JP2019148134A - Sound absorption structure - Google Patents

Abstract

To provide a sound absorption structure capable of absorbing sound appropriately on the inner wall of the tunnel at a low construction cost.SOLUTION: When a railway vehicle 300 travels in a tunnel 400, a sound absorption structure 1 that absorbs the pit mouth radiation sound R generated at the pit mouth has a casing row 15 which is formed by connecting a plurality of casings 10 formed convex portions 11 or concave portions 12 formed on both opposing surfaces. The casing row 15 provides the arch shape along an inner wall surface of the tunnel 400, as shown the side view of the tunnel 400 in the short length direction by fitting convex portions 11 and concave portions 12 of a plurality of casings 10.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a sound absorbing structure that absorbs wellhead radiated sound generated when a railway vehicle travels in a tunnel.

  Railroads are operated over a wide area in the country, from urban areas to rural areas. Especially, along railway lines in urban areas and urban areas, noise generated during the running of railway vehicles is a problem. Although railway vehicles cannot be run silently, there is a need to reduce this noise as much as possible.

  In the vicinity of the tunnel, the sound generated when the railway vehicle travels in the tunnel echoes in the tunnel and radiates from the wellhead and the direct sound generated when traveling in the light section overlaps. It propagates along the railway and becomes noise. In particular, at the position where the inside of the tunnel can be seen, the noise effect of the wellhead radiated sound may become large, and countermeasures against the wellhead radiated sound are an important issue in the noise problem near the tunnel wellhead.

  As an existing technology to reduce the sound emitted from the wellhead, Non-Patent Document 1 discloses that a new beam (H steel) is attached to the main structure of the existing tunnel buffer in parallel with the track, and a sound absorbing plate is installed in the groove of the beam. Is sent in and fixed. As mentioned above, the sound emitted from the wellhead echoes inside the tunnel and is radiated from the wellhead. Thus, by installing a sound absorbing plate in parallel with the track inside the shock absorber provided outside the tunnel wellhead, the reverberant sound is absorbed. In addition, the sound emitted from the wellhead radiated from the buffer work to the light section is reduced.

  Also, in Non-Patent Document 2, new groove-type rails are installed on both side walls in the tunnel, and a sound absorbing plate is inserted from the tunnel pit side to the back so that the rail groove slides, and the bolts are raised. It is described to do. In this way, by installing the sound absorbing plate on the tunnel wall, it is possible to absorb the sound that reverberates on the inner wall of the tunnel, and to reduce the sound emitted from the tunnel entrance from the tunnel mine to the light section.

67th Annual Academic Lecture by Japan Society of Civil Engineers Takuma Nitta, September VII-101 “Verification of the effects of sound absorption work at Sanyo Shinkansen tunnel tunnel noise” Masayoshi Ogata et al. “Study on noise reduction at Shinkansen tunnel exit”, [online], [Search on February 1, 2018], Internet <URL: https://www.ntsel.go.jp/forum/16files/ 16-24k.pdf>

  However, the method described in Non-Patent Document 1 described above is a method in which a beam is installed on a main structure of a shock absorber having a polygonal cross section, and a sound absorbing plate is sent along the beam to be installed on the inner wall of the tunnel. It does not install a sound absorbing plate. In particular, in the portion where the main structures of the shock absorbers are connected to each other, a beam cannot be appropriately provided, and the sound absorbing plate cannot be completely spread on the inner surface of the shock absorber in a side view in the short side direction of the tunnel.

  In addition, the method described in Non-Patent Document 2 is a method of installing a sound absorbing plate on a tunnel wall surface rather than a shock absorber. However, due to concerns such as the fall of the installed sound absorbing plate, the sound absorbing plate is limited to introduction to the lower side walls except for the ceiling, and the sound absorbing plate is appropriately attached to the inner wall of the tunnel in a side view in the short side of the tunnel. It cannot be completely laid.

  Furthermore, in Non-Patent Document 1 and Non-Patent Document 2, it is necessary to install a new beam or grooved rail when installing the sound absorbing plate in a tunnel or shock absorber, which requires a great deal of cost and time. It was.

  This invention is made | formed in view of the said situation, and it aims at providing the sound absorption structure which can absorb a sound appropriately in the inner wall of a tunnel with low construction cost.

