JPS6351510A - Deformed caisson for revetment - Google Patents

Abstract

PURPOSE:To raise the stability of revetment by suppressing the slide movement of a caisson by a method in which the back wall of caisson is shaped into an upwardly extended tapered face and a backwardly extended footing is formed from the back upper end of the caisson. CONSTITUTION:The back wall 2b of a caisson 2 is shaped into a backwardly expanding tapered face toward upper part, and a plurality of through holes 11 are formed in the front wall 2a. A backwardly extending footing 3b is also formed on the upper rear end of the caisson 2. A bottom upped peripheral wall projecting from the tip of the front and back footings 3a and 3b to below may also be provided. The contact face between back-filled soil 7 and the caisson is sloped to reduce and remove the pressure of back-filled soil. Also, the back-filled soil 7 acts as an upper load to increase the apparently weight of the caisson 1, enhancing the stability of the caisson.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to a caisson used for, for example, port structures such as seawalls and breakwaters, and is particularly aimed at reducing or eliminating horizontal external forces acting on the caisson. This article concerns a modified caisson for seawalls.

"Prior Art and its Problems" Conventionally, caissons as gravity-type structures have been frequently used in relatively large-scale port structures such as sea walls and breakwaters. Third
The figure shows a seawall to which the conventional caissons are applied.

In FIG. 3, reference numeral I indicates a caisson, and this caisson 1 is placed and fixed on a rubble mound M constructed on the seabed ground G near the quay. This caisson
includes a box-shaped caisson main body 2 with an open top, a pair of footings 3a and 3b provided at the bottom of the main body 2 and extending forward and backward from the main body 2, and closing the top opening of the main body 2. It is roughly composed of a cover concrete 4. Further, reference numeral 5 indicates filling sand filled in the caisson main body 2, reference numeral 6 indicates a concrete block provided on the upper part of the caisson l, and reference number 7 indicates backfilling rocks stacked at the rear of the caisson l.

In the caisson 1 having the above configuration, its main body 2
and counteracts own slipping and falling by the own weight of the filling sand 5,
Further, if the bearing pressure of the navigation footing 3a is smaller than the bearing force of the ground G, the caisson l will be in a stable state on this ground G. In particular, if the sea area where this caisson 1 is installed is not a deep water area, the factor that controls the stability of the caisson l is the sliding of this caisson l itself.

If the sliding resistance of the caisson I itself is insufficient due to insufficient weight of the caisson body 2, a method is adopted in which the width of the caisson body 2 is increased to increase the weight of the caisson I. However, as the weight of caisson 1 increases, the seismic force acting on caisson 1 also increases, resulting in a loss of stability of caisson 1 in an emergency.
This is not a rational solution.

"Means for Solving the Problems" As a result of intensive research in view of the above-mentioned problems, the inventor of the present invention has found that it is possible to reduce the large element of the horizontal external force that is the sliding force of the caisson, that is, to reduce the backfilling earth pressure applied to the caisson. It was discovered that the stability of the caisson itself could be improved by removing it.

In other words, by forming the rear wall surface of the caisson body into a tapered surface that widens rearward as it goes upwards, the contact surface of the caisson with backfilling soil (rock) stacked at the rear of the caisson is sloped, so that the backfilling soil (rock) that is piled up at the rear of the caisson is sloped. This reduces backfilling soil pressure. In particular, if the inclination of the rear wall surface of the caisson body is made to match the active collapse angle of the backfilling rock during an earthquake, the backfilling earth pressure acting on the backwall surface can be completely removed.

At the same time, by extending the rear footing of the caisson rearward from the rear upper end of the caisson, the weight of the backfilling earth and sand placed on the upper surface of the rear footing causes an apparent increase in the caisson's own weight. It is also possible to further improve the stability of the caisson.

Based on the knowledge shown above, the present invention provides an irregularly shaped caisson for seawalls comprising a generally box-shaped caisson body and a pair of footings provided at the bottom of the caisson body and extending forward and backward from the body. The rear wall surface of the caisson body is formed into a tapered surface that widens rearward as it goes upward, and the footing extending rearward extends rearward beyond the rear upper end of the caisson body.

Here, it is preferable that a raised bottom space is formed in the bottom surface of the caisson main body, and that the caisson main body is provided with an injection pipe that communicates with the raised bottom space.

