Installation structure of driftwood capture body and driftwood capture structure

Abstract

To mitigate damage caused by driftwood flowing down from mountainous areas, the present invention provides a driftwood trapping structure that is easy to construct, economical, and versatile, requiring no large construction machinery, with detachable pile foundations and driftwood trapping column members, and allowing for arbitrary placement in an optimal planar arrangement at the location where countermeasures are needed. [Solution] A driftwood trap is installed along rivers or roads on the mountain side of the area to be protected. The driftwood trap consists of a pile foundation that rotates autonomously and becomes fixed in the ground when the pile head is struck or pressed in the direction of penetration, and a driftwood trapping column member joined to the pile foundation. The driftwood trapping column member is configured to stand upright by being joined in a series by insertable joints provided within the pile foundation. The driftwood capture structure, installed with an optimal planar arrangement, can capture and preserve the driftwood generated from mountainous areas and the like.

Description

Technical Field

[0001] The present invention relates to a driftwood catcher for capturing driftwood flowing down from slopes in mountainous areas, rivers, etc. for the purposes of sand prevention, mountain management, and road disaster control, etc., and reducing or protecting against damage caused by driftwood to protected areas such as roads and houses, and an installation structure of a driftwood catching work in which a plurality of the driftwood catchers are installed.

Background Art

[0002] In recent years, the development of driftwood catching countermeasures has been promoted, and there has been a demand for more efficiently preventing disasters associated with the outflow of driftwood occurring in mountainous areas, etc. within limited land areas. Hitherto, there have been proposed driftwood catching works having a plurality of columns and cross beams supported by the columns (Patent Document 1), driftwood catching works combining a concrete foundation and a plurality of columns (Patent Document 2), and further, driftwood catching works combining a frame and columns that do not require on-site concrete placement (Patent Document 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] [[ID=四十四]] However, these have had the following drawbacks. When driftwood collides with the structure, it is necessary to ensure the stability of the driftwood capture structure. This requires multiple support columns or a combination of these columns to resist horizontal external forces, resulting in a larger structure and consequently, concerns about limitations on the installation location (Patent Document 1). Furthermore, when arranging the support columns in combination with underground foundation structures (concrete or frame), securing space for the loading and unloading of large construction machinery necessary for installation and earthwork excavation also results in concerns about limitations on the installation location (Patent Documents 2 and 3). In addition, the driftwood capture structures described in Patent Documents 1 to 3 are integrated with multiple support columns and underground foundation structures, which presents challenges such as the difficulty of replacing only the support columns due to aging of the members, and the difficulty of temporarily removing the support columns when vehicles drive over them if the structure is installed near a road. Therefore, the present invention was devised in view of the above problems, and its purpose is to provide a driftwood capture body and a driftwood capture structure that uses multiple driftwood capture bodies, which have excellent constructability, economy, and flexibility, and which do not require a large underground foundation structure or large-scale construction work associated with its installation in order to stabilize the driftwood capture structure when driftwood collides with it, and which have a structure in which the underground foundation structure and the support column can be easily attached and detached, and which can be optimally arranged in a planar manner in the location where countermeasures are needed. [Means for solving the problem]

[0005] To solve the above problems, the present invention provides a driftwood trapping body to be installed along rivers or roads on the mountain side of the area to be protected, characterized in that the driftwood trapping body consists of a pile foundation which autonomously rotates and becomes fixed in the ground when the pile head is struck or pressed in the direction of penetration, and a driftwood trapping column member fixed to the pile foundation. Furthermore, it is preferable that the driftwood trapping body is characterized in that the pile foundation and the driftwood trapping column member are joined together in a continuous manner by a detachable joint. Furthermore, it is preferable that the pile foundation is a driftwood trapping body characterized by comprising a rod-shaped pile body portion having a tapered pile tip portion that gradually decreases in diameter in the direction of penetration, and a spiral portion that is formed in a spiral shape along at least a part or all of the outer circumferential surface of the pile body portion, and has spiral-shaped wing surfaces that convert the reaction force received from the ground when the pile body portion penetrates the ground into a rotational force of the pile body portion. Furthermore, it is preferable that the driftwood trapping column member comprises a cylindrical body and an elongated reinforcing device provided inside the cylindrical body, wherein the reinforcing device has an outer cylindrical body made of a square cylindrical body having four corners and four faces, and an inner cylindrical body made of a square cylindrical body having four corners and four faces, inserted inside the outer cylindrical body, and each corner of the inner cylindrical body abuts against the corresponding face of the outer cylindrical body. The driftwood trapping structure is characterized by comprising any of the driftwood trapping bodies described above, wherein the plurality of driftwood trapping bodies are installed with a horizontal spacing between the driftwood trapping column members that is within approximately half of the expected maximum length of driftwood.

