Field

[01] The present disclosure relates to column formation tools, and more particularly to column formation tools for forming columns in wetlands.

Background

[02] With the increasing demand of land for human use, conversion of wetland into useable or buildable land has become an important social topic. Formation of useable orbuildable land from soft land such as wetlands require sophisticated engineering techniques to mitigate damage to environment. ‘Deep Cement Mixing’ or OCM’ is an engineering technique which is employed to convert wetlands, including seabed, into buildable land. DCM techniques are desirable as less damage will be caused to the environment. It is known that foundations formed by DCM techniques requires a shorter time to form, have better seismic resistance and do not require many years of consolidating settlement post formation.

[03] A DCM process requires the use of column formation tools. A typical column formation tool comprises an auger-type head and a cylindrical shank portion which is used to deliver binding materials after a bore has been formed by the head portion.

[04] It is noted that the DCM process is not effective or sufficiently cost effective in certain types of sea bed. Upon field investigations, it is noted that such a seabed is densely populated with cobblestones. A cobblestone is a clast of rock which is larger than a pebble and smaller than a boulder, and is defined on the Udden-Wentworth scale as having a particle size of 64- 256 millimeters (2.5-10.1 in). A cobblestone herein has the same meaning as a cobble-sized stone. As many types of wet land are densely populated with lose stones, improvements in DCM techniques are advantageous.

Summary of disclosure

[05] A column formation tool for forming a column in a column region below a surface is disclosed. The tool comprises a first portion and a second portion.

[06] The head portion comprises a core portion and an outer peripheral portion which surrounds the core portion. The outer peripheral portion comprises protuberances which are distributed between a first axial end and a second axial end to surround the core portion and define the outermost periphery of the head portion. At least some of the protuberances are configured as cutting teeth for breaking hard substances during advancement of the column formation tool. [07] The first portion is a leading portion comprising a core portion and a peripheral portion having an outermost periphery which surrounds the core portion, wherein the core portion extends along an axial direction between a first axial end and a second axial end, the axial direction being defined by a core axis which is a center axis defining an advancement axis and a first advancement direction which is an advancement direction of the first portion. The second portion is a trailing portion comprising an elongate shank portion which extends between a first longitudinal end which is proximal to the first portion and a second longitudinal end which is distal to the first portion, and wherein a channel which is configured for delivery of column-formation materials into the region is defined inside the shank portion defining. The peripheral portion comprises a plurality of protuberances, and the protuberances are distributed between the first axial end and the second axial end and to surround the core portion and define the outermost periphery of the head portion.

Figures

[08] The present disclosure is described with reference to the accompanying figures, in which,

[09] Figures 1A, 1 B and 1C are side views of an example column-formation tool, taken at different angular positions with respect to the core axis,

[10] Figures 2A, 2B, 2C and 2D are side views of the example column-formation tool with stirrers distributed along the shank portion,

[11] Figure 3A and 3B are schematic side views of an example head portion of an example column-formation tool,

[12] Figures 3C, 3D and 3E are perspective views of the head portion, respectively from bottom, from top at a first angle, and from top from another angle;

[13] Figures 4A, 4B and 4C are, respectively, top, side and bottom views of an example cutting tooth;

[14] Figures 4A1 and 4B1 are, respectively, top and side views of an example cutting tooth showing example dimensions;

[15] Figure 5 is a side view of an example column formation tool having a detachable head,

[16] Figure 6 is a side view showing an ensemble of column formation tools including the column formation tool of Figure 5, and

[17] Figure 7 is a side view showing an ensemble of column formation tools including the column formation tool of Figure 2A. Description of embodiments

[18] A column formation tool of the present disclosure comprises a first portion which is a head portion and a second portion which is a shank portion. The head portion is a leading portion which is also a forward portion of the tool. The forward portion has a forward end which is to first encounter the surface during bore-formation operations. During bore-formation operations, the forward end is pressed against a surface to be broken and the tool is rotated about its axis while being pressed against the surface. As a result of the pressing and rotation, the head portion is driven to advance into the region. The shank portion is configured to follow the advancement of the head portion and to occupy the region cleared by the head portion. Advancement by the head portion, followed by advancement of the shank portion into the region previously occupied by the head portion, results in the formation of a bore which is to be filled with a column-formation material. When the head portion has advanced for a predetermined depth inside the region so that a bore of sufficient depth is formed, column- formation materials are delivered into the bored region through a material outlet on the shank portion, whereby a column is formed.

