JP7745975B2 - Ground vibration reduction method using ground vibration reduction slab for viaduct - Google Patents

Description

The present disclosure relates to a method for reducing ground vibration using a ground vibration reduction slab for a viaduct.

Conventionally, along railway and road viaducts, ground vibrations caused by the movement of vehicles such as trains and automobiles can propagate to the surrounding area, causing environmental problems. Therefore, as a countermeasure against ground vibrations, it has been proposed to install vertically extending vibration isolation walls underground (see, for example, Non-Patent Document 1).

Figure 1 is a schematic diagram explaining the vibration-damping effect of a conventional vibration-damping wall.

Generally, ground vibrations along railways and roads are considered to be surface waves known as Rayleigh waves. Figure 1 shows a schematic diagram of the transmission and diffraction of surface waves through a vibration-isolating wall, which is a vertically extending flat plate buried underground to block such surface waves. A vibration-isolating wall (underground wall) with a depth of H is buried at the position x = 0, and an incident wave with an underground amplitude distribution of _a0 (z) is assumed to be incident from the seismic source. The underground amplitude distribution immediately after passing through the vibration-isolating wall is a(z). Furthermore, at locations shallower than H, the amplitude is the amplitude of the incident wave multiplied by the vibration transmittance β (β < 1) of the vibration-isolating wall.

However, because vertically extending vibration-damping walls can only achieve sufficient vibration reduction effects when installed away from the vibration source, they are difficult to implement in areas where large plots of land are not available along railway lines, as is the case with typical railways and roads. Therefore, it has been proposed to bury horizontally extending flat blocks underground around structures such as railway and road viaducts (see, for example, Patent Document 1).

Figure 2 is a cross-sectional view showing conventional horizontally extending flat blocks buried underground around a structure.

In Figure 2, 101 is a structure that emits vibrations, such as a railway viaduct pier. 102 is a caisson foundation that supports structure 101, and its width is B. 103 is a flat block with a thickness of t and a width of W, which is more rigid than the surrounding ground. This flat block 103 is arranged in a disk shape with its inner periphery separated from caisson foundation 102 so that it does not come into contact with the caisson foundation, and is buried underground at a depth H from the ground surface. This provides a greater vibration reduction effect than a vertically extending vibration isolation wall.

Kimitoshi Ashiya, "Method for Evaluating the Vibration Isolation Effect of Vibration Isolation Works," Geophysical Exploration, Vol. 58, No. 4, pp. 351-362, August 1, 2005

Japanese Patent Application Publication No. 7-3829

However, conventional technologies require burying vibration-isolating walls or flat blocks underground, resulting in long construction times and high costs. The main waves in environmental vibrations, such as ground vibrations caused by the movement of vehicles like trains and automobiles, are surface waves. For example, a vibration-isolating wall like the one shown in Figure 1 must be constructed to a width and depth corresponding to the wavelength of the surface waves propagating through the ground, which generally necessitates large-scale construction work with a width of 10-100 m, a depth of 2-10 m, and a thickness of 0.3-1 m. Furthermore, because such vibration-isolating walls can only achieve sufficient vibration reduction when installed away from the vibration source, large areas of land must be secured around railway and road viaducts.

Furthermore, in the case of flat blocks 103 as shown in Figure 2, the inventor of this technology has reported that it is effective for vibration control if the width W of the flat block 103 is approximately equal to or greater than the width B of the caisson foundation 102, the thickness t of the flat block 103 is approximately 1/5 or greater than the width W, the rigidity of the flat block 103 is 3 to 5 times greater than the surrounding ground in terms of shear wave velocity, and it is installed at a depth of α·Vs/4f. Note that α = 0.5 to 0.8, Vs is the shear wave velocity of the ground, and f is the frequency. This technology also focuses on the vibration path, burying flat blocks 103 underground around a structure 101 such as a viaduct pier. The buried flat blocks 103 disrupt the underground amplitude distribution of surface waves, thereby suppressing the propagation of vibrations to distant locations. However, although the scale is smaller than the technology shown in Figure 1, since the flat blocks 103 are buried underground, large-scale construction is still required, and furthermore, since the flat blocks 103, which are wider than the caisson foundation 102, are installed around the caisson foundation 102, a large area of land must be secured around the structure 101, even if it is not as large as the technology shown in Figure 1.

