WO2000022244A1

WO2000022244A1 - Auger

Info

Publication number: WO2000022244A1
Application number: PCT/AU1999/000864
Authority: WO
Inventors: William Joseph Kingwell
Original assignee: Vibro-Pile (Aust.) Pty. Ltd.
Priority date: 1998-10-08
Filing date: 1999-10-08
Publication date: 2000-04-20

Abstract

An auger (1) for use in ground penetration, including: an axially extending stem (12) with first and second helical auger flights (30, 34) carried by respective first and second portions (18, 16) of the stem; a third portion (14) of the stem, of cylindrical form and of substantially constant diameter substantially the same as the maximum diameters of the first and second flights, being positioned between the first and second portions; and the first and second portions extending oppositely away from the first portion with the first end constituting a soil penetration free end of the auger; wherein the third portion carries one or more helical third flights of the same pitch and hand as the first flight.

Description

AUGER

Field of the Invention

This invention relates to an auger.

Background of the Invention

Augers may be used in forming ground holes, such as in piling. A known form of auger is provided with a ground engaging thread defined by a flange, which is wound helically around a central stem of the auger. An enlarged displacement body is provided on the stem for the purpose of displacing soil radially outwardly for compaction against sides of a hole formed by the auger, as the auger is driven into a ground surface. The soil displacement increases the density of the soil adjacent the hole and improves the load bearing capacity of the soil for when a pile is subsequently formed therein.

Summary of the Invention

The present invention seeks to provide an auger design which allows for a pile to be formed in a hole, with improved load bearing capacity.

In one aspect, the invention provides an auger for use in ground penetration, including: an axially extending stem with first and second helical auger flights carried by respective first and second portions of the stem; a third portion of the stem, of cylindrical form and of substantially constant diameter substantially the same as a maximum diameter of the first and second flights, being positioned between the first and second portions; and the first and second portions extending oppositely away from the third portion with an end of the first portion constituting a soil penetrating free end of the auger; wherein the third portion carries one or more helical third flights of the same pitch and hand as the first flight.

Provision of one or more third flights on the third portion of the stem allows the auger to grip into a wall of a hole produced by the auger, in soil compacted by the third portion, whilst forming associated spiral groove(s) in the soil which may later be filled with injected concrete of a pile to enhance load transfer capacity between the soil and the pile.

The first and second flights are preferably of the same pitch and hand, and may be of substantially the same diameter. The first flight may however taper towards said free end. For example, it may uniformly taper, or it may taper more severely close to the free end. The first flight is also preferably of uniform pitch.

In another aspect, there is provided an auger for use in ground penetration, including: an axially extending stem with first and second portions, at least the first portion carrying a first flight; and a third portion of the stem, of cylindrical form and of substantially constant diameter substantially the same as a maximum diameter of the first flight; wherein the first portion extends away from the third portion so as to constitute a soil penetrating end of the auger; and wherein the first portion has a substantially uniform taper toward said end.

Preferably, the first flight has a substantially uniform pitch. This second aspect focuses on the advantageous configuration of the first portion of the auger which has been found to minimise torque requirements for installation. In particular, the continuous smooth or uniform taper in combination with the uniform pitch of the first flight allows for soil moving up the auger to be progressively displaced toward the hole wall, which reduces torque requirements, as compared to a conventional auger which has a stepped taper and/or increasing flight pitch. Further, the taper allows the length dimension of the first portion to be minimised so that the third portion is positioned near to the end of the auger so that soil compaction occurs along a maximum length of the pile to be formed and, in particular near to the base of a pile, for maximum structural advantage.

Preferably there are two third flights, equi-spaced in the lengthwise direction of the extend of the third portion.

The first and second portions may taper uniformly, but stepped formations could be employed. The lower portion may also be formed with outer surfaces of helical form, generally parallel to the auger axis, but of progressively decreasing radius.

The first and second flights may be single start flights.

The flights may each be of uniform thickness, and that thickness may be the same for each flight. However, it may be advantageous for at least the thickness of the first flight to vary, such as being of greater thickness at locations near the axis of the auger.

There may be, associated with the first flight, a movable blocking element which, when the auger is rotated in a direction for advancement into the ground, is positioned in a non-blocking position, but which is moved to a blocking position on subsequent rotation of the auger in the opposite direction under influence of contact with surrounding ground, the blocking element, in the blocking position blocking the first flight between axially adjacent convolutions thereof at a location towards the free end of the first portion.

