JP7304141B2 - Manufacturing method of compressible member - Google Patents

Description

The present invention relates to a method for manufacturing a compressible member.

In tunnel construction using the mountain tunneling method, the tunnel is stabilized by shotcrete sprayed on the side of the tunnel, steel support erected along the ground surface, and tunnel support such as rock bolts driven into the ground. ensure the sex.
In the ground of a large earth-covered tunnel with poor ground, the amount of deformation of the ground increases, and a large ground pressure may act on the tunnel support. In tunnels where large stresses are expected to occur, the rigidity and strength of the tunnel support may be increased in order to ensure the safety of the tunnel. However, if the rigidity and strength of tunnel shoring are increased by improving the cross-sectional performance and rigidity of steel shoring, and by increasing the strength and thickness of shotcrete, material costs and construction work will increase. As it increases, it also affects the cross-sectional dimensions of the tunnel.
Therefore, a method of stabilizing the tunnel has been studied that reduces the stress acting on the tunnel shoring by inserting a compressible member across the tunnel shoring and absorbing the deformation of the ground with the compressible member. ing.
As a compressible member used in such a tunnel stabilization method, the present applicant has disclosed in Patent Documents 1 and 2 that a main body portion having a compressive strength lower than that of the tunnel support and a A compressible member is disclosed that includes a reinforcing body of polypropylene fibers disposed therearound. According to this compressible member, brittle fracture can be suppressed and toughness can be ensured by applying an appropriate restraining force to the main body by the reinforcing body.

JP 2018-003361 A JP 2018-040147 A

SUMMARY OF THE INVENTION An object of the present invention is to propose a method for manufacturing a compressible member which is further improved through research and development of the compressible member described in Patent Documents 1 and 2.

The present invention for solving the above-mentioned problems is a method for manufacturing a compressible member capable of absorbing a large amount of axial deformation , comprising the steps of producing a cementitious material comprising cement, a porous lightweight aggregate and water; The method includes a step of placing the cementitious material inside a cylindrical body made of a spiral tube to form a columnar main body in the cylindrical body, and a step of winding a sheet material around the outer peripheral surface of the cylindrical body. .

According to the manufacturing method of such a compressible member, toughness is ensured by the restraining force of the cylindrical body, so brittle fracture of the shoring is suppressed. Therefore, when the compressible member is arranged so as to cross the tunnel support, even if a large ground pressure acts on the tunnel support, the strength of the tunnel support structure is rapidly reduced. is prevented. In addition, since a cylindrical body is used, it is possible to save time and effort in manufacturing the compressible member. That is, since the cylindrical body is used as the remaining formwork, it is possible to reduce labor compared to the conventional manufacturing method that requires stripping of the formwork.
If the cylindrical body is formed of a spiral tube, the cylindrical body is less likely to buckle, and a rapid decrease in the stress of the compressible member can be suppressed.
Also, the main body portion of the compressible member is formed with lower strength than the tunnel shoring by using a porous lightweight aggregate. In general, concrete has a positive correlation between strength and rigidity. If the strength of the main body is lower than the strength of the surrounding tunnel shoring, the rigidity of the main body will also be lower than the surrounding tunnel shoring. . Therefore, even if the natural ground is deformed, the deformation is concentrated on the compressible member, so that the supporting structure of the tunnel can be maintained.
Furthermore, since the main body is composed of the cement-based solidifying material and the porous lightweight aggregate, it is easy to knead and manufacture.

When a spiral tube is used as the cylindrical body, the spiral tube can be cut to an arbitrary length to form a length corresponding to the shape of the tunnel support. This compressible member makes it possible to ensure the stability of the tunnel interior. In addition, if the compressible member is used, it is possible to secure the stability of the tunnel inner space in tunnel excavation under natural ground conditions where large ground pressure acts, such as in tunnels covered with large earth.

(a) is a sectional view showing a tunnel according to the present embodiment, and (b) is a vertical sectional view showing a support structure of the tunnel. (a) is a perspective view showing an installation state of a contractible member, and (b) is a perspective view showing an installation state of a contractible member according to another embodiment. FIG. 4 is a perspective view showing a contractible member; FIG. 11 is a cross-sectional view showing a compressible member according to another embodiment; Fig. 2 is a perspective view of a specimen used in the experiment of the compressible member, where (a) is an example and (b) is a comparative example. 4 is a graph showing experimental results of compressible members.

