Compression strength confirmation method on grout and construction method of grout anchor

Abstract

To provide a compression strength confirmation method for reducing curing period of grout after pressured injection during ground anchor construction.SOLUTION: A compression strength confirmation method on grout is to confirm compression strength at a predetermined time after completion of pressured injection to a specific pressure for specific grout 40 used for the ground anchor construction, carrying out in order: a filling step filling the grout 40 in a grout packer 1 on the ground; a pressure step applying pressure on the grout 40 filled in the grout packer 1 to the specific pressure; a sampling step sampling the pressured grout 40 to the specific pressure in the pressure step in a mold can 20 in a state the grout is fully filled therein; and a compression strength confirmation step carrying out a compression strength test on the grout 40 sampled from the mold can 20 when a specific time passes after the completion of the pressure step.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for confirming the compressive strength of grout used in installing ground anchors after pressure injection, and a method for installing ground anchors based on the confirmation results. [Background technology]

[0002] Ground anchors have traditionally been used in civil engineering projects to stabilize slopes, above-ground structures, and retaining walls. In ground anchors, an anchor body, which is constructed in stable ground using grout made from cement milk, mortar, or other materials, is connected to an anchor head on the ground via a tensioning part. The tensioning part typically includes a tension transmission member made of, for example, a prestressing steel rod, a prestressing steel strand, or continuous fiber reinforcement, and a sheath that covers the tension transmission member to protect it from corrosion.

[0003] In constructing ground anchors, a cylindrical casing is used to drill a hole in the ground, and a tendon is inserted into the hole and grout is injected (see Patent Document 1). After the injected grout hardens and achieves the target compressive strength, tension is applied and the anchor head is treated, completing the construction.

[0004] Generally, after grout injection is completed, the target compressive strength (the compressive strength required when tension is applied to the anchor) (e.g., 24 N / mm 2 The curing period for this to occur is 72 hours or more if high-early-strength cement is used as grout, and about one week if normal cement is used.

[0005] In principle, grout injection is carried out in the following order: replacement injection, in which grout is gradually filled to replace the water in the hole with grout before or after inserting the tendon, and pressure injection, in which further grout is injected under pressure after filling is complete to promote dehydration.

[0006] The pressurized injection is carried out by, for example, packer pressurization or casing pressurization. In packer pressurization, a grout packer is used that is attached to the outside of the anchor body part, the tension part, or both in order to reduce the grout filling loss, and in casing pressurization, the above-mentioned casing is used. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-034412 Summary of the Invention [Problem to be solved by the invention]

[0008] It is known that when pressure injection is performed using packer pressurization, or when casing pressurization is used but the ground geology is sandy, the target compressive strength is achieved earlier than the general curing period mentioned above.

[0009] However, there is no established method to specifically prove this. As a result, when packer pressurization is performed or casing pressurization is performed in sandy soil, the curing period cannot be shortened, even though it is thought that the target compressive strength will actually be achieved sooner, and there is an issue that it is not possible to fully meet the demand for shortened construction periods at disaster sites, etc.

[0010] Therefore, an object of the present invention is to shorten the curing period of grout after pressure injection in the installation of ground anchors. [Means for solving the problem]

[0011] One aspect of the present invention is a method for confirming the compressive strength of grout for confirming the compressive strength after pressurized injection of a specified grout used in the construction of a ground anchor, the method comprising the steps of: a filling step of filling a grout packer with the grout; a pressurizing step of pressurizing the grout filled in the grout packer by the filling step to a specified pressure; a sampling step of sampling the grout pressurized to the specified pressure by the pressurizing step while it is filled in a molded can; and a compressive strength confirmation step of conducting a compressive strength test on the grout removed from the molded can when a specified time has elapsed since the completion of the pressurizing step.