[19] The shank portion comprises a shank body, a channel defined inside the shank body, a material inlet at one end of the channel, and a material outlet at another end of the channel. The shank body is elongate and extends along a longitudinal axis between a first longitudinal end and a second longitudinal end to define a column. The shank body typically has a circular cross-section to mitigate rotational resistance during bore-formation operations, but may have a cross-section of any low rotational resistance shapes, for example, regular hexagon, octagons, etc. The cross-section of the shank body is a section taken in a transversal direction, the transversal direction being orthogonal to the longitudinal axis of the shank body. Where the shank body has a circular cross-section, the shank body is cylindrical or substantially cylindrical, and the center axis of the shank body is a cylindrical axis which is parallel to or aligned with the longitudinal axis. The shank body is typically a column-shaped body made of a strong steel, preferably stainless steel, to better withstand harsh working conditions and to facilitate delivery of column-formation materials into the region where the column is to be formed during column-formation operations.

[20] The head portion comprises a core portion and a peripheral portion which surrounds the core portion. The core portion has core axis, a first end on a first axial end of the core axis, and a second end on a second axial end of the core axis. The first end is the forwardmost end of the tool which is distal to the shank portion and the second end is in abutment with the shank portion. The core axis is a center axis which extends from the second axial end to the first axial end to define an axial direction. The axial direction is a vectored direction which is also a direction of advancement, or advancement direction in short, of the core portion. The direction of advancement is a direction along which the head portion moves during pressing- and-rotation bore-formation operations.

[21 ] The core portion comprises an outer surface which extends between the first and second ends of the core portion. The outer surface of the core portion extends to surround the core axis and defines an outer periphery and an outer peripheral surface of the core portion. The outer peripheral surface of the core portion has a facing orientation which is away from the core axis. The core portion is preferably made of steel, for example, a strong steel to better withstand the harsh operation conditions.

[22] The peripheral portion comprises a plurality of protuberances. The plurality of protuberances comprises protuberances which are distributed to define an outer periphery of the head portion. The outer periphery of the head portion surrounds the core portion and defines the outermost surface of the head portion. In other words, the outer surface of the core portion is intermediate the outermost surface of the head portion and the core axis.

[23] A protuberance which is one of the protuberances defining the outer periphery comprises a base portion, an end portion, and an intermediate portion which interconnects the end portion and the base portion. The base portion is proximal to the core portion and has a base surface. The end portion is distal to the core portion and has an end surface, which is a free surface. The end surface is a crest surface which defines the outermost surface of the protuberance. The outermost surfaces of the plurality of protuberances cooperate to define the outermost surface and the outer periphery of the head portion. The outermost surface and the outer periphery of the head portion are with reference to the core portion. For example, what is inside the core portion, that is, what is surrounded by the outer periphery and/or the outer peripheral surface of the core portion, is referred to as “inside”, “inner” and/or “interior”, and what is not surrounded by the outer periphery and/or the outer peripheral surface of the core portion is referred to as “outside”, “exterior” and/or “outer”.

[24] The intermediate portion projects from the base portion and extends in a projection direction away from the base surface and towards the end portion. The projection direction is defined by a projection axis which is a center axis projecting from the center of the base surface and extending orthogonally to the base surface.

[25] The intermediate portion includes a leading flank, a trailing flank which is opposite-facing to the leading flank, and side flanks interconnecting the leading flank and trailing flank.

[26] The protuberance extends from the trailing flank to the leading flank in a forward direction which is defined by a forward axis. The forward axis is a center axis of the trailing flank which is parallel to the base surface, that is, orthogonal to the projection axis. The forward axis is a vectored axis which is directional and defines a forward direction.

[27] The plurality of protuberances comprises a first protuberance. The first protuberance is a forwardmost protuberance which is configured as a first cutting tooth. The first cutting tooth is a protuberance on the head portion which is furthest away from the shank portion, measured in the axial direction. The first cutting tooth is a protuberance which is most proximal to the first end of the core portion, measured in the axial direction. As a protuberance which is most proximal to the first end of the core portion, the first protuberance will be the first cutting tooth to encounter the surface during surface-breaking operations.