In this embodiment, as shown in FIG. 1(a), in a tunnel 1 constructed by the mountain construction method, a support structure in which a compressible member 3 is interposed in a part of a tunnel support 2 will be described.
The tunnel shoring 2 of this embodiment includes shotcrete 21, steel shoring 22 and rock bolts 23, as shown in FIG. 1(b). The shotcrete 21 and the steel shoring 22 are formed in an arch shape (horseshoe shape). The shape of the shotcrete 21 and the steel shoring 22 is not limited, and may be ring-shaped, for example.

The tunnel shoring 2 is constructed by first spraying 21a (part of the shotcrete 21) on the natural ground G (tunnel side) exposed by excavating the natural ground G, and then erecting the steel shoring 22. , secondary shot 21b (remaining portion of shotcrete 21) and rock bolt 23 are placed. The steel shoring 22 is erected at a predetermined interval from the steel shoring 22 erected in the previous construction cycle. The rock bolts 23 are driven by drilling rock bolt holes in the ground G around the tunnel 1 and inserting the lock bolts 23 into the rock bolt holes.
The structure of the tunnel support 2 can be changed as appropriate according to the natural ground conditions. For example, the thickness of the shotcrete 21, the presence or absence of installation of the steel shoring 22 and the rock bolts 23, the installation pitch, the dimensions, etc. may be changed as appropriate. Further, instead of the lock bolts 23 in the upper half, a fore-polling construction method, an AGF construction method, or the like may be adopted. Furthermore, you may combine an auxiliary construction method as needed. Also, the shotcrete 21 does not necessarily need to be divided into a plurality of layers (the primary shot 21a and the secondary shot 21b). Further, the rock bolts 23 may be cast together with the erection of the steel shoring 22 after the primary spraying 21a.

As shown in FIG. 1(a), the compressible member 3 is arranged so as to traverse (divide) an arch-shaped shotcrete 21 (tunnel shoring 2). In this embodiment, the compressible member 3 is arranged by spraying the shotcrete 21 against the natural ground G in a state where the compressible member 3 is arranged in advance at a predetermined position. The installation method of the compressible member 3 is not limited, and for example, a recess for installing the compressible member 3 may be formed after the shotcrete 21 is applied. Alternatively, when the shotcrete 21 is constructed, a gap along the tunnel axis direction may be formed in advance in the shotcrete 21 by box extraction or the like, and the compressible member 3 may be arranged in this gap. Further, after the primary spraying 21a is applied, the compressible member 3 may be arranged so as to traverse (divide) the secondary spraying 21b, and the secondary spraying 21b may be applied. The collapsible members 3 are arranged at four locations with respect to one cross section of the tunnel 1 . Moreover, the compressible member 3 is continuously arranged with respect to the axial direction of the tunnel 1, as shown in FIG. 2(a). It is desirable that gaps are formed between the adjacent compressible members 3 and on the rear surface of the compressible member 3 (the surface of the natural ground G). In addition, the number and arrangement of the compressible members 3 are not limited. Moreover, the compressible member 3 may be interposed between the steel materials 22a constituting the steel support 22, as shown in FIG. 2(b).
As shown in FIG. 3, the collapsible member 3 includes a cylindrical body portion 4 having two opposing surfaces to be pressed, and a cylindrical body portion 4 covering surfaces other than the two opposing surfaces (pressurized surfaces) of the body portion 4. It consists of a body 5 and a belt-like fiber sheet (sheet material 6 ) surrounding (covering) the outer surface of the cylindrical body 5 .

The main body 4 is made of a hardened cementitious material containing cement, porous lightweight aggregate, and water. In this embodiment, perlite is used as the porous lightweight aggregate. Here, "perlite" in this specification is a porous lightweight aggregate that is produced by rapidly heating and foaming a rock material (for example, volcanic rock such as obsidian) at a high temperature. The porous lightweight aggregate is not limited to perlite as long as it is a granular material containing many voids. good. Moreover, as the porous lightweight aggregate, a commercially available material may be used, or a material manufactured for the compressible member 3 may be used. Moreover, the cement-based material forming the main body 4 may be mortar or concrete. Although the composition of the main body 4 is not limited, the composition should be such that the compressive strength of the main body 4 is lower than the compressive strength of the shotcrete 21 . Since the compressive strength of the main body 4 is expected to depend on the strength of the porous lightweight aggregate, it is desirable to select or manufacture a porous lightweight aggregate that can ensure a desired compressive strength.

