JP7115923B2 - Foundation structure reinforcement method and foundation structure reinforcement structure - Google Patents

Description

The present invention relates to a foundation structure reinforcement method and a foundation structure reinforcement structure for reinforcing an existing foundation structure.

In recent years, attempts have been made to improve earthquake resistance by reinforcing existing foundation structures such as abutments. In particular, as a reinforcement structure for increasing the shear resistance against the horizontal force of an earthquake, as described in Non-Patent Document 1 below, it is conceivable to provide a projection on the bottom surface of the footing of the foundation structure. According to this structure, the projections function as shear keys to increase the shear resistance of the footing against horizontal forces.

Japan Road Association, "Specifications for Highway Bridges and Commentaries I Common Volume IV Substructures", March 2012, p.319-320

However, in order to additionally provide the above-mentioned projections to the foundation structure such as the existing abutment, it is necessary to excavate the ground so as to get under the footing of the foundation structure and work in the underground space below the footing. Such a large-scale construction is required. In particular, existing foundation structures are often reinforced during service, and it is sometimes difficult to carry out such large-scale construction as described above. In view of such problems, an object of the present invention is to provide a basic structure reinforcing method and a basic structure reinforcing structure that make it possible to reinforce an existing basic structure more easily.

A foundation structure reinforcement method of the present invention is a foundation structure reinforcement method for reinforcing an existing foundation structure having a retaining wall and a footing provided at the lower end of the retaining wall, wherein a shear key is added to the existing foundation structure. The shear key is rigidly connected to the horizontal end face of the footing and extends upwardly or downwardly from the end face.

In this foundation structure reinforcement method, since the shear key is rigidly connected to the end face in the horizontal direction of the footing, the ground near the end face can be excavated from the ground surface to access the end face and provide the shear key. . Therefore, large-scale construction work can be avoided, and seismic reinforcement of the foundation structure can be easily carried out.

The shear key construction process may include an excavation process of excavating the ground to expose the end face, and a concrete placing process of constructing the shear key by pouring concrete so as to be continuous with the exposed end face. .

In the excavation process, an earth retaining wall is installed at a position spaced horizontally from the end face, and the ground between the end face and the earth retaining wall is excavated to a position below the end face. Concrete may be cast using the earth retaining as part of the formwork. In this case, since the concrete formwork is used for the earth retaining, there is no need to separately prepare a formwork for molding one end face of the shear key.

The shear key construction step may include an excavation step of excavating the ground to expose the end face, and a member joining step of rigidly connecting a shear key member constituting the shear key to the exposed end face.

The shear key member is a steel material, and in the member joining process, the steel material may be driven downward from the space excavated in the excavation process to protrude downward from the end face, and the steel material may be rigidly connected to the end face. .

The foundation structure is an abutment where the retaining wall receives earth pressure from the back, and the shear key may be rigidly connected to the front end face of the footing.

The foundation structure reinforcement structure of the present invention is a foundation structure reinforcement structure that reinforces an existing foundation structure having a retaining wall and a footing provided at the lower end of the retaining wall, and is constructed additionally to the existing foundation structure. An additional shear key is rigidly connected to the end face of the footing and extends upwardly or downwardly from the end face.

ADVANTAGE OF THE INVENTION According to this invention, the foundation structure reinforcement method and foundation structure reinforcement structure which can perform reinforcement of the existing foundation structure more simply can be provided.

(a) is a cross-sectional view showing an existing abutment that is a target of the abutment reinforcing method of the embodiment, and (b) is a cross-sectional view showing the abutment after reinforcement. 4A and 4B are cross-sectional views showing states in each stage of the abutment reinforcement method according to the first embodiment; FIG. 3A and 3B are cross-sectional views showing the state of each stage of the abutment reinforcing method according to the first embodiment following FIG. 2; FIG. 4(a) and 4(b) are cross-sectional views showing the state of each stage of the abutment reinforcing method according to the first embodiment following FIG. 3. FIG. (a), (b) is sectional drawing which shows the state of each step of the abutment reinforcement method based on 2nd Embodiment. (a), (b) is sectional drawing which shows the state of each step of the abutment reinforcement method based on 3rd Embodiment. 7A and 7B are cross-sectional views showing the state of each stage of the abutment reinforcing method according to the third embodiment following FIG. 6; FIG. (a), (b) is sectional drawing which shows the state of each stage of the abutment reinforcement method based on 4th Embodiment. 9A and 9B are cross-sectional views showing the state of each step of the abutment reinforcing method according to the fourth embodiment following FIG. 8; FIG. (a), (b) is sectional drawing which shows the abutment reinforcement structure based on a modification.

