Wood column for ground improvement and its manufacturing method

Abstract

To provide a wooden column for use in ground improvement, which can widen the range of wood usable as a material by bundling and using a plurality of pieces of wood including rod-shaped wood pieces obtained by cutting at least a log along its longitudinal direction or splitting it like firewood, and a method for manufacturing the same. [Solution] The wooden column of the present invention is a wooden column that is installed in the ground and used for ground improvement, and is characterized by comprising a plurality of pieces of wood, including at least rod-shaped pieces of wood formed by cutting a log along its length or splitting it into pieces like firewood, and a restraining material that tightens and bundles the plurality of pieces of wood from the outer periphery into an approximately cylindrical shape with a predetermined outer diameter.

Description

[Technical Field]

[0001] The present invention relates to a wooden column used for ground improvement and a method for manufacturing the same, and in particular to a wooden column used for ground improvement that can expand the range of wood that can be used as a material by bundling and using a plurality of pieces of wood, including rod-shaped wood pieces obtained by cutting or splitting logs along the longitudinal direction, and a method for manufacturing the same. [Background technology]

[0002] Recently, there have been many cases of soft ground liquefaction caused by large earthquakes, resulting in serious damage to roads and above-ground structures, as well as to lifeline facilities such as underground water pipes. Liquefaction problems are likely to occur in reclaimed land and reclamation lands, but liquefaction damage can also occur in areas with high sand content and areas with high groundwater levels.

[0003] Ground improvement is carried out as a measure to prevent damage from liquefaction. One method of ground improvement is to bury an improvement material underground to make the soil more dense. By making the soil dense, even in an environment with a lot of groundwater, fluid materials such as sand become less likely to flow, and the occurrence of liquefaction can be suppressed.

[0004] There is another aspect to ground improvement work that involves burying improvement materials underground. That is, using wood as an improvement material makes it possible to store carbon underground. Trees, the raw material for wood, absorb carbon dioxide from the atmosphere during their growth process, and through photosynthesis convert the carbon dioxide into starch while releasing oxygen. Therefore, if wood is buried underground as an improvement material, the carbon dioxide in the atmosphere, which is thought to be a cause of global warming, will be transformed and stored underground, making it an effective measure against global warming. Several technologies for improving ground by burying wood have already been proposed and put into practical use.

[0005] The most basic method involves sharpening the ends of logs and then driving them directly into the ground. In this case, logs with a maximum diameter of approximately 0.2 m are used, which requires multiple driving in soft ground, resulting in slow construction speed. Furthermore, since logs with a maximum diameter of approximately 0.2 m are used, this method cannot be used for deep construction. The heavy machinery used is also small, making it difficult to use in slightly harder ground. Furthermore, since long, straight logs are required, logs with large curvatures cannot be used, resulting in a low yield rate for producing usable logs. Even if usable logs are used, driving a large number of logs densely into the ground can increase excess pore water pressure in the short term, potentially resulting in ground with reduced shear resistance and liquefaction resistance.

[0006] Patent Document 1 discloses a ground improvement wooden pile in which an axial scratch is made on the side of a carbon stock log made from aged felled wood, and the log is left in the air to dry and shrink, causing the scratch to widen, forming a drainage groove, which is then filled with drainage material. Patent Document 1 also describes a method in which multiple logs are bundled together, a bottom cap is attached to the tip, and the bundle is driven into the ground as a single ground improvement wooden pile.

[0007] According to the invention described in Patent Document 1, it is expected that drainage material filled into drainage ditches will quickly dissipate excess pore water pressure, thereby ensuring reliable ground improvement. Furthermore, Patent Document 1 also states that logs with a maximum diameter of approximately 0.2 m can be bundled together for use, which is expected to reduce the number of logs that need to be poured and increase construction speed. However, there are still many issues with the material restrictions, such as the inability to use logs with large curvatures and the difficulty of bundling logs with uneven thicknesses.