The cylindrical body 5 consists of a spiral tube. A spiral tube is formed in a circular tube shape by joining side edges of a strip-shaped steel plate to each other while spirally winding the steel plate. In this embodiment, a commercially available spiral tube is cut into a predetermined length and used. The cylindrical body 5 does not necessarily have to be a spiral pipe, and may be, for example, a steel pipe, or may be formed by working a steel plate into a cylindrical shape. Moreover, the cylindrical body 5 does not necessarily have to be made of metal.

As shown in FIG. 3, the sheet material 6 is spirally wound around the cylindrical body 5 with the edges thereof overlapping each other. In this embodiment, as the sheet material 6, a woven fabric formed by weaving polypropylene fibers vertically and horizontally is used. This woven fabric is commonly used as a so-called civil engineering sheet. The sheet material 6 is formed by cutting the woven fabric into strips having a width of 5 cm. Note that the width of the sheet material 6 is not limited to 5 cm. Also, the fibers forming the sheet material 6 are not limited to polypropylene, and may be, for example, aramid fibers, polyethylene fibers, or the like.

A method of manufacturing the compressible member 3 is as follows. First, cement, porous lightweight aggregate, water, etc. are kneaded to produce a cementitious material. The cylindrical body 5 is formed by cutting the spiral tube at a predetermined height. Next, the cement-based material is placed inside the cylindrical body 5 and cured to form the main body 4 . The end surface (pressurized surface) of the main body 4 in the tunnel circumferential direction is exposed. When the body portion 4 develops a predetermined strength, the sheet material 6 is wound around the outer peripheral surface of the cylindrical body 5 . That is, the sheet material 6 is wound around the cylindrical body 5 in a direction intersecting the circumferential direction of the tunnel. At this time, the overlapping allowance when winding the sheet material 6 is set to 1 cm. The sheet material 6 may be wrapped around the cylindrical body 5 in advance before placing the cement-based material. Also, the width and overlapping margin of the sheet material 6 are not limited and may be determined as appropriate. Also, the sheet material 6 may be wound around the cylindrical body 5 in multiple layers. In the present embodiment, after applying an appropriate amount of epoxy resin as an adhesive to the cylindrical body 5, the sheet material 6 is wound thereon, and further the epoxy resin is applied to the outer circumference of the compressible member 3 (the sheet material 6). Let it soak in. Note that the adhesive is not limited to epoxy resin. Moreover, the timing and the number of times to apply the adhesive are not limited.

According to the compressible member 3 of the present embodiment, since toughness is ensured by the binding force of the cylindrical body 5, brittle fracture of the tunnel support 2 is suppressed. Since the body portion 4 has a columnar shape and is covered with the cylindrical body 5, it is constrained by the cylindrical body 5 at the same time when a compressive force acts on it. The compressible member 3 exerts the effect of restraining the external restraining member (cylindrical body 5 and sheet member 6) when the body portion 4 expands in the radial direction due to the compressive force. Further, by making the cross-sectional shape of the body portion 4 circular, the restraint effect by the cylindrical body 5 is exhibited even at a small strain (about several percent) level. If the main body 4 has a rectangular cross section, it takes time until the tensile force is applied to the external restraint member. Therefore, the stress (yield strength) does not drastically decrease after yielding. Also, the compressible member 3 that does not break due to brittleness is formed by the binding force of the cylindrical body 5 and the sheet material 6 . Therefore, even if the compressible member 3 is compressed to a strain of 50%, for example, the function as the tunnel support 2 is maintained. As a result, the collapsible member 3 continues to strain until the inner space of the tunnel 1 stabilizes, thereby maintaining the stability of the support structure.

Also, the body portion 4 of the compressible member 3 is formed to have lower strength than the tunnel shoring 2 by using a porous lightweight aggregate. Concrete generally has a positive correlation between strength and stiffness. Therefore, if the strength of the body portion 4 is lower than the strength of the surrounding tunnel shorings 2, the rigidity of the body portion 4 is likewise smaller than the rigidity of the surrounding tunnel shorings 2. Therefore, in the tunnel 1 of the present embodiment, even if the natural ground G is deformed, the deformation is concentrated on the compressible member 3, so the support structure of the tunnel 1 can be maintained. In addition, since the main body 4 is composed of a mixture of a cement-based solidifying material and a porous lightweight aggregate, it can be easily kneaded and mixed compared to concrete containing a large amount of steel fibers. It makes it possible to reduce labor.

