AU7306998A - Methods of and apparatus for forming in-ground columns - Google Patents

Description

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Ii METHODS OF AND APPARATUS FOR FORMING IN-GROUND COLUMNS This invention relates to methods of and apparatus for forming in-ground piers or columns.

This invention has particular but not exclusive application to auger apparatus for boring into, or forming columns or piers in, sand or unstable soils or foundations where the water table is close to the surface such- that bored holes may be inundated with water. For illustrative purposes, reference wil be mrade such application. .However, it is to be understood that this invention could be used in other applications such as providing bores or columns in stable soils.

In building constructions and other civil works, a structure is frequently supported on its 10 foundations by columns, pieciSsor piles extending downwardly into bores formed in the foundation to provide a firm footing. Often the f6undation is bored for in-situ formation of piers beneath the footing and a settable liquid such-as concrete is poured into the bore with or without reinforcing to form the piers.

Where the foundation is unstable or the water table-is high, preventing the in-situ 15 formation of columns or piers by traditional casting methods, piles are often driven (using percussion) into the foundation for supporting the structure. Driving piles into the foundation is costly and time consuming and the driven piles are occasionally skewed, thus not providing a firm support or interfering with adjacent piles. The present invention aims to alleviate one or more of the above disadvantages and provide auger apparatus which will be reliable and efficient in use.

This invention in one aspect resides broadly in auger apparatus for attachment to a rotational drive, said auger apparatus including: a hollow shaft assembly operatively connectable to the rotational drive for rotation about a central drive axis; flight means disposed about the outer surface of the hollow shaft assembly, and a cutting head assembly releasably connectable to said hollow shaft assembly and arranged for cutting into a foundation upon rotation of the rotational drive assembly.

2 IPreferably, the cutting head assembly is a disposable cutting head assembly which remains attached to the distal end of the hollow shaft assembly upon and during rotation in a forward direction, but is released from the hollow shaft assembly when rotated in a reverse I direction opposite to the forward direction.

5 Suitably, the cutting head assembly engages with the distal end of the hollow shaft assembly when placed in operative alignment therewith and the hollow shaft means is rotated in the forward direction. For this purpose the cutting head assembly locates operatively about, Swithin, or on the end of, the holloi' haft assembly and may engage non-rotatably therewith in the forward direction by a dog clutcpor ratchet type mechanism or such like. The engagement of the cutting head assembly may inclua- a selective latching arrangement of the cutting head assembly onto the hollow shaft.

Preferably, the cutting head assembly includes a complementary thread portion so formed and arranged as to be engageable with a thread portion on the distal end of the hollow shaft assembly. Preferably, the complementary thread portion is provided about the internal surface of a cylindrical or frustoconical recess in the cutting head assembly, and the thread portion is provided about an external surface of the hollow shaft assembly. Both the thread portion and the complementary thread portion preferably include a lead-in portion so as to facilitate engagement of the hollp; shaft assembly with the cutting head assembly whilst accommodating a modest misalignment of the cutting head assembly with the hollow shaft assembly.

If desired the driving connection between the hollow shaft assembly and the cutting head assembly may be formed so that the connection will remain operatively engaged, irrespective of the direction of rotation, while a positive downwards force is applied to the cutting head assembly by the hollow shaft assembly. For this purpose, the thread portion and the complementary thread portion may include land and abutment portions which are adapted to permit the hollow shaft assembly to move axially with 'spect to the cutting head assembly L r" 1* 2.

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^s "S such that when the engagement is in compression, the cutting head assembly is unable to rotate with respect to the hollow shaft assembly, but upon movement of the hollow shaft assembly axially with respect to the cutting head assembly in the opposite direction, the cutting head assembly is able to rotate with respect to the hollow shaft assembly.

5 The connection may also permit positive axial engagement between the cutting head assembly and the hollow shaft assembly during boring operations to permit the hollow shaft to be axially removed at least partly from the borehole with substantially no rotation of the hollow shaft assembly.

In a preferred embodiment, the cutting head assembly is sealingly engageable with the ~distal end of the hollow shaft assembly to prevent water or such like from entering the hollow shaft assembly. The sealing engagement is preferably provided by an o-ring seal. Since the Scutting head assembly is to be left in situ after boring, it is preferred that the o-ring be provided on the hollow shaft asserbly and the cutting head assembly be provided with a mating surface for sealing engagement of the o-ring therewith.

The flight means may be continuous, such as in the form of a screw thread, or the flight means may include an array of discrete bearing surfaces such as fins, blades or such like angled for bearing axially against a foundation when rotated with the hollow shaft assembly and in operative engagement with the foundation.

