JP6723786B2 - Double structure casing and ground anchor construction method using the same - Google Patents

Description

The present invention relates to a double structure casing for penetrating into the ground, and a method of constructing a ground anchor using the same.

In the construction of the ground anchor, if the support layer is a ground with a relatively low degree of consolidation, the frictional stress between the ground and the anchor body is small by design, so the length that penetrates into the support ground (anchor body length) Need to be long. However, there is a maximum length of 10 m for the anchor body, and in order to prevent crossing the site boundary, the anchor body length is suppressed and the diameter of the drilling casing is increased to increase the required yield strength or even higher. Ensuring proof stress. That is, the ultimate yield strength of the anchor is “Pmax (kN)”, the effective diameter of the anchor (drilling diameter) is “Da (m)”, the anchor body length is “La (m)”, and the ultimate circumferential surface friction resistance between the ground and the anchor body Is defined as “τu(kN/m ² )”, the relationship of “Pmax=Da×π×La×τu” is satisfied. Therefore, in the ground where the frictional resistance (τu) with the anchor body is small, the anchor body length (La In order to secure a required proof stress (Pmax) while shortening (1), it is necessary to increase the drilling diameter to increase the effective anchor diameter (Da).

On the other hand, when performing construction of the ground anchor in a high water pressure environment, in order to prevent groundwater and backside sediment from spouting from inside the casing during construction, use a tension material (tendon) with a casing packer attached to the end. It is performed by inserting the casing packer into the casing (see, for example, Patent Document 1). At this time, generally, a casing packer having a size corresponding to the diameter of the casing used for construction is used. That is, for example, when constructing a ground anchor using a casing of φ135 mm, a casing packer for φ135 mm is used, and when constructing a ground anchor using a casing of φ165 mm, a casing packer for φ165 mm is used.

Further, in order to prevent the spouting of groundwater and the like from the casing, a water discharge force proportional to the area inside the casing acts on the casing packer installed in the casing. For example, comparing a casing of φ135 mm (inner diameter 106 mm) with a casing of φ165 mm (inner diameter 135 mm), the area in the casing of φ135 mm is “106 ² ×π/4=8820 mm ² ”, and the area in the casing of φ165 mm is “ 135 ² ×π/4=14307 mm ² ”. Therefore, the casing packer for Fai165mm, the casing packer for Fai135mm, "14307mm ² / 8820mm ² ≒ 1.62" times of flooding force will act.

Japanese Patent No. 3789992

Here, as described above, in order to secure the required yield strength while suppressing the anchor body length, when the diameter of the casing for hole drilling is increased, the size of the casing packer or the like installed in the casing is also increased accordingly. There is a need to. That is, an increase in the diameter of the casing causes an adverse effect that a device such as a casing packer used inside the casing before the diameter becomes large cannot be used. Also, if the size of the casing packer is increased according to the size of the casing, the weight of the casing packer also becomes heavier, so the work of attaching the casing packer to the tension member, the work of inserting the tension member into the casing, and after collecting the casing The work load is increased and the work efficiency is reduced when the work is removed. Further, as the casing packer becomes larger, the price of the casing packer itself increases. Further, since the water output force that is proportional to the area inside the casing acts on the casing packer, the casing packer installed in the casing with a larger diameter is subject to a greater burden, which results in expensive rubber wear. And the repair and maintenance costs increase. Further, if the casing packer were to be damaged, it would stop the jet of water and earth and sand against the water output greater than usual, increasing the risk of subsidence on the backside of the mountain.

The present invention has been made in view of the above problems, and an object thereof is to efficiently use a device used inside a casing in a plurality of casings having different outer diameters.

(Aspect of the invention)
The following aspects of the invention exemplify the constitution of the present invention, and are explained separately for each item in order to facilitate understanding of various constitutions of the present invention. Each section does not limit the technical scope of the present invention, while referring to the best mode for carrying out the invention, a part of the constituent elements of each section is replaced, deleted, or further The addition of the constituent elements of (5) is also included in the technical scope of the present invention.

(1) A casing for penetrating into the ground, an outer casing, an inner pipe having an outer diameter smaller than an inner diameter of the outer casing, the inner pipe being installed inside the outer casing, and a length of the inner pipe. in opposite ends, double structure casings grayed comprising a pair of sealing members subjected to sealing treatment in the gap between the inner tube and the outer casing.
The dual structure casing described in this section is used by penetrating into the ground during various construction works on the ground, and includes an outer casing, an inner pipe, and a pair of seal members. The inner pipe has an outer diameter smaller than the inner diameter of the outer casing, and is inserted and installed inside the outer casing. Further, the pair of sealing members seals a gap generated between the outer casing and the inner pipe arranged inside the outer casing at both longitudinal ends of the inner pipe.

Because of the structure as described above, for example, if the outer diameter of the outer casing is adjusted to the outer diameter of the general φ165 mm casing, and the inner diameter of the inner tube is adjusted to the inner diameter of the general φ135 mm casing, The equipment used inside the φ135 mm casing is also used inside the double structure casing having an outer diameter corresponding to the φ165 mm casing. That is, by installing the inner pipe inside the outer casing, the inner diameter of the double structure casing is reduced from the inner diameter of the outer casing to the inner diameter of the inner casing, so that the inner diameter of the inner pipe is the same as that of the inner pipe. The device that is supposed to be used in the casing that is used is also used in the inside of the double structure casing that has an outer diameter larger than the outer diameter of the casing. As a result, the device used inside the casing can be efficiently used in a plurality of casings having different outer diameters. Furthermore, since the gap between the outer casing and the inner pipe is sealed by the pair of seal members at both ends in the longitudinal direction of the inner pipe, even if the double structure casing is penetrated into the ground, it is not Etc. are prevented from flowing in. Further, if a casing that is in general circulation is used as the outer casing that constitutes the double structure casing, the manufacturing cost of the double structure casing can be suppressed.

