Technical Field

The present invention relates to a method of forming an in ground stone column, with or without a tension linked device to minimise uplift, where the stone column is formed using a drill assembly with twin concentric drills.

Background Art

Bonded stone columns are normally formed by drilling a hole and filling it with concrete or similar bonded aggregate materials. The concrete is then vibrated to form a consolidated bonded stone column with minimum or no voids. In many cases reinforcing rods or cages are plunged into the setting concrete prior to vibration. Surface vibration of the concrete may not be sufficient to consolidate deep bonded stone columns. This method does not work in ground where the walls of the hole collapse and alternative methods need to be employed.

Some bonded stone columns are formed by inserting a drill into the ground then feeding the concrete through a hollow core to the base. As the drill is removed concrete is forced into the ground forming a bonded stone column. The diameter of the bonded stone column formed is difficult to predict as it depends on the ground and concrete properties.

Current building techniques that utilise ground improvement for foundation stabilisation can be limited when the building design requires resistance to uplift forces putting foundation elements into tension (e.g. piles). These uplift forces can be generated by seismic, and/or wind action, buoyancy if the building has a sealed basement below water table, or differential settlements within the building. The uplift forces are usually resisted by piles, micro-piles, ground anchors or a similar element that is anchored into the ground beneath the building foundation. These elements are separate to any ground improvement elements (granular columns) and require a separate installation step which increases the costs.

If the ground improvement technique uses un-bonded granular columns then these cannot easily be attached to building in a way that resists uplift forces, so separate elements for addressing uplift forces are at present needed. Any discussion of the prior art throughout the specification is not an admission that such prior art is widely known or forms part of the common general knowledge in the field.

It is an object of the present invention to overcome the deficiencies in current methods of producing a bonded or un-bonded stone column, or at least provide the consumer with a useful choice.

Disclosure of Invention

The present invention provides a method of using a drill assembly to form an in ground bonded stone column, wherein said drill assembly includes a first drill and a second drill, where the first drill is a tube, and the second drill includes a drill flight, wherein said first and second drills are concentric, and the second drill is configured to lie at least partially within a hollow core of the first drill; said method includes the following steps in order:

alpha insertion step: Insert the drill assembly into the ground to the desired depth; alpha feed step: Feed at least one material through the hollow core of the first drill to exit out of the drill assembly at a lowest point;

alpha formation step: Withdraw the drill assembly whilst controlling a feed rate of the at least one material to form a bonded stone column;

where the at least one material fed into the hollow core are independently selected from the list consisting of concrete, aggregate, sand, rubble, bonding agents, cement/water mixtures, water and other additives.

Preferably between the alpha insertion and alpha feed steps there is an alpha separation step, where the alpha separation step is as below:- alpha separation step: Adjust the relative position of the drills, if necessary, until the first terminal end is spaced apart from the primary end.

Preferably in the alpha formation step the second drill rotates forcing the or each of the at least one material radially and/or axially outwards.

The present invention also includes the drill assembly used to form the bonded stone columns. A column assembly including a drill assembly and a feed section for forming an in ground bonded or un-bonded stone column, where the drill assembly includes a first drill and a second drill, where the first drill is a tube with a hollow core, and the second drill includes a drill flight coterminous with a first terminal end of said second drill, wherein:- said first and second drills are concentric, and the second drill is configured to lie at least partially within the hollow core of the first drill;

the first terminal end is located close to, or forms all or part of, an end of the drill assembly configured to enter a ground surface first;

the feed section is configured to deliver at least one material into the hollow core of the drill assembly;

the hollow core is configured to act as a pathway to for the at least one material to the drill flight;

the drill flight, in use, is configured to force the at least one material away from the drill assembly radially and axially.

The present invention also includes a column produced using this method, drill or column assembly. Preferably said column formed has radially compacted side walls.

The present invention also provides a second variation of the column assembly including a drill assembly and a feed section for forming an in ground bonded stone column, where the drill assembly includes a first drill and a second drill, where the first drill is a tube with a hollow core, and the second drill includes a drill flight coterminous with a first terminal end of said second drill, wherein:- said first and second drills are concentric, and the second drill is configured to lie at least partially within the hollow core of the first drill;

the first terminal end is located close to, or forms all or part of, the drill assembly configured to enter a ground surface first;

the second drill includes a primary section and a secondary section where the first terminal end forms all or part of the primary section and the secondary section is coterminous with a second terminal end of the second drill;

the first terminal end and the second terminal end are opposite ends of the second drill;

the second drill includes a feed conduit which is a longitudinal void extending along the second drill; the feed conduit includes an alpha end and a beta end where the alpha end is located in the primary section and the beta end is located in the secondary section; the alpha end and the beta end include one or more apertures located at, or close to, the terminal ends of the feed conduit;

the feed section is configured to deliver at least one material into the hollow core of the drill assembly;

the hollow core is configured to act as a pathway for the at least one material to the drill flight; such that the feed conduit is configured to deliver a conduit fluid to the primary section of the second drill and the drill flight is configured to mix the conduit fluid and the at least one material as the drill assembly is moved, said second drill is further configured to move said mixed at least one material and conduit fluid radially and axially away from the drill assembly.

Preferably the alpha end is located in the first terminal end.

Preferably the conduit fluid is, or includes, one or more bonding agent.

Preferably the column assembly includes an isolation section configured to provide a rotationally isolated fluid connection between a conduit fluid source and the feed conduit.

Preferably the isolation section includes an annulus surrounding a portion of the secondary section which includes the beta end which is configured to be flooded with the conduit fluid and in fluid connection to the conduit fluid source.

The present invention also includes a method of using the second variation of the column assembly which includes the following steps in order: beta insertion step: Insert column assembly into the ground to the desired depth; beta feed step: Dislodge the conduit seal, if present, and feed one or more material from the feed section through the drill assembly to the base of the hole whilst feeding a conduit fluid through the feed conduit; beta formation step: Withdraw the drill assembly whilst controlling the feed rate and other parameters of the material or materials and the conduit fluid to form a bonded stone column with the desired characteristics. Preferably after the beta insertion step is undertaken a beta separation step is undertaken, where the beta separation step is: beta separation step: Adjust the position of the drills, if necessary, until the first terminal end is spaced apart from the primary end;

The present invention also provides a third variation of the column assembly including a drill assembly and a feed section for forming an in ground bonded stone column, where the drill assembly includes a first drill and a second drill, where the first drill is a tube with a hollow core, and the second drill includes a drill flight coterminous with a first terminal end of said second drill, wherein- said first and second drills are concentric, and the second drill is configured to lie at least partially within a hollow core of the first drill;

the first terminal end is located close to, or forms all or part of, of the drill assembly configured to enter a ground surface first;

- the second drill includes a primary section and a secondary section where the first terminal end forms all or part of the primary section and the secondary section is coterminous with a second terminal end of the second drill;

the first terminal end and the second terminal end are opposite ends of the second drill;

- the second drill includes a feed conduit which is a longitudinal void extending along the second drill;

the feed conduit includes an alpha end and a beta end where the alpha end is located in the primary section and the beta end is located in the secondary section; the alpha end and the beta end are the terminal ends of the feed conduit;

- said feed conduit is dimensioned to releasably contain a feed insert which is a length of plain or corrugated tube including a first insert end and a second insert end; the first insert end and second insert ends are opposite terminal ends of the feed insert with the first insert end initially located close to or at the alpha end of the feed conduit;

- the feed section is configured to deliver at least one material into the hollow core of the drill assembly; and the hollow core is configured to act as a pathway for the at least one material to the drill flight; the primary section of the second drill and the drill flight are configured to move the at least one material radially and axially as the drill assembly is withdrawn from the ground.

Preferably the feed insert is releasably retained in the feed conduit. Preferably the feed insert includes a feed insert seal configured to seal the feed insert. Preferably the feed insert seal is releasably retained.

Preferably the feed insert is configured to deliver a conduit fluid to the primary section of the second drill and the drill flight is configured to mix the conduit fluid and the at least one material as the drill assembly is moved. Preferably the conduit fluid is, or includes, one or more bonding agent.

Preferably the third variation of the column assembly includes an isolation section configured to provide a rotationally isolated fluid connection between a conduit fluid source and the feed conduit.