The flight means may include a screw thread or the like as a contir.uous ridge or channel of constant section disposed about the outer surface of the hollow shaft in the form of a spirally coiled helix. Alternatively, the flight means may include a continuous flute indented in.o a cylindrical hollow shaft comprising the hollow shaft assembly. It will be appreciated that discontinuous flight surfaces may also be provided and the flight pattern may be provided on double or multiple start helixes. It is also preferred that the flight means, in addition to providing an axial force when rotated about its central axis, be adapted to remove at least some of the material of the foundation into which the bore is being driven.

4 I In another aspect, this invention resides broadly in a method of forming a pier in a foundation, including.

providing auger apparatus including a hollow shaft assembly operatively connectable to a rotational drive for rotation about a central drive axis, flight means disposed about the outer surface of the hollow shaft assembly, and a cutting head assembly releasably connectable to sid hollow shaft assembly; attaching said releasable cutting head assembly to the distal end of said hollow shaft 1-gK assembly for rotation therewith; advancing the hollow shaft assembly into the foundation by rotation of said hollow said to hollow shaft assembly aboutsaid central drive axis in a forward direction; inserting pier means into said hollow shaft assembly; operatively associating said pier means with said cutting head assembly, and Sreleasing said cutting head assembly from said shaft assembly.

1. The pier means may be preformed and integrally formed with the cutting head assembly, in which case, the pier means is inserted into the hollow shaft assembly por to drilling. Preferably, however, the shaft mneans is hollow and the pier means s provided by a "i settable material being charged into the hollow shaft assembly, whereby the operative association of the pier means .with the cutting head assembly is by way of the provision of reinforcing means integrally formed with and projecting from the cutting head assembly.

The hollow shaft assembly may be filled with the settable liquid such as concrete whilst attached to the drive assembly, the hollow shaft assembly including a settable liquid inlet for this purpose. Preferably however, the hollow shaft assembly is disengaged from the drive means to enable reinforcing material such as steel reinforcing to be placed in situ and subsequently encapsulated by the liquid concrete.

It is also preferred that the hollow shaft assembly is removed from the foundation Ssubsequent to the placement of the pier means.

1 I The drive assembly may use axial force to pierce the foundation, however, the drive means is a rotational drive means and the hollow shaft assembly includes flight means as hereinbefore described. Accordingly, the hollow shaft assembly may be driven into the foundation in a forward rotational direction to bore into the foundation, but rotated in a reverse direction opposite to the forward rotational direction to release the cutting head assembly from the hollow shaft assembly and remove the hollow shaft assembly from the foundation, leaving the cutting head assembly, and the pier means associated therewith, in the bore.

Preferably, the rotation in the reverse direction compacts the material surrounding the pier by providing a downward force upon the hollow shaft assembly as it is removed from the o 0 foundation to provide a backfill pressure. However, it will be appreciated that the rotation of the hollow shaft assembly is controlled to prevent, in soft foundations, either so high a backfill pressure that the column of liquid concrete is pinched off, or so low or negative a backfill pressure that an excess of liquid concrete forms an expansion or ballooning out of the concrete into the foundation.

The hollow shaft assembly may be removed after setting of the settable liquid, and the hollow shaft assembly may be provided with a suitable mould release agent for this purpose.

However, it is preferred that the hollow shaft assembly is removed from the foundation before the settable liquid has set, the settable liquid having like density to the foundation and sufficient wet stiffness to be supported in the bore created in the foundation by the method of this invention.

The piers formed according to the method of this invention may be vertical, horizontal or oblique as required, and it is believed that the hollow shaft assembly prevents collapse of the bore prior to the insertion of the settable liquid, but subsequent to the addition of the settable liquid and the removal of the hollow shaft assembly, the settable liquid will be able to set substantially in the shape of the bore.

In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a typical preferred embodiment of the invention and wherein: FIG. 1 is a diagrammatic sectional view of an auger assembly; FIG. 2 is a diagrammatic sectional view of an upper portion of the auger assembly of FIG. 1; FIG. 3 is a diagrammatic sectional view of a lower portion of the auger assembly of FIG.

1; FIG. 4 is collectively a view of a cutting head assembly for the auger assembly of FIG. 1 from the underside and front; FIG. 5 is a side view of a cutting head assembly in an alternative embodiment; FIG. 6 is a plan view of the cutting head assembly of FIG. FIG. 7 is a front view of an alterative cutting head assembly for the auger assembly of 1 FIG. 1; FIG. 8 is a side view of the alternative cutting head assembly of FIG. 7, and FIG. 9 is a plan view of the alternative cutting head assembly of FIGS. 7 and 8.

SReferring to FIG. 1, an auger assembly 10 includes an upper portion 11 releasably connectable to an auger portion 12 by way of an auger connector assembly 13. The auger portion 12 includes a plurality of flights shown typically at 14 extending spirally along the outer surface of the auger portion 1 2 The auger portion 12 is hollow to permit the insertion of components for construction of a pie-, such as reinforcing bars 25 and concrete 26. A cutting head 15 is releasably attachable to the distal end of the auger portion 12 by way of a connector assembly 16.