[0008] Patent Document 2 discloses a ground improvement method for reinforcing the ground with wood, in which a pipe is inserted into the ground to form a space inside the pipe, multiple pieces of wood are filled into the space, the pipe is removed after the wood is filled, and finally an aggregate layer is formed around the periphery of the wood, which is left underground.

[0009] According to the invention described in Patent Document 2, a space is first formed in the ground using a pipe body, and then the space is filled with wood, so there is no resistance from the ground when the wood is installed, and the diameter and depth of the space formed in the ground can be set without worrying about the strength of the wood. The invention described in Patent Document 2 exemplifies a method in which the wood to be filled into the pipe body is bundled together before being inserted. Even in this case, it is difficult to bundle logs with large curves or tapered shapes, and since gaps tend to become large, there is also the problem that if soil gets into the gaps in the log bundle, the density-increasing effect will not last.

[0010] Therefore, it is desirable to develop a wooden column for ground improvement and a method for manufacturing the same that allows the use of wood that could not be used in the past, such as logs with large curves, so that more wood can be used to contribute to ground improvement and carbon storage. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 4459173 [Patent Document 2] Japanese Patent Application Publication No. 2018-021325 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention has been made in consideration of the problems with the conventional wooden columns used for ground improvement and the methods for manufacturing them described above, and the object of the present invention is to provide a wooden column used for ground improvement and a method for manufacturing the same that makes it possible to expand the range of wood that can be used as material by bundling together and using multiple pieces of wood, including stick-shaped wood made by cutting or splitting logs along their length. [Means for solving the problem]

[0013] The wooden column of the present invention, which has been made to achieve the above-mentioned object, is a wooden column that is installed in the ground and used for ground improvement, and is characterized by comprising a plurality of pieces of wood, including rod-shaped pieces of wood that are at least logs cut or split into firewood-like pieces along their longitudinal direction, and a restraining material that tightens and bundles the plurality of pieces of wood from the outer periphery into an approximately cylindrical shape with a predetermined outer diameter.

[0014] It is preferable that a sand-proof sheet be further provided on the outer periphery of the wooden column to prevent sand from entering from the outside. The sand-proof sheet preferably has water permeability.

[0015] The wooden column is used with its longitudinal direction facing up and down relative to a horizontal plane, and when the sand-proof sheets are wrapped around the outer periphery of the wooden column in multiple overlapping layers, it is preferable that the sand-proof sheets located on the downward side are wrapped on the outside.

[0016] The method for manufacturing a wooden column according to the present invention, which has been made to achieve the above-mentioned object, is a method for manufacturing a wooden column to be installed in the ground and used for ground improvement, and comprises the steps of: tightening and bundling a plurality of pieces of wood, including rod-shaped pieces of wood obtained by cutting at least a log longitudinally or splitting it into firewood-like pieces, from the outer periphery using a restraining material into an approximately cylindrical shape of a predetermined outer diameter; and wrapping and fixing a sand-proof sheet around the outer periphery of the wooden column to prevent sand from entering from the outside, wherein the bundling step is characterized in that the plurality of pieces of wood are gradually tightened while being shaken to form a dense mass, and then shaped into an approximately cylindrical shape. [Effects of the Invention]

[0017] According to the wooden column used for ground improvement and its manufacturing method of the present invention, even logs with large curvatures or multiple logs of varying thicknesses can be used as wooden columns by cutting or splitting the logs longitudinally into stick-shaped pieces before bundling them together and then tightening them tightly. This makes it possible to use even logs with large curvatures as wooden columns. In particular, according to the method for manufacturing wooden columns used for ground improvement of the present invention, the step of bundling multiple pieces of wood is performed by shaking the pieces of wood to gradually tighten them and shape them into a roughly cylindrical shape, making it easy to manufacture roughly cylindrical shapes of any outer diameter. Therefore, when combined with a construction method in which a wooden column is inserted into a space formed by a pipe, construction that minimizes the gap between the pipe and the wood column can be easily achieved.