The purpose of this study is to solve the problems of the conventional technology and provide a method for reducing ground vibration using a ground vibration reducing slab for viaducts, which does not require new land, is easy to construct, can be constructed at low cost in a short period of time, and can effectively suppress ground vibration along the railway line, by installing a slab directly below the viaduct above the top surface of the footing of the viaduct pier.

To this end, in a method for reducing ground vibration using a ground vibration reduction slab for a viaduct, a thick concrete plate member 1 m thick is installed directly below the viaduct so as to face the upper surface of a footing that is buried underground and has its upper surface exposed to the ground surface and at least a portion of its lower surface protruding laterally from the pier of the viaduct, and the thick plate member absorbs waves that enter the ground from the upper surface of the footing, thereby reducing the amplitude of the waves propagating through the surface layer of the ground .
In another method for reducing ground vibration using a ground vibration reduction slab for viaducts, the frequency of the wave motion is 25 to 50 Hz and 80 to 100 Hz.

In another method for reducing ground vibration using a ground vibration reduction slab for a viaduct, the thick plate member is further installed at a distance from the pier and the footing.

In yet another method for reducing ground vibration using a ground vibration reduction slab for an elevated bridge, the thick plate member is installed so as to cover 50% or more of the upper surface of the footing.

In yet another method for reducing ground vibration using a ground vibration reduction slab for a viaduct, the thick plate members are installed within a range not exceeding the overall width of the viaduct girder.

In yet another method for reducing ground vibration using a ground vibration reduction slab for an elevated bridge, the thick plate member further includes an outer slab installed in the range from the pier to a position corresponding to the outer widthwise end of the viaduct's bridge girder.

In yet another method for reducing ground vibration using a ground vibration reduction slab for an elevated bridge, when there are multiple piers in the width direction of the viaduct's girder, the thick plate member includes an inner slab installed in the area between the piers in the width direction of the bridge girder.

In yet another method for reducing ground vibration using a ground vibration reduction slab for an elevated bridge, the outer slab further has an underground wall provided at the outer end of the bridge girder in the width direction of the outer slab and buried in the ground.

In yet another method for reducing ground vibration using a ground vibration reduction slab for an elevated bridge, the thick plate member is further fitted with slab attachment piles that are buried in the ground and arranged in a row in the longitudinal direction of the viaduct's bridge girder.

In yet another method for reducing ground vibration using a ground vibration reduction slab for an elevated bridge, a slab accessory plate is further attached to the thick plate member, extending in the longitudinal direction of the viaduct's bridge girder and buried in the ground.

This disclosure does not require new land, is highly constructable, can be constructed at low cost in a short period of time, and can effectively suppress ground vibrations along the railway line.

1 is a schematic diagram illustrating the vibration-isolating effect of a conventional vibration-isolating wall. FIG. 1 is a cross-sectional view showing a state in which conventional horizontally extending flat blocks are buried underground around a structure. 1 is a schematic diagram showing an example of construction of a ground vibration reduction slab for a viaduct in the first embodiment. FIG. FIG. 2 is a schematic diagram showing the state of vibration propagation when the viaduct ground vibration reduction slab according to the first embodiment is not installed. 3 is a schematic diagram showing the state of vibration propagation when a ground vibration reduction slab for a viaduct according to the first embodiment is installed. FIG. FIG. 2 is a diagram showing a simulation model for confirming the effect of the viaduct ground vibration reduction slab in the first embodiment. FIG. 10 is a diagram showing the results of a simulation analysis of the vibration propagation state when the viaduct ground vibration reduction slab in the first embodiment is not constructed. 10 is a diagram showing the results of a simulation analysis of the vibration propagation state when a ground vibration reduction slab for a viaduct in the first embodiment is constructed. FIG. 10 is a graph comparing vibrations at the output point position of the footing in a simulation model for confirming the effect of the viaduct ground vibration reduction slab in the first embodiment. 10 is a graph comparing vibrations at a position away from the structure in a simulation model for confirming the effect of the viaduct ground vibration reduction slab in the first embodiment. FIG. 10 is a schematic diagram showing an example of construction of a ground vibration reduction slab for viaducts in the second embodiment. FIG. 10 is a schematic diagram showing an example of construction of a ground vibration reduction slab for viaducts in the third embodiment. FIG. 11 is a schematic diagram showing the state of vibration propagation when a ground vibration reduction slab for viaducts according to the third embodiment is installed. FIG. 10 is a schematic diagram showing an example of construction of a ground vibration reduction slab for viaducts in the fourth embodiment. FIG. 10 is a first schematic diagram showing the state of vibration propagation when a ground vibration reduction slab for viaducts according to the fourth embodiment is constructed. FIG. 10 is a second schematic diagram showing the state of vibration propagation when a ground vibration reduction slab for a viaduct according to the fourth embodiment is constructed.

