JP2012161754A - Bottom sediment improving structure and bottom sediment improving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means that can acquire a distribution situation after charging a bottom sediment improving agent into a closed water area or the like and supply bottom sediment improving components more surely into the object water area.SOLUTION: A bottom sediment improving structure A having a solid agent 1 containing bottom sediment improving components 12, and containing magnetic bodies M as components is charged into a closed or semiclosed water area. Then the bottom sediment improving structure A is retained in bottom mud where the solid agent 1 dissolves to improve a bottom sediment therearound. At the same time, since the bottom sediment improving structure A includes the magnetic bodies M, the distribution situation can be acquired by a magnetic searching means or the like after charging the bottom sediment improving structure A. Bottom sediment improvement in the object water area can thereby be uniformly and surely made even when the object water area is wide and the transparency of the water area is low.

Description

  The present invention relates to a sediment improvement means using a drug in a closed / semi-closed water area. More specifically, the bottom sediment improving structure having a solid agent containing a bottom sediment improving component and containing a magnetic substance as a constituent element, and a bottom sediment improving method including a step of dropping the bottom sediment improving structure into water. Related to such.

  In recent years, sediment contamination in closed and semi-enclosed waters such as harbors, lakes, tidal flats, canals and moats has become a problem.

  If industrial wastewater or domestic wastewater flows excessively into closed water areas, the concentration of nitrogen compounds, phosphorus, etc., along with organic matter, will rise and the water areas will become eutrophication. Plankton grows abnormally in eutrophied waters, and dead bodies accumulate on the bottom of the water. Plankton carcasses and other accumulated organic matter are decomposed by aerobic microorganisms, and oxygen is consumed at that time, and the vicinity of the bottom of the water becomes hypoxic. When the bottom mud is in an oxygen-deficient state, organic matter is oxidatively decomposed to produce organic acids, the bottom mud is in an acidic state or reduced state, and hydrogen sulfide is produced by anaerobic microorganisms. . Moreover, when the bottom mud is in a reduced state, phosphorus in the bottom mud elutes and promotes eutrophication.

  As a means to improve and purify the bottom sediment, a method of removing sludge with dredging, a method of covering the bottom sediment with sand, a method of supplying oxygen into the bottom mud by plowing and aeration, a method using chemicals, etc. Has been done.

  As a bottom improvement means using a chemical, for example, a method of reducing the activity of anaerobic microorganisms by suppressing the bottom mud to weak alkalinity using magnesium hydroxide to suppress the generation of hydrogen sulfide (Patent Document 1, etc.) And a method of activating aerobic microorganisms by supplying oxygen into the bottom mud using calcium peroxide or the like (see Patent Document 2, etc.).

  In addition, a method of injecting calcium nitrate or the like into bottom mud has been put into practical use as a bottom improvement means using a drug (see Patent Document 3).

  Calcium nitrate is a strong oxidizing agent, and is a compound that is easily soluble in water and highly deliquescent. When an oxidizing agent such as calcium nitrate is injected into the bottom mud, the bottom mud in a reduced state is improved to an oxidizing atmosphere, and sulfides are oxidized to prevent the generation of malodor due to hydrogen sulfide. In addition, divalent iron is oxidized to trivalent and immobilization of soluble phosphorus suppresses eutrophication of water areas due to phosphorus elution. Furthermore, activation of denitrifying bacteria promotes a reaction for decomposing organic substances into nitrogen gas and carbon dioxide gas.

  Currently, as a method of injecting calcium nitrate into the bottom mud, an aqueous solution of calcium nitrate is confined in the gel, and a pipe is installed to feed the gel from the ship to the bottom mud. In general, a method of injecting is used. However, since calcium nitrate has strong deliquescence properties, it is necessary to prepare an aqueous solution immediately before the work, and it is necessary to manage the state of the gel and have skills, and when this gel-like material is poured into the bottom mud. Large-scale equipment is required, and the injection work is relatively complicated.

On the other hand, Patent Document 4 discloses a technique for solidifying calcium nitrate or the like. As a result, it is only necessary to directly drop the solid agent on the bottom mud, so that it is not necessary to prepare calcium nitrate or the like immediately before the work, and handling is simplified. In addition, by solidifying, calcium nitrate or the like can be supplied to the bottom mud without using a large-scale injection facility and without performing complicated operations.
JP 2001-181117 A JP-A-2-218488 JP 2000-218296 A JP 2002-45888 A

  In the bottom improvement means using chemicals, for example, if the bottom improvement component can be solidified, it is only necessary to drop the solid agent into the bottom mud from the ship etc. it can.

