Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: SCREW PILE ANCHOR
BACKGROUND OF THE INVENTION
1. Field of the Invention
THIS INVENTION relates to a screw pile anchor. The
anchor is particularly suitable for, but not limited to, supporting
lighting columns.
2. Prior Art
The use of screw pile anchors, eg., of the type
manufactured by A. B. Chance Co., Centralia, Missouri, USA, to
to support a wide range of loads, is well known. The pile anchors usually
have a shaft, with a base plate at the upper end (to which is bolted or
welded a mounting plate on the lighting column or the load to be
supported), and at least one helical screw or flyte at, or adjacent, the
ground engaging end. Usually, the ground engaging end is provided
with a digging point which cuts a hole in the ground for the shaft, as
the pile anchor is rotatably driven into the ground.
Such pile anchors may only have a tow lateral stability
and so may not be suitable, particularly in loose or sandy soils, to
support lighting columns or the like. This means that the speed of
2o installation possible with pile anchors, as supports for lighting
columns, cannot be enjoyed and conventional supports, which may
have an installation span of two weeks (while the concrete pile sets)
must be employed.
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One attempt to increase the lateral stability of known
screw pile anchors is disclosed in AU-A-14807/97 (VANDERFEEN). A
pair of pipes, fitted one inside the other, are mounted on the shaft via
a collar and are operable to compress the ground down onto the helical
screw or flyte. However, the increase in lateral stability due to the
vertical compression of the ground is only marginal.
SUMMARY OF THE PRESENT INVENTION
It is an object of the present invention to provide a means
to increase the lateral stability of the pile anchors.
1o It is a preferred object of the present invention to provide
such means immediately below the base plate.
It is a further preferred object to provide such means
where the degree of increased lateral stability can be selected
dependent on the ground in which the anchor is to be driven.
It is a still further preferred object to provide a simple,
efficient method for interconnection of respective portions of the
shaft.
It is a still further preferred object to provide a simple,
efficient method for the manufacture of the helical screws or flytes.
Other preferred objects of the present invention will
become apparent from the following description.
In one aspect, the present invention resides in a
stabilizing assembly for a screw pile anchor, of the type having a shaft
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with at least one helical screw or flyte at or adjacent a ground
engaging end of a shaft (and an optional base plate at or adjacent the
other end of the shaft), the stabilizing assembly including:
at least one collar or plate rotatably mountable on the
shaft; and
a plurality of fins radiating from the collars) or plates)
and adapted to be pulled into the ground as the screw pile anchor is
driven into the soil, the stabilizing assembly providing resistance
against lateral movement to at least the portion of the shaft to which
1o the stabilizing assembly is mounted.
Preferably, three, four or more, fins are provided on the
collars) or plate(s), preferably at equal spacings, about the shaft.
Preferably, the fins extend substantially radially to the
shaft, although the fins may be curved, S-shaped or other shape in
plan view.
The fins may extend from a single collar rotatably
journalled about the shaft, or from two or more vertically spaced
collars or annular plates rotatably journalled about the shaft.
Preferably, the lower edges of the fins are inclined to the
2 o horizontal, so that they will progressively cut into the ground as the
screw pile anchor is driven into the ground. Where the fins have
ground engaging points distal from the shaft, they will tend to
vertically stabilize the pile anchor before it is fully driven into the
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ground.
Preferably, one or more bolts are provided on the fins,
collarfs) and/or annular plates and extend upwardly for releasable
engagement with a mounting on a lighting column or other load to be
supported.
In a second aspect, the present invention resides in a
screw pile anchor including:
a shaft;
at least one helical screw or flyte at or adjacent a ground
1o engaging end of the shaft;
an optional base plate at or adjacent the other end of the
shaft; and
a stabilizing assembly, having at least one collar or plate
rotatably mounted on the shaft, and a plurality of fins radiating from
the shaft and adapted to be pulled into the ground as the screw pile
anchor is driven into the soil, the stabilizing assembly providing
resistance against lateral movement to at least the portion of the shaft
on which the stabilizing assembly is mounted.
The screw pile anchor may be provided with two or more
2 o of the stabilizing assemblies at spaced intervals along the shaft.
Preferably, a cable entry slot is provided in the wall of the
tubular shaft below the fins.
In a third aspect, the present invention resides in a
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method of coupling respective portions of a tubular shaft of a screw
pile anchor, where one end of one of the portions is telescopically
interfitted into an adjacent end of the other of the portions, wherein:
the one end of the one portion has a first coupling zone
5 having an angular inclination (relative to the longitudinal axis of the
shaft) greater than the inclination of a second coupling zone, the
coupling first and second coupling zones being engageable in
complementary coupling zones at the adjacent end of the other
portion.