The stem of the auger may be hollow so as to define a passageway to permit flowable settable material such as concrete to be passed therethrough to emerge from an opening at said free end. The end of the first portion may also be provided with a cap member which is releasable from a position at which it closes the passageway in the stem to a position at which the passageway is open. The invention also provides a method of forming a ground void by use of the described auger, wherein the auger is disposed in an upright position on a ground surface with the first portion lowermost, and the auger is rotated in a first direction to cause it to penetrate the ground and be drawn thereinto by screwing action, so as to displace the ground laterally.

The method may further comprise rotating the auger in a second direction, opposite the first direction, to withdraw the auger from the ground. During withdrawal, whether by said rotating in the second direction and/or by lifting, concrete, or other settable material may be passed through the auger to the exit from a location at the lower end, for filling the ground opening with concrete to form a set pile.

The invention also provide a method of forming a ground pile by use of the described auger, including: a) disposing the auger in upright position on a ground surface and with the first portion lowermost, b) rotating the auger in a first direction to cause it to penetrate the ground beneath the ground surface and be drawn thereinto by screwing action, and to cause the auger to form a void, c) withdrawing the auger from the void, and passing flowable settable material into the void below the auger, d) allowing the settable material to set whereby to form the pile.

In these methods, rotation of the auger may be stopped as the auger reaches founding level, to avoid shearing of ground material adjacent the outer edges of the flights.

The withdrawal may be effected by rotating the auger in a direction opposite to said first direction, and/or by upward lifting, such as by winching. Brief Description of the Drawings

The invention is further described by way of example only with reference to the accompanying drawings in which: Figure 1 is partly axially sectioned side view of an auger constructed in accordance with the invention;

Figure 2 is a side view of the auger of Figure 1 ; and

Figure 3 is a bottom end view of the auger of Figure 1.

Detailed Description of a Preferred Embodiment

The illustrated auger 10 is designed to be rotationally driven to drive the auger lengthwise into the ground to form a hole in which a pile may be formed. The auger 10 is a single start continuous flighted auger of constant pitch and constant diameter (although not of the same dimension everywhere). The auger, as illustrated, has right-handed flights, but the flights could of course be left-handed if desired.

Auger 10 has a stem 12 having an enlarged end part 15 which is in use of the auger lowermost. The part 15 has a lower first portion 18 at the free end of the stem, an upper second portion 16, and an intermediate portion 14 which is intermediate portions 16, 18. Portion 14 is of cylindrical form, and portions 16, 18 are of frusto-conical, tapered, form. Portions 14, 16, 18 are each of circular form viewed along the axis 50 of the auger and stem 12.

The end portion 18 away from portion 14 in use constitutes the bottom end of the auger, and may be fitted with replaceable cutting teeth 20 which may be of known form, being selected in accordance with the nature of soil or rock to be penetrated with the auger. The end of tapered portion 16 is attached to an elongate cylindrical tubular stem part 22 of stem 15, which is attached, at the end thereof opposite to the stem portion 16, to a suitable connection 24 which, in use of the auger is uppermost, and which is connected to suitable drive means for rotating the auger.

The following auger flights are provided on the auger 10. These being of substantially the same, constant, outer diameter: (A) helical flight 30 on portion 18;

(B) flights 32a, 32b on portion 14; and

(C) single start flight 34 on portion 16.

Flights 30, 34 are of the same diameter, hand and pitch. The diameter of the portion 14 is substantially constant throughout its length, and substantially the same as the diameters of the flights 30, 34.

Flights 32a, 32b constitute a multi start flight structure 32. Flight 32b is a continuation of the lower and upper single start flights 32, 30 and convolutions of this are situated mid- way between convolutions of the flight portion 32a. The diameter of flights 32a, 32b, are preferably the same, and only a small amount greater than the diameter of the flights 30, 34. Flights 32a, 32b may, for example, be formed from 20mm square steel section, the outside diameter of these thus being 40mm greater than the diameter of the portion 14 and the upper and lower flights 30, 34. Flights 32a, 32b are of the same pitch and hand as flights 30, 34.

The ratio of the lengths of the central, top and bottom portions 14, 16, 18 of the stem 12 may be approximately 2:3:5, but may be varied to suit conditions and objectives. The constant pitch of the flights may be 0.45 times, such as 0.3 to 0.6 times, the diameter of the central portion 14.

The stem 12 as shown is largely hollow. As shown in Figure 1, it is has an elongate axially extending tubular member 40, of circular cross-section, this defining the stem part 22, and also, however, continuing into and carrying the stem part 15. At its lower end, the member 40 is affixed to a frusto conical end piece 42 which forms the lower end of portion 18 of the stem. This end piece 42 is hollow, as is the connector 24 at the opposite end of the auger, so that there is defined, within the auger, an axial passageway 38 which extends from end to end thereof. This opens to a lower port 36 at the lower end of portion 18 of the auger stem. This port is however closed and sealed by 5 means of a watertight drop off recessed plug 26, which may be retained for re-use by an attached chain 28.

Also mounted on the end piece 42, at the end of the lower end flight 30, is an optional hinged flap 36, which pivots vertically in use of the auger, and about a hinge pin

10 44 recessed into the portion of the flight 30 above the cutting teeth. This flap 36 is free to move through an arc of approximately 50° between a fully closed position (illustrated), with the bottom end resting on the end of flight 30 below the hinge pin 44 and back up the flight, to a fully open position, shown by broken lines 36a, where it makes an angle of approximately 5° to the flight on which it is hinged.

15

The top end of auger portion 16 may taper to approximately 325mm outside diameter, the lower end tapering to 220mm at its base. The top end of the upper auger stem portion 16, may continue at 325mm diameter for a distance of approximately 300mm where it terminates in a semi-flush joint for attaching the auger to the hollow main stem 0 part 22.

The auger 10 is intended to be employed to construct cast in place, concrete injected, fully or partially reinforced load bearing (vertical and lateral) piling. The auger design is such that ground or soil will be displaced to the full diameter of the pile to be 5 formed and as such this greater than, a driven precast concrete pile of the same proportions or displacement. The pile will be installed with little vibration or impact noise.

The auger 10, coupled to a rotary drill table is screwed into the soil by applying 0 torque as required to enable as high a rate of penetration per revolution of the auger as possible. Ideally the rate of penetration would be one flight pitch per auger revolution.

The auger can be allowed to penetrate either under its own weight and that of the drill stem or by assisting penetration by downwards winching or jacking the drill stem of the auger into the soil.

As the auger 10 penetrates, the tapered stem forces the soil at any point, laterally and progressively further as the portion of the auger stem passing that point, increases in diameter. This lateral soil displacement continues until the auger stem passes that point, at its maximum diameter, which occurs as the cylindrical central portion 14 of the auger passes that point.

In penetrating the soil, the auger makes use of the uniform pitch and continuity of the auger flights, to screw itself in rather than penetrating by excavating and 'lifting' soil on its flights and clearing the way for the auger to penetrate, although in very dense soils or weak rock this latter technique can be used for limited penetration in such strata when 'screwing in' is not possible owing to torque limitations or the auger penetration rate falling such as to be below one flight pitch per revolution. It has been found that the continuous smooth or uniform taper in combination with the uniform pitch of the first flight allows for soil moving up the auger to be progressively displaced toward the hole wall, which reduces torque requirements, as compared to a conventional auger which has a stepped taper and/or increasing flight pitch. The taper also allows the overall length of the first portion to be reduced whilst still achieving suitable soil displacement.

Auger penetration continues until the predetermined founding level or penetration resistance is reached and the auger is restrained from further penetration while one full revolution is completed, to ensure that the boundary of the cylinder of soil contained within the lower tapered stem flight 30 is completely sheared by and will be retained on, the auger. Alternatively, when the auger reaches the founding level (corresponding to the intended pile depth), rotation may be stopped immediately so as to avoid shearing the soil at the outer edge of the auger flights, ensuring that when the auger rotation is reversed at the commencement of extraction, the soil contained between the flights will remain in place and not be lifted out on the auger flights. In this alternative application, the optional, movable blocking element is not fitted.

Highly workable concrete is pumped under pressure through the stem 12, forcing the sealing plug 26 off the lower end of the auger and injecting concrete into the void that the auger leaves behind as it is extracted by a reverse direction screwing action. The extraction may be assisted by upwards winching.

As the auger rotation direction is reversed at the commencement of extraction, the highly compacted soil in between the flanges of the auger flights tends to remain in place, relative to the surrounding soil, as the auger screws out; but as its relative downward movement on the auger flights commences, the protruding hinged flap 36, if fitted, at the bottom of the flight is forced to close, trapping the soil on the flights. Thus the auger is extracted, leaving a void of the full diameter of the auger, to be concreted.

The extraction/concreting action is continued until the auger tip reaches surface level. It is possible, for example by use of computer operated monitoring devices, to ensure that the void is completely filled by concrete under pressure, partial or full length steel reinforcing being then inserted into the highly workable pile concrete, such as by using vibration assistance from a clamp-on hydraulic vibrating piling hammer.

During extraction, not only the flights on the upper portion of the auger contribute to the screwing out process, but the lower flights similarly are effective owing to the high lateral pressure and the friction developed between the edges of the flights and the adjacent soil. The proportions of the components of the auger 10 may be varied to suit specific purposes. However, the following considerations may be taken into account when selecting dimensions.

(i) The portion 18, in use below central cylindrical portion 14, may be of a length sufficient to enable the auger to "grip" the soil in a similar manner to a wood screw, and thus draw itself deeper into the soil, minimizing or dispensing with the need to apply a vertical thrust to assist penetration. This length is preferably kept short enough to ensure that full compaction or densification of the soil occasioned by the passage of the cylindrical portion 14 of the auger at the founding level of the auger, occurs near to the base of the auger and therefore the base of the pile being formed. To that end, the tapering of the first portion allows the length dimension of that portion to be reduced so that compaction by the cylindrical portion can occur as close to the end of the auger as possible. This is desirable so as to ensure that the maximum end or base resistance of the pile is obtained. Thus the diameter of the lower end of portion 18 may be 220mm, and the portion 18 may increase uniformly in diameter to that of the cental cylindrical portion 14 such as an angle of approximately 15° degrees to the central longitudinal axis of the auger, such as an angle in the range 10 to 20°.

(ii) The length of the central cylindrical portion 14 of the auger stem is preferably proportioned so as to provide a length to diameter ratio sufficient to prevent displaced soil below and adjacent to this portion from flowing vertically up and around the central portion and into the void created by the passage of the auger through the soil. The configuration of portion 14 should also minimize the surface friction area of this portion and thus the amount of auger driving torque required to overcome this. A ratio of length/diameter of 0.67 has been found satisfactory. Higher ratios, such as 1.5 may be useful in some cases. Generally ratios in the range 0.5 to 2 may be satisfactory. The small (20 x 20) double start flight portions 32a, 32b on portion 14 of the auger provide additional 'thread' to assist the auger in maintaining its 'grip' on the soil, enabling it to continue to spiral into the soil at the rate of one pitch per revolution. These flights, while small, are very effective in gripping the soil which, at this location on the auger has been very highly compacted and presents high resistance to shearing by the flights, thus enabling them to drive the rotary auger downwards.

Flights 32a, 32b, being larger in diameter than the upper and lower flights 34, 32 and the portion 14 of the auger stem, leave a double start spiral groove in the wall of the soil cavity formed by the auger during driving. During subsequence reverse rotation for auger extraction, these grooves may be filled with the injected concrete, adding to the finished pile shaft to soil, load transfer capacity and therefore pile load capacity.

(iii) The upper portion 16 of the auger 10 is also tapered, but in the opposite direction to the bottom portion 18, although the pitch and diameter of the flight on this is preferably the same as for the lower portion 16. This portion 16 contributes to the penetration capacity of the auger but functions primarily during extraction of the auger when the direction of rotation of the auger is reversed to assist extraction.

During the extraction stage, the auger 10 is winched upwards whilst reversing the direction of the auger rotation to that used for penetration. As the auger moves upwards, the tapered upper stem portion 16, and auger flight 34 function by drawing in any loosened or collapsed soil and compacting it by lateral displacement into the adjacent soil. This recompaction also assists extraction of the auger in a similar manner to the screwing- in action of the auger. The taper of this upper portion 16 is preferably set to optimise this function and may be 15° to the vertical axis of the auger, commencing at full diameter of the central cylindrical portion 14 of the auger and reducing to 325mm diameter at its top end.

In one form the part 15 is about 2400mm long, with portions 16, 18, 14 being about 750mm, 400mm and 1250mm long, respectively, portion 14 being of 650mm diameter, excluding the flights 32a, 32b.

Although, in the described auger, the lower flight 30 is of substantially constant diameter, it may also, in an alternative construction, taper, decreasing in diameter towards the lower end of the auger. That is it may, for example, decrease in diameter uniformly towards the lower end. Generally, it is possible to uniformly or otherwise progressively reduce the outer diameter of flight 30 commencing with full diameter at the top and reducing to say 100mm lesser diameter at the lower end of the flight. It may also taper more severely towards its free end, such as over the last half turn (ie. about 180°).

The described auger flights are formed from uniform thickness plate, however it may be advantageous in certain circumstances to form the flight 30 with a greater thickness near the root of the flight where it connects to the lower first portion 18 of the auger. For example, the flight may be made up of concentric co-joined annular portions of successively greater diameter, and of successively lesser thickness away from the auger axis. Thus, for example, the lower flight 30 may increase in thickness, either uniformly or in steps, from say 25mm at its outer edge, to say 50mm or more at its lower end, where it joins the lower tapered auger portion 18. This may occur for the entire length of flight 30. By this, at the top end of the flight 30 the width of the flight approaches zero and therefore, for uniform rate of thickness increase, in this case the thickness of the flight where it joins portion 18 would be only marginally more than at its outer edge.

The portion 18 may be formed with an outer surface being the locus of a line generally parallel to the auger axis, rotated about the auger axis with progressively decreasing diameter, as it is progressively moved along the auger axis, the pitch of the so- formed helix being substantially equal to the length of the generating line. Thus, the outer surface may be of lengthwise extending helical form, of decreasing diameter along the auger axis. In such case, the flight 30 may extend outwardly at steps formed between adjacent convolutions of the helix. Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims

THE CLAIMS:

1. An auger for use in ground penetration, including: an axially extending stem with first and second helical auger flights carried by respective first and second portions of the stem; a third portion of the stem, of cylindrical form and of substantially constant diameter substantially the same as a maximum diameter of the first and second flights, being positioned between the first and second portions; and the first and second portions extending oppositely away from the third portion with an end of the first portion constituting a soil penetrating free end of the auger; wherein the third portion carries one or more helical third flights of the same pitch and hand as the first flight.

2. An auger as claimed in claim 1, wherein the first portion tapers toward the free end.

3. An auger as claimed in claim 2, wherein the taper of the first portion is substantially uniform.

4. An auger as claimed in any one of claims 1 to 3, wherein the first flight has a uniform pitch.

5. An auger as claimed in any one of claims 1 to 4, wherein the second portion tapers in a direction away from the third portion.

6. An auger as claimed in any one of claims 1 to 5, wherein the first and second flights are of the same pitch and handedness.

7. An auger as claimed in any one of claims 1 to 6, wherein the first and second flights are of substantially the same diameter.

8. An auger as claimed in any one of the preceding claims, including two third flights, equi-spaced in the length direction of extent of the third portion.

9. An auger as claimed in any of the preceding claims, wherein at least the first flight has a thickness which is greater at locations toward an axis of the auger.

10. An auger as claimed in any one of the previous claims, including a movable blocking element associated with the first flight, between axially adjacent convolutions thereof at a location toward the free end of the first portion, the element being arranged to move between a non-blocking position, when the auger is rotated in a direction for advancement into the ground, and a blocking position on subsequent rotation of the auger is in an opposite direction in order to block soil moving along the first flight towards the free end thereof.

11. An auger as claimed in any one of the preceding claims, wherein the auger is hollow so as to define a passageway to permit flowable settable material such as concrete to be passed therethrough to emerge from an opening at said free end.

12. An auger as claimed in claim 10, wherein the end of the first portion is provided with a cap member which is releasable from a position at which it closes the passageway in the stem to a position at which the passageway is open.

13. An auger for use in ground penetration, including: an axially extending stem with first and second portions, at least the first portion carrying a first flight; and a third portion of the stem, of cylindrical form and of substantially constant diameter substantially the same as a maximum diameter of the first flight; wherein the first portion extends away from the third portion so as to constitute a soil penetrating end of the auger; and wherein the first portion has a substantially uniform taper toward said end.

14. An auger as claimed in claim 13, wherein the first flight has a substantially uniform pitch.