  However, in this case, since the distribution of the solid agent in the target water area is not known after dropping, it cannot be determined whether or not the target amount of the bottom improver could be supplied to the target location.

  Therefore, an object of the present invention is to provide means capable of grasping the distribution situation after dropping a bottom sediment improving agent into a closed water area and the like and improving the bottom sediment in the target water area more reliably.

  In the present invention, a bottom material improving structure including a solid agent containing a bottom material improving component and containing a magnetic substance as a component, and a step of dropping the bottom material improving structure into water. Provide a method.

  For example, when this bottom sediment improvement structure is dropped into a closed / semi-closed water area such as a harbor, lake, mudflat, canal, moat, etc., the bottom mud generally falls soft and falls into the bottom mud. Invades and stays in the bottom mud. Therefore, the solid agent dissolves, the bottom sediment improving component leaches out, and the surrounding sediment is improved.

  Since this bottom sediment improvement structure contains a magnetic substance, after dropping the bottom sediment improvement structure, the drop position is monitored by magnetic exploration means, etc. Whether the agent can be supplied or not can be grasped. Therefore, for example, even when the target water area is wide or when the transparency of the water area is low, the bottom sediment improving component can be supplied uniformly, reliably and effectively into the target water area.

  According to the present invention, in the bottom sediment improvement using a solid agent, after dropping the bottom sediment improving agent into a closed water area, the distribution situation can be grasped, and therefore the target water area can be improved more reliably.

<About the bottom sediment improvement structure according to the present invention>
The present invention includes all bottom sediment improving structures having a solid agent containing a bottom sediment improving component and containing a magnetic substance as a constituent element.

  FIG. 1 is an external perspective view and a partial cross-sectional schematic view showing an example of a sediment improvement structure according to the present invention.

  A bottom material improving structure A in FIG. 1 has a solid agent 1 containing a bottom material improving component 12, a magnetic material M as a constituent element, and a magnetic material M contained in the solid material 1. Is provided. That is, as shown in the cross section 11, the solid agent 1 contains the bottom sediment improving component 12 and the magnetic substance M.

  The solid agent 1 is not particularly limited as long as it contains a sediment improving component as an active ingredient and is solidified.

  A well-known thing can be widely used for a bottom substance improvement component, and it is not limited narrowly. For example, it includes a wide variety of compounds that can improve the bottom sediment by modifying the bottom mud to weak alkaline, compounds that can improve the bottom sediment by supplying oxygen into the bottom mud, oxidizing agents, and the like.

  Examples of the compound capable of improving the bottom sediment by modifying the bottom mud to be weakly alkaline include magnesium compounds such as magnesium hydroxide, magnesium oxide, and magnesium nitrate. Examples of the compound that can improve the bottom sediment by supplying oxygen into the bottom mud include calcium peroxide, magnesium peroxide, and iron oxide.

  Examples of the oxidizing agent include calcium nitrate, potassium nitrate, ammonium nitrate, magnesium nitrate, manganese nitrate, and alum. These oxidants can improve the bottom mud in a reduced state to an oxidizing atmosphere, oxidize sulfides, suppress the generation of malodor due to hydrogen sulfide, etc., further oxidize divalent iron to trivalent, soluble By immobilizing phosphorus, eutrophication of the water area due to phosphorus elution is suppressed, so that it is suitable as a bottom sediment improving component according to the present invention. Of these, nitrate is more preferable because it activates denitrifying bacteria and promotes the reaction of decomposing organic matter into nitrogen gas and carbon dioxide gas.

  Of these, calcium nitrate is most preferred because it has the most powerful action as an oxidant and has a high effect of improving the bottom sediment, particularly the deodorizing effect. The calcium salt in calcium nitrate also has an action of adsorbing and fixing components such as organic acid and phosphorus dissolved in water and suppressing elution into water.

A known technique can be used for solidifying the bottom substance improving component, and is not particularly limited. For example, it can be produced by mixing the above-mentioned compound and a binder, putting them in a mold, pressurizing them (for example, 20 to 100 kg / cm ² ), and molding them into a predetermined shape. The shape of the solid agent 1 may be designed according to the purpose and application, and is not particularly limited.