"Function" In the present invention, since the rear wall surface of the caisson body is formed into a tapered surface, the contact surface of the caisson with backfilling earth piled up behind the caisson is inclined, thus reducing the backfilling earth pressure acting on the caisson. Can be removed. Furthermore, since the footing provided at the rear of the caisson extends rearward beyond the rear upper end of the caisson body, the backfilling earth and sand placed on the upper surface of the footing acts as an overburden load, which causes the caisson to The apparent dead weight can be increased above.

"Embodiments" Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a seawall to which a modified caisson for seawall according to the first embodiment of the present invention is applied. In the following description, the same components as those of the conventional caisson will be denoted by the same reference numerals, and the description thereof will be omitted.

In the caisson 1 according to the first embodiment of the present invention, the rear wall portion 2b of the main body 2 (rear wall surface) is formed into a tapered surface that widens rearward as it goes upward.
A plurality of through holes 11 are formed in the front wall portion 2a at the water surface level and near the bottom, respectively. Further, a rear footing 3b extending rearward from the caisson main body 2 is formed to extend rearward from the rear upper end of the main body 2. Furthermore, the concrete block 6 placed on the upper part of the caisson body 2 has a front wall 6a that acts as a wave barrier from the sea surface, and a tapered surface that is continuous with the slope of the wall surface of the rear wall 2b of the caisson body. A rear wall 6b is formed at the rear wall 6b.

The manufacturing method and the installation method of the irregularly shaped caisson l for seawall shown above on the quay wall etc. are the same as the manufacturing method and the installation method of the conventional caisson. In other words, a caisson 1 is manufactured in a factory or a caisson yard located at a location suitable for marine transportation, such as along the coast, and then a temporary floating body is attached to the caisson 1 as appropriate and the caisson 1 is towed on the water by a towing boat or the like. The caisson L is then transported to the vicinity of the caisson L installation location, and the caisson L is placed on the rubble mound M that has been leveled in advance. Install the lever caisson l on the quay.

Then, a concrete block 6 is placed on top of this caisson L.
The revetment work is completed by placing and fixing.

Normally, the caisson 1 is overturned in the water and towed and transported with the front wall 2a or the rear wall 2b of the caisson main body 2 facing the bottom of the water. The vertical cross-sectional shape is not symmetrical like the conventional caisson, so a temporary floating body larger than usual is attached to the part sandwiched between the main body rear wall 2b and the rear footing 3b to improve stability during towing. It is necessary to aim for this. Furthermore, in order to float and tow the caisson 1, the through hole 11 provided in the front wall 2a of the caisson 1 must be closed with a watertight temporary cover or the like. Incidentally, if the caisson I is relatively small, the means of transportation is not limited to water towing as described above, and it is also possible to load it on a barge or the like and transport it.

In the irregularly shaped caisson l for seawall constructed as described above, the rear wall portion 2b of the caisson main body 2 is formed into a tapered surface, so that the contact surface of the caisson l of the front 7 stacked behind the caisson 1 is This caisson is sloped to the ! The backfilling earth pressure acting on (the wall surface of the main body rear wall portion 2b) is reduced.

In particular, if the slope of the wall surface of the rear wall portion 2b is formed to match the active collapse angle of the RQ backfilling rock 7 during an earthquake, the backfilling earth pressure can be completely removed. Further, the rear footing 3b of the caisson l extends rearward from the rear upper end of the caisson main body 2, so that the front backing 7 placed on the upper surface of the rear footing 3b is attached to the caisson l. On the other hand, the caisson l acts as an overload load, and therefore the caisson l's own weight is apparently increased, so that the stability of the caisson l is further improved. In particular, by appropriately widening this rear footing 3b, it is possible to obtain an increase in apparent dead weight equivalent to 5 weights of filling sand filled inside the conventional caisson body 2. The weight of the caisson 1 can be reduced by the filling sand 5, and therefore, the seismic force acting on the caisson 1 can be reduced. Therefore, by reducing or eliminating horizontal external forces such as seismic force and backfilling earth pressure acting on caisson 1, and increasing the apparent weight of caisson 1, the sliding of caisson 1 can be suppressed as much as possible. Therefore, it is possible to realize a modified caisson l for a seawall that can improve the stability of the constructed seawall.

In addition, in this irregularly shaped caisson l for seawall, there is no need to fill the main body 2 with the filling sand 5, as described above.
By forming the through hole 11 in the front wall portion 2a, the inside of the main body 2 can be used as a water play space.Therefore, if this caisson I is used, a sea wall with wave overtopping prevention and wave dissipation functions can be created. It becomes possible to construct.