  The present invention for solving the above problems is a sound absorbing structure that absorbs sound emitted from a wellhead when a railway vehicle travels in a tunnel, and has a casing in which concave or convex portions are formed on both opposing surfaces. There are a plurality of connected casing rows, and the casing rows are fitted in the concave portions and the convex portions of the adjacent casings, and are provided in an arch shape along the inner wall surface of the tunnel in a short side view of the tunnel. It is characterized by being.

  According to the present invention, the casing row which is an arch structure is configured along the inner wall surface of the tunnel by connecting a plurality of recesses and projections by fitting the recesses and projections at the connecting portion of the casing. It is possible to form a sound absorbing structure with an appropriate shape according to the above and form an arch that covers the entire surface from the lower part of the inner wall surface of the tunnel to the ceiling. In addition, since the arch can be formed simply by fitting the concave and convex portions as the connecting portion of the casing, there is no need to newly install beams and guide rails in the tunnel, and the cost and time for construction can be reduced. Can be suppressed.

  A plurality of the casing rows may be arranged side by side in the longitudinal direction of the tunnel.

  A plurality of openings may be formed on a surface of the casing facing the inside of the tunnel.

  The casing may have a hollow portion that communicates with the plurality of openings, and the hollow portion of the one or more casings in the casing row may be filled with a sound absorbing member.

  The sound absorbing member only needs to be filled in the hollow portion of the casing located on the inner wall surface portion of the tunnel that can be visually recognized along the railway line in the light section.

  ADVANTAGE OF THE INVENTION According to this invention, the sound absorption structure which can absorb sound appropriately in the inner wall of a tunnel can be provided at low construction cost.

It is a wellhead front view of a tunnel provided with a sound absorbing structure according to an embodiment of the present invention. It is explanatory drawing which expanded and showed the principal part of FIG. It is the perspective view which showed the outline of the structure of the casing typically. It is explanatory drawing which showed the connection method of the casing typically. It is explanatory drawing in the case of arranging a plurality of casing rows along the longitudinal direction of the tunnel. It is explanatory drawing which showed the reflection of the sound in the tunnel well vicinity around which the sound absorption structure was installed, and a sound absorption image. It is a front view of the tunnel wellhead in FIG. It is explanatory drawing which showed the case where damage generate | occur | produced in a casing. It is explanatory drawing which showed typically the outline of the structure of the casing concerning another embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification and drawings, elements having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

<Configuration of sound absorbing structure>
A sound absorbing structure 1 according to an embodiment of the present invention will be described. FIG. 1 is a front view of a wellhead of a tunnel 400 when the sound absorbing structure 1 is provided in the tunnel 400. FIG. 2 is a schematic enlarged view of a main part (region X in FIG. 1) of the sound absorbing structure 1. It is explanatory drawing shown in figure. In this specification, it is assumed that the railroad track in the light section, that is, the track outside the tunnel, is provided on the elevated as shown in FIG.

  As shown in FIGS. 1 and 2, the sound-absorbing structure 1 includes a casing row 15 in which a plurality of casings 10 described later are connected along an inner wall surface of the tunnel 400 in the front direction of the wellhead. The casing 10 is formed to be sufficiently smaller than the size of the tunnel 400, and the casing 10 is configured by stacking the casings 10. The casing row 15 is configured in an arch shape along the inner wall surface of the tunnel 400 when the tunnel 400 is viewed in the lateral direction. With this configuration, the sound absorbing structure 1 having an appropriate shape can be configured in accordance with the cross-sectional shape of the tunnel 400.

  FIG. 3 is an explanatory view schematically showing the outline of the configuration of the casing 10 constituting the sound absorbing structure 1 (casing row 15). As shown in FIG. 3, the casing 10 which comprises the sound-absorbing structure 1 concerning embodiment of this invention consists of a substantially rectangular parallelepiped column shape which has the hollow part 10a, for example, for example, is comprised with metals, such as aluminum. In addition, in order to maintain the strength as a structure, the casing 10 is preferably made of a metal such as aluminum as described above, but is not limited thereto. The casing 10 only needs to be able to support the weight of the casing row 15 when the casing row 15 is formed, and to withstand external pressure, for example, wind pressure generated when passing through a railway vehicle. Or ceramics.