This embodiment will be described in detail below with reference to the drawings.

3 is a schematic diagram showing an example of construction of a viaduct ground vibration reduction slab in the first embodiment, FIG. 4 is a schematic diagram showing the state of vibration propagation when a viaduct ground vibration reduction slab in the first embodiment is not constructed, FIG. 5 is a schematic diagram showing the state of vibration propagation when a viaduct ground vibration reduction slab in the first embodiment is constructed, FIG. 6 is a diagram showing a simulation model for confirming the effect of the viaduct ground vibration reduction slab in the first embodiment, FIG. 7 is a diagram showing the results of a vibration propagation analysis by simulation when a viaduct ground vibration reduction slab in the first embodiment is not constructed, FIG. 8 is a diagram showing the results of a vibration propagation analysis by simulation when a viaduct ground vibration reduction slab in the first embodiment is constructed, FIG. 9 is a graph comparing vibrations at the output point position of the footing using a simulation model for confirming the effect of the viaduct ground vibration reduction slab in the first embodiment, and FIG. 10 is a graph comparing vibrations at a position away from the structure using a simulation model for confirming the effect of the viaduct ground vibration reduction slab in the first embodiment. In Figure 3, (a) shows the cross section, and (b) shows the top surface of the slab.

In the figure, 20 denotes a viaduct in this embodiment, which may be for a railway, a road, or any other purpose, but for the sake of convenience, it will be described as being for a railway. Furthermore, the viaduct 20 may be either a rigid-frame viaduct or a girder-type viaduct, and 21 is a bridge girder, but when the viaduct 20 is a rigid-frame viaduct, it is called an elevated slab.

Furthermore, reference numeral 22 denotes a pier that supports the bridge girder 21 from below and is a long member made of reinforced concrete. Here, the piers 22 are described as being arranged side by side to form two columns on the left and right sides extending in the longitudinal direction of the bridge girder 21. A footing 23 that protrudes laterally is formed at the lower end of each pier 22, and the upper ends of underground piles 24, which are long members made of reinforced concrete, are connected to the underside of the footings 23. The footings 23 and underground piles 24 are entirely buried underground 32.

In this embodiment, a slab 11 serving as a viaduct ground vibration reduction slab is installed directly below the viaduct 20, above the upper surface 23a of the footing 23. The slab 11 is a thick concrete plate member, and its thickness t is preferably set to approximately 0.5 to 2 m. The slab 11 is installed so that its upper surface 11d is exposed to the ground surface 31, and so that at least a portion of its lower surface 11e faces the upper surface 23a of the footing 23, and is spaced apart from the pier 22 and footing 23. The upper surface 11d is preferably flat with the ground surface 31, i.e., approximately flush with the ground surface 31.

The slab 11 is installed so as to cover at least a portion of the upper surface 23a of the footing 23. Preferably, it is installed so as to cover 50% or more of the area of the upper surface 23a of the footing 23, excluding the piers 22. Furthermore, as shown in Figure 3(a), the slab 11 is installed within an area that does not exceed the overall width A of the bridge girder 21. In other words, it is installed within the area directly below the bridge girder 21 of the viaduct 20 installed within railway land (road land).

The slab 11 may be a member of any shape and size, but in the example shown in Figure 3, it includes an outer slab 11A and an inner slab 11B, each of which has a roughly rectangular planar shape. When describing the outer slab 11A and the inner slab 11B collectively, they will be referred to as slab 11.

The outer slab 11A is a slab 11 arranged outside the two rows of piers 22. As shown in Figure 3(b), in plan view, it is rectangular with a pair of long sides 11a extending in the longitudinal direction of the bridge girder 21 and a pair of short sides 11b extending in the width direction of the bridge girder 21. The long side 11a near the center of the width of the bridge girder 21 has a recess 11c formed to avoid contact with the piers 22. The long side 11a is long enough to surround two adjacent rows of piers 22 extending in the longitudinal direction of the bridge girder 21, and is long enough to create a gap between adjacent outer slabs 11A in the longitudinal direction of the bridge girder 21. Furthermore, the short side 11b is long enough to extend from the center of the pier 22 to a position corresponding to the outer edge of the width direction of the bridge girder 21.