Next, FIG. 2 is a diagram showing a seawall to which a modified caisson for seawall, which is a second embodiment of the present invention, is applied.

In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

This caisson l of the second embodiment is a so-called raised-belly type caisson, and has front and rear footings 3a and 3b.
A raised bottom peripheral wall 12 protruding downward from the tip of the
A and 12b form a raised bottom space 13 at the bottom of the caisson body 2. Further, in this caisson l, an injection pipe 14 whose lower end communicates with the raised bottom space 13 is embedded in the main body rear wall part 2b, and this injection pipe 14 is connected in the axial direction of the caisson main body 2 ( The caisson body 2 extends in the vertical direction), and its upper end is opened at the upper end of the caisson body 2.

The method of manufacturing the caisson I of the second embodiment and the method of installing it on a quay etc. are almost the same as those of the caisson of the first embodiment. A slight difference is that when this caisson I is placed on the rubble mound M, underwater concrete is injected into the raised bottom space 13 through the injection pipe 14, and this raised bottom space 13 is filled with concrete. , This makes it possible to increase the sliding resistance between the caisson I and the rubble mound M. That is, by creating an engagement between the caisson L and the upper end of the rubble mound M using this underwater concrete and integrating the caisson L and the rubble mound M, the sliding resistance coefficient of the caisson L with the rubble mound M can be reduced to 0. It can be raised from 6 to 0.8, which is the same as the coefficient for rubble stones. Further, according to the raised prefabricated caisson l, the caisson l can be stably placed without actually leveling the surface of the rubble mound M, so that the leveling of the mound can be simplified.

The second embodiment of the irregularly shaped caisson 1 for bank protection constructed as described above reduces or eliminates horizontal external forces such as backfilling earth pressure, and the apparent dead weight of the caisson 1 is increased. By suppressing the sliding of the caisson 1 as much as possible, and further increasing the sliding resistance between the caisson L and the rubble mound M, we have realized an irregularly shaped caisson l for seawalls that can improve the stability of a trench-built seawall. can do.

Note that the shape and structure of the irregularly shaped caisson 1 for bank protection of the present invention are not limited to those of the embodiments described above, and can be modified as appropriate depending on construction conditions and the like.

"Effects of the Invention" As explained in detail above, according to the present invention, a seawall is provided with a substantially box-shaped caisson body and a pair of footings provided at the bottom of the caisson body and extending forward and backward from the body. In the irregularly shaped caisson, the rear wall surface of the caisson body is formed into a tapered surface that widens rearward as it goes upward, so that the contact surface of the caisson with backfilling earth and sand piled up at the rear of the caisson is inclined, so that it acts on the caisson. It is possible to reduce and eliminate backfilling soil pressure.

Further, since the footing extending rearward from the caisson body is extended rearward beyond the rear upper end of the caisson body, the backfilling earth and sand placed on the upper surface of the footing acts as an overload load, and therefore, the caisson The apparent weight of the caisson increases, which improves the stability of the caisson and eliminates the need for sand filling, which was previously required. Furthermore, since the weight of the caisson can be reduced by the amount of sand filling, it is possible to reduce the seismic force acting on the caisson. Therefore, according to the present invention, horizontal external forces such as seismic force and backfilling earth pressure acting on the caisson are reduced or eliminated, and the caisson's own weight is apparently increased, thereby preventing the caisson from sliding. It becomes possible to realize a deformed caisson for a seawall that can suppress the damage as much as possible and improve the stability of the constructed seawall.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view showing a seawall to which a modified caisson for seawall is applied, which is a first embodiment of the present invention, and Fig. 2 is a seawall to which a modified caisson for seawall, which is a second embodiment of the present invention, is applied. Figure 3 is a vertical cross-sectional view showing a seawall to which a conventional caisson is applied. ! ... Deformed caisson for bank protection, 2 ... Caisson body, 2b ... Rear wall part (rear wall surface), 3a
, 3b...footing, 13...raised bottom space, 14...injection pipe.

Claims (2)

[Claims] (1) In a caisson comprising a substantially box-shaped caisson body and a pair of footings provided at the bottom of the caisson body and extending forward and backward from the body, the rear wall surface of the caisson body widens rearward as it goes upward. A deformed caisson for a seawall, characterized in that the footing is formed into a tapered surface and extends rearward beyond a rear upper end of the caisson main body. (2) A raised bottom space is formed in the bottom surface of the caisson body, and the caisson body is provided with an injection pipe communicating with the raised bottom space. Deformed caissons for bank protection as described in Section 1.