Since a spiral tube is used as the cylindrical body 5, the restraint effect is high, and stress reduction at a small strain level can be suppressed. Therefore, a rapid decrease in yield strength of the compressible member 3 is suppressed. When the main body 4 is deformed, the cylindrical body 5 slides in the axial direction (tunnel circumferential direction) of the main body 4 and overlaps with each other, so that the effect of restraining the main body 4 is enhanced. Therefore, even if the main body portion 4 is deformed, a rapid decrease in the strength of the support structure of the tunnel 1 is prevented. In addition, since the cylindrical body 5 formed of the spiral tube functions as a residual mold, molding of the main body 4 is easy. That is, compared to the case where the main body portion 4 is molded individually, the labor required for assembling and removing the formwork can be reduced. Further, the cylindrical body 5 can be formed into a length corresponding to the scale of the tunnel support 2 by cutting the spiral tube to an arbitrary length.

Further, by winding the sheet material 6 around the cylindrical body 5, it is possible to adjust the stress state after yielding. Further, since the band-shaped sheet material 6 is spirally wound around the cylindrical body 5, even when the body portion 4 is compressed (axially compressed) in the tunnel circumferential direction, the sheet material 6 does not slide. , the effect of restraining the cylindrical body 5 (main body portion 4) can be maintained without bending. Moreover, since the sheet members 6 slide when the body portion 4 is axially compressed, the sheet members 6 are stacked, thereby improving the lateral restraint effect.
Since each material (main body portion 4, cylindrical body 5, and sheet material 6) constituting the compressible member 3 is composed of relatively easily available materials, the compressible member 3 can be manufactured easily.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and the constituent elements described above can be modified as appropriate without departing from the scope of the present invention.
For example, the sheet material 6 may be omitted. That is, as shown in FIG. 4, the compressible member 3 comprises a main body 4 made of a hardened cementitious material containing porous lightweight aggregate, and a cylindrical body 5 covering the surface of the main body 4 other than the pressurized surface. It may be configured by
Further, the sheet material 6 does not necessarily have to be wound with the edges overlapping each other as long as the side surfaces of the main body portion 4 can be restrained. Moreover, the sheet material 6 may be strip-shaped, and does not necessarily have to be a fiber sheet.

Next, a uniaxial compression test was performed on the compressible member 3 of this embodiment, and it was confirmed that brittle fracture did not occur until the axial strain reached 50%.
In this experiment, as an example, as shown in FIG. 5(a), a cylindrical body 5 made of a spiral tube and a columnar main body formed by filling the inside of the cylindrical body 5 with mortar using pearlite as an aggregate 4 and a polypropylene sheet material 6 spirally wound around the outer surface of the cylindrical body 5, the compressible member 3 was subjected to a uniaxial compression test. The compressible member 3 has a main body 4 with a diameter of φ200 mm and a height of 400 mm, and a cylindrical body 5 with a wall thickness of 0.6 mm. double wrapped.
As a comparative example, as shown in FIG. 5B, a sheet material 6 having a width of 5 cm is superimposed on the outer surface of the main body 4 made of mortar with perlite as an aggregate and having a width W800×depth D300×height H400. A uniaxial compression test was also performed on the specimen 30 that was double-wrapped with a length of 1 cm.

The uniaxial compression test results are shown in FIG.
As shown in FIG. 6, in the comparative example (L ₀ ), when the body portion 4 yields due to the compressive force, the stress drops significantly (up to 5 N/mm ² or less). On the other hand, in the compressible member 3 of Example (L ₁ ), the cylindrical body 5 with high rigidity exerts a restraining effect at a small strain level, and the stress hardly decreases.
In addition, in the embodiment (L ₁ ), since the body portion 4 is formed in a columnar shape, it expands in the circumferential direction when a compressive force is applied. Tensile force acts and provides a restraining effect even at small strain levels.
According to the compressible member 3 of the present embodiment, it has been demonstrated that the effect of restraining the body portion 4 is improved, there is no significant decrease in stress after yielding, and brittle fracture does not occur up to an axial strain of 50%.

REFERENCE SIGNS LIST 1 Tunnel 2 Tunnel Shoring 21 Shotcrete 22 Steel Shoring 3 Collapsible Member 4 Main Body 5 Cylindrical Body 6 Sheet Material

Claims (1)

A method for manufacturing a compressible member that absorbs a large amount of deformation in the axial direction, comprising:
producing a cementitious material comprising cement, a porous lightweight aggregate, and water;
A step of placing the cementitious material inside a cylindrical body made of a spiral tube to form a columnar main body in the cylindrical body;
and winding a sheet material around the outer peripheral surface of the cylindrical body.

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