JP2016084675A - Caisson type composite breakwater structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a caisson type composite breakwater structure that enables a greater horizontal resistance force to be obtained in a backfilled treatment soil layer, when a caisson type composite breakwater is backfilled with treatment soil.SOLUTION: In a caisson type composite breakwater structure, a caisson C is installed on a mound M that is constructed on water bottom ground G; treatment soil backfilling is applied to the caisson; and slide prevention work 10 for preventing a slide on a boundary surface between a treatment soil layer B and the water bottom ground G is provided on the back side of the treatment soil layer B.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a caisson type hybrid bank structure.

  A caisson-type mixed levee is a type of breakwater, and a caisson is provided as an upright wall on a rubbing foundation. In the Great East Japan Earthquake that occurred on March 11, 2011, many of the existing caisson-type mixed dams were severely damaged by tsunamis and high waves. The large horizontal force caused by the tsunami acted on the caisson-type mixed embankment, and the tsunami overflowed the caisson-type mixed embankment and scoured the foundation mound behind it. It is considered the cause.

  In order to improve the stability of the caisson type hybrid bank, it is considered effective to backfill the back of the caisson (see, for example, Patent Document 1). Further, Patent Document 2 discloses that a support structure is vertically driven through the mound into the ground at a position separated from the caisson on the rear surface side of the caisson disposed on the mound on the ground. A gravitational breakwater filled with a filler containing gravel, crushed stone and the like that transmits horizontal force from the caisson to the support structure is proposed between the protruding portion of the support structure protruding from the caisson. A large horizontal force acting on the caisson due to a tsunami or the like is received by the filling body and the support structure to suppress destruction as much as possible.

On the other hand, in recent years, there is a serious shortage of disposal sites for dredged soil. Dredged soil is generated when the water depth and anchorage are maintained and deepened, and about 20 million m ³ is generated annually. However, it is difficult to construct a new disposal site due to environmental constraints. The effective use of dredged soil is to prepare treated soil by mixing solidified material with dredged soil, and this solidified treated soil is used for backfill and backfill material on the back of the revetment. A construction method that assumes this is already established.

JP 2001-115429 A Japanese Unexamined Patent Publication No. 2014-101663

  Then, the present inventors considered using the solidification processing soil which mixed the solidification material with dredged soil for the backfilling of a caisson type hybrid bank. However, the width of the backfill of the treated soil applied to the back of the caisson cannot be increased to infinite due to restrictions on use of the port. This restriction means securing fishing boats to and from the port. Therefore, when applying backfilling, a structure that uses solidified soil within a width of about several tens of meters and has the maximum horizontal resistance is desired.

  As shown in Fig. 1, when the caisson-type mixed levee with caisson C installed on the mound M constructed on the sand ground G at the bottom of the water is treated with two types in the treated soil layer B Slippage may occur. That is, the slip 1 that occurs substantially horizontally in the treated soil layer B along the solid line in FIG. 1 and the slip that occurs at the boundary between the treated soil layer B and the sand ground G from within the treated soil layer B along the broken line in FIG. 2.

The horizontal resistance ΔP1 in the slip 1 in the treated soil layer B in FIG. 1 is expressed by the following equation (1).
ΔP1 ＝ cu × L (1)
The horizontal resistance ΔP2 in the slip 2 in the treated soil layer B in FIG. 1 is expressed by the following equation (2).
ΔP2 ＝ cu × L / 2 + Ws × μ (2)
However, cu: Shear strength of treated soil (= qu / 2), L: Width of backfill of treated soil, Ws: Mass of treated soil (portion surrounded by one-dot chain line in FIG. 1), μ: between treated soil and sand Coefficient of friction

  The occurrence of slip 1 and slip 2 is distinguished by the magnitude of the horizontal resistance force. That is, it is considered that slip 1 occurs when ΔP1 <ΔP2, and slip 2 occurs when ΔP1> ΔP2. However, in a normal case, the unit volume weight of the treated soil is reduced by receiving buoyancy, so that ΔP1> ΔP2 and slip 2 is likely to occur. As a result, even if the amount of cement added is increased and the uniaxial compressive strength qu of the treated soil is increased, the horizontal resistance force corresponding to the increased uniaxial compressive strength qu cannot be obtained, and a large horizontal resistance force is obtained. The problem that cannot be done.

