WO1994002687A1

WO1994002687A1 - Apparatus and method for forming piles

Info

Publication number: WO1994002687A1
Application number: PCT/AU1993/000364
Authority: WO
Inventors: John Paul Wagstaff; Roderick Thomas Campbell
Original assignee: Wagstaff Piling Pty. Ltd.
Priority date: 1992-07-24
Filing date: 1993-07-21
Publication date: 1994-02-03
Also published as: ZA935287B; TW232041B; CN1087397A

Abstract

A pile forming apparatus (10) comprises a drill stem (11) having a tapered nose (12) adapted to be drilled into the ground to form a bore. The drill stem (11) has radially expandable arms (16) which displace surrounding soil outwardly to form a cavity around the bore when the drill stem (11) is rotated. The cavity is filled with grout pumped from the ground surface through a pipe (20) in the drill stem to openings (21, 22) near the arms (16) and the tip of the nose (12). The bore is also filled with grout as drill stem (12) is raised. Additional cavities may be formed at selected depths to suit the soil profile. The resultant pile is a cast displacement pile having one or more radially enlarged portions at selected depths. Alternatively, a radial extension of the pile may be formed helically along the pile by raising and rotating the pile with the arms (16) extended.

Description

"APPARATUS AND METHOD FOR FORMING PILES" THIS INVENTION relates to a concrete displacement pile having sections of varying diameter, and apparatus and method for forming the pile. BACKGROUND ART

There are various known types of concrete piles. For example, concrete piles may be precast, or cast in place. Precast piles are normally hammered into the ground to form so-called "displacement" piles, i.e. the surrounding soil is displaced to accommodate the passage of the pile into the soil. On the other hand, piles which are cast in place are normally non- displacement piles as the concrete is poured into predrilled bores or tubes. Displacement piles have greater pile bearing capacity due to greater skin friction and greater end bearing between the pile and the displaced surrounding soil.

However, the installation of displacement piles has certain inherent disadvantages or problems. For example, a pile driver of high power rating is normally required for hammering the piles into the soil, and the associated noise and vibration may limit the area and times of operation of such pile drivers, thereby increasing construction times and costs. The bearing capacity of a pile is largely dependent on the cross sectional area of the pile, particularly at the pile base. However, increasing the diameter of a constant section displacement pile for the purpose of increasing pile bearing capacity will require much more material and higher pile driving power. To overcome this problem, it is known to provide an increased diameter portion on a pile only at its base. German patent specification no. 3035346 describes a method for producing a concrete foundation pile with a larger diameter foot. A tube is driven into the ground, and the soil within the tube is excavated. Wet concrete is placed in the bottom of the tube and a rotatable shaft with radially expandable scraper arms is lowered into the tube. The tube is then raised by an amount equal to the required height of the foot and the arms are extended so that the setting concrete mixes with soil which is loosened or excavated by the radial arms. The shaft is then removed, reinforcing is inserted in the tube which is then filled with concrete, and finally the tube is removed to leave a cast concrete pile with an enlarged footing. The. abovedescribed procedure is time consuming, and hence expensive, and the resulting pile is a non- displacement pile. Furthermore, the enlarged diameter is provided only at the foot.

To obtain the benefits of displacement piling, it is known to expand the base of a tube inserted in the ground by forcing unset concrete under pressure into the base of the tube to thereby expand the base into the surrounding soil. Examples of such piles can be found in United States patents 4906141 and 4544515, and British patent 2122241. However, the known techniques are suitable for forming enlarged diameter portions only at the foot of the pile, and have associated noise and vibration problems.

British patent specification 2143565 describes a foundation pile comprising a tube having radially deformable sections. The tube is first driven into the ground and then progressively filled with concrete. At each stage, the concrete is tamped down, causing the deformable sections of the tube to form enlargements. French patent specification no. 2386646 describes a tubular metal pile which is driven into the soil in the normal manner and then radially enlarged at spaced locations along its length by an internal hydraulic cell which applies radial pressure to the tube, causing it to deform outwardly. The tubular pile may be filled with concrete once so deformed. Although the piles formed by the methods described in the British and French patents have enlarged diameter portions along their length, the piles are primarily non-displaceme t piles, the only "displacement" being the increase in diameter at each deformation of the tube. Further, these piles require the preliminary step of driving a metal tube into the ground, and leaving the tube in the ground, thereby adding to the time and cost of construction. It is also known to screw precast piles into the ground. However, such piles require high power drivers and the auger-like flights around the pile weaken the surrounding soil thereby losing some of the benefit of displacement piles. It is an object of the present invention to provide an improved pile, and apparatus and method for forming same, which overcome or ameliorate the abovedescribed disadvantages, or which at least provide the consumer with a useful choice. SUMMARY OF THE INVENTION

In one broad form, the present invention provides a method of forming a pile having one or more radially enlarged portions. An elongate drill member is inserted into the ground to form a bore by displacing the surrounding earth radially outwardly. The term "earth" is used generally in this specification to include soil, sand, mud and other ground materials.

