JP2014001539A - Artificial tideland structure and repair method of artificial tideland - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an artificial tideland structure that has stability against ocean waves and takes long-term operation and maintenance into consideration, and to provide a repair method of artificial tideland.SOLUTION: The artificial tideland structure has a sand-cover layer 12 provided on a filling material layer 11. The sand-cover layer 12 comprises: a lower layer 13 that is provided on the filling material layer and formed of a material having a particle diameter of 2 mm or more and a specific gravity of 2.6 or more; and an upper layer 14 that is provided on the lower layer and formed of sand having a particle diameter of less than 2 mm.

Description

  The present invention relates to an artificial tidal flat structure considering long-term maintenance and a repair method thereof.

  Conventional artificial tidal flat structures are generally constructed by dredging clay in the enclosed dike and covering it with sand. When the tidal flat is reduced due to consolidation settlement, sand is thrown in again to restore the ground height.

  According to Patent Document 1, a sheet-like bag is laid at the bottom of the sand-covering layer when creating a tidal flat, and when the drainage area decreases due to consolidation settlement, clay is poured into this bag to restore the ground height. We propose a method for repairing settlement of artificial tidal flats.

JP 2005-281999 JP

  In the conventional tidal flat structure, the sand-covering layer is locally thinned by the waves, and the dredged soil layer is easily exposed. Since sand is introduced every time the dry area is reduced, a large amount of sand, which is a natural resource, is required, resulting in high maintenance costs. In addition, every time sand is added, living organisms are killed and the formed ecosystem is reset.

  The subsidence repair method for artificial tidal flats in Patent Document 1 cannot be applied to tidal flats in which bags are not buried at the time of creation. In addition, the bag may deteriorate over time, and the bag may break when clay is injected. Furthermore, since the repair range is limited by the burying position and size of the bag, there is a possibility that the range that should be repaired cannot be repaired. As long as dredged soil is used as a filling material, long-term maintenance and restoration work is necessary, so a tidal flat structure that takes into account the restoration of living creatures in advance is necessary.

  An object of the present invention is to provide an artificial tidal flat structure and a method for repairing an artificial tidal flat that are stable against waves and take long-term maintenance into account, in view of the above-described problems of the prior art.

  In order to achieve the above object, the artificial tidal flat structure according to the present embodiment is an artificial tidal flat structure in which a sand covering layer is provided on the filling material layer, and the sand covering layer is provided on the filling material layer. A lower layer made of a material having a particle size of 2 mm or more and a specific gravity of 2.6 or more, and an upper layer made of sand having a particle size of less than 2 mm provided on the lower layer.

  According to this artificial tidal flat structure, stability against waves can be ensured by disposing a material having a large particle size under the sand-capping layer. In other words, the material of the lower layer is heavier than the particles of sand, and the sand material at the top of the sand-capping layer is easy to move and flow out by waves, but the material of the lower layer is stable against waves and moves Therefore, there is no exposure or outflow of the filling material.

  In addition, the gap between the materials of the lower layer of the sand covering layer is filled with the upper sand material, and the density thereof is higher than that of the case of only sand or crushed stone, so that the weight of the entire sand covering layer is increased. In the future, when the drainage area of the artificial tidal flat decreases due to consolidation settlement, the ground can be raised and the ground height can be restored by pressing the slurry-like material into the filling material layer. Can be secured by the lower layer. In this way, an artificial tidal flat structure considering long-term maintenance can be realized.

  In the artificial tidal flat structure, it is preferable that the material of the lower layer is any one of crushed stone, concrete block, and steel slag, or a mixture of any two or more.

  The lower layer preferably has a layer thickness of 0.15 to 0.3 m. With this layer thickness, it is possible to secure a supporting force that does not step out even if a person walks and loads in a state where the sand material of the upper part flows out due to the action of waves (only the material of the lower layer remains). .

  By placing a planar reinforcement between the filling material layer and the lower layer, the tension of the planar reinforcement against the lifting pressure (earth pressure) when the slurry-like material is pressed in during tidal flat repair. Works and can suppress the ejection of the slurry-like material and local bulge.

  An artificial tidal flat repair method according to the present embodiment is a method for repairing an artificial tidal flat having the above-described artificial tidal flat structure, and when the drainage area of the artificial tidal flat is reduced by subsidence, the slurry-like material is replaced with the filling material. It is characterized by recovering the ground height by press-fitting into the layer.

