Screw anchor drilling method

Abstract

The invention relates to a spiral anchor drilling method, which is characterized in that a spiral anchor is drilled into a soil layer by using a spiral anchor drilling machine, in the drilling process, a power head of the spiral anchor drilling machine applies torque to the spiral anchor, and meanwhile, the power head of the spiral anchor drilling machine actively applies downward pressure to the spiral anchor. In the whole drilling process of the spiral anchor, the power head actively applies drilling pressure to the spiral anchor while outputting torque to the spiral anchor, and F / T = (1 + mu * tg alpha 0) / (mu-tg alpha 0) / R0 is kept through control over F and T, namely the pressure-torsion ratio, so that slipping between a spiral anchor disc and a soil layer in the drilling process can be reduced, and disturbance to the soil layer on the upper side of the spiral anchor disc is reduced.

Description

Technical Field

[0001] This invention relates to the field of power construction technology, and in particular to a spiral anchor drilling method. Background Technology

[0002] During the construction of high-voltage transmission lines, it is inevitable that they will pass through areas with relatively soft geology, such as silt and sand. Spiral anchors are widely used in these areas as the foundation support for the towers.

[0003] Existing technologies for spiral anchor construction include Figures 1-2 As shown: During use, a spiral anchor is screwed into the foundation using a spiral anchor drilling rig. The spiral anchor drilling rig includes a drilling column 1, on which a power head 2 is mounted for vertical movement. The power head 2 is driven by a lifting drive mechanism and can move up and down along the column. The power head has a torque output end, which is usually driven by a gear ring. The power head includes at least two drive motors arranged circumferentially, and the motor shaft of the drive motor is equipped with a motor shaft gear that meshes with the gear ring. The spiral anchor 4 includes an anchor rod 5, on which multiple spiral anchor discs 6 are arranged at intervals. The number of spiral anchor discs 6 is usually 3 to 5. The spiral anchor disc is composed of a 360-degree spiral blade plate. The upper and lower axial surfaces of the spiral blade plate are spiral surfaces. The upper circumferential end face 7 and the lower circumferential end face 8 of the spiral blade plate are staggered.

[0004] The anchor bolt includes a smooth rod section 3 located on the uppermost spiral anchor plate. The length of the smooth rod section 3 accounts for about one-third of the total length of the anchor bolt. In use, the upper end of the smooth rod section is connected to the anti-rotation power head. The power head rotates the anchor bolt, and an axial force is generated between the spiral anchor plate and the foundation during the rotation, thereby causing the anchor bolt and the power head to move downward as a whole. When the spiral anchor is drilled to the specified depth, the connection between the anchor bolt and the power head is removed, and the bottom of the tower or other support is fixed to the upper end of the anchor bolt. The force between the spiral anchor plate and the foundation is used to ensure the foundation bearing capacity of the spiral anchor.

[0005] The existing spiral anchor construction has the following problems: When the power head drives the spiral anchor to rotate by transmitting power to the upper end of the anchor rod, the length of the polished rod section is relatively long, making it prone to bending and deformation. This not only affects the construction quality of the spiral anchor, but the deformed polished rod section also generates a reverse force on the power head, which will exacerbate the damage to the power head. During the drilling process of the spiral anchor in the foundation, ideally, that is, when the spiral anchor disc does not slip with the foundation soil, the spiral anchor should advance axially by one pitch of the spiral anchor disc with each rotation of the spiral anchor. This ensures that the spiral anchor disc minimizes disturbance to the soil layer during the spiraling process. However, in the existing technology, the power head moves downward with the spiral anchor during operation. The power head cannot provide sufficient downward pressure to the spiral anchor, causing the spiral anchor disc to slip with the soil layer during the spiraling process, disturbing the soil layer and compromising the bearing capacity of the spiral anchor foundation after drilling. Summary of the Invention

[0006] The purpose of this invention is to provide a spiral anchor drilling method that can reduce the disturbance of the soil layer by the spiral anchor disc during drilling.