EMBODIMENT OF THE INVENTION Hereafter, embodiment of the basic structure reinforcement method and basic structure reinforcement structure which concern on this invention is described in detail, referring drawings. In this embodiment, the foundation structure to be reinforced is an abutment. FIG. 1(a) is a cross-sectional view showing an existing abutment 1 (foundation structure) to be seismically strengthened, and FIG. 1(b) is a cross-sectional view showing the abutment 1 after the seismic reinforcement. The horizontal direction in FIG. 1 is the direction of the bridge axis, and the direction perpendicular to the plane of FIG. 1 is the direction perpendicular to the axis. In the following description, terms such as "front" and "rear" are used assuming that the left side in FIG. 1 is the front side and the right side is the rear side (rear side).

[First Embodiment]
As shown in FIG. 1(a), the abutment 1 is a part of an existing bridge 100 in service, and supports one end of a bridge girder 102 of the bridge 100 via bearings. The abutment 1 has a retaining wall 3 and a footing 5. The retaining wall 3 extends vertically and receives the earth pressure of the ground G from the rear surface to support the ground behind. The footing 5 is provided at the lower end of the retaining wall 3 and extends horizontally. Furthermore, the abutment 1 comprises a plurality of foundation piles 7 extending downward from the bottom surface of the footing 5 to a suitable bearing layer.

As shown in FIG. 1(b), the reinforcing structure 2 of the abutment 1 comprises a shear key 11 additionally constructed on the front end face of the footing 5 (hereinafter "footing front end face 9"). That is, the method of reinforcing the abutment 1 is to additionally construct the shear key 11 provided on the front end face 9 of the footing to the existing abutment 1 . The footing front end surface 9 is substantially vertical, and the shear key 11 is rigidly connected to the footing front end surface 9 . That is, the shear key 11 is connected to the footing 5 at the footing front end face 9 so as to be structurally integrated. Further, the shear key 11 is entirely arranged in front of the footing front end surface 9 and extends downward from the lower end of the footing front end surface 9 .

The shear key 11 may extend across the entire width of the footing 5 in the direction perpendicular to the bridge axis, or may exist for a required width in the direction perpendicular to the bridge axis. Also, a plurality of shear keys 11 may be intermittently installed at predetermined intervals. The shear key 11 may be a section made of reinforced concrete. In this case, the shear key 11 may be constructed of cast-in-place reinforced concrete, or may be constructed by connecting a precast member to the front end face 9 of the footing. Further, the shear key 11 may be a steel material (for example, H steel, steel sheet pile, etc.) coupled to the footing front end face 9 . More preferably, the shear key 11 is embedded to a good support layer.

In the abutment 1, the additional construction of the shear key 11 as described above increases the shear resistance of the footing 5, and provides the same reinforcing effect as the projections on the bottom surface of the footing in Non-Patent Document 1 described above.

Next, a shear key construction process for additionally constructing the shear key 11 for the abutment 1 will be described. The shear key construction process includes an excavation process of excavating the ground in front of the footing front end face 9 to expose the footing front end face 9, and a concrete being poured continuously in front of the exposed footing front end face 9 to form the shear key. and a concrete placing step for building 11. Details of each step will be described below with reference to FIGS. 2 to 4 are enlarged cross-sectional views showing the vicinity of the front end face 9 of the footing.

(Excavation process)
First, as shown in FIG. 2(a), a steel sheet pile 15 as an earth retaining is inserted from the ground surface into the ground G at a position ahead of the footing front end surface 9 by a predetermined distance. Next, as shown in FIG. 2(b), the ground G between the steel sheet pile 15 and the retaining wall 3 is excavated from the ground surface. Furthermore, the ground G between the steel sheet pile 15 and the footing front end surface 9 is excavated to a position deeper than the lower end of the footing front end surface 9, and the footing front end surface 9 is exposed. Also, the ground directly below the bottom surface of the footing 5 is not excavated here. Next, a formwork 16 extending vertically downward continuously from the lower end of the footing front end surface 9 is installed.