(2) In the above (1), a dual structure casing used for construction of a ground anchor, wherein the outer casing has an outer diameter corresponding to a design effective diameter of the ground anchor (claim 1 ).
The dual structure casing described in this section is used for construction of a ground anchor, and the outer casing has an outer diameter corresponding to the design effective diameter of the ground anchor to be constructed. As a result, the hole penetrating the dual structure casing and drilled in the ground satisfies the design effective diameter of the ground anchor. Furthermore, as the equipment such as the casing packer used inside the double structure casing during the construction of the ground anchor, the equipment used in the casing having the same inner diameter as the inner diameter of the inner pipe of the double structure casing is used. It That is, it is not necessary to prepare a relatively large casing packer or the like matching the size of the outer casing, and a relatively small casing packer or the like matching the size of the inner pipe may be used. Therefore, the price of the casing packer and the like is suppressed, and the weight is also suppressed. Thereby, for example, when the casing packer is attached to the tension member, the tension member is inserted into the casing, and the removal work after the casing is recovered, the work load is reduced, and thus the work efficiency is improved. ..

In addition, the casing packer has a water output force that is proportional to the area inside the casing due to groundwater, earth and sand, etc. that flow backwards inside the casing, but the double structure casing described in this section has a smaller inner diameter than the outer casing. Since the casing packer is used inside the lowered inner pipe, the load on the casing packer is reduced. As a result, expensive rubber wear of the casing packer is suppressed, so that repair costs and maintenance costs of the casing packer are suppressed. Furthermore, even if the casing packer should be damaged, the risk of subsidence on the back of the mountain retaining can be reduced because it is possible to stop the jet of water and sediment against the water output proportional to the area of the inner pipe. To be done.

(3) In the above items (1) and (2), the inner pipe has a length shorter than that of the outer casing, and the position of one end in the longitudinal direction is aligned with the position of one end in the longitudinal direction of the outer casing. And a male screw structure is provided on the outer peripheral portion of the one end portion in the longitudinal direction of the outer casing, and a female screw that can be screwed with the male screw structure on the inner peripheral portion of the other end portion in the longitudinal direction of the outer casing. A dual structure casing provided with a structure (claims 2, 3).

In the double-structured casing of this section, the length of the inner pipe is shorter than the length of the outer casing, and in the inside of the outer casing, the position of one longitudinal end of the inner pipe is the length of the outer casing. It is arranged in accordance with the position of one end of the direction. Further, the present dual structure casing is provided with a male screw structure and a female screw structure capable of being screw-fitted to this male screw structure, and the male screw structure is provided on the outer peripheral portion of one end in the longitudinal direction of the outer casing. Is provided on the inner peripheral portion of the other end portion in the longitudinal direction of the outer casing. That is, since the inner pipe shorter than the outer casing is arranged inside the outer casing at one end in the longitudinal direction, the inner pipe is not arranged inside the other end in the longitudinal direction of the outer casing. Exists. A female screw structure is provided on the inner peripheral portion of such an area of the outer casing. With such a structure, the double-structured casings according to this section are not interfered with by the inner pipe arranged inside the outer casing, and the double-structured casings according to the present invention are screw-fitted via the male screw structure and the female screw structure. It is firmly connected.

(4) The double structure casing as described in (2) and (3) above, wherein urethane is injected into a gap between the outer casing and the inner pipe (claim 4 ).
In the double-structured casing described in this section, urethane is injected into the gap between the outer casing and the inner pipe, so that if the seal member that seals the end of this gap is damaged. However, the intrusion of groundwater, earth and sand, grout, etc. into the gap is prevented. Further, since urethane is lightweight, even if it is injected into the gap between the outer casing and the inner pipe, it hardly affects the weight of the double structure casing.

(5) A method of constructing a ground anchor in the ground by filling grout into the hole drilled while adding a casing to the rear end of the hole drilling bit and inserting a tensile material, and the design of the ground anchor is effective. An inner pipe having an outer diameter smaller than the inner diameter of the outer casing is inserted into the outer casing having an outer diameter corresponding to the diameter, and the outer casing and the inner pipe are provided at both longitudinal ends of the inner pipe. A method for constructing a ground anchor, wherein a double structure casing having a gap between the two is hermetically sealed is used as the casing (claim 5 ).

The construction method of the ground anchor described in this section is to construct the ground anchor in the ground by using the double structure casing. That is, the double structure casing has an outer casing having an outer diameter corresponding to the design effective diameter of the ground anchor to be constructed, and an inner pipe inserted into the outer casing, and both ends in the longitudinal direction of the inner pipe. In the section, the gap between the outer casing and the inner pipe is sealed. For this reason, the hole drilled in the ground using this double structure casing will be drilled with a diameter not less than the outer diameter of the outer casing, so the design effective diameter of the ground anchor to be created must be satisfied. Become.

Also, the dual structure casing will have, as a substantial inner diameter, the inner diameter of the inner tube which is downsized from the inner diameter of the outer casing. Therefore, due to the filling of the grout and the insertion of the tension material into the drilled holes, the various equipment used inside the double structure casing is a general casing with an inner diameter similar to the inner diameter of the inner pipe. You can use the device that is supposed to be used. Thereby, the equipment used inside the casing is both a double structure casing having an outer casing and an inner pipe, and a general casing having an inner diameter similar to the inner diameter of the inner pipe of the double structure casing, Common ones will be used. Furthermore, since the double structure casing used in this construction method seals the gap between the outer casing and the inner pipe at both longitudinal ends of the inner pipe, the gap may cause soil, sand, etc. Will never flow in. Further, in manufacturing the double structure casing, the manufacturing cost can be suppressed by using a casing which is generally in circulation and has an outer diameter corresponding to the design effective diameter of the ground anchor.

(6) In the above item (5), a boring step for boring a hole in the ground while adding the double structure casing to the rear end of the hole forming bit, and a grout for injecting grout into the double structure casing. Injecting step, and a casing packer having a size corresponding to the inner diameter of the inner pipe of the double-structured casing is attached to the rear end side of the tension member, and the tension member is inserted into the inner pipe. In the material insertion step and in a state where the casing packer is expanded inside the inner pipe, while pulling out the grout into the inner pipe from the rear in the drilling direction with respect to the casing packer, the double structure casing is pulled out. A method of constructing a ground anchor including a casing collecting step of collecting the ground anchor (claim 6).