  According to this artificial tidal flat repair method, in the artificial tidal flat structure, the gap between the material of the lower layer is filled with the upper sand material, and the density of the lower layer of the sand cover layer is larger than that of only sand or crushed stone. As a result, the total weight of the sand-covering layer increases, but when the artificial tidal flat area decreases due to consolidation settlement, etc., the ground is raised by pressing the slurry-like material into the filling material layer. Can be recovered. The loading load at this time can be ensured by the lower layer.

  ADVANTAGE OF THE INVENTION According to this invention, it has stability with respect to a wave, and can provide the repair method of the artificial tidal flat structure and artificial tidal flat which considered long-term maintenance management.

It is sectional drawing which shows roughly the artificial tidal flat structure by this embodiment. It is sectional drawing which shows the artificial tidal flat structure similar to FIG. 1, and shows repair process (a)-(c). It is principal part sectional drawing for demonstrating the repair press-fit process of FIG.2 (b), Before press-fit (a), after press-fit in the case where a sand covering layer has a lower layer and an upper layer (b), the sand covering layer is only sand. Each state after press-fitting in (c) is schematically shown. It is the figure (b) which cut | disconnected in the BB line direction of the schematic top view (a) of FIG. 4 (a), and the experimental soil tank used by this experiment example. It is a graph which shows the result of this experiment example, and shows the relationship between the distance from a press-fit position (injection position) and the measured amount of protrusion.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing an artificial tidal flat structure according to the present embodiment.

  The artificial tidal flat structure shown in FIG. 1 includes an intermediate filler layer 11 disposed so as to be gently inclined by inserting dredged soil between the revetment 1 and the submerged dike 2, and sand on the intermediate filler layer 11. And the sand-covering layer 12 arranged by putting them in.

  The sand covering layer 12 is composed of a lower layer 13 made of crushed stone having a particle size of 2 mm or more and a specific gravity of 2.6 or more arranged on the filling material layer 11 and sand having a particle size of less than 2 mm arranged on the lower layer 13. And an upper layer 14. The layer thickness h of the lower layer 13 is preferably 0.15 to 0.3 m.

  In the artificial tidal flat structure shown in FIG. 1, the height gradually decreases from the revetment 1 toward the submerged dike 2 below the surface of the water, and the dry area A extends from the revetment 1 toward the submerged dike 2 at a predetermined distance. Is formed.

  According to the artificial tidal flat structure of FIG. 1, the material of the lower layer 13 (crushed stone having a particle size of 2 mm or more and a specific gravity of 2.6 or more) in the sand-clad layer 12 is stable against waves because the particle weight is larger than that of sand particles. do not do. Therefore, the lower layer 13 remains even if the material of the upper layer 14 (sand having a particle size of less than 2 mm) is washed away during the wave action, and prevents the padding layer 11 from being exposed and discharged, and the tidal flat ground Can be maintained. Thus, by arranging a material (crushed stone) having a large particle size in the lower layer 13 of the sand covering layer 12, stability against waves can be ensured.

  In the sand covering layer 12, the sand density of the upper layer 14 increases because the sand of the upper layer 14 enters the crushed stone gaps in which the particle size of the lower layer 13 is large. That is, the gap between the crushed stones of the lower layer 13 is filled with the upper material (sand). For this reason, the density of the soil of the lower layer 13 is larger than the case of only sand or crushed stone. Since the weight of the lower layer 13 is large, it is possible to secure a loading load when the ground clay is raised by press-fitting slurry clay into the filling material layer 11 during repair. That is, the density is large and the load is large as compared with the sand-covered structure using only sand.

  Also, crushed stones with a square shape have a larger internal friction angle and a higher shear strength than sand. Since it has a protective function against the wave action, there is no risk that the sand-covering layer 12 will flow out completely, and the tidal flat can function for a long time.

  Further, in the sand covering layer 12, the lower layer 13 has a layer thickness h of 0.15 to 0.3 m, so that the sand of the upper layer 14 flows out due to the action of waves (the state where only the crushed stone of the lower layer 13 remains). Even if you walk and load, you can secure the support force that will not step on.

  Next, a repairing method when the artificial tidal flat shown in FIG. 1 is reduced due to consolidation settlement will be described with reference to FIGS. FIG. 2 is a cross-sectional view schematically showing an artificial tidal flat structure similar to FIG. 1 and shows repair steps (a) to (c). FIG. 3 is a cross-sectional view of the main part for explaining the repair press-fitting process of FIG. 2 (b), before press-fitting (a), after press-fitting when the sand covering layer has a lower layer and an upper layer (b), and the sand covering layer. Each state after press-fitting in the case where the sand is only sand is schematically shown.