The drill member is provided with at least one arm which is extendible and retractable in a radial direction. Once the elongate member has been drilled to the desired depth, the arm member is extended radially to further displace surrounding earth outwardly. The drill member is rotated, causing the arm member to form a cavity around the drill member. This cavity is filled with settable material, such as cementitious grout, from which the pile is to be made. This material is typically fed through a conduit passing longitudinally through the drill member and having an opening adjacent the arm(s).

The conduit also has an opening adjacent the leading end or toe of the drill member such that when the drill member is raised, the bore formed below the drill member is also filled with the settable material under pressure. Portions of increased diameter are formed on the pile by maintaining the drill member at a constant depth while it is rotated with the arm(s) extended, and filling the annular cavity so formed with grout. Typically, a foot of enlarged diameter is formed near the bottom end of the pile. However, the flange-like collar portions on the pile can be formed at other selected depths to maximise pile bearing capacity for that particular soil profile. As each portion of the bore is filled shortly after each annular cavity of increased diameter is filled, the resultant pile is an integrally formed, cast in place, displacement pile having portions of increased diameter at desired depths.

In an alternative method, the arm is extended while the drill stem is simultaneously raised and rotated. The arm therefore forms a spiral cavity around the bore cavity, both of which are filled with grout under pressure to form an integral spiral pile.

In another broad form, this invention provides apparatus for forming a pile, comprising an elongate drill member adapted to be inserted into the ground to form a bore by displacing surrounding earth radially outwardly, the drill member having at least one arm member which is extendible and retractable in a radial dimension; means for rotating the drill member about its longitudinal axis; means for extending the arm member to further displace surrounding earth radially outwardly and form a cavity around the drill member as it is rotated; means for withdrawing the drill member along the bore; and delivery means for forcing settable material into the cavity, and the bore as the drill member is withdrawn, to thereby form an cast pile having at least one enlarged diameter portion.

The elongate drill member typically comprises a steel pipe drill stem which may be driven or screwed into the ground. Preferably, the drill stem is rotated into the ground and is provided with a conical nose and a spiral flight auger around its nose for that purpose. As the drill stem is screwed into the ground, it forms a bore by displacing and compacting the soil around it, until the design depth has been reached.

In one embodiment of the invention, two arms are mounted in the drill stem in diametrically opposed positions. The pair of arms are pivotable about respective longitudinal axes displaced from the central longitudinal axis of the elongate member. Each arm is of a predetermined (axial) thickness and has an outer surface which matches the curvature of the drill stem. When the arms are retracted, their outer surfaces are substantially flush with the outer cylindrical surface of the drill stem. However, when the arms are extended radially by pivoting about their respective pivot axes, they form hump-like radial projections, which further displace the surrounding soil and form a generally annular cavity around the drill stem as it is rotated.

Typically, the radially expandable arms are located near the leading end of the drill stem, behind its nose.

The radially expandable arms may be extended and/or retracted by any suitable means. Preferably, the arms are operated by a hydraulic cylinder mounted between the arms. The cylinder is operated remotely via a hydraulic hose passing through the elongate member and connected, via a suitable swivel assembly, to user- operated hydraulic control means on the ground surface.

Any suitable means may be provided for rotating the drill stem. Typically, the drill stem is rotated hydraulically.

The delivery means for introducing settable material into the bore and the annular cavity suitably comprises a feed tube or other conduit extending longitudinally through the drill stem and connected to a supply of the settable material on the surface of the ground, via a suitable swivel assembly. The conduit has an opening between the radially expandable arms to enable the settable material to be fed into the cavity formed by the arms. The tube/conduit typically has another opening adjacent the nose so as to feed the settable material into the bore as the drill stem is retracted.

Typically, the settable material is grout, concrete or similar cementitious material.