The method for constructing the ground anchor described in this section includes a drilling step, a grout injection step, a tensile material insertion step, and a casing recovery step. In the drilling process, while adding the double structure casing to the rear end of the drill bit, for example, while pumping the drilling water from the rear end of the double structure casing at the rear end in the drilling direction into the inner pipe, Drill holes in. Therefore, as described in the above item (5), a hole that satisfies the design effective diameter of the ground anchor without water or earth and sand entering the gap between the outer casing and the inner pipe of the double structure casing. Is drilled. Also, in the grout injection step, for example, by inserting an injection hose into the inner pipe of the double structure casing to inject the grout, the drilling water filling the inside of the inner pipe in the drilling step is removed. Replace with grout from the tip side in the hole direction.

Further, in the pulling material inserting step, the pulling material having the casing packer attached to the rear end in the insertion direction is inserted into the inner pipe of the double structure casing. The casing packer used at this time is of a size corresponding to the inner diameter of the inner pipe of the double structure casing, and a casing packer for a general casing having an inner diameter similar to the inner diameter of the inner pipe is used. .. Therefore, as compared with the case of using a general casing having the same outer diameter as that of the outer casing of the double structure casing, a smaller casing packer is used. Price and weight are suppressed. As a result, the work load is reduced and the work efficiency is improved when the casing packer is attached to and removed from the tension member and the tension member with the casing packer is inserted.

In the casing recovery step, the casing packer is inflated with air inside the inner pipe, and the grout is pressure-fed into the inner pipe from the rear end side in the drilling direction from the position where the casing packer is arranged. The double structure casing that penetrated the ground in the process is pulled out and collected. At this time, the air pressure for inflating the casing packer is made larger than the pressure of water, earth and sand, etc. which try to flow backward in the double casing and jet, and the pressure for pumping the grout inflates the casing packer. Make pressure greater than air pressure. As a result, while the pumping of the grout is stopped, the casing packer expands and comes into close contact with the inner peripheral portion of the inner pipe, so that the spouting of water, earth and sand, etc. is prevented, and the grout is pumped during the pumping of the grout. The grout is supplied to the tip end side in the drilling direction of the double structure casing through a gap formed by the pressure between the casing packer and the inner pipe. Furthermore, since a gap is formed between the casing packer and the inner pipe, the frictional force disappears between the casing packer and the inner pipe, so that the casing packer does not follow the double structure casing that moves by pulling out. , The double structure casing is pulled out.

Furthermore, the method of constructing the ground anchor described in this section is such that the casing packer arranged in the inner pipe of the double structure casing has a water output force (that is, the outer diameter of the outer casing) that tries to flow backward in the inner pipe. With a similar outer diameter to the inside of a general casing that is smaller than the water output force that attempts to flow back inside a general casing. Only water output equivalent to hydraulic power) will be added. As a result, the load on the casing packer is reduced, so that repair costs and maintenance costs of the casing packer are suppressed. In addition, in the unlikely event that the casing packer is damaged, the risk of subsidence of the back of the mountain retaining due to the spouting of groundwater, earth and sand, etc. is reduced.

Since the present invention has the above-described configuration, it is possible to efficiently use the device used inside the casing in a plurality of casings having different outer diameters.

It is sectional drawing which shows the structure of the double structure casing which concerns on embodiment of this invention. It is a structural diagram showing an example of a casing packer used with a construction method of a ground anchor concerning an embodiment of the invention. It is a flowchart which shows an example of the procedure of the construction method of the ground anchor which concerns on embodiment of this invention. It is an image figure for demonstrating the soil drilling process in the construction method of the ground anchor which concerns on embodiment of this invention. It is an image figure for explaining a guide pipe driving process in a construction method of a ground anchor concerning an embodiment of the invention. It is an image figure for demonstrating the attachment process of the water stop box and the drill bit in the construction method of the ground anchor which concerns on embodiment of this invention. It is an image figure for demonstrating the drilling process in the construction method of the ground anchor which concerns on embodiment of this invention. It is an image figure for demonstrating the state of the drill bit at the time of drilling and completion of drilling. It is an image figure for demonstrating the grout primary injection|pouring process in the construction method of the ground anchor which concerns on embodiment of this invention. It is an image figure for demonstrating the tension material insertion process in the construction method of the ground anchor which concerns on embodiment of this invention. It is an image figure for explaining a casing packer operation process in a construction method of a ground anchor concerning an embodiment of the invention. It is an image figure for demonstrating the casing collection process in the construction method of the ground anchor which concerns on embodiment of this invention. It is an image figure for demonstrating the free packer operation process in the construction method of the ground anchor which concerns on embodiment of this invention. It is an image figure for explaining a mouth packer operation process in a construction method of a ground anchor concerning an embodiment of the invention. It is an image figure for demonstrating the free packer back surface injection process in the construction method of the ground anchor which concerns on embodiment of this invention. It is an image figure for explaining a tip replenishment pouring process in a construction method of a ground anchor concerning an embodiment of the invention. It is an image figure for demonstrating the tension|tensile_strength and fixing process in the construction method of the ground anchor which concerns on embodiment of this invention.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings. Here, throughout the drawings, the same portions or corresponding portions are denoted by the same reference numerals.
First, a double structure casing according to an embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1( a ), the double-structured casing 10 is roughly configured by a cylindrical outer casing 12 and an inner casing 14 which is installed inside the outer casing 12. The inner pipe 14 has a shorter length than the outer casing 12, and the left end portion in the figure of the inner pipe 14 is installed so as to match the left end portion of the outer casing 12 in the diagram. Further, a pair of annular seal members 16A and 16B is installed at both ends of the gap C between the outer casing 12 and the inner pipe 14 in the left-right direction in the drawing, whereby the gap C is sealed. There is. Further, urethane is injected into the clearance C before being sealed by the seal members 16A and 16B. The gap C may be filled with a material other than urethane, or may be hollow.

