JP2021008720A - Caisson, pneumatic caisson method and structure - Google Patents

Abstract

To provide a caisson allowing a structure to have better earthquake resistance than that of the conventional ones.SOLUTION: A caisson 1 used in a foundation of a structure comprises: a main section 2 forming a cylindrical shape and extending in a vertical direction; and a projected section 3 formed on at least one part of a periphery at a lower end of the main section 2 and projecting further than the main section 2 in a horizontal direction.SELECTED DRAWING: Figure 1

Description

It relates to a caisson used as a foundation of a structure, a pneumatic caisson method for constructing this caisson in the ground, and a structure having the above caisson.

Conventionally, a pneumatic caisson method has been known in which a caisson is constructed in the ground by laying a skeleton made of highly rigid reinforced concrete or the like while excavating the ground (for example, Patent Document 1).

Since the caisson constructed by using this pneumatic caisson method has high rigidity, the seismic resistance of the structure can be improved by adopting the caisson as the foundation of a structure such as a building. In recent years, various methods of using caissons for the purpose of increasing the rigidity of harbor structures such as quays / guards (sheet pile type quays and gravity type quays) and piers have been studied.

The sheet pile type quay has a structure that prevents the steel sheet pile wall from collapsing toward the sea by making a wall from steel sheet piles and connecting this wall with a steel pipe as a pile with a tie rod. The quay has a structure that prevents the wall body from collapsing toward the sea side by making a wall body with high rigidity and heavy weight. In addition, the pier has a structure that supports the upper structure of reinforced concrete by constructing a large number of steel pipe piles. All of these have a height difference between the seabed and the ground surface in order to enable berthing and cargo handling of vessels. For example, when enabling berthing of large vessels, the height difference becomes very large. Therefore, it is difficult to secure sufficient seismic resistance with the conventional structure.

Therefore, in order to increase the rigidity of the sheet pile type quay, gravity type quay and pier to ensure sufficient earthquake resistance, studies have been made to replace the steel pipe piles used for these sheet pile type quay and pier with a more rigid caisson. Also, regarding the gravity type quay, studies are being made to replace the caisson with a caisson having a root.

Japanese Patent No. 4455543

By the way, as mentioned above, even if the steel pipe piles of the sheet pile type quay and the pier are replaced with caissons, or the caisson of the gravity type quay is replaced with a caisson with rooting, there is a problem that there is a limit to the improvement of seismic resistance. There is. This problem will be described in detail below.

When an earthquake occurs, a seismic load acts on the structure, and this seismic load is usually treated as a horizontal load. In the sheet pile type quay and pier, the caisson replaced from the steel pipe pile has the rigidity of the caisson itself (does not bend significantly with respect to the horizontal load) and the horizontal resistance of the ground (the caisson that collapses when the horizontal load acts). It is expected to resist with the two effects of (the ground supports). It is expected that the caisson with the replaced rooting in the gravity quay will also resist with the same two effects as above.

However, when an earthquake occurs, the rigidity of the soft ground decreases, and the horizontal resistance of the ground supporting the caisson is greatly reduced compared to before the earthquake. For this reason, the horizontal resistance of the ground is insufficient, and the horizontal resistance acting on the caisson is only the reaction force from the highly rigid ground (engineering foundation) deep in the ground, so how much is the rigidity of the caisson itself? Even if it is increased, the horizontal resistance is insufficient, and deformation such as inclination due to an increase in inertial force and earth pressure is unavoidable. In particular, as mentioned above, in the quays / revetments and piers installed in harbors, there is a height difference between the seabed and the ground surface, so a strong load acts on the sea side due to the influence of earth pressure. The caisson tends to tilt greatly toward the sea side.

In this way, even if a highly rigid caisson is used for the foundation of the structure, if the horizontal resistance of the ground is insufficient, the rigidity of the caisson itself hardly contributes to earthquake resistance, and inertial force and soil pressure Since deformation such as inclination due to the increase in the number of caisson is unavoidable, there is a limit to the improvement of earthquake resistance by simply adopting a caisson as the foundation of the structure, and there is room for improvement.

The present invention has been made in view of the above circumstances, and includes a caisson capable of improving the seismic resistance of a structure, a pneumatic caisson method for constructing this caisson in the ground, and a pneumatic caisson method. The purpose is to provide a structure having a caisson constructed using it.

The characteristic configuration of the caisson according to the present invention for achieving the above object is the caisson used as the foundation of the structure.
The main part, which has a tubular shape and extends in the vertical direction,
It is a point having a protruding portion formed on at least a part of the outer periphery of the lower end portion of the main portion and protruding in the horizontal direction from the main portion.