1o Preferably, the one coupling zone and complementary
zone provide coupling of the portions in a direction longitudinal of the
shaft; and the second coupling zone and its complementary zone
provide coupling of the portions for rotation of the shaft.
In a fourth aspect, the present invention resides in a
coupling between two portions of a tubular shaft for a screw pile
anchor of the type where one end of one of the portions is
telescopically interfitted in an adjacent end of the other of the
portions, wherein:
the one end of the one portion has a first coupling zone
2 o having an angular inclination (relative to the longitudinal axis of the
shaft~ greater than the angular inclination of a second coupling zone,
the first and second coupling zones being engageable in
complementary coupling zones at the adjacent end of the other
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portion.
In a fifth aspect, the present invention resides in a helical
flyte of a screw pile anchor including:
a pair of flyte plates, each of substantially helical
configuration, mountable on the shaft at spaced locations and
convergent at a peripheral rim.
The leading and trailing portions of the flyte plates may
be convergent to respective leading and trailing edges. One or more
flanges may be formed integrally with the flyte plates to enable
1o mounting of the flyte plates on the shaft; and the flanges and flyte
plates may be formed integrally from a single piece of sheet metal.
BRIEF DESCRIPTION OF THE DRAWINGS
To enable the invention to be fully understood, preferred
embodiments will now be described with reference to the
accompanying drawings in which:
FIG. 1 is a view of a typical installation of a lighting
column on a first embodiment of a screw pile anchor in accordance
with the present invention;
FIG. 2 is a perspective (exploded) view of the mounting
of the lighting column on the screw pile anchor in more detail;
FIG. 3 is a perspective view of the screw pile anchor of
FIGS. 1 and 2;
FIGS. 4 and 5 are perspective views of second and third
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embodiments of the screw pile anchor;
FIG. 6 is a plan view illustrating how the stabilizing
assembly of the present invention operates;
FIG. 7 is a sectional side view corresponding to FIG. 6;
FIG. 8 is a similar view to FIG. 7, the screw pile anchor
having a pair of the stabilizing assemblies of the present invention;
FIG. 9 is an (exploded) perspective view of a fourth
embodiment of the screw pile anchor;
FIG. 10 is a perspective view of a first embodiment of the
1o coupling between two shaft portions;
FIG. 1 1 is a sectional side view of a second embodiment
of the coupling between two shaft portions;
FIG. 12 is a perspective view of a first embodiment of a
helical flyte; and
FIG. 13 is a similar view of a second embodiment of the
helical flyte.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIGS. 1 and 2, this shows a typical
installation of a lighting column on a screw pile anchor in accordance
2 0 with the present invention.
The screw pile anchor 10 has a tubular shaft 11
terminating at its ground engaging end in a removal drilling point or bit
12. A base plate 13 is welded (or otherwise fixed) to the upper end of
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the shaft 1 1 and may be provided with slots or recesses 14.
The stabilizing assembly 30 has three, vertically spaced,
collars 31, 32, 33 rotatably journalled on the shaft, the collar 31 being
immediately below the base plate 13, and a locating ring (not shown)
is provided adjacent the lower collar 33 to limit movement of the
stabilizing assembly along the shaft 1 1.
Four fins 34, 35, 36, 37 extend radially from the collars
31 to 33 at equal, angular spacings.
Each fin 34, 35, 36, 37 has a lower, cutting edge 38
1o which is inclined downwardly in a radially-outward direction and
terminates in a ground engaging point 39 distal from the collar 33.
A respective mounting bolt or stud 40 extends vertically
from the top edge 41 of each of the fins 34 to 37 and may be
provided with nuts 42 to secure a mounting plate 51 of a lighting
column assembly 50 to the screw pile anchor 10 after the latter has
been installed.
Referring to FIG. 3, the screw pile anchor 10 is provided
with an alternative helical screw or flyte 20a, to be hereinafter
described in more detail and an alternative drilling point or bit 12a.
2o A cable hole 52 is provided in a locating ring 33a, below
the lower collar 33, enabling electrical cables to be fed to the interior
of the tubular shaft 11 for connection to cables (not shown) for the
light assembly 52 mounted on the lighting column 53 (see FIG. 1 ).
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Referring to F1G. 4, the screw pile anchor 1 10 is modified
in that the stabilizing assembly 130 only has three fins 134 to 136
spaced at 120° intervals. This embodiment may be preferred where
the ground into which the screw pile 110 is to be driven has a higher
mechanical strength than the ground where the screw pile anchor 10
is to be employed. It will also be noted that the screw pile anchor 1 10
can only provide three mounting bolts 140 for the mounting plate of
the fighting column assembly or other load to be supported.
