Underground anchor

Abstract

We propose an anchor that can utilize the earth pressure of the soil and sand to efficiently add the resistance forces of multiple piles driven into the ground, and can obtain a specified lateral resistance force with a relatively shallow driving depth. [Solution] An anchor that can utilize multiple pile bodies installed underground as a single unit, comprising a base plate that restrains the positions of the pile bodies on the ground surface, a main pile body to which an object that applies a tensile force is connected, and an even number of secondary pile bodies that are installed in symmetrical positions with the line of action of the tensile force as the center line.

Description

[Technical Field]

[0001] The present invention relates to an anchor used in slope prevention works, slope protection works, avalanche prevention works, etc. [Background technology]

[0002] Ropes are laid on slopes to prevent rockfalls and to protect facilities from falling and rolling rocks in covered rockfall prevention works and pocket-type rockfall protection netting works. As tension forces are applied to the laid ropes depending on the situation, anchors are required to secure the ends of the ropes. Such anchors must be able to withstand the tension forces from the ropes. When there is bedrock, piles are driven into the bedrock. On the other hand, when installing anchors underground, various methods have been proposed to ensure resistance to the tension forces from the ropes, such as using anchors attached to concrete structures.

[0003] Generally, pouring concrete at the location where the rope anchor is to be installed can be difficult, so the following method has been proposed that does not involve pouring concrete. The tension in the rope is secured by the pull-out resistance of the pile body from the ground (H08-302677). The direction of the tensile force from the rope and the pull-out resistance of the pile must be aligned, and there are cases where it is not possible to secure a sufficient driving length to secure the pull-out resistance of the pile. A fixed plate that receives the bearing pressure from the pile body is installed on the contact surface of the ground, and its frictional resistance acts as a resistance to the tension of the rope (2003-239280). There is a limit to the length required to ensure bearing pressure from the tensile force of the pile body, and in some cases it may not be possible to ensure a large bearing capacity.

[0004] Anchor piles of a certain diameter are driven into the ground, and lateral resistance is utilized in the driving direction. In this case, there is a proposal to install an earth pressure plate to compensate for the driving depth (H08-302678). There is also a proposal to drive multiple anchor piles of a certain diameter in series into the mainland to provide lateral resistance (2024-160012).

[0005] Earth pressure plates provide resistance in the direction of the tensile force, and can provide a resistance proportional to the area of ​​the earth pressure plate, but they are installed close to the ground surface during construction, and cannot be installed deep below the ground surface where the earth pressure is greater, so their effectiveness is limited. Also, with regard to the proposal to provide resistance by driving multiple anchor piles, arranging them in series in the tensile direction does not allow for the additive effect of the pile resistance, and fluctuations in the distance between the piles can cause instability. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. H08-302677 [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-239280 [Patent Document 1] Japanese Patent Application Laid-Open No. H08-302678 [Patent Document 1] Japanese Patent Application Publication No. 2024-160012 Summary of the Invention [Problem to be solved by the invention]

[0007] We propose an anchor that utilizes the shear resistance caused by passive earth pressure in the soil and can efficiently add the resistance of multiple piles driven into the soil and can obtain a specified lateral resistance force with a relatively shallow driving depth. [Means for solving the problem]

[0008] An anchor consisting of multiple pile bodies installed in soil and sand, Among the pile bodies, a main pile body to which an object that applies a tensile force in the shear direction of the pile body is connected; An even number of sub-pile bodies installed in symmetrical positions with the line of action of the tensile force as the center line; A base plate that constrains the relative positions of the main pile body and the sub-pile body on the ground surface; Anchor with. [Effects of the Invention]