In an alternative embodiment, the drill member has only one radially expandable arm. This arm can be used to form portions of enlarged diameter on the pile at spaced locations as described above, or may be extended while the drill stem is simultaneously raised and rotated to form a pile having a radially enlarged integral portion wound spirally therearound.

The pile forming apparatus, method and resultant pile of this invention have several advantages over the prior art. First, the arm(s) may be expanded at any given selected depth during casting of the pile (or anchor) to utilise the soil strength profile to its best advantage. In other words, the pile diameter can be expanded at depths where the soil will provide maximum support, thereby maximising pile bearing capacity for that particular size pile. Further, in soils providing little or no support (e.g. mud) or soils susceptible to movement (e.g. clay), a smooth pile section of minimum core diameter can be retained. Thus, the pile can be custom-made to suit the particular geomechanicε at its location.

Secondly, the pile so formed is a full displacement pile, thereby providing higher bearing capacity than non-displacement piles of comparable size. Thirdly, the pile of this invention can be installed with very little noise, and without creating vibrations which may damage surrounding surfaces and/or structures.

Fourthly, the pile uses less concrete for a given load capacity than other known piles.

Fifthly, the pile can incorporate a special flight section to pull it into the ground and also increase bearing capacity. Sixthly, the pile has good radial stress loads. Finally, by suitable control of the depth and rotation of the drill stem and the extension of the arm(s), various pile designs can be achieved. Preferred embodiments of the invention will now be described by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic sectional view of the pile forming apparatus of one embodiment; Fig. 2 is a part sectional view of the leading portion of the apparatus of Fig. 1;

Fig. 3 is a sectional plan view of the radial arms of the pile forming apparatus of Fig. 1;

Fig. 4 is a sectional plan view of the radial arm of another embodiment of the pile forming apparatus;

Fig. 5 is a sectional plan view of the radial arm of Fig. 4 when extended.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in Figs. 1-3, the pile forming apparatus 10 of one embodiment comprises an elongate drill member, which typically is a steel pipe drill stem

11 provided with a conical nose portion 12. A spiral flight 13 is provided around the nose portion 12 to form an auger-like arrangement to enable the drill 11 to be screwed into the ground. The nose tip 14, which typically is of triangular blade shape, is fitted to a tubular member 23 which is telesσopically mounted in the nose portion 12, as can be seen more clearly in Fig. 2.

As shown more clearly in Figs. 2 and 3, the pipe forming apparatus 10 of this embodiment is provided with a pair of diametrically opposed, radially extendable or expandable arms 16 located directly behind the nose portion 12. Each arm 16 is fixed to a respective axial shaft 17 which is journalled for rotation about a longitudinal axis offset from the central longitudinal axis of the pipe 11. Each shaft 17 is provided with a crank arm 18. A hydraulic cylinder 19 is pivotally connected between the crank arms 18. Extension of the hydraulic cylinder 19 causes the arms 16 to pivot radially outwardly, while retraction of the cylinder 19 will cause the arms 16 to retract within their annular recess in pipe 11. When the arms 16 are fully retracted, their outer surfaces are substantially flush with the cylindrical surface of the base portion of the nose cone 12. (An enlarged drill head may be used in sandy locations) .

The hydraulic cylinder 19 is selectively operated by a master hydraulic cylinder or a pump (not shown) controlled by the operator. Typically, the cylinder control lever is located with the drilling controls on the ground surface. The master cylinder on the surface provides an indication of the extension of the slave cylinder 19, and hence the extent of radial expansion of the arms 16. The slave hydraulic cylinder 19 is connected to its master hydraulic cylinder via a hydraulic hose extending up through the interior of drill pipe 11 and connected to the master cylinder via a suitable swivel assembly. In this manner, the arms 16 can be selectively extended/retracted by the operator while the drill pipe 11 is rotating.

A central feed tube 20 extends longitudinally within pipe 11 and has its upper end connected to a supply of grout, concrete or other settable material, via a suitable swivel assembly.

The lower end of feed tube 20 has a pair of diametrically opposed openings 21 located between the arms 16. Another pair of openings 22 is provided in the tubular telescopic mount 23 for nose tip 14.

The drill pipe 11 is provided with a relatively thin sleeve 15 behind the arms 16. The sleeve 15 may be retracted axially along the pipe 11 to allow access to the arm operating mechanism, e.g. for servicing. During normal operations however, the sleeve 15 is closed.