[28] A cutting tooth is oriented at a cutting angle to cut and/or break a target. The target is typically hard substances such as rocks or pebbles which are embedded in the surface or the region to be broken. A cutting tooth is typically oriented at a cutting angle so that its cutting edge is to face the target to be cut or broken during cutting or breaking operations. The cutting angle is an angle of inclination Q measured between the core axis of the core portion and the forward axis of the protuberance.

[29] To facilitate cutting and breaking of hard substances which is ahead so that the tool can advance towards a target depth, the first protuberance is configured as a forward cutting tooth. A forward cutting tooth is oriented at a forward cutting angle so that its cutting edge is facing the forward direction. In general, a forward cutting angle has an angle of inclination of less than 90 degrees, and an angle of inclination of 60±15 degrees is preferred.

[30] The plurality of protuberances comprises a second protuberance. The second protuberance is a rearmost protuberance on the head portion, which is most proximal to the shank portion (that is, most distal to the first end of the core portion), measured in the axial direction.

[31] The second protuberance is configured as a peripheral cutting tooth, which is to cut and break hard substances surrounding the head portion. To facilitate cutting and breaking of surrounding hard substances, a peripheral cutting tooth is oriented at a peripheral cutting angle so that its cutting edge is facing the target depth. In general, a peripheral cutting angle of about 90 degrees is preferred, although the peripheral cutting angle may be at 90+5 degrees or 90-15 degrees.

[32] The first protuberance and the second protuberance are end tooth members of a train of protuberances, which is also referred to as a train of teeth members (teeth-train or train in short). [33] The train may comprise one intermediate protuberance or a multitude of two or more intermediate protuberances in addition to the first and second protuberances. The multitude may be 2, 3, 4, 5, 6, depending on the axial length and peripheral dimensions of the head portion. The protuberances of the plurality of protuberances are distributed at a plurality of different angular positions to surround the core portion.

[34] For example, the first protuberance is at a first angular position and a first axial level, and the second protuberance is at a second angular position and a second axial level. The angular position of a protuberance is measured in an orthogonal direction with respect to the core axis, the orthogonal direction is a radial direction with respect to the core axis. For example, the position of a protuberance, angular or axial, may be measured with respect to the center of the protuberance. The center of a protuberance may be taken as where the projection axis and the forward axis meet, as a convenience reference.

[35] The train may comprise a third protuberance which is at a third angular position that is intermediate the first and second angular positions and a third axial level which is intermediate the first and the second axial levels.

[36] The train may comprise a fourth protuberance which is at a fourth angular position that is intermediate the second and the third angular positions and a fourth axial level which is intermediate the second and the third axial levels.

[37] The train may comprise a fifth protuberance which is at a fifth angular position that is intermediate the first and the third angular positions and a fifth axial level which is intermediate the first and the third axial levels.

[38] The train may comprise more than five protuberances between the first and second protuberances, depending on the actual dimensions of the head portion and the target substances to be broken without loss of generality.

[39] A protuberance of the train is referred to as a tooth member or a tooth. The teeth or tooth members of a train are distributed along a track to form a teethed track which extends between a first track end and a second track end. The first track end is defined by the first protuberance which is at a first angular portion and a first axial level, the first protuberance being the first tooth of the track. The second track end is defined by the second protuberance which is at a second angular portion and a second axial level, the second protuberance being the second or last tooth of the track. Two immediately adjacent protuberances on a track are separated by a separation angle and a separation distance. The separation angle is measured with respect to the core axis and the separation distance is an axial separation distance which is measured in the axial direction defined by the core axis. In other words, the track extends between a first axial level and a second axial level, and between a first angular position and a second angular position.

[40] The teeth members of a teethed track are distributed around the core portion to correspond to about one revolution or one turn of the tool. In example embodiments, separation angles between all immediately adjacent teeth on a teethed track have a total sum corresponding to about one revolution, for example, between 300 degrees and 360 degrees or more.

[41] The teethed track is configured to facilitate more effective penetration through the surface and into the region. To facilitate more effective penetration, the first tooth of a teethed track is a leading tooth at a leading angle and a leading axial level with respect to the second tooth, and the second tooth of the teethed track is a trailing tooth at a trailing angle and at a trailing axial level relative to the first tooth. A leading tooth is ahead of a trailing tooth during bore-formation rotations of the tool.