[0009] Multiple piles driven into the ground can be used as a single anchor to resist tensile forces parallel to the ground surface, maintaining the relative positions of the piles on the ground surface and providing resistance according to the load applied to the entire anchor.The overall resistance of an anchor using multiple piles can be achieved by additively utilizing the resistance of each pile. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is an explanatory diagram of an anchor using three pile bodies (Example 1). [Figure 2] 1 is an explanatory diagram of a base plate of the anchor of Example 1 (Example 1). [Figure 3] 1 is an explanatory diagram of a procedure for installing an anchor according to the first embodiment (first embodiment). [Figure 4] 1 is a graph comparing the tensile resistance of the anchor of Example 1 with the sum of the tensile resistance of the constituent pile bodies (Example 1). [Figure 5] FIG. 10 is an explanatory diagram of an anchor using three pile bodies according to Example 2 (Example 2). [Figure 6] 10 is a graph comparing the tensile resistance of the anchor of Example 2 with the sum of the tensile resistance of the constituent pile bodies (Example 2). DETAILED DESCRIPTION OF THE INVENTION

[0011] When a pile body is used as an anchor to ensure bearing strength in a direction parallel to the ground, the direction parallel to the ground is the direction in which the pile shears. The pile used has a certain diameter and sufficient shear resistance to the required lateral tensile force. Therefore, this specification does not consider shear failure of the pile body. In this specification, the bearing strength of an anchor refers to its resistance to the tensile force applied to the anchor, and this bearing strength is considered to be primarily due to the earth pressure generated in the soil in the ground. This refers to the earth pressure acting on the pile body and the earth pressure plate attached to the pile body, and this earth pressure is the adhesion and friction of the soil, which manifests the shear strength of the soil. The ability to support the pile body against lateral tensile force is generally considered to be resistance to tilting and overturning of the pile body, known as passive earth pressure. Although the base plate of this invention may generate slip resistance between the base plate and the ground as part of the anchor's bearing strength, this is not particularly considered. Furthermore, the phrase "the line of action of the tensile force is the center line" in the claims means that if a tensile material is indicated, it is within the tensile material, and the indication may be omitted. [Example]

[0012] Figure 1 shows an overall view of the anchor 1 of the present invention. Figure 1(1) is a schematic diagram of the anchor installation position, and in this example, it is used as an anchor for the suspension rope of a pocket-type rockfall protection net work. Figure 1(1) shows the projection direction of Figures 1(2) and (3). Figure 1(2) is a plan view, and Figure 1(3) is a front view from below the slope in and on the ground. Figure 1(4) is a right side view in and on the ground.

[0013] In the plan view of Figure 1 (2), a tension rope 11 is installed on a main pile body 21 using a cylindrical pipe anchor, and sub-pile bodies 22 of the same shape as the main pile body are shown symmetrically on either side of the tension rope. Each pile body 2 is installed by penetrating a base plate 3. Wing-shaped earth pressure plates 23 are fixed to the left and right of the main pile body. Each pile body is provided with a cap 25 and a cap stopper 26, and the cap stopper on the main pile body serves to prevent the tension rope hung on the tension force connection part 24 from coming off. In this example, reinforcing members (32, 33) are fixed to the base plate 3, which has a through-hole 31 for the pile body, and between the main pile body and the sub-pile body. Details will be explained in Figure 2.

[0014] The front view of Figure 1(3) shows the shapes of the main pile body 21 and the sub-pile body 22 extending through the base plate 3. The pipe anchor forming the pile body 2 is cylindrical (not shown), and a pipe pile driver can be inserted into it. The tip of the pipe anchor facing the ground is open, allowing the driver's driving section to be installed and the pile driver to drive the pipe anchor further into the ground. Also shown as an example is the attachment of the earth pressure plate 23 to the main pile body, along with its position. The left and right ends of the earth pressure plate are shown with dashed lines, as they are located behind the sub-pile body. The side view of Figure 1(4) shows the lateral positional relationship between the main pile body and the sub-pile body, and shows the shape of the earth pressure plate attached to the main pile body from the side.