The space below the upper end of the footing front end surface 9 of the excavated space is a shear key constructing space Q in which the shear key 11 (see FIG. 1) is constructed. The shear key construction space Q is surrounded by the bottom of the excavated space, the steel sheet pile 15 , the footing front end face 9 and the formwork 16 . The shear key construction space Q does not protrude rearward from the front end face 9 of the footing. The footing front end surface 9 of the footing 5 is exposed to the shear key building space Q during the excavation process.

Next, a post-installed anchor 17 is embedded in the exposed front end face 9 of the footing as shown in FIG. 3(a). Here, for example, the front end surface 9 of the footing is perforated from the front, and the hole is filled with a curable material such as an organic adhesive or an inorganic adhesive, and the rear end of the post-installed anchor 17 is inserted. , the post-installed anchor 17 is fixed to the footing 5 by curing the curable material. The post-installed anchor 17 may be an anchor bolt or a reinforcing bar. After that, as shown in FIG. 3B, reinforcing bars are attached to the post-installed anchors 17 projecting forward from the front end face 9 of the footing, and the reinforcing bars 19 are assembled in the shear key construction space Q. The post-installed anchors 17 are not limited to the adhesive anchors fixed with a hardening material as described above, but are metal anchors composed of metal parts (for example, metal expansion anchors, metal expansion anchors, etc.). or other known types of anchors can be employed as appropriate.

(Concrete placing process)
After that, as shown in FIG. 4(a), concrete C is placed in the shear key construction space Q. As shown in FIG. Concrete C comes into contact with the earth retention made up of steel sheet piles 15, the front end face 9 of the footing, the formwork 16, and the bottom surface of the excavated space. When the concrete C hardens, a rectangular parallelepiped reinforced concrete mass 21 is formed in the shear key construction space Q. As shown in FIG. The reinforced concrete mass 21 is rigidly connected to the footing front end face 9 via post-installed anchors 17 and extends downward from the footing front end face 9 at a position forward of the footing front end face 9 .

After that, as shown in FIG. 4(b), the upper portion of the steel sheet pile 15 exposed in the excavated space is cut off and removed, and the ground G in the excavated space is backfilled to complete the reinforcement work. It should be noted that it is not essential to cut and remove the upper portion of the steel sheet pile 15 as described above, and the entire steel sheet pile 15 may be buried. The reinforced concrete mass 21 formed as described above constitutes the shear key 11 .

Effects of the abutment reinforcing method and the abutment reinforcing structure of the present embodiment described above will be described. In this type of abutment reinforcement method and abutment reinforcement structure, if the shear key projecting below the footing 5 were to be connected at a position behind the footing front end surface 9 of the footing 5, it would be likely to slip under the footing 5. Large-scale construction such as excavating the ground and working in the underground space below the footing 5 is required. In particular, when the foundation piles 7 are present below the footing 5, it is necessary to excavate the ground while avoiding the foundation piles 7, which may increase the scale of the construction work.

In contrast, in the abutment reinforcement method and abutment reinforcement structure of the present embodiment, the shear key 11 is rigidly connected to the front end face 9 of the footing. The shear key 11 can be provided by exposing the footing front end face 9 and installing post-installed anchors 17 on the exposed footing front end face 9 . Therefore, it is possible to avoid large-scale construction work as described above, and to easily carry out seismic reinforcement of the abutment 1 . Further, since the entire shear key 11 is arranged in front of the footing front end surface 9, it is not necessary to excavate the ground under the bottom surface of the footing 5. In addition, since the earth retaining structure made of the steel sheet piles 15 is used as a formwork for the concrete C, there is no need to separately prepare a formwork for forming the front end surface of the shear key 11 .

Further, as a method for increasing the shear resistance of the abutment 1, a method of improving the entire ground G in front of the retaining wall 3 and the footing 5 is also conceivable. However, there are cases where an underground buried object is installed in the space above the footing 5 in front of the retaining wall 3, and in that case the above method cannot be adopted. In contrast, in the abutment reinforcement method and abutment reinforcement structure of the present embodiment, the shear key 11 is added in front of the front end face 9 of the footing. .