[42] The track may be a curved track which gradually curves to change its angle of inclination with respect to the core axis from a larger angle to a smaller angle on approaching the first end of the head portion. A larger angle of inclination means less-close to being parallel to the core axis while a smaller angle of inclination means more-close to being parallel to the core axis. The angle of inclination of the track at the first axial end may be at 25±15 degrees, that is, at 10, 15, 20, 25, 30, 35, 40 degrees with respect to the core axis, or a range or ranges of angles selected from any combination of the aforesaid angles.

[43] The curved track may have an overall S-shape, for example a compressed or slim S- shape which is compressed in lateral directions.

[44] The curved track may comprise a first curved portion which includes the first protuberance and a second curved portion which includes the second protuberance. The first and second curved portion may be interconnected by a third portion which may be a curved portion or an inflexion portion.

[45] The curved track may be a three-dimensional curved track comprising a first flank portion, a second flank portion, and a crest portion interconnecting the first and second flank portions. The first flank portion and the second flank portion project from the core portion and extends outwardly away to converge at and join the crest portion. The first flank portion is a lower flank portion which is proximal to the first axial end and the second flank portion is an upper flank portion which is proximal to the second axial end of the core portion. The first and second flank portions cooperate to shift the crest surface away from the core portion to form an elevated crest surface and a bank-like 3-dimensional track which revolves around the core portion. The crest surface may converge to form an edge or a tip at the first track end.

[46] The 3-dimensional (3D) track may be configured to resemble an auger or a corkscrew having an auger thread to facilitate more effective target penetration. The auger thread may be a tapered thread which tapers on extending towards its forward end to form a tip, for example, a chisel tip, at its forward end.

[47] The head portion may be configured such that the teeth train is elevated by the track so the base portions of the protuberances are in abutment with the crest surface of the elevated track, and the elevated track is an intermediate track which is intermediate the teeth train (which defines the teethed track) and the core portion.

[48] As the teeth train forming the teethed track is elevated by the 3-D track and defines the outer periphery of the head portion, the outer periphery of the head portion is defined by a plurality of protruding tooth members defined by the teethed track, and the tooth members are spaced apart such that immediately adjacent tooth members have an inter-tooth spacing. The inter-tooth spacing may be comparable to the length of a tooth, measured in the forward direction.

[49] As the plurality of protuberances is distributed along the elevated track, the protuberances of the teeth train cooperate to define an outer track which follows the elevated track, which is an intermediate track between the outer track and the core portion. The outer track resembles a spiral or helical track of an auger or a corkscrew.

[50] The outer periphery of the head portion, as defined by the protruding tooth members of the outer track, is tapered at its forward end.

[51 ] In example embodiments, the core portion has a tapered first end so that the outer track has a tapered forward end by following the tapered profile of the core portion on extending from the second track end to the first track end.

[52] In example embodiments, the core portion has a conical or frustoconical shape, with the first axial end being a tipped or chisel end.

[53] In example embodiments, the head portion may comprise a plurality of elevated tracks each comprising a teethed track. The plurality of elevated tracks may comprise a first elevated track having a first chirality and a second elevated track having a second chirality opposite to the first chirality. The first chirality may be right-handed (clockwise) and the second chirality be or left-handed (anticlockwise). Alternatively, the first chirality may be left-handed (anticlockwise) and the second chirality may be right-handed (clockwise) without loss of generality.

[54] The first and second elevated tracks may be merged to form the forward end of the head portion and the merged forward end may be a tipped end, for example, a chisel end which extends to pass through the tapered first end of the core portion.

[55] Where there is a plurality of elevated tracks on the core portion, each elevated track may span across less than a turn of the core portion. For example, the first elevated track may have a span of about half a turn, for example, between 150 and 210 degrees, including 150, 160, 170, 180, 190, 200, 210 and a range or ranges selected from any combination of the aforesaid values.

[56] The teeth members of the two teethed tracks may be alternately disposed along the axial direction of the core axis. For example, a tooth of one teethed track may be intermediate two teeth of another teethed track, although there can be some extent of overlap in the axial direction.