In the embodiment of FIG. 5, the screw pile anchor 210
1o has eight fins 234 to 237, 234a to 237a, where the four primary fins
234 to 237 are provided at 90° intervals and are bisected by a
respective one of the secondary fins 234a to 237a. In addition, the
primary fins 234 are deeper and extend from the upper collar 231 to
the lower collar 233, while the secondary fins 234a to 237a extend
from the upper collar 231 only to the central collar 232. It will be
noted that both the primary and secondary fins have inclined cutting
edges 238, 238a terminating in ground engaging points 239, 239a
distal from the shaft 211.
The screw pile anchors 10, 110, 210 are driven into the
2 o ground using a standard power driving head, the drilling bits 12, 1 12,
212 cutting a hole for the tubular shafts 1 1, 11 1, 211. The screw
pile anchors 10, 110, 210 pull themselves into the ground until the
ground engaging points 39, 139, 239 engage the ground surface. The
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stabilizing assemblies 30, 130, 230, which have tended to rotate with
the shafts 1 1, 1 1 1, 21 1, cease rotation and the cutting edges 38,
138, 238 (and 238a1 on the fins 34 to 37, 134 to 136, 234 to 237
cut downwardly into the soil. In the embodiment of FIG. 5, the
5 cutting edges 238a will enable the secondary fins 234a to 237a to
enter the ground when their digging points 239a engage the soil.
The screw pile anchors 10, 1 10, 210 are driven into the
ground until their respective base plates 13, 113, 213 are at, or just
above, the ground surface.
1o Referring to FIGS. 5 and 6, where a cable trench 60 has
been cut in the ground 61, back-filling 62 of the trench will result in
reduced resistance to lateral movement of the upper end of the screw
pier 10, particularly when medium to high wind loads 70 are applied to
the light column assembly 50 in the direction of the arrow in FIG. 6.
However, by providing the stabilizing assembly 30, the
fins 34 to 37 tend to compress the ground in the area generally
indicated by the triangular shaded area 63 in FIG. 6. Tests have
shown that the compression of the ground may increase the resistance
of the upper end of the shaft 11 (and thereby the screw pile anchor
2 0 10) against lateral movement by a factor of five to ten times, more
generally six times. The rate of degree of resistance depends on
factors such as the number of fins provided on the stabilizing
assembly, the depth and the width of the fins, and the structure of the
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surrounding soil. Where the ground has a low mechanical strength, it
is preferable to use the screw pile anchors 10, 210, illustrated in FIGS.
3 and 5 over the screw pile anchor 110 of FIG. 4, as greater lateral
resistance is provided by increasing the number of tins.
By use of the stabilizing assemblies 30, 130, 230, it is
possible to use thinner gauge material in the manufacture of the
tubular shafts 11, 1 1 1, 21 1 without loss of vertical load capacity or
reduction in lateral bending resistance below prescribed limits.
FIG. 8 shows a modified embodiment of the screw pile
1o anchor of FIG. 7 which is suitable for use in soils which have stratas
having different mechanical strengths. In this embodiment, a pair of
the stabilizing assemblies 30 are provided at spaced intervals along the
shaft 11 of the screw pile anchor 10, where the upper end of the
shaft 1 1 and the lower end of the shaft 1 1 are in ground stratas 64,
65 of relatively low mechanical strength, and are separated by a
ground strata 66 of relatively higher mechanical strength.
It will be readily apparent to the skilled addressee that
where any soils strata is of relatively low mechanical strength, two or
more of the stabilizing assemblies 30 may be provided along the shaft
11 to increase the resistance of the shaft 11 to lateral movement
within that strata or stratas.
In the preferred embodiments shown in FIGS. 1 to 8, the
cutting edges 38, 138, 238 (and 238a) have been shown to be
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downwardly inclined to the ground engaging paints, 39, 139, 239
(and 239a) distal from the shafts 1 1, 1 1 1, 211. In alternative
embodiments (see FIG. 9), the cutting edges 338a may be upwardly
inclined radially outwardly (as shown in dashed lines) so that they
initially cut the ground adjacent the lower collar 33, 133, 233.
In a further alternative embodiment (not shown), the
spaced collars 31 to 33, 131 to 133, 231 to 233 may be substituted
by a single tubular collar or by one or more annular plates rotatably
journalled about the shafts 1 1, 1 1 1, 21 1.