According to the above characteristic configuration, when a horizontal load is applied to the caisson, a large reaction force acts on the bottom surface of the main portion and the protruding portion in the vertical direction from the ground, and the protruding portion is formed. A large horizontal resistance acts on the lower end of the caisson. Therefore, compared to the case where there is no protrusion as in the past, the reaction force and horizontal resistance in the vertical direction acting on the caisson are larger, so it is difficult to incline even if the inertial force and earth pressure increase. ..
When a strong load acts on the sea side against the cason due to the influence of unbalanced earth pressure, the load on the sea side is resisted by forming a protrusion on the sea side at the outer periphery of the lower end of the main part. As described above, since a large reaction force acts on the bottom surface of the protruding portion in the vertical direction, deformation such as inclination due to an increase in inertial force and earth pressure is suppressed as compared with the conventional case.
In addition, since a protruding portion is provided on at least a part of the outer periphery of the lower end portion of the main portion so that a reaction force or horizontal resistance in the vertical direction acts on the protruding portion, the entire main portion is thickened to make the ground thicker. If the inertial force can be reduced and the rigidity of the caisson itself can be sufficiently secured compared to the case where the horizontal resistance of the caisson is increased, the material required for constructing the caisson is reduced. It is also possible to reduce costs.

Further, the characteristic configuration of the pneumatic caisson method according to the present invention for achieving the above object is the pneumatic caisson method for constructing the caisson in the ground.
The landing process of excavating the ground and landing the caisson,
The point is to perform a backfilling step of backfilling the backfilling space formed above the protruding portion in the bottoming step.

According to the above characteristic configuration, the bottoming step is performed to land the lower end of the caisson. At this time, since a protruding portion is formed on the outer periphery of the lower end portion of the main portion of the caisson, it is necessary to excavate a region larger than the cross section of the main portion when landing the caisson. Therefore, a space (backfill space) that is not filled with earth and sand or the like is formed above the protrusion in the ground during the bottoming process. Therefore, in the above-mentioned feature configuration, the backfilling step is performed at the same time as the bottoming step, or the backfilling step is performed after the bottoming step to backfill the backfilled space formed in the bottoming step. As a result, a caisson having a protruding portion formed on the outer periphery of the lower end portion of the main portion can be constructed in the ground.
And, the caisson constructed by this pneumatic caisson method is less likely to tilt even if the inertial force and earth pressure increase as compared with the conventional caisson, and this caisson is used as the foundation of the structure. By adopting it in, the earthquake resistance of the structure can be improved more than before.

Further, a further characteristic configuration of the pneumatic caisson method according to the present invention is that the backfill space is backfilled with granules in the backfilling step.

According to the above characteristic configuration, since the backfill space is backfilled with granules, it is possible to create columns of granules in the ground, which can quickly dissipate the excess pore water pressure generated during an earthquake. This makes it possible to suppress the adverse effects of liquefaction.

Further, a further characteristic structure of the pneumatic caisson method according to the present invention is that the granules are crushed stones.

According to the above characteristic configuration, a crushed stone column can be created in the ground, the excess pore water pressure generated at the time of an earthquake can be dissipated at an early stage, and the adverse effect of liquefaction can be suppressed.

Further, the characteristic configuration of the structure according to the present invention for achieving the above object is that it has the above caisson that has landed on the ground.

According to the above characteristic configuration, the caisson having a protruding portion formed on at least a part of the outer periphery of the lower end portion of the main portion has a structure of landing on the ground, and this caisson has an inertia as compared with a conventional caisson. It is difficult to incline even if the force or earth pressure increases. Therefore, the structure having the above-mentioned characteristic configuration has improved seismic resistance as compared with the conventional one.

Further, a further characteristic configuration of the structure according to the present invention is that a pillar made of granular material is formed above the protruding portion in the caisson.

According to the above characteristic configuration, the formation of columns made of granules in the ground makes it possible to dissipate the excess pore water pressure generated during an earthquake at an early stage, and suppress the adverse effects of liquefaction. it can.

Further, a further characteristic structure of the structure according to the present invention is that the granules are crushed stones.

According to the above characteristic composition, since the crushed stone pillars are formed in the ground, the excess pore water pressure generated at the time of an earthquake can be dissipated at an early stage, and the adverse effect of liquefaction can be suppressed. be able to.

