Insert structure and ground reinforcement method

Abstract

To provide an insert structure and a natural ground reinforcement method that can form a uniform improved body over the entire length of a long steel pipe.SOLUTION: An insert structure 1 includes an injection tube 2 for injecting an inorganic natural ground improvement material into a long steel pipe P, an exhaust tube 3 for exhausting air from inside the steel pipe, and a packer 4 that is fixed to the injection and exhaust tubes and partitions the inside of the steel pipe into multiple injection sections R1 - R4 in the longitudinal direction. Furthermore, when the injection tube is inserted into the steel pipe, its length L is as such that the insertion tip reaches the front end part of the steel pipe, the injection tube is provided with multiple discharge holes 7a -7d in the longitudinal direction which are opened in every injection section, and the opened area of the discharge holes in each injection section becomes smaller from the insertion end side to the distal end side of the injection tube.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an insert structure that is inserted into a long steel pipe that has been driven into the ground where a tunnel has not yet been excavated, and a ground reinforcement method that uses the insert structure. [Background technology]

[0002] When excavating a tunnel, a method known as long steel pipe forepiling is known in which long steel pipes are cast into the ground around the tunnel in front of it and ground improvement material is injected into the long steel pipes to improve the ground (see, for example, Patent Document 1).

[0003] The long steel pipes are constructed by connecting several steel pipes each about 3 m long, so that multiple long steel pipes about 10 to 20 m long are cast around the periphery of the tunnel, and ground improvement material is injected into the long steel pipes through injection tubes inserted into the long steel pipes. Ground improvement materials are classified into urethane-based and inorganic types (cement-based and water glass-based), and when inorganic ground improvement materials are injected, the injection material 101 is equipped with one injection tube 102 and one exhaust tube 103, and the injection tube 102 is shorter than the exhaust tube 103 (see Figure 6(a)).

[0004] Injection work using such an injection material 101 is carried out according to the following procedure. First, after the steel pipe P is driven, the injection material 101 is inserted into the steel pipe P, and the opening of the steel pipe P is closed with a check valve 105 provided at the end of the injection material 101 (see FIG. 6(b)). Then, an injection adapter 108 provided at the end of the injection tube 102 is connected to an injection hose (not shown) extending from a pump that pressure-feeds the ground improvement material, and injection of the ground improvement material begins. The ground improvement material passes through the injection tube 102 and flows into the steel pipe P from the tip opening 102a of the injection tube 102. The ground improvement material that has flowed into the steel pipe P fills the inside of the steel pipe P, and then fills cracks in the ground G around the steel pipe P from discharge holes provided on the outer periphery of the steel pipe P. When the ground improvement material that has flowed into the steel pipe P reaches the tip of the steel pipe P, it flows through the exhaust tube 103 to the end of the steel pipe P and then flows out from the end of the exhaust tube 103 that protrudes from the check valve 105. After it is confirmed that the ground improvement material is flowing out from the end of the exhaust tube 103, the exhaust tube 103 is closed by bending it or the like, and injection continues, and injection is stopped when a predetermined injection amount or a predetermined injection pressure is reached. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-121073 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the injection tube 102 used in the above-mentioned ground reinforcement method has only one outlet for the ground improvement material, the tip opening 102a of the injection tube 102, and the long steel pipe P is cast at an angle of elevation. In addition, the inorganic injection material used as the ground improvement material has a large specific gravity of approximately 1.5, so the injection material tends to accumulate at the mouth of the steel pipe P. Therefore, in ground with large voids, the injection material may not be able to be filled all the way to the tip of the steel pipe, and a uniform improvement cannot be formed along the entire length of the steel pipe, making it difficult to achieve the desired ground improvement effect.

[0007] The present invention has been made to solve the above problems, and aims to provide an insert structure and a ground reinforcement method that can form a uniform improved body over the entire length of a long steel pipe. [Means for solving the problem]