Further, in the double structure casing 10, a male screw structure 18 is formed on the outer peripheral portion of the left end portion of the outer casing 12 in the drawing. In addition, the inner pipe 14 having a shorter length than the outer casing 12 is installed inside the outer casing 12 so as to be left-justified in the drawing, so that the inner pipe 14 is in a range where the inner pipe 14 is not arranged. An internal thread structure 20 that can be screwed into the external thread structure 18 is formed on the inner peripheral portion of the end portion. As a result, as shown in FIG. 1B, the male screw structure 18 of the one double structure casing 10 and the female screw structure 20 of the other double structure casing 10 are screw-fitted to each other, whereby the double structure The casings 10 are connected to each other.

The double structure casing 10 having such a structure has, for example, a length of about 1.5 m, which is the same as a standard casing, and the outer and inner diameters of the outer casing 12 are general φ165 mm casings. 165 mm and 135 mm, which are similar to the above. The outer diameter of the inner pipe 14 is 114 mm, and the inner diameter of the inner pipe 14 is 105 mm, which is about the same as the inner diameter of a general φ135 mm casing. In the following description, the outer diameter and the inner diameter of the dual structure casing 10 represent the outer diameter of the outer casing 12 and the inner diameter of the inner pipe 14, respectively. , The inside of the inner tube 14 is shown.

Next, FIG. 2 shows an example of a casing packer used in the method for constructing the ground anchor according to the embodiment of the present invention. The casing packer 30 includes a cylindrical portion 32, an elastic member 34 such as rubber mounted around the cylindrical portion 32, and an air valve 42 connected to the cylindrical portion 32. Has a structure in which the elastic member 34 expands around the cylindrical portion 32 by being fed. In addition, the casing packer 30 includes hose nipples 36A and 36B provided at both ends in the longitudinal direction of the cylindrical portion 32, and a connecting pipe 36C that penetrates the cylindrical portion 32 and connects the hose nipples 36A and 36B. An injection hose for injecting grout is connected to the nipples 36A and 36B. That is, as will be described later, the grout supplied from the injection hose passes through the inside of the casing packer 30 via the hose nipples 36A and 36B and the connecting pipe 36C.

Further, the casing packer 30 is connected to each of the tension material insertion tubes 38A and 38B penetrating the cylindrical portion 32 and each of the tension material insertion tubes 38A and 38B, and a tension material fixing tube provided at one longitudinal end of the cylinder portion 32. It has parts 40A and 40B. Then, as will be described later, a part of the tensile member (tendon) (PC steel wire) is inserted into the tensile member insertion tubes 38A and 38B, and a part of the inserted tensile member is a tensile member using a wedge structure or the like. By fixing with the fixing portions 40A and 40B, the casing packer 30 is fixed to the tension member.
The casing packer 30 has a size corresponding to the double structure casing 10 shown in FIG. 1. For example, the double structure casing 10 has a general φ165 mm outer diameter (about 165 mm). When having a general φ135 mm casing inner diameter (about 105 mm), the cylindrical portion 32 of the casing packer 30 has an outer diameter of about 96 mm.

Subsequently, an example of the procedure of the method for constructing the ground anchor according to the embodiment of the present invention will be described with reference to FIGS. 4 to 17 along the flow chart shown in FIG. In addition, in the present embodiment, a case will be described in which a ground anchor having an effective anchor diameter of 165 mm is formed using the double structure casing 10 shown in FIG. 1. Further, please refer to FIG. 1 for the detailed structure of the double structure casing 10 and FIG. 2 for the detailed structure of the casing packer 30. Further, in FIGS. 4 to 17, illustration of a hole drilling machine and the like is omitted.
S10 (Soil drilling): As shown in FIG. 4, a soil drilling bit 50 of φ165 mm is attached to the drilling direction tip of the double structure casing 10, and the rear end side of the double structure casing 10 is drilled. The soil S that covers the surface of the ground G to be constructed is drilled to a depth of about 300 mm by the drilling machine that has been set. In the present embodiment, the soil S is an SMW (Soil Mixing Wall).

S20 (guide pipe driving): As shown in FIG. 5, a guide pipe 52 for φ165 mm is driven into the hole drilled in S10 by a drilling machine (not shown).
S30 (Water stop box/drilling bit attachment): As shown in FIG. 6, a water stop box 56 is attached to the end of the guide pipe 52, and a drill bit 54 (for example, a special bit with a reverse support valve) is provided at the tip in the drilling direction. ) Is attached to the waterproof box 56 and the guide pipe 52. At this time, for example, a pre-pender is installed between the inner peripheral portion of the water blocking box 56 and the outer peripheral portion of the double structure casing 10, and the guide tube 52 and the water blocking box 56 are connected by a victor band. use.

S40 (drilling): As shown in FIG. 7, by the drilling machine in which the rear end side in the drilling direction of the double structure casing 10 having the drilling bit 54 attached to the tip in the drilling direction in S30 is set, Drill hole H in G. At this time, the double structure casing 10 is added to the rear end side in the drilling direction, and the drilling is performed to a depth satisfying the designed anchor body length of the ground car to be constructed. That is, as shown in FIG. 1B, a male screw structure 18 and a female screw structure 20 are screw-fitted to the rear end side of the double-structure casing 10 at the rear end in the hole-drilling direction so as to be different from each other. While connecting the double structure casing 10 and drilling with the drill bit 54, a plurality of double structure casings 10 penetrate into the ground G. Furthermore, from the rear end side of the double structure casing 10 at the rear end in the hole forming direction, the hole forming water W is supplied to the inside of the double structure casing 10 (that is, the inside of the inner pipe 14 ). As shown in the drawing, the drilling water W at the time of drilling reaches the drilling bit 54 through the inside of the double-structured casing 10 and is discharged from the drilling bit 54 into the hole H, and the inner peripheral portion of the hole H. After reaching the water shut-off box 56 through between the outer peripheral portion of the double structure casing 10 and the water shut-off box 56, the water is drained from a drain pipe provided in the water shut-down box 56.