Preferably the isolation section includes an annulus surrounding a portion of the secondary section which includes the beta end which is configured to be flooded with the conduit fluid and in fluid connection to the conduit fluid source. Preferably the feed insert includes at least one feed insert aperture, where the at least one feed insert aperture is a pathway from an interior of the feed insert which is configured to convey conduit fluid to the at least one material

The present invention also includes a first method of using the third variation of the column assembly which includes the following steps in order: gamma insertion step: Insert column assembly into the ground to the desired depth;

gamma feed step: Feed one or more material from the feed section through the drill assembly to the base of the hole whilst feeding a conduit fluid through the feed insert; gamma formation step: Withdraw the drill assembly whilst controlling the feed rate and other parameters of the material or materials and the conduit fluid to form a bonded stone column with the desired characteristics; such that during gamma formation step the first insert end of the feed insert remains at the base of the bonded stone column being formed.

Preferably after the gamma insertion step a beta separation step is undertaken, where the beta separation step is: beta separation step Adjust the position of the drills, if necessary, until the first terminal end is spaced apart from the primary end.

Preferably in the gamma formation step or the gamma formation step a feed insert seal is dislodged to allow conduit fluid to be delivered from the first insert end of the feed insert.

The present invention also includes a second method of using the third variation of the column assembly which includes the following steps in order: gamma insertion step: Insert column assembly into the ground to the desired depth;

delta feed step: Feed one or more material from the feed section through the drill assembly to the base of the hole;

delta formation step: Withdraw the drill assembly whilst controlling the feed rate and other parameters of the material or materials to form a granular stone column with the desired characteristics;

delta injection step: Feed conduit fluid through the feed insert embedded in the formed granular stone column to form a bonded stone column. such that during the delta feed step and/or delta formation step the first insert end of the feed insert remains at the base of the granular stone column being formed.

Preferably after the gamma insertion step a beta separation step undertaken, where the beta separation step is: beta separation step Adjust the position of the drills, if necessary, until the first terminal end is spaced apart from the primary end.

Preferably in the delta feed step or the delta formation step the feed insert seal has been dislodged to allow conduit fluid to be delivered from the first insert end of the feed insert.

The present invention also provides a further variant of the column assembly including a drill assembly and a feed section for forming an in ground bonded stone column, where the drill assembly includes a first drill and a second drill, where the first drill is a tube with a hollow core, and the second drill includes a drill flight coterminous with a first terminal end of said second drill, wherein:- said first and second drills are concentric, and the second drill is configured to lie at least partially within the hollow core of the first drill;

the first terminal end is located close to, or forms all or part of, the drill assembly configured to enter a ground surface first;

the second drill includes a primary section and a secondary section where the first terminal end forms all or part of the primary section and the secondary section is coterminous with a second terminal end of the second drill;

the first terminal end and the second terminal end are opposite ends of the second drill;

the second drill includes a feed conduit which is a longitudinal void extending along the second drill;

the feed conduit includes an alpha end and a beta end where the alpha end is located in the primary section and the beta end is located in the secondary section; the alpha end includes one or more apertures;

the beta end includes zero or more apertures;

the feed section is configured to deliver at least one material into the hollow core of the drill assembly;

the hollow core is configured to act as a pathway for the at least one material to the drill flight.

Preferably the beta end is a blind end. In an alternative variant the beta end includes at least one aperture. Preferably the second drill is an auger with an open ended tubular shaft. Preferably the one or more apertures in the alpha end pass through a side wall of the second drill. Preferably the one or more apertures in the beta end pass through a side wall of the second drill. In a preferred variant form there are zero or more apertures in a side wall of the second drill and a single aperture located at the first terminal end. Preferably there is also a single aperture located at the second terminal end.

Preferably the drill assembly releasably retains a tension device which includes a tension unit and a tension link, in an insertion position the tension unit is located at the first terminal end and the tension link is attached to the tension unit and passes through the feed conduit from the first terminal end to extend beyond the second terminal end. Preferably the tension unit includes a planar surface that lies perpendicular to a longitudinal axis of the second drill and extends at least partially across an open end of the hollow core. Preferably said planar surface is in contact with both the first drill and the second drill. In some variants at least part of the tension unit extends beyond the periphery of the first drill.

In a preferred form the drill assembly includes one or more blanking devices configured to minimise or prevent the ingress of material into the hollow core or feed conduit during insertion. In a preferred form one of the blanking devices is a tension unit.

Preferably the feed conduit is configured to deliver a conduit fluid to the primary section of the second drill and the drill flight is configured to mix the conduit fluid and the at least one material as the drill assembly is moved, said drill flight is also configured, in use, to move the mixed at least one material and conduit fluid, radially and axially, away from the drill assembly.

In a preferred form the feed conduit is dimensioned to releasably retain a feed insert, where said feed insert is a length of plain or corrugated tube including a first insert end and a second insert end; such that the first insert end and second insert ends are opposite terminal ends of the feed insert, with the first insert end initially located close to or at the alpha end of the feed conduit.

Preferably one of the methods described earlier is used with this further variant. Where a tension unit is present the present invention also includes the following method of forming a stone column with an integrated tension unit, said method includes the following steps in order: epsilon insertion step - insert the column assembly into the ground to the desired depth;

epsilon feed step - dislodge the tension unit from the drill assembly and feed one or more materials from the hopper to a base of the hole;

epsilon formation step - withdraw the drill assembly whilst controlling the feed rate and other parameters of the material or materials;

epsilon connection step connect the tension link a structure.

Preferably the epsilon connection step includes tensioning the tension link to a predetermined tension.

Preferably between the epsilon insertion step and the epsilon formations step there is an epsilon separation step where the relative position of the drills is adjusted until the first terminal end and the tension unit are spaced apart from the primary end.

Preferably, when the drill assembly includes a releasably retained feed conduit, this is formed into the stone column during the formation step. Preferably conduit fluid is passed through the feed conduit during an injection step, where the injection step can occur at the same time as the formation step, connection step or as a step after the formation step or as a step after the connection step.

Preferably in any of the methods described reinforcing or reinforcing cages can be inserted during or after the uncured bonded stone column is formed, where the uncured bonded stone column is an un-bonded stone column with the conduit fluid mixed with the at least one material but the conduit fluid has not cured or at least not fully cured.

Brief Description of Drawings

By way of example only, a preferred embodiment of the present invention is described in detail below with reference to the accompanying drawings, in which: Figure 1 is a pictorial view of a column assembly for forming in ground stone columns attached to a drilling rig;

Figure 2 is a cross sectional side view of the column assembly;

Figure 3 is a side view of a second embodiment of the column assembly;

Figure 4 is a series of cross sectional pictorial views showing the preferred method of forming a bonded stone column with the column assembly;

Figure 5 is a cross sectional expanded view of the primary end of the drill assembly with a space between the first drill and the second drill for inserting reinforcing;

Figure 6 is a cross sectional expanded view of the primary end of the drill assembly showing step D of the method where a reinforcing cage is inserted as the stone column is formed;

Figure 7 is a side view of a second embodiment of the column assembly;

Figure 8. is a cross sectional side view of the second embodiment of the column assembly;

Figure 9 is a series of cross sectional pictorial views showing the preferred method of forming a bonded stone column with the column assembly;

Figure 10 is a cross sectional view of a third embodiment of the column assembly; Figure 11 is an expanded section of part of Figure 10 showing the primary end and first terminal ends of the first and second drills respectively showing a portion of the feed insert in more detail;

Figure 12 is a cross sectional view of part or all of the primary section of the first drill with a plain un-corrugated feed insert;

Figures 13 -15 are cross sectional views of the primary section of the second drill showing some alternative methods of retaining the insert seals/conduit seals;

Figure 16 is a series of cross sectional pictorial views showing a first method of preparing a bonded stone column using the third embodiment;

Figure 17 is a series of cross sectional pictorial views showing a second method of preparing a bonded stone column using the third embodiment;

Figure 18 is a cross sectional view of a fourth embodiment of the column assembly;

Figure 19 is an expanded section of part of Figure 18 showing the primary end and first terminal ends of the first and second drills respectively showing a portion of the tension device in more detail; Figure 20 is a series of cross sectional pictorial views showing a method of preparing a bonded or un-bonded stone column with a tension device using the fourth embodiment, steps A4, B4 and C4 are shown;

Figure 20A is the continuation of the method commenced in Figure 20 which is a series of cross sectional views commenced in Figure 20, steps D4 and F4 are shown; Figure 21 is a series of side view and top views showing variants of tension units or blanking devices that may be used, these are examples only.

Definitions:

Aggregate: when used herein is construction aggregate above about 0.1 mm in size (including sand, stones, crushed rock, crushed concrete, slag, etc).