  When the artificial tidal flat in FIG. 1 decreases as shown in FIG. 2 (a) due to the progress of consolidation settlement, the artificial tidal flat in FIG. Repair the tidal flat and restore the ground height.

  First, as shown in FIG. 3A, the press-fit pipe 20 is inserted into the filling material layer 11 from the ground surface through the sand covering layer 12.

  Next, as shown in FIGS. 2 (b) and 3 (b), the slurry-like clay is press-fitted into the filling material layer 11 through a press-fitting pipe 20 by means of a compressor (not shown) or the like, and injected. A press-fit portion 21 made of slurry clay is formed in the material layer 11.

  By forming the press-fit portion 21 made of slurry clay in the filling material layer 11 as described above, a local bulge is formed in the vicinity of the pressure inlet as shown in FIGS. 2 (c) and 3 (b). Therefore, the ground height can be recovered gradually over a relatively wide range. In other words, since the lower layer 13 is present, the load on the sand-capping layer 12 is large and the shear resistance is large, so that when the clay clay is pressed into the tidal flat for the restoration of the tidal flat, local bulging occurs in the vicinity of the inlet. However, it is possible to recover the ground height by gently raising the ground over a wide area.

  According to the repair method of the artificial tidal flat of this embodiment, when the artificial tidal flat of FIG. 1 reduces the squeezed area due to consolidation settlement, the clay is pressed into the filling material layer 11 and the ground is gently spread over a wide area. Can be raised to restore the ground height. For this reason, it is not necessary to re-input sand as in the past, so it is not necessary to use natural resource sand, and maintenance costs are not increased. Moreover, living organisms are killed by additional inputs of sand and the formed ecosystem is not reset.

  When the ground clay is raised by press-fitting slurry clay, the lifting pressure acts by dispersing 45 ° from the intermediate filler layer 11 toward the sand covering layer 12 as shown in FIG. Compared to the case of the conventional sand-only sand covering layer 19 as shown in FIG. 3C, the lower layer 13 made of crushed stone having a large internal friction angle and high shear strength is arranged as shown in FIG. 3B. Thus, the ground cover layer 12 is likely to rise gently over a wider range without shear failure of the sand-clad layer 12 against the lifting pressure.

  In addition, when there are local soft parts or discontinuous surfaces in the tidal flats, the injected slurry clay concentrates on the soft parts or discontinuous surfaces from the inside of the tidal flats, causing split fractures, and on the ground surface. Although there is a concern of jetting out, placing the lower layer 13 as in the present embodiment increases the load of the sand-capping layer 12, which causes split fractures at such soft parts and discontinuous surfaces. There is an effect to make it difficult. When the loaded load is small or the shear strength of the sand-capping layer is small, even if slurry-like clay is pressed into the filling material layer, it does not spread horizontally but is likely to be ejected near the press-fit position.

  The effect which makes it difficult to produce a split fracture in the soft part in a ground and a discontinuous surface by enlarging the loading load of the sand covering layer 12 as mentioned above is further demonstrated. Tests to determine the undrained shear strength of clay (uniaxial compression test ("Soil uniaxial compression test method" JIS A 1216: 2009), triaxial (UU) test ("unconsolidated undrained (UU) triaxial compression of soil)" It can be inferred from the application status of “Test method”, JGS 0521)). In other words, in a uniaxial compression test performed under conditions that do not give restraint pressure to specimens where weak parts such as cracks exist, stress is likely to concentrate in such weak parts and shear failure occurs. A lower strength is evaluated compared to the strength. On the other hand, it is known that in the triaxial (UU) test performed under the condition that a restraint pressure is applied to the specimen, the original strength of the soil can be examined without stress concentration on the weak part. In the soil test, a triaxial (UU) test is adopted when investigating accurate undrained shear strength under conditions where there are weak parts such as cracks. From the above, it is considered that clay slurry can be stably injected without causing splitting fracture in the tidal flat ground when the pressure on the sand cover is large and the pressure that restrains the tidal flat ground is high.

(Experimental example)
Next, experimental examples in which the effect of the present invention has been confirmed will be described. This experimental example was performed using the experimental soil tank of FIGS. 4 (a) and 4 (b). FIG. 4 is a schematic plan view (a) of the experimental soil tank used in the present experimental example and a diagram (b) obtained by cutting in the BB line direction of FIG.