[0012] Another aspect of the present invention is a method for installing a ground anchor that utilizes the confirmation results obtained by the above-mentioned method for confirming the compressive strength of grout, the method comprising: confirming, by the above-mentioned method for confirming the compressive strength of grout, the compressive strength of the grout when a predetermined time has elapsed since the completion of pressurized injection to a predetermined pressure; if the confirmed compressive strength of the grout is equal to or greater than a predetermined target strength, injecting the grout into the ground; pressurizing the grout injected into the ground with a pressure equal to or greater than the predetermined pressure; and curing the grout until the predetermined time has elapsed since the completion of the pressurized injection. [Effects of the Invention]

[0013] According to the present invention, it is possible to check, before installing a ground anchor, whether the compressive strength of the grout will reach the target strength a specified time after the completion of pressurized injection to a specified pressure. Therefore, by installing the ground anchor using the results of this check, it is possible to significantly shorten the curing period of the grout after pressurized injection compared to conventional methods. As a result, the construction period of the ground anchor can be shortened. [Brief explanation of the drawings]

[0014] [Figure 1]3A to 3C are diagrams showing a procedure for attaching a mold can to a grout packer in the method for checking the compressive strength of grout according to the first embodiment of the present invention. [Figure 2] 10A to 10C are diagrams showing the procedure for fixing a molded can to a fixing fixture in the method. [Figure 3] FIG. 2 is an enlarged perspective view of a molded can used in the method. [Figure 4] 10A and 10B are diagrams showing the procedure for hanging a grout packer from a hanging stand in the same method. [Figure 5] FIG. 2 is a diagram showing the procedure for injecting grout into a grout packer in the method. [Figure 6] 10A and 10B are diagrams showing the procedure for pressurizing the grout filled in the grout packer in the same method. [Figure 7] 10A to 10C are diagrams showing the procedure for recovering the mold can filled with grout in the method. [Figure 8] FIG. 10 is a diagram showing the procedure for checking the compressive strength of grout collected in a mold can in the same method. [Figure 9] FIG. 10 is a diagram showing a procedure for injecting grout into a grout packer in a method for checking the compressive strength of grout according to a second embodiment of the present invention. [Figure 10] 10A and 10B are diagrams showing the procedure for refilling grout from a grout packer into a mold can in the same method. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following description is merely exemplary in nature and is not intended to limit the present invention, its application, or its uses.

[0016] [How to check the compressive strength of grout] Hereinafter, the methods for checking the compressive strength of grout according to the first and second embodiments will be described. The methods for checking the compressive strength of grout are carried out to check the compressive strength after pressurized injection (specifically, the compressive strength when a predetermined time has elapsed since the completion of pressurized injection to a predetermined pressure) of a predetermined grout that is planned to be used in installing a ground anchor.

[0017] In the method for checking the compressive strength of grout according to any of the embodiments, all steps are carried out above ground, not in the ground where the ground anchors are installed. Below, the flow of the method for checking the compressive strength of grout will be specifically described for each embodiment.

[0018] [First embodiment] A method for checking the compressive strength of grout according to a first embodiment will be described with reference to FIGS.

[0019] In the first embodiment, the steps of preparing for collection shown in Figures 1 to 3, the hanging step shown in Figure 4, the filling step shown in Figure 5, the pressurizing step shown in Figure 6, the collection step (mold can recovery step) shown in Figure 7, and the compressive strength confirmation step shown in Figure 8 are carried out in this order. The flow of the method for confirming the compressive strength of grout in the first embodiment will be specifically described below.

[0020] [Collection preparation steps] First, as shown in Fig. 1, in a sampling preparation step, a plurality of mold cans 20 are mounted in the grout packer 1. The sampling preparation step is performed before the start of the subsequent filling step (see Fig. 5) so that the mold cans 20 are filled with grout 40 in the filling step.

[0021] Specifically, in the collection preparation step, first, as shown in Fig. 2, a plurality of mold cans 20 are fixed to a fixing device 10. For example, a rope is used as the fixing device 10. The length of the fixing device 10 is longer than the overall length of the grout packer 1.

[0022] The multiple molded cans 20 are fixed to the fixing tool 10 so as to be lined up at intervals from each other in the longitudinal direction of the fixing tool 10. At this time, each molded can 20 is arranged parallel to the fixing tool 10. The multiple molded cans 20 are fixed to a portion of the fixing tool 10 ranging from one end to the middle, and the other end of the fixing tool 10 is left as a margin to which no molded cans 20 are attached. The molded cans 20 are fixed to the fixing tool 10, for example, by wrapping adhesive tape (e.g., vinyl tape) 12 across the side surface (outer peripheral surface) of the fixing tool 10 and the side surface (outer peripheral surface) of the molded can 20.