[0007] To solve the above-mentioned technical problems, the technical solution of the spiral anchor drilling method in this invention is as follows:

[0008] A method for drilling a spiral anchor involves using a spiral anchor drilling rig to drill a spiral anchor into the soil layer. During drilling, the power head of the spiral anchor drilling rig applies torque to the spiral anchor, and simultaneously, the power head actively applies downward pressure to the spiral anchor. The torque T experienced by the spiral anchor is measured by a torque sensor, and the downward pressure F experienced by the spiral anchor is measured by a pressure sensor.

[0009] in,

[0010] F / T=(1+μ*tgɑ0) / (μ-tgɑ0) / R0

[0011] In the formula,

[0012] μ represents the coefficient of friction between the upper and lower axial plates of the spiral anchor disc;

[0013] α0 represents the helix angle of the resultant force of the soil layer on the helical anchor plate;

[0014] R0 represents the radius of the helix of the resultant force of the soil layer on the helical anchor plate;

[0015] In the formula,

[0016]

[0017] Where r represents the anchor bolt radius and R represents the radius of the helical blade disk.

[0018] a0 is obtained through the following formula:

[0019] tgɑ0=(2*Pi*R0) / H

[0020] In the formula, Pi represents pi (circular diameter), and H represents the pitch of the spiral anchor disc.

[0021] Furthermore, the power head applies torque and downward pressure to the auger anchor through the auger anchor connector. The auger anchor drilling process involves two steps. First, the auger anchor connector is driven to the uppermost auger anchor disc of the auger anchor, and the uppermost auger anchor disc applies torque and downward pressure to the auger anchor, causing the auger anchor to drill into the soil layer. Second, when the lower end of the uppermost auger anchor disc reaches the ground, the auger anchor connector is driven to the upper end of the polished rod section of the auger anchor, and the polished rod end applies torque and downward pressure to the auger anchor, causing the auger anchor to continue drilling into the soil layer.

[0022] The beneficial effects of the present invention are as follows: In the present invention, during the entire drilling process, the power head outputs torque to the spiral anchor while actively applying drilling pressure to the spiral anchor. By controlling F and T, i.e., the pressure-torque ratio, F / T = (1 + μ*tgɑ0) / (μ-tgɑ0) / R0 can be maintained, thereby reducing slippage between the spiral anchor disc and the soil layer during drilling and reducing disturbance to the soil layer above the spiral anchor disc.

[0023] Furthermore, during the first drilling step, the power head applies torque and downward pressure to the uppermost spiral anchor disc. The torque transmission position is closer to the contact point between the lower end of the spiral anchor and the ground, making the power transmission more direct and efficient. This also avoids the problem of the anchor rod being prone to bending and deformation due to a long torque transmission path. Attached Figure Description

[0024] The above and other objects, features, and advantages of this disclosure will become readily apparent from the following detailed description of exemplary embodiments with reference to the accompanying drawings. In the drawings, several embodiments of this disclosure are illustrated by way of example and not limitation, and like or corresponding reference numerals denote like or corresponding portions, wherein:

[0025] Figure 1 This is a schematic diagram of the structure of the spiral anchor drilling machine in the prior art of this invention;

[0026] Figure 2 yes Figure 1 Enlarged view of point A in the image;

[0027] Figure 3 This is a usage state diagram of an embodiment of the present invention;

[0028] Figure 4 yes Figure 3 A schematic diagram showing the connection between the helical anchor, the power head, and the helical anchor connector;

[0029] Figure 5 yes Figure 4 Enlarged view of point B in the image;

[0030] Figure 6 yes Figure 4 A schematic diagram showing the connection between the power head and the spiral anchor connector;

[0031] Figure 7 yes Figure 6 Schematic diagram of the structure of the spiral anchor connector;

[0032] Figure 8 yes Figure 7 Side view;

[0033] Figure 9 yes Figure 7 Top view;

[0034] Figure 10 This is a schematic diagram of the transmission between the power head, the spiral anchor connector and the upper end of the smooth rod section in this invention;

[0035] Figure 11 yes Figure 10 A schematic diagram of the fit between the spiral anchor connector and the upper end of the smooth rod section;