Further, a further characteristic structure of the structure according to the present invention is installed in a port.
The protrusion in the caisson is at least formed on the sea side.

As mentioned above, harbor structures such as quays, seawalls and piers have a height difference between the sea surface and the ground surface, so a strong load acts on the sea side due to the influence of earth pressure, and the caisson moves to the sea. It is easy to tilt greatly toward the side.
However, in the above-mentioned characteristic configuration, since the caisson protrusion is formed at least on the sea side, a large reaction force in the vertical direction acts on the bottom surface of the protrusion so as to resist the load on the sea side. Therefore, the inclination of the caisson due to the increase in inertial force and earth pressure is suppressed. Therefore, the structure having the above-mentioned characteristic structure has improved seismic resistance as compared with the structure having a conventional caisson.

Further, the structure further characterized by the present invention includes a first caisson having a protrusion protruding in at least the first direction.
It has at least a second caisson having a protrusion protruding in the second direction opposite to the first direction.

According to the above characteristic configuration, the first caisson having a protruding portion protruding in the first direction is less likely to be deformed such as tilting in the first direction, and the second caisson having a protruding portion protruding in the second direction. Is unlikely to cause deformation such as inclination in the second direction. Therefore, since the structure has these first and second caissons, a phenomenon in which the structure sways and floats alternately in the first direction and the second direction when an earthquake occurs (so-called locking phenomenon). ) Is suppressed.

It is a front view which shows the schematic structure of the caisson which concerns on one Embodiment. It is a top view which shows the schematic structure of the caisson which concerns on one Embodiment. It is a top view which shows the schematic structure of the caisson which concerns on another embodiment. It is a top view which shows the schematic structure of the caisson which concerns on another embodiment. It is a figure for demonstrating the procedure of the pneumatic caisson method which concerns on one Embodiment. It is a figure for demonstrating the procedure of the pneumatic caisson method which concerns on one Embodiment. It is a figure for demonstrating the procedure of the pneumatic caisson method which concerns on one Embodiment. It is a figure for demonstrating the problem which arises in a conventional caisson. It is a figure for demonstrating the effect of the caisson which concerns on one Embodiment. It is a figure which shows the schematic structure of the structure which concerns on one Embodiment. It is a figure which shows the schematic structure of the structure which concerns on another embodiment. It is a figure which shows the schematic structure of the structure which concerns on another embodiment. It is a graph which shows the relationship between the protrusion amount and resistance moment. It is a graph which shows the relationship between the deformation amount and the height about the caisson in which a protrusion is not formed. It is a graph which shows the relationship between the amount of deformation and the height about the caisson in which a protrusion is formed. It is a graph which shows the relationship between the bending moment and the height about the caisson which the protrusion is not formed. It is a graph which shows the relationship between the bending moment and the height about a caisson in which a protrusion is formed. It is a graph which shows the relationship between the protrusion amount and the deformation amount ratio.

Hereinafter, the caisson, pneumatic caisson method, and structure according to the embodiment of the present invention will be described with reference to the drawings.

[caisson]
1 and 2 are diagrams showing a schematic configuration of a caisson 1 according to an embodiment. As shown in FIGS. 1 and 2, the caisson 1 is a caisson used as a foundation of a structure, and has a main portion 2 forming a hollow cylinder and extending in the vertical direction, and a lower end portion of the main portion 2. It has a protruding portion 3 formed on at least a part of the outer periphery and protruding in the horizontal direction from the main portion 2.

In the caisson 1, the portion of the main portion 2 on which the protruding portion 3 is formed has a solid shape, and the cutting edge 4 is formed on the lower end surface of the caisson 1 from the main portion 2 to the protruding portion 3. A through hole 5 for transporting earth and sand and materials and allowing people to enter and exit is formed in communication between the blade edge 4 and the inside of the main portion 2 when the caisson 1 is constructed by the pneumatic caisson method described later. There is. The blade edge 4 and the through hole 5 are appropriately filled with concrete after the caisson 1 is constructed in the ground.

Regarding the caisson 1 according to the embodiment, as shown in FIGS. 1 and 2, the caisson having a structure in which the protruding portion 3 extends in one direction from a part of the outer periphery of the lower end portion of the main portion 2 (hereinafter, also referred to as a one-side protruding caisson). However, the shape of the protruding portion 3 is not limited to this. As shown in FIG. 3, for example, the caisson according to the present invention protrudes horizontally from the outer periphery of the lower end portion of the main portion 2a to the entire circumference of the main portion 2a, and has an outer shape larger than the outer shape of the main portion 2a. It may be a caisson 1a having a protruding portion 3a of the configuration (hereinafter, also referred to as a circular protruding caisson), or as shown in FIG. 4, centered on the axial center of the main portion 2b from the outer periphery of the lower end portion of the main portion 2b. It may be a caisson 1b (hereinafter, also referred to as a bilateral protruding caisson) having a protruding portion 3b having a structure extending in two opposite directions.