The experimental conditions are as follows.
・ Original ground: Tokuyama Port clay (w = 130%) layer thickness 50cm
・ Material of sand cover layer:
Without case 1 With case 2 (sand) Particle size less than 2.0mm, layer thickness 10cm
Case 3 (crushed stone) particle size around 10mm, layer thickness 10cm
・ Press-in clay: Cement bentonite (property with the same flow value as Tokuyama Port clay (W = 165%))
・ Press-in process: 75L press-in at a press-in speed of 15L / min (5 minutes)

  In the upper part of the clay layer, sand (case 2) and crushed stone (case 3) are provided as sand-capping material. The amount of surface bulge was measured. FIG. 5 is a graph showing the results of this experimental example, and shows the relationship between the distance from the press-fitting position (injection position) and the measured bulge amount.

  As a result of the experiment, the slurry-like clay was ejected in the ejection range of FIG. 5 immediately after the press-fitting without the sand-capping material, and the uplift gradient was steep as shown in FIG. 5 with the sand-capping material present (sand). On the other hand, in the presence of sand-capping material (crushed stone), as shown in FIG. By comparing Cases 1 and 2 of this experimental example, the effect of the overlay load on the sand was confirmed. Moreover, the effect of using a material with large shear strength for covering sand was confirmed by comparing Cases 2 and 3.

  As described above, the desired layer thickness h of the lower layer 13 (crushed stone) in FIG. 1 is about 0.15 to 0.3 m, but this is a state in which the upper material flows out by the action of waves (only the material of the lower layer 13 remains). Based on the result of calculating the layer thickness that can secure the supporting force that cannot be stepped on even if a person is loaded. This calculation will be described below.

  Table 1 shows the loading load by humans. This calculation is for the case where the thickness of the lower layer is h = 0.2 m.

  Moreover, the bearing capacity of the clay is as shown in Table 2 below.

  The same calculation as for the lower layer thickness of 0.2 m is performed for the lower layer thicknesses of 0.1, 0.15, 0.3, 0.4, and 0.5 m, and the calculation results are shown in Table 3. If the layer thickness h of the lower layer 13 (crushed stone) is 0.15-0.3m, the upper load (lower layer (crushed stone) + human) is smaller than the supporting capacity of the viscous soil, and humans have to step on the viscous land Conceivable.

  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, although crushed stone was used in this embodiment as the material for the lower layer of the sand-capping layer (particle size 2 mm or more, specific gravity 2.6 or more), the present invention is not limited to this, and there is no problem in repair work. In addition to the crushed stone, a material having no or low hydraulic property can be substituted. For example, a concrete lump, steel slag (dephosphorization / decarburization, etc.) can be used, and a mixture thereof may be used.

  In FIG. 1, a planar reinforcing material such as a geotextile may be laid between the filling material layer 11 and the lower layer 13. Since the material (crushed stone) of the lower layer 13 of the sand covering layer 12 has a large specific gravity, the crushed stone may sink into the filling material layer 11, but this can be prevented. In addition, the tension of the planar reinforcing material works against the lifting pressure (earth pressure) when the slurry-like material is pressed in to repair the artificial tidal flat, and the slurry-like clay eruption and local uplift can be suppressed.

DESCRIPTION OF SYMBOLS 11 Filling material layer 12 Sand covering layer 13 Lower layer 14 Upper layer 20 Press-in pipe 21 Press-in part A Drying area h Lower layer thickness

Claims (5)

An artificial tidal flat structure with a sand-covering layer on the filling material layer,
The sand covering layer is a lower layer made of a material having a particle size of 2 mm or more and a specific gravity of 2.6 or more provided on the filling material layer, and an upper layer made of sand having a particle size of less than 2 mm provided on the lower layer. An artificial tidal flat structure characterized by comprising.   The artificial tidal flat structure according to claim 1, wherein the material of the lower layer is any one of a crushed stone, a concrete lump, and a steel slag, or a mixture of any two or more.   The artificial tidal flat structure according to claim 1 or 2, wherein the lower layer has a layer thickness of 0.15 to 0.3 m.   The artificial tidal flat structure according to any one of claims 1 to 3, wherein a planar reinforcing material is disposed between the filling material layer and the lower layer. A method for repairing an artificial tidal flat having the artificial tidal flat structure according to any one of claims 1 to 4,
A method for repairing an artificial tidal flat characterized in that when the drained area of the artificial tidal flat decreases due to subsidence, the ground height is recovered by press-fitting a slurry-like material into the filling material layer.

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