  As the binder, for example, an aliphatic carboxylic acid solid at normal temperature having 11 to 31 carbon atoms (for example, stearic acid, myristic acid, behenic acid) or an ester thereof, an aromatic carboxylic acid or an ester thereof can be used. . These compounds are hydrophobic. Accordingly, for example, by appropriately adjusting the mixing ratio of these binders in the range of 1 to 40% by weight, the elution rate of the oxidizing agent in water can be appropriately adjusted according to the purpose and application.

  In addition, when the above compound and the binder are mixed, another compound may be added as appropriate according to the purpose / use and the like, followed by pressing / molding.

  The solid agent 1 may be coated with a water-insoluble or poorly water-soluble substrate. By coating the solid agent 1 with these base materials, the elution of the solid agent 1 can be further delayed. Therefore, for example, both the bottom sediment improvement structures of the solid agent 1 coated and not coated with the base material insoluble or sparingly soluble in water, or a plurality of bottom sediment improvement structures having different coating degrees Can be extended simultaneously or continuously to extend the duration of the effect.

  Examples of water-insoluble or poorly water-soluble base materials include waxes (carnauba wax, beeswax, white beeswax, hydrogenated oil, paraffin, stearic acid and stearyl alcohol), polyoxyethylene, polyoxypropylene glycols, rosin, and hydrogenated rosin glycerin. Examples include esters, ester gums, vinyl acetate resins, agar, alginic acid, polyvinyl alcohol and the like. The coating treatment (coating treatment) of the solid agent 1 can be performed by a known means.

  The magnetic body M should just be formed with the material detected by a magnetic search means, and a material, a shape, etc. are not specifically limited. Since the bottom sediment improving structure A includes the magnetic substance M, the dropping position can be monitored by magnetic exploration means after dropping the bottom sediment improving structure A. Therefore, a target amount of bottom sediment improving agent is applied to the target location. You can grasp the distribution status or not.

  As the magnetic body M, for example, a material exhibiting strong magnetism such as iron, nickel, or cobalt can be used. Note that the iron magnetic substance M has little environmental impact even when dropped in water. When an oxidizing agent is used as the solid agent 1, iron oxidizes divalent iron to trivalent and immobilizes soluble phosphorus. By doing so, it is most preferable because eutrophication of the water area due to phosphorus elution can be suppressed.

  The means for containing the magnetic substance M in the solid agent 1 can be a known technique and is not particularly limited. For example, when solidifying the bottom sediment improving component, the bottom sediment improving compound, the binder, and the magnetic material M are mixed, put into a mold, and pressed and molded.

  FIG. 2 is a schematic external perspective view showing another example of the bottom sediment improving structure according to the present invention, FIG. 3 is a schematic external side view, and FIG. 4 is a schematic cross sectional view.

  The bottom sediment improvement structure A ′ shown in FIGS. 2 to 4 is composed of a solid agent 1 containing a bottom sediment improvement component, and a surveyed member 2 formed of a magnetic material.

  The to-be-searched member 2 is a member made of a magnetic material, and when this member is detected by the magnetic searching means, it is possible to monitor the drop position. The to-be-searched member 2 may be formed only with a magnetic material, and may contain another material. The thing of the shape according to the objective, a function, etc. can be used suitably.

  2 to 4 has a structure in which a through hole is formed in the solid agent 1 and each solid agent 1 is inserted into a substantially rod-shaped exploration member 2. In this bottom substance improving structure A ′, the four solid agents 1 are each formed into a substantially cylindrical shape having a through hole, and the exploration member 2 includes a bolt 21 and a nut 22. The solid agent 1 is inserted into a bolt 21 as a support in a layered manner, and a nut 22 is attached to a screw portion 21 ′ at the other end to be tightened. Thereby, solid member 1 is fixed and bolt 21 and nut 22 are used as magnetic bodies to form exploration member 2.

  This configuration has an advantage that the bottom sediment improving structure A ′ can be produced at low cost and in large quantities. The substantially rod-shaped exploration member 2 may be a member that can hold the same configuration, such as a bolt and a nut, as well as bolts and nuts.

  FIG. 5 is a schematic external side view showing still another example of the bottom sediment improving structure according to the present invention.