Further, the shape of the protruding portions 3, 3a, 3b of the caisson 1, 1a, 1b as viewed from above is not particularly limited. As shown in FIGS. 2 and 3, the protruding portion of the caisson may be rectangular in top view or circular in top view, semicircular in top view, elliptical shape in top view, semi-elliptical shape in top view, and top surface. It may have a triangular shape. Further, the area of the lower surface of the protruding portion is preferably a certain size, but is not particularly limited. As a preferable range of the area of the lower surface of the protruding portion, about twice or less the area of the lower surface of the main portion can be exemplified.

Further, the main portions 2, 2a, 2b of the caisson 1, 1a, 1b are not limited to a cylindrical shape, and the cross-sectional shape thereof may be a quadrangle, a triangle, or any other shape as long as it is cylindrical.

According to the caisson 1,1a, 1b, when a horizontal load is applied to the caisson 1,1a, 1b while buried in the ground, the main parts 2, 2a, 2b and the protruding parts 3, 3a, 3b A reaction force acting in the vertical direction from the ground acts on the bottom surface of the surface, and horizontal resistance acts on the protruding portions 3, 3a and 3b. As a result, the reaction force and horizontal resistance in the vertical direction acting on the caissons 1, 1a and 1b are larger than those of the caisson in which the protrusions 3, 3a and 3b are not formed, so that the inertial force and the earth pressure are increased. It is difficult to tilt even if it increases.

The widths W, Wa, Wb1 and Wb2 of the protruding portions 3, 3a and 3b should be increased from the viewpoint of increasing the reaction force and the horizontal resistance acting on the protruding portions 3, 3a and 3b in the vertical direction. However, by increasing the widths W, Wa, Wb1 and Wb2, the amount of material for caissons 1,1a and 1b and the amount of excavation of the ground when constructing caissons 1,1a and 1b in the ground increase. The cost increases. Therefore, the widths W, Wa, Wb1, Wb2 of the protrusions 3, 3a, 3b are set to have a size such that a reaction force or a horizontal resistance that can sufficiently suppress the inclination of the caisson 1, 1a, 1b acts, and are larger than necessary. It is preferable not to do so. For example, the width W of the protruding portion 3 of the one-sided protruding caisson 1, the width Wa of the protruding portion 3a of the circular protruding caisson 1a, and the widths Wb1 and Wb2 of the protruding portion 3b of the two-sided protruding caisson 1b are all about 5 m or less. Is preferable.

[Pneumatic caisson method]
Next, the procedure of the pneumatic caisson method according to the embodiment will be described with reference to FIGS. 5 to 7. In the following, the case where the caisson 1 is constructed in the ground by the pneumatic caisson method will be described as an example. However, in the caisson according to the present invention, the caisson after submerging a plurality of ring bodies as a main part is described. It also includes a caisson constructed by forming a protrusion at the lower end of the.

First, the bottoming process is performed. In the bottoming step, the caisson 1 is landed while the base 11a and the plurality of annular bodies 11b prepared in advance are sequentially subsided and the base 11a and the plurality of annular bodies 11b are connected. Specifically, first, as shown in FIG. 5, the base 11a to be the main portion 2 and the protruding portion 3 of the caisson 1 prepared in advance is installed on the ground and communicates with the through hole 5 formed in the base 11a. The man shaft 12, the material shaft 13, and the like are constructed by the crawler crane Ca. Then, the ground G inside and below the blade edge 4 is excavated by a remotely controllable excavator S, and the base 11a is subsided by the weight of the base 11a. The earth and sand generated by excavation is transported to the ground surface through the material shaft 13 and appropriately carried out by the skater crane Cb.

After that, while sequentially connecting the plurality of annular bodies 11b serving as the main portion 2 onto the base 11a, the ground G inside and below the cutting edge 4 is excavated, and the base 11a and the plurality of annular bodies 11b are subsided. Place the caisson 1 in place. The predetermined position is preferably a position where the lower end side of the caisson 1 reaches the engineering base. For example, about 1 m of the lower end side of the caisson 1 reaches the engineering base. It is a position like.