SThe auger portion 12 and upper portion 11 of the auger assembly 10 as shown in FIG. 1 are partly removed from a pier excavation showing the cutting head 15 left in place beneath the Sconcrete and steel of a pier 17, and the upper portion is operatively associated with a drive 7 assembly (not shown) for rotating and lowering or raising the auger assembly 10. The cutting head 15 constitutes a disposable head which is left in the foundation under the concrete pier.

The reinforced concrete forms a pier as the auger is screwed out of the excavation once the concrete has set The pier 17 extends below the level of the water table 18 which is usually below the ground level 19.

Referring to FIG. 2, the upper end of the auger connector assembly 13 includes a plurality of castellations shown typically at 20 which mate with complementary castellations on the lower end of the upper portion 11 (not shown). Additionally, an aperture 22 is provided in the auger connector assembly 13 for receiving a locking pin 22 (shown in FIG. 1).

Referring to FIG. 3, the connector assembly 16 on the lower end of the auger portion 12 includes two male thread portions 33 which engage with respective slots 31 in the cutting head 15. The proximal edge 34 of the cutting head 15 abuts an end stop 35 on the auger portion 12 when the connector assembly 16 is inserted into the cutting head 15. The cutting head 15 is preferably made of concrete which may include abrasion resistant material such as river gravel, metal fibres or such like. A reinforcing bar cage 38 is embedded into the cutting head 15 with some of the ends thereof forming protruding bars 36 extending axially of the cutting head The protruding bars 36 are stiffened by two rings 37 welded in place encircling the protruding bars 36.

Referring to FIG. 4. the cutting head 15, which is similar to that shown in FIG. 3, has its lower surface shaped substantially as a twist dril or auger bit, including two res ective lips 16 extending from the outer periphery of the cutting head 15 to the ends of a chisel edge 45, thus defining two respective lands 47 Preferably, the cutting head 15 is not fluted such that each land 47 extends back to the preceding lip 16- It will be appreciated that other cutting head i profiles may be used. The lips 16 provide a cutting edge and, upon rotation of the cutting head 15, a biting action into the subsurface foundation- 8 y- 4..

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i i S I? Referring to FIGS. 5 and 6, a basic rolled cone cap 40 includes a conical section 41 and a pair of flute members 42 formed onto the conical section 41. The flute members 42 are formed upstanding from the conical section 41 at an angle as shown in particular in FIG. 6.

Referring to FIGS. 7 to 9, a basic flat tap 50 having curved triangular flights has three triangular sections 51 formed to meet at a point 52.

In use, an auger apparatus of this invention may be used to provide bores for piers in unstable strata such as that having a high water table. The auger apparatus of this invention may be attached to a backhoe or such like and located in position by operative placement of the backhoe and operative alignment of the backhoe's implement arm.

The disposable cutting assembly is attached to the hollow shaft assembly, and the assembled auger is rotated and advanced into the foundation to form a bore suitable for a concrete pier to be cast in place.

The rotational drive assembly is disengaged from the assembled auger to permit reinforcing for concrete to be inserted. Suitably, the reinforcing includes starter bars attachable to the reinforcing protruding from the concrete cutting head assembly. For example, the reinforcing for the pier may have the lower ends of the axial bars held together by a releasable clasp, such as a zip tie or such like, which is released after placement of the reinforcing to permit the reinforcing of the pier to engage with the reinforcing of the cu tting head assembly.

Once the reinforcing is in place, the bore is charged with liquid concrete in a quantity appropriate for forming the pier. Prior to setting of the concrete, the hollow shaft assembly is reverse rotated to remove it from the foundation.

During reverse rotation, the backhoe exerts a downward force, such as by limiting the rate of retraction to less than would be provided by the flights around the hollow cylinder in order to compact the foundation about the pier. If required, extra matenal may be provided at the top of the flights to provide for thecompaction.

9 One or more pier bores may be prepared using a plurality of hollow shaft assemblies, or the same hollow shaft assembly may repeatedly at the same site, depending upon the time taken to provide the reinforcing in the bore. Alternatively, a leap frog arrangement may be Sprovided in which two or more hollow shaft assemblies are used in a repeated cycle in which the earliest poured pier has its hollow shaft assembly removed for forming the next bore whilst Sthe remaining bores are filled with reinforcing and concrete.

Additionally, the hollow shaft assemblies may be arranged to interconnect lengthwise to S' permit the excavation of a bore deeper than the length of one hollow shaft assembly.

The auger apparatus may be constructed from a steel tube with auger flights wrapped around and welded to the outer surface. In use, the flights remove sand, soil or such like material as may be present on the site.