  The bottom sediment improvement structure A ″ in FIG. 5 is composed of a solid agent 1 containing a bottom sediment improvement component, a member to be investigated 2 formed of a magnetic material, and a container 3 that stores the solid agent 1.

  As shown in FIG. 5, the solid agent 1 is fixed by being accommodated in a container 3 in which water can freely enter and exit, and the solid agent is dissolved in the same manner as described above by dropping the structure A ″ into water. The bottom quality improving component is leached and the surrounding bottom quality can be improved.

  Further, by attaching the member 2 to be investigated to the container 3, the dropping position can be monitored by the magnetic exploration means or the like after dropping the bottom sediment improving structure A ″.

  In addition, since the specific gravity of the solid agent 1 is generally in the range of 1.5 to 2.0 in a dry state, and the specific gravity of the exploration member 2 is higher than that of the solid agent 1 and the container 3, the bottom when falling in water The direction of the quality improvement structure (see arrow X) can be specified so that the portion to which the member to be searched 2 is attached faces downward, and the bottom can be stabilized.

  A known material can be used for the container 3 and is not particularly limited. For example, those made of biodegradable plastics such as polylactic acid, polycaprolactone, polyglycolic acid, modified polyvinyl alcohol, casein, and modified starch are preferable in that the environmental load after dropping is small.

  6 and 7 are external side view schematic diagrams showing an example of a bottom quality improving structure provided with an underwater dropping speed adjusting means.

  In the bottom sediment improvement structure A1 of FIG. 6, the underwater drop speed increasing member 41 is attached to the screw portion 21 'of the bottom sediment improvement structure A' shown in FIG.

  The underwater falling speed increasing member 41 is preferably made of a material having a high specific gravity, for example, iron. Moreover, the shape with little water resistance at the time of falling in water, for example, a substantially pyramid shape, is suitable.

  By mounting the underwater drop speed increasing member 41, it is possible to specify the orientation (see arrow X) of the bottom sediment improving structure A1 when dropping in water, and to increase the underwater drop speed. Therefore, in the case of bottom mud having a normal hardness, the bottom quality improving structure A1 can reach a relatively deep position, and even if the bottom mud is harder than usual, the bottom quality is improved to the bottom mud. The structure A1 can be reached.

  On the other hand, in the bottom sediment improvement structure A2 of FIG. 7, the underwater drop speed suppressing member 42 is attached to the screw portion 21 'of the bottom sediment improvement structure A' shown in FIG.

  The underwater falling speed suppressing member 42 is preferably made of a material having a low specific gravity, such as a biodegradable plastic. Further, a shape having a large resistance to water when falling in water, for example, a substantially umbrella shape is suitable.

  By mounting the underwater drop speed suppressing member 42, it is possible to specify the direction (see arrow X) of the bottom sediment improving structure A1 when dropping in water, and to slow down the underwater drop speed. Therefore, in the case of bottom mud having a normal hardness, the bottom quality improving structure A2 can be kept at a shallow position.

<About the sediment improvement method according to the present invention>
The present invention includes all bottom sediment improving methods including at least a step of dropping a bottom sediment improving structure having a solid agent containing a bottom sediment improving component and containing a magnetic substance as a constituent element into water. That is, the present invention is not narrowly limited because it does not include other steps.

This qualitative improvement method is, for example,
(1) A process of investigating the hardness of the bottom mud in advance,
(2) The process of digging up the bottom mud before dropping the bottom quality improvement structure,
(3) A step of dropping the bottom sediment improvement structure,
(4) After dropping the bottom sediment improving structure, the step of monitoring the dropping position by the magnetic exploration means can be performed in this order.

  In the step (1), it is preferable to first investigate the hardness of the bottom mud before dropping a large amount of the bottom quality improving structure. Considering the hardness of the bottom sediment and the underwater falling speed of the bottom sediment improvement structure A, it is examined whether the bottom sediment improvement structure reaches the target depth in the bottom mud. When the bottom sediment improving structure cannot reach the target depth, the underwater drop speed is adjusted by, for example, the above-described underwater drop speed adjusting means.

  In step (2), before dropping the bottom sediment improvement structure, for example, by towing a chain or the like attached to the tip of a stirrer with a ship, or sending a water flow by pumping from the ship, Dig up the bottom mud. Thereby, the surface layer of the bottom mud can be broken, and the bottom quality improving structure can easily reach the bottom mud.