[0036] 1. Drilling rig column; 2. Power head; 3. Polished rod section; 4. Spiral anchor; 5. Anchor bolt; 6. Spiral anchor disc; 7. Upper circumferential end face of the spiral anchor disc; 8. Lower circumferential end face of the spiral anchor disc; 9. Anchor bolt connection hole; 10. Spiral anchor connector; 11. Pressure sensor; 12. Torque sensor; 13. Gear ring; 14. Drive motor; 15. Vertical bolt; 16. Torque output flange; 17. Connector flange; 18. Force transmission head; 19. Horizontal bolt; 20. Reversing protrusion; 21. Circumferential end face of the force transmission head; 22. Lower end face of the force transmission head; 23. Connecting head flap; 24. Force transmission head connection hole; 25. Polished rod section through hole; 26. Drive pin. Detailed Implementation

[0037] To facilitate understanding of the present invention, a more detailed description is provided below with reference to the accompanying drawings and specific embodiments. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0038] It should be noted that, unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0039] An example of an implementation of a spiral anchor drilling method in this invention. Figures 3-11 The following describes a method for drilling a spiral anchor, characterized in that: a spiral anchor drilling rig is used to drill the spiral anchor into the soil layer; during the drilling process, the power head of the spiral anchor drilling rig applies torque to the spiral anchor, and simultaneously, the power head of the spiral anchor drilling rig actively applies downward pressure to the spiral anchor; the torque T experienced by the spiral anchor is measured by a torque sensor, and the downward pressure F experienced by the spiral anchor is measured by a pressure sensor.

[0040] in,

[0041] F / T=(1+μ*tgɑ0) / (μ-tgɑ0) / R0

[0042] In the formula,

[0043] μ represents the coefficient of friction between the upper and lower axial plates of the spiral anchor disc;

[0044] α0 represents the helix angle of the resultant force of the soil layer on the helical anchor plate;

[0045] R0 represents the radius of the helix of the resultant force of the soil layer on the helical anchor plate;

[0046] In the formula,

[0047]

[0048] Where r represents the anchor bolt radius and R represents the radius of the helical blade disk.

[0049] a0 is obtained through the following formula:

[0050] tgɑ0=(2*Pi*R0) / H

[0051] In the formula, Pi represents pi (circular diameter), and H represents the pitch of the spiral anchor disc.

[0052] Furthermore, the power head applies torque and downward pressure to the auger anchor through the auger anchor connector. The auger anchor drilling process involves two steps. First, the auger anchor connector is driven to the uppermost auger anchor disc of the auger anchor, and the uppermost auger anchor disc applies torque and downward pressure to the auger anchor, causing the auger anchor to drill into the soil layer. Second, when the lower end of the uppermost auger anchor disc reaches the ground, the auger anchor connector is driven to the upper end of the polished rod section of the auger anchor, and the polished rod end applies torque and downward pressure to the auger anchor, causing the auger anchor to continue drilling into the soil layer.

[0053] The specific structures of the spiral anchor drilling rig and spiral anchor in this embodiment are as follows:

[0054] The spiral anchor drilling rig includes a drilling column 1, on which a power head 2 is guided and moved. The power head 2 is driven by a power head lifting mechanism and has a torque output end. The torque output end includes a gear ring 13 whose rotation axis is aligned with the lifting direction of the power head. The power head includes three drive motors 14 spaced circumferentially. Each drive motor 14 has a motor shaft gear on its shaft that meshes with the gear ring for transmission. All of the above are prior art and will not be described in detail here.

[0055] The torque output end also includes a torque output end flange 16 coaxially fixed to the lower end of the gear ring, and bolt holes are provided on the torque output end flange 16.