[0015] Figure 2 shows a detailed view of the base plate 3, with Figure 2(1) being a plan view, Figure 2(2) being an AA cross-sectional view, and Figure 2(3) being a BB cross-sectional view. The dashed lines within the three pile penetration holes 31 shown in the plan view indicate the outline of the pile when penetrated. The through-holes are large enough to allow the pile to penetrate, but are small enough to fix the position of the pile on the base plate relative to changes in position measured when a tensile force is applied. Therefore, the base plate is a fixture that fixes the relative positions of the main pile body 21 and the sub-pile body 22. The base plate may be any plate-like fixture with sufficient thickness to withstand various stresses from the pile body. However, in this example, a steel plate as thin as possible is used with the necessary reinforcement, taking into account transportation to the anchor installation location and material costs. As shown in Figure 2(1), a through-hole protection ring 32 is provided around the periphery of the pile through-hole 31 in the base plate. This thick ring protects the base plate from various stresses, such as those caused by driving the pile body and tensile loads on the main pile body. In addition, a pile-to-pile load-transmitting reinforcement member 33 with a predetermined thickness and height is attached to the centerline between the pile through-holes of the main pile body and the sub-pile body. These protective and reinforcing members are attached to the steel base plate by welding, as shown in Figures 2(2) and 2(3). The base plate described in the claims is not limited to the plate material of Example 1, as long as it is a member that constrains the relative positions of the main pile and the sub-pile on the ground surface and can apply constant tensile and compressive forces to resist changes in relative position between the piles. Base plates made of a combination of rods are also included.

[0016] Figure 3 illustrates the installation procedure for this anchor. As a relatively simple anchor, a pile body 2 is installed in the soil and sand, and to ensure maximum bearing capacity, a driven pile is desirable, as it does not disturb the surrounding ground. A base plate 3 (see Figure 3(1)) is temporarily placed for the anchor to be installed in the designated location. A small air hammer, a compressor-driven pile driver, is then used to drill a casing with a diameter smaller than the outer diameter of the main pile body 21 and the sub-pile body 22, as shown in Figures 3(1) and 3(2), through the pile body through-hole 31 in the base plate. The air hammer body is located at the tip of the casing in Figure 3(2), and an air hose 27 for supplying compressed air is connected to the hammer. While only the main pile body is shown in this figure, trial drilling is performed at all pile installation locations. This is because it is necessary to check for boulders and bedrock at the pile installation location. Next, the base plate is removed and the main pile body is driven into the test hole using an air hammer. In this example, the main pile body is a pile body with an earth pressure plate, so it cannot be driven through the pile body through-hole in the base plate. After the main pile body is driven to a predetermined depth, the head of the main pile body is inserted into the pile body through-hole in the base plate. Next, the two sub-piles are driven into the test drilling position through the pile through-holes with an air hammer to the specified depth, completing the pile driving. Next, a rope 11 is hung on the main pile, which acts as a tension member, and a locking device 26 for the pile cover 25 is installed, which also serves to prevent the rope from coming off. The pile cover is then similarly attached to the sub-piles.

[0017] The experimental results of the tensile test on the anchor 1 of Example 1 are shown in Table 1. The experimental results on the pile body constituting the anchor are also shown, and the relationship between them is shown in Figure 4. The specifications of the pile body 2 in Table 1 and the anchor with base plate 1 of the present invention are as follows. Pipe pile body: Steel pipe anchor, outer diameter 114.3 mm, thickness 4.5 mm, length 1.63 m (including underground section 1.5 m) These piles are used as two sub-piles 22 in the present invention. Pipe pile with earth pressure plate: Steel pipe anchor, outer diameter 114.3 mm, thickness 4.5 mm, length 1.63 m (1.5 m in the center of the inland area) Earth pressure plate: Steel plate, 4.5 mm thick, 200 mm wide, 600 mm long (bottom edge processed), pipe anchors welded to the left and right, top edge is 500 mm from the ground Base plate: Steel plate, thickness 4.5 mm, width 600 mm, length 800 mm (processed into a hexagonal shape as shown in Figure 2, Through-hole protection ring: thickness 6 mm, width 60 mm, Inter-pile load transfer reinforcement member: width 6 mm, height 25 mm, length 300 mm) The experiment was conducted by applying a tensile force to the ground surface by rope, increasing it from a constant load by 5 kN (kilonewtons) each time, and measuring the displacement of the pile position above the ground surface for the secondary pile, the main pile with an earth pressure plate, and the anchor with base plate of Example 1. In the experiment, the displacement at the effective maximum tensile force was measured, and then the load was released and the remaining displacement was measured. In tensile tests of the pipe pile and the pipe pile with earth pressure plate separately, the effect of the earth pressure plate was clearly evident at loads exceeding 25 kN, but the effect of the earth pressure plate was not clear for measured values ​​of 20 kN or less. It is not clear whether this is due to variations in measured values ​​depending on the measurement location, measurement accuracy, or disturbance of the ground caused by driving the pipe pile with earth pressure plate. However, it is thought that this effect does not affect the entire experiment.