[0023] As shown in Fig. 3, the mold can 20 is a formwork used to prepare specimens for compressive strength tests of cementitious materials. The mold can 20 is a cylindrical member that can be used to prepare cylindrical specimens of predetermined dimensions (e.g., 50 mm in diameter, 100 mm in height). One end of the mold can 20 is an open end surface 20a, and the other end is a closed end surface 20b. The material of the mold can 20 is not limited, but it may be made of tinplate, for example.

[0024] In this embodiment, a plurality of holes 22 are formed in advance in the side surface (outer peripheral surface) 20c of the molded can 20 before use. The plurality of holes 22 are formed so as to remove excess water when the grout 40 is filled into the molded can 20 from the open end surface 20a. The plurality of holes 22 are provided, for example, at intervals from one another over substantially the entire surface of the side surface 20c of the molded can 20. The diameter of the holes 22 is, for example, 5 mm.

[0025] Returning to Fig. 1, the fixture 10 to which multiple mold cans 20 are fixed is inserted into and attached to the grout packer 1. Specifically, most of the fixture 10 is inserted into the grout packer 1 so that all of the mold cans 20 fixed to the fixture 10 are housed within the grout packer 1. The remaining part of the fixture 10 is exposed to the outside of the grout packer 1. One end of a grout injection hose 2 is also inserted into the grout packer 1.

[0026] When the fixing device 10 to which multiple mold cans 20 are fixed and the grout injection hose 2 are inserted into the grout packer 1, the fixing device 10 and the grout injection hose 2 are fixed to the grout packer 1 by a fastening member (e.g., vinyl tape and cable ties) 14 (see Figure 4) wrapped around the open end 1a of the grout packer 1.

[0027] [Hanging step] In the subsequent hanging step, the grout packer 1 is hung from a hanging platform 30 installed on the ground, as shown in Fig. 4. Note that Fig. 4 shows an example in which one grout packer 1 is hung from one hanging platform 30, but multiple grout packers 1 may be hung from one hanging platform 30 at the same time.

[0028] The configuration of the suspending base 30 is not limited, but for example, the suspending base 30 may be assembled using a plurality of (e.g., three) single pipes 32. Specifically, the lower ends of the plurality of single pipes 32 are inserted obliquely into the ground and fixed, and the upper ends of these single pipes 32 are connected to each other, for example, by connecting fittings. A support part 34 for suspending and supporting the grout packer 1 is provided at the connecting part of these single pipes 32.

[0029] The ends of the fixing devices 10 exposed from the grout packer 1 are fixed to the supports 34 of the hanging base 30 using, for example, connecting fittings. As a result, the grout packer 1 is suspended and supported by the hanging base 30 via the fixing devices 10. In this suspended state, each mold can 20 in the grout packer 1 is positioned with its open end face 20a (see FIG. 3) facing upward and its closed end face 20b (see FIG. 3) facing downward.

[0030] After the hanging step is completed, the subsequent filling step (see FIG. 5) and pressurizing step (see FIG. 6) are carried out with the grout packer 1 hanging from the hanging base 30.

[0031] [Filling step] As shown in Figure 5, in the filling step, a predetermined grout 40 that is planned to be used in constructing the ground anchor is filled into the grout packer 1 from a grout injection hose 2. In the filling step, the grout 40 is injected little by little until the entire grout packer 1 is filled with the grout 40.

[0032] In the filling step, each of the mold cans 20 mounted in the grout packer 1 is also filled with grout 40 .

[0033] [Pressure step] As shown in Figure 6, in the pressurizing step, the grout 40 filled in the grout packer 1 in the filling step is pressurized to a predetermined pressure. The pressurizing step is performed by pressurizing and injecting the grout 40. The pressure of the pressurized injection in the pressurizing step is preferably set to the same value (e.g., 0.2 MPa) as the pressure planned for the pressurized injection in the construction of the ground anchor. The water contained in the grout 40 is dehydrated through the holes 22 in the side surface 20c of the mold can 20 by the pressure.