[Second embodiment]
Next, a second embodiment of the abutment reinforcement method and abutment reinforcement structure according to the present invention will be described. In the present embodiment, the same reference numerals are given to the same or equivalent components as those of the first embodiment described above, and overlapping descriptions will be omitted.

This embodiment differs from the first embodiment in the concrete placing process. As described above, in the concrete placing step of the first embodiment, the concrete C is placed using the steel sheet pile 15 as part of the formwork. On the other hand, in the concrete placing process of the present embodiment, as shown in FIG. A formwork 18 is installed separately. Therefore, the installation position of the steel sheet pile 15 is set further forward than in the first embodiment in order to secure the installation space for the formwork 18 and the installation work space.

After that, as shown in FIG. 5(b), the formwork 18 is removed after the concrete C hardens and the reinforced concrete mass 21 is formed. Further, the steel sheet pile 15 is removed, the ground G in the excavated space is backfilled, and the reinforcement work is completed. In addition, it is not essential to remove the steel sheet pile 15 as described above, and the steel sheet pile 15 may be buried. The reinforced concrete mass 21 formed as described above constitutes the shear key 11 .

The abutment reinforcing method and abutment reinforcing structure of the present embodiment as described above also provide the same effects as those of the first embodiment. In the above-described shear key construction process in this embodiment, as shown in FIG. 5B, a backfill layer exists in front of the shear key 11 after completion. The backfill layer is often softer than the ground before excavation. On the other hand, in the shear key construction process in the first embodiment, as shown in FIG. Horizontally supported. Therefore, compared with the present embodiment, the abutment reinforcing method and abutment reinforcing structure of the first embodiment have a higher reinforcing effect.

[Third Embodiment]
Next, a third embodiment of the abutment reinforcement method and abutment reinforcement structure according to the present invention will be described. In this embodiment, the same reference numerals are given to the same or equivalent components as in the first or second embodiment described above, and overlapping descriptions will be omitted.

This embodiment differs from the first embodiment in the shear key construction process. The shear key construction process in this embodiment includes an excavation process of excavating the ground G in front of the footing front end face 9 to expose the footing front end face, and a shear key forming the shear key 11 with respect to the exposed footing front end face 9. and a member joining step of rigidly joining the members. The above shear key member is steel. In the member joining process, the steel material is driven downward from the space excavated in the excavation process to protrude downward from the front end face 9 of the footing, and the steel material is rigidly connected to the front end face 9 of the footing. Details of each step will be described below with reference to FIGS.

(Excavation process)
As shown in FIG. 6(a), similarly to the first embodiment, the steel sheet piles 15 are installed and the ground G is excavated to expose the footing front end face 9. As shown in FIG. Here, it differs from the first embodiment in that the ground G is excavated to the depth position of the lower end of the footing front end surface 9 .

(Member joining process)
Next, as shown in FIG. 6(b), a post-installed anchor 17 is embedded in the exposed front end face 9 of the footing. Anchor bolts are used as post-installed anchors 17 . After that, as shown in FIG. 7(a), the H steel 29 (shear key member) is carried in between the steel sheet pile 15 and the front end face 9 of the footing. The vertical length of the H steel 29 is longer than the vertical length of the footing front end surface 9 . The H steel 29 is driven downward from the bottom of the excavated space, and the H steel 29 is embedded at a depth where the upper end of the H steel 29 substantially coincides with the upper end of the footing front end face 9 . The H steel 29 protrudes downward from the footing front end surface 9 . Thereafter, the H steel 29 is fixed to the front end surface 9 of the footing by bolting the upper end flange of the H steel 29 to the post-installed anchor 27 .

A plurality of H steels 29 as described above are intermittently installed at predetermined intervals in the direction perpendicular to the bridge axis. Alternatively, a plurality of H steels 29 may be installed continuously without spacing in the direction perpendicular to the bridge axis. Each H steel 29 is rigidly connected to the footing front end face 9 via a post-installed anchor 27 and extends downward from the footing front end face 9 at a position forward of the footing front end face 9 . After that, as shown in FIG. 7(b), the steel sheet pile 15 is removed and the ground G in the excavated space is backfilled to complete the reinforcement work. The H steel 29 installed as described above constitutes the shear key 11 .

