as illustrated, a compressible flap, a wadding
material stuffed
between the outside of the column 12 and the bottom of the casing 35 (this can
require
clearing some of the soft ground around the top of the column 12 to access the
gap from
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below), by pouring a compactable filler, such as sand, into the cap 16 through
one or
more inlets 34 to fill up the bottom of the chamber to be then filled up with
the settable
material 36, or the soft ground surrounding the bottom of the casing 35 can be
suitably
compacted to be sufficiently nonporous while the settable material 36 sets in
the cap 16.
[0043] It will be appreciated that the rod 18 is anchored in the column 12
to provide
resistance when the leg of the tower (or of any other structure being
supported) pulls up.
Such traction could be greater than the resistance of the cement or other
settable material
36 and cause cracking. However, it will be appreciated that there are
alternatives to using
a rod 18 that is anchored in the material 14 or attached to a column
structural member.
For example, in the case that the column's cylindrical tube is strong enough
to withstand
the pulling forces, the column foundation 12 does not need rod 18, and the cap
16 could
be secured to the column after the material 36 is hardened by drilling two
orthogonal and
spaced apart holes across casing 35 and the upper end of the cylinder of the
column 12.
Bolts extending through the holes can then secure the cap 16 to the column 12.
Alternatively, the rod 18 need not be anchored into material 14 and instead
can be
anchored to the upper part of the tube 12 using a bracket with radial arms
that can be
bolted to the tube wall of the upper end of the column 12 so as to connect the
rod 18 to
the side wall of the upper end of the column 12. In this way, the length of
rod 18 can be
shorter and does not require embedding the material 14.
[0044] Figure 5 illustrates an oblique view of Figure 3 with the column and
cap partly
cut-away.
[0045] Figure 6 shown an installation of a foundation column 12 of the type
shown in
Figure 3 at an angle to the vertical. The tower leg can be in-line with the
lengthwise axis
of the column 12.
[0046] Figure 7 illustrates a top of the cap according to the embodiment of
Figures 3
and 6. The cap 16 can be made for example of corrosion resistant steel. While
the leg
supports 38 and 40 illustrated are for receiving an angle iron shaped leg, it
will be
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appreciated that other suitable supports for the structure to be supported are
possible.
The angle iron shaped support 38 is provided with holes for fastening the
tower leg to the
support 38.
[0047] Figure 8 illustrates a cap 16 adapted for use with side anchors 45.
As described
in US patent application publication 2017/0321388, published on November 9,
2017, a
side anchor 45 is installed in a small borehole 47 and filled with a sealant
48 that can be
a suitable cement. The anchor is thus supported by the length of its borehole
in the
overburden layer and/or by its anchoring in the bedrock. The anchor can be a
rod or a
cable that is placed under tension, for example using a threaded member 50.
The anchor
can be connected to the cap 16 at pivotable supports 52 that are received in
sockets 54
of cap 16, as shown in Figure 9. The anchors 45 pass through an opening 56 in
cap 16
such that a range of angular motion is possible by pivotable supports 52 that
are
connected to the anchors 45. By applying sufficient tension at each anchor 45,
the
foundation column 12 can be stabilized at the cap 16.
[0048] It will be appreciated that when three or more tension anchors 45
are used, the
column 12 can be always subject to a compression load. In this case, the use
of rod 18
to provide the cap with the ability to resist an upward pulling force is not
required. Thus in
the embodiment of Figure 8, the rod 18 is optional, as the cap 16 can be held
in position
during setting of the material 36 using the set screws 32 and/or other
adjustable supports.
[0049] Figure 10 is a schematic illustration of a tower having four legs
installed on
borehole column-type foundations. As shown, the lengths of the tower legs can
be
adjusted in accordance with the terrain such that some legs are longer than
others. The
length of the columns can likewise vary in accordance with the depth of the
overburden
layer 2.
[0050] Figures 11A-11B illustrate a borehole column type foundation with an
adjustable cap, showing a side view cross-section, an oblique, partly-break-
away view,
and a top view, respectively. Figures 11A-11B illustrate an embodiment similar
to that
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shown in Figures 3 and 5. Like elements are labelled with like reference
signs, and some
elements which do not differ between the embodiments may not be described
here.
Features described with respect to Figures 3 and 5 may be combined with
features
described here and advantages described with respect to Figures 3-5 may apply
to the
embodiments discussed here.