[57] An example column formation tool 100 comprises a first portion which is a head portion 120 and a second portion which is a shank portion 140, as shown in Figures 1A, 1 B and 1C. The head portion is configured as a leading portion and the shank portion is configured as a trailing portion which is to follow the head portion to advance into a target region during bore- formation operations. The head portion 120 comprises a core portion 122 and a plurality of protuberances 124.

[58] To loosen materials surrounding the bore formed by the head portion, the tool of 100 may be modified to form a tool 100A which comprises a plurality of stirrers 142, as shown in Figures 2A, 2B, 2C and 2D. The stirrers may be arranged into stirrer groups which are distributed along the length of the shank portion. Each stirrer groups may comprise a plurality of 3 or 4 stirrer blades and the stirrer blades may be distributed at uniform angular intervals around the shank portion. Adjacent stirrer groups may be displaced by a displacement angle. Additional binder outlets may be distributed alone the length of the shank portion, for example, intermediate adjacent stirrer groups.

[59] Referring to Figures 3A-3E, 4A to 4C, 4A1 and 4B1 , each protuberance 124 comprises a base portion having a bottom surface B, a top portion having a top surface which is an end surface E that is distal to the bottom surface, and a peripheral portion interconnecting the base portion and the top portion. The peripheral portion comprises a forward surface F, a rearward surface R and a pair of side surfaces S. [60] The protuberance extends along a forward direction T T which is defined by a forward axis T-T. The forward axis is a center axis T -T is a center axis which passes through the center of the rearward surface and the center of the forward surface. The peripheral portion extends in a projection direction P®P’ defined by a projection axis P-P’. The projection axis P-P’ is a center axis of the bottom surface and extends orthogonally away from the bottom surface B. The protuberance has a forward portion (shown in hatched lines) which is a cutting portion defining a cutting edge of the protuberance. The cutting portion is made of a strong cutting material such as titanium carbide and is mounted on a base portion which is made of a strong steel, and has a forward length t , measured in the forward direction. The protuberance is configured as a cutting tooth which to cut and break hard substances which are embedded in the target surface or in the target region. The protuberance has a length l which is defined in the forward direction, a width w which is defined in a direction transversal to the forward direction and the projection direction, and a height h which is defined in the projection direction. I may be L or L ₂ , as shown in Figures 4A1 and 4B1 .

[61] The plurality of protuberances is arranged into two teethed tracks, namely a first teeth track T _A and a second teeth track T _B . In this example, first teeth track T _A is a clockwise teethed track and second teeth track T _B is a counterclockwise teethed track. Each teethed track comprises an example plurality of four protuberances, including a first tooth member 124A1 , 124B1 which defines the first track end, a second tooth member 124A2, 124B2 which defines the second track end, a third tooth member 124A3, 124B3 which is intermediate the first tooth member and the second tooth member, and a fourth tooth member 124A4, 124B4 which is intermediate the first and the third tooth members. The first tooth member is proximal to the first end of the core member. In the example embodiment, the first tooth member is at an axial distance from the axial end of the core portion, which is a tipped end. The example axial distance is 60-80cm. In general, the distance may be selected to be between 0.8 to 1 .5 times the length of a tooth.

[62] The first tooth member, which is a leading cutting tooth, is oriented at a first cutting angle Q for forward cutting. In the example, the first tooth member 124A1 , 124B1 has a cutting angle ^, 02 of approximately 60 degrees so that the cutting surface is to face the target region at a downward cutting angle. The second tooth member 124A2, 124B2, which is a trailing tooth configured for peripheral cutting, is oriented at a second cutting angle to cut and break target substances surrounding the second axial end of the head portion 122. In this example, the second cutting angle is approximately 90 degrees so that the forward cutting edge of the second tooth is approximately parallel to the core axis. The third and fourth tooth members are oriented at cutting angles which are intermediate the first and the second cutting angles. For example, the third cutting angle may be approximately 80 degrees while the fourth cutting member may be at approximately 70 degrees.