After that, as shown in FIG. 6, concrete is injected into the blade edge 4 and the through hole 5 from the outside (broken line arrow in FIG. 6), and the blade edge 4 and the through hole 5 are filled with concrete and attached. Finish the bottom process.

Here, as shown in FIG. 6, in the pneumatic caisson method according to the present embodiment, when the caisson 1 is landed, it is necessary to excavate a region larger than the cross section of the main portion 2, so that the caisson 1 is landed. In the ground after the process, a backfill space Ga that is not filled with earth and sand is formed above the protrusion 3.

Therefore, when the caisson 1 having the protruding portion 3 is constructed in the ground by the pneumatic caisson method, the backfilling step of backfilling the backfilled space Ga is performed after the bottoming step. In the pneumatic caisson method according to the present embodiment, in the backfilling step, the backfilled space Ga is backfilled with crushed stone D to create a crushed stone pillar D1 (see FIG. 7).

As described above, according to the pneumatic caisson method according to the present embodiment, the caisson 1 in which the protruding portion 3 is formed can be constructed in the ground by performing the bottoming step and the backfilling step. In the backfilling process, the backfilled space Ga is backfilled with crushed stone D, so that the crushed stone pillar D1 can be created in the ground, so that the excess pore water pressure generated during an earthquake can be dissipated at an early stage. And the adverse effects of liquefaction can be suppressed.

The amount of protrusion of the protrusions 3, 3a, 3b in each caisson 1, 1a, 1b is the same so that the amount of excavation of the ground when constructing the one-sided protruding caisson 1, the circular protruding caisson 1a, and the two-sided protruding caisson 1b is the same. When is set, the caisson is preferably a circular protruding caisson 1a from the viewpoint of forming the crushed stone column D1 and increasing the surface area of the crushed stone column D1 in order to suppress the adverse effect due to liquefaction.

Further, the material used for backfilling the backfill space Ga is not limited to crushed stone, but is a granular material having a particle size of about 10 to 100 mm within a range in which the water permeability coefficient required for liquefaction countermeasures can be secured. There may be. Even in this case, since granular columns can be created in the ground, the excess pore water pressure generated during an earthquake can be dissipated at an early stage, and the adverse effects of liquefaction can be suppressed. Can be done.

Further, in the above-mentioned pneumatic caisson method, the backfilling step is performed after the bottoming step is performed, but the backfilling step may be performed at the same time as the bottoming step.

Next, with reference to FIGS. 8 and 9, the caisson 1 constructed by the pneumatic caisson method according to the present embodiment is less likely to tilt even if the inertial force and earth pressure increase as compared with the conventional caisson 100. The principle will be explained. In addition, in FIG. 8 and FIG. 9, the state where the caisson 1,100 was constructed in the port was shown as an example.

First, as shown in FIG. 8, in the conventional caisson 100, the rigidity of the soft layer of the ground decreases when an earthquake occurs, and the horizontal resistance of the ground supporting the caisson 100 is greatly reduced as compared with that before the earthquake. Therefore, the horizontal resistance of the ground is insufficient, and the horizontal resistance acting on the caisson 100 is only the reaction force from the engineering foundation, and the force contributing to the suppression of the inclination of the caisson 100 is the reaction force from this engineering foundation. (Right-pointing arrow in FIG. 8) and reaction force acting on the bottom surface of the caisson 100 (up-pointing arrow in FIG. 8). In this way, when the horizontal resistance acting on the caisson 100 is insufficient, even if the caisson 100 has high rigidity, the rigidity hardly contributes to seismic resistance and suppresses inclination due to an increase in inertial force and earth pressure. Due to the weak force, deformation such as tilting occurs.

On the other hand, as shown in FIG. 9, when the caisson 1 according to the present embodiment is installed so that the protruding portion 3 protrudes toward the sea side, an earthquake occurs and the caisson 1 is horizontal to the caisson 1. When a load is applied, a large reaction force (upward arrow in FIG. 9) acting in the vertical direction from the engineering base acts on the bottom surfaces of the main portion 2 and the protruding portion 3, and the protruding portion 3 is formed. A large horizontal resistance (arrow pointing to the right in FIG. 9) acts on the lower end of the caisson 1. As a result, the reaction force in the vertical direction and the horizontal resistance acting on the caisson 1 become larger than those of the conventional caisson 100, that is, the force for suppressing the inclination due to the increase in inertial force and earth pressure becomes larger. Therefore, the caisson 1 is less likely to tilt.