[0056] The spiral anchor drilling rig also includes a spiral anchor connector 10 for connecting the torque output end to the spiral anchor drive. The spiral anchor 4 is prior art. The spiral anchor includes an anchor rod 5, on which multiple spiral anchor discs 6 are spaced apart. Each spiral anchor disc is composed of a spiral blade plate, with the upper and lower axial surfaces of the spiral blade plate being spiral surfaces. The upper circumferential end face 7 and the lower circumferential end face 8 of the spiral blade plate are staggered. The anchor rod includes a smooth rod section 3 located at the uppermost spiral anchor disc. The upper end of the smooth rod section 3 is provided with an anchor rod connection hole 9 for torque input. In this embodiment, there are three anchor rod connection holes, which are arranged side by side at intervals in the vertical direction. Each anchor rod connection hole penetrates the upper end of the smooth rod section radially.

[0057] The upper end of the spiral anchor connector has a connector connection structure that connects to the torque output end. In this embodiment, the connector connection structure is connector method 17, and the connector flange 17 is detachably connected to the torque output end flange 16 by vertical bolts 15.

[0058] The spiral anchor connector 10 and the power head have a through hole 25 for the smooth rod section of the spiral anchor to pass through in the vertical direction. The bottom of the spiral anchor connector is a force transmission head 18 that presses down on the corresponding spiral anchor disc. The lower end face 22 of the force transmission head is a connector spiral surface for adapting and contacting with the upper spiral surface of the spiral anchor disc of the spiral anchor. The circumferential end face 21 of the force transmission head is used to abut against the upper circumferential end face 7 of the spiral anchor disc to drive the spiral anchor forward through the spiral anchor connector.

[0059] In this embodiment, the spiral anchor connector consists of two circumferentially arranged connector segments 23, each with a circumferential span of 180 degrees. The two connector segments 23 are detachably connected by transverse bolts 19. That is, half of the connector flange is located on one connector segment, and the other half is located on the other connector segment; half of the spiral surface of the connector is formed by the lower end face of one connector segment, and the other half is formed by the lower end face of the other connector segment.

[0060] A torque sensor 12 and a pressure sensor 11 are installed along the force transmission path between the power head and the helical anchor. Specifically, the pressure sensor 11 is located between the torque output flange 16 and the connecting flange 17, while the torque sensor 12 is connected in series between the gear ring 13 and the torque output flange 16. The torque sensor 12 is used to detect the output torque of the power head 2 on the helical anchor 4, and the pressure sensor 11 is used to detect the downward pressure of the power head 2 on the helical anchor 4.

[0061] A reversing protrusion 20 is provided at the lower end of the circumferential end face of the power transmission head. The reversing protrusion 20 is used to abut against the lower circumferential end face of the spiral anchor disc so that the spiral anchor disc rotates in the reverse direction when the spiral anchor connector rotates in the reverse direction. In this invention, forward rotation and reverse rotation are relative. Forward rotation of the power head can enable the spiral anchor to drill into the formation. When the spiral anchor is not drilling smoothly, it is occasionally necessary to reverse the power head to lift the spiral anchor and then rotate forward again. The reversing protrusion 20 is not used frequently and is not necessary. Therefore, in other embodiments of this invention, the reversing protrusion may be omitted.

[0062] The force transmission head is provided with radially penetrating force transmission head connection holes 24, which are used to cooperate with the corresponding anchor bolt connection holes 9.

[0063] When using it, firstly as Figure 3 As shown, the smooth section 3 of the anchor bolt passes through the smooth section of the power head from bottom to top. The power head descends to the uppermost auger disc, and then the auger connector is connected to the output flange, so that the lower end face of the force transmission head is in contact with the upper end face of the uppermost auger disc, and the circumferential end face of the force transmission head is in contact with the upper circumferential end face of the uppermost auger disc. The reverse protrusion is in contact with the lower circumferential end face of the uppermost auger disc. The power head rotates the auger forward through the auger connector, and at the same time, the power head actively descends to apply pressure to the upper end of the auger, realizing the drilling of the auger into the soil layer, which is the first step in the auger drilling process.