[0008] The present invention is as follows. 1. An insert structure inserted into a long steel pipe installed in the ground where a tunnel has not yet been excavated, an injection tube for injecting an inorganic ground improvement material into the long steel pipe; an exhaust tube for exhausting air from inside the long steel pipe; and packers fixed to the injection tube and the exhaust tube for dividing the inside of the long steel pipe into a plurality of injection sections in the longitudinal direction, the injection tube has a length such that, when inserted into the long steel pipe, the insertion tip of the injection tube reaches the tip of the long steel pipe; The injection tube is provided with a plurality of discharge holes in the longitudinal direction, each of which opens to each of the injection sections, An insert structure characterized in that the opening area of ​​the discharge hole for each injection section decreases from the insertion end side to the distal end side of the injection tube. 2. The insert structure according to 1 above, wherein the discharge holes are arranged so that one is open for each of the injection sections. 3. A ground reinforcement method using the insert structure described in 1. or 2. above, A ground reinforcement method characterized by: casting a plurality of long steel pipes into ground where a tunnel has not yet been excavated; inserting the insert structure into the long steel pipes; injecting inorganic ground improvement material from each of the discharge holes of the injection tube into each of the injection sections separated by the packers; and allowing the ground improvement material to penetrate into cracks in the surrounding ground through discharge holes provided on the outer periphery of the long steel pipes. [Effects of the Invention]

[0009] According to the present invention, in preliminary ground reinforcement during tunnel excavation, a long steel pipe is cast into the ground where the tunnel has not yet been excavated, an insert structure is inserted into the long steel pipe, and an inorganic ground improvement material is injected from each discharge hole of the injection tube into each injection section separated by packers, and the ground improvement material penetrates into cracks in the surrounding ground through discharge holes provided on the periphery of the long steel pipe. This allows the inorganic ground improvement material to be filled up to the tip of the long steel pipe, even in ground with large voids, and a uniformly improved body can be formed along the entire length of the long steel pipe. [Brief explanation of the drawings]

[0010] The present invention will be further described in the following detailed description, which provides non-limiting examples of exemplary embodiments according to the present invention, and with reference to the several figures mentioned, in which like reference numerals refer to like elements throughout the several views of the drawings. [Figure 1] 1A and 1B are explanatory views of an insert structure according to an embodiment, in which FIG. 1A shows an assembled state and FIG. 1B shows an exploded state. [Figure 2] 1A and 1B are explanatory views of a packer according to an embodiment, in which (a) is a front view and (b) is a side view. [Figure 3] 1A and 1B are explanatory views of a check valve according to an embodiment, in which FIG. 1A is a front view and FIG. 1B is a side view. [Figure 4] 1A and 1B are explanatory diagrams of the natural ground reinforcement method (steel pipe installation step) according to the embodiment, in which (a) shows a longitudinal section along the axial direction of the tunnel, and (b) shows a cross section perpendicular to the axial direction of the tunnel. [Figure 5] An explanatory diagram of the ground reinforcement method (improvement material injection process) according to the embodiment, where (a) shows the state in which an insert structure has been inserted into a steel pipe, and (b) shows the state in which an improvement body has been formed along the entire length of the steel pipe. [Figure 6] 1 is an explanatory diagram of a conventional ground reinforcement method, where (a) shows the injection material and (b) shows an enlarged view of the mouth side of the steel pipe into which the injection material has been inserted. DETAILED DESCRIPTION OF THE INVENTION

[0011] The matters set forth herein are for illustrative purposes only and are intended to provide an illustrative description of the embodiments of the present invention, with the aim of providing what is believed to be the most effective and easily understandable explanation of the principles and conceptual features of the present invention. In this regard, it is not intended to show structural details of the present invention beyond the extent necessary for a fundamental understanding of the present invention, and the description, taken together with the drawings, will make clear to those skilled in the art how some forms of the present invention may be actually embodied.

[0012] Hereinafter, the present invention will be specifically described by way of embodiments with reference to the drawings.

[0013] 1, the insert structure 1 of this embodiment comprises one injection tube 2 for injecting an inorganic ground improvement material into a long steel pipe P, one exhaust tube 3 for exhausting air from inside the long steel pipe P, and a plurality of packers 4 fixed to the injection tube 2 and the exhaust tube 3 for dividing the inside of the long steel pipe P into a plurality of injection sections R1 to R4 in the longitudinal direction (axial direction). Furthermore, the insert structure 1 comprises check valves 5 provided on the end sides (front sides) of the injection tube 2 and the exhaust tube 3.

[0014] Inorganic ground improvement materials include cement-based (cement milk, cement + accelerator, etc.), water glass-based (water glass + cement, water glass + acidic reactant, etc.), and special silica-based inorganic injection materials. Inorganic injection materials generally have lower viscosity than urethane-based injection materials, take longer to harden, and have a higher specific gravity. They are also highly recyclable and have a smaller environmental impact.