The abutment reinforcing method and abutment reinforcing structure of the third embodiment as described above also provide the same effects as those of the first embodiment. Note that, instead of the H steel 29, another steel material (for example, a steel sheet pile) may be adopted. If the member (shear key member) constituting the shear key 11 is made of steel, the shear key member is driven downward from the front end face 9 of the footing by driving the shear key member downward from the excavated space as described above. It can be extended. That is, in the excavation step, it is not necessary to excavate the ground G to a position below the lower end of the footing front end face 9, and the amount of excavation is reduced.

[Fourth Embodiment]
Next, a fourth embodiment of the abutment reinforcement method and abutment reinforcement structure according to the present invention will be described. In this embodiment, the same reference numerals are given to the same or equivalent components as in the first to third embodiments described above, and overlapping descriptions are omitted.

This embodiment differs from the third embodiment in that the shear key member is a precast block. The excavating process and the member joining process in this embodiment will be described below with reference to FIGS. 8 and 9. FIG.

(Excavation process)
As shown in FIG. 8A, similarly to the first embodiment, the steel sheet pile 15 is installed and the ground G is excavated to expose the footing front end face 9 . Here, the ground G is excavated to a position deeper than the lower end of the footing front end face 9 .

(Member joining process)
Next, as shown in FIG. 8(b), a post-installed anchor 17 is embedded in the exposed front end face 9 of the footing. Anchor bolts are used as post-installed anchors 17 . After that, as shown in FIG. 9( a ), a precast block 31 (shear key member) made of reinforced concrete is inserted between the steel sheet pile 15 and the front end face 9 of the footing. The precast block 31 has a substantially rectangular parallelepiped shape, and the vertical length of the precast block 31 is longer than the vertical length of the footing front end surface 9 . Here, the precast block 31 is installed so that the upper end of the precast block 31 substantially coincides with the upper end of the footing front end surface 9 , and the precast block 31 protrudes downward from the footing front end surface 9 . After that, the precast block 31 is fixed to the footing front end face 9 by bolting the precast block 31 to the post-installed anchor 27 . Note that the precast block 31 is provided in advance with a box cut-out portion for bolting.

A plurality of precast blocks 31 as described above are intermittently installed at predetermined intervals in the direction perpendicular to the bridge axis. Each precast block 31 is rigidly connected to the footing front end face 9 via a post-installed anchor 27 and extends downward from the footing front end face 9 at a position forward of the footing front end face 9 . After that, as shown in FIG. 7(b), the steel sheet pile 15 is removed and the ground G in the excavated space is backfilled to complete the reinforcement work. The precast block 31 installed as described above constitutes the shear key 11 .

The abutment reinforcing method and abutment reinforcing structure of the fourth embodiment as described above also provide the same effects as those of the first embodiment. Moreover, by adopting the precast block 31, the construction period can be further shortened compared to the case of constructing the shear key 11 with cast-in-place concrete.

The present invention can be embodied in various forms with various modifications and improvements based on the knowledge of those skilled in the art, including each embodiment described above. Moreover, it is also possible to configure a modified example using the technical matters described in the above-described embodiments. You may use it, combining the structure of each embodiment suitably.

In each embodiment, the abutment 1 of the pile foundation structure has been described as an example, but the present invention is also applicable to the abutment of the direct foundation structure. In addition, the present invention is not limited to the reinforcing structure and method of abutments, and can be applied to methods of reinforcing foundation structures other than abutments (for example, piers, retaining walls, building foundations, facility foundations, etc.). Further, in each embodiment, the shear key 11 extending downward from the footing front end face 9 has been described as an example, but as shown in FIG. A shear key 11 may be employed that extends to the Further, a shear key 11 extending from the front end face 9 of the footing so as to protrude in both vertical directions may be employed. In these cases, following the shear key construction process of the abutment reinforcement method described in each embodiment, a shear key made of cast-in-place reinforced concrete, steel material, or precast block is rigidly connected to the front end face 9 of the footing to form the abutment reinforcement structure. can be built.

In the first embodiment, when the excavation surface in the shear key construction space Q is not good, excavation is performed by filling the shear key construction space Q with a stabilizing liquid in the excavation step, and underwater concrete is poured in the concrete placing step. You may make it set.

