DRILL TIP FOR FOUNDATION PILE

Abstract

An improved drill tip for a foundation pile comprises a frustro-conical upper section, a cylindrical middle section, and a generally conical lower section, all disposed in coaxial alignment about a center axis, the upper section for attachment to a foundation pile, and having a bottom edge diameter smaller than a top edge diameter and an upper helical flight having a radial extent less than the top edge diameter, the middle section extending from the bottom edge of the upper section and having approximately the same diameter as the bottom edge diameter, and the lower section extending from a lower edge portion of the middle section and having a plurality of symmetrically disposed helical fins having a radial extent less than the bottom edge diameter, the lowermost portion of the fins extending freely below the conical main body of the lower section in a configuration resembling a swiveling fishtail.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Application No. 61/243,495 filed Sep. 17, 2009.

FIELD OF THE INVENTION

This invention is directed to rotary foundation pile drilling technology and in particular to a drill tip for screw-type foundation piles that has an improved ability to penetrate the soil.

BACKGROUND

Deep foundations are widely used as foundation elements for structures. Two well known classes of piles are non-displacement piles and displacement piles. The former are installed by excavating a cylinder of soil from the ground and replacing it with some form of reinforcement, commonly, concrete. By far the most common method of excavating the soil is by use of an auger, giving rise to the term auger cast-in-place (ACIP) piles.

Displacement piles are either driven or drilled into the ground. Displacement piles laterally displace soil surrounding the pile shaft and load soil materials below the toe of the pile. Displacement piles are generally understood to have a stiffer response than non-displacement piles, and are capable of carrying larger loads than non-displacement piles. However, driving piles into the ground can result in excessive vibration and noise and are, therefore, problematic under certain conditions.

Drilled displacement piles are rotary displacement piles installed by inserting an auger into the ground with the combined application of torque and vertical force, the latter commonly referred to as “crowd.” The auger may be a continuous flight auger or a pile to the bottom end of which is attached an auger tip. Drilled displacement piles have favorable end bearing and skin friction capacities compared to ACIP piles. However, they are more expensive to install due to the need for heavy drill rigs required to produce the torque and crowd forces to drive the pile into the soil. An installation process that is less efficient correspondingly increases the expense of the foundation. There is, therefore, a need for improved drilled displacement piles to reduce the power requirements and expense associated with their installation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view of an improved drill tip according to the invention, attached to the lower end of a foundation pile.

FIG. 2 is a side elevation view of the drill tip shown in FIG. 1.

FIG. 3 is a side elevation view of the drill tip taken at approximately right angles to the view shown in FIG. 2.

FIG. 4 is a lower perspective view of the drill tip shown in FIGS. 1 and 2.

FIG. 5 is a bottom view of the drill tip shown in FIGS. 1 and 2.

FIG. 6 is a sectional view of the drill tip shown in FIG. 2 taken along lines 6-6 of FIG. 2.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

An improved drill tip according to the invention is indicated generally in FIG. 1 at 10 and is shown attached to the lower end of a conventional cylindrical foundation pile 12. With reference to FIG. 2, the drill tip 10 includes an upper section 14, a middle section 16 and a lower section 18 firmly secured together in coaxial alignment about a center axis A. The upper section 14 has a top edge 20 and a bottom edge 22, the top edge 20 having a cross-sectional top diameter D_T larger than the bottom diameter D_B of the bottom edge 22, giving the section 14 an overall frustro-conical geometry. The top of the upper section 14 is attached to pile 12. In the illustrated embodiment the top diameter D_T is the same as the diameter of the pile 12, but it will be readily understood by those of skill in the art that top diameter D_T could exceed that of the pile 12 as needed.

An upper helical flight 24 is provided on the tapered outer surface 26 of upper section 14 extending vertically from near top edge 20 to bottom edge 22, and passing through an arc of approximately 180° around center axis A. Upper helical flight 24 has a comparatively shallow upper flight depth 28, shown in FIG. 2, such that it does not extend radially beyond the top diameter D_T. Those of skill in the art will recognize, however, that considerable variations in the depth of upper flight are possible such as variable depth of upper flight 24, e.g., an increasing depth toward the bottom of the flight, and a depth which extends somewhat beyond top diameter D_T.

The middle section 16 is attached to the bottom edge 22 of and depends from the upper section 14. Middle section 16 has a diameter equivalent to bottom diameter D_B as illustrated, but it will be readily appreciated that the middle section diameter may be somewhat smaller or larger than bottom diameter D_B as appropriate for soil conditions. A middle helical flight 30 is provided on the surface of middle section 16 and extends vertically from approximately the intersection of the upper and middle sections 14, 16, at bottom edge 22, to approximately the lower edge portion 32 of middle section 16 as seen in FIGS. 2 and 3, and extends through an arc of approximately 180° partially overlapping the arc through which upper flight 24 extends. The depth 34 of middle flight 30 is noticeably greater than the depth 28 of upper flight 24, such that the middle flight 30 extends radially from the surface of middle section 16 to a distance approximately the same as top diameter D_T. See FIG. 5. Those of skill in the art will understand that the depth of middle flight 30 may extend a distance somewhat greater than that of top diameter D_T. Middle flight 30, as illustrated, is disposed roughly opposite to upper flight 24 with respect to center axis A providing a symmetrical relationship between the actions of the flights 24, 30.

As perhaps best shown in FIG. 2, upper and middle flights 24, 30 have approximately the same pitch, that being less than the distance between top edge 20 of upper section 14 and lower edge portion 32 of middle section 16, but greater than half that distance.

As shown in FIG. 4, lower section 18 is attached to and depends from the lower edge portion 32 of middle section 16. Lower section 18 comprises a generally conical main body 38 and a plurality of symmetrically disposed inwardly sweeping helical fins 40 extending outwardly from main body 38. The upper part of main body 38 is fixed to and has a diameter smaller than that of middle section 16. While the embodiment illustrated in FIG. 4 shows the lower section 18 depending from the lower face 36 of middle section 16, those of skill in the art will understand that the connection between middle section 16 and lower section 18 may have other structural designs such as a gradually sloping transition between the lower edge portion 32 of middle section 16 and the upper part of the main body 38 of lower section 18. In the illustrated embodiment, outwardly radiating fins 40 extend from an upper portion 42 (see FIGS. 4, 5, and 6) just below lower edge portion 32 and terminate below the low point 44 (see FIG. 2) of main body 38 in a plurality of overlapping freely extending blades 46 having a form resembling a swiveling fishtail. The upper portions 42 of fins 40 have a radial extent no greater than the diameter of middle section 16 in the illustrated embodiment. However, it will be understood that fins 40 could extend beyond the diametric footprint of middle section 16. Each of the fins 40 has a relatively uniform fin depth throughout its length. That depth is carried through to blades 46 which are disposed adjacent to axis A. The illustrated embodiment shows two fins 40, but it is intended that the invention also embrace three, four, or more symmetrically disposed helical fins.

Fins 40 have a pitch substantially greater than the pitches of upper and middle helical flights 24, 30, given them more of a scooping action than flights 24, 30. Conversely, flights 24, 30, having shorter pitches, exhibit more of a biting or grabbing action on the surrounding medium.

Piles typically have diameters of 12, 14, 16, 18, 20, 22, 24, 30 or 36 inches. Although the drill tip described above can be constructed according to any of these pile diameters, it is expected that the improved drill tip will most commonly be used with piles have diameters of 12.75″ and 16.00″.

It will also be understood that the configuration of the drill tip may be modified as required to accommodate different soil profiles.

In normal operation in the field, after the drill tip 10 is attached to a hollow foundation pile 12 as shown in FIG. 1, the combination is gripped in a pile drilling rig or drill table and placed on the ground surface. Torque is then applied to the pile together with downward force that causes the tip and pile to penetrate the ground. In extensive testing, applicants have determined that the combination of features in the pile tip described above results in an improved ability to penetrate the soil. One aspect of the favorable penetrating properties of the tip, is an improved capacity to pull the pile into the ground. The improved soil penetration capacity of the improved drill tip decreases the amount of torque required to turn the pile into the soil and optimizes the time needed to install the pile. The improved drill tip also has a better end bearing capacity than existing drilled displacement piles. After the pile reaches the desired depth, the pile is cut off at the proper pile elevation according to the foundation design and reinforcement and concrete is inserted into the pile. Alternatively, the pile may be left hollow and a mechanical connection added to the outside of the pile to connect the pile to a pile cap.

There have thus been described and illustrated certain preferred embodiments of an improved drill tip for a foundation pile according to the invention. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims and their legal equivalents.

Claims

1. A drill tip for a foundation pile, the drill tip comprising:

a frustro-conical upper section having a top edge and a bottom edge, said top edge for attachment to the foundation pile, said top edge having a top edge diameter, said bottom edge having a bottom edge diameter smaller than said top edge diameter, and said upper section having an upper helical flight having a radial extent generally no greater than said top edge diameter,

a cylindrical middle section extending from said bottom edge and having approximately the same diameter as said bottom edge diameter, and

a generally conical lower section extending from said lower edge portion of said middle section, said upper, middle and lower sections disposed in coaxial alignment about a center axis.

2. The drill tip for a foundation pile of claim 1 wherein:

said middle section has a lower edge portion and a middle helical flight having a radial extent generally no greater than said top edge diameter.

3. The drill tip for a foundation pile of claim 2 wherein:

said lower section has a generally conical main body and a plurality of symmetrically disposed helical fins having a radial extent generally no greater than said bottom edge diameter, a lowermost portion of each said fin extending freely below said conical main body forming a plurality of blades resembling a swiveling fishtail.