Further, since the crushed stone column D1 is formed in the ground, the excess pore water pressure generated at the time of the earthquake is dissipated at an early stage, and the adverse effect due to liquefaction (seismic resistance of the structure adopted based on the caisson 1 according to the present embodiment). It is also possible to suppress (such as lowering the sex).

[Structure]
Next, a structure including the caisson that has landed on the ground will be described. In the following, a case where the structure is a pier installed in a port will be described as an example.

As shown in FIG. 10, the pier T according to the embodiment is composed of a plurality of caisson 1s that have landed on the ground and a superstructure 20 installed on the caisson 1, and is above the protrusion 3 of the caisson 1. The crushed stone pillar D1 is formed. Each caisson 1 is arranged in a row at a predetermined interval (for example, 20 m) along the shore so that the protruding portion 3 protrudes toward the sea side. In the present embodiment, the configuration in which the row consisting of the caisson 1 is two rows is adopted, but the present invention is not limited to this, and as long as various technical standards are satisfied, one row may be used, or a plurality of rows may be used. It may be a row.

The pier T having such a configuration is provided with a plurality of caissons 1 arranged so that the protruding portion 3 protrudes toward the sea side, thereby resisting the load on the sea side. As described above, a large reaction force in the vertical direction acts on the bottom surface of the protruding portion 3. Therefore, even if a load from the land side to the sea side acts when an earthquake occurs, a large reaction force acts on the bottom surface of the protruding portion 3 in each caisson 1 so as to resist this load, and the inertial force. The inclination of each caisson 1 due to the increase in force and earth pressure is suppressed, and the formation of the crushed stone pillar D1 in the ground causes the excess pore water pressure generated during an earthquake to be dissipated at an early stage, which also has an adverse effect due to liquefaction. It can be suppressed. As a result, the pier T according to the present embodiment has improved seismic resistance as compared with the pier adopted based on the conventional caisson.

FIG. 11 is a diagram showing a schematic configuration of a pier Ta according to another embodiment. As shown in the figure, the pier Ta is composed of a plurality of caissons 1 and a superstructure 20 installed on the caisson 1, and the crushed stone pillar D1 is above the protrusion 3 of the caisson 1. Is formed. On the other hand, at this pier Ta, some caisson 1 (first caisson) of each caisson 1 is along the shore so that the protruding portion 3 protrudes toward the sea side (first direction). The other caisson 1 (second caisson) is arranged in a row at a predetermined interval (for example, 20 m) so that the protruding portion 3 protrudes toward the land side (second direction). They are arranged in a row along the shore at predetermined intervals (for example, 20 m).

In the pier Ta having such a configuration, the caisson 1 (first caisson) arranged so that the projecting portion 3 protrudes toward the sea side and the projecting portion 3 project toward the land side. By providing the caisson 1 (second caisson) arranged so as to be in a state, the bottom surface of the protruding portion 3 of the first caisson 1 is directed in the vertical direction so as to resist the load on the sea side. A large reaction force acts, and a large reaction force acts in the vertical direction on the bottom surface of the protruding portion 3 of the second caisson 1 so as to resist the load on the land side. Therefore, in the pier Ta, as in the case of the pier T, the inclination of each caseon 1 due to the increase in inertial force and earth pressure is suppressed, the adverse effect due to liquefaction is also suppressed, and the pier Ta is in the sea side direction and on land. The occurrence of the phenomenon of swaying and floating alternately toward the side is also suppressed.

Further, as shown in FIG. 12, the structure according to the present invention includes a steel sheet pile wall 30 made of steel sheet piles driven to a predetermined depth along the quay, and a pile 32 buried in the ground on the land side. A caisson 1 may be provided on an existing sheet pile type quay Tb provided with a tie rod 31 or the like for connecting the steel sheet pile wall 30 and the retaining pile 32. For example, a caisson 1 was constructed in the vicinity of the retaining pile 32 of the sheet pile type quay Tb, a crushed stone pillar D1 was formed, and the upper portion of the caisson 1 and the upper portion of the retaining pile 32 were connected and integrated by a connecting member 33. It may have a configuration.

In the sheet pile type quay Tb having such a configuration, the caisson 1 and the retaining pile 32 are integrated, so that the seismic resistance is improved as compared with the configuration without the caisson 1. In this way, simply by constructing the caisson 1 and integrating it with the retaining pile 32 of the existing sheet pile type quay Tb, the seismic resistance of the existing sheet pile type quay Tb can be improved, so that the size of the ship can be increased. When it is necessary to improve seismic resistance due to deepening, or when it is necessary to improve seismic resistance to meet new seismic standards, it is possible to respond without carrying out expensive ground improvement. Is.