[63] The tooth members of a teeth track are arranged to form a conical outer periphery of the head portion on rotation about the core axis. To form a conical outer periphery by revolution about the core axis, the first tooth member 124A1 , 124B1 has a first radial distance r from the core axis, the second tooth member 124A2, 124B2 has a second radial distance r ₂ from the core axis, the third tooth member 124A3, 124B3 has a third radial distance r ₃ from the core axis, and the fourth tooth member 124A4, 124B4 has a fourth radial distance r ₄ from the core axis, such that r ₂ > r ₃ > r ₄ > r _x .

[64] In example embodiments, the second axial end has a maximum transversal dimension D _2, measured diametrically across the core axis at the second axial end. In the present example, r ₂ > D ₂ > r ₄ .

[65] In example embodiments, the core portion has an axial extent of between 30cm and 80 cm, for example, about 40cm or 50 cm. The core portion may have a transversal extent of between 50cm and 80 cm. The shank may have a length of 2-20m and can be longitudinally extended where necessary.

[66] In example embodiments, two adjacent intermediate tooth members, for example the third and fourth tooth members, are interconnected by a curved portion having a very large radius of curvature (compared to the radii of curvature of the curved portion connecting the first and the fourth tooth members or the curved portion connecting the second and the third tooth members) or by an inflexion portion.

[67] The cutting angles of corresponding tooth members on the two teethed tracks are approximately same, although in opposite directions because of their differences in chirality.

[68] Referring to Figures 3A to 3D, teeth members on the first teethed track T _A and the second teethed tracks TB are alternately arranged in the axial directions. For example, the second tooth member of the second teethed track T _B is intermediate the first and third tooth members of the first teethed track T _A , the second tooth member of the first teethed track is axially above the second tooth member of the second teethed track, the first tooth member of the first teethed track is axially above the first tooth member of the second teethed track.

[69] Each teethed track comprises a train of tooth members and each train of tooth members is formed on an elevated track and follows the extension direction of the elevated track. In this example, the train of tooth members has an angular extent of less than 180 degrees and the angular extent of the two trains of tooth members have a sum of about 360 degrees, and the angular extent can be between 0.8 and 1 .5 turn.

[70] The example head portion comprises a plurality of elevated tracks, including a first elevated track and a second elevated track. Each elevated track is a curved track which is curved to facilitate more efficient advancement of the head portion. Each elevated track has a first track end and the first track ends of the two elevated tracks merge at the first axial end of the core portion to form a unified chisel tip. Each elevated track has a second track end and the second track ends of the two elevated tracks are at about the same axial level and cooperate to define the second axial end of the core portion. The second elevated end of each elevated track has a curved peripheral wall which extends for an angular extent of less than 180 degrees to partially surround the second axial end of the head portion.

[71] A train of tooth members is mounted on an elevated track, and an elevated track is integrally formed on the core portion but extends to project away from the core portion such that an elevated track is intermediate a teethed track and the core portion.

[72] In this example, the first train of tooth members is mounted on the first elevated track and follow the direction of extension of the first elevated track, and the second train of tooth members is mounted on the second elevated track and follow the direction of extension of the second elevated track, with the direction of extension of the second elevated track being opposite to the direction of extension of the first elevated track.

[73] The example core portion is a conical portion having a conical end which is a tapered first end. The elevated tracks and the teethed tracks are integrally built on the tapered conical core portion and follow the outer profile of the core portion. In this example, the teethed tracks cooperate to extend along the conical-shaped core portion and form a tapered outermost periphery of the head portion comprising spaced apart teeth, and the elevated tracks cooperate to extend along the core portion and form a tapered intermediate periphery of the head portion. The elevated track is a continuous track which extends continuously from the second track end to the first track end. The curved upper flank surface of the elevated track also helps to transport excavation of substances away from the first axial end after target substances have been broken by the cutting teeth.

[74] The shank portion extends along a longitudinal center axis and defines a material deliver channel which extends in the longitudinal direction. The example shank portion comprises a material inlet at its upper longitudinal end and a material outlet at its lower longitudinal end, which is proximal to the head portion. [75] During bore formation operations, the tool is mounted on a supporting frame and a machine is configured to rotate the tool and press the head portion against the target region to be penetrated. When the head portion has reached a predetermined depth, a binder material, usually cement, is dispensed through a binder outlet and blended with slurry in the vicinity of the auger. Once the binder-slurry mixture is hardened, solidified columns are embedded in the seabed. This process significantly increases the load bearing capacity of the seabed. Column formation tools, also referred to as drilling devices, are tools used to form columns in DCM processes. In some processes, column forming materials are delivered into the region where a column is to be formed when the tool is being retracted.