As shown in FIG. 8, the ball 58 is biased inside the drill bit 54, which is a special bit with a check valve, and to the opening 54a of the drill bit 54 for the double-structure casing 10. And a spring 60. Then, as shown in FIG. 8A, at the time of drilling while the drilling water W is being supplied to the inside of the double structure casing 10, the water pressure of the drilling water W counters the biasing force of the spring 60 and causes the ball 58 to move. By pressing, the opening 54a is opened. Further, as shown in FIG. 8B, when the boring is completed when the supply of the boring water W is stopped, the urging force of the spring 60 and the pressure of the ground water or the like in the hole H are applied to the ball 58. Therefore, the opening 54a is sealed by the ball 58.

S50 (Grout primary injection): As shown in FIG. 9, injected into the inside of the double structure casing 10 (inside the inner pipe 14) from the rear end in the hole forming direction of the double structure casing 10 at the rear end in the hole forming direction. The hose 62 is inserted, and is inserted up to the vicinity of the tip in the hole-drilling direction of the double-structured casing 10 at the tip in the hole-drilled direction. Then, the grout GM is pressure-fed from the plant into the double-structure casing 10 via the injection hose 62. As a result, the drilling water W filling the interior of the double-structured casing 10 in S40 is replaced with the grout GM from the tip side in the drilling direction. The drilling water W replaced by the grout GM is drained from the rear end in the drilling direction of the double structure casing 10 at the rearmost end in the drilling direction. When the inside of the double structure casing 10 is filled with the grout GM, the feed of the grout GM is stopped and the injection hose 62 is pulled out from the double structure casing 10.

S60 (Tensile material insertion): As shown in FIG. 10(a), inside the double structure casing 10 filled with grout GM (inside the inner pipe 14), the double structure casing 10 at the rear end in the drilling direction. The tensile member (tendon) 64 is inserted from the rear end in the hole drilling direction. At this time, in the tension member 64, the casing packer 30 has reached the rear end side in the drilling direction, the pilot cap 66 has reached the tip in the drilling direction, and the pilot cap 66 has reached the tip in the drilling direction of the double-structure casing 10. In this state, the free packers 68 are attached to the parts located near the boundary between the soil S and the ground G, respectively. Also, the hose nipple 36A (see FIG. 2) of the casing packer 30 and the free packer 68 are connected by an injection hose. Then, in this step, the tensile member 64 is attached to the position where the pilot cap 66 attached to the tip of the pulling member 64 in the drilling direction reaches the vicinity of the drill bit 54 attached to the tip of the dual structure casing 10 in the drilling direction. Is inserted inside the double structure casing 10. The pilot cap 66 has a shape with a sharp tip so that the tension member 64 can be easily inserted into the double-structure casing 10.

Here, the tension member 64 is, for example, a bundle of 1 to 12 PC steel wires formed by twisting a plurality (about 7) of element wires, and is used as a core material of a ground anchor. Further, as described with reference to FIG. 2, when the casing packer 30 is attached to the tension member 64, a part of the PC steel wire forming the tension member 64 (two in this embodiment) is attached to the casing. This is performed by inserting the pulling material insertion tubes 38A and 38B of the packer 30 into the pulling material insertion tubes 38A and 38B, respectively, and fixing the two inserted PC steel wires by the tension material fixing portions 40A and 40B.
The double-structure casing 10 and the casing packer 30 arranged inside the double-structure casing 10 have a positional relationship as shown in FIGS. That is, the inner pipe 14 having the outer diameter d3 smaller than the inner diameter d2 of the outer casing 12 is arranged inside the outer casing 12 having the outer diameter d1 of the dual structure casing 10, and further inside the inner pipe 14. The casing packer 30 having the outer diameter d5 smaller than the inner diameter d4 of the inner pipe 14 is arranged.

S70 (Casing packer operation): As shown in FIG. 11A, the casing packer 30 is operated inside the dual structure casing 10. That is, the air hose 70 is connected to the air valve 42 (see FIG. 2) of the casing packer 30, and air is pumped from the pump 72 to the casing packer 30 via the air hose 70. Then, as shown in FIG. 11B, the elastic member 34 mounted around the cylindrical portion 32 of the casing packer 30 is expanded inside the double structure casing 10. As a result, the expanded elastic member 34 comes into close contact with the inner peripheral portion of the inner pipe 14 of the double structure casing 10. In addition, since the role of the casing packer 30 is to prevent the jetting of groundwater or the like that flows backward inside the double-structured casing 10, the air pressure sent to the casing packer 30 is set to a pressure higher than the pressure of groundwater or the like. .. For example, when the pressure of groundwater or the like is about 0.2 MPa, the air pressure to be sent to the casing packer 30 is set to about 0.3 MPa.

S80 (casing collection): As shown in FIG. 12(a), while pumping the grout GM from the rear end of the double structure casing 10 at the rear end in the drilling direction to the inside of the double structure casing 10, The double structure casing 10 is pulled out, and the double structure casing 10 that has been added to the rear end side in the drilling direction is recovered. At this time, the pressure of the grout GM pressure-fed to the inside of the double structure casing 10 is set to be higher than the air pressure pressure-fed to the casing packer 30. For example, when the air pressure sent to the casing packer 30 is about 0.3 MPa, the pressure of the grout GM sent to the inside of the double structure casing 10 is set to about 0.4 MPa. As a result, as shown in FIG. 12B, a gap is formed between the elastic member 34 of the casing packer 30 and the inner peripheral portion of the inner pipe 14, which were in close contact with each other in S70, and passes through this gap. Then, the grout GM is pressure-fed to the tip end side of the double-structure casing 10 in the drilling direction.