[0018] According to the wooden column used for ground improvement and the method for manufacturing it of the present invention, the periphery of the wooden columns bundled together in a roughly cylindrical shape is covered with a sand-proof sheet that prevents sand from entering from the outside. The sand-proof sheet is also permeable, so that the intrusion of sand is prevented after the wooden columns are installed underground, and the density-increasing effect is likely to be sustained. In addition to the vertical drainage effect due to the gaps between the bundled wooden pieces, a horizontal drainage effect due to the permeability of the sand-proof sheet is expected, which allows excess pore water pressure around the wooden columns to be effectively dissipated.

[0019] According to the wooden columns used for ground improvement and the manufacturing method thereof of the present invention, wooden columns can be manufactured using logs of a wide range of shapes, not just straight logs. This means that even wood that could not be used before can be installed underground for ground improvement, resulting in a high yield, reducing the amount of wood that is discarded or burned, and potentially achieving a significant carbon storage effect. Furthermore, since wood is used, there is no contamination of the groundwater level or the ground. Furthermore, if a device that splits logs into logs, like a log splitter, is used instead of cutting them, the processing speed is fast and energy consumption is low, making it possible to achieve environmentally friendly ground improvement, including the carbon storage effect. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a plan view showing a schematic diagram of a wood splitting device for preparing wood to be used in a wood column according to an embodiment of the present invention. [Figure 2] 1 is a diagram showing a situation in which a piece of wood is set in a restraining device for restraining a piece of wood according to an embodiment of the present invention. FIG. [Figure 3] 1 illustrates a situation in which wood is densified using a wood restraining device according to an embodiment of the present invention. [Figure 4] 1A and 1B are diagrams illustrating a situation in which a piece of wood is restrained by a restraining material according to an embodiment of the present invention. [Figure 5] FIG. 5 is a diagram showing a situation in which a sandproof sheet is wrapped around the outer periphery of the wood piece restrained by the restraining material shown in FIG. 4. [Figure 6] FIG. 6 is a diagram showing a state in which the wood wrapped with the sand-proof sheet shown in FIG. 5 is restrained with a new restraining material. [Figure 7] 10A and 10B are diagrams showing a situation in which a piece of wood is set in a restraining device for restraining a piece of wood according to another embodiment of the present invention. [Figure 8] 1 is a diagram showing a situation in which wooden columns according to an embodiment of the present invention are stacked and used. FIG. [Figure 9] 1 is a flowchart illustrating a method for producing a wood column according to an embodiment of the present invention. [Figure 10] FIG. 1 is a diagram showing an example of a conventional wooden pile for ground improvement made by bundling logs. DETAILED DESCRIPTION OF THE INVENTION

[0021] Next, specific examples of embodiments for carrying out the wood column used for ground improvement and the method for manufacturing the same according to the present invention will be described in detail with reference to the drawings. First, the conventional technology and its problems will be described in order to clarify the improvements made by the embodiments of the present invention compared with the conventional technology.

[0022] Figure 10 shows an example of a conventional wooden pile for ground improvement made by bundling logs. Wooden piles have already been used for ground improvement. Typically, the logs are sharpened and then driven into the ground one by one. However, the logs used are approximately 0.2 m in diameter, which makes large-scale ground improvement projects inefficient and unsuitable for deep driving. Therefore, when burying a large number of wooden piles or driving them deeper into the ground, bundles of logs are sometimes used. Figure 10 shows an example of such a pile. In this example, three logs 101 are bound together with a restraining material 102, and a bottom cap 103 is attached to the bottom end, which becomes the tip during driving. The bottom cap 103 facilitates penetration into the ground and prevents sand and other materials from entering the gaps between the three logs 101, which form the drainage channel 104, during driving.

[0023] However, to make a wooden pile by bundling logs 101 as shown in Figure 10, each log 101 needs to be straight and of uniform thickness. If the logs 101 used as material are curved or have thick sections in the middle, the logs 101 will not fit tightly together when they are bundled together, and gaps will form on the sides, allowing sand to seep into the drainage channel 104 while it is buried underground, reducing the functionality of the drainage channel 104. Furthermore, the intrusion of sand will reduce the effect of the wooden pile in compacting the ground.