The inner slab 11B is a slab 11 disposed between two rows of piers 22. As shown in Figure 3(b), in plan view, it is rectangular with a pair of long sides 11a extending in the longitudinal direction of the bridge girder 21 and a pair of short sides 11b extending in the width direction of the bridge girder 21. Both long sides 11a have recesses 11c formed to avoid contact with the piers 22. The long sides 11a are long enough to surround two adjacent rows of piers 22 extending in the longitudinal direction of the bridge girder 21, and are long enough to create a gap between the inner slabs 11B adjacent to each other in the longitudinal direction of the bridge girder 21. The short sides 11b are the length from the center of one pier 22 in the two rows to the center of the other pier 22. The length of the short side 11b of the inner slab 11B, like the length of the short side 11b of the outer slab 11A, is set to a length that leaves a gap between the outer slab 11A and the inner slab 11B, which are adjacent in the width direction of the bridge girder 21.

In Figure 3(b), the dotted lines surrounding each pier 22 indicate the outer periphery of the footing 23 buried in the ground 32. From this, it can be seen that in the example shown in Figure 3(b), the slab 11 is installed so as to cover more than 50% of the area of the upper surface 23a of the footing 23, excluding the piers 22.

It can also be seen that, due to the formation of the recessed portions 11c, each of the slabs 11 is not connected or in contact with the piers 22, i.e., the edges are cut off from the piers 22. This eliminates the need for structural design. It also prevents vibrations from being transmitted directly from the piers 22 to the slabs 11. If necessary, the gap between the slabs 11 and the piers 22 can be filled with an elastic material, etc.

Note that if there is only one row of piers 22 extending in the longitudinal direction of the bridge girder 21, i.e., if there is only one pier 22 in the width direction of the bridge girder 21, then the slab 11 will only consist of the outer slab 11A, and there will be no inner slab 11B. On the other hand, if there are three or more rows of piers 22 extending in the longitudinal direction of the bridge girder 21, i.e., if there are three or more piers 22 in the width direction of the bridge girder 21, then two or more inner slabs 11B will be installed side by side in the width direction of the bridge girder 21.

As shown in Figure 4, when the slab 11 has not been constructed, i.e., when the slab 11 is not installed, a portion of the waves indicated by arrow 41 that are incident on the ground surface 31 from the upper surface 23a of the footing 23 are reflected and propagate into the ground 32, as indicated by arrow 43. The remaining waves propagate through the surface layer of the ground as Rayleigh waves, as indicated by arrow 42. Note that waves that are incident on the ground from the pier 22 and footing 23 structures are considered to mainly enter from the footing 23, and the majority of the waves propagating through the surface layer of the ground are considered to enter from the upper surface 23a of the footing 23.

On the other hand, as shown in Figure 5, when a slab 11 is constructed and placed above the upper surface 23a of the footing 23, due to the high reflectivity of concrete, most of the waves indicated by arrow 41 that enter the ground from the upper surface 23a of the footing 23 are reflected by the lower surface 11e of the concrete slab 11 and propagate into the ground 32 as indicated by arrow 43. The remaining waves pass through the lower surface 11e of the slab 11 and propagate within the slab 11 as indicated by arrow 44, and some of these waves pass through the lower surface 11e of the slab 11 again as indicated by arrow 45 and propagate into the ground 32. This achieves a high vibration reduction effect.

This vibration reduction effect can be confirmed by performing a simulation analysis using a simulation model such as that shown in Figure 6. In Figure 6, 23c indicates the output point position on the footing 23.

Figures 7 and 8 show the results of a simulation analysis when the slab 11 is not installed and when it is installed, respectively. In Figures 7 and 8, arrow 51 indicates the position of the excitation point in the simulation. In this case, the simulation analysis was performed assuming that vertical excitation was applied to the center of a track (not shown) laid on the bridge girder 21. Figures 7 and 8 also show the amplitude distribution, with curves 53 drawn at the nodes of the amplitude distribution, which, together with arrow 52, indicate the propagation direction of the wave within the ground.

As shown in Figure 7, when the slab 11 has not been constructed, i.e., when the slab 11 is not installed, the nodes of the amplitude distribution are spread out concentrically underground 32. Furthermore, at the ground surface 31, the height of the amplitude peak is located significantly higher than the height of the ground surface 31 indicated by the dotted line, indicating that the amplitude of the waves propagating through the surface layer of the ground is large.