[0006] Furthermore, it is preferable that the driftwood trapping structure is characterized in that the multiple driftwood trapping bodies are installed spaced apart in a substantially straight line with respect to the river's transverse direction when viewed from above.

[0007] Furthermore, it is preferable that the driftwood trapping structure is characterized in that the multiple driftwood trapping bodies are installed spaced apart in a substantially fan shape or a substantially inverted fan shape when viewed from above.

[0008] Furthermore, it is preferable that the driftwood trapping structure is characterized in that the multiple driftwood trapping bodies are installed spaced apart in a plan view along the meandering river crossing direction.

[0009] Furthermore, it is preferable that the driftwood trapping structure is characterized in that, in a plan view, the multiple driftwood trapping bodies are installed at approximately straight line intervals along the roadside. [Effects of the Invention]

[0010] According to the present invention, by installing a driftwood capture body consisting of a pile foundation that autonomously rotates and becomes fixed in the ground when the pile head is struck or pressed in the direction of penetration, and a driftwood capture column member fixed to the pile foundation, in rivers or plains on the mountain side of the area to be protected, construction using large construction machinery is unnecessary. Furthermore, since the driftwood capture column member is connected in a series by an insertable, detachable joint provided on the vertical upper part of the pile foundation, the pile foundation and the driftwood capture column member can be easily attached and detached or replaced as needed. Moreover, by arranging multiple of these driftwood capture bodies optimally at locations along rivers or roads where countermeasures are needed, driftwood generated from mountains and other areas can be effectively captured, thus enabling the installation of a driftwood capture structure that is excellent in terms of constructability, economy, and flexibility. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram showing the driftwood trap according to the present invention and an installation structure (driftwood trapping structure) composed of multiple (two or more) such driftwood traps, where A is an elevation view from the side and B is an elevation view from the front. [Figure 2] This is a perspective view showing the driftwood trapping device according to the present invention. [Figure 3] This is a side view showing a pile foundation according to the present invention. [Figure 4] (a) A perspective view showing a driftwood catching column member according to the present invention. (b) A top view showing a reinforcing device according to the present invention. [Figure 5] This is a side view of the driftwood trap according to this embodiment. [Figure 6] This is a schematic diagram illustrating the outline of the load-bearing capacity experiment according to this embodiment. [Figure 7] This table shows the experimental conditions for load-bearing capacity according to this embodiment. [Figure 8] This is a schematic diagram illustrating the underwater rotation mechanism of driftwood according to this embodiment. [Figure 9] This is a schematic diagram illustrating the outline of an experiment concerning the effect of differences in the installation structure of the driftwood capture device according to this embodiment on the driftwood capture function. [Figure 10]It is a schematic diagram showing the definition regarding the evaluation of the control effect of driftwood rotation in an experiment on the influence of the difference in the installation structure of the driftwood catching work according to this embodiment on the driftwood catching function. [Figure 11] It is a table showing the conditions of an experiment on the influence of the difference in the installation structure of the driftwood catching work according to this embodiment on the driftwood catching function. [Figure 12] It is a diagram showing the results of an experiment on the influence of the difference in the installation structure of the driftwood catching work according to this embodiment on the driftwood catching function (change in the driftwood rotation effect due to the difference in the supply flow rate). [Figure 13] It is a diagram showing the results of an experiment on the influence of the difference in the installation structure of the driftwood catching work according to this embodiment on the driftwood catching function (change in the driftwood rotation effect due to the difference in the driftwood diameter and water depth). [Figure 14] It is a diagram showing the results of an experiment on the influence of the difference in the installation structure of the driftwood catching work according to this embodiment on the driftwood catching function (change in the driftwood rotation effect due to the difference in the riverbed gradient change). [Figure 15] It is a diagram showing the results of an experiment on the influence of the difference in the installation structure of the driftwood catching work according to this embodiment on the driftwood catching function (change in the driftwood rotation effect due to the difference in the downstream extension of the driftwood). [Figure 16] It is a schematic diagram showing the installation structure variations of the driftwood catching work according to this embodiment. A is an elevation view in the side direction, and B is the same elevation view from the front direction. [Figure 17] It is a schematic diagram showing the installation structure variations of the driftwood catching work according to this embodiment. A is an elevation view in the side direction, and B is the same elevation view from the front direction.