[0018] [Table 1]

[0019] The anchor in Example 1 has one main pile body and two sub-piles whose relative positions are fixed by a base plate. Therefore, it is estimated that the sub-piles not only synchronize with the displacement measured in the main pile body, but also have the same displacement in the same direction. Because there are two sub-piles, it is estimated that twice the load strength can be obtained for the same displacement of the pipe pile body, as shown in Table 1. Therefore, regarding the method for comparing loads at the same displacement, the bottom row of Table 1 shows a simple linear calculation of the load strength in 1mm increments for a 20kN load and 5mm measured displacement of the anchor with base plate. For the pipe pile body with earth pressure plate, the load strength is also calculated in 1mm increments, using the linear change in displacement between two adjacent points for each measurement. In this way, for the pipe pile body, as shown on the right side of the table, the load strength is 6.8kN for a 5mm displacement, and 5.3kN for the pipe pile body with earth pressure plate.

[0020] Next, for the two pipe piles corresponding to the sub-piles, a load of 6.8 kN × 2 is applied, and the load of the pipe pile with earth pressure plate corresponding to the main pile, 5.3 kN, is added to obtain a total of 18.9 kN. This value is close to the 20 kN measured with the base plate anchor of the present invention. Figure 4 shows a comparison of the simple sum of the displacements of the three piles due to the same displacement with the measured values ​​of the anchors. As shown in Figure 4, the simple sum and the measured values ​​of the anchors follow a similar upward-sloping curve. At loads of approximately 20 kN or less, they are roughly on the same curve, but as the load increases, the difference becomes larger, with the maximum measured value being approximately 20% lower than the estimated value. Note that for displacements of the pipe piles exceeding 61 mm, the corresponding load is calculated as a constant value. [Example]

[0021] Figure 5 shows an overall view of the anchor 1 of Example 2. Figure 5(1) is a plan view, and Figure 5(2) is a front view from below the slope in the ground and on the ground. Figure 5(3) is a right side view in the ground and on the ground. Compared to Figure 1(2) and Figure 1(3), Figure 5(1) and Figure 5(2) are the same except for the width (lateral length) of the earth pressure plates attached to the left and right sides of the main pile body. Figure 5(3) and Figure 1(4) are the same because the length of the earth pressure plates (longitudinal extension of the main pile) is the same.

[0022] For the anchor 1 of Example 2, an experiment similar to that of Example 1 was conducted, and the experimental results are shown in Table 2. The experimental results for the pile body constituting the anchor are shown, and the relationship with the simple addition is shown in Figure 6. The specifications of the pile body 2 in Table 1 and the anchor with base plate 1 of the present invention are all the same, except for the earth pressure plate of the main pile body described below. Earth pressure plate: Steel plate, 4.5mm thick, 300mm wide, 600mm long (bottom edge processed), pipe anchors welded to the left and right, top edge positioned 500mm from the ground.

[0023] [Table 2]

[0024] Table 1 is reproduced for the load-displacement of the pipe pile body in Table 2. The relationship between this pipe pile body, the pipe pile body with earth pressure plate in Table 2, and the base plate anchor of the present invention is shown in Figure 6. Pipe piles of 61 mm or more and pipe piles with earth pressure plate of 73 mm or more are treated in the same way as Figure 4, and the corresponding load is assumed to be constant. As in Figure 4, Figure 6 compares the load-displacement of the simple addition of the tensile resistance values ​​of the three piles with the load-displacement of the anchors. This graph also shows the same trends as Figure 4. In the low load range, the simple addition and the measured anchor values ​​are almost the same, and as the load increases, the difference becomes larger, forming an upward sloping curve. The measured anchor values ​​are up to about 20% lower than the estimated simple addition values. The curves are the same only when the load is approximately 40kN or less.