On the other hand, as shown in Figure 8, when the slab 11 is constructed and placed above the upper surface 23a of the footing 23, the nodes of the amplitude distribution underground 32 spread out in the shape of a horizontally long ellipse. This is thought to be because, as shown in Figure 5, most of the waves indicated by arrows 41 that enter the ground from the upper surface 23a of the footing 23 are reflected by the lower surface 11e of the slab 11. Furthermore, at the ground surface 31, the height of the amplitude peaks that protrude above the ground surface 31 indicated by the dotted lines is small, indicating that the amplitude of the waves propagating through the surface layer of the ground is small.

Figures 9 and 10 are graphs showing the magnitude of vibration at the output point position 23c of the footing 23 based on the results of simulation analysis, and the magnitude of vibration at a position 15 m across the width of the girder 21 from the center of the pier 22 and footing 23 as structures based on the results of simulation analysis. In Figures 9 and 10, the horizontal axis represents the 1/3 octave band center frequency (Hz), and the vertical axis represents the vibration acceleration level (dB). Also in Figures 9 and 10, squares indicate vibrations when no slab 11 is installed, circles indicate vibrations when a slab 11 with a thickness t of 0.2 m is installed above the upper surface 23a of the footing 23, and triangles indicate vibrations when a slab 11 with a thickness t of 1 m is installed above the upper surface 23a of the footing 23.

As shown in Figure 9, at the output point position 23c of the footing 23, when a slab 11 with a thickness t of 1 m is installed above the upper surface 23a of the footing 23, vibrations in the 25-50 Hz and 80-100 Hz bands are reduced. This is thought to be because the installation of a slab 11 with a thickness t of 1 m above the upper surface 23a of the footing 23 restrains the footing 23, resulting in reduced vibrations at specific frequencies. Furthermore, when a slab 11 with a thickness t of 0.2 m is installed above the upper surface 23a of the footing 23, vibrations in the 80-100 Hz band are reduced. However, because this band has a greater attenuation over distance than the 25-50 Hz band, it is less noticeable at positions further away from the pier 22 and footing 23 as structures in the width direction of the bridge girder 21. Therefore, it is believed that a slab 11 with a thickness t of 0.2 m has a smaller effect on reducing ground vibrations than a slab 11 with a thickness t of 1 m.

Furthermore, as shown in Figure 10, at a position 15 m across the width of the bridge girder 21 from the center of the pier 22 and footing 23 structures, when a slab 11 with a thickness t of 0.2 m is installed above the upper surface 23a of the footing 23, there is no significant change in vibration across most frequency bands compared to when no slab 11 is installed. On the other hand, when a slab 11 with a thickness t of 1 m is installed above the upper surface 23a of the footing 23, vibrations in the 25-40 Hz and 63-100 Hz bands are significantly reduced. Therefore, it is believed that using a slab 11 with a thicker thickness t (a larger numerical value for t) can achieve a significant effect in reducing ground vibration.

Incidentally, roads and parking lots are often paved around train stations and in urban areas, but the thickness of the asphalt portion of a typical pavement is less than 0.2 m for roadways and less than 0.05 m for sidewalks. Since this is thinner than the slab 11, which has a thickness t of 0.2 m as mentioned above, it is believed that the effect of reducing ground vibrations cannot be substantially achieved.

In this way, the slab 11 in this embodiment is a thick concrete plate member installed directly below the viaduct 20, with its upper surface 11d exposed to the ground surface 31 and at least a portion of its lower surface 11e installed above and facing the upper surface 23a of the footing 23 that protrudes laterally from the pier 22 of the viaduct 20 and is buried underground 32.

Furthermore, in the ground vibration reduction method using the slab 11 of this embodiment, a thick concrete plate member is installed directly below the viaduct 20 so that its upper surface 11d is exposed to the ground surface 31 and at least a portion of its lower surface 11e faces the upper surface 23a of the footing 23, which is buried underground 32 and protrudes laterally from the pier 22 of the viaduct 20.

This means that no new land is required, construction is easy, can be done at low cost and in a short period of time, and ground vibrations along the viaduct 20 can be effectively suppressed.

Furthermore, the slab 11 is installed at a distance from the piers 22 and footings 23. This prevents vibrations from being transmitted directly from the piers 22 to the slab 11.