Auger: when used herein includes a flight without a central shaft, similar to a corkscrew.

Bonded Stone Column: Is a pile, or other in ground column, of bonded aggregate, where the bonding agent may be cement based. A stone column is intended to cover bonded and un-bonded granular columns made from aggregate or similar granular materials normally used in the building industry.

Bonding agents: This is intended to cover adhesives and other materials used to bond aggregates, sand and other common building materials used to form piles and stone columns. It includes cement/water mixtures, with or without adhesive additives, grouts and similar materials. A bonding agent can be, for example, a grout, cement + water, epoxy based adhesive, polyurethane based adhesives, mineral oxide based adhesives, or any other adhesive material normally used for the purpose.

Flight: when used herein is a strip of material following a helical path like a spiral staircase.

Tube: when used herein a tube is meant to indicate a long hollow member whose outer cross sectional profile may be circular or any other shape (triangular, square, hexagonal, elliptical, etc.) and whose inner cavity is circular (or approximately circular/elliptical) in cross section. Please note the drawings are representative only and the relative dimensions may be exaggerated for clarity.

First Mode for Carrying Out the Invention

We will firstly describe the equipment used to perform the method of forming an in ground bonded stone column.

Referring to Figure 1 a first embodiment of a column assembly (1) including a drill assembly (2), a hopper (3) and a support (4) is shown. The column assembly (1) in use is attached to a crane or excavator (5). The crane/excavator (5) is of a known type used in the industry and it provides the support and services to the column assembly (1). The drill assembly (2) includes a first drill (10) and a second drill (11).

Referring to Figure 2 the column assembly (1) is shown in cross section. The first drill (10) is essentially a hollow tube with the second drill (1 1) lying coaxially aligned with, and at least partially within, said first drill (10). That is the second drill (1 1) lies in the hollow core (1 1A) of the first drill (10).

The second drill (1 1) includes a primary section (12) and a secondary section (13), where one terminal end of the primary section (12) is coterminous with a first terminal end (14) of the second drill (11), and one terminal end of the secondary section (13) is coterminous with a second terminal end (15) of the second drill (1 1). The first terminal end (14) and second terminal end (15) are the opposite terminal ends of the second drill (1 1). The primary section (12) is the end of the second drill (11) that is located closest to a primary end (16) of the first drill (10), where the primary end (16) is the open terminal end of the first drill (10) that enters the ground first.

The hopper (3) is optional but when present it is a container or feed section (17) for the aggregate, aggregate + bonding material and/or bonding material used to form or bond the bonded stone column. In this case the hopper (5) is essentially a truncated cone with a cylindrical section extending from the cone's base, the truncated end forming the base (20) of the hopper (3) that surrounds a portion of the first drill (10). In this embodiment the hopper (3) includes feed apertures (21) that pass through the feed wall (22), where the feed wall (22) is the wall of the first drill (10) that is common to, and separates the interior of, the first drill (10) and the hopper (3).

The column assembly (1) further includes a movement device (30) and a gearbox (31). Where the movement device (30) is attached to the support (4) and indirectly/directly to the secondary section (13) and/or second terminal end (15), and the gearbox (31) is configured or adapted to drive, when in use, either one or both drills (10,11). It should be noted that the gearbox (31) is optional and the drive to the first and second drills (10, 1 1) could be separate or common drive devices (hydraulic motors, electric motors, diesel motors etc.).

The movement device (30) is most likely to be a pneumatic or hydraulic ram of known type, but, it could be any device that can move the second drill (1 1) longitudinally within the first drill (10). The movement device (30) is optional and the first and second drills (10, 1 1) may have a fixed longitudinal arrangement.

The primary section (12) is an auger which includes a drill flight (40), one end of which is coterminous with the first terminal end (14). The drill flight (40) may extend along part or all of the length of the primary section (12).

The drill assembly may include blanking devices (41) that are configured to seal the primary end (16) of the first drill (10) as the drill assembly (2) is inserted to prevent material contaminating the bonded stone column formed. The blanking devices (41) shown are small pieces of material releasably attached between the first drill (10) and the second drill (1 1) that are able to be dislodged when necessary but, the blanking device (41) could be a concrete/metal cone (not shown) or plate that shields the primary end (16) completely.

Figure (3) shows a second embodiment of the column assembly (1) where the first drill (10) includes a first drill flight (42) where the first drill flight (42) is a flight located on the exposed surface (43) of the first drill (10) which commences at or close to the primary end (14).

It should be noted that the flights (40,42) on the first and second drill (10, 11), where present, can be right or left handed, and the first and second drills (10, 1 1) may be driven co or counter rotationally at the same or different speeds, or one may remain rotationally static whilst the other is not.

Referring to Figure 4 the preferred method of preparing a bonded stone column (54) using the column assembly (1) described will be outlined. The method includes the following steps, in order:

Step A: Insert column assembly (1) into the ground (50) to the desired depth;

Step B: Adjust the position of the drills (10, 1 1), if necessary, until the first terminal end (14) is spaced apart from the primary end (16);

Step C: Feed one or more materials (51 ,52,53) from the hopper (3) through the drill assembly (2) to the base of the hole (55);

Step D: Withdraw the drill assembly (2) whilst controlling the feed rate and other parameters to form a bonded stone column (54) with the desired characteristics.

Step B is optional, but preferred.

In step A the column assembly (1) is pushed into the ground by the excavator (5), this may be assisted by rotating the first drill (10) or drill assembly (2). To prevent any detrimental amount of ground material entering the centre of the first drill (10) the second drill (11) may be rotated, alternatively blanking device/s (41) (shown in Figure 2) may be present that prevent the ground material moving along the drill flight (40) during this step. It should be noted that a detrimental amount of ground material is an amount of ground material sufficient to affect the integrity of the bonded stone column (54) formed. Once the drill assembly (2) is at the required depth the excavator/crane (5) stops forcing the drill assembly (2) into the ground (50) and step B is undertaken.

It should be noted that where the term 'forced' is used with reference to the insertion of the drill assembly (2) this force is only sufficient to push the drill assembly (2) into the ground at the desired rate and it may be negligible if the first drill (10) is rotated and includes a first flight (42) (shown in Figure 3) or other features that reduce skin friction.

In step B, when undertaken, the relative vertical positions of the first and second drills (10, 1 1) is adjusted until the first terminal end (14) is spaced apart (vertically displaced) from the primary end (16) of the first drill (10). This may be accomplished by forcing the second drill (1 1) further into the ground (50), withdrawing the first drill (10) a small amount or a combination of these. If blanking devices (41) are present then these need to be dislodged, for example by a momentary reversal of the second drill (1 1) before step B is undertaken, or dislodged as step B is undertaken. The blanking device/s (41) may be retained by a breakable link (a small weld for example) between the first and second (10, 11) drills, be hinged/pivoted flaps, a combination of these or any other suitable means to prevent the ingress of foreign material into the first drill (10). It should be noted that the vertical separation may involve the second drill (1 1) being withdrawn into the first drill (10) or vice versa. It is believed that the separation between the first and second drills (10, 1 1) will be in the range of 50mm and 450mm to ensure successful radial compaction.

The optimum separation distance, if present, is determined by the aggregate size and composition, the diameter of the drills (10, 1 1), the configuration of the drill flight (40), the properties of the bonding agent/s, the characteristics of the bonded stone column required or a combination of these parameters. Step C is then actioned

In step C one or more materials (51 ,52,53) are allowed to pass from the hopper (3), or a storage area/feed section (17), through the hollow core (11A) of the first drill (10) to the base of the hole (55). This step will normally require that the second drill (11) is rotationally driven directly or indirectly in the direction that feeds these materials to the base of the hole (55) to start forming the bonded stone column (54).

The materials (51 ,52,53) can, for example, be any or all of the following aggregate, cement + water, one or more bonding agents compatible with aggregate, aggregate + bonding agent/cement/water, geopolymer and concrete.

Step D is then undertaken to form the bonded stone column (54) with the desired characteristics.