Further, since a gap is formed between the elastic member 34 of the casing packer 30 and the inner peripheral portion of the inner pipe 14, a frictional force disappears between the elastic member 34 and the inner pipe 14, so that the casing packer 30 And the tension member 64 to which it is fixed will maintain the relative position with respect to the hole H without following the movement of the double structure casing 10 that is pulled out. Then, since the double structure casing 10 moves relatively to the rear end side in the drilling direction with respect to the tension member 64 that maintains the relative position with respect to the hole H, as shown in FIG. Of the double structure casing 10 in such a manner that the drill bit 54 attached to the tip of the double structure casing 10 in the drilling direction is pushed out by the pilot cap 66 attached to the tip of the tensile member 64 in the hole forming direction. Direction is removed from the tip. As a result, the grout GM that has been pressure-fed to the inside of the double structure casing 10 is supplied into the hole H from the tip in the hole forming direction of the double structure casing 10 that is opened by removing the hole forming bit 54. .. In addition, the grout GM pressure-fed into the double structure casing 10 has an opening portion of the hole drill bit 54 that is opened by the pressure feed of the grout GM before the hole drill bit 54 is removed from the double structure casing 10. A small amount is supplied from the tip of the drill bit 54 into the hole H via 54a (see FIG. 8).

Further, the collection of the double-structure casing 10 while pumping the grout GM is performed while interrupting the pumping of the grout GM every time one of the double-structure casing 10 located at the rear end in the drilling direction is collected. That is, when the double-structured casing 10 located at the rearmost end in the drilling direction passes the installation position of the casing packer 30 and the pumping of the grout GM is interrupted, as shown in FIG. The elastic member 34 of 30 and the inner peripheral portion of the inner pipe 14 are brought into close contact with each other again, and the jetting of groundwater or the like that flows backward inside the double structure casing 10 is prevented. In this state, the dual structure casing 10 located at the rear end in the drilling direction is collected, and the drilling direction rear end of the double structure casing 10 connected to the collected drilling direction front end side of the double structure casing 10 is collected. Then, the pumping of the grout GM is restarted. By repeating such a process, all the double structure casings 10 other than the double structure casing 10 located at the tip of the drilling direction are collected. The drill bit 54 removed from the double structure casing 10 is left in the hole H without being recovered.

S90 (Free packer operation): As shown in FIG. 13, the double structure casing 10 located at the tip in the drilling direction is moved until the tip in the drilling direction passes the position of the free packer 68 attached to the tension member 64. At the time of pulling out, the free packer 68 is operated. That is, the injection hose 74 connected to the hose nipple 36B (see FIG. 2) of the casing packer 30, the connection pipe 36C (see FIG. 2) of the casing packer 30, and the hose nipple 36A (see FIG. 2) of the casing packer 30 are free. The free packer 68 is inflated by the grout GM by pressure-feeding the grout GM to the free packer 68 via an injection hose that is connected in advance to the packer 68. Then, when the operation of the free packer 68 is completed, the pressure feeding of air to the casing packer 30 is stopped, the air is discharged from the casing packer 30, and the casing packer 30 is contracted. The last double structure casing 10, the casing packer 30 attached to the tension member 64, and the water shut-off box 56 attached to the end of the guide pipe 52 are recovered.

S100 (mouth packer operation): As shown in FIG. 14, the mouth packer 76 is installed inside the guide tube 52, and the grout GM is pressure-fed to the mouth packer 76 via the injection hose 78, thereby grouting the mouth packer 76. Inflated and operated by GM.
S110 (Injection into back surface of free packer): As shown in FIG. 15, a chemical grout material LW composed of water glass and cement is formed on the back surface of the free packer 68 via an injection hose previously attached to the tension member 64. Inject.

S120 (Tip replenishment injection): As shown in FIG. 16, the grout GW is injected through the injection hose that is attached to the tension member 64 in advance, and the tip reaches the vicinity of the tip in the drilling direction of the tension member 64. By doing so, the grout GW is replenished and injected from the tip end side of the hole H in the drilling direction to the entire hole H.
S130 (tension/fixation): When the fixing of the grout GW in the hole H is completed, as shown in FIG. 17, the water-reactive injection material IM or the like is injected through the guide tube 52 to form the anchor body formed in the ground G. Stop the mouth of the water. After that, unnecessary equipment is removed, and the construction method of the ground anchor according to the embodiment of the present invention is completed.

The double-structured casing 10 according to the embodiment of the present invention is not limited to the use in the ground anchor construction method, and may be used in other constructions such as chemical injection work as necessary. Is also good. Further, in the ground anchor construction method according to the embodiment of the present invention, the ground G to be constructed is not limited to one whose surface is covered with SMW, and the ground covered with another kind of wall body. Alternatively, the ground not covered by the wall may be used.

By the way, according to the embodiment of the present invention having the above-mentioned configuration, the following operational effects can be obtained. That is, the dual structure casing 10 according to the embodiment of the present invention is used by penetrating into the ground during various constructions on the ground, and as shown in FIG. It includes a tube 14 and a pair of sealing members 16A, 16B. The inner pipe 14 has an outer diameter d3 (see FIG. 10C) that is smaller than the inner diameter d2 of the outer casing 12, and is inserted and installed inside the outer casing 12. In addition, the pair of seal members 16A and 16B has a gap C generated between the outer casing 12 and the inner pipe 14 arranged inside the outer casing 12 in the longitudinal direction of the inner pipe 14 (left-right direction in FIG. 1). It seals at both ends.

Because of the above-described structure, for example, the outer diameter d1 of the outer casing 12 (see FIG. 10C) is adjusted to the outer diameter of a general φ165 mm casing, and the inner diameter d4 of the inner pipe 14 (see FIG. 10( If c) is adjusted to the inner diameter of a general φ135 mm casing, the equipment used inside the φ135 mm casing can be used even inside the double structure casing 10 having an outer diameter corresponding to the φ165 mm casing. Can be used. That is, by installing the inner pipe 14 inside the outer casing 12, the inner diameter of the double-structured casing 10 is reduced from the inner diameter d2 of the outer casing 12 to the inner diameter d4 of the inner pipe 14. A device that is supposed to be used in a casing having an inner diameter approximately equal to the inner diameter d4 can also be used inside the double structure casing 10 having an outer diameter larger than the outer diameter of the casing.