  Convex portions 11 and concave portions 12 are formed on both surfaces of the casing 10, that is, a pair of opposing surfaces. The convex part 11 and the recessed part 12 formed in the casing 10 are comprised so that casings 10 and 10 can be connected by being mutually fitted, as shown in FIG. Thereby, a plurality of casings 10 are connected, and a casing row 15 of the sound absorbing structure 1 as shown in FIG. 1 can be configured.

  As described above, the adjacent casings 10 and 10 can be connected to each other by fitting the convex portion 11 and the concave portion 12, whereby a plurality of casings 10 are connected to each other, and an arch-shaped casing row 15 can be configured. . That is, since the casings 10 and 10 can form the casing row 15 only by fitting the convex portions 11 and the concave portions 12 to each other, there is no need to install new beams or guide rails in the tunnel 400. No fixing tool is required for fixing between the tunnel 400 and the sound absorbing structure 1 or connecting the casings 10 and 10.

  As shown in FIG. 3, in the casing 10, a plurality of punching holes 13 as openings are formed on one surface 10 b of the surfaces orthogonal to the surfaces on which the convex portions 11 and the concave portions 12 are formed. The surface 10b on which the plurality of punching holes 13 are formed is arranged so as to face the inner space side of the tunnel 400 as shown in FIG. Hereinafter, for clarity of explanation, the surface on which the plurality of punching holes 13 are formed is referred to as an inner surface 10b, and the surface that faces the inner surface 10b and that faces the inner wall surface of the tunnel 400 is referred to as an outer surface 10c.

  As shown in FIG. 3, the punching hole 13 formed in the inner surface 10 b communicates with the hollow portion 10 a of the casing 10. In addition, the sound absorbing member 14 is filled in the hollow portion 10 a of the casing 10. For the sound absorbing member 14, for example, glass wool having a sound absorbing effect is used. With this configuration, the casing 10 can take in the sound generated in the tunnel 400 into the casing 10 through the punching hole 13 and absorb the sound taken in by the sound absorbing member 14 filled in the hollow portion 10a. can do. That is, the casing 10 is configured to be able to attenuate sound that reverberates in the tunnel 400.

  2, the casing row 15 is configured such that the inner surface 10b of the casing 10 is on the inner space side of the tunnel 400, that is, the outer surface 10c is opposed to the inner wall surface of the tunnel 400, as described above. ing.

  As shown in FIG. 5, the sound absorbing structure 1 may have a configuration in which the casing row 15 is arranged in a plurality of rows along the longitudinal direction of the tunnel 400. In such a case, a wall surface for absorbing sound generated in the tunnel 400 can be formed by extending in the longitudinal direction of the tunnel 400. In addition, the number of arrangement rows of the casing rows 15 in the sound absorbing structure 1 can be arbitrarily selected depending on the tunnel inner wall area that requires sound absorption, the time required for construction, the cost, and the like.

<Effects of sound absorbing structure>
Next, the noise absorbing action of the sound absorbing structure 1 configured as described above will be described. 6 shows the sound reflection and sound absorption images around the tunnel entrance of the tunnel 400 when the sound absorbing structure 1 according to the present embodiment is installed in the tunnel 400, from the noise measurement point P provided on the outer railway line. It is explanatory drawing shown by the viewpoint. FIG. 7 is an explanatory view of the wellhead of the tunnel 400 in FIG. 6 as viewed from the front.

  Sound generated from the railway vehicle 300 traveling in the tunnel 400 is reflected in the tunnel 400 and propagates in the direction of the tunnel head of the tunnel 400, and is radiated to the light section as a headhole radiated sound R. In the vicinity of the tunnel head of the tunnel 400, the sound noise R generated from the railway vehicle 300, the track and the viaduct in the light section is added to the sound D of the tunnel head, so that the noise level is generally increased.

  As described above, the sound generated from the railway vehicle 300 and the track traveling in the tunnel 400 is reflected in the tunnel 400 and propagates toward the tunnel wellhead. Conventionally, of the sound generated from the railway vehicle 300 and the track, the sound reflected by both wall surfaces below the tunnel 400 can be absorbed and attenuated by, for example, the sound absorbing plate described in Non-Patent Document 2 described above. However, especially in the vicinity of the ceiling portion of the tunnel 400 where it was difficult to install a sound absorbing plate, the sound propagates to the tunnel entrance of the tunnel 400 without being attenuated, and is emitted to the light section as the well exit radiated sound R. .