[0015] The injection tube 2 is made of a soft material (such as soft resin or rubber) and is flexible. The injection tube 2 has a length such that when the insert structure 1 is inserted into the long steel pipe P, its insertion tip reaches the tip of the long steel pipe P. In other words, the insertion length L of the injection tube 2 into the long steel pipe P is 70% (preferably 80%) or more of the total length of the long steel pipe P.

[0016] The injection tube 2 is provided with a plurality of discharge holes 7a-7d in the longitudinal direction (axial direction), each opening in each of the injection sections R1-R4. The discharge holes 7a-7d are arranged so that one discharge hole opens in each of the injection sections R1-R4. The discharge holes 7a-7d are formed in a planar circular shape. The opening area of ​​the discharge holes 7a-7d in each of the injection sections R1-R4 (i.e., the diameter of the discharge holes 7a-7d) decreases from the insertion end (tip end) of the injection tube 2 toward the end (near side). In other words, the injection tube 2 is provided with a plurality of discharge holes 7a-7d at the axial tip and middle portions, and the plurality of discharge holes 7a-7d have different diameters that decrease from the insertion end to the end (near side) of the injection tube 2. Furthermore, a packer 4 is disposed between adjacent discharge holes 7a-7d in the injection tube 2. An injection adapter 8 is connected to the rear end of the injection tube 2. An injection pump (not shown) is connected to the injection adapter 8. Furthermore, the tip opening of the injection tube 2 is closed with a rubber stopper 9.

[0017] In this embodiment, the diameter of discharge hole 7a is 8 mm, the diameter of discharge hole 7b is 7 mm, the diameter of discharge hole 7c is 6 mm, and the diameter of discharge hole 7d is 5 mm. However, the reduction ratio of the opening area of ​​discharge holes 7a to 7d is not particularly limited, and is selected appropriately depending on, for example, the driving angle of steel pipe P and the lengths of injection sections R1 to R4. Furthermore, the planar shape of discharge holes 7a to 7d is not particularly limited, and for example, discharge holes 7a to 7d that are polygonal in plan view may be used.

[0018] The exhaust tube 3 is made of a soft material (e.g., soft resin, rubber, etc.) and is flexible. The length of the exhaust tube 3 inserted into the long steel pipe P is longer than the length L of the injection tube 2 inserted into the long steel pipe P. Furthermore, the exhaust tube 3 has an exhaust hole 11 formed on its insertion end side (tip side). The exhaust hole 11 is arranged so as to be located in the compartment region R1 on the innermost side of the long steel pipe P when the insert structure 1 is inserted into the long steel pipe P. A mixer may be provided at the tip of the exhaust tube 3.

[0019] The packers 4 restrict the flow (leakage) of ground improvement material between adjacent injection sections R1-R4 while allowing the flow (leakage) of air. The packers 4 are made of an elastic material (sponge, soft rubber, etc.). The packers 4 have support holes 13 for supporting the tubes 2 and 3, as well as slits 14 extending from their outer peripheries to the support holes 13 (see Figure 2). The tubes 2 and 3 are inserted into the support holes 13 from the outer periphery of the packers 4 through the slits 14. The packers 4 are fixed to the tubes 2 and 3 by taping, adhesive, or other means. The packers 4 may also be configured by wrapping adhesive strips (elastic material) such as soft tape around the tubes 2 and 3. The restriction of the flow of ground improvement material by the packers 4 includes complete restriction of the flow as well as restriction of the flow with a very small amount of leakage.

[0020] In this embodiment, a configuration is adopted in which a long steel pipe P with a total length of 12 m is divided into four injection sections R1 to R4 (i.e., a configuration with three packers 4). However, the number of injection sections R1 to R4 and packers 4 is not particularly limited and can be selected appropriately depending on, for example, the total length of the long steel pipe P. Furthermore, in this embodiment, a configuration is adopted in which the length of injection section R1 is 3500 mm and the length of injection sections R2 to R4 is 3000 mm. However, the length of injection sections R1 to R4 is not particularly limited. For example, a configuration including multiple injection sections of the same length and one or more injection sections of different lengths may be adopted, or a configuration in which all injection sections have the same length or different lengths may be adopted.

[0021] The check valve 5 prevents the backflow of ground improvement material from the end of the long steel pipe P. The check valve 5 is made of an elastic material (such as rubber). The check valve 5 has insertion holes 16 through which the tubes 2 and 3 can be inserted (see Figure 3). The check valve 5 is fixed to the tubes 2 and 3 by taping, adhesive, or the like.