Mode for Carrying Out the Invention

[0012] Preferred embodiments of the present invention will be described with reference to the drawings. Note that the embodiments shown below are merely examples, and various forms can be adopted within the scope of the present invention.

[0013] Figure 1 is a schematic diagram showing the driftwood trapping body 4 according to the present invention and an installation structure (driftwood trapping work 5) composed of multiple (two or more) driftwood trapping bodies 4, where A is an elevation view from the side and B is an elevation view from the front. The driftwood trapping work 5 according to this embodiment has an installation structure in which, in plan view, multiple (two or more) driftwood trapping bodies 4 are arranged at approximately straight lines and spaced apart in the direction transverse of the river 6 on the mountain side of the protected object 3 such as roads and houses, in order to prevent driftwood 2 that flows down the river 6 together with the flowing water 7 from mountainous areas 1 such as where trees that cause driftwood 2 to be generated to hit protected object 3 such as roads and houses. The driftwood trapping body 4 is equipped with a cylindrical driftwood trapping column member 12 for capturing driftwood 2 by allowing the flowing water 7 to pass through, and a pile foundation 11 for stabilizing against external forces (load-bearing capacity) caused by collisions as the driftwood 2 flows down. Furthermore, in order to address deterioration and damage to the driftwood trapping body 4 over time during maintenance, the structure is equipped with a concave insertable joint 13 for vertically joining the driftwood trapping column member 12 and the pile foundation 11 and fixing them in the horizontal direction. The horizontal spacing of the driftwood trapping bodies 4 that constitute the driftwood trapping structure 5 according to this embodiment shall be within half the maximum length of the driftwood 2 as indicated in the Commentary on the Design Technical Guidelines for Debris Flow and Driftwood Countermeasures (P72) of the Guidelines for Formulating Basic Plans for Sediment Control (Debris Flow and Driftwood Countermeasures) (P36) of the Guidelines for Formulating Basic Plans for Sediment Control stipulated by the Ministry of Land, Infrastructure, Transport and Tourism. In this embodiment, the driftwood trap 5 is installed vertically and independently on the ground 14, and it is desirable for maintenance purposes to install it as widely as possible to avoid blockage by anything other than driftwood 2. The material constituting the driftwood trap 4 can be selected from metal, wood, composite plastic, etc., from the viewpoint of strength and durability. In the maintenance of the driftwood trapping structure 5 according to this embodiment, the status of the driftwood trapping structure 5, such as its driftwood trapping function and load-bearing capacity, is grasped through periodic on-site inspections after installation, and if it is blocked, the obstructing material is removed as necessary to restore its function.

[0014] Figure 2 is a perspective view showing the driftwood trapping body 4 according to the present invention. The driftwood trapping body 4 according to this embodiment comprises a driftwood trapping column member 12 and a pile foundation 11. The driftwood trapping column member 12 is inserted into an insertable joint 13 located at the top of the pile foundation 11 in the vertical axis direction and joined thereto, and is particularly fixed against external forces from the horizontal direction. Furthermore, in maintenance management after installation of the driftwood trapping body 4, the driftwood trapping column member 12 can be replaced as needed by attaching and detaching it in the vertical axis direction. In addition, when the pile foundation 11 is struck or pressed in the penetration direction, it is possible for it to automatically rotate and penetrate into the ground 14.

[0015] Figure 3 shows a pile foundation 11 according to the present invention. The pile foundation 11 according to this embodiment is an underground foundation structure used as the foundation of a structure, and comprises a pile body 21 and an insertable joint 13. The pile body 21 is a rod-shaped portion having a tapered pile tip 22 that gradually decreases in diameter in the direction of penetration and a pile base 23 with a constant axial diameter, and the pile head 26 of the pile foundation 11 is struck or pressed in the direction of penetration. The spiral portion 24 is formed in a spiral shape along the outer surface of the pile body 21, and has a spiral-shaped wing surface 25 that converts the reaction force from the ground 14 when the pile body 21 penetrates the ground 14 into a rotational force of the pile body 21.

[0016] Since the pile tip 22 has a tapered shape that gradually decreases in diameter in the direction of penetration, when the pile head 26 of the pile foundation 11 is struck or pressed, the pile body 21 can advance through the ground 14 without disturbing the surrounding ground by pushing the soil constituting the ground 14 laterally in the direction of penetration. Depending on the properties of the ground 14 into which the pile foundation 11 is driven and the material of the pile foundation 11, for example, if the outer surface of the pile tip 22 gradually decreases in diameter in the direction of penetration so that it is at an inclination angle of 10 degrees or less with respect to the central axis of the pile body 21, then in the case of ground 14 composed of soil and sand, the pile body 21 can advance through the ground 14 without disturbing the surrounding ground, regardless of the properties of the ground 14.

