Earth anchor apparatus having improved load bearing element

An earth anchor apparatus includes a hub having a longitudinal axis and first and second axial ends, and a load-bearing helix affixed to the hub. The load-bearing helix includes a generally radially extending leading edge adjacent the first end of the hub, a generally radially extending trailing edge adjacent the second end of the hub, an inner circumferential section connected to the hub, and an outer circumferential section extending radially outward from the inner circumferential section and having an outer circumferential edge separated from the inner section. A pair of opposed surfaces extend between the inner section and the outer edge and define a thickness of the helix. The thickness of the helix at the trailing edge is greater adjacent the inner circumferential section than at the outer circumferential edge, and the thickness of the helix adjacent the inner circumferential section is greater at the trailing edge of the helix than at the leading edge. In this manner, material is removed from areas of the helix where less loading stress develops during installation and use of the anchor while materials is added to areas of higher loading stress.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to earth anchors and, more 
particularly, to an earth anchor having a load-bearing helix shaped to 
compensate for relatively high loading stresses which occur adjacent a 
trailing edge of the helix during installation and use of the anchor. 
2. Discussion of the Prior Art 
It is known, e.g. from U.S. Pat. No. 4,316,350, issued to Watson on Feb. 
22,1982to provide an anchor with a load-bearing element in the form of an 
anchoring spiral which extends radially outward from a central body of the 
anchor by an amount which varies in the circumferential direction of the 
spiral between a lead point of the anchor and a trailing segment of the 
spiral. 
In such constructions, it is further known to provide the spiral with a 
thickness which is constant across the radial extent of the spiral, but 
which increases in the circumferential direction of the spiral between a 
minimum thickness adjacent the lead point of the anchor and a maximum 
thickness at a trailing point of the spiral. 
Although it is possible to increase the strength of an anchor by increasing 
the thickness of the load-bearing element in such a uniform manner, the 
use of a thickened element increases the weight of the anchor as well as 
the amount of material required to construct it. Accordingly, it would be 
beneficial to construct an anchor having a load-bearing element which is 
thickened only in the region where the load experienced by the anchor is 
at a maximum, while providing a reduced thickness in areas where loads of 
smaller magnitude are carried. 
Earth anchors of conventional type are typically used to provide anchoring 
against a tensile load such as a utility pole or the like which is to be 
supported above the ground and retained against falling in a direction 
away from the anchor. When employed in this manner, an anchor is generally 
subjected to a tensile load which is believed to exert a substantially 
uniform pressure on the upper surface of the load-bearing element, i.e. 
the surface facing the object exerting the load on the anchor. 
In the past, it has been a belief by some practitioners in the art of 
designing earth anchors that when such a uniform pressure is experienced 
by the upper surface of an earth anchor having a helix which extends 
around almost the entire circumference of the anchor, the location on the 
load-bearing element of highest stress is or should be immediately 
opposite the leading and trailing edge of the load-bearing element. 
This theory is based upon consideration of the effect of such a uniform 
pressure on a generally C-shaped, annular flat plate having a radial 
cut-out portion extending completely through the plate. When such a plate 
is attached to an interior hub and a surface of the plate is loaded with a 
uniform pressure, failure of the plate would be expected to occur along a 
radial line located immediately opposite the radial cut since it is along 
this line that the least surface area of the plate exists to resist the 
load. 
However, the present inventors have found that the predicted effect of 
failure occurring opposite the trailing or leading edge does not occur, 
and that by properly locating the actual point of high load stress on the 
load-bearing helix, an anchor may be locally strengthened to withstand a 
desired predetermined load limit. 
OBJECTS AND SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide an earth 
anchor having a load-bearing element shaped to compensate for relatively 
high loading stresses which the inventors have found to occur adjacent a 
trailing edge of the load-bearing element near the point of intersection 
between the trailing edge and the hub. 
Further, it is an object of the invention to provide an earth anchor having 
a construction which assists in preventing bending or failure of a 
trailing edge of a load-bearing element in order to avoid detrimental 
effects created by such bending of the element. Other objects will become 
evident from the detailed description of a preferred embodiment of the 
invention as well as from a review of the attached drawing figures. 
The construction of the present invention was developed only after it was 
discovered by the inventors, by uncovering anchors which had been 
intentionally submitted to a tensile load greater than that which the 
anchors were capable of supporting, that failure of the anchors occurred 
at the trailing edge of the load-bearing element in a region immediately 
adjacent the point of intersection between the trailing edge of the 
load-bearing element and the hub of the anchor. This observation made of 
actual anchors was confirmed through computer analysis of a simplified 
configuration of conventional anchors, the analysis illustrating that when 
a uniform load was exerted on the upper surface of a helical load-bearing 
element of the type employed in conventional earth anchors, the highest 
stress experienced by the load-bearing element occurred at the point of 
intersection between the trailing edge of the load-bearing element and the 
hub. 
In addition to considering the effect of a uniform pressure on the upper 
surface of the load-bearing helix, the inventors also considered the 
effect of point loading a trailing tip of the helix in order to determine 
the location of maximum stress on the helix when such loading occurs. 
Again, it was determined that the point of maximum load stress experienced 
by the helix occurred at the point of intersection between the trailing 
edge and the hub. 
In view of these observations and conclusions, the inventors developed an 
earth anchor construction addressing the need for additional strength in 
the region surrounding the point of intersection between the trailing edge 
of the load-bearing helix and the hub. Other needs were also addressed 
which will become evident from a review of the disclosure of the preferred 
embodiment of the invention. 
In accordance with one aspect of the invention, an earth anchor apparatus 
includes a hub having a longitudinal axis and first and second axial ends, 
and a load-bearing helix affixed to the hub. The load-bearing helix 
includes a generally radially extending leading edge adjacent the first 
end of the hub, a generally radially extending trailing edge adjacent the 
second end of the hub, an inner circumferential section connected to the 
hub, and an outer circumferential section extending radially outward from 
the inner circumferential section and having an outer circumferential edge 
separated from the inner section. 
Further, a pair of opposed surfaces extend between the inner section and 
the outer edge of the helix and define the thickness of the helix. The 
thickness of the helix at the trailing edge is greater adjacent the inner 
circumferential section of the helix than at the outer circumferential 
edge, and the thickness adjacent the inner circumferential section of the 
helix is greater at the trailing edge than at the leading edge. 
By providing this construction, numerous advantageous results are realized. 
For example, by providing the helix with a thickness which is greater 
within a radially inner region of the helix adjacent the trailing edge 
than elsewhere on the helix, an earth anchor is obtained which possesses 
increased strength in the area of the point of intersection between the 
trailing edge of the helix and the hub. Further, by removing material from 
the remaining areas of the helix, or by providing such areas with less 
material, a savings in material used in the anchor is achieved without an 
attendant loss of overall strength of the anchor. 
Additional features of the inventive construction further add to the 
strength characteristics of the anchor. For example, the thickness of the 
helix at the trailing edge may be tapered from the inner section toward 
the outer circumferential edge to give the helix a uniform shape, or the 
thickness adjacent the inner circumferential section may be made to 
decrease in the circumferential direction of the helix within a region 
extending at least 90 degrees around the helix from the trailing edge. 
Further, the inner circumferential section may include a generally curved 
surface extending between the hub and each of the opposed surfaces, 
wherein each of the curved surfaces defines a first radius adjacent the 
trailing edge of the helix and a second radius adjacent the leading edge 
of the helix, the first radius being greater than the second radius.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
An earth anchor constructed in accordance with a preferred embodiment of 
the invention is illustrated in FIG. 1, and includes a hub 10, a lead 
point 12 extending from one axial end of the hub, and a load-bearing 
element 14 in the form of a helix extending radially outward from the hub. 
The hub 10 includes a longitudinal axis 16 and includes two axial ends 18, 
20. As mentioned, the lead point 12 of the anchor extends axially from one 
of the axial ends 18. The other axial end 20 is adapted to be connected, 
via a threaded connection or the like such as that shown in FIG. 3, to an 
elongated rod 22 capable of carrying a load once the anchor is installed 
to a desired depth beneath the surface of the soil. 
As shown in FIG. 2, the hub 10 includes a cavity 24 having a non-circular 
shape when viewed in a plane transverse to the longitudinal axis. By 
forming the hub 10 with a cavity of this shape, it is possible to insert a 
wrench (not shown) having a cooperating shape into the hub and to turn the 
wrench about the longitudinal axis in order to screw the anchor into the 
soil. When viewing FIG. 2, the anchor must be turned in the clockwise 
direction during such installation. 
The cavity 24 is also shown in FIG. 3, and extends circumferentially around 
an insert 26 which is connected to the anchor during construction thereof. 
The insert 26 is preferably constructed of a hot rolled steel and 
preferably is formed of a steel such as AISI No. C 1035 steel of standard 
bar quality. However, it is possible to form the insert 26 of other known 
materials or to form the insert of the same material as the remainder of 
the anchor. The insert 26 is provided with a threaded opening in the 
exposed axial end thereof for receiving the elongated rod, and may include 
an annular groove 28 adjacent the end thereof which is embedded in the 
anchor material. This groove 28 insures a reliable fit between the insert 
and the anchor during formation of the anchor. 
A mold 30 is illustrated in FIG. 7, which is used to construct the earth 
anchor of the preferred embodiment. The mold 30 defines a cavity 32 in the 
shape of the anchor to be formed therein, and room is provided for 
receiving a sand core 34. The core 34 positions the insert 26 relative to 
the cavity 32 so that when the anchor material is cast, the material 
surrounds and becomes connected to the axial end of the insert which 
includes the annular groove 28. After molding, the sand core 34 is removed 
leaving a space defining the cavity 24 of the finished anchor. 
The preferred material for use in the anchor is a medium carbon steel such 
as a Grade 70-36[485-250] steel. However, one of skill in the art will 
recognize that other materials may also be used in the anchor. 
Returning to FIG. 1, the lead point 12 is shown as including an axially 
extending protruding tip 36 adapted to break the soil immediately beneath 
the hub 10 during installation of the anchor and to move broken soil 
radially outward toward the load-bearing helix 14. By providing such a 
tip, the anchor is capable of passing through the soil without the hub 10 
becoming caught-upon unbroken soil and impending the movement of the 
anchor into the ground. An example of a preferred lead point 12 
construction for use in relatively high strength anchors is disclosed in 
U.S. patent application Ser. No. 451,215, filed Dec. 15, 1989, by Platz 
and assigned to the assignee of the present invention. A copy of the 
specification of this referenced application is submitted herewith as 
appendix A. 
The helical load-bearing element 14 includes a single piece of material and 
is unitary with the hub when the anchor is cast in the mold as shown in 
FIG. 7. The helix 14 extends in the circumferential direction of the hub 
10 between a generally radial leading edge 38, shown in FIG. 2, to a 
trailing edge 40 which also extends radially outward from the hub 10. The 
leading edge 38 of the helix may be provided with a cutting edge 42 for 
improving penetration of the anchor into soils, and the trailing edge 40 
preferably tapers off to a trailing tip 44. 
The helix 14 includes a predetermined constant pitch sufficient to provide 
a desired lift of the anchor during installation while preventing reverse 
rotation or removal of the anchor through the soil when the anchor is 
loaded with a tensile load. The helix 14 further includes a generally 
constant diameter such that a substantially circular outer circumferential 
edge 46 is defined which extends between the leading and trailing edges 
38, 40 of the helix. 
An upper surface 48 of the helix 14 is defined by the surface facing the 
axial end 20 of the hub 10 at which the elongated rod 22 is attached such 
that when a tensile load is exerted on the anchor through the rod, 
pressure is exerted on the upper surface 48 of the helix 14. This upper 
surface 48 opposes a lower surface 50 which is separated from the upper 
surface by a distance defining the thickness of the helix 14. This 
thickness is not constant, but rather is varied in dependence upon the 
stress expected to be experienced at different locations on the helix 14 
during loading. 
For example, because it has been observed that anchors loaded beyond their 
capacity frequently fail at the point of intersection between the trailing 
edge 40 of the helix 14 and the hub 10, an anchor in accordance with the 
present invention is provided with additional material in the vicinity of 
this point. Of course, it would not be advantageous to thicken the helix 
14 at only this point, with a sharp drop in the thickness of the helix 
immediately adjacent the point of intersection. Such sharp changes in the 
thickness of the load-bearing helix 14 would create weak spots in the 
helix thus serving only to move the point of failure from the point of 
intersection between the trailing edge 40 and the hub 10 to the point of 
intersection between the thickened region and the remainder of the helix 
14. 
Accordingly, in the preferred embodiment, the helix 14 is provided with a 
thickened region adjacent the point of intersection between the trailing 
edge 40 and the hub 10, and gradually tapers off to a relatively smaller 
thickness in both the radial and circumferential directions of the helix 
14 so that a smooth transition between the thickened region and the 
remainder of the helix is provided. For example, the thickness of the 
helix 14 at the trailing edge 40 should decrease in the radial direction 
of the helix within a region extending at least about one-half the 
distance from the hub 10 toward the outer circumferential edge 46, and 
preferably decreases in the radial direction within a region extending 
substantially the entire distance between the inner section and the outer 
circumferential edge. This gradual decrease in the thickness of the helix 
between the hub 10 and the outer circumferential edge 38 at the trailing 
edge 40 is shown in FIG. 6. 
In addition to being tapered in the radial direction, the helix 14 is also 
tapered in the circumferential direction about the hub 10. For example, 
the thickness of the helix 14 adjacent the hub 10 should decrease in the 
circumferential direction of the helix within a region extending at least 
90 degrees around the helix from the trailing edge 40, and preferably 
decreases within a region extending about 180 degrees around the helix 
from the trailing edge. Additionally, as the thickness of the helix 14 
adjacent the hub 10 decreases, the amount of tapering in the radial 
direction of the helix also decreases such that the helix becomes 
gradually more flat in the circumferential direction extending from the 
trailing edge 40 toward the leading edge 38. This tapering of the 
thickness of the helix both in the radial and circumferential directions 
is shown in FIGS. 4-6, which illustrate the thickness of the helix at 
various angular positions around the hub 10. By tapering the helix 14 in 
this manner, material is added in the region adjacent the critical point 
of load stress while being left off of the helix in areas where higher 
strength is not needed. 
As shown in FIG. 1, the helix 14 is also provided with an inner 
circumferential section 52 extending between the hub 10 and the remainder 
of the helix 14. The inner circumferential section 52 defines a transition 
zone between the helix 14 and the hub 10 and includes generally curved 
surfaces 54 extending between the hub 10 and the upper and lower surfaces 
48, 50. 
These curved surfaces provide a smooth transition between the generally 
transverse planer surfaces 48, 50 of the helix 14 and the surface of the 
hub 10 which extends in a direction generally parallel to the longitudinal 
axis. Although it is possible to provide each of the curved surfaces 54 
with a radius which remains constant in the circumferential direction of 
the helix 14 between the leading edge and the trailing edge, it is 
preferred that each of the curved surfaces defines a first radius adjacent 
the trailing edge 40 of the helix and a second radius adjacent the leading 
edge 38 of the helix, the first radius being greater than the second 
radius. 
In this manner, additional material is added to the point of intersection 
between the trailing edge 40 of the helix 14 and the hub 10, and the 
radius gradually decreases in the circumferential direction from the 
trailing edge toward the leading edge 38 such that less material is used 
in areas expected to experience lower load stresses. In an exemplary 
embodiment, the radius of each of the curved surfaces 54 decreases in the 
circumferential direction of the helix within a region extending at least 
90 degrees around the helix from the trailing edge 40, and the radius of 
each of the curved surfaces preferably decreases within a region extending 
about 180 degrees around the helix from the trailing edge. 
In use, once the anchor has been installed by conventional means known in 
the art, the rod 22 is connected to a load, such as to a utility pole to 
be retained in an upright orientation by a plurality of lines extending 
between the pole and a number of anchors, and a tensile load is exerted on 
the anchor which creates a pressure acting downward on the upper surface 
48 of the helix 14. This pressure acts on the helix in such a manner as to 
exert a relatively high load on the point of intersection between the 
trailing edge 40 of the helix and the hub 10. However, because the helix 
14 is thickened in the region of the point of intersection, and because a 
smooth transition is provided between this region and adjacent areas of 
the helix and hub, the anchor is capable of withstanding loads which are 
relatively larger than loads sufficient to cause failure of an anchor 
lacking the localized thickening of the helix. 
Although the invention has been described with reference to the attached 
drawing figures illustrating a preferred embodiment of the invention, 
equivalents may be used and substitutions made herein without departing 
from the scope of the invention as recited in the claims.