In step D the one or more materials (51 ,52,53) are fed to the base of the hole (55) whilst the drill assembly (2) is withdrawn at a controlled rate and the second drill (1 1) is rotated at a controlled rate. Various parameters are measured and controlled to form a bonded stone column (54) with the desired characteristics, these characteristics include the density and porosity of the column at any point. The parameters measured and controlled include one or more of rotational speed and direction of the drills (10, 1 1) and/or drill assembly (2), the speed the drill assembly (2) is withdrawn, the feed rate of the drill (10,1 1)/drill assembly(2), the drill (10, 11)/drill assembly (2) torque requirement, materials (51 ,52,53) feed rate etc. By controlling the torque requirements of the second drill (11) and the feed rate of materials (51 ,52,53) the radial and vertical compaction of the bonded stone column (54) can be varied, in addition the penetration of the materials (51 ,52,53) into the ground (50) surrounding the bonded stone column (54) can be controlled. Thus it is possible to form a bonded stone column (54) with specific wall properties. It is preferred that one of the materials (51 ,52,53) is the dry aggregate and a second is a bonding agent so that the relative concentration of each material (51 ,52,53) used to form the bonded column can be controlled. It should be noted that to form a bonded stone column (54) a bonding agent, separate or incorporated with the other materials will be necessary. In this case a bonding agent is an adhesive material that is suitable for bonding dry building materials such as aggregate.

The first drill (10) provides support for the ground (50) surrounding the drill assembly (2) as the bonded stone column (54) is formed and the radially forced materials (51 ,52,53) assist in compacting this ground (50) and the surface of the bonded stone column (54) as it is formed. In some configurations the first drill (10) includes an expanded section (not shown) that compacts the ground (50) around the drill assembly (2) as it is inserted

The bonded stone columns (54) are expected to have the aggregate present forced out radially forming compressed walls with good ground penetration and require much less, if any, vibration.

If the first drill (10) and second drill (1 1) are spaced apart then the spacing may also be varied as the drill assembly (2) is withdrawn to modify the bonded stone column (54) properties at specific points.

By controlling the composition of the bonded stone column (54) at any point it is possible to create zones in the column which have increased density, increased porosity for drainage at specific levels, or other specific properties. It should also be noted that the aggregate size/composition/structure can be varied by feeding in different materials (51 ,52,53) into the hopper (3) or feed section (17). . In some cases there may be the requirement to insert reinforcing into the bonded stone column (54), either as it is formed or as one of the final steps. In some cases the reinforcing may simply be plunged into the curing bonded stone column (54), though it is uncertain if this will affect the properties of the final bonded stone column (54).

Referring to Figures 5 and 6 which shows an enlarged section of the drill assembly (2) that includes the primary end (16) of the first drill (10) and the primary section (12) of the second drill (11) an alternative configuration of the drill assembly (2) is shown. In these alternative embodiments, a drill gap (60), which is a space, is present between, an inner wall (61) of first drill (10) and outer edge (62) of the drill flight (40).

The drill gap (60) is dimensioned to allow reinforcing bars (63) to be inserted into the bonded stone column as it is formed. Alternatively the reinforcing can be designed such that, it can be inserted as the drill assembly is withdrawn. In some embodiments the reinforcing is in the form of a reinforcing cage (64) which is an essentially cylindrical cage including vertical and angled (any suitable angle) reinforcing bars (65,66) attached to form a cylindrical mesh cage.

Please note that vertical when referring to the vertical reinforcing bars (65) used to form the reinforcing cage (64) is meant to indicate that those reinforcing bars run essentially lengthwise within the bonded stone column (54) once the reinforcing cage (64) is installed. These vertical reinforcing bars (65) may follow a helical path, or be at a preferred angle other than 90°.

In some embodiments there is no hopper (3) and the or each material (51 ,52,53) is fed directly into the drill assembly (2) at the feed section (17).

SECOND EMBODIMENT

Referring to Figure 7 a second embodiment of a column assembly (1) including a drill assembly (2), a hopper (3), a support (4), an isolation section (70) and drill assembly feed (71) is shown. As previously described the drill assembly (2) includes a first drill (10) and a second drill (11). Referring to Figure 8 the second embodiment of the column assembly (1) is shown in cross section, without any of the gearbox (31) components shown for clarity. As before the first drill (10) is essentially a hollow tube with the second drill (1 1) lying coaxially aligned with, and at least partially within, said first drill (10). That is the second drill (11) lies in the hollow core (11 A) of the first drill (10).

In this case the second drill (1 1) includes a feed conduit (75), where the feed conduit (75) is a void running the length of the second drill (1 1) with an alpha end (76) and a beta end (77). Where the alpha end (76) is a terminal end of the feed conduit (75) that is close to, or coterminous with, the first terminal end (14) of the second drill (11). The beta end (77) is the opposite open end of the feed conduit (75) which is located at the opposite distal end of the second drill (1 1) to the alpha end (76). The beta end (77) may exit through the side of the second drill (1 1), be coterminous with the second terminal end (15) or both. The beta end (77) is fluidly connected to the drill assembly feed (71) which when in use conveys bonding agent from a source (not shown) to the column assembly (1). Thus in the simplest form the second drill (1 1), in this second embodiment, is simply an open ended tube. There may be more than one alpha and beta end (76,77) that are, or include, one or more apertures through a side wall of the second drill (11) in the primary and secondary sections (12, 13) , located close to, but not coterminous with, the first or second terminal ends (14, 15) respectively.

The isolation section (70) rotationally isolates the second drill (1 1) whilst still providing a fluid connection between the feed conduit (75) and the drill assembly feed (71). Devices and configurations that allow fluid to be fed to a rotating member are well known, for example a pressurised/unpressurised reservoir surrounding the open end of tube, an annulus surrounding the rotating member which is fed the fluid and this fluid passes through apertures in the wall of the rotating member to connect a central void within the rotating member to the fluid source. In addition there are many ways to feed a fluid to the outside of a rotating shaft where the source remains stationary, if the shaft is hollow it is a simple matter to provide apertures in the shaft wall that a fluid can pass through to feed that hollow section.

The hopper (3) is optional in this embodiment as well but when present it is a container or feed section (17) for aggregate or possibly aggregate + a bonding material. In this case the hopper (5) has essentially the same form as the first embodiment and is numbered accordingly. The movement device (30) in this case moves the isolation section (70), though it could move the second drill directly if the isolation section included a wide annulus that surround the beta end (77) throughout the movement range of the second drill (1 1) as it is moved longitudinally. Again the movement device (30) is optional and the first and second drills (10, 11) may have a fixed longitudinal arrangement, but it is preferred that the longitudinal relationship of the drills can be changed.

The primary section (12) is an auger which includes a drill flight (40), one end of which is coterminous with the first terminal end (14). The drill flight (40) may extend along part or all of the length of the primary section (12).

The drill assembly may include blanking devices (41) that are configured to seal the primary end (16) of the first drill (10) as the drill assembly (2) is inserted to prevent material contaminating the bonded stone column formed. The blanking devices (41) shown are small pieces of material releasably attached between the first drill (10) and the second drill (1 1) that are able to be dislodged when necessary but, the blanking device (41) could be a concrete/metal cone (not shown) or plate that shields the open end of the first drill (10).

In this second embodiment the second drill preferably includes a conduit seal (78) to seal the alpha end (76) as the drill assembly (2) is inserted into the ground, this conduit seal (78) needs to seal against the ingress of material into the feed conduit (75). For example: a. The conduit seal (78) is a plug of material kept in place by a pressurised fluid within the feed conduit (75), the pressure being increased to dislodge the conduit seal (78) when the bonded stone column (54). is formed.

b. The conduit seal (78) is a flow of fluid through the feed conduit (74) at a sufficient pressure to prevent ground material accessing the feed conduit (75). c. The conduit seal (78) is a cap over the beta end (76) held in place by a tensioned wire as the drill assembly (2) is inserted.

d. The conduit seal (78) is a cap held in place by an adhesive as the drill assembly (2) is inserted, the adhesive being dissolved by a solvent when the bonded stone column (54) needs to be formed. e. The conduit seal (78) is a cap resting against an annular ring inside the feed conduit, (75) the cap is prevented from falling out as the drill assembly is inserted by tack welds or another form of frangible connection (wax, adhesive etc). When the drill assembly (2) reaches the required depth pressurised fluid is fed into the feed conduit (75) breaking the frangible connection (s) and dislodging conduit seal (78) as the drill assembly (2) is withdrawn.