  In step (3), the bottom quality improving structure is continuously dropped from the ship or the like. The dropping means is not particularly limited. For example, a dropping device that can automatically drop at a fixed interval may be installed on the ship and used.

  This step is preferably performed after the bottom mud has been dug up in step (2) and before the rising bottom mud settles again. The dropped sediment improvement structure penetrates into the bottom mud and stays in the bottom mud. Therefore, the solid agent is gradually dissolved, and the bottom sediment improving component is leached, and the surrounding sediment is improved.

  In step (4), after dropping the bottom sediment improving structure, the dropping position is monitored by magnetic exploration means. Since the sediment improvement structure contains a magnetic substance, monitoring the drop position with a magnetic exploration means, etc., ascertains whether or not the targeted amount of sediment improvement agent has been supplied to the target location it can. Thereby, for example, even when the target water area is wide or when the transparency of the water area is low, the sediment improvement component can be supplied uniformly, reliably and effectively into the target water area.

  As the magnetic exploration means, for example, a known machine / device that can detect the presence of a magnetic material by detecting a change in magnetic characteristics, such as an ordinary metal detector, can be used.

  FIG. 8 is a schematic diagram showing an example of the bottom sediment improvement method according to the present invention.

  In FIG. 8, in order to modify the bottom mud S1 deposited on the bottom S, the bottom mud S1 is digged up by towing a chain or the like with a stirring tool 51 attached to the tip of the ship 5 and the bottom mud soared Before S2 sinks again, bottom sediment improvement structure A is continuously dropped into water W from dropping means 52 on ship 5.

  For example, the bottom sediment improvement structure A1, the bottom sediment improvement structure A2 to which the underwater drop speed increasing member is attached, and the bottom sediment improvement structure A3 to which the underwater drop speed suppression member is attached are dropped simultaneously or successively in FIG. As described above, the bottom sediment improvement structure is made to reach different positions in the bottom mud by dropping a plurality of types of bottom sediment improvement structures having different underwater dropping speeds simultaneously or successively. Can do.

  As a result, even in the water area where the bottom mud is thickly accumulated, the bottom sediment improvement component can be supplied to the respective depths, so the area where the bottom sediment improvement structure in the bottom mud does not reach can be reduced and effective. The bottom quality can be improved.

  In addition, the bottom sediment improvement structures of both the solid agent coated and non-coated with the solid agent with a base material that is insoluble or hardly soluble in water, or a plurality of the bottom sediment improvement structures having different coating degrees By dropping simultaneously or continuously, the effect can be maintained for a long time after construction.

<Distribution monitoring method of sediment improvement structure using magnetic exploration means>
The present invention has a solid agent containing a bottom sediment improving component, and after dropping a bottom sediment improving structure containing a magnetic substance as a component into water, the bottom of each bottom sediment improving structure is dropped by a magnetic exploration means. All the distribution status monitoring methods for the bottom sediment improvement structure including at least a procedure for monitoring the position or distribution status are included.

  For example, even in the case of improving sediments in relatively large closed / semi-enclosed waters, each sediment is monitored by magnetic exploration means after a large amount of sediment improvement structures are dropped into water. The drop position and distribution status of the improved structure can be grasped. Therefore, even when constructing a large-scale bottom improvement, the distribution unevenness of the bottom improvement structure can be reduced, and the bottom improvement component can be uniformly and reliably supplied into the target water area.

<Sediment improvement evaluation method using magnetic exploration means>
The present invention evaluates the progress of bottom sediment improvement by a magnetic exploration means after dropping a bottom sediment improvement structure having a solid agent containing a bottom sediment improvement component and containing a magnetic substance as a constituent element into water. Includes all methods for evaluating sediment improvement including at least procedures.

  For example, when the magnetic material is contained in the solid agent as shown in FIG. 1 or when a part of the magnetic material is covered with the solid agent as shown in FIG. The degree of exposure and the exposed area of the body change. Therefore, by detecting the change in magnetic properties based on the degree of exposure of the magnetic substance and the change in the exposed area using a magnetic exploration means, etc., after a predetermined period of time has passed since the bottom sediment improvement structure was dropped into the water area, The degree of elution of the solid agent can be estimated, and the degree of progress of bottom sediment improvement can be evaluated based on this. Thereby, since a diver etc. can evaluate a sediment quality improvement comparatively easily from the ship etc., without diving etc., labor can be reduced.