In use, the pipe 11 is drilled into the ground using any suitable drilling head. As the pipe 11 is rotated, auger 13 pulls the pipe into the ground, and the conical nose portion 12 displaces and compacts the surrounding soil to form a bore through which the pipe 11 passes. An auger-like flight (not shown) can be provided on the drill stem 11 to assist the drill stem dig into the ground (and also to assist in removing the drill stem, particularly in stiff cohesive soils). Such drilling continues until the desired depth has been reached.

The depth of the pipe 11 is then adjusted so that the arms 16 are located at the depth at which the lowermost radial extension of the pile is to be formed, shown in Fig. 1 as location "A". Typically, the first radial extension will be formed when the pipe 11 is at its lowermost position, i.e. near the foot of the pile, although this need not necessarily be so.

The arms 16 are then rotated by hydraulic cylinder 19 under the control of the operator, so as to expand radially outwardly. (Due to pressure equalisation on the arms, they will extend equally on both sides). At the same time, the pipe 11 is rotated (in the direction shown) so that the extended arms 16 displace the surrounding soil outwardly and compact it so as to form a generally annular cavity around the bore. The height of the cavity is equal to the thickness of the arms 16. Grout or other suitable material is then forced under pressure through feed tube 20 and openings 21 into the cavity being formed by arms 16. The pressurised grout assists in keeping the soil displaced outwardly as the arms 16 are retracted. The pipe 11 is then raised so as to position the arms at the next location (if any) at which a radial extension of the pile is required, shown for exemplary purposes as location "B" in Fig. 1. As the pipe 11 is being raised, the grout is forced through openings 22 at the tip of the nose portion 12 so as to fill the bore below the nose portion. The telescopic mounting of nose tip 14 permits the tip 14 to abut against the remainder of the nose portion while the bore is being drilled, yet extend under grout pressure to allow the grout to exit through apertures 22 on withdrawal of the drill stem 11.

The above procedure is repeated until the required number of radial extensions of the pile have been formed at the desired depths, and the remainder of the pile stem has been cast.

It will be apparent to those skilled in the art that the pile so formed is a displacement pile yet cast in place. The pile has radially enlarged portions to increase pile bearing capacity at selected depths to take advantage of the soil profile, thereby maximising pile bearing capacity for the particular quantity of concrete used.

A second embodiment of the invention is illustrated in Figs. 4 and 5. In this embodiment, the pile forming apparatus 30 comprises a drill stem having only one arm 31. This arm 31 is similar to the arms 16 of the embodiment of Figs. 1-3, and is mounted on a rotatable shaft 32 which is suitably journalled within the drill stem. The shaft 32 is rotatable about its longitudinal axis which is parallel to, and offset from, the central longitudinal axis of the drill stem.

A hydraulic cylinder 33 is connected between the drill stem and a crank arm 34 connected to shaft 32. The hydraulic cylinder 33 is operated remotely by the operator on the surface of the ground, in a similar manner to the cylinder 19 of Fig. 2.

The arm 31 also comprises a tapered bore 36. A radial plug 37 extends outwardly from a central pipe fitting 38 in the drill stem and serves to close the bore 36 in arm 31 when the arm is retracted.

A grout pipe 39 which delivers grout to the toe of the drill stem has an opening 40 adjacent the arm 31, as shown in Fig. 4. In use, the cylinder 33 is extended to cause arm 31 to pivot and displace the surrounding soil outwardly. As the drill stem is rotated, the arm 31 displaces the surrounding soil outwardly to form a cavity around the drill stem, in a similar manner to the embodiment of Figs. 1-3. However, unlike the trailing arm configuration of the arms 16 of Fig. 2, the arm 31 of the embodiment of Fig.s 4-5 is mounted in the reverse orientation. Thus, as the drill stem rotates in the direction shown, the reaction of the surrounding soil on the arm 31 assists in the radial extension of the arm. When the arm 31 is fully extended, the leading edge of the arm is still within the circumferential perimeter of the drill stem and does not dig into the surrounding soil. Rather, the surrounding soil is displaced by the outer face 35 of the arm. To minimise wear, the outer face 35 is hardfaced with a wear resistant material.

As the arm 31 is extended outwardly, the bore 36 is no longer closed by plug member 37. Grout exiting under pressure from aperture 40 in grout pipe 39 is forced through the bore 36 and fills the cavity around the drill stem formed by the extended arm 31. As this grout is pumped under pressure, it keeps the soil displaced while the arm 31 is retracted.