Referring to Figure 9 the preferred method of preparing a bonded stone column (54) using the column assembly (1) of the second embodiment is shown, and will now be described. The method includes the following steps, in order:

Insert column assembly (1) into the ground (50) to the desired depth; Adjust the position of the drills (10, 1 1), if necessary, until the first terminal end (14) is spaced apart from the primary end (16);

Dislodge the conduit seal (78), if present, and feed one or more materials (51 ,52,53) from the hopper (3) through the drill assembly (2) to the base of the hole (55) whilst feeding a conduit fluid (80) through the feed conduit (75);

Withdraw the drill assembly (2) whilst controlling the feed rate and other parameters of the material or materials (51 ,52,53) and the conduit fluid (80) to form a bonded stone column (54) with the desired characteristics.

Step B1 is optional, but preferred, and the conduit seal (78) may not be present.

In step A1 the column assembly (1) is pushed into the ground by the excavator (5), this may be assisted by rotating the first drill (10) or drill assembly (2). To prevent any detrimental amount of ground material entering the centre of the first drill (10) the second drill (11) may be rotated, alternatively blanking device/s (41) (shown in Figure (8) may be present that prevent the ground material moving along the drill flight (40) during this step. It should be noted that a detrimental amount of ground material is an amount of ground material sufficient to affect the integrity of the bonded stone column (54) formed. If a conduit seal (78) is present this prevents any detrimental amount of ground material entering the feed conduit (75). If the blanking device (41) is a concrete cone then this should also act as conduit seal (78), in fact it is believed that a unitary conduit seal (78) and blanking device (41) may have advantages over separate devices. Once the drill assembly (2) is at the required depth the excavator/crane (5) stops forcing the drill assembly (2) into the ground (50) and step B1 is undertaken.

It should be noted that where the term 'forced' is used with reference to the insertion of the drill assembly (2) this force is only sufficient to push the drill assembly (2) into the ground at the desired rate and it may be negligible if the first drill (10) is rotated, is rotated and includes a first flight (42) (as shown in Figure 3) or other features that reduce skin friction.

In step B1 , when undertaken, the relative vertical positions of the first and second drills (10, 1 1) is adjusted until the first terminal end (14) is spaced apart (vertically displaced) from the primary end (16) of the first drill (10). This may be accomplished by forcing the second drill (1 1) further into the ground (50), withdrawing the first drill (10) a small amount or a combination of these. If blanking devices (41) are present then these need to be dislodged or removed, for example by a momentary reversal of the second drill (11) before step B1 is undertaken, or dislodged as step B1 is undertaken. The blanking device/s (41) may be retained by a breakable link (a small weld for example) between the first and second (10, 11) drills, be hinged/pivoted flaps, a combination of these or any other suitable means to prevent the ingress of foreign material into the first drill (10). It should be noted that the vertical separation may involve the second drill (1 1) being withdrawn into the first drill (10) or vice versa.

The optimum separation distance, if present, is determined by the aggregate size and composition, the diameter of the drills (10, 11), the configuration of the drill flight (40), the properties of the bonding agent/s, the characteristics of the bonded stone column required or a combination of these parameters. It is expected that the longitudinal separation will be present and in the range of 100mm to 350mm. Once step B1 is completed then step C1 is then actioned

In step C1 the conduit seal (78) is dislodged or removed and then one or more materials (51 ,52,53) are allowed to pass from the hopper (3), or a storage area/feed section (17), through the hollow core (1 1A) of the first drill (10) to the base of the hole (55). At the same time, if appropriate, the conduit fluid (80) is fed through the feed conduit (75) and the second drill (1 1) rotated to mix the materials with the conduit fluid (80) and drive the mixed material (material (51 ,52,53) blended with conduit fluid (80)) radially outward. This step will normally require that the second drill (11) is rotationally driven directly or indirectly in the direction that feeds these materials to the base of the hole (55) to start forming the bonded stone column (54). The conduit fluid (80) is most likely to be grout or a similar known aggregate bonding agent with or without additional additives, the materials are likely to simply be aggregate that falls within a predetermined size range. During this and step D1 the isolation section (70) rotationally isolates the drill assembly feed (71) from the second drill (1 1) which allows the conduit fluid (80) to be fed as required.

The materials (51 ,52,53) can, for example, be any or all of the following aggregate, cement + water, one or more bonding agents compatible with aggregate, aggregate + bonding agent/cement/water and concrete.

Step D1 is then undertaken to form the bonded stone column (54) with the desired characteristics.

In step D1 the one or more materials (51 ,52,53) are fed to the base of the hole (55) whilst the drill assembly (2) is withdrawn at a controlled rate and the second drill (1 1) is rotated at a controlled rate. At the same time, the required amount of conduit fluid (80) is fed through the feed conduit (75) and the second drill (1 1) rotated to mix the materials (51 ,52,53) with the conduit fluid (80) and force the mixed material (material (51 ,52,53) blended with conduit fluid (80)) axially and radially. By controlling the type and amount of conduit fluid (80) mixed with the material (50,51 ,52) and measuring and controlling various drill assembly (2) parameters a bonded stone column (54) with the desired characteristics can be formed, these characteristics include the density and porosity of the column at any point. The parameters measured and controlled include one or more of rotational speed and direction of the drills (10, 1 1) and/or drill assembly (2), the speed the drill assembly (2) is withdrawn, the feed rate of the drill (10, 11)/drill assembly(2), the drill (10, 11)/drill assembly (2) torque requirement, materials (51 ,52,53) feed rate, conduit fluid feed (80) rate, etc. By controlling the torque requirements of the second drill (11) and the composition fed to the first terminal end (14) the radial and vertical compaction of the bonded stone column (54) can be varied, in addition the penetration of the materials (51 ,52,53) into the ground (50) surrounding the bonded stone column (54) can be controlled. Thus it is possible to form a bonded stone column (54) with specific wall properties. As with the first embodiment, the first drill (10) provides support for the ground (50) surrounding the drill assembly (2) as the bonded stone column (54) is formed and the radially forced materials (51 ,52,53) assist in compacting this ground (50) and the surface of the bonded stone column (54) as it is formed. In some configurations the first drill (10) includes an expanded section (not shown) that compacts the ground (50) around the drill assembly (2) as it is inserted

The bonded stone columns (54) are expected to have the aggregate present forced out radially forming compressed walls with good ground penetration and require much less, if any, vibration.

If the first drill (10) and second drill (1 1) are spaced apart then the spacing may also be varied as the drill assembly (2) is withdrawn to modify the bonded stone column (54) properties at specific points.

By controlling the composition of the bonded stone column (54) at any point it is possible to create zones in the column which have increased density, increased porosity for drainage at specific levels, or other specific properties. It should also be noted that the aggregate size/composition/structure can be varied by feeding in different materials (51 ,52,53) into the hopper (3) or feed section (17), and the type and amount of conduit fluid (80) fed through the feed conduit (75) can be varied at the same time.. .

In some cases there may be the requirement to insert reinforcing into the bonded stone column (54), either as it is formed or as one of the final steps. With this second embodiment it is believed that it will be possible to insert reinforcing rod through the feed conduit (75) as the bonded stone column (54) is formed alleviating the need to install this later.

It should be noted that the alpha end (76) may be one or more apertures through the second drill (11) located close to the first end (14) or between turns of the drill flight (40). In fact to get good mixing it may be necessary to have one or more alpha end (76) located a short distance away from the first end (14).

THIRD EMBOIDMENT Referring to Figs 10 and 1 1 , cross sectional views of a third embodiment are shown. Fig. 11 is an expanded view of a section of the column assembly (1) showing the first terminal end (14) and primary end (16) in more detail.

In this third embodiment a feed insert (85) is located within the feed conduit (75) as the drill assembly (2) is inserted. This feed insert (85) is essentially a plain or corrugated tube aligned approximately co-axially with the second drill (11). The feed insert is shown essentially filling the feed conduit (75) though this is optional and it may well have a smaller cross section.

The feed insert (85) includes a first insert end (86) and a second insert end (87) which are the terminal ends of the feed insert (85). The first insert end (86) is located close to or at the first terminal end (14) of the second drill (11) and the second insert end

(87) is the opposite terminal end of the feed insert (85). The feed insert is shown approximately the same length as the bonded stone column (54) (see Fig. 15) to be formed, but it could be longer and trimmed or shorter so that it is hidden by a surface layer of the finished bonded stone column (54). The feed insert (85) can be any polymeric (organic or inorganic) or metallic material or combination of these, but initially an organic polymer pipe, for example polyethylene, polypropylene or possibly nylon will be used.

The column assembly (1) is shown without an isolation section (70) but in some configurations this may be present so that the feed insert (85) can be fed the conduit fluid (80), for example grout or a bonding agent, rather than the feed conduit (75).