[76] The head portion may be detachable from the shank portion, as shown in Figure 5. In the example tool 100B of Figure 5, the head portion and the shank portion are fastened by releasable fasteners and the material outlet 144 is formed on a longitudinal end of the shank portion which is proximal to the head portion 120.

[77] In example applications, a plurality of column formation tools is assembled in parallel to form an ensemble 10, as shown in Figure 6. Adjacent tool members may be configured to operate in opposite rotational directions. The ensemble comprises a first tool 100B and a second tool 100C, which is a variant of first tool 100B in that the stirrer groups of the second tool 100C are arranged at axial levels to avoid the stirrer groups of the first tool 100B.

[78] Another ensemble 20 of column formation tools shown in Figure 7 comprises tools 100D and 100E, which are variants of the tools of Figure 2A, that is, have shank portion and the core portion integrally formed and not detachable.

[79] A tooth and an adjacent tooth next to the tooth are separated by a separation distance which is referred to as inter-teeth spacing or inter-teeth distance. The inter-teeth spacing is defined by the circumferential separation distance between the trailing surface of a leading tooth and the leading surface of a trailing tooth which is next to the leading tooth.

[80] The leading surfaces of the teeth are configured to move loose stones along the elevated track when the device rotates in the first direction. The trailing surfaces of the teeth are configured to move loose stones along the elevated track when the device rotates reversely in the second direction. When a loose stone encounters a leading surface or a trailing surface, the stone will move in a tangential direction to the elevated track until contact between the contact surface and the stone is lost.

[81] To facilitate effective movement of loose cobblestones sideways, the leading surface may be planar or curved, and has dimensions comparable to dimensions of cobblestones. The leading surface of a tooth which is configured to move loose cobblestones may have a width of between 40mm and 150mm, a height of between 40mm and 150mm, and a length of between 40mm and 150mm. In example embodiments, the leading surface is parallel (including substantially parallel) to the helix radius of curvature. Substantially parallel herein means a small deviation from being parallel, for example, a deviation of ±5 degrees or ±10 degrees.

[82] Two immediately adjacent teeth on the elevated track are interconnected by an inter teeth portion. An inter-teeth portion has a leading end which is defined by the trailing surface of a leading tooth, a trailing end which is defined by the leading surface of a trailing tooth next to the leading tooth, and a base portion interconnecting the leading tooth and the trailing tooth, and defining an inter-teeth recess or an inter-teeth recess indentation which is delimited by the trailing surface of one tooth and the leading surface of next tooth. The inter-teeth portion and therefore the inter-teeth recess or indentation has a length which is equal to the inter teeth distance, and a width which is equal to the width of the leading surface.

[83] An example device is configured to have an inter-teeth distance which is larger than the size of a cobblestone so that a loose cobble stone in vicinity of the head portion can easily enter the inter-teeth recess. The inter-teeth distance may be selected according to the expected size of cobblestones in the target layer. In general, the inter-teeth distance may be set at 1 .5 times the expected size of a cobblestone or more. The inter-teeth distance may be set to smaller than two-times the expected size of a cobblestone so that not too many loose cobblestones are received in a single inter-teeth recess. In some embodiments, the inter-teeth distance may be larger than two-times the expected size of a cobblestone so that more loose cobblestones can be received in a single inter-teeth space. In example embodiments, the or some of the inter-teeth distances may be larger than two times or three times the expected size of a cobblestone. The inter-teeth distance may be uniform or non-uniform along the elevated track. In example embodiments, the inter-teeth distance on the forward portion of the elevated track is smaller and the inter-teeth distance on the rearward portion is larger. The expected size of the cobblestones (or cobblestone size in short) in a target layer may be obtained by sampling prior to performance of operation.

[84] The plurality of teeth may be integrally formed on the head portion, for example, by casting or by welding. The teeth may be made of a strong steel, for example, steel made of tungsten carbide. The teeth may be reinforced at the outer edge of the leading surfaces to reduce costs while enhancing durability.