[0017] The spiral section 24 receives the reaction force from the ground 14 when the pile head 26 of the pile foundation 11 is struck or pressed. The spiral wing surface 25 converts this reaction force into rotational force for the pile body 21, thereby rotating the pile foundation 11. The spiral section 24 also exhibits bearing capacity in the penetration direction and pull-out resistance when penetrated. Therefore, the spiral section 24 has sufficient strength to not undergo plastic deformation even when subjected to the reaction force from the ground 14 when the pile head 26 of the pile foundation 11 is struck. The spiral section 24 also has a number of turns sufficient to allow the pile body 21 to rotate. The strength of the spiral section 24 is determined by its thickness, shape, material, etc. Therefore, for example, the thickness of the spiral section 24 is determined appropriately by considering the magnitude of the force applied to strike or press the pile head 26 of the pile foundation 11, the material of the pile foundation 11, the properties of the ground 14, the length from the outer surface of the pile body 21 to the outer edge of the spiral wing surface 25, the pitch of the spiral section 24, the ratio of the number of turns of the spiral section 24 to the total length of the pile body 21, and various other factors. Furthermore, although the number of turns of the spiral section 24 depends on the properties of the ground 14, the length from the outer surface of the pile body 21 to the outer edge of the spiral wing surface 25, etc., it is considered that the performance of the pile is efficiently realized by having at least two turns.

[0018] In the spiral section 24, the length from the outer surface of the pile body 21 to the outer edge of the spiral wing surface 25 gradually increases as you move from the upper end to the lower end of the pile body 21, while the outer diameter of the spiral wing surface 25 remains constant. Furthermore, in the lower end portion of the pile body 21, the length from the outer surface of the pile body 21 to the outer edge of the spiral wing surface 25 gradually decreases as you move in the direction of penetration, in order to allow the spiral section 24 to penetrate the ground more easily.

[0019] In this embodiment, the pile foundation 11 can be driven into the ground 14 by driving or pressing the pile head 26 of the pile foundation 11 using various methods such as impact, vibratory, or pressing. In the initial stages of penetration when the pile foundation 11 is not yet buried, the spiral portion 24 at the tip, whose diameter gradually decreases as it moves in the direction of penetration, gradually becomes embedded in the ground. As a result, the spiral portion 24, which receives the reaction force from the ground 14 when the pile head 26 of the pile foundation 11 is driven or pressed, gradually begins to exert a rotational force that rotates the pile foundation 11. Then, the spiral portion 24 begins to be embedded in the ground. As the spiral portion 24 receives the reaction force from the ground, a sufficient rotational force is obtained to rotate the pile body 21, and as it is embedded in the ground 14, the pile body 21 can be rotated sufficiently.

[0020] With the pile foundation 11 according to this embodiment, if the pile head 26 of the pile foundation 11 is struck or pressed using various methods such as impact, vibratory, or pressing methods, it will autonomously rotate and penetrate into the ground 14. Therefore, there is no need to use a rotary penetration machine that presses and rotates the pile while penetrating into the ground 14. In other words, with the pile foundation 11 according to this embodiment, there is no need to use a large rotary penetration machine, which improves constructability and reduces costs.

[0021] Furthermore, the pile foundation 11 according to this embodiment has a tapered shape at the pile tip 21, which gradually decreases in diameter in the direction of penetration, thus providing high penetration capability. Therefore, compared to piles that do not have a tapered tip, the impact force or pressing force applied to the pile is relatively small. Consequently, for example, with the pile foundation 11 according to this embodiment, even if the supporting layer is located somewhat deep below the ground surface, the pile foundation 11 can easily reach the supporting layer in the ground 14.

[0022] As shown in Figure 3, the spiral section 24 is formed spirally along the central axis of the pile body base 21 at a uniform pitch. If the spiral section 24 is formed spirally along the central axis of the pile body base 21 at a uniform pitch, when the pile foundation 11 penetrates the ground 14, the spiral section 24 can easily advance spirally through the ground 14 without scraping the surrounding ground. However, the spiral section 24 is not limited to being formed at a completely uniform pitch along the central axis of the pile body base 21; for example, the pitch near the tip may be slightly different from other parts.