[0024] The wooden column according to an embodiment of the present invention, similar to the wooden pile shown in Figure 10, is a wooden column installed in the ground for ground improvement. To address these issues, the wooden column is fabricated using a plurality of pieces of wood, including rod-shaped pieces of wood obtained by cutting or splitting logs longitudinally, and a restraining material that tightens and bundles the pieces into a roughly cylindrical shape with a predetermined outer diameter. Even curved pieces of wood can be made more flexible by thinning them by cutting or splitting them longitudinally. By tightening and restraining them, the wooden column can be made into a compact, more cylindrical shape. Because the wooden column according to the embodiment of the present invention can be fabricated into a roughly cylindrical shape, similar to the wooden pile shown in Figure 10, it can be fabricated to the required length and used as a single wooden pile with a bottom cap attached. Alternatively, it can be fabricated to an appropriate length and combined with a cylindrical drilling tube. The tube can be stacked vertically within the tube, and then the entire column can be buried in the ground. This allows for the effective use of logs that are too short to be used as wooden piles.

[0025] Next, a method for producing a wooden column according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a plan view schematically showing a wood splitting device for preparing wood to be used in a wood column according to an embodiment of the present invention. The wood used in the wood column according to the embodiment of the present invention can be straight logs of uniform thickness, which can be used as is. However, logs with curves or uneven thicknesses can be thinned by cutting or splitting them longitudinally. Even if all the logs are straight and uniform in thickness, when they are bundled together for use, the outermost periphery will be a collection of logs with a shape that follows the outer diameter of the logs. Therefore, when viewed in cross section, gaps remain near the boundaries between the logs, rather than the desired circular shape, and the resulting columnar shape cannot be achieved. Therefore, the wood column according to the embodiment of the present invention includes rod-shaped wood, which is at least obtained by cutting or splitting the logs longitudinally to fill these gaps. Figure 1 shows a log splitting device for splitting logs into logs.

[0026] Referring to FIG. 1 , a firewood splitting device 10 includes an engine 13, a hydraulic cylinder 14 that pushes a log 16 longitudinally, and a splitting blade 15 that splits the log 16 pushed by the hydraulic cylinder 14 into pieces, all mounted on a support base 11. In the embodiment of the firewood splitting device 10 shown in FIG. 1 , the support base 11 that supports the engine 13 and hydraulic cylinder 14 and the support base 11 that supports the splitting blade 15 are provided separately, and wheels 12 allow each to move independently. These two support bases 11 are connected by a connecting part 18 to form a single firewood splitting device 10. In this embodiment, the connecting part 18 is provided in multiple lengths, or is configured to have multiple screw holes for fastening so that the two support bases can be connected at various lengths after adjusting the length to the required maximum, or is configured with elongated holes for bolts that allow the connection length to be adjustable. By changing the installation length of the connecting part in this way, it is possible to accommodate hydraulic cylinders 14 with different strokes and logs 16 of different lengths. Furthermore, because the connecting part 18 allows for attachment and detachment, the combination of hydraulic cylinder 14 and splitting blade 15 can be changed as needed. This makes it easy to change the stroke of hydraulic cylinder 14 and to change to a splitting blade 15 with various shapes.

[0027] The splitting blade 15 has blades arranged in a geometric shape to divide the cross section of the log 16 in a plane, and the log 16 that passes through the splitting blade 15 is divided into multiple pieces of wood 17 in accordance with the geometric shape of the splitting blade 15. There are no restrictions on the blade arrangement, but in this embodiment, the blades are formed by a combination of multiple radially arranged blades arranged along radial lines extending from the center of the log 16 toward the periphery, like a spider web, and multiple connected blades arranged along connecting lines that connect the radially arranged blades in a ring or polygonal shape. The blade arrangement is not limited to this, and may also be a hexagonal combination like a honeycomb, or may even be an arrangement in a lattice pattern or a closely spaced triangle pattern.