The alpha end (76) and first insert end (86) are shown sealed by a feed insert seal

(88) which in Fig. 10 and 1 1 is a disc of material that sits against the alpha end (76). The feed insert seal (88) may be larger in diameter than the feed conduit (75) and even extend to the inner wall (61) of the first drill (10), possibly acting as, or being part of, the blanking device (41).

Fig. 12 shows the primary section (12) of the second drill (11) with a plain uncon ^j ugated feed insert (76), with the insert seal (88) being a disk that does not extend beyond the outside wall surface (90) of the second drill (11). The outer wall surface (90) is the outer exposed surface of the second drill (1 1) excluding the drill flight (40) which is attached to or formed into the outside wall surface (90). There are a number of possible configurations for the feed insert seal (88) and a number of these are shown in Fig. 13 to Fig. 15, which all show all or part of the primary section (12) second drill (1 1) only for clarity.

In Fig. 13 the feed insert seal (88) is a disc that is held in place by a retention connector (91) which is a wire, rod or similar. The retention connector (91), if rigid, or able to apply force to the feed insert seal (88), can be used to keep the feed insert seal (88) and the feed insert (85) at the base of the sealed stone column (54) as it is formed. If the retention connector (91) is rigid enough it may act as reinforcing (fibreglass rod, fibre reinforced polymeric materials, reinforcing bar, high tensile steel rods or wires, or a combination of one or more of these).

In Fig. 14 the feed insert seal (88) is basically a plug which is a friction fit with the first insert (86) end of the feed insert (85), the section inserted may incorporate additional features such as grooves, protrusions or pins which may be frangible.

In Fig. 15 the feed insert seal (88) is a plug similar to that shown in Fig.14 but the disc extends well beyond the outside wall surface (90) of the second drill (1 1), possibly allowing the feed insert seal (88) to act as a blanking means (41). This variant also shows feed insert apertures (92) that are passages from the central void of the feed insert (85) to the outside. These optional feed insert apertures (92), when present, may be located anywhere along the length of the feed insert (85) but some will most likely be located close to the first insert end (86).

Referring to Figure 16 one preferred method of preparing a bonded stone column (54) using the column assembly (1) of the third embodiment is shown, and will now be described. The method includes the following steps, in order:

Step A2: Insert column assembly (1) into the ground (50) to the desired depth; Step B1 : (not shown in Fig. 16 but similar to that shown in Fig. 9) and adjust the position of the drills (10, 11), if necessary, until the first terminal end (14) is spaced apart from the primary end (16);

Step C2: Dislodge the feed insert seal (88) and/or the feed insert (85) from the feed conduit (75), if necessary, and feed one or more materials

(51 ,52,53) from the hopper (3) through the drill assembly (2) to the base of the hole (55) whilst feeding a conduit fluid (80) through the feed insert (85);

Step D2: Withdraw the drill assembly (2) whilst controlling the feed rate and other parameters of the material or materials (51 ,52,53) and the conduit fluid (80) to form a bonded stone column (54) with the desired characteristics.

Step B1 is optional, but preferred, and the conduit seal (78) may not be present.

In step A2 the column assembly (1) is pushed into the ground by the excavator (5), this may be assisted by rotating the first drill (10) or drill assembly (2). To prevent any detrimental amount of ground material entering the centre of the first drill (10) the second drill (11) may be rotated, alternatively blanking device/s (41) (shown in Figure (10) may be present that prevent the ground material moving along the drill flight (40) during this step. In some cases the feed insert seal (88) will provide the required sealing. It should be noted that a detrimental amount of ground material is an amount of ground material sufficient to affect the integrity of the bonded stone column (54) formed. The feed insert seal (88) should prevent any detrimental amount of ground material entering the feed conduit (75) or feed insert (85). If the blanking device (41) is a concrete cone then it should also act as the feed insert seal (88). Once the drill assembly (2) is at the required depth the excavator/crane (5) stops forcing the drill assembly (2) into the ground (50) and step B1 is undertaken.

It should be noted that where the term 'forced' is used with reference to the insertion of the drill assembly (2) this force is only sufficient to push the drill assembly (2) into the ground at the desired rate and it may be negligible if the first drill (10) is rotated and includes a first flight (42) (as shown in Figure 3) or other features that reduce skin friction. For example the first drill (10) may include an expanded section.

In step B1 , when undertaken, the relative vertical positions of the first and second drills (10, 1 1) is adjusted until the first terminal end (14) is spaced apart (vertically displaced) from the primary end (16) of the first drill (10). This may be accomplished by forcing the second drill (1 1) further into the ground (50), withdrawing the first drill (10) a small amount or a combination of these. If blanking devices (41) are present then these need to be dislodged or removed, for example by a momentary reversal of the second drill (11) before step B1 is undertaken, or dislodged as step B1 is undertaken. The blanking device/s (41) may be retained by a breakable link (a small weld for example) between the first and second (10, 11) drills, be hinged/pivoted flaps, a combination of these or any other suitable means to prevent the ingress of foreign material into the first drill (10). It should be noted that the vertical separation may involve the second drill (11) being withdrawn into the first drill (10) or vice versa. The feed insert seal (88) may be dislodged in the same manner or it may remain connected to the feed insert (85) whilst disengaging from the second and or first drills (11 , 10).

The optimum separation distance, if present, is determined by the aggregate size and composition, the diameter of the drills (10, 11), the configuration of the drill flight (40), the properties of the bonding agent/s, the characteristics of the bonded stone column required or a combination of these parameters. It is expected that the longitudinal separation will be present and in the range of 100mm to 350mm. Once step B1 is completed then step C2 is then actioned

In step C2 the feed insert (85) is dislodged from the feed conduit (75) and if necessary the feed insert seal (88) is dislodged or removed from the first insert end (86). It should be noted that if there are feed insert apertures (92) then the feed insert seal (88) may be dislodged from the drill assembly (2) but remain engaged with the feed insert (85). Once the feed insert (85) is dislodged the drill assembly (2) is withdrawn leaving the first insert end (86) at the base of the hole (55). A corrugated feed insert (85) will be retained by the stone column as it is formed providing extra friction to keep it in place as the drill assembly (2) is removed.

As the drill assembly (2) is removed one or more materials (51 ,52,53) are allowed to pass from the hopper (3), or a storage area/feed section (17), through the hollow core (1 1A) of the first drill (10) to the base of the hole (55). At the same time, if appropriate, the conduit fluid (80) is fed through the feed insert (85) and the second drill (11) is rotated to mix the materials with the conduit fluid (80), and drive the mixed material (material (51 ,52,53) blended with conduit fluid (80)) radially outward. This step will normally require that the second drill (11) is rotationally driven directly or indirectly in the direction that feeds these materials to the base of the hole (55) to start forming the bonded stone column (54). The conduit fluid (80) is most likely to be grout or a similar known aggregate bonding agent with or without additional additives, the materials (51 ,52,53) are likely to simply be aggregate that falls within a predetermined size range. During this and step D2 the isolation section (70) (shown in the second embodiment), if present rotationally isolates the drill assembly feed (71) from the second drill (11) which allows the conduit fluid (80) to be fed as required.

The materials (51 ,52,53) can, for example, be any or all of the following aggregate, cement + water, one or more bonding agents compatible with aggregate, aggregate + bonding agent/cement/water and concrete.

Step D2 is then undertaken to form the bonded stone column (54) with the desired characteristics.

In step D2 the one or more materials (51 ,52,53) are fed to the base of the hole (55) whilst the drill assembly (2) is withdrawn at a controlled rate and the second drill (1 1) is rotated at a controlled rate. At the same time, the required amount of conduit fluid (80) is fed through the feed insert (85) and forced out of the first insert end (86), if clear, and the feed insert apertures (92), when present. At the same time the second drill (1 1) rotated to mix the materials (51 ,52,53) with the conduit fluid (80) and force the mixed material (material (51 ,52,53) blended with conduit fluid (80)) axially and radially.

By controlling the type and amount of conduit fluid (80) mixed with the material

(50.51.52) and measuring and controlling various drill assembly (2) parameters a bonded stone column (54) with the desired characteristics can be formed, these characteristics include the density and porosity of the column at any point. The parameters measured and controlled include one or more of rotational speed and direction of the drills (10,1 1) and/or drill assembly (2), the speed the drill assembly (2) is withdrawn, the feed rate of the drill (10, 11)/drill assembly(2), the drill (10, 11)/drill assembly (2) torque requirement, materials (51 ,52,53) feed rate, conduit fluid feed (80) rate, etc. By controlling the torque requirements of the second drill (1 1) and the composition fed to the first terminal end (14) the radial and vertical compaction of the bonded stone column (54) can be varied, in addition the penetration of the materials

(51.52.53) into the ground (50) surrounding the bonded stone column (54) can be controlled. Thus it is possible to form a bonded stone column (54) with specific wall properties.