  In view of the problems of the prior art as described above, the present invention is a caisson-type hybrid that can obtain greater horizontal resistance in the back-treated soil layer when the caisson-type hybrid bank is backfilled with the treated soil. The purpose is to provide a bank structure.

  As shown in FIG. 2, the present inventors forcibly prevent the slip 2 (FIG. 1) by applying a slip prevention work 10 to the lower back surface of the treated soil layer B, and the slip 1 having a large horizontal resistance (FIG. 1). ), It was possible to realize an increase in the horizontal resistance, and the present invention was conceived.

  That is, the caisson-type hybrid embankment structure for achieving the above purpose is to install a caisson on the mound built on the bottom of the ground, apply the treated soil back to the caisson, and on the back of the treated soil layer, A slip prevention work is provided for preventing slippage at the boundary surface between the treated soil layer and the water bottom ground.

  According to this caisson-type hybrid bank structure, slippage at the boundary surface between the treated soil layer and the water bottom ground can be prevented by providing the back surface of the treated soil layer with a slip prevention work. This slip occurs from within the treated soil layer along the boundary surface between the treated soil layer and the bottom ground, and the horizontal resistance force is smaller than the horizontal resistance force in the horizontal direction within the treated soil layer. As a result of providing the slip prevention work, the slip occurs along the horizontal direction in the treated soil layer, and a larger horizontal resistance force is generated. In this way, when the caisson type hybrid bank is filled with the treated soil, the horizontal resistance force becomes greater in the treated soil layer.

  In the caisson type hybrid bank structure, the slip prevention work is preferably constructed from a steel sheet pile, a steel pipe sheet pile, an H-shaped steel pile, or a continuous underground wall.

  The treated soil is preferably mixed with a solidifying material. Thereby, uniaxial compressive strength becomes large according to the addition amount of a solidification material, and horizontal resistance force becomes large according to it.

  Moreover, it is preferable to provide a drain pipe on the back side of the caisson so as to penetrate the treated soil layer and reach the mound. If the treated soil is backfilled, wave pressure acts on the entire bottom surface of the caisson, reducing the sliding resistance of the caisson, but by providing a drain hole on the back side of the caisson, the wave pressure at the bottom of the back of the caisson is zero. Therefore, the wave pressure does not act, and there is no possibility of reducing the sliding resistance of the caisson.

  According to the caisson type mixed bank structure of the present invention, when the caisson type mixed bank is backfilled with treated soil, a larger horizontal resistance force can be obtained in the backfilled treated soil layer.

It is a figure which shows roughly the slip 1 and the slide 2 which arise in the caisson type mixed embankment which performed the conventional treatment soil backfill. It is a figure which shows roughly the basic composition of the caisson type mixed embankment structure which gave the processing soil back provided with a slip prevention work. It is a side view of the caisson type hybrid embankment by this embodiment. It is a table | surface which shows the example of a mixing | blending of the solidification process soil in this embodiment. It is a side view of the real model made into object in this experiment example. It is a table | surface which shows the experimental field conditions in this experiment example. It is a sgraph which shows the relationship between a caisson displacement amount and an applied load as an experimental result of this experiment example. It is a table | surface which shows the slip form on the calculation of this experiment example. (A)-(e) is a figure which shows the displacement vector and slip line in a process soil layer in case 2, 3, 4 of this experiment example. It is a graph which shows the relationship between the uniaxial compressive strength in water obtained by converting from this experimental example, and a horizontal resistance force.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 3 is a side view schematically showing the caisson type hybrid bank according to the present embodiment.

  As shown in FIG. 3, the caisson-type mixed embankment of the present embodiment has a caisson C installed on a mound M constructed by rubble on the bottom of the ground G, and the mound M is covered with a cladding T, and the caisson C The back surface (land side) has a structure in which the solidified soil is filled so as to cover the coating T, and the anti-slip work 10 is constructed at the back end of the solidified soil layer B.