[0028] The firewood splitter 10 has a faster processing speed than cutting devices such as sawmills that cut logs 16, and the equipment can be made smaller, and less energy is required for processing. It also produces less wood waste, allowing for more efficient use of the logs 16. The wood split by the firewood splitter 10 or the wood cut by a cutting device such as a sawmill is then bundled into a roughly cylindrical shape.

[0029] FIG. 2 is a diagram showing a situation in which a piece of wood is set in a restraining device for restraining a piece of wood according to an embodiment of the present invention. Referring to Figure 2, a restraining device 20 for restraining wood 17 according to an embodiment of the present invention includes a support base 21, a guide 22 for gathering the wood 17 into an approximately cylindrical shape with a required outer diameter, and a roller 23 for supporting the rotation of the guide 22.

[0030] The guide 22 has the shape of a circular pipe with an inner diameter that matches the outer diameter of the wooden column to be made, divided into two along a line including the diameter. For example, to make a wooden column with an outer diameter of 0.6 m, a circular pipe such as a PVC pipe of an appropriate length with an inner diameter of 0.6 m can be divided into two. In this embodiment, although not shown, one circumferential end of the divided circular pipe is connected to the other circumferential end with a rotatable connecting device such as a hinge, and a fastener is provided at the other circumferential end to secure the original circular pipe closed when closed.

[0031] In this embodiment, as shown in FIG. 2, with the guide 22 open, the wooden pieces 17 are stacked and set on one half of the arc-shaped portion of the guide 22. The required amount of wooden pieces 17 can be set by stacking enough wooden pieces 17 so that no gaps are left when the guide 22 is closed. As described below, the stacked wooden pieces 17 are gradually tightened while being shaken to form a roughly cylindrical shape, so they may become thinner than their initial state. If a gap appears between the bundle of wooden pieces 17 and the guide 22 as the tightening progresses, additional wooden pieces 17 may be added as needed. While the above example illustrates the use of a circular tube with an inner diameter equal to the target outer diameter of the wooden column, in one embodiment, the inner diameter of the guide 22 is formed slightly larger than the target outer diameter of the wooden column to account for the narrowing caused by tightening.

[0032] The guides 22 are provided in at least two locations so as to support both ends of the wooden piece 17. A connecting frame 24 is also provided to connect the two guides 22 so that the two guides 22 can rotate in unison. To prevent the guides 22 from sliding and rotating without moving the wooden piece 17 inside when the guides 22 rotate, the inner surface of the guides 22 may be provided with irregularities, or a sheet made of a non-slip material may be attached to it.

[0033] The rollers 23 are rotatably attached to the upper side of the support base 21 and rotatably support the guides 22. The rollers 23 may be individually provided on the underside of each guide 22, or may be long rollers 23 having approximately the same length as the wood 17 so as to be common to the guides 22 at both ends. The rollers 23 may be passive rollers 23 that rotate in conjunction with the rotation of the guides 22, thereby supporting the guides 22 without interfering with their rotation, or may be active rollers 23 that are connected to a drive unit such as a servo motor (not shown), and support the guides 22 so as to rotate by their own rotation. In one embodiment, the restrainer 20 includes a pivoting or vibrating means for rocking the bundle of wood 17 through the guide 22 .

[0034] FIG. 3 is a diagram illustrating a situation in which wood is densified using a constraint device for constraining wood according to an embodiment of the present invention. Referring to FIG. 3 , the guide 22 of the restraining device 20 with the wooden pieces 17 set inside is closed and secured with a fastener (not shown) to maintain the closed state. Furthermore, the tightening wire 25 is attached by wrapping it around the bundle of wooden pieces 17. In FIG. 3 , one end of the tightening wire 25 is formed into a ring shape, and the other end is inserted through the inside of the ring-shaped end and pulled upward, thereby applying tension to the wooden pieces 17 to compress them. In addition to this method of attachment, the tightening wire 25 may be attached by fixing one end and wrapping the other end around the bundle of wooden pieces 17, and then applying tension in the opposite direction to the one end to apply a similar external force. While the tightening wire 25 is referred to as a wire here, it does not have to be a wire, and may be a rope, string, or strip-like material as long as it can apply the external force necessary to compress the wooden pieces 17.