As with the first embodiment and second embodiments, the first drill (10) provides support for the ground (50) surrounding the drill assembly (2) as the bonded stone column (54) is formed and the radially forced materials (51 ,52,53) assist in compacting this ground (50) and the surface of the bonded stone column (54) as it is formed. In some configurations the first drill (10) includes an expanded section (not shown) that compacts the ground (50) around the drill assembly (2) as it is inserted.

The bonded stone columns (54) are expected to have the aggregate present forced out radially forming compressed walls with good ground penetration and require much less, if any, vibration.

If the first drill (10) and second drill (1 1) are spaced apart then the spacing may also be varied as the drill assembly (2) is withdrawn to modify the bonded stone column (54) properties at specific points.

By controlling the composition of the bonded stone column (54) at any point it is possible to create zones in the column which have increased density, increased porosity for drainage at specific levels, or other specific properties. It should also be noted that the aggregate size/composition/structure can be varied by feeding in different materials (51 ,52,53) into the hopper (3) or feed section (17), and the type and amount of conduit fluid (80) fed through the feed conduit (75) can be varied at the same time.. .

In Fig. 17 an alternative method of forming a bonded stone column (54) is provided. In this variant steps A2 and B1 (optional but preferred) are undertaken but no conduit fluid (80) is passed through the feed insert (85) as the column is formed. So initially an un-bonded granular stone column (93) is formed. Once the column assembly (1) is completely removed the conduit fluid (80) can be fed into the feed insert (85) to flow (or be pressure forced) into the granular stone column (93) forming a bonded stone column (54). By using this method the granular stone column can be formed without the conduit fluid lubricating the materials (51 ,52,53) as the column is formed. If necessary reinforcing could be inserted into the second insert end (87).

In more detail this variant method for the third embodiment includes, with some steps optional:

Step A2: Insert column assembly (1) into the ground (50) to the desired depth; Step B1 : (not shown in Fig. 17 but similar to that shown in Fig. 9) Adjust the position of the drills (10, 11), if necessary, until the first terminal end (14) is spaced apart from the primary end (16);

Step C3: Dislodge the feed insert seal (88) and/or the feed insert (85) from the feed conduit (75), if necessary, and feed one or more materials (51 ,52,53) from the hopper (3) through the drill assembly (2) to the base of the hole (55);

Step D3: Withdraw the drill assembly (2) whilst controlling the feed rate and other parameters of the material or materials (51 ,52,53) required for an unbonded granular stone column (93);

Step E3: Feed conduit fluid (80) into the feed insert (85) forcing it into the unbonded granular stone column (93) to form a bonded stone column (54) with the desired properties.

Step B1 is optional, but preferred, and the conduit seal (78) may not be present.

Steps A2 and B1 (where present) are the same as described previously.

In step C3 the feed insert (85) is dislodged from the feed conduit (75) and if necessary the feed insert seal (88) is dislodged or removed from the first insert end (86). It should be noted that if there are feed insert apertures (92) then the feed insert seal (88) may be dislodged from the drill assembly (2) but remain engaged with the feed insert (85). Once the feed insert (85) is dislodged the drill assembly (2) is withdrawn leaving the first insert end (86) at the base of the hole (55). A corrugated feed insert (85) will be retained by the stone column as it is formed providing extra friction to keep it in place as the drill assembly (2) is removed. It is believed that an un-corrugated feed insert (85) will also be retained but if necessary the second insert end (87) could be held in place to assist.

As the drill assembly (2) is removed one or more materials (51 ,52,53) are allowed to pass from the hopper (3), or a storage area/feed section (17), through the hollow core (1 1A) of the first drill (10) to the base of the hole (55). At this stage the second drill (1 1) will be rotated to force the materials (51 ,52,53), which in this case will most likely be dry materials (aggregate for example), radially outward. Some water or other fluid may be added to lubricate the aggregate at times. D3 is the same as D2 except no conduit fluid (80) is passed through the feed insert (85) to the base of the hole and the drill assembly (2) forms an un-bonded granular stone column (93) with the feed insert (85) retained within.

In step E3 conduit fluid (80) is passed through the feed insert (85) to form a bonded stone column. A pipe (94) could be dropped to the first insert end (86) and the conduit fluid (80) pumped in as the pipe (94) is removed. The second insert end (87) could be formed with, or configured to engage with, an attachment that allows the feed insert (85) to be filled then pressurised forcing the conduit fluid into the un-bonded stone column (93). For example the pipe (94) could include a collar (95) which retains the pipe (94) in the feed insert (85) and could act as a seal to allow the pressurisation of the bonding agent/conduit fluid (80) within the feed insert (85). In some forms the collar (95) could be a pneumatic collar which is pressurised to seal against the pipe (94) and the feed insert (85). In other configurations the collar (95) could be a resilient foam ring, or a ring of flexible material, which is able to be forced past first corrugation in the feed insert (85) or anything similar. The connection could also include threaded or keyed components, or other known means of releasably attaching two pipes in fluid connection.

It is expected that for all embodiments the volume or mass of bonding agent and/or conduit fluid (80) will be monitored to ensure the required amount is present in the final bonded stone column (54). This monitoring could take the form of a flowmeter, a pressure gauge, a combined pressure flowrate gauge, or similar. This monitoring is undertaken to ensure the correct amount (volumetrically or on a mass basis) of bonding agent and/or conduit fluid (80) is added for the materials (51 ,52,53) placed, and to be able to confirm this for inspection or other purposes.

BEST METHOD FOR CARRYING OUT THE INVENTION

FOURTH EMBODIMENT

Referring to Figures 18 and 19 a fourth embodiment of the column assembly (1), which is similar to the second and third embodiments in that it includes a feed conduit (75), is shown. This fourth embodiment includes a releasable tension device (100) including a tension unit (101) and tension link (102). The tension unit (101) is intended to form part or all of the base of a stone column formed, possibly extending beyond the side walls of the stone column (54) formed. The tension link (102) is intended to link the base of the stone column (54) to a structure to reduce or eliminate the effect of uplift on that structure.

The tension device (100) includes a tension unit (101) and a tension link (102). The tension unit (101) is shown as a flat disk extending across the primary end (16) effectively sealing the open ends of the first and second drills (10, 1 1), however, it may extend beyond the edges of the first drill (1).

The tension unit (101) may be a plate of any shape (circular, elliptical, triangular, rectangular or any other polygonal shape), or even a three dimensional object such as a cone, pyramid (truncated or not), portion of a sphere or ellipsoid, or similar. The tension unit (101) may extend beyond the edges of the first drill (10), or be combined with at least one blanking device (41) to seal the primary end (16). Some of these variants are shown in side view in Fig. 21 as (a), (b), (c), and in top view as (d), (e), (f) and (g), noting that they may be flat plates or three dimensional, and regular or irregular polygons.

The tension link (102) is shown as a rod or solid wire that lies at least partially within the feed conduit (75). The tension link (102) is shown attached to and extending from the tension unit (75) to the second terminal end (15) of the second drill (1 1). The tension link (102) is expected to be a rod, chain, wire (solid or stranded) or a combination of these. The tension link (102) may include additional surface features such as, ribs or rings (helical, linear or circumferential, continuous or broken) that are configured to engage with the material (51 ,52,53) of a column (54) as it is formed.

In some variants the tension unit (101) extends beyond the outside of the first drill (10), in others it may not completely close the hollow core (11A). In the latter case this may require the use of blanking devices (41) to prevent unwanted material from entering the hollow core (11 A) or feed conduit (75). The size of the tension unit (101) will determine the uplift overcome and as such it can be sized for specific purposes. In some configurations there may be features incorporated into the tension unit (101) to allow it to be driven by the first or second drill (10, 1 1), for example teeth, keys, keyways, slots, notches, or combinations of these, these features may disengage automatically as the stone column, bonded or not, is formed. As the blanking devices (41) are optional they are not shown in Figure 19. The tension unit (101) can be releasably attached to one or more of the following: the primary end (16), the first terminal end (14), the first insert end (86), the alpha end (76) or any other feature of the drill assembly (2) by any suitable releasably connection type known including keyway, threaded section, magnetically, pneumatic connection, frangible connection, friction, dissolvable bonding agent or combination of these. The tension unit (101) can also be held in place by tension in the tension link (102).