[0051] The advantage of the embodiment of Figures 11A to 11B over the
embodiment
of Figures 3 and 5 is that the adjustable cap can be set into its desired
position using
vertically adjustable set screws 68, for example three in number, that allow
the cap to be
positioned in height and inclination with respect to the column 12 using
gravity to stabilize
the cap 35 until the settable material is used to solidify the combination.
Lateral
adjustment members or screws 32 can be used to better hold the desired
position of the
cap until the settable material is used to solidify the combination. The use
of the vertical
adjustment members 68 makes the installation of the cap 35 easier.
[0052] The embodiment of Figures 11A to 11B also offer the option that the
base 16
be a separable component from the cap 35. This allows for the base 16 to be
customized
and it also makes the cap lighter during its installation. The base 16 can be
bolted to the
top of the cap 35.
[0053] Figures 11A-11B show a borehole column type foundation in which a
column
12 and a bar 18 are set in a pilot hole 42 and a borehole 44 formed in bedrock
3. The
pilot hole 42 and the bar 18 may extend below the borehole 44 and the column
12. Both
the bar 18 and the column 12 may be set using a sealant 14, 15, such as
concrete. In
some embodiments, the column 12 and the bar 18 may be attached to each other.
[0054] The column 12 and the rod 18 may be anchored in the bedrock 3 and
rise up
through the overburden layer 2. The column 12 may alternatively be set on the
bedrock
(rather than in it) and stabilized using side anchors as described in
Applicant's US patent
application publication 2017/0321388, published on November 9, 2017. If the
column 12
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is set on the bedrock 3, the bar 18 may be set on the bedrock 3 or embedded in
the
bedrock 3.
[0055] A cap assembly 46 may cover the top of the column 12. The cap
assembly 46
may comprise a cap 16, a casing 35, one or more screws 32, and an adjustable
plate 50.
The cap assembly 46 may also be connected to the bar 18. The cap assembly 46
may
be configured to attach the column 12 and the bar 18 to a leg support member
38, which
may support an electrical tower leg (not shown). The cap assembly 46 may
thereby
anchor the electrical tower leg to the borehole foundation. In some
embodiments, the
cap assembly 46 may be partially disposed in a hole formed in the overburden
layer 2.
Overburden material 2 may or may not be replaced to partially cover the cap
assembly
46.
[0056] The cap 16 may cover the top of the column 12 and may be connected
to it
through any means known in the art. In some embodiments, the cap 6 may be
rigidly
connected to the column 12. The bar 18 may extend through a hole formed in the
cap 16
and may or may not be attached to the cap 16.
[0057] The casing 35 may be disposed around an outer surface of the column
12 and
may be connected to the column 12 via the screws 32. A seal 24 may be disposed
between the column 12 and the casing 35. The screws 32 may be used to adjust
the
orientation of the casing 35 relative to the column 12. Namely, the specific
degree to
which each screw 32 is tightened may impact the orientation of the top of the
casing to
which the adjustable plate 50 is attached. The cap assembly 46 may include any
number
of screws 32. In some embodiments, the cap assembly 46 may include eight
screws 32
arranged around the casing 35 in pairs, as shown in Figure 12B. The screws 32
may be
tightened to the casing 35 using nuts.
[0058] The adjustable plate 50 may be disposed on the top surface of the
casing 35
above the cap 16. The bar 18 may extend through the center of the adjustable
plate 50.
One or more nuts 30 may be used to attach the bar 18 to the adjustable plate
50. The
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attachment between the bar 18 and the adjustable plate 50 may provide most of
the
strength of the connection between the adjustable plate 50 and the borehole
foundation;
the attachment may provide the strength necessary to support the electrical
tower leg.
[0059] The adjustable plate 50 may comprise one or more fine adjustment
screws 48.
As discussed above, gross positioning of the adjustable plate 50 may be made
by
positioning the casing 35 using the screws 32. The screws 32 may orient the
casing 35
such that the adjustable plate 50 rests on the casing 35 in a desired
orientation. However,
the adjustable plate 50 may not be at the precisely desired orientation.
Accordingly, the
fine adjustment screws 48 may be used to make fine adjustments to the
orientation of the
adjustable plate 50. As shown in Figure 12B, a number of fine adjustment
screws 48 may
be arranged around the diameter of the adjustable plate 50. Adjusting the
length of each
fine adjustment screw 48 extending below the adjustable plate 50 may allow for
fine
adjustments to be made to the orientation of the adjustable plate 50.