[0023] Furthermore, although Figure 3 shows a pile body base 21 having a pile base 23 with a constant axial diameter, the pile foundation 11 according to this embodiment is not limited to having a pile base 23. In the pile foundation 11, most of the pile body base 21 gradually decreases in diameter in the direction of penetration, and the pile base 23 may be omitted.

[0024] Furthermore, Figure 3 shows a spiral portion 24 formed in a spiral shape along the outer circumferential surface of the pile tip portion 21 and the outer circumferential surface of the pile base portion 23, but the pile foundation 11 according to this embodiment is not limited to this form. The spiral portion 24 may be formed only on all or part of the outer circumferential surface of the pile tip portion 21, and may be omitted from the outer circumferential surface of the pile base portion 23.

[0025] Figure 4a is a perspective view showing a driftwood catching column member 12 according to the present invention. The driftwood catching column member 12 according to this embodiment comprises a cylindrical body 41 that is inserted into and fixed to an insertable joint 13 installed in the ground 14, and an elongated reinforcing device 42 provided inside the cylindrical body 41.

[0026] Figure 4b is a top view showing an elongated reinforcing device 42 provided inside the cylindrical body 41 of the driftwood capture column member 12 according to the present invention. The reinforcing device according to this embodiment has an outer cylinder 43 made of a regular square cylinder having four corners 43a and four faces 43b, and an inner cylinder 44 made of a regular square cylinder having four corners 44a and four corners 44b, which is mounted inside the outer cylinder 43. Each corner 44a of the inner cylinder 44 is in contact with the face 43b corresponding to the outer cylinder 43. In this embodiment, each corner 44a of the inner cylinder 44 is welded and fixed to the central portion 43c of the corresponding surface 43b of the outer cylinder 43. In this embodiment, the central portion 43c of the corresponding surface 43b of the outer cylinder 43 is the central portion between the corners 43a of the outer cylinder 43. Since each corner 44a of the inner cylinder 44 abuts against the central portion 43c of the corresponding surface 43b of the outer cylinder 43, the outer cylinder 43, which is made of a regular square cylinder, and the inner cylinder 44, which is also made of a regular square cylinder, are arranged in a shape that is similar to each other but rotated by 45°. The reinforcing device 42 according to this embodiment is composed of an outer cylindrical body 43 and an inner cylindrical body 44 that are similar in shape to each other and rotated by 45°, thereby giving the reinforcing device 42 itself high bending rigidity. The central portion 43c of the corresponding surface 43b of the cylindrical body 43 is the central portion between the corners 43a of the outer cylinder body 43. Since each corner 44a of the inner cylinder body 44 abuts against the central portion 43c of the corresponding surface 43b of the outer cylinder body 43, the outer cylinder body 43, which is made of a regular square cylinder, and the inner cylinder body 44, which is also made of a regular square cylinder, are arranged in a shape that is similar to each other but rotated by 45°.