  As the slip prevention work 10, a steel pipe sheet pile is installed in the vertical direction on the bottom bottom ground G at the back end of the solidified soil layer B. Further, on the back surface of the caisson C, for example, a drain pipe 11 having a diameter of 50 cm is installed so that the lower end reaches the inside of the mound M at intervals of 1.0 m.

For example, the solidified soil is blended as shown in FIG. 4, cement is used as the solidified material, and its uniaxial compressive strength is qu = 200 kN / m ² . The uniaxial compressive strength of the solidified soil is an example, and can be adjusted by the amount of cement added.

  The treated soil layer B shown in FIG. 3 can be constructed by placing the above-mentioned solidified soil on the back surface of the caisson C by applying the mixed solidification treatment method in the pipe. The mixed solidification treatment method in the pipe is detailed in, for example, the “Technical Manual for Mixed Solidification Treatment Method in Pipe (Revised)” (issued by the Coastal Technology Center in July 2008), so the explanation is omitted.

  For example, a steel pipe sheet pile having a diameter of 500 mm, a thickness of 13 mm, and a length of 16 m can be used as the slip prevention work 10, and FIG. 3 shows each dimension, each data, and an arrangement example. The dimensions, data, and arrangement examples can be appropriately changed.

  According to the caisson-type hybrid embankment structure of this embodiment, by providing the steel pipe sheet pile of the slip prevention work 10 on the back surface of the solidified soil layer B, the slip 2 at the boundary surface between the solidified soil layer B and the water bottom ground G ( 1) can be prevented. As shown in FIG. 1, the slip 2 is generated from the solidified soil layer B along the boundary surface between the solidified soil layer B and the water bottom ground G, and the horizontal resistance force is horizontal in the solidified soil layer B. As a result of the provision of the slip prevention work 10 where the horizontal resistance force in the direction is smaller, the slip 2 in FIG. 1 is suppressed, and the slip occurs in the solidified soil layer B as the slip 1 in FIG. 1 along the horizontal direction. In this slip 1, a larger horizontal resistance force is generated. In this way, when the caisson-type hybrid bank is solidified soil backfilled, a greater horizontal resistance can be obtained in the solidified soil layer B.

Further, the horizontal resistance ΔP1 in the slip 1 can be expressed by the following equation (1 ′) from the above equation (1).
ΔP1 = cu × L = (qu / 2) × L (1 ')
Where cu: shear strength of treated soil, L: width of treated soil backfill, qu: uniaxial compressive strength of treated soil

  As can be seen from the above equation (1 '), the horizontal resistance force ΔP1 in the slide 1 varies depending on the uniaxial compressive strength of the solidified soil, so that a horizontal resistance force corresponding to the uniaxial compressive strength can be obtained. For this reason, when the amount of cement added is increased and the uniaxial compressive strength qu of the solidified soil is increased, a horizontal resistance force corresponding to the increased uniaxial compressive strength qu can be obtained, and the amount of cement added is increased. A greater horizontal resistance can be obtained.

  In addition, by installing the drain pipe 11 on the back surface of the caisson C so that the lower end reaches the inside of the mound M, the following effects can be obtained. That is, when there is no backfilling of the solidified soil, the lifting pressure to the caisson C has a triangular distribution with wave pressure acting at the lower part of the caisson front and zero at the lower part of the caisson. However, if the solidified soil is filled, the water supply to the back of the caisson is blocked, so that the wave pressure acts on the entire bottom of the caisson. This leads to a decrease in the sliding resistance of the caisson. In order to solve such a problem, by providing the drain pipe 11 on the back side of the caisson C, the lifting pressure to the caisson C is reduced to zero or close to zero at the lower part of the back of the caisson C, and there is no solidification soil backfill. In the case of. In addition, since the drainage pipe 11 installs near the back surface of the caisson C, since the lifting pressure reduction effect in the caisson back lower part increases, it is preferable.

  Further, according to the gravity breakwater of Patent Document 2, a large horizontal force acting on the caisson due to a tsunami or the like is received by the support structure through the filler, but the filler includes gravel, crushed stone, and the like. The function of the slip prevention work 10 for suppressing the slip 2 (FIG. 1) in the solidified soil layer is completely different.