  On the other hand, as shown in FIGS. 6 and 7, the sound absorbing structure 1 according to the present embodiment is configured so that the casing row 15 is configured in an arch shape, so The entire surface can be covered along the wall surface, and the plurality of casing rows 15 can be formed side by side along the longitudinal direction of the tunnel 400 to form the wall surface.

  Thereby, the sound generated from the railway vehicle 300 and the track can be guided to the hollow portion 10a from the punching hole 13 formed in the inner surface 10b of the casing 10 installed in the tunnel 400, and can be absorbed by the sound absorbing member 14. In addition, sound can be appropriately absorbed even in the vicinity of the ceiling portion of the tunnel 400 where it has been difficult to install a sound absorbing plate.

(Selection example of filling location of sound absorbing member 14)
In the above embodiment, the sound absorbing member 14 is filled in all the casings 10 constituting the casing row 15, but the sound absorbing member 14 is filled only in the casing 10 located in the tunnel 400 where sound absorption is necessary. You may make it do.

  As shown in FIG. 6, the sound reaching the noise measurement point P provided along the railway is reflected in the light section as described above, and the sound D generated from the railway vehicle 300, the track and the viaduct, and the inside of the tunnel 400. This is a wellhead radiated sound R radiated from the wellhead. Among these, as shown in FIG. 7, the sound generated from the railway vehicle 300 and the track among the sound D is, for example, a sound attenuated by shielding when a soundproof wall W is provided on the track side of the light section. Reaches the noise measurement point P. Further, of the pit radiated sound R, the pit radiated sound R reflected at the lower portions of both side walls of the tunnel 400 is conventionally provided with sound absorbing plates at the lower portions of both side walls of the tunnel 400 as described in Non-Patent Document 2, for example. In this case, since the sound is absorbed by the sound absorbing plate, the noise at the noise measurement point P is smaller than in the case where the sound absorbing plate is not installed. Further, when the noise measurement point P is at a position lower in the vertical direction than the soundproof wall W, the wellhead radiated sound R reflected by the lower portions of both side walls of the tunnel 400 is attenuated by the shielding of the soundproof wall W. Sound reaches the noise measurement point P.

  Therefore, in this embodiment, the main wellhead radiated sound R that reaches the noise measurement point P is the inner wall surface portion of the tunnel 400 (hereinafter referred to as “visible portion A”) that is visible when the tunnel 400 is looked up from the noise measurement point P. "), That is, the pit radiated sound R reflected near the ceiling of the tunnel 400.

  From this, in order to suppress the noise caused by the wellhead radiated sound R measured at the noise measurement point P, it is necessary to fill the sound absorbing member 14 in the casing 10 positioned at least in the portion A where the inner wall surface of the tunnel 400 can be seen. There is.

  For example, according to the “Regular Railway Noise Measurement Manual” issued by the Ministry of the Environment, the areas that are subject to noise measurement are standard at 12.5 m and 25 m in the horizontal direction from the center of the near side track. a. That is, the “railway line” provided with the noise measurement point P in the present invention is an example of a range B from the center of the near side track to 25 m in the horizontal direction in accordance with such a reference. That is, the sound absorbing member 14 constitutes the sound absorbing structure 1. It can be said that the casing 10 located in the portion A where the tunnel 400 can be seen from the noise measurement point P belonging to the range B of 25 m in the horizontal direction from the center of the orbit is filled. However, it is naturally not limited to this standard, and the casing 10 to be filled with the sound absorbing member 14 may be determined by designating the range B independently.

  In the above embodiment, since the noise measurement point P is set at a position lower than the railroad track due to an overhead or the like, the sound absorbing member 14 is filled only in the vicinity of the ceiling portion of the tunnel 400. However, the present invention is not limited to this. . For example, when trying to improve the noise caused by the pit radiated sound R on the upper floor of a high-rise building, the noise measurement point P is set at a position higher than the railway track. You may comprise so that the member 14 may be filled.

  As described above, the sound absorbing structure 1 according to the present embodiment can be configured to fill the sound absorbing member 14 only in the casing 10 located at an arbitrary position according to the need for sound absorption in the casing row 15. Compared to the prior art, it is possible to reduce the construction cost required for sound absorption and shorten the construction time.