[0027] Figure 5 is a side view showing an example of a driftwood trapping body 4 according to this embodiment. In this embodiment, a portion of the lower part of the cylindrical body 41 and reinforcing device 42 that constitute the driftwood trapping column member 12 are inserted into a concave insertable joint 13 on the upper part of the pile foundation 11 and embedded in the ground 14. The lower part of the cylindrical body 43 and reinforcing device 42 are then excavated manually using a shovel or a simple rock drill, and in the space secured within the ground 14, they are reinforced by being surrounded by mortar 31 that fills the space within the ground 14. Note that concrete or crushed stone may be used instead of mortar 31. The standard lengths and structure of the driftwood capture body 4 according to this embodiment are shown in Figure 5, and can be modified according to the installation conditions. The length L1 from the ground surface 14 to the upper end of the driftwood capture body 4 is the length necessary to capture the driftwood 2, and the length L2 from the ground surface 14 to the lower end is determined by the load expected when the driftwood 2 collides with the body and the strength of the ground 14. Other lengths should be determined similarly as necessary. <Example 1> Next, we will describe an example of an experiment concerning the load-bearing performance of the driftwood trapping body 4. A 1 / 1 scale model of the driftwood trapping body 4, which is composed of a pile foundation 11 and a driftwood trapping column member 12, will be created, and the stability performance of the driftwood trapping body 4 will be examined in response to the impact of driftwood 2, which is assumed to be flowing down by a debris flow. Figure 6 is a schematic diagram showing an overview of the load-bearing capacity experiment conducted in this invention, and Figure 7 is a table showing the conditions for the load-bearing capacity experiment conducted in this invention. As shown in Figures 6 and 7, the stability was evaluated by assuming that an iron block 51 weighing 1805 kg was impacted horizontally at a height of 200 mm into the driftwood trapping body 4 at a generally assumed maximum velocity of 47.1 km / h for a debris flow. The total length of the driftwood trapping column member 12 was 850 mm, and the total length of the pile foundation was also 850 mm. The results of this impact test showed that driftwood trap 4 could adequately resist external forces, although it deformed in some areas. As described above, the proposed driftwood trapping pile 4 is considered to be a useful structure that is generally capable of capturing driftwood 2 that flows down with debris flows. <Example 2> Next, we will describe an example of an experiment regarding the capture function of the driftwood capture structure 5. Based on past disaster cases caused by driftwood 2, we will examine the impact of differences in the placement conditions of the proposed driftwood countermeasure structure 5 in mountainous watersheds 1 and forest areas on its capture function. Here, when installing the driftwood capture structure 2 in rivers 6, etc., there are generally concerns about blockages caused not only by driftwood 5 but also by debris, etc. Furthermore, it is necessary to consider securing additional land when capturing driftwood 2 and daily maintenance (inspection, maintenance and repair). In this regard, the impact of changes in the flow directly upstream of the driftwood capture structure 5 should be considered. Figure 8 is a schematic diagram illustrating the rotation mechanism of driftwood 2 in water as expected by the present invention. However, when affected by a sudden change from a gentle slope to a steep slope, the driftwood 2 rotates in the direction of the flow (for example, the difference of flow velocity Vn±1 shown in Figure 8 affects the rotational force + ωn of the driftwood 2), and there is concern that the commonly used spacing of the driftwood traps 4 (half the maximum length of driftwood that may flow down, as indicated in the Commentary on the Design Technical Guidelines for Debris Flow and Driftwood Countermeasures by the Ministry of Land, Infrastructure, Transport and Tourism) will not function sufficiently, and the driftwood 2 will pass straight through the space between the driftwood traps 4. On the other hand, if the spacing between the driftwood traps 4 is significantly narrowed, a great deal of additional maintenance will be required to prevent blockage by debris and other materials on a daily basis. Therefore, in order to effectively capture driftwood 2 even when the relatively wide driftwood traps 4 are spaced far apart, we propose an installation structure for the driftwood trap 5 that rotates the driftwood 2 in a direction in which the driftwood trap 5 is advantageous (as shown in Figure 8, perpendicular to the flow: θn+1 is large), focusing on installation in flat areas such as debris flow deposits and roadsides where the flow is generally expected to change significantly (change from rapid to slow flow: +ωn). Here, we will discuss the expected rotation of driftwood 2 (Figure 8) as it flows from a steep channel to a gently sloping flat area, based on an experiment. Figure 9 is a schematic diagram showing the outline of an experiment conducted in this invention regarding the effect of differences in the installation structure of the driftwood capture structure 5 on the capture function of driftwood 2. As shown in Figure 9, assuming a scale of approximately 1 / 100 of the actual scale, water 61 (qin) and driftwood 2 (however, circular material, driftwood length 8 cm, specific gravity in dry state: approximately 0.75, manually introduced: introduction rate of approximately 1 piece / 0.5 seconds per hour) were supplied from the upstream of an inclined straight waterway 62 (width 10 cm), and the axial direction θn of the driftwood 2 was measured just before it was captured on the downstream flat floodplain 63. Figure 10 is a schematic diagram showing the definition of the evaluation of the driftwood rotation control effect in an experiment concerning the effect of differences in the installation structure of the driftwood capture structure 5 implemented in the present invention on the driftwood capture function. Regarding the input of driftwood 2, it is known that driftwood 2 flowing down in groups is easily captured, and in order to mitigate these effects, driftwood 2 is input individually. In addition, in order to ensure that differences in the supply conditions of driftwood 2 (initial input direction) do not affect the rotation control effect of driftwood 2 (Figure 8), the direction of driftwood 2 is input so that it is approximately the same in all directions within the horizontal plane of the flow. The inclination angle of the straight waterway 62 is based on the debris flow section (a general debris flow section of 10 degrees or more as shown in the commentary on the guidelines for formulating basic erosion control plans). Furthermore, the input position Lw of driftwood 2 and the evaluation position (capture structure position) Lp of the direction of driftwood 2 on the planar floodplain 63 are changed (Figure 9). In addition, preliminary experiments have already identified the effects of differences such as the mixing of sediment into water 61, the addition of branches to driftwood 2, and the rate