Furthermore, the slab 11 is installed so as to cover 50% or more of the upper surface 23a of the footing 23. As a result, most of the waves incident on the ground from the upper surface 23a of the footing 23 are reflected by the lower surface 11e of the slab 11 and propagate into the ground 32, thereby achieving a high vibration reduction effect.

Furthermore, the slab 11 is installed within an area that does not exceed the overall width A of the bridge girder 21 of the viaduct 20. Therefore, there is no need to secure land for installing the slab 11 outside the site acquired for installing the viaduct 20.

Furthermore, the slab 11 includes an outer slab 11A that is installed in the range from the pier 22 to a position corresponding to the outer widthwise end of the bridge girder 21 of the viaduct 20.

Furthermore, when there are multiple piers 22 in the width direction of the bridge girder 21 of the viaduct 20, the slab 11 includes an inner slab 11B that is installed in the area between the piers 22 in the width direction of the bridge girder 21.

Next, we will explain the second embodiment. Note that components with the same structure as those in the first embodiment will be assigned the same reference numerals and their explanations will be omitted. Furthermore, explanations of the same operations and effects as those in the first embodiment will also be omitted.

Figure 11 is a schematic diagram showing an example of construction of a ground vibration reduction slab for viaducts in the second embodiment. In the figure, (a) shows a cross section, and (b) shows the top surface of the slab.

In this embodiment, restraining underground piles 15 are attached to the slab 11 as slab-attached piles. The restraining underground piles 15 are rod-shaped concrete members that extend vertically underground 32, and their length is preferably set to approximately 2 to 20 m. The upper ends of the restraining underground piles 15 are embedded in the slab 11 without being exposed above the ground surface 31. The restraining underground piles 15 may be manufactured integrally with the slab 11, but in the example shown in the figure, they are manufactured separately from the slab 11, and their upper ends are embedded and attached to the slab 11.

As shown in the figure, in the outer slab 11A, the restraining underground piles 15 are installed in a row to form a single column row extending in the longitudinal direction of the bridge girder 21. Specifically, in each outer slab 11A, three restraining underground piles 15 are installed in a row at a position further outward in the width direction of the bridge girder 21 than the upper surface 23a of the footing 23.

In addition, in the inner slab 11B, the restraining underground piles 15 are installed side by side to form two columns on the left and right that extend in the longitudinal direction of the bridge girder 21. Specifically, in each inner slab 11B, three restraining underground piles 15 are installed side by side in two rows at a position inside the bridge girder 21 in the width direction relative to the upper surface 23a of the footing 23.

In this way, the slab 11 is attached to restraining underground piles 15 buried in the ground 32, so the slab 11 is firmly fixed to the ground, achieving a greater vibration reduction effect.

Note that the rest of the configuration, operation, and effects are the same as those of the first embodiment, so their explanation will be omitted.

In this manner, in this embodiment, multiple restraining underground piles 15 are attached to the slab 11, arranged in a line along the longitudinal direction of the bridge girder 21 of the viaduct 20 and buried in the ground 32.

This firmly secures the slab 11 to the ground, achieving a greater vibration reduction effect.

Next, we will explain the third embodiment. Note that components with the same structure as those in the first and second embodiments will be assigned the same reference numerals and their explanations will be omitted. Furthermore, explanations of the same operations and effects as those in the first and second embodiments will also be omitted.

Figure 12 is a schematic diagram showing an example of construction of a ground vibration reduction slab for viaducts in the third embodiment, and Figure 13 is a schematic diagram showing the state of vibration propagation when a ground vibration reduction slab for viaducts in the third embodiment is constructed. In Figure 12, (a) shows a cross section, and (b) shows the top surface of the slab.

In this embodiment, restraining steel sheet piles 16 are attached to the slab 11 as slab attachment plates. The restraining steel sheet piles 16 are steel plate-shaped members that extend vertically underground 32 and in the longitudinal direction of the bridge girder 21. Their vertical length is preferably set to approximately 2 to 20 m, and the longitudinal dimension of the bridge girder 21 is set to approximately the same as the length of the long side 11a of the slab 11. Furthermore, the upper ends of the restraining steel sheet piles 16 are embedded in the slab 11 without being exposed above the ground surface 31.

As shown in Figure 12, in the outer slab 11A, the restraining steel sheet piles 16 are installed to form a row extending in the longitudinal direction of the bridge girder 21. Specifically, in each outer slab 11A, the restraining steel sheet piles 16 are attached at a position further outward in the width direction of the bridge girder 21 than the upper surface 23a of the footing 23.