  According to the above embodiment, the sound absorbing structure 1 can be easily installed only by stacking without providing new beams and guide rails in the tunnel 400 and without using a fixture between the casings 10. Therefore, the construction cost can be reduced and the construction time can be shortened. In addition, since a plurality of casing rows 15 are arranged in units of rows along the longitudinal direction of the tunnel 400 to form a wall surface and the arbitrary casing 10 can be filled with the sound absorbing member 14, only an arbitrary range on the inner wall surface of the tunnel 400 can be obtained. Can be appropriately absorbed.

  Since the sound absorbing structure 1 can be easily assembled and installed as described above, for example, as shown in FIG. 8, only some of the casings 100 among the casings 10 forming the wall surface need to be replaced. Even in the case of replacement, it is possible to replace the casing 10 units. Moreover, since only the casing row 15 to which the casing 100 that needs to be replaced needs to be removed as indicated by the arrows in the figure, maintenance costs and time can be further reduced.

  The sound absorbing structure 1 can be installed without providing a new beam or guide rail in the tunnel 400 as described above, and without using a fixture between the casings 10 and 10. However, this does not limit the use of a fixture or the like, and the structural strength of the sound absorbing structure 1 may be improved by using a fixture or the like. For example, among the casings 10 constituting the casing row 15, the casing 10 positioned at the top may be fixed to the ceiling of the tunnel 400 by an anchor or the like, or the casing 10 positioned at the lowermost position may be fixed to the floor surface of the tunnel 400. You may make it fix to a wall surface. Moreover, you may fasten between the casings 10 and 10 with a volt | bolt etc. Even in such a case, since the sound absorbing structure 1 can be assembled and removed in units of the casing row 15, the construction cost and time can be reduced as compared with the conventional structure, and the structural strength of the sound absorbing structure 1 can be reduced. Can be reinforced.

  Furthermore, as described above, since the sound absorbing structure 1 can be assembled in units of the casing row 15, the construction is sequentially performed from the wellhead side of the tunnel 400 or sequentially from the back in the longitudinal direction of the tunnel 400. There is no need to proceed. That is, since it is possible to absorb only sound from an arbitrary place in the tunnel 400, construction costs and time can be further reduced.

  According to the embodiment described above, the casing row 15 is configured by connecting a plurality of casings 10 each having the convex portion 11 and the concave portion 12 to a pair of opposed surfaces. It is not limited. For example, the casing may have convex portions 11 and 11 on a pair of opposing surfaces as in the casing 20 shown in FIG. 9, or the concave portions 12 and 12 on a pair of opposing surfaces as in the casing 30. You may have.

  In such a case, the casing row 15 may be configured by alternately stacking the casings 20 having only the convex portions 11 and the casings 30 having only the concave portions, or the casing 20 is disposed only at the top portion of the casing row 15 and the top portion. Otherwise, the casing 10 having the convex portion 11 and the concave portion 12 on a pair of surfaces may be stacked. Of course, the casing 10, the casing 20, and the casing 30 can be mixed and stacked.

  Moreover, you may comprise so that the length of the convex part 11 formed in the casing 10 and the depth of the recessed part 12 can be adjusted arbitrarily with a slide mechanism etc. Thereby, it becomes possible to give the joining width | variety of the casing 10 at the time of the assembly of the casing row | line | column 15, and the sound-absorbing structure 1 can be assembled more easily.

  Furthermore, the convex part 11 of the casing 10 may be provided so that the protruding direction can be inclined from the parallel direction with the inner surface 10b and the outer surface 10c. Since the casing row 15 forms an arch shape along the inner wall surface of the tunnel 400, an inclination occurs between the casings 10 and 10 along the longitudinal direction of the casing 10. Such an inclination can usually be ignored because the casing 10 is sufficiently small compared to the size of the tunnel 400. However, for example, when the tunnel is a single wire, the influence becomes large. End up. Therefore, since the convex portion 11 can be inclined with respect to the parallel direction with the inner surface 10b and the outer surface 10c, it is possible to connect the casings 10 and 10 with an inclination. Even if it is small, the convex part 11 and the recessed part 12 can be appropriately connected along the inner wall surface of the tunnel.