In the above piers T, Ta, and sheet pile type quay Tb, one-sided protruding caisson 1 is adopted as the caisson, but the present invention is not limited to this, and circular protruding caisson 1a or both-sided protruding caisson 1b may be adopted. .. Further, depending on the ground conditions and the seismic performance required for the structure, all the caissons to be adopted may have the same shape of the protruding portion, or may be used in combination with different caissons having different shapes of the protruding portions. good. Further, not all caissons need to have protrusions 3, 3a, 3b at the bottom, and some of the plurality of caissons 1 may be used depending on the ground conditions, seismic performance required for the structure, and the like. A conventional caisson (caisson without a protrusion) may be adopted.

Further, the structure according to the present invention uses a caisson 1 instead of a pile of a sheet pile type quay, a caisson 1 as a foundation of a gravity type quay, and a caisson 1 on the sea side of an existing pier. It may be an integrated one, or one based on the above caisson and a wind generator or the like installed on it.

Further, in the above example, the mode in which the crushed stone pillar D1 is formed is shown, but the present invention is not limited to this, and in the structure according to the present invention, a pillar made of granules is formed instead of the crushed stone pillar. It may be used, or columns made of crushed stone or granules may not be formed.

Further, the structure according to the present invention is not limited to a structure installed in a harbor, but is a structure installed in a place where tilt suppression is required or a structure installed in a place where locking suppression is required. It is also preferable that the caisson provided in the structure installed in a place where tilt suppression is required has a protruding portion protruding in the direction opposite to the direction in which the force for tilting the caisson acts. It is preferable that the caisson provided in the structure installed in a place where locking suppression is required has a protrusion protruding at least in the opposite direction. That is, it is preferable that the caisson provided in the structure appropriately sets the protruding direction of the protruding portion according to the place where the structure is installed.

[Numerical analysis result]
Next, the results of evaluating the seismic resistance of caisson by numerical analysis using the beam theory on the elastic floor will be described with reference to FIGS. 13 to 18.

In the numerical analysis, only the caisson was modeled, and the effect of the ground was reflected as the spring reaction force. The caisson had a rooting length of 20 m, a circular cross section with a diameter of 6.5 m, and a moment of inertia of area of 67 m ⁴ . The load conditions are a structural condition in which the share width in the direction perpendicular to the normal line (direction from the sea to the land) is 14 m and the share width in the normal direction is 20 m per pier cason, and the horizontal seismic intensity equivalent to a level 2 earthquake is high. The conditions were set to about 0.41, and the specific conditions were as follows. Its own weight was 54281 kN, the horizontal load on the seafloor was 22500 kN, and the acting moment on the seafloor was 365800 kNm. The horizontal ground reaction force coefficient was set to 5380 kN / m ^{3, which} is a constant value from the upper end to the lower end of the caisson, and the vertical ground reaction force coefficient was set to 71225 kN / m ^3, which is an assumed value in consideration of the decrease in rigidity. In addition, the weight of the soil on the protrusion of the caisson was estimated as the wall weight, and the weight of the protrusion was ignored. Furthermore, in the numerical analysis, the resistance moment generated by the reaction force from the ground is taken into consideration at the lower end of the caisson, the inclination angle of the caisson is calculated ignoring the moment, and then the moment corresponding to the inclination angle is given and calculated again. Then, the calculation was repeated until the deformation on the ground surface finally converged. The resistance moment is set with the caisson center as the center of rotation in accordance with the setting of the road bridge specification. The theory of beams on elastic floors was applied to the calculations. This theory is a theory that considers a caisson as a beam and calculates the response of a beam that receives external forces such as horizontal loads and moments and ground reaction forces, and is a classical and widely used theory. However, since a theoretical solution cannot be obtained when the load conditions are complicated, the difference method was applied to the calculation in this analysis. The length of the caisson was divided at intervals of 0.5 m, and two virtual nodes were added to the upper end and the lower end of the caisson for the calculation of the difference method.