at which driftwood 2 is introduced. To understand the effect of different experimental conditions on the rotation of driftwood 2, the flow rate of water 61 (qin), the channel gradient (straight channel 62: θw, flat flood platform 63: θp), and the diameter φ1 of driftwood 2 were varied, and the effect of controlling the rotation of driftwood 2 (Figure 10) under each condition was compared. In addition, to reduce the influence of manually introducing driftwood 2, the experiment was conducted three times under the same conditions to average the results. Figure 11 is a table showing the experimental conditions regarding the effect of differences in the installation structure of the driftwood capture structure 5 implemented in the present invention on the driftwood capture function. Regarding the rotation of driftwood 2 in the experimental results, the rotation effect of driftwood 2 (driftwood rotation rate) fc due to changes in the flow during evaluation is the ratio obtained by dividing n0 by nw. Here, n0 is the number of driftwood 2 at measurement position Lp on the planar flood platform 63 where θn was 45 degrees or more (Figure 10), and nw is the number of driftwood 2 supplied (Figure 9). The effect of differences in experimental conditions on the rotation effect of driftwood 2 will be discussed below. Figure 12 shows the results of an experiment concerning the effect of differences in the installation structure of the driftwood capture structure 5 according to this embodiment on the capture function of the driftwood 2 (changes in the driftwood rotation effect due to differences in the supply flow rate of water 61). As shown in Figure 12, the rotation effect of the driftwood 2 became more pronounced as the flow rate of water 61 increased. Observations during the experiment suggest that when the driftwood 2 is transported from the straight channel 62 to the flat floodplain 63, the driftwood 2 rotates due to the influence of the difference in flow velocity generated upstream and downstream (Figure 8), and this is thought to be because the difference in flow velocity upstream and downstream became more pronounced as the flow rate of water 61 increased. Figure 13 shows the results of an experiment concerning the effect of differences in the installation structure of the driftwood capture structure 5 according to this embodiment on the capture function of driftwood 2 (changes in the rotation effect of driftwood 2 due to differences in the diameter of driftwood 2 and the depth of water 61). As shown in Figure 13, the rotation effect became more pronounced as the diameter of the driftwood 2 decreased and the depth of water 61 increased. Observations during the experiment suggest that this is because the difference in flow velocity between the upstream and downstream areas became more pronounced as the water 61 (flow rate) increased, and the driftwood 2 became more susceptible to the influence of the flow as its weight decreased. Therefore, it is considered that in the upstream areas where the width of the river 6 is narrow and the size of the driftwood 2 flowing downstream is small, the driftwood is particularly susceptible to the influence of the flow. Figure 14 shows the results of an experiment concerning the effect of differences in the installation structure of the driftwood capture structure 5 according to this embodiment on the capture function of the driftwood 2 (changes in the rotational effect of the driftwood 2 due to differences in riverbed gradient). As shown in Figure 14, it was confirmed that changes in flow velocity influenced by the riverbed gradient affect the rotational effect of the driftwood 2 (Figure 8). Figure 15 shows the results of an experiment concerning the effect of differences in the installation structure of the driftwood capture structure 5 according to this embodiment on the capture function of the driftwood 2 (changes in the rotation effect of the driftwood 2 due to differences in the length of the driftwood 2's flow). As shown in Figure 15, it was confirmed that the length of the driftwood 2's flow had almost no effect on the rotation effect of the driftwood 2. Observations during the experiment suggest that the rotation of the driftwood 2 mainly occurs near changes in the flow velocity of the water 61, as mentioned above. Based on these results, it is considered that by utilizing the topography and associated flow changes found in flat areas between roads and valleys, or in the sedimentation areas of existing dams, it is possible to economically arrange the driftwood capture bodies 4 of the driftwood capture structure 5 at relatively wide intervals, which is rational in terms of maintenance and land use. <Example 3> This shows an example of the installation of the driftwood capture structure 5 of the present invention in a sediment deposit area 72 directly upstream of a weir 71. Figure 16 is a schematic diagram showing variations in the installation structure of the driftwood capture structure 5 according to the present invention, where A is an elevation view from the side and B is an elevation view from the front. As shown in Figure 16, the weir 71 is at the confluence of two rivers 6 (mountainous section 1) upstream, and the flow is concentrated in the center of the river channel by a spillway (water passage) wing section about 1 m high. It is considered effective to arrange the driftwood capture structures 5 in a roughly fan shape in a plan view directly upstream of this spillway to capture the driftwood. Furthermore, according to the partnership conditions, if it is desired to avoid capturing driftwood 2 in the driftwood capture structure 5, in a plan view, the structure shall be installed spaced apart in a roughly inverted fan shape opposite to the flow direction in order to transport a portion of the driftwood 2 to the outside of the transverse direction of the weir 71. Also, in a plan view, if the river 6 flows meandering rather than in a straight line due to the surrounding topographic conditions, the structure shall be installed spaced apart in the transverse direction of the river 6, taking into account the meandering topographic conditions. On the other hand, since this watershed is in the upper reaches, the drainage area is small, and the water depth of the flowing water 7 passing through the spillway is considered to be shallow. Therefore, as an alternative to conventional driftwood trapping piles (minimum total length: 2m), a new, smaller driftwood trapping body (total length of driftwood trapping column member 12: 850mm) is provided. <Example 4> This shows an example of the installation of the driftwood capture structure 5 of the present invention on a flat area 82 adjacent to a road 81. Figure 17 is a schematic diagram showing variations in the installation structure of the driftwood capture structure 5 according to the present invention, where A is an elevation view from the side and B is an elevation view from the front. As shown in Figure 17, the driftwood capture structure 5 is installed in a plan view, spaced approximately in a straight line along the road 81 adjacent to the road 81, taking advantage of the topographical conditions of the flat area 82 located between the road 81 and the river 6 in the mountainous area 1. Similarly, a small driftwood capture body 4 (total length of driftwood capture column member 12: 850 mm) is used. [Explanation of Symbols]