As a result, the device used inside the casing can be efficiently used in a plurality of casings having different outer diameters. Furthermore, since the gap C between the outer casing 12 and the inner pipe 14 is sealed by the pair of seal members 16A and 16B at both ends in the longitudinal direction of the inner pipe 14, the double structure casing 10 penetrates into the ground. Even in the open state, it is possible to prevent the inflow of earth and sand into the gap C. If a casing that is generally in circulation is used as the outer casing 12 that constitutes the double structure casing 10, the manufacturing cost of the double structure casing 10 can be suppressed.

Further, the double structure casing 10 according to the embodiment of the present invention may be used for construction of a ground anchor as shown in FIGS. 3 to 17, and in this case, the outer casing 12 forms the ground. It has an outer diameter d1 corresponding to the design effective diameter of the anchor. As a result, the hole H that penetrates the dual structure casing 10 and is drilled in the ground G can satisfy the design effective diameter of the ground anchor. Further, as a device such as a casing packer 30 (see FIG. 2) used inside the double structure casing 10 during construction of the ground anchor, it has an inner diameter similar to the inner diameter d4 of the inner pipe 14 of the double structure casing 10. In the casing, the equipment used can be used. That is, it is not necessary to prepare a relatively large casing packer or the like matching the size of the outer casing 12, and a relatively small casing packer 30 or the like matching the size of the inner pipe 14 may be used. Therefore, the price of the casing packer 30 and the like can be suppressed and the weight can be suppressed. Thereby, for example, the work of attaching the casing packer 30 to the tension member 64, the work of inserting the tension member 64 into the double-structure casing 10 (see FIG. 10), and the work of removing the casing packer 30 from the tension member 64. In some cases, the work load is reduced, so that work efficiency can be improved.

In addition, the casing packer 30 has a water output force proportional to the area of the casing due to groundwater, earth and sand, etc. flowing back in the casing. However, the double structure casing 10 according to the embodiment of the present invention is not limited to the outer casing. Since the casing packer 30 is used inside the inner pipe 14 whose inner diameter is smaller than 12, the load on the casing packer 30 is reduced. As a result, expensive rubber wear of the casing packer 30 can be suppressed, so that repair costs and maintenance costs of the casing packer 30 can be suppressed. Furthermore, even if the casing packer 30 is damaged, it is sufficient to stop the jet of water and earth and sand against the water output force proportional to the area of the inner pipe 14, so that the risk of subsidence of the back of the mountain retaining pipe, etc. Can be reduced.

Further, in the double structure casing 10 according to the embodiment of the present invention, as can be seen in FIG. 1A, the length of the inner pipe 14 is shorter than the length of the outer casing 12, and Inside, the inner pipe 14 has its longitudinal end (left end in FIG. 1A) at the longitudinal end (left end in FIG. 1A) of the outer casing 12. It is aligned and arranged. Further, the dual structure casing 10 is provided with a male screw structure 18 and a female screw structure 20 that can be screwed into the male screw structure 18, and the male screw structure 18 is an outer peripheral portion of one longitudinal end of the outer casing 12. The female screw structure 20 is provided on the inner peripheral portion of the other end portion of the outer casing 12 in the longitudinal direction (the right end portion in FIG. 1A).

That is, since the inner pipe 14 shorter than the outer casing 12 is arranged inside the outer casing 12 at one end in the longitudinal direction, the inner pipe 14 is internally provided at the other end in the longitudinal direction of the outer casing 12. There is a range that is not placed. The internal thread structure 20 is provided on the inner periphery of the outer casing 12 in such a range. With such a structure, as shown in FIG. 1B, the double structure casing 10 according to the embodiment of the present invention is not hindered by the inner pipe 14 arranged inside the outer casing 12. The two can be firmly connected to each other by screw fitting via the male screw structure 18 and the female screw structure 20.

Further, in the double structure casing 10 according to the embodiment of the present invention, urethane may be injected into the gap C between the outer casing 12 and the inner pipe 14. Even if the seal members 16A and 16B that seal the end portion of C are damaged, it is possible to prevent infiltration of groundwater, earth and sand, grout, or the like into the gap C. Furthermore, since urethane is lightweight, even if it is injected into the gap C between the outer casing 12 and the inner pipe 14, it has almost no effect on the weight of the double structure casing 10.

On the other hand, the construction method of the ground anchor according to the embodiment of the present invention utilizes the double structure casing 10 as shown in FIG. 1 to construct the ground anchor on the ground G as shown in FIGS. 3 to 17. To do. More specifically, it includes a hole making step S40, a grout primary injection step S50, a tensile material inserting step S60, and a casing collecting step S80 (see FIG. 3). In the drilling step S40, as shown in FIG. 7, the dual structure casing 10 is added to the rear end of the drill bit 54, and the rear end of the double structure casing 10 from the rear end in the drilling direction extends from the inside of the inner pipe 14. The hole H is drilled in the ground G while pumping the drilling water W into the ground. Therefore, the hole H that satisfies the design effective diameter of the ground anchor can be drilled without water, earth and sand, or the like entering the gap C between the outer casing 12 and the inner pipe 14 of the double structure casing 10. it can. Further, in the grout primary injection step S50, as shown in FIG. 9, the injection hose 62 is inserted into the inner pipe 14 of the double structure casing 10 to inject the grout GM, so that the inner pipe is drilled in the drilling step S40. The drilling water W filling the inside of 14 is replaced with grout GM from the tip side in the drilling direction.

Further, in the tension member inserting step S60, as shown in FIG. 10, the tension member 64 having the casing packer 30 attached to the rear end in the insertion direction is inserted into the inner pipe 14 of the double structure casing 10. The casing packer 30 used in this case has a size corresponding to the inner diameter d4 of the inner pipe 14 of the double structure casing 10, and is a casing for a general casing having an inner diameter similar to the inner diameter of the inner pipe 14. The packer 30 can be used. That is, since it is possible to use a small casing packer 30 as compared with the case of using a general casing having an outer diameter similar to the outer diameter d1 of the outer casing 12 of the double structure casing 10. The price and weight of the casing packer 30 itself can be suppressed. As a result, the work load can be reduced when the casing packer 30 is attached to and removed from the tension member 64, and when the tension member 64 with the casing packer 30 attached is inserted, the work efficiency can be improved. Become.