[0035] Because the lumber 17 set in the guide 22 is stacked in a disorderly manner, there may be many unnecessary gaps between the individual pieces of lumber 17. Therefore, tightening the lumber 17 in this state may not result in sufficient compaction. Therefore, in this embodiment, the bundle of lumber 17 is gradually tightened by the tightening wire 25 while being subjected to a rocking motion, such as rotation or vibration, via the guide 22. The rocking motion may be performed manually, or, if the restraining device 20 is equipped with a rotation means or vibration means, it may be performed mechanically using the rotation means or vibration means. Since the tightening wire 25 is wound around the bundle of lumber 17, when a rocking motion is applied by rotation, it is rotated within a limited angular range so as not to rotate the lumber 17 one full turn. Furthermore, tightening by the tightening wire 25 may be performed manually, or, if the restraining device 20 is equipped with a tensioning means, such as a winding machine, it may be performed mechanically using the tensioning means.

[0036] FIG. 4 is a diagram showing a situation in which a piece of wood is restrained by a restraining material according to an embodiment of the present invention. The wooden pieces 17 are tightly bound together by the shaking action and the tightening wires 25, and are then restrained at multiple locations with restraining materials 26 to maintain the tight state. Similar to the tightening wires 25, the restraining materials 26 may be wire, string, rope, strip-shaped material, or any other material or shape that can be wrapped around and secured to the outer periphery of the wooden pieces 17. After the multiple locations have been restrained with the restraining materials 26, the tightening wires 25 may also be used as the restraining materials 26 by fixing them so that they do not loosen.

[0037] Since the restraining material 26 is buried underground below the groundwater level while restraining the bundle of timber 17, it is preferable to use a material that is resistant to deterioration by water. The external shape of the bundle of wooden pieces 17 is determined at the stage of restraining with the restraining material 26, but if the ends of the plurality of wooden pieces 17 are not aligned at the end, the end faces are cut while still in the bundled state to make them even.

[0038] FIG. 5 is a diagram showing a situation in which a sand-proof sheet is wrapped around the outer periphery of the wood piece restrained by the restraining material shown in FIG. Even if the bundle of wooden pieces 17 restrained by the restraining material 26 is densified, it cannot be said with certainty that there will be no gaps around the periphery. Therefore, over time after burying the bundle in the ground, sand may seep into the gaps and fill the spaces between the pieces of wooden pieces 17 that form the drainage channel. In this case, not only will the drainage channel function be impaired, but the effect of densifying the ground may also be diminished. For this reason, a sand-proof sheet 27 is wrapped around the periphery of the bundle of wooden pieces 17 removed from the restraining device 20 to prevent sand from entering during actual use.

[0039] It is preferable that the sand control sheet 27 prevents the intrusion of sand while not hindering the discharge of groundwater. For this reason, a permeable sand control sheet 27 is used. Permeability can be achieved by using a permeable material for the fabric of the sand control sheet 27 itself, or by drilling tiny holes in the fabric of the sand control sheet 27 that allow water to pass through but not sand. By making the sand control sheet 27 permeable, it is possible to prevent the intrusion of sand while allowing water to pass through, allowing water to be drained from the gaps between the pieces of wood 17.

[0040] After completion, the bundle of timber 17 is buried in an upright position with the z-axis pointing upward. Therefore, as shown in Figure 5, when multiple sandproof sheets 27 are used, depending on how they are stacked, the bottom ends of the sandproof sheets 27 may curl up when buried in the ground, impairing the functionality of the sandproof sheets 27. Therefore, in this embodiment, the sandproof sheets 27 positioned on the lower side are wrapped around the outside.