The modified form of the pile forming apparatus of Figs. 4-5 can be used to form a pile having enlarged diameter portions at discrete spaced locations therealong in a similar manner to the embodiment of Figs. 1-3, except that the single arm 31 performs the function of the pair of arms 16. The embodiment of Figs. 4-5 can also be used to form a spiral pile cast in place. In this pile forming method, the drill stem is rotated and lifted simultaneously, while the arm 31 is extended so that a spiral cavity is formed around the bore drilled by the drill stem. The bore and spiral cavity are filled with grout under pressure as the drill stem is raised so that the spiral pile is cast integrally in place. To assist the arm 31 in its upward spiral travel, the square leading edge of the arm may be rounded to a generally triangular form.

A spiral pile may also be formed with the pile forming apparatus of Figs. 1-3, such a pile having a double helix around its cylindrical surface.

The foregoing describes only some embodiments of the invention, and modifications which are obvious to those skilled in the art may be made thereto without departing from the scope of the invention as defined in the following claims. For example, although the preferred embodiment has been described with reference to its use in forming vertical piles, it can also be used for forming ground anchors at other orientations. Further, the pivoted arms 16, 31 of the illustrated embodiments may be replaced by other radially extendable devices.

Claims

CLAIMS :

1. A method for forming a pile, comprising the steps of inserting an elongate drill member into the ground to form a bore by displacing surrounding earth, the drill member having at least one arm member which is extendable and retractable in a radial dimension; radially extending the arm member to further displace surrounding earth outwardly; rotating the drill member to cause the arm member to form a cavity around the drill member; and filling the cavity with settable material.

2. A method as claimed in claim 1, further comprising the step of withdrawing the drill member axially along the bore and filling the bore below the drill member with the settable material, to thereby form a cast pile having at least one radially enlarged portion.

3. A method as claimed in claim 2, wherein the drill member is held at a constant depth in the bore while it is rotated with the arm member extended to thereby form an annular portion of increased diameter integral with the pile.

4. A method as claimed in claim 3, wherein the arm member is located near the leading end of the drill member, and the increased diameter portion is thereby formed near the foot of the pile.

5. A method as claimed in claim 3, wherein a plurality of annular portions of increased diameter integral with the pile are so formed successively at selected spaced axial locations along the pile.

6. A method as claimed in claim 2, wherein the drill member is simultaneously raised and rotated with the arm member extended to form a spiral formation around the pile and integral therewith.

7. A method as claimed in claim 2 wherein the settable material is concrete, and further wherein the concrete is pumped through a conduit in the drill member to openings located adjacent the arm member and the leading end of the drill member.

8. A pile when formed by the method of claim 2.

9. Apparatus for forming a pile, comprising an elongate drill member adapted to be inserted into the ground to form a bore by displacing surrounding earth, the drill member having at least one arm member which is extendible and retractable in a radial dimension; means for rotating the drill member about its longitudinal axis; means for extending the arm member to further displace surrounding earth radially outwardly and form a cavity around the drill member as it is rotated; means for withdrawing the drill member along the bore; and delivery means for forcing settable material into the cavity, and the bore as the drill member is withdrawn, to thereby form a cast pile having at least one radially enlarged portion.

10. Apparatus as claimed in claim 9, wherein the arm member is pivotally mounted in the drill member and is extendible and retractable by pivoting in a radial plane.

11. Apparatus as claimed in claim 10, wherein the arm member is extendible by a hydraulic cylinder connected between the arm member and the drill member, the cylinder being remotely operated via a connecting hose passing through the drill member.

12. Apparatus as claimed in claim 9, comprising a pair of diametrically opposed arm members pivotally mounted in the drill member in the same radial plane and a hydraulic cylinder connected between the pair of arm members, the cylinder being remotely operable to cause the arm members to extend or retract radially relative to the drill member.

13. Apparatus as claimed in claim 9, wherein the drill member comprises a metal pipe drill stem adapted to be screwed into the ground, and the arm member is located near the leading end of the drill stem.

14. Apparatus as claimed in claim 13, wherein the delivery means comprises a conduit extending longitudinally through the drill stem and having an opening adjacent the arm member and an opening at the leading end of the drill member, said apparatus further comprising a pump for pumping the settable material through the conduit to the openings.

15. Apparatus as claimed in claim 14, wherein a conical nose portion is provided at the leading end of the drill member and the opening is located at the apex of the conical nose portion, the conical nose portion having an auger-like formation thereon.