[85] The base portion of an inter-teeth portion comprises a base surface of the inter-teeth recess. The base surface interconnects two immediately adjacent teeth and is an outward facing surface with respect to the shank axis. More specifically, the base surface interconnects the inner edges of the trailing surface and the leading surface of two immediately adjacent teeth. In example embodiments, the base surface is orthogonal to the helix radius of curvature. The base surface is preferably configured as a non-retaining surface to mitigate unwanted retention of cobblestones in the inter-teeth recess. The non-retaining surface may be a convexly curved surface, a planar surface, or a plurality of planar surfaces combined to found a convex surface extending between the adjacent teeth. In example embodiments, the base surface is a convexly curved surface which extends to follow an elevated track.

[86] An elevated track herein comprises a first flank surface which is an upper flank surface, a second flank surface which is a lower flank surface, and a crest surface interconnecting the upper flank surface and the second flank surface. The upper flank surface comprises an inner edge which is on the base of the elevated track and an outer edge which is the outermost edge of the upper flank surface. The lower flank surface comprises an inner edge which is on the base of the elevated track and an outer edge which is the outermost edge of the lower flank surface. The outer edges of the upper and lower flank surfaces cooperate to define the upper and lower edges of the crest surface. The crest surface is an outward-facing surface with respect to the head body and/or the shank axis. In example embodiments, the crest surface is orthogonal (including substantially orthogonal) to the helix radius of curvature. In example embodiments, the outer edges are parallel (including substantially parallel) to each other. The axial separation distance between the outer edges of the upper and lower flank surface defines the axial extent of the crest surface, which may be referred to as width or thickness of the track. The length of the elevated track is measured in a circumferential direction with respect to the helix radius of curvature.

[87] The elevated track may have a uniform thickness or a variable thickness along its length. The elevated track may have a diminishing thickness or an increasing thickness on extending towards the leading end. Where an elevated track portion is an inter teeth portion, the elevated track portion comprises a crest surface which extends between the upper outer edge and the lower outer edge of the flank surfaces. The elevated track portion slopes at a helix angle with respect to the helix axis. The helix angle may be between 15 and 90 degrees. The helix angle may be a downward angle or an upward angle and may change along the length of the elevated track. For example, the helix angle may increase or decrease on extending towards the leading end.

[88] The elevated track may comprise one helical turn or a plurality of helical turns. Where the elevated track comprises more than one turn, there is an inter-turn space which is between adjacent helical turns and which defines an inter-turn space. The inter-turn space defines an inter-turn channel having an axial extent preferably larger than the size of a cobblestone to mitigate trapping of cobblestones in the inter-turn space, the axial extent being measured with respect to the shank axis. In example embodiments, the inter-turn space defines an interturn clearance of up to 2 times or 3 times the cobblestone size, and may be between 1 .2, 1 .4, 1 .6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 8 times or any range or ranges formed by combination of any of the aforesaid values.

[89] The elevated track may have a constant gradient or a varying gradient. The gradient of an elevated track portion is a measure of inclination of the elevated track portion with respect to the helix radius associated with that elevated track portion, and the helix radius is orthogonal to the shank axis. The inclination is also a measure of the angle between the tangential line of the elevated track portion and a radial plane defined by the helix axis, the radial plane being orthogonal to the shank axis. The gradient of the elevated track may increase or decrease on extending towards the leading end. An elevated track herein may be continuous or non- continuous, that is, broken or discontinuous.

[90] In embodiments where the teeth are distributed to form an elevated track, the upper flank surfaces of the teeth cooperate to define the upper flank surface of the elevated track, the lower flank surfaces of the teeth cooperate to define the upper flank surface of the elevated track, and the crest surfaces of the teeth cooperate to define the crest surface of the elevated track, which is a broken helical track.

[91] In embodiments where the teeth are distributed along a helical track, the bases of the teeth may be founded on the crest surface of the elevated track, and/or the crest surfaces may cooperate to define the crest surface of the elevated track, which is a broken elevated track.

[92] In example embodiments, the core portion comprises a cylindrical portion and a conical portion in abutment with the cylindrical portion. The teethed track and/or the elevated track may start from the cylindrical portion and ends on the conical portion, for example, at an axial level proximal the conical tip.

[93] While the present disclosure has been made with example embodiments, it should be appreciated that the embodiments are not intended to be limiting.