Further, in the embodiment, the steel sheet pile 15 (earth retaining) is installed in the excavation process, but the installation of the earth retaining is not essential. For example, when the ground G is hard ground, if the excavated ground is self-sustaining, it is possible to omit earth retaining. Similarly, if the excavated ground is self-supporting, it is possible to omit the formwork 16 in the first and second embodiments. Moreover, even when the excavated ground does not stand on its own, it is possible to excavate the ground G widely and excavate while forming a loose slope so that the excavated surface does not collapse, thereby omitting earth retaining. In particular, when it is not necessary to deepen the excavation depth, it is preferable to omit the earth retaining as described above.

Further, in order to further reinforce the abutment 1, in addition to constructing the shear key 11 as in each embodiment, another abutment reinforcing structure may be adopted. For example, a reinforcing structure that adds shear reinforcing bars to the retaining wall 3 may also be adopted. Moreover, as shown in FIG.10(b), the ground anchor 41 fixed to the front surface of the retaining wall 3 and extending diagonally downward and rearward from the said fixing part 41a may further be added.

DESCRIPTION OF SYMBOLS 1... Abutment (foundation structure), 3... Retaining wall, 5... Footing, 9... Front end face of footing, 11... Shear key, 15... Steel sheet pile (earth retaining), 29... H steel (shear key member), 31... Precast block (Shear key member), C... concrete, G... ground.

Claims (5)

A foundation structure reinforcement method for reinforcing an existing foundation structure having a retaining wall and a footing provided at the lower end of the retaining wall, comprising:
A shear key construction step for additionally constructing a shear key for the existing foundation structure,
The shear key is
rigidly connected to a horizontal end surface of the footing and extending upwardly or downwardly from the end surface;
The shear key building step includes:
an excavation step of excavating the ground in front of the end face to a position below the lower end of the end face in a groove shape to expose the end face in an excavation space;
A reinforcing bar group extending from the end face to a position below the lower end of the end face is installed in a shear key construction space that is continuous with the end face exposed in the excavation space and extends to a position below the lower end of the end face. and a concrete placing step of placing concrete and constructing the shear key made of reinforced concrete containing the hardened concrete. In the excavation step, a retaining wall is installed at a position horizontally spaced from the end face, and the ground between the end face and the retaining wall is excavated to a position below the end face;
2. The method of reinforcing a foundation structure according to claim 1, wherein, in said concrete placing step, said concrete is placed in the space excavated in said excavating step using said earth retaining as part of a formwork. A foundation structure reinforcement method for reinforcing an existing foundation structure having a retaining wall and a footing provided at the lower end of the retaining wall, comprising:
A shear key construction step for additionally constructing a shear key for the existing foundation structure,
The shear key is
rigidly connected to a horizontal end surface of the footing and extending upwardly or downwardly from the end surface;
The shear key building step includes:
an excavation step of excavating the ground in front of the end surface to expose the end surface in an excavation space;
a steel material driving step of driving a plurality of steel materials downward from the excavated space along the exposed end face to project the steel materials below the end face;
and a steel rigidly connecting step of rigidly connecting the steel materials to the end face without connecting the plurality of steel materials with a connecting member to construct the shear key made of the steel material. A foundation structure reinforcement method for reinforcing an existing foundation structure having a retaining wall and a footing provided at the lower end of the retaining wall, comprising:
A shear key construction step for additionally constructing a shear key for the existing foundation structure,
The shear key is
rigidly connected to a horizontal end surface of the footing and extending upwardly or downwardly from the end surface;
The shear key building step includes:
an excavation step of excavating the ground in front of the end face to a position below the lower end of the end face in a groove shape to expose the end face in an excavation space;
A state in which a precast block is inserted into a shear key building space that continues to the end face exposed in the excavation space and extends to a position below the lower end of the end face, and the precast block protrudes below the end face. rigidly connecting the precast block to the end face in step (b) to construct the shear key made of the precast block. The foundation structure is an abutment in which the retaining wall receives earth pressure from the back,
The method of reinforcing a basic structure according to any one of claims 1 to 4, wherein the shear key is rigidly connected to the front end face of the footing.

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