[0022] Next, we will explain a ground reinforcement method using the insert structure 1 configured as described above. In this ground reinforcement method, multiple long steel pipes P are cast into the ground G where the tunnel has not yet been excavated (see Figure 4), and the insert structure 1 is inserted into the long steel pipes P (see Figure 5). Then, an inorganic ground improvement material is injected from each of the discharge holes 7a-7d of the injection tube 2 into each of the injection sections R1-R4 separated by packers 4, and the ground improvement material penetrates into cracks in the surrounding ground through discharge holes 21 provided on the outer periphery of the long steel pipes P. In this case, the ground improvement material is injected into the ground, hardens, and forms an improved body A, thereby improving the ground G around the tunnel. Note that multiple discharge holes 21 are provided along the entire length of the steel pipe P.

[0023] Specifically, first, a plurality of long steel pipes P are driven into unexcavated ground G around the periphery of the tunnel by a known method. The steel pipes P driven into the ground in front of the tunnel extend diagonally and linearly with respect to the tunnel axis, and are spaced apart in the circumferential direction of the arch portion of the tunnel.

[0024] Next, the insert structure 1 is inserted into the steel pipe P, and the check valve 5 is fixed with a stopper (not shown). Then, by controlling the injection pump according to predetermined injection conditions, the ground improvement material is injected from the discharge holes 7a to 7d of the injection tube 2 into each of the injection sections R1 to R4 within the long steel pipe P. The ground improvement material injected into each of the injection sections R1 to R4 penetrates into voids and cracks in the ground G around the long steel pipe P through multiple discharge holes 21 provided on the outer periphery of the long steel pipe P, and solidifies to form an improved body A, thereby reinforcing the ground G.

[0025] When the ground improvement material is injected into each of the injection sections R1 to R4, the air inside each of the injection sections R1 to R4 leaks out from the end to the innermost end of the long steel pipe P in that order, and in the innermost injection section R1, it is exhausted from the exhaust hole 11 through the exhaust tube 3 to the outside of the steel pipe P. Furthermore, after it is confirmed that the ground improvement material filled in the innermost injection section R1 flows from the exhaust hole 11 through the exhaust tube 3 to the end of the steel pipe P and flows out from the end of the exhaust tube 3 protruding from the check valve 5, the exhaust tube 3 is closed by bending it, for example, and injection continues, and when the specified injection amount or injection pressure is reached, injection is stopped.

[0026] As described above, according to this embodiment, the insert structure 1 comprises an injection tube 2 for injecting an inorganic ground improvement material into the long steel pipe P, an exhaust tube 3 for exhausting air from inside the long steel pipe P, and a packer 4 fixed to the injection tube 2 and the exhaust tube 3 for dividing the inside of the long steel pipe P into a plurality of injection sections R1 to R4 in the longitudinal direction. Furthermore, the injection tube 2 has a length L such that, when inserted into the long steel pipe P, its insertion tip reaches the tip of the long steel pipe P, and the injection tube 2 is provided with a plurality of discharge holes 7a to 7d in the longitudinal direction, each opening in each of the injection sections R1 to R4, and the diameters of the discharge holes 7a to 7d for each of the injection sections R1 to R4 become smaller from the insertion end side of the injection tube 2 toward the end side. During preliminary ground reinforcement during tunnel excavation, a long steel pipe P is cast into the ground G where the tunnel has not yet been excavated, and an insert structure 1 is inserted into the long steel pipe P. An inorganic ground improvement material is injected from each of the discharge holes 7a-7d of an injection tube 2 into each of the injection sections R1-R4 separated by packers 4, and the material penetrates into cracks in the surrounding ground G through discharge holes 21 provided on the periphery of the long steel pipe P. As a result, even in ground G with large voids, the inorganic ground improvement material can be filled all the way to the tip of the long steel pipe P, forming a uniformly improved body A along the entire length of the long steel pipe P. In particular, even when the inorganic grouting material used as the ground improvement material has a high specific gravity, the grouting material does not accumulate at the mouth of the steel pipe P, enabling uniform improvement along the entire length of the steel pipe P, thereby enhancing the improvement effect.