[0064] When the lower end of the uppermost spiral anchor plate reaches the ground, meaning the uppermost spiral anchor plate is in contact with the ground or within 50cm of the ground, it may be necessary to loosen the two connecting head flaps and move the reversing protrusion to the upper side of the lower circumferential end face of the spiral anchor plate. Then, the power head moves the entire spiral anchor connecting head upward until the force transmission head connecting hole on the force transmission head corresponds to the anchor rod connecting hole on the smooth section of the anchor rod. Then, the transmission pin 26 is inserted into the force transmission head connecting hole 24 and the anchor rod connecting hole 9 to connect the spiral anchor connecting head and the anchor rod. The power head then drills the entire spiral anchor into the soil through the spiral anchor connecting head, completing the second step in the spiral anchor drilling process.

[0065] The torque sensor detects the torque on the helical anchor in real time, and the pressure sensor detects the pressure on the helical anchor in real time. In order to avoid the helical anchor disc from slipping on the soil, the helical anchor disc causes minimal disturbance to the soil, so that when the helical anchor rotates one revolution, the helical anchor advances axially by the pitch of one helical anchor disc. This process is also called ideal advance.

[0066] It needs to be guaranteed that: F / T = (1 + μ * tgɑ0) / (μ - tgɑ0) / R0

[0067] In the formula, F represents the downward pressure exerted by the power head on the helical anchor, which is measured by a pressure sensor;

[0068] T represents the output torque of the power head to the helical anchor, which is measured by a torque sensor;

[0069] μ represents the coefficient of friction between the upper and lower axial plates of the spiral anchor disc;

[0070] α0 represents the helix angle of the resultant force of the soil layer on the helical anchor plate;

[0071] R0 represents the radius of the helix of the resultant force exerted by the soil layer on the helical anchor plate.

[0072] In the formula,

[0073]

[0074] Where r represents the anchor bolt radius and R represents the radius of the helical blade disk.

[0075] a0 is obtained through the following formula:

[0076] tgɑ0=(2*Pi*R0) / H

[0077] In the formula, Pi represents pi (circular diameter), and H represents the pitch of the spiral anchor disc.

[0078] The downward pressure of the anchor rod changes with the drilling torque. To screw in the auger without causing significant disturbance to the soil above the auger disc, the downward pressure F on the anchor rod must increase with the drilling torque F of the anchor rod, as shown in the figure above (F / T). Otherwise, slippage will occur, resulting in a situation where the anchor rod "screws but does not advance".

[0079] The origin of F / T is as follows:

[0080] The cutting edge of the helical blade is subjected to a normal force in contact with the soil, called the resultant force F0 of the soil. Different radial positions on the helical blade correspond to a helix angle α, tanα = (2*Pi*R) / H. The helix angle is smallest at the anchor point and largest at the maximum diameter of the helical blade. Assuming the force acting perpendicularly on the helical blade is uniform, the resultant force F0 acts on a helix with radius R0 on the helical blade. This helix is ​​defined as the helix of the resultant force of the soil, and the helix angle corresponding to this helix is ​​called the helix angle α0. The resultant force F0 acts perpendicularly on the helix of the resultant force of the soil and generates a frictional force f0 = F0*μ on the helical blade.

[0081] In other words, during the spiral anchor bolt's advance, it is subjected to the resultant force F0 of the soil acting perpendicularly on the spiral line of the resultant force of the soil with a radius of R0 on the spiral blade, as well as the frictional force f0 generated between the resultant force F0 of the soil and the spiral blade.

[0082] Anchor radius r, maximum radius R of helical blade, pitch H of helical blade.

[0083] From the anchor radius r to the maximum radius R of the helical blade, the helix angle of the helical blade changes continuously, and the radius R0 of the helical line of the soil resultant force acting on the helical blade is equal to the area of ​​the helical line formed by the circle with anchor radius r and the circle with radius R0 of the soil resultant force helical line. That is:

[0084]

[0085] When the helical anchor is subjected to a thrust F = F z Propulsion torque T = F x When R0 is reached, the helical anchor bolt operates under the assumed ideal spiraling state in uniform soil.

[0086] Summarizing the above assumptions, we get:

[0087] The vertical component of the resultant force on the soil is: F1 = F0 * cosα0.

[0088] The horizontal component of the resultant force of the soil mass is: F2 = F0 * sinɑ0;

[0089] The perpendicular component of the frictional force is: f1 = F0 * μ * sinα0.