On the bottom of this tube is provided a rubber O-Ring for the purpose of sealing the end to prevent any material, including water, from entering the auger from the bottom. A disposable cutting head assembly is placed over the end of the auger so as to effectively seal the Is" 15 tube, and will be held in place by a simple clip system so that when the auger is removed in the Sreverse direction this cutting head assembly will remain in the foundation under the concrete.

Accordingly, the auger apparatus is a tube auger with a disposable cutting head assembly made of concrete. However, alternative embodiments may use sheet metal, plastic, fiberglass (or any suitable material). The tube may be of any suitable inside diameter (depending on the bore diameter required). This tube allows for a dry hole into which can be placed (with the auger still in the ground) any steel reinforcing or other requirements for the pier- Once steel and/or other material has been placed into the auger, concrete is poured into the said auger and vibrated into place. Moreover, the concrete cutting head assembly may be provided in a considerably larger diameter than that of the pier to provide a floating footing having a stability suitable for supporting a structure above the footing and supported thereby.

Once the concrete is in place, and while the concrete is still wet, the auger is rotated in the opposite direction and with this, material excavated may- be compacted around the concrete leaving the concrete auger bit in situ and the required depth and diameter of concrete to torm the pier. Thus, the disposable cutting head assembly is left under concrete pier as it has been released from the auger by the process of reversing the auger.

The auger apparatus of this invention will permit the bornn preparng for and pouring concrete (or any required raaterial) into the bore in any area where the water table may be close to the ground surface or the site is otherwise unstable.

It will of course be realised that the above has been given only by way of illustrative to example of the invention and that all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the Sinvention as claimed in the following claims.

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Claims (6)

1. Auger apparats or attachment to a rotational drive, said .uger apparatuas including: a hollow shaft assembly opera tively connectable to the ro tational. drive for rotation -about a central drive axis; flight means disposed about the outer surface off the hollow shaft assembly, ard -a cuftng head, assembly releasably connectable to said hollo w shaft. assembly and arranged for cutting into a foundation upon rotation of the rotational drive as~emnblv. 1 Auger apparat us as claimr-id in~ claim 1, %vherein, said the cutting head isembiv Ls a disposable cutting head assembly which remnain aached to the distal end of said hollov*. shaft assembly.~ipon and dluring rotation. in a forward dix-e-torr, but is relea-sable from said hollow shaft asisembly when-rotated in areverse direction opposite to the forward direction.

3- Auger- apparatus as- caimed in claimn I or claim 2, where-in said cutting head assembly includes a ccmplemnentary thread portion so formed an ragdas to hE engagt±abl ih thread prtion on the distaiLend of said hollow shallt assemcv

4- kuOe paau a lir in any one oat Lne preceding claans, wherein said cutting head assembly is sealingly eng-ageable istm oist]r.3 ot said hollow shaft assemnbly to prevent water or~stioh Ik5from ente-ring said hollow-% shaft assembly. A. method of forminxg a pier in a foundation. icludm'g pro-ndinga-uger apparatus including a hollow6 shf&ssemnbl 0-ertive&y connectable'to a oainL dr fo-oato-bota Ieta drive axis, flight means disposed 3bout thE outer hollow shaft assembly; attaching said releasable cutting head assembly to the distal end of said hollow shaft Sassembly for rotation therewith; Iadvancing the hollow shaft assembly into the foundation by rotation of said hollow said hollow shaft assembly about said central drive axis in a forward direction; Sinserting pier means into said hollow shaft assembly; operatively associating said pier means with said cutting head assembly, and releasing said cutting head assembly from said shaft assembly.

6. A method as claimed in claim 5, wherein said pier means is provided by a settable material being charged into the hollow shaft assembly. S7. A method as claimed in claim 6, and including providing reinforcing means integrally I 15 formed with and projecting from the cutting head assembly to be encapsulated by said settable material.

8. A method as claimed in claim 6 or claim 7, wherein said hollow shaft assembly is disengaged from said rotational drive, and including inserting reinforcing material into said hollow shaft assembly, and subsequently encapsulating said reinforcing material with said settable liquid.

9. A method as clainedin any one of claims 5 to 8, wherein said hollow shaft assembly is removed from the foundation subsequent to the placement of said pier means. I N I 13 A method as claimed in claim 9, wherein, the rotation in the reverse direction compacts the material surrounding the pier by providing a downward force upon the hollow shaft assembly as it is removed from the founda6ti)n to provide a backfill pressure. DATE OTEES Nineteenth DAY OF June, 1998. RODGER PAUL PETERS- AND PATRICIA EVELYN PETERS BY PIZZEYS PATE NT AND TRADE MARK ATTORNEYLS 2 .q.