[0025] The effects of the present invention will be examined based on the experimental results of Examples 1 and 2, using the following equation 1. Equation 1(1) shows the earth pressure that a pile receives from the ground when a shear load of F acts on the pile. To prevent the pile from overturning, a passive earth pressure of p proportional to the depth acts vertically on the pile, and the resultant force is shown in the figure. Next, to estimate how the earth pressure acting on the pile is affected as stress in the ground, we will describe the relationship between position and stress in the ground based on Boussinet's theory of elasticity. Based on these, we will then show an iso-stress distribution diagram for a single pile and an assumed iso-stress distribution diagram acting on an anchor formed by combining multiple piles according to the present invention. Equation 1(3) is for the case of a single pile. In elasticity theory, some of the stresses that affect a semi-infinite area are estimated and expressed as three iso-stress lines. Equation 1 (4) assumes Example 1 and shows a main pile with an earth pressure plate and two sub-piles installed symmetrically about the centerline indicated by the dashed-dotted line. Similarly, equation (5) assumes Example 2, with different sizes of earth pressure plates. The conditions shown in each figure are approximately 20 kN for (4) and 40 kN for (5). As shown in this figure, in states (4) and (5), the stress distribution on the main pile is not affected by the sub-piles, and the sub-piles are not affected by each other. Therefore, as previously noted, in Example 1, at stresses below 20 kN, the simple addition of the resistance values ​​of the three piles is likely to roughly correspond to the tensile resistance value of the entire anchor. The same is true for Example 2. Therefore, the greater the spacing between the main pile and the sub-piles and the spacing between the sub-piles, the greater the additive effect of the resistance of each pile, but the larger and stronger the base plate becomes. The same applies to the distance between the positions of the secondary piles symmetrical to the center line shown in equations 1(4) and (5). However, in relation to the base plate, if they are close to the center line they are easily affected by the main pile, and there are issues with adding up the resistance forces of the individual piles. On the other hand, if they are farther away from the center line, the base plate is subjected to a large load due to the transfer of the tensile force. It is necessary to consider the appropriate number and placement of secondary piles.

[0026]

number

[0027] 1 Anchor for multiple piles and soil, 11 Pull rope 2 pile body, 21 main pile body, 22 sub-pile body, 23 pile body soil pressure plate, 24 tension force connection part, 25 pile body cover (cap), 26 cap stopper (fastening device), 27 air hose 3 base plate, 31 pile body through hole, 32 through hole protection ring, 33 inter-pile load transfer reinforcement member

Claims

1. An anchor for tensile forces in a direction parallel to the ground surface installed in soil and sand, a plurality of pipe pile bodies that are erected into the soil and sand ground substantially perpendicular to the ground surface, have shear resistance to an external force parallel to the ground surface on the upper tip of the pipe pile body, and have a width that can receive passive earth pressure against the inclination from the lower tip of the pipe pile due to the external force, thereby obtaining lateral resistance; A base plate that constrains the relative positions of the plurality of pipe piles on the ground surface; Equipped with The plurality of pipe piles include a main pipe pile connected to an object that applies a tensile force to the anchor in a direction parallel to the ground surface, and an even number of sub-pipe piles installed at positions symmetrical to the left and right with the line of action of the tensile force as the center line, The base plate is provided with a main pipe pile body through-hole and a secondary pipe pile body through-hole through which the pipe pile body passes, and a pile-to-pile load transmission reinforcement member that reinforces the transmission of the tensile force applied to the main pipe pile body to the secondary pipe pile body between the main pipe pile body through-hole and the secondary pipe pile body through-hole.

2. 2. The anchor according to claim 1, wherein the number of said secondary pipe piles is two.

3. 2. An anchor according to claim 1, further comprising through-hole protection rings around the periphery of the main pipe pile through-hole and the sub-pipe pile through-hole in the base plate to protect the base plate from the load caused by contact between the pipe pile and the base plate.

4. The anchor of claim 1, wherein an earth pressure plate is installed below the ground surface of the pipe pile body to provide resistance to the tensile force.

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