[0034] [Collection step] After a predetermined time (for example, 30 minutes or more and 1 hour or less) has elapsed since the completion of the pressurizing step, the collecting step is performed. In the collecting step, the grout 40 pressurized to a predetermined pressure in the pressurizing step is collected in a state where it is filled in the mold can 20.

[0035] The collection step in this embodiment is a mold can recovery step in which, after the pressurizing step is completed, the mold cans 20 filled with grout 40 are recovered. In the mold can recovery step, after the grout packer 1 is dismantled, each mold can 20 is removed from the fixing tool 10 and recovered, as shown in FIG.

[0036] [Compression strength confirmation step] Finally, in the compressive strength confirmation step, cylindrical grout 40 is removed from each mold can 20 as shown in Figure 8(a), and a compressive strength test is performed on each of the grout 40 removed from the mold can 20 as shown in Figure 8(b).

[0037] The compressive strength test is carried out when a predetermined time has elapsed since the completion of the pressurizing step, specifically, when the same time as the planned grout curing period (e.g., 18 hours) has elapsed after the pressurized injection in the construction of the ground anchor. The compressive strength test is carried out, for example, in accordance with the JIS A 1108 standard.

[0038] The results of this compressive strength test make it possible to confirm the compressive strength of the grout 40 when a predetermined time (e.g., 18 hours) has elapsed since the completion of pressurized injection to a predetermined pressure (e.g., 0.2 MPa).

[0039] [Second embodiment] A method for checking the compressive strength of grout according to the second embodiment will be described with reference to FIGS.

[0040] In the second embodiment, the hanging step, filling step, pressurizing step, sampling step, and compressive strength confirmation step are performed in this order. In the second embodiment, the sampling preparation step (attaching the mold can 20 to the grout packer 1) as in the first embodiment is not performed.

[0041] [Hanging step] First, in the hanging step, as shown in Fig. 9, the grout packer 1 with one end of the grout injection hose 2 inserted therein is hung and supported on a hanging base 30 installed in the same manner as in the first embodiment. At this time, the grout packer 1 may be hung on the hanging base 30 via a fixing device 10 similar to that in the first embodiment, or may be hung directly on the hanging base 30.

[0042] [Filling step and pressurizing step] Next, the filling step and pressurizing step are performed on the grout packer 1 suspended from the suspension base 30 as shown in FIG. 9, in the same manner as in the first embodiment.

[0043] [Collection step] After a predetermined time (for example, 30 minutes or more and 1 hour or less) has elapsed since the completion of the pressurizing step, the collecting step is performed. As shown in Fig. 10, the collecting step in this embodiment is a refilling step in which the grout 40 is refilled from the grout packer 1 into the mold can 20 after the completion of the pressurizing step. At this point, the hardening of the grout 40 has progressed only to the extent that it can be refilled into the mold can 20.

[0044] In the refilling step, for example, the grout packer 1 is disassembled, and the grout 40 is refilled into each of the multiple mold cans 20. As a result, the grout 40 pressurized to a predetermined pressure in the pressurizing step is collected in a state where it is filled into the mold can 20.

[0045] [Compression strength confirmation step] Finally, the compressive strength confirmation step is performed on the grout 40 collected in each mold can 20 in the same manner as in the first embodiment (see FIGS. 8(a) and 8(b)). As a result, as in the first embodiment, it becomes possible to confirm the compressive strength of the grout 40 when a predetermined time (e.g., 18 hours) has elapsed since the completion of pressurized injection to a predetermined pressure (e.g., 0.2 MPa).

[0046] [Ground anchor installation method] Hereinafter, an example of a method for installing a ground anchor using the results confirmed by the method for confirming the compressive strength of grout according to the first or second embodiment will be briefly described.

[0047] First, the results of the above-mentioned compressive strength test, that is, the compressive strength of the grout 40 after a predetermined time (for example, 18 hours) has elapsed since the completion of pressurized injection to a predetermined pressure (for example, 0.2 MPa), is confirmed.