[0090] The horizontal component of the frictional force is: f2 = F0 * μ * cosα0;

[0091] F = F z =F1+f1=F0*cosɑ0+F0*μ*sinɑ0

[0092] T = Fx *R0=(f2-F2)*R0=(F0*μ*cosɑ0-F0*sinɑ0)*R0

[0093] In summary:

[0094] f0=F0*μ................................................Formula 1

[0095]

[0096] tgɑ0=H / (2*Pi*R0).........................................Formula 3

[0097] F=F0*cosɑ0+F0*μ*sinɑ0.....................................Formula Four

[0098] T=(F0*μ*cosɑ0-F0*sinɑ0)*R0................................Formula 5

[0099] Formula 4 / Formula 5:

[0100] F / T=(F0*cosɑ0+F0*μ*sinɑ0) / (F0*μ*cosɑ0-F0*sinɑ0) / R0

[0101] = (1+μ*tgɑ0) / (μ-tgɑ0) / R0

[0102] Therefore, F / T = (1 + μ * tgɑ0) / (μ - tgɑ0) / R0....................Formula Six

[0103] In the foregoing description of this specification, unless otherwise expressly specified and limited, the terms "fixed," "installed," "connected," or "linked" should be interpreted broadly. For example, the term "linked" can refer to a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; or it can refer to the internal communication of two components or the interaction between two components. Therefore, unless otherwise expressly limited in this specification, those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0104] Based on the above description in this specification, those skilled in the art will also understand that terms used, such as "upper," "lower," "front," "rear," "left," "right," "length," "width," "thickness," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," "circumferential," "center," "longitudinal," "transverse," "clockwise," or "counterclockwise," are terms indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings of this specification. They are only for the purpose of facilitating the explanation of the present invention and simplifying the description, and do not imply that the devices or elements involved must have the specific orientation, or be constructed and operated in a specific orientation. Therefore, the above-mentioned orientation or positional relationship terms should not be understood or interpreted as limitations on the present invention.

[0105] Furthermore, the terms "first" or "second," etc., used in this specification to refer to numbers or ordinal numbers are for descriptive purposes only and should not be construed as indicating, explicitly or implicitly, relative importance or specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this specification, "a plurality of" means at least two, such as two, three, or more, unless otherwise explicitly specified.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A spiral anchor drilling method, characterized in that: A auger anchor drill is used to drill the auger anchor into the soil layer. During the drilling process, the power head of the auger anchor drill applies torque to the auger anchor, and at the same time, the power head of the auger anchor drill actively applies downward pressure to the auger anchor. The torque T on the auger anchor is measured by a torque sensor, and the downward pressure F on the auger anchor is measured by a pressure sensor. in, F / T=(1+μ*tgɑ0) / (μ-tgɑ0) / R0 In the formula, μ represents the coefficient of friction between the upper and lower axial surfaces of the spiral anchor disc; α0 represents the helix angle of the resultant force of the soil layer on the helical anchor plate; R0 represents the radius of the helix of the resultant force of the soil layer on the helical anchor plate; In the formula, Where r represents the anchor bolt radius and R represents the radius of the helical blade disk. a0 is obtained through the following formula: tgɑ0=(2*Pi*R0) / H In the formula, Pi represents pi (circular diameter), and H represents the pitch of the spiral anchor disc.

2. The spiral anchor drilling method according to claim 1, characterized in that: The power head applies torque and downward pressure to the auger anchor through the auger anchor connector. The auger anchor drilling process has two steps. First, the auger anchor connector is driven to the uppermost auger anchor disc of the auger anchor, and the uppermost auger anchor disc applies torque and downward pressure to the auger anchor, causing the auger anchor to drill into the soil layer. Second, when the lower end of the uppermost auger anchor disc reaches the ground, the auger anchor connector is driven to the upper end of the smooth rod section of the auger anchor, and the smooth rod end applies torque and downward pressure to the auger anchor, causing the auger anchor to continue drilling into the soil layer.

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