  The present invention can monitor the distribution status of bottom sediment improving components when the bottom sediment is improved using an agent that can be solidified in closed / semi-closed water areas such as harbors, lakes, tidal flats, canals, moats, etc. The distribution of bottom quality improving components can be reduced, the bottom quality improving components can be supplied to the target water area uniformly and reliably, the construction can be done with relatively low labor and cost, and the bottom quality of a relatively wide range of water areas can be improved. It is useful in that it can be applied when you want to.

  As described above, the bottom sediment improvement method using calcium nitrate is a method having a bottom sediment improvement effect, particularly a high deodorizing effect. At present, a method is generally used in which an aqueous solution of calcium nitrate is confined in a gel, a tube for pumping from the ship to the bottom mud is installed, and the gel is injected into the bottom mud. .

  However, in this method, since calcium nitrate is highly deliquescent, it is necessary to prepare an aqueous calcium nitrate solution immediately before work at a construction site or the like. Moreover, in order to maintain the uniform state of the calcium nitrate aqueous solution at the construction stage, a stirring operation is required, and construction management is complicated. Furthermore, if the state management of the gel is necessary and the management is insufficient, the gel fed by pressure does not mix in the bottom mud and leaks to the bottom mud surface and dissolves in water. Therefore, there is a problem that it is difficult to inject a certain amount and uniform calcium nitrate unless a skilled worker performs it. In other words, there has been a problem that sufficient experience and a great deal of labor are required when constructing by this method.

  On the other hand, when solidified calcium nitrate is used, the labor of dropping and spraying the solid agent is greatly reduced, and handling becomes easy. However, in this case, it is not possible to grasp whether or not the target amount of the bottom sediment improving agent has been supplied to the target location. For this reason, it is necessary for a diver or the like to directly check the state of the drop, and there is a problem that large-scale construction is difficult.

  On the other hand, the present invention is a bottom sediment improving means that can grasp whether or not a target amount of bottom sediment improving agent has been supplied to a target location and its distribution state, and can also be applied to solidified calcium nitrate. In addition, since it is only necessary to drop the bottom sediment improvement structure into the water area, labor and cost can be greatly reduced, construction management is easy, and it can be applied to large-scale construction. Therefore, this invention is useful at the point which can construct bottom sediment improvement construction simply, effectively, and large scale using calcium nitrate.

The external appearance perspective view and the partial cross section schematic diagram which show the example of the bottom quality improvement structure which relates to this invention. The external appearance schematic perspective view which shows another example of the sediment improvement structure which concerns on this invention. The external appearance side view schematic diagram which shows another example of the sediment improvement structure which concerns on this invention. The cross-sectional schematic diagram which shows another example of the sediment improvement structure which concerns on this invention. The external appearance side view schematic diagram which shows another example of the sediment improvement structure which concerns on this invention. The external appearance side view schematic diagram which shows the example of the bottom quality improvement structure provided with the underwater fall speed adjustment means (when the underwater fall speed increase member 41 is mounted | worn). The external appearance side view schematic diagram which shows another example of the bottom quality improvement structure provided with the underwater fall speed adjustment means (when the underwater fall speed suppression member 42 is mounted | worn). The schematic diagram which shows the example of the sediment improvement method which concerns on this invention.

DESCRIPTION OF SYMBOLS 1 Solid agent 2 Searched member 21 Bolt 22 Nut 3 Container 41 Underwater fall speed increasing member 42 Underwater drop speed suppressing member 5 Ship 51 Stirring tool 52 Dropping means A Bottom sediment improvement structure M Magnetic body S Water bottom S1 Bottom mud W Water

Claims (9)

  A bottom improvement structure having a solid agent containing a bottom improvement component and containing a magnetic substance as a constituent element.   The bottom sediment improvement structure according to claim 1, wherein the magnetic material is contained in the solid agent or comprises a member to be searched formed of the magnetic material.   The bottom sediment improving structure according to claim 2, further comprising an underwater dropping speed adjusting means.   The bottom sediment improvement structure according to claim 1, wherein the solid agent is coated with a water-insoluble or hardly water-soluble base material.   A bottom quality improving method comprising a step of dropping the bottom quality improving structure according to claim 1 into water.   The bottom sediment improvement method of Claim 5 including the process of monitoring a drop position by a magnetic exploration means after dropping of the said bottom sediