Patent Application
20130101360
The present invention relates to a helical screw pile for use as a ground anchor having a longitudinal shaft with a top end and a bottom end with a plurality of helical screw plates arranged along the shaft in increasing diameter from the top to the bottom. The screw pile includes at least two helical plates but can include three, four or more helical plates where the lower helical plate of two adjacent plates has a larger diameter. The distance between the lower plate and the plate directly above can vary depending on the soil type and diameter of the helical plates.
Conventional helical screw piles include a plurality of helical plates arranged on a longitudinal shaft having a square cross section. Typically, the helical plate with the largest diameter is disposed towards the top of the shaft and the helical plate with the smallest diameter is disposed towards the bottom of the shaft that first penetrates the ground. Turning to
Inter-helix spacing is critical to the design of the helical screw pile. Inter-helix spacing is the distance between each of the helical plates. Standard practice is to space the helical plates as a function of plate diameter so that the spacing between the uppermost plate and the middle plate is greater than the spacing between the middle plate and the lowermost plate. The most common inter-helix spacing in the industry provides spacing between the first lowermost plate and a second plate being less than the spacing between the second plate and the third uppermost plate.
A conventional screw pile shown in
With this configuration, the smallest helical plate 124 adjacent the tip 130 of the pile 100 is the first helical plate that disturbs, or breaks, the surface when the pile 100 is inserted into the ground. As the helical plate diameter increases, the amount of torque required to insert the pile 100 increases. Thus, when the top helical plate 120 with the largest diameter is driven into the ground, the greatest amount of torque that is required for rotating the helical plate 120 is compromised because of the force or impact on the smaller helical plates 120, 122, 124 already positioned below the ground surface.
In response to this recognition, certain devices have been designed to better withstand the rigors of digging large holes in the ground. Examples of prior art are disclosed in U.S. Pat. No. 2,603,319 to Dyche, U.S. Pat. No. 7,635,240 to Gantt, Jr., and U.S. Pat. No. 7,494,299 to Whitsett which are hereby incorporated by reference.
The present invention provides an easy to use helical screw pile that penetrates the ground and enables subsequent, smaller helical plates on a pile to penetrate the ground after the lowermost helical plate with the largest diameter has penetrated the ground. The helical screw pile of the invention provides a helical pile where a larger torque is concentrated towards the bottom end of the pile than the torque at the top end of the pile. In one embodiment, the helical pile is designed such that the distance between the lowermost helical plate and the adjacent helical plate is greater than that of the prior conventional piles although the spacing can vary depending on the soil and intended use of the helical pile. The spacing between the lowermost helical plate and the adjacent plate can be greater than the spacing between the uppermost helical plate and the adjacent plate.
The helical pile of the present invention has at least two helical plates on a shaft for penetrating the ground where the larger diameter of the helical plates is positioned closest to the bottom end of the shaft. The helical pile can have three or more helical plates where each helical plate has a diameter less than the diameter of the helical plate toward the lower, ground-engaging end.
The spacing between two adjacent helical plates of the invention is a function of the diameter of the lower helical plate. In one embodiment, the spacing can be three times the diameter of the lowermost helical pile although the spacing can vary. This generally results in the spacing between two adjacent helical plates being greater than the spacing of the prior devices where the smaller plate is positioned below the larger plate. The spacing between the adjacent helical plates can vary depending on the soil type, the required strength or holding force and the intended depth of penetration.
Accordingly, an object of the invention is to provide a helical screw pile having a longitudinal shaft with a top and a bottom and a plurality of helical screw plates with different diameters arranged thereon with the plate having the largest diameter located adjacent or near the bottom end of the pile. In one embodiment of the invention, each of the helical plates are spaced apart from each other a distance to provide a relatively constant torque at the bottom end of the shaft during rotation and penetration of the helical screw pile into the ground to the desired depth. The screw pile is provided with the largest diameter helical screw plate toward the bottom end of the shaft and the smallest diameter helical screw plate toward the top end of the shaft. The larger helical screw plate penetrates the ground first so that the largest amount of the torque is applied at the bottom end of the shaft. The small helical screw plates located above the lowermost plate penetrate the ground after the larger lowermost plate so that the torque necessary for the screw pile to penetrate the ground is generally less than when the smaller diameter helical plates penetrate the ground first. The arrangement of the helical screw plates enables the screw pile to penetrate the ground while applying a more constant torque to the shaft with each of the subsequent helical screw piles penetrating the ground to anchor into the ground.
Another object of the invention is to provide a helical screw pile having a longitudinal shaft with a top end and a bottom end and a plurality of helical plates arranged thereon with the plate having the smaller diameter located above a large diameter plate.
A further object of the invention is to provide a helical screw pile having a longitudinal shaft with a top and a bottom and a plurality of helical plates arranged thereon with the distance between the bottom plate and the plate second from the bottom being larger than the distance between the top plate and the plate second from the top.
Yet another object of the invention is to provide a helical screw pile having a plurality of helical plates arranged thereon wherein each of the helical plates has a thickness that is directly proportional with its diameter.
Still another object of the invention is to provide a helical screw pile having a plurality of helical plates arranged thereon wherein each of the helical plates has a diameter ranging from about six inches to about thirty inches, a plate thickness between about ⅜ to about 1.0 inch, a pitch angle between about 15° to about 30°, and a pitch opening between three and six inches.
The foregoing objects are basically attained by providing a helical screw pile for penetrating the ground and forming a support having a longitudinal shaft with a top end and a bottom end and a plurality of helical plates arranged on the longitudinal shaft in increasing diameter from the top to the bottom. A first helical plate is disposed toward the bottom end of the shaft and a second helical plate is disposed toward the top end of the shaft. The first helical plate has the largest diameter of the plurality of helical plates and the second helical plate has the smallest diameter of the plurality of helical plates.
The foregoing objects are also attained by providing a helical screw pile as explained above and further including an inter-helical spacing between adjacent helical plates equivalent to three times the plate diameter of the larger helical plate. For example, in embodiments where there are at least three helical plates arranged in descending order of helical plate diameter from the tip at the bottom end of the pile adjacent or near the bottom end of the longitudinal shaft towards the top end of the pile, the distance between the bottom plate and the middle plate directly above is greater than the distance between the top plate having the smallest diameter and the middle plate directly below the top plate.
The foregoing objects are further attained by providing a ground anchor for penetrating the ground to anchor a structure. The ground anchor comprises a shaft having a longitudinal dimension with a first leading end for penetrating the ground and a second trailing end for coupling to a drive assembly. A first helical plate is coupled to the shaft proximate the first end. The first helical plate has a first diameter and requires a first torque for penetrating the ground. A second helical plate is coupled to the shaft and longitudinally spaced from the first helical plate toward the second trailing end. The second helical plate has a second diameter less than the first diameter and generally requires a second torque for penetrating the ground that is less than the first torque where the greatest torque is concentrated toward the first end of the shaft.
As used in this application, the terms “top”, “bottom”, and “side” are intended to facilitate the description of the helical screw pile, and are not intended to limit the description of the invention.
Other objects, advantages, and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the invention.
Referring to the drawings which form a part of this disclosure:
Throughout the drawings, like reference numerals will be understood to refer to like parts, components, and structures.
The present invention is directed to a helical screw pile defining an earth or ground anchor for anchoring, supporting or stabilizing a structure. The helical screw pile for example can be used as a ground anchor or foundation anchor to inhibit movement of pipelines, towers and the like, and to support a load such as a building or other structure. The helical screw pile is attached to a suitable coupling mechanism that is attached to the structure being anchored, supported or stabilized. For purposes of convenience, the structures being anchored or stabilized are not shown in the drawings. It will be understood to those skilled in the art that in use, the screw pile is coupled to a structure such as a building to support the building or to a pipeline anchor to prevent movement of the pipeline.
Turning to
In the embodiment of
Referring to the embodiment of
The largest diameter helical plate 20 shown in
In the embodiment illustrated in
As seen in
Each helical plate 20, 22, 24 typically forms a substantially 360° helical turn. Alternatively, each helical plate can extend around the shaft less than 360° or more than 360° depending on the intended use and soil conditions. Generally, the helical plates 20, 22, 24 have a pitch angle substantially between 15° and about 30° and a pitch opening substantially between about three inches and about six inches. The pitch opening 28 is determined by the pitch angle of the helical plate in a 360° turn and corresponds to the distance between the threads of the helical plate for each 360° rotation of helical plate 20, 22, 24. In other words, the pitch opening 28 is equivalent to approximately the distance from the top of the bottom portion of the plate at the leading edge 40 to the bottom of the top portion of the opposing side of the plate at the trailing edge 42. At least one of the helical plates 20, 22, 24 has a plate thickness between about 3/8 inch and about 1.0 inch. Typically, each of the plates has the same pitch angle and pitch opening.