Referring to Fig. 20 and Fig 20A an alternative method of forming a bonded or unbonded stone column (54) is provided. In this variant a bonded stone column is formed with a tension device (100) to counter or reduce the effect of uplift.

In more detail this variant method for the fourth embodiment includes, with some steps optional (B4 and F4 for example) or the same as for the third embodiment thus omitted for clarity (E3 for example):

Step A4: Insert the column assembly (1) into the ground (50) to the desired depth;

Step B4: Adjust the position of the drills (10, 1 1), if necessary, until the first terminal end (14) and the tension unit (102) are spaced apart from the primary end (16);

Step C4: Dislodge the tension unit from the second drill (11)/ feed conduit (75), if necessary, and feed one or more materials (51 ,52,53) from the hopper (3) through the drill assembly (2) to the base of the hole (55);

Step D4: Withdraw the drill assembly (2) whilst controlling the feed rate and other parameters of the material or materials (51 ,52,53), similar to step D2. For example conduit fluid (80) may also be fed through the feed conduit (75) or the feed insert (85), or the feed insert (85) may be fed into the column (54) when these are present (please see Fig.16 and/or Fig. 17 for these features);

Step F4: The tension link (102) is connected to the structure (110) and, at the appropriate time, may be tensioned to the required level. This depends on the building code requirements and the materials used,

Step A4 is similar to step A, A1 or A2, as it involves inserting the column assembly into the ground (50) until it is at the desired depth. The tension unit (101) acting alone or in combination with other features (blanking devices (41)) to minimise the ingress of undesirable material into the hollow core (1 1A) and/or, where present, the feed conduit (75) and/or the feed insert (85) (not shown in Fig. 20/20A see Fig. 16 or Fig. 17). Step B4 or step C4 is then undertaken.

Step B4 is optional, though if present in this step the tension device (100) is released from the primary end (16) and remains releasably attached to the second drill (11) as the primary end (16) and first terminal end (14) are vertically spaced .apart by moving the first drill (10) and /or the second drill (11). It should be noted that releasing the tension device (100) may be accomplished by releasing the tension unit (101). Once the primary end (16) and first terminal end (14) are at the desired spacing step C4 is undertaken. If blanking devices (41) are present then they may dislodged in this step or any following step.

Step C4 involves releasing the tension unit (101) from the drill assembly (2) and dislodging or releasing any blanking device/s (41) that is/are present then withdraw carry out step D4. Step C4 may include some operations detailed in C1 , C2 or C3 where items such as feed inserts (85) and conduit fluid (80) are used, though these are optional (not shown in Fig. 20/20A see Fig. 16 or Fig. 17).

In step D4, as the drill assembly (2) is withdrawn, one or more materials (51 ,52,53) are allowed to pass from the hopper (3), or a storage area/feed section (17), through the hollow core (11 A) of the first drill (10) to the base of the hole (55). At this stage the second drill (11) will be rotated to force the materials (51 ,52,53), which in this case can be dry materials (aggregate for example), premixed dry and bonding materials, or separate dry and bonding materials, radially outward. Some water or other fluid may be added to lubricate the dry materials. If a conduit fluid (75) and/or feed insert (85) are to be used they may be fed in at this step at the required time (not shown in Fig. 20/20A see Fig. 16 or Fig. 17).

The materials (51 ,52,53) move into contact with at least part of the tension unit (101) to assist in retaining the tension unit (101) at the base of the column (54) as it forms. If a rigid tension link (102) is used this may also assist in retaining the tension unit (101) at the base of the column (54) as it is formed. Certain elements of steps present in the previous embodiments may additionally be necessary if items such as feed inserts (85) or conduit fluids (80) are used, these are detailed in steps D1 , D2 and D3 (not shown in Fig. 20/20A see Fig. 16 or Fig. 17).

Step D4 may be followed by step E3, but this depends on whether a feed insert (85) is used, and if a conduit fluid (75) needs to be fed into the column (54) (not shown in Fig. 20/20A see Fig. 16 or Fig. 17). After step D4, or E3, step F4 may be undertaken.

In step F4 the tension link (102)) is disconnected from the column assembly (1) and either attached to an appropriate part of a structure (1 10) and tensioned, or left in a position so that once the column (54,93) is sufficiently bonded (where a bonded column is formed) or the structure (1 10) is completed it can be.

In any of the embodiments measuring and controlling various drill assembly (2) parameters a bonded stone column (54) with the desired characteristics can be formed, these characteristics include the density and porosity of the column at any point. The parameters measured and controlled include one or more of rotational speed and direction of the drills (10, 1 1) and/or drill assembly (2), the speed the drill assembly (2) is withdrawn, the feed rate of the drill (10, 11)/drill assembly (2), the drill (10, 1 1)/drill assembly (2) torque requirement, material (51 ,52,53) feed rate, if used the conduit fluid feed (80) rate, the vertical separation between the first terminal end (14) and the primary end (16), etc. By controlling the torque requirements of the second drill (11) and the composition fed to the first terminal end (14) the radial and vertical compaction of the bonded stone column (54) can be varied, in addition the penetration of the materials (51 ,52,53) into the ground (50) surrounding the bonded stone column (54) can be controlled. Thus it is possible to form a bonded or un-bonded stone column (54) with specific wall properties.

It should be noted that features of various embodiments may be combined, for example the tension device (100) may be used with a feed insert (85), the feed conduit (75) can releasably retain a tension device (100) and, as the column (54) is formed, be used to feed a conduit fluid (80); aggregate + boning agent can be separately fed through the hollow core (11 A) and additional conduit fluid (80) fed in to vary the composition at specific depths (possibly feed a catalytic agent to accelerate/decelerate curing, improve bond between tension unit (101) and column (54), use specific bonding agent to bond the tension link (102) to the column (54), etc.). In addition some variants may have a conduit seal (78), one or more blanking device (41), a feed insert seal (88), a feed insert seal (88) that acts as the tension unit (102) or one or more of the previous to seal the end of the drill assembly (2).

The feed conduit (75) can also be used to feed specific sensors or monitoring devices (103) into a column (54) during construction to monitor conditions at specific locations in the column (54). For example the sensor or monitoring device (103) could be pressure gauges, strain gauges, temperature probes, conductivity probes, seismic monitoring equipment, etc. the data cables carrying the output could be protected by a feed insert (85), with or without a tension device (100) installed at the same time. In some cases a strain gauge (104) could be built into the tension link (102) so that the uplift load could be monitored, possibly real time. In this case the cross sectional shape of the feed conduit (75), the feed insert (85), the tension link (102), or a combination of these, may be other than essentially circular, so that the orientation, and/or location of any specific sensor or monitoring device used can have a predetermined location and orientation as a column (54,93) is formed.

In some configurations the feed conduit (75) may have a cross sectional shape than essentially circular so that an item can be fed through the inner cavity and maintain a predetermined required orientation. For example inserting a probe into a previously formed column (54,93) which includes an unfilled feed insert (85) to determine the height of the water table or other required parameter. By not having the probe permanently installed in the column (54,93) any probe failure can be better managed.

In the embodiments described the steps have been identified with a letter these steps could equally be given a word label as follows.

The steps labelled containing an A (A, A1 , A2 and A4) are essentially an insertion step where the drill assembly is inserted to the proper depth for the column required.

The steps containing a B (B, B1 and B4), are optional but, where present, are essentially a separation step where the position of the first drill (10) relative to the second drill (1 1) is adjusted. The steps containing a C (C, C1 , C2, C3 and C4) are essentially a feed step where the steps following the separation step necessary to move from the insertion step to the formation step are undertaken.

The steps containing a D (D, D1 , D2, D3 and D4) are essentially a formation step where the drill assembly (2) is withdrawn from the ground (5) forming a bonded or unbonded stone column (54,93).

The steps containing an E (E3) are optional but, where present, are an injection step where conduit fluid (80) is injected into a feed insert (85).

The steps containing an F (F4) are optional but, where present, are a connection step where a structure (110) is attached to the bonded or un-bonded stone column (54,93) via the tension link (102) or other connection device.

Where a tension device (100) is used it provides the link between the structure (110) and the column (54,93) as such an un-bonded column is able to act as ground improvement and provide a means of resisting uplift forces.