Further, in the casing collecting step S80, as shown in FIG. 11, the casing packer 30 is expanded with air inside the inner pipe 14, and as shown in FIG. The double-structure casing 10 that has penetrated into the ground G in the drilling step S40 is pulled out and collected while the grout GM is pressure-fed into the inner pipe 14 from the end side. At this time, the air pressure for inflating the casing packer 30 is made larger than the pressure of water, earth and sand, or the like that flows backward in the double casing 10 and is jetted, and the pressure for pumping the grout GM is set to the casing packer 30. Make the pressure higher than the expanding air pressure. Thus, while the pumping of the grout GM is stopped, as shown in FIG. 11B, the casing packer 30 expands and comes into close contact with the inner peripheral portion of the inner pipe 14, so that water, earth and sand, etc. Spouting can be prevented. During pumping of the grout GM, as shown in FIG. 12( b ), the grout GM is passed through the gap between the casing packer 30 and the inner pipe 14 formed by the pressure of the grout GM, and the grout GM of the double structure casing 10 is passed through. It can be supplied to the tip side in the drilling direction. Furthermore, since a gap is formed between the casing packer 30 and the inner pipe 14, a frictional force disappears between the casing packer 30 and the inner pipe 14, so that the casing packer in the double structure casing 10 that moves by pulling is removed. The double-structured casing 10 can be pulled out without being followed by 30.

Further, in the method of constructing the ground anchor according to the embodiment of the present invention, with respect to the casing packer 30 arranged in the inner pipe 14 of the double structure casing 10, the water output force that tries to flow backward in the inner pipe 14 ( That is, the outer diameter of the outer casing 12 is about the same as the outer diameter d1, which is smaller than the water discharge force that tends to backflow inside the general casing, and the inner diameter is the same as the inner diameter d4 of the inner pipe 14. Only the water output force equivalent to the water output force that tries to flow backward inside the casing is added. As a result, the load on the casing packer 30 is reduced, so that repair costs and maintenance costs of the casing packer 30 can be suppressed. Further, in the unlikely event that the casing packer 30 is damaged, it is possible to reduce the risk of subsidence of the backside of the mountain retaining due to jetting of groundwater, earth and sand, and the like.

In the description of the present invention, the expression that the outer casing has an outer diameter corresponding to the design effective diameter of the ground anchor indicates that the outer diameter of the outer casing does not necessarily match the design effective diameter of the ground anchor. However, the outer diameter of the outer casing is the same as the design effective diameter of the ground anchor as long as the ground anchor formed in the hole drilled using the double structure casing including this outer casing can satisfy the design effective diameter. It will be appreciated that they may be different.

10: Double structure casing, 12: Outer casing, 14: Inner pipe, 16A, 16B: Seal member, 18: Male screw structure, 20: Female screw structure, 30: Casing packer, 54: Drill bit, 64: Tensile material, C: Gap between outer casing and inner tube, G: ground, H: hole, GM: grout

Claims (6)

A casing for penetrating the ground,
An outer casing,
An inner pipe having an outer diameter smaller than the inner diameter of the outer casing and installed inside the outer casing;
In the longitudinal direction both end portions of the inner tube, seen including a pair of sealing members subjected to sealing treatment in the gap between the inner tube and the outer casing,
Used for construction of ground anchors,
A dual structure casing , wherein the outer casing has an outer diameter corresponding to a design effective diameter of the ground anchor . The inner pipe has a length shorter than that of the outer casing, and the position of the one end in the longitudinal direction is aligned with the position of the one end in the longitudinal direction of the outer casing.
A male screw structure is provided on the outer peripheral portion of the one end in the longitudinal direction of the outer casing, and a female screw structure that can be screwed into the male screw structure is provided on the inner peripheral portion of the other end in the longitudinal direction of the outer casing. claim 1 Symbol placement of double structure casing, characterized in that there. A casing for penetrating the ground,
An outer casing,
An inner pipe having an outer diameter smaller than the inner diameter of the outer casing and installed inside the outer casing;
A pair of seal members for performing a sealing process on a gap between the outer casing and the inner pipe at both longitudinal ends of the inner pipe,
The inner pipe has a length shorter than that of the outer casing, and the position of the one end in the longitudinal direction is aligned with the position of the one end in the longitudinal direction of the outer casing.
A male screw structure is provided on the outer peripheral portion of the one end in the longitudinal direction of the outer casing, and a female screw structure that can be screwed into the male screw structure is provided on the inner peripheral portion of the other end in the longitudinal direction of the outer casing. Double structure casing characterized by The double structure casing according to any one of claims 1 to 3, wherein urethane is injected into a gap between the outer casing and the inner pipe. A method of constructing a ground anchor in the ground by filling grout and inserting a tensile material into a hole drilled while adding a casing to the rear end of the drill bit,
An inner pipe having an outer diameter smaller than the inner diameter of the outer casing is inserted into the outer casing having an outer diameter corresponding to the design effective diameter of the ground anchor, and the outer pipe is provided at both longitudinal ends of the inner pipe. A method for constructing a ground anchor, characterized in that a double structure casing in which a gap is sealed between the casing and the inner pipe is used as the casing. A boring step of boring a hole in the ground while adding the double structure casing to the rear end of the boring bit,
A grout injection step of injecting grout into the inside of the double structure casing;
A casing packer of a size corresponding to the inner diameter of the inner pipe of the double structure casing, in a state of being attached to the rear end side of the tension member, a tension member inserting step of inserting the tension member inside the inner pipe, ,
In a state where the casing packer is inflated inside the inner pipe, while the grout is being pumped into the inner pipe from the rear in the drilling direction with respect to the casing packer, the double structure casing is pulled out and recovered. The method of constructing a ground anchor according to claim 5, further comprising:

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