The primary difference between each of the helical plates 20, 22, 24 is the diameter size D1, D2, D3. Each of the helical plates 20, 22, 24 has a diameter D1, D2, D3, respectively. In one embodiment, the diameters range from about six inches to about 30 inches. Each helical plate 20, 22, 24 has a thickness that is directly proportional to the diameter D1, D2, D3 to provide the necessary strength. As the diameter D1, D2, D3 of the helical plate 20, 22, 24, respectively, increases, the thickness of the helical plate 20, 22, 24 also increases. Thus, helical plate 20, illustrated in
The spacing between the helical plates is generally a function of the plate diameter of the lower plate, soil conditions and desired anchoring strength. In one embodiment as shown in
In other embodiments, the spacing between the helical plates can be selected depending on the soil conditions, the desired depth of penetration, as well as other conditions. For example, the spacing between adjacent helical plates can be about 0.5, 1.0 or 1.5 times the diameter of the lower helical plate. In other embodiments of the invention, the spacing can be about 6 inches corresponding to about 0.5 times the diameter of the lower plate. A smaller spacing may be desirable when used in lighter soils. A typical soil condition generally benefits from the spacing between two adjacent helical plates of about three times the diameter of the lower helical plate.
The diameter of each of the helical plates can be selected as needed. In one exemplary embodiment, a three-plate pile can have plates with diameters of 12/10/8 inches and 12/8/6 inches. In other two-plate piles, the plates can have diameters of 12/10 inches, 12/8 inches and 12/6 inches.
The spacing between two adjacent helical plates can be a function of the diameter of the lower helical plate so that the spacing between the adjacent helical plates will vary depending on the diameter of the lower helical plate. The spacing can range from about 0.5 to 3 times the diameter of the lower plate. In the present invention, the larger helical plate is positioned below the smaller adjacent helical plate. The spacing between the adjacent helical plates of the present invention can be greater than the spacing between the helical plates of the prior screw piles for similar size helical plates. In the embodiment illustrated where three helical plates are provided, the spacing between the bottom helical plate and the middle helical plate is generally greater than the spacing between the corresponding helical plates of the prior devices. This embodiment results in the overall length of the screw pile of the invention being greater than the length of the prior devices for similar diameter helical plates. In one embodiment of the invention, the length of the screw pile can be similar to the length of the prior devices by reducing the diameter of the helical plates without loss of holding power during use.
In another embodiment, illustrated in
Each of the helical plates 20, 22, 24 can be integrally formed with the shaft 12 as a one piece unit. In the embodiment illustrated in
One advantage of arranging the helical pile 10 as described in the preferred embodiment with the helical plate 20 having the largest diameter D 1 on the bottom 16 of the shaft 12, closest to the tip 30 of the pile 10 penetrates the ground first and enables the smaller helical plates 22 and 24 of the pile 10 to drill into the ground surface 1 shown in
The arrangement of the helical plates on the shaft according to the present invention provides a more constant torque at the bottom end portion 16 of the shaft compared to a helical pile having the larger plate at the top end. Providing the larger of the helical plates toward the bottom end of the shaft and the smaller plate toward the top end of the shaft does not cause significant increases in torque on the upper portion of the shaft 12 as each successively smaller plate penetrates the ground. The smaller plates are able to penetrate the ground more readily by the lowermost larger plates having penetrated the ground while still providing anchoring and supporting ability. The smaller helical plates experience less penetration resistance in the ground so there is a smaller increase in torque applied to the shaft as each helical plate penetrates the ground.
Field tests have demonstrated that the preferred embodiment arrangement of the plates shown in
Field tests also demonstrate that arranging the helical pile 10 with the helical plate 20 having the largest diameter D1 toward the bottom 16 of the shaft 12 provides greater anchoring capacity and strength over a conventional helical pile 10 having the larger plate at the top end. The preferred embodiment was tested in sand and clay soils exhibit and increase in tension capacity from about 25% to about 40% when compared to the conventional configuration at similar depths. This is a significant capacity increase when the soils are homogenous and relatively consistent.
While a particular embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.