In addition, in the inner slabs 11B, the restraining steel sheet piles 16 are installed side by side to form two rows, one on each side, extending in the longitudinal direction of the bridge girder 21. Specifically, in each inner slab 11B, the restraining steel sheet piles 16 are installed side by side to form two rows at a position further inward in the width direction of the bridge girder 21 than the upper surface 23a of the footing 23.

As shown in Figure 13, when a slab 11 with attached restraint steel sheet piles 16 is constructed and placed above the upper surface 23a of a footing 23, most of the waves indicated by arrow 41 that enter the ground from the side surface 23b of the footing 23 pass through the restraint steel sheet piles 16 and propagate into the ground 32, as indicated by arrow 45. The remaining waves are reflected by the restraint steel sheet piles 16 toward the inside of the bridge girder 21 in the width direction, and propagate into the ground 32, as indicated by arrow 43.

Note that, as explained in the first embodiment, the waves incident on the ground from the upper surface 23a of the footing 23 behave as shown in Figure 5, and therefore further explanation is omitted.

In this way, the restraining steel sheet piles 16 buried underground 32 are attached to the slab 11, which not only provides a high vibration reduction effect by firmly fixing the slab 11 to the ground, but also provides a vibration reduction effect by the restraining steel sheet piles 16 in response to waves entering the ground from the side surface 23b of the footing 23.

Note that the rest of the configuration, operation, and effects are the same as those of the first embodiment, so their explanation will be omitted.

In this manner, in this embodiment, restraining steel sheet piles 16 extending in the longitudinal direction of the bridge girder 21 of the viaduct 20 and buried underground 32 are attached to the slab 11.

This allows the restraining steel sheet piles 16 to attenuate waves that enter the ground from the side surface 23b of the footing 23.

Next, we will explain the fourth embodiment. Note that components with the same structure as those in the first to third embodiments will be assigned the same reference numerals and their explanations will be omitted. Furthermore, explanations of the same operations and effects as those in the first to third embodiments will also be omitted.

Figure 14 is a schematic diagram showing an example of construction of a viaduct ground vibration reduction slab in the fourth embodiment, Figure 15 is a first schematic diagram showing the state of vibration propagation when a viaduct ground vibration reduction slab in the fourth embodiment is constructed, and Figure 16 is a second schematic diagram showing the state of vibration propagation when a viaduct ground vibration reduction slab in the fourth embodiment is constructed. In Figure 14, (a) is a diagram showing a cross section, and (b) is a diagram showing the top surface of the slab.

In this embodiment, the outer slab 11A of the slab 11 has a diaphragm wall 12. The diaphragm wall 12 is a thick concrete plate member extending vertically and longitudinally of the bridge girder 21 within the ground 32. Its thickness, i.e., the width of the bridge girder 21, is preferably set to approximately 0.3 to 2 m, its vertical length is preferably set to approximately 2 to 20 m, and the longitudinal dimension of the bridge girder 21 is set to approximately the same as the length of the long side 11a of the outer slab 11A. The diaphragm wall 12 is preferably provided along the outer long side 11a of the bridge girder 21 in the width direction of the outer slab 11A. The diaphragm wall 12 may be manufactured integrally with the outer slab 11A, or may be manufactured separately from the outer slab 11A with its upper end attached to the outer slab 11A.

As shown in the figure, the outer surface 12a of the underground wall 12 is preferably flat with the outer long side 11a of the bridge girder 21 in the outer slab 11A in the width direction, i.e., is approximately flush with the outer long side 11a of the bridge girder 21 in the width direction. Therefore, the cross section of the outer slab 11A having the underground wall 12 is preferably approximately L-shaped.

Note that the inner slab 11B does not have an underground wall 12.

As shown in Figure 15, when an outer slab 11A with a diaphragm wall 12 is constructed and the outer slab 11A is placed above the upper surface 23a of the footing 23, due to the high reflectivity of concrete, most of the waves indicated by arrow 41 that enter the ground from the upper surface 23a of the footing 23 are reflected by the lower surface 11e of the concrete outer slab 11A and then reflected by the inner surface 12b of the concrete diaphragm wall 12, propagating into the ground 32 as indicated by arrow 43. The remaining waves propagate through the lower surface 11e and inner surface 12b within the outer slab 11A as indicated by arrow 44, and some of them then propagate again through the outer surface 12a of the diaphragm wall 12 and into the ground 32 as indicated by arrow 45. This provides a high vibration reduction effect.

Also, as shown in Figure 16, most of the waves indicated by arrow 41 that enter the ground from the side surface 23b of the footing 23 pass through the inner surface 12b as indicated by arrow 44, then pass through the outer surface 12a again, and propagate into the ground 32 as indicated by arrow 45. The remaining waves are reflected by the inner surface 12b and outer surface 12a toward the inside of the bridge girder 21 in the width direction, and propagate into the ground 32 as indicated by arrow 43.

In this way, since the outer slab 11A has a diaphragm wall 12 buried in the ground 32, not only is there a high vibration reduction effect due to the slab 11 being firmly fixed to the ground, but there is also a vibration reduction effect due to the diaphragm wall 12 of waves entering the ground from the side surface 23b of the footing 23.

Note that the rest of the configuration, operation, and effects are the same as those of the first embodiment, so their explanation will be omitted.

As such, in this embodiment, the outer slab 11A has an underground wall 12 that is provided at the outer end of the bridge girder 21 in the width direction of the outer slab 11A and buried in the ground 32.

This firmly fixes the slab 11 to the ground, and the underground wall 12 reduces the vibrations of waves that enter the ground from the side surface 23b of the footing 23, resulting in a greater vibration reduction effect.

The disclosure herein describes features related to preferred and exemplary embodiments. Various other embodiments, modifications, and variations within the scope and spirit of the appended claims will naturally occur to those skilled in the art upon reviewing the disclosure herein.

This disclosure can be applied to ground vibration reduction slabs for viaducts and methods for reducing ground vibration using them.

11 Slab 11A Outer slab 11B Inner slab 11d, 23a Upper surface 11e Lower surface 12 Diaphragm wall 15 Restraining underground pile 16 Restraining steel sheet pile 20 Viaduct 21 Bridge girder 22 Bridge pier 23 Footing 31 Ground surface 32 Underground

Claims (10)

Directly under the viaduct,
A thick concrete plate member with a thickness of 1 m is
The top surface is exposed above ground,
At least a part of the lower surface is installed above the upper surface of a footing that protrudes laterally from the pier of the viaduct and is buried in the ground, so as to face the upper surface of the footing ,
A method for reducing ground vibration using a ground vibration reduction slab for viaducts, characterized in that the thick plate member absorbs waves incident on the ground from the top surface of the footing, thereby reducing the amplitude of waves propagating through the surface layer of the ground . 2. The method for reducing ground vibration using a ground vibration reducing slab for viaducts according to claim 1, wherein the frequency of the wave is 25 to 50 Hz and 80 to 100 Hz. 2. The method for reducing ground vibration using a ground vibration reducing slab for viaducts according to claim 1 , wherein the thick plate member is installed at a distance from the pier and the footing. 2. The method for reducing ground vibration using a ground vibration reducing slab for viaducts according to claim 1 , wherein the thick plate member is installed so as to cover 50% or more of the upper surface of the footing. 2. The method for reducing ground vibration using a ground vibration reducing slab for a viaduct according to claim 1 , wherein the thick plate member is installed within an area not exceeding the overall width of the viaduct girder. A method for reducing ground vibration using a ground vibration reduction slab for an elevated bridge as described in claim 1 , wherein the thick plate member includes an outer slab installed in the range from the pier to a position corresponding to the outer end of the viaduct's bridge girder in the width direction. A method for reducing ground vibration using a ground vibration reduction slab for an elevated bridge as described in claim 6 , wherein when there are multiple piers in the width direction of the viaduct's girder , the thick plate member includes an inner slab installed in the area between the piers in the width direction of the bridge girder . The method for reducing ground vibrations using a ground vibration reduction slab for an elevated bridge, as described in claim 6 , wherein the outer slab has an underground wall provided at the outer end of the bridge girder in the width direction of the outer slab and buried in the ground . A method for reducing ground vibration using a ground vibration reduction slab for an elevated bridge as described in claim 1 , wherein the thick plate members are fitted with slab-attached piles that are buried in the ground and arranged in a row in the longitudinal direction of the viaduct's bridge girder. A method for reducing ground vibration using a ground vibration reduction slab for an elevated bridge as described in claim 1 , wherein a slab accessory plate extending in the longitudinal direction of the viaduct's bridge girder and buried underground is attached to the thick plate member .