[0041] FIG. 6 is a diagram showing a situation in which the wood wrapped with the sandproof sheet shown in FIG. 5 is restrained with a new restraining material. The outer periphery of the bundle of wooden pieces 17 wrapped with sand-proof sheet 27 is restrained with new restraining material 26 to fix the sand-proof sheet 27 in place. In this state, the wooden column 1 is completed. The new restraining material 26 is called new restraining material 26 in the sense that it is used separately from the restraining material 26 that restrains the wooden pieces 17 inside the sand-proof sheet 27, but there is no need to distinguish between the material or shape of the restraining material 26 inside the sand-proof sheet 27 and the restraining material 26 outside the sand-proof sheet 27. Although the method for producing the wooden column 1 by placing the wooden piece 17 horizontally has been described above using FIGS. 2 to 6, it is also possible to produce the wooden piece 17 in a vertically standing state.

[0042] FIG. 7 is a diagram showing a situation in which a piece of wood is set in a restraining device for restraining a piece of wood according to another embodiment of the present invention. 7, the restraining device 30 is provided with a lower guide 32 and an upper guide 33 that serve as guides when setting the lumber 17 upright on a horizontal support base 31. Also, a vibration device 35 that vibrates the support base 31 is provided below the support base 31.

[0043] The lower guide 32 and the upper guide 33 are both cylindrical, and their inner diameters are either matched to the outer diameter of the wooden column 1 to be fabricated as described above, or are larger than the outer diameter of the wooden column 1 by an amount that takes into account the reduction in the outer diameter of the bundle of wooden pieces 17 when tightened. The upper guide 33 has an insertion widening section 34 that widens at the top to make it easier to load the wooden pieces 17 from above. The insertion widening section 34 may also be provided on the lower guide 32. Because the wooden pieces 17 are loaded from above, the lower guide 32 and the upper guide 33 do not need to be divided into two sections to set the wooden pieces 17, as with the guide 22 shown in Figure 2, but it is preferable to divide them into two sections that can be opened and closed to make it easier to remove the bundle of wooden pieces 17 restrained by the restraining material 26.

[0044] After the wooden pieces 17 are set in place, the support base 31 is vibrated by the vibration device 35, causing the wooden pieces 17 to vibrate, while the tightening wires 25 tighten the bundle of wooden pieces 17. In this case, the tightening wires 25 are pulled horizontally to apply a tightening force to the bundle of wooden pieces 17. Once the pieces have been tightened sufficiently, they are restrained at multiple points by the restraining materials 26, resulting in a bundle of restrained wooden pieces 17. When the wooden pieces 17 are bundled upright on the horizontal support base 31, the end faces naturally align, so there is no need to cut and smooth the end faces to make them flat. The pieces are then removed, wrapped with sand-proof sheet 27, and secured with new restraining materials 26, just as in the method described with reference to Figures 5 and 6.

[0045] FIG. 8 is a diagram showing a situation in which wooden columns according to an embodiment of the present invention are stacked and used. As described above, the wooden columns 1 can be formed to an appropriate length and stacked vertically inside a cylindrical drilling tube. In this case, handling can be improved by connecting the wooden columns 1 to be stacked together in advance. Therefore, in this embodiment, a hollow pipe 40 is provided in advance in the center of the wooden columns 1 to be stacked, and a connecting rope 41 is passed through the pipe 40 to connect the wooden columns 1 to each other. The pipe 40 can be embedded in the bundle of wooden pieces 17 by setting it together with the wooden pieces 17 in the center of the bundle when preparing the bundle of wooden pieces 17 using the method described above.

[0046] Instead of the pipe 40, a rod thicker than the connecting rope 41 is embedded in a bundle of timber 17, and one end of the rod is connected to the connecting rope 41, and the rod is pulled out to the other end side, thereby inserting the connecting rope 41 into the wooden column 1 without using the pipe 40, and this can be repeated to connect the wooden columns 1 together.