In addition, numerical analysis was performed on a one-sided protruding caisson, a circular protruding caisson, and a two-sided protruding caisson in which the amount of protrusion of the protruding portion was a predetermined amount. The amount of protrusion in FIGS. 13 and 18 is the amount of protrusion of the protruding portion in the circular protruding caisson, and in FIGS. 13 and 18, the amount of excavated soil for the one-sided protruding caisson and the two-sided protruding caisson is the same as that of the circular protruding caisson. The resistance moment when the protrusion amount was set under the condition of excavated soil amount was plotted against the value of the protrusion amount of the corresponding circular protruding caisson. For example, with the amount of protrusion set under the condition that the amount of excavated soil is the same as the amount of excavated soil when the amount of protrusion of the circular protruding caisson is 1 m (2.93 m for one-sided protruding caisson and 1.12 m for both-sided protruding caisson). The resistance moment in a certain case was plotted as a value when the protrusion amount was 1 m.

FIG. 13 is a graph showing the relationship between the protrusion amount and the resistance moment of each caisson, and as can be seen from the figure, the resistance moment of each caisson increases as the protrusion amount increases, and the excavated soil amount. When the amount of protrusion is set under the same condition, the one-sided protruding caisson has the largest resistance moment and is highly effective in suppressing deformation.

14 and 15 are graphs showing the relationship between the amount of deformation in the horizontal direction and the height position, and FIGS. 16 and 17 are graphs showing the relationship between the bending moment and the height position. 14 and 16 are graphs relating to a caisson having no protrusion, and FIGS. 15 and 17 are graphs relating to a one-sided protruding caisson having a protrusion amount of 2.93 m. As shown in FIGS. 14 and 15, the amount of deformation of the one-sided protruding caisson at each height position is smaller, and as shown in FIGS. 16 and 17, the bending moment at each height position is smaller. Is larger on one side protruding caisson. From this, it was confirmed that the formation of the protruding portion enhances the effect of suppressing deformation. By forming the protruding portion, the bending moment acting on the caisson is increased as a whole, but it can be sufficiently dealt with by increasing the amount of reinforcement of the caisson.

FIG. 18 is a graph showing the relationship between the protrusion amount of each caisson and the deformation amount ratio, and the deformation amount ratio in the figure is a ratio to the deformation amount when the protrusion is not formed. As can be seen from the figure, as the amount of protrusion increases, the deformation amount ratio of each caisson becomes smaller, and the deformation can be further suppressed by increasing the amount of protrusion. Further, for the circular protruding caisson, the reduction rate of the deformation amount is about 10% when the protrusion amount is 1 m, whereas the bilateral protrusion under the condition that the excavated soil amount is the same (the protrusion amount is 1.12 m). For the caisson, the reduction rate of the deformation amount is about 12%, and the excavated soil amount is the same as the excavated soil amount of the circular protruding caisson having the protruding amount of 1 m (the protruding amount is 2.93 m). The reduction rate of the amount of deformation is about 30%. It was found that when the amount of protrusion of each caisson was set under the condition that the amount of excavated soil was the same, the one-sided protruding caisson could further suppress the deformation.

The configurations disclosed in the above embodiments (including other embodiments) can be applied in combination with the configurations disclosed in other embodiments as long as there is no contradiction, and are disclosed in the present specification. The embodiment described is an example, and the embodiment of the present invention is not limited to this, and can be appropriately modified without departing from the object of the present invention.

The present invention can be used for a caisson capable of improving the seismic resistance of a structure, a pneumatic caisson method for constructing the caisson in the ground, and a structure having the above caisson.

1,1a, 1b Caisson 2,2a, 2b Main part 3,3a, 3b Protruding part D Crushed stone T, Ta Pier Tb Sheet pile type quay

Claims (9)

A caisson used as the foundation of a structure
The main part, which has a tubular shape and extends in the vertical direction,
A caisson having a protruding portion formed on at least a part of the outer periphery of the lower end portion of the main portion and protruding in the horizontal direction from the main portion. A pneumatic caisson method for constructing the caisson according to claim 1 underground.
The landing process of excavating the ground and landing the caisson,
A pneumatic caisson method in which a backfilling step of backfilling the backfilling space formed above the protrusion in the bottoming step is performed. The pneumatic caisson method according to claim 2, wherein in the backfilling step, the backfilling space is backfilled with granules. The pneumatic caisson method according to claim 3, wherein the granular material is crushed stone. The structure having a caisson according to claim 1, which has landed on the ground. The structure according to claim 5, wherein a pillar made of a granular material is formed above the protrusion in the caisson. The structure according to claim 6, wherein the granular body is crushed stone. Installed in the harbor
The structure according to any one of claims 5 to 7, wherein the protruding portion in the caisson is formed at least on the sea side. A first caisson having at least a protrusion protruding in the first direction,
The structure according to any one of claims 5 to 7, which has at least a second caisson having a protrusion protruding in the second direction opposite to the first direction.

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