  Alternatively, instead of inclining the convex portion 11 as described above, the respective surfaces on which the convex portion 11 and the concave portion 12 are formed are inclined, that is, in the above embodiment, the casing 10 has a rectangular cross-sectional shape. However, as shown in the configuration of FIG. 2, the side view of the casing may be configured to have a substantially trapezoidal shape. By adopting such a configuration, similarly to the example in which the convex portion 11 is inclined as described above, the convex portion 11 and the concave portion 12 can be appropriately connected even when the tunnel is small, for example.

  However, in particular, when the tunnel 400 has a straight wall surface by providing an inclination to the convex portion 11 and the concave portion 12 or by inclining the surface having the convex portion 11 and the concave portion 12 as described above. In this case, it may be difficult to stack the sound absorbing structure 1 in an arbitrary shape that matches the shape of the tunnel 400. Therefore, the casing 10 is formed to be sufficiently small with respect to the tunnel 400, and the surfaces having the convex portions 11 and the concave portions 12 are configured in parallel so that the casings 10 are connected in an arbitrary shape to form the casing row 15. Most preferably, it is configured to be able to.

  In the above embodiment, the casing 10 is formed in a columnar shape made of a substantially rectangular parallelepiped, but the shape of the casing 10 is not limited to this. For example, it may be constituted by a cylinder or a semi-cylinder, or may have six or more faces. Even in such a case, the same effect can be obtained by forming the punching hole 13 in the inner surface 10b other than the convex portion 11 and the concave portion 12 and filling the hollow portion 10a with the sound absorbing member 14.

  Furthermore, as shown in FIG. 2 and FIG. 9B, for example, when the cross-sectional shape of the tunnel 400 is an arch shape, the casing 10 is formed so as to be in close contact with the inner wall surface of the tunnel 400. Have difficulty. In this case, it is preferable that the casing has a shape where the contact portion between the casing and the inner wall surface of the tunnel 400 is as large as possible. For example, when the shape of the casing is a cylinder, since the casing and the inner wall surface of the arched tunnel 400 are in point contact, the inner wall surface of the tunnel 400 and the casing are likely to slip at the contact point, that is, the strength of the tunnel 400 in the longitudinal direction. Will fall. On the other hand, since the casing 10 and the inner wall surface of the arch-shaped tunnel 400 are in contact with each other as in the casing 10 of the above-described embodiment, for example, the contact location is increased and the strength can be secured.

  In the above embodiment, the punching hole 13 is provided as the opening of the casing 10, but the opening shape is not limited to this, and the sound generated in the tunnel 400 appropriately reaches the sound absorbing member 14 in the casing 10. It only has to be made. The surface on which the opening is formed is not limited to the inner surface 10b of the casing 10, and may be formed on a plurality of surfaces. However, when the casing row 15 is configured, it is necessary to ensure strength that can withstand the weight of the casing row 15 and external pressure.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this example. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs to.

  The present invention is useful for reducing downhole radiated sound, and particularly useful when the tunnel is an arch-shaped tunnel.

DESCRIPTION OF SYMBOLS 1 Sound absorption structure 10, 20, 30, 100 Casing 10a Hollow part 10b Inner surface 10c Outer surface 11 Convex part 12 Concave part 13 Punching hole 14 Sound absorption member 15 Cascade row | line | column 300 Railway vehicle 400 Tunnel A The part D which can be seen D Sound P Noise generated Measuring point R

Claims (5)

A sound absorbing structure that absorbs sound emitted from a wellhead when a railway vehicle travels in a tunnel,
It has a casing row in which a plurality of casings in which concave portions or convex portions are formed on both opposing surfaces are connected,
The said casing row | line | column fits the said recessed part and the said convex part of the said adjacent casing, and is provided in the arch shape along the tunnel inner wall surface in the transversal direction side view of a tunnel, The sound absorption structure characterized by the above-mentioned body. The sound absorbing structure according to claim 1, wherein a plurality of the casing rows are arranged in the longitudinal direction of the tunnel. The sound absorbing structure according to claim 1, wherein a plurality of openings are formed in a surface of the casing facing the inside of the tunnel. The casing has a hollow portion communicating with the plurality of openings,
The sound absorbing structure according to claim 3, wherein a sound absorbing member is filled in the hollow portion of one or more casings in the casing row. 5. The sound absorbing structure according to claim 4, wherein the sound absorbing member is filled in the hollow portion of the casing located on an inner wall surface portion of a tunnel that can be visually recognized along a railway line in a light section. .

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