[0027] Furthermore, in this embodiment, a small injection machine can be used because the ground improvement material is injected into each of the injection sections R1 to R4 from the multiple discharge holes 7a to 7d of the single injection tube 2. In contrast, a large injection machine must be used in an embodiment in which the ground improvement material is injected into each of the injection sections from the respective discharge holes of multiple injection tubes.

[0028] Furthermore, in this embodiment, the discharge holes 7a to 7d are arranged so that one is open for each of the injection sections R1 to R4, which allows the diameter of each of the discharge holes 7a to 7d to be large, thereby preventing the discharge holes 7a to 7d from clogging with the ground improvement material.

[0029] Here, a discharge test of the injection tube 2 will be described. In this discharge test, the injection tube 2 used in the experimental example had a diameter of 8 mm for the discharge hole 7a, 7 mm for the discharge hole 7b, 6 mm for the discharge hole 7c, and 5 mm for the discharge hole 7d. On the other hand, the injection tube 2 used in the comparative example had a diameter of 8 mm for all of the discharge holes 7a to 7d. Then, water was fed into the injection tube 2 from the distal end at a rate of 15 liters / minute while tilted 3 degrees from the horizontal, and the discharge amount from each of the discharge holes 7a to 7d was measured. In the injection tube 2, the distance between the discharge holes 7a and 7b was 2100 mm, the distance between the discharge holes 7b and 7c was 3000 mm, and the distance between the discharge holes 7c and 7d was 3000 mm.

[0030] As a result, in the injection tube 2 of the experimental example, the discharge amount from discharge hole 7d was 3.5 kg, the discharge amount from discharge hole 7c was 3.5 kg, the discharge amount from discharge hole 7b was 3.6 kg, and the discharge amount from discharge hole 7a was 3.9 kg, so the discharge amounts from each of the discharge holes 7a to 7d were almost the same. Note that the discharge amount from the tip discharge hole 7a was slightly higher, but this was because the improved length at the tip was set to 3.5 m and the other improved lengths were set to 3.0 m.

[0031] In contrast, in the comparative example of the injection tube 2, the discharge amount from the discharge hole 7d was 11 kg, the discharge amount from the discharge hole 7c was 3 kg, the discharge amount from the discharge hole 7b was 1 kg, and the discharge amount from the discharge hole 7a was 0 kg (i.e., no water reached the discharge hole 7a).

[0032] The present invention is not limited to the embodiment, and various modifications can be made within the scope of the present invention depending on the purpose and application. That is, in the above embodiment, an example is given in which one discharge hole 7a-7d is opened for each of the injection sections R1-R4, but the present invention is not limited to this, and a configuration in which multiple discharge holes are opened in at least one injection section of the multiple injection sections R1-R4 may also be adopted.

[0033] The present invention is not limited to the above-described embodiments, and various modifications and variations are possible within the scope of the claims of the present invention. [Industrial Applicability]

[0034] The present invention can be widely used as a technology for injecting inorganic ground improvement materials for preliminary ground reinforcement work during tunnel excavation. [Explanation of symbols]

[0035] 1; insert structure, 2; injection tube, 3; exhaust tube, 4; packer, 7a-7d; discharge hole, P; long steel pipe, R1-R4; injection area, L; insertion length of the injection tube.

Claims

1. An insert structure inserted into a long steel pipe installed in unexcavated ground, an injection tube for injecting an inorganic ground improvement material into the long steel pipe; an exhaust tube for exhausting air from inside the long steel pipe; and packers fixed to the injection tube and the exhaust tube for dividing the inside of the long steel pipe into a plurality of injection sections in the longitudinal direction, the injection tube has a length such that, when inserted into the long steel pipe, the insertion tip of the injection tube reaches the tip of the long steel pipe; The injection tube is provided with a plurality of discharge holes in the longitudinal direction, each of which opens to each of the injection sections, An insert structure characterized in that the opening area of ​​the discharge hole for each injection section decreases from the insertion end side to the distal end side of the injection tube.

2. The insert structure according to claim 1 , wherein the discharge holes are arranged so that one is open for each of the injection sections.

3. A ground reinforcement method using the insert structure according to claim 1 or 2, A ground reinforcement method characterized by: casting a plurality of long steel pipes into ground where a tunnel has not yet been excavated; inserting the insert structure into the long steel pipes; injecting inorganic ground improvement material from each of the discharge holes of the injection tube into each of the injection sections separated by the packers; and allowing the ground improvement material to penetrate into cracks in the surrounding ground through discharge holes provided on the outer periphery of the long steel pipes.

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