[0028] 1 Mountain area 2 Driftwood 3. Roads, houses, and other structures subject to preservation. 4. Driftwood trap 5. Driftwood Capture Work 6 Rivers 7 Running water 11. Pile foundation 12 Driftwood catching post member 13 Insertion type fittings 14 Ground 21 Pile Body Headquarters 22 Pile tip 23 Pile base 24 Spiral section 25 Spiral-shaped blade surface 26 Pile head 31 Mortar 41 Cylindrical body 42 Reinforcement device 43 Outer cylinder 44 Inner tube 45 caps 43a Corner 43b side 43c central part 44a Corner 44b side 51 Iron mass 61 water 62 straight waterway 63 Flat flood platform 64 pumps 71 Dam 72 Sediment land 81 Road 82 Flat land

Claims

1. These driftwood traps are installed in rivers and plains on the mountain side of the conservation area. The driftwood trapping body is a pile foundation that, when the pile head is struck or pressed in the direction of penetration, autonomously rotates and becomes fixed within the ground, A driftwood trapping body characterized by comprising a driftwood trapping column member fixed to the aforementioned pile foundation.

2. The driftwood trapping body according to claim 1, characterized in that the pile foundation and the driftwood trapping column member are joined in a series by a detachable joint.

3. The aforementioned pile foundation comprises a rod-shaped pile body having a tapered pile tip that gradually decreases in diameter in the direction of penetration, The driftwood trapping body according to claim 1, further comprising a spiral portion having spiral-shaped wing surfaces formed spirally along at least a part or all of the outer circumferential surface of the pile tip portion of the outer circumferential surface of the pile body portion, and which converts the reaction force received from the ground when the pile body portion penetrates the ground into a rotational force of the pile body portion when the reaction force is received from the ground.

4. The driftwood trapping column member comprises a cylindrical body and The cylindrical body is provided with an elongated reinforcing device, The reinforcing device consists of an outer cylinder made of a rectangular tube having four corners and four faces, It has an inner cylinder which is inserted into the outer cylinder and is made up of a rectangular cylinder having four corners and four faces, The driftwood trapping body according to claim 1, characterized in that each corner of the inner cylinder abuts against the corresponding surface of the outer cylinder.

5. It consists of the driftwood trapping body according to any one of the multiple claims 1 to 4, The driftwood trapping structure is characterized in that the plurality of driftwood trapping bodies are installed with the horizontal spacing between the driftwood trapping column members being within approximately half of the expected maximum length of driftwood.

6. The installation structure for the driftwood trapping work described in claim 5, characterized in that the plurality of driftwood trapping bodies are installed spaced apart in a substantially straight line with respect to the river's transverse direction when viewed from above.

7. The driftwood trapping structure installation structure according to claim 5, characterized in that the plurality of driftwood trapping bodies are installed spaced apart in a substantially fan shape or substantially inverted fan shape when viewed from above.

8. The installation structure for a driftwood trapping structure according to claim 5, characterized in that the plurality of driftwood trapping bodies are installed spaced apart in a plan view along the meandering river crossing direction.

9. The installation structure for driftwood trapping work according to claim 5, characterized in that the multiple driftwood trapping bodies are installed at substantially straight line intervals along the roadside in a plan view.

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