<Experimental example>
Next, the results of a centrifuge model experiment conducted on the real model of FIG. 5 will be described. Experimental conditions are shown in FIG. Case 1 has no solidification soil backfilling, and cases 2 to 4 have solidification soil backfilling. Case 2 and case 3 are experiments in which the cross section is the same and the uniaxial compressive strength qu is changed. Case 3 and case 4 are the same in the uniaxial compressive strength qu and there is no slip prevention work.

FIG. 7 shows the relationship between the caisson displacement and the applied load as an experimental result, and FIG. 8 shows the calculated slip form. The following can be said from these results.
(1) Compared to case 1 without backfilling, the horizontal resistance (= loading load) of cases 2 to 4 with backfilling is greater.
(2) Comparing Case 2 and Case 3, the horizontal resistance of Case 3 having a large uniaxial compressive strength qu is large.
(3) When the case 3 and the case 4 are compared, the horizontal resistance of the case 4 provided with the anti-slip work is large.

  From the above results, it was possible to confirm the effect of installation of the solidified soil lining and to confirm the effect of the anti-slip construction by increasing the horizontal resistance.

  FIGS. 9A to 9E show the displacement vectors and slip lines in the treated soil layer in cases 2, 3 and 4 of this experimental example. As a slip form in each case, slip 1 (FIG. 1) occurs in case 2 of FIGS. 9A and 9B, and slip 2 (FIG. 1) occurs in case 3 of FIGS. 9C and 9D. In case 4 of FIGS. 9 (e) and 9 (f), slip 2 occurred because slip 2 was hindered by the slip prevention work. The result of FIG. 9 agrees with the calculated slip form of FIG.

Since the above centrifugal model experiment was carried out in the air, the unit volume weight γ of the solidified soil was 13.8 kN / m ³ . This is replaced with 3.8 kN / m ³ of unit volume weight in water, and the mass Ws of the treated soil in (2) above is calculated. Using this mass Ws, the uniaxial compressive strength qu and the horizontal resistance force ΔP2 for the slip 2 are calculated. FIG. 10 shows the relationship obtained from the above equation (2). FIG. 10 also shows the relationship between the uniaxial compressive strength qu and the horizontal resistance force ΔP1 (obtained from the above equation (1)) regarding the slip 1. From FIG. 10, it can be seen that when the slip configuration is the slip 1, the horizontal resistance force ΔP can be increased to about 1.6 times the slip 2.

  As described above, the modes for carrying out the present invention have been described. However, the present invention is not limited to these, and various modifications can be made within the scope of the technical idea of the present invention. For example, in this embodiment, although the slip prevention work was constructed | assembled from the steel pipe sheet pile, it is not limited to this, For example, you may construct | assemble from a steel sheet pile, an H-shaped steel pile, or a continuous underground wall.

  In addition, clay can be used as a material for the solidified soil. Thereby, effective utilization of dredged soil can be aimed at and it can contribute to the solution of the problem of the disposal site of dredged soil.

  According to the present invention, when the caisson type mixed bank is backfilled with the treated soil, a greater horizontal resistance can be obtained in the backfilled treated soil layer, so that the caisson type mixed bank can prevent tsunami and high waves. Stability can be improved.

B treated soil layer, solidified treated soil layer C caisson G ground, water bottom ground M mound T coating work 10 slip prevention work 11 drainage pipe

Claims (4)

  A caisson is installed on the mound constructed on the bottom of the ground, and the caisson is backfilled with treated soil, and on the back of the treated soil layer, slippage at the boundary between the treated soil layer and the bottom of the ground is prevented. A caisson-type hybrid dam structure with anti-slip work to do.   The caisson-type hybrid embankment structure according to claim 1, wherein the slip prevention work is constructed from a steel sheet pile, a steel pipe sheet pile, an H-shaped steel pile, or a continuous underground wall.   The caisson type hybrid bank structure according to claim 1 or 2, wherein the treated soil is mixed with a solidifying material.   The caisson-type hybrid bank structure according to any one of claims 1 to 3, wherein a drainage pipe is provided on the back side of the caisson so as to penetrate the treated soil layer and reach the mound.

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