[0048] Subsequently, the compressive strength of the grout 40 thus confirmed is set to a predetermined target strength (for example, 24 N / mm 2 ) or more, it is determined that the grout 40 is to be used for constructing a ground anchor.

[0049] The construction of ground anchors is carried out in the same manner as in the past, that is, by drilling holes in the ground, inserting tendons into the drilled holes and injecting grout 40 into the holes, injecting the grout 40 under pressure into the ground, fixing it in tension, and processing the anchor head.

[0050] In this construction, the pressurized injection of the grout 40 is carried out using, for example, a grout packer, which effectively promotes dehydration of the grout 40. However, if the ground geology is sandy, dehydration can be effectively promoted by pressurizing the casing even without using a grout packer. Furthermore, the pressurized injection of the grout 40 is carried out at a pressure equal to or greater than the predetermined pressure (for example, 0.2 MPa).

[0051] Thereafter, the grout 40 is cured for the predetermined time (e.g., 18 hours) after the completion of the pressurized injection of the grout 40. Specifically, the curing period may be set to the same time as the predetermined time (e.g., 18 hours), or may be set to a time slightly longer than the predetermined time.

[0052] According to the method for installing a ground anchor according to this embodiment, the curing period of the grout 40 after pressure injection is significantly shorter than the conventional curing period (for example, 72 hours or more for high-early-strength cement, and about one week for normal cement). Therefore, it is possible to shorten the construction period of the ground anchor.

[0053] Although the present invention has been described above with reference to the above-mentioned embodiments, the present invention is not limited to the above-mentioned embodiments. For example, in the method for checking the compressive strength of grout in the above-mentioned embodiments, grout 40 is injected into the grout packer 1 suspended from the suspension platform 30. However, the use of the suspension platform is not essential in the present invention. For example, grout may be injected into a grout packer placed on the ground. [Explanation of symbols]

[0054] 1 grout packer 2 grout injection hoses 10 Fixtures 20 Molded cans 22 holes 30 Hanging stand 40 Grout

Claims

1. A method for confirming the compressive strength of a grout used in the construction of a ground anchor after pressure injection, comprising: On the ground, a filling step of filling a grout packer with the grout; a pressurizing step of pressurizing the grout filled in the grout packer by the filling step to a predetermined pressure; a collecting step of collecting the grout pressurized to the predetermined pressure by the pressurizing step in a state where the grout is filled in a mold can; a compressive strength confirmation step of performing a compressive strength test on the grout removed from the mold can when a predetermined time has elapsed since the completion of the pressurizing step; A method for checking the compressive strength of grout, characterized by carrying out the above steps in sequence.

2. Further provided is a hanging step for hanging the grout packer from a hanging stand installed on the ground, 2. The method for checking the compressive strength of grout according to claim 1, wherein after the hanging step, the filling step and the pressurizing step are performed in a state where the grout packer is hung from the hanging stand.

3. a collection preparation step of attaching the mold can to the grout packer before the filling step is started so that the mold can is filled with the grout by the filling step; The collection step is a mold can recovery step of recovering the mold can filled with the grout after the pressurizing step is completed.

2. The method for checking the compressive strength of grout according to claim 1.

4. In the preparation step, a fixing tool to which the mold can is fixed is inserted into the grout packer and attached.

4. The method for checking the compressive strength of grout according to claim 3.

5. A plurality of holes are formed on the side surface of the molded can to remove excess water.

5. The method for checking the compressive strength of grout according to claim 4.

6. The collecting step is a refilling step of refilling the grout from the grout packer into the mold can after the pressurizing step is completed.

2. The method for checking the compressive strength of grout according to claim 1.

7. The compressive strength of grout is confirmed when a predetermined time has elapsed since the completion of pressurized injection to a predetermined pressure by the method for confirming the compressive strength of grout according to any one of claims 1 to 6, If the confirmed compressive strength of the grout is equal to or greater than the predetermined target strength, the ground anchor is tensioned and fixed. A method for installing a ground anchor.

Images