[0060] In some embodiments, modeling software or another computer program
may
be used to determine how the screws 32 and the fine adjustment screws 48
should be
adjusted to position the adjustable plate 50 at a particular angle. In some
embodiments,
measurement devices may be used on-site to make the adjustments.
[0061] The leg support members 38, 40 which support an electrical tower leg
may be
attached to the adjustable plate 50 via a leg support mount 52. The leg
support mount
52 may be rigidly attached to the leg support members 38, 40 and may comprise
an
attachment plate 54 and a mounting base 56. The attachment plate 54 may be
configured
to be attached to the adjustable plate 50 via bolts 58 or through any other
means known
in the art. The mounting base 56 may extend from the attachment plate 54 and
include
a hollow central region to contain the bar 18 and nuts 30.
[0062] Figures 12A-12B illustrate embodiments of an electrical tower 90
supported by
legs 92 mounted on borehole foundations. Each leg 92 of the electrical tower
90 may be
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connected to a leg support member 38, 40 supported by a borehole foundation as
described above.
[0063] The
leg support members 38, 40 may extend from the mounting base 56 at an
angle. As shown in Figures 12A-12B, the leg support members 38, 40 may be in
line with
the legs 92 of the electrical tower. The leg support mounts 52 may be
configured to be
approximately parallel to the surface of the overburden layer 2. In the
embodiments
illustrated in Figures 11-12, the borehole foundations may be perpendicular to
the surface
of the overburden layer 2. Accordingly, the adjustable plates 50 may be
adjusted to be
approximately parallel to the surface of the overburden layer 2. In some
embodiments,
the leg support mounts 52 and the adjustable plates 50 may be at a different
orientation.
For example, local variations in the surface of the overburden layer 2, as
shown in Figures
12A-12B may necessitate variations in the orientation of the adjustable plates
50.
[0064]
Comparing Figures 11A-11B to Figures 3 and 5, one skilled in the art will
recognize two key areas of difference: the base of the foundation and the
cap/cap
assembly. Namely, Figures 11A-11B illustrate a base which includes a rod 18
extending
below a column 12 and a cap assembly featuring an adjustable plate. The
foundation
base illustrated in Figures 11A-11B may be used with the cap illustrated in
Figures 3 and
and the foundation base illustrated in Figures 3 and 5 may be used with the
cap
assembly illustrated in Figures 11A-11B without departing from the scope of
this
disclosure. One skilled in the art will recognize that features from the
different illustrated
embodiments may be combined and modified in other ways, also without departure
from
the scope of the disclosure.
[0065]
Figures 13A-13F illustrate a method of installing a borehole foundation as
illustrated in Figures 11-12.
[0066]
Figure 13A illustrates the formation of three holes: a pilot hole 42 extending
into
the bedrock 3, a borehole 44 extending through the overburden layer 2 and into
the
bedrock 3, and a surface hole 60 formed at the surface of the overburden layer
2. The
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holes may be formed through drilling, excavating, or any other means known in
the art.
In some embodiments, these holes may be formed using techniques well known
from
petroleum production applications. Figure 13B illustrates the insertion of a
bar 18 into the
pilot hole 42 and a column 12 into the borehole 44. Figure 13C illustrates the
filling of the
pilot hole 42 and the borehole 44 with a filler 14, 15 such as cement. The
region of the
pilot hole 42 surrounding the bar 18 may be filled. The regions of the
borehole 44
surrounding the column 12 and between the column 12 and the bar 18 may be
filled. The
filling may be performed using any means known in the art, including
techniques well
known from petroleum production applications.
[0067] Figures 13D-13F illustrate the installation of a cap assembly 46 on
the bar 18
and column 12. A cap 16 may be disposed on top of the column 12. A casing 35
may
be installed around the column 12 at a desired angle using screws 32. An
adjustable
plate 50 may be disposed on top of the casing 35, and the orientation of the
adjustable
plate 50 may be adjusted using fine adjustment screws 48. One or more nuts 30
may be
used to secure the cap assembly 46 to the bar 18. A washer may or may not be
disposed
between the nuts 30 and the adjustable cap 50. In some embodiments, these
steps may
be performed with the guidance of modelling software and/or measurement tools
to
ensure a desired orientation of the adjustable plate 50.
[0068] Figure 13F illustrates the installation of a leg support mount 52
and attached
leg support members 38, 40. An attachment base 54 of the leg support mount 52
may
be attached to the adjustable plate 50 via screws or any other means known in
the art.
The orientation of the adjustable plate 50, which was carefully selected and
achieved as
illustrated in Figures 13D-13E may ensure that the leg support members 38-40
are
oriented correctly to support the leg of an electrical tower as illustrated in
Figures 12A-
12B.
[0069] Figures 14-15 illustrate an alternative to the embodiments
illustrated in Figures
11-13. Figure 14 illustrates a borehole foundation including the same
components as
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those illustrated in Figures 11A-11B. Figure 15 illustrates an electrical
tower 90 supported
by such borehole foundations. The borehole foundation illustrated in Figure 14
is oriented
at an angle to the surface of the overburden 2. In contrast to the embodiments
illustrated
in Figures 11-13, Figures 14-15 illustrate leg support members 38, 40 which
extend
perpendicular to the mounting base 56. The leg support members 38, 40 may be
in line
with the legs 92 of the electrical tower 90. Accordingly, the borehole
foundation may be
formed at an angle equal to or similar to the angle of the legs 92. Technology
for drilling
or otherwise forming angled boreholes is well known in the art. One skilled in
the art will
readily understand how to use the method of Figures 13A-13F to install
borehole
foundations at an angle.
[0070]
Figures 16A-16D illustrate the use of side anchors 45 to secure tower legs 92
anchored to borehole foundations. Figure 16A illustrates an electrical tower
90 with four
legs 90, each leg being attached to a borehole foundation. Figure 16B
illustrates detail
of a cap assembly 46, a leg support mount 52, and leg supports 38, 40
illustrated in Figure
16A. Figures 16C-16D show cross sections of Figures 16A and 16B, respectively.
[0071] As
discussed above, it will be appreciated that when three or more tension
anchors 45 are secured to a borehole foundation, the column 12 of the borehole
foundation can be always subject to a compression load. The compression load
provides
for a strong foundation. As shown in Figure 16A, each foundation/leg 92 is
secured by
one external tension anchor 45, which is connected to the ground, and two
inter-leg
tension anchor 45, which is secured to another foundation/leg 92. The inter-
leg tension
anchors 45 are illustrated as being connected between neighboring legs 92 but
could be
connected in a different pattern.
[0072] The
leg support mount 52 shown may be adapted similarly to the cap illustrated
in Figure 8. Specifically, the leg support mount may include extensions which
provide for
the attachment of side anchors 45. In some embodiments, the leg support mount
52 may
include one external mount 62 for an external tension anchor 45 and two inter-
leg mounts
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64 for inter-leg tension anchors 45. The external mount 62 may comprise an
extension
angled upward with a hole formed therethrough, such that it supports an
external tension
member 45 which extends at an outward angle from the foundation. The tension
member
45 may be connected through the hole with one or more nuts or through any
other means
known in the art. In some embodiments, the external tension member 45 and the
external
mount 62 may be connected via a rotatable/pivotable connection as illustrated
in Figures
8 and 9.
[0073] The inter-leg mounts 64 may comprise vertical extensions with holes
formed
therethrough, such that the tension members 45 may be attached thereto via a
pivot
attachment or any other means known in the art. A leg support mount 52 may
include
extensions/mounts which differ from those illustrated in Figures 16A-16D. One
skilled in
the art will readily envision different ways in which a tension anchor 45 may
be attached
to a leg support mount 52.
[0074] The inter-leg tension members 45 may include tensioning mechanisms
66,
which may allow them to be tightened/loosened after they have been attached to
two legs
92. These mechanisms 66 may operate via a screw or any other means known in
the art
and may allow a desired amount of tension to be applied to the borehole
foundations and
the legs 92 they support. Each of the external tension members 45 may be
secured in a
borehole. The borehole may be angled and the external tension member 45 may be
cemented into the borehole. The borehole may extend into the bedrock.
[0075] The configuration of tension members 45 shown in Figures 16A-16D may
provide several advantages. As discussed above, connecting three tension
members 45
to each leg/borehole foundation allows each of the legs/foundations to be
maintained in
tension at all times. By connecting two inter-leg tension members 45 to each
leg, the
configuration reduces the number of tension members 45 which must be
installed, and in
particular, reduces the number of external tension members 45 which must be
secured
to the ground. This reduces the number of boreholes which must be formed in
the
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overburden and the bedrock, thereby reducing the time and cost necessary to
install
tension members. Further, by having numerous tension members accessible above-
ground, this configuration may allow for adjustments to be made more readily
after the
tension members have been installed.
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