[0047] FIG. 9 is a flowchart illustrating a method for producing a wood column according to an embodiment of the present invention. 9, in step S910, the log 16 is cut or split into logs 17. The method for splitting logs using the log splitter 10 is as described with reference to Fig. 1. When cutting logs 17, the logs are first cut into boards using a sawmill equipped with a band saw, and then the boards are cut into logs.

[0048] Next, in step S920, the wooden pieces 17 are placed in a bundle along the guides. The wooden pieces 17 are placed either lying down or standing up according to the type of restraint device (20, 30) and aligned with the semicircular or circular guides to form a roughly cylindrical shape. When the length of the wooden pieces 17 is short and a wooden column 1 is to be made by stacking them, a hollow pipe 40 for passing a connecting rope 41 through is set at approximately the center of the wooden pieces 17, if necessary. In step S930, the wooden pieces 17 arranged in a bundle are subjected to a rocking motion, and are tightened with the tightening wire 25 while being rocked, and the bundle of wooden pieces 17 is restrained by the restraining member 26 into a substantially circular shape.

[0049] In step S940, a permeable sand-proof sheet 27 is wrapped around the periphery of the approximately cylindrical bundle of wooden pieces 17 restrained by the restraining material 26, and then in step S950, the periphery of the wrapped sand-proof sheet 27 is restrained with a new restraining material 26 to complete the wooden column 1. At this time, the inner bundle of wooden pieces 17 does not lose its shape due to the restraining material 26 attached in step S930, and no special tightening force is required to restrain the sand-proof sheet 27, so the attachment of the restraining material 26 in step S950 may be done manually. When producing a large number of wooden columns 1 at once, the attachment of the restraining material 26 in step S950 may be done mechanically using a device such as a strapping machine.

[0050] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the technical scope of the present invention. [Explanation of symbols]

[0051] 1. Wood column 10. Firewood splitting equipment 11, 21, 31 Support stand 12 wheels 13 Engine 14 Hydraulic cylinder 15 Wood Splitter 16 Logs 17, 101 wood 18 Connection part 20, 30 restraints 22 Guide 23 Laura 24 Connecting Frame 25 tightening wire 26, 102 Restraint material 27 Sand prevention sheet 32 Lower guide 33 Upper guide 34 Insertion widening section 35 Vibration device 40 Pipe 41 Connecting rope 103 Bottom Cap 104 Drainage Channel

Claims

1. A wooden column that is installed in the ground and used for ground improvement, A plurality of pieces of wood including at least stick-shaped pieces of wood obtained by cutting or splitting a log along its longitudinal direction; A wooden column characterized by comprising a restraining material that tightens and bundles the plurality of wooden pieces from the outer periphery into a substantially cylindrical shape with a predetermined outer diameter.

2. 2. The wooden column according to claim 1, further comprising a sand-proof sheet on the outer periphery of the wooden column to prevent sand from entering from the outside.

3. The wooden column according to claim 2, wherein the sand-proof sheet has water permeability.

4. The wooden column described in claim 2, characterized in that the wooden column is used with its longitudinal direction facing up and down relative to a horizontal plane, and when the sand-proof sheets are wrapped around the outer periphery of the wooden column in an overlapping manner, the sand-proof sheets located on the downward side are wrapped so that they are on the outer side.

5. A method for producing a wooden column to be installed in the ground for ground improvement, a step of bundling a plurality of pieces of wood, including stick-shaped pieces of wood obtained by cutting or splitting logs along the longitudinal direction, into a substantially cylindrical shape having a predetermined outer diameter by using a restraining material from the outer periphery; and a step of wrapping and fixing a sand-proof sheet around the outer periphery of the wooden column to prevent sand from entering from the outside. The method for producing a wooden column is characterized in that the bundling step involves gradually tightening the plurality of pieces of wood while shaking them to make them dense, and shaping them into a roughly cylindrical shape.

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