1o Referring to FIG. 9, it is possible to provide the stabilizing
assembly 330 as a kit for mounting on the tubular shaft of an existing
screw pile anchor (eg., of the type manufactured by A. B. Chance
Co.); or on tubular shaft portions not especially adapted to receive the
stabilizing assemblies 330. An example of such a kit is illustrated
where the fins 334 to 336 are radially mounted on spaced collars 331
to 333 dimensioned to be rotatably journalled on a tubular shaft
portion 31 1 a, adapted to be coupled to a second tubular shaft portion
31 1 b fitted with the helical flyte 320 and, in turn, adapted to be
coupled to a third tubular shaft portion 31 1 c having the digging point
312.
A method of coupling the respective tubular shaft
portions 31 1 a to 31 1 b and 31 1 b to 31 1 c will hereinafter be described
with reference to FIGS. 10 and 11.
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Locating rings 331 a and 333a are provided with locking
screws (not shown) to enable them to be secured to the tubular shaft
portion 31 1 a to locate the stabilizing assembly 330 along the tubular
shaft portion 31 1 a while permitting rotation of the stabilizing assembly
330 about the shaft portion.
Referring to FIG. 10, a first embodiment of a coupling
between the adjacent tubular shaft portions, eg., 31 1 a and 311 b, the
lower end of tubular shaft portion 31 1 a has a first coupling zone 380
and a second coupling zone 381 adapted to be telescopically
l0 interfitted with, and engaged with, complementary first and second
coupling zones 390 and 391 at the upper end of the tubular shaft
portion 31 1 b. It will be noted that the angular inclination of the first
coupling zone 380, eg., of 2-5 ° relative to the longitudinal axis of
the
tubular shaft portion 31 1 a, is less than the angular inclination of the
second coupling zone 381, eg., 5-15 °, more preferably 5-10°.
The
shallow angle of inclination, and large surface area, of the
complementary first zones 380, 390 enables a larger driving torque to
be provided down the shaft portions 31 1 a, 31 1 b, to enable the drill bit
312 and helical flyte 320 to cut respective pathways down the soil.
2o The higher angle of inclination of the second coupling zones 381, 391
provides longitudinal location between the respective tubular shaft
portions 311 a, 311 b, to resist the downward force on the shaft
portions supplied by the driving head.
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In the alternative embodiment shown in FIG. 1 1, the first
driving zones 380a, 390a have the increased angular inclination
relative to their longitudinal axis of the tubular shaft portions and the
secondary coupling zones 381 a, 319a may be inclined in the range of
0-5 °, more preferably, 0-2 ° to the longitudinal axis.
Referring to FIG. 12, this illustrates a first embodiment of
the helical flyte or screw in accordance with the present invention.
The helical flyte 320 is formed from two helical flyte
plates 321, 322 which are each cut from a steel sheet and are
to deformed into a substantially helical shape. Each plate 321, 322 is
welded, brazed or otherwise fixed to the tubular shaft portion 31 1 and
is oppositely inclined so that the two plates 321, 322 are convergent
at the peripheral rim 323 of the helical flyte. The plates are joined by
welding, brazing or other suitable fixing means, and the "triangulation"
formed by the inclination of the two plates to each other results in a
helical flyte which is easily manufactured but which has a high
mechanical strength.
In use, the space between the plates is quickly filled with
soil, which forms a "plug" which pushes other ground out of the way
2 o as the helical screw flyte 320 is rotatably driven into the ground.
In the second embodiment shown in FIG. 13, the two
helical plates 321 a, 322a are formed integrally (eg., by folding) from a
single piece of sheet metal, and flanges 324a and 325a enable the
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helical flyte 320a to be welded, brazed or otherwise fixed to the
tubular shaft portion 311. (Reinforcing ribs 329a can be formed
integrally in the helical plates 321 a, 322a to increase the strength
thereof.)
5 It will be readily apparent to the skilled addressee that the
helical screw flytes 320, 320a illustrated in FIGS. 12 and 13 can be
manufactured from thinner section steel than would otherwise be
required for a conventional helical screw flyte having the same load
characteristics.
to It will be readily apparent to the skilled addressee that the
stabilizing assembly, and associated features hereinbefore described
for the screw pile anchors, enable anchors to be manufactured with
the same, or higher, resistance to lateral movement, and the same or
higher vertical loadings, than conventional screw pile anchors using
15 thicker section, and thereby heavier, components. For example, the
stiffness of the composite section of the anchor which comprises the
stabilizing assembly and shaft is approximately 50% more than the
shaft stiffness alone.
The stabilizing assembly can provide resistance to lateral
2 o movement of the shaft of the screw pile anchor which can be many
times greater than the resistance of a conventional unrestrained (or
unstabilized) anchor. The use of the fins increases the effective area
of the ground restraining the shaft against lateral movement, not only
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to many times greater than the diameter of the shaft, but also many
times greater than the width of the fins.
Various changes and modifications may be made to the
embodiments described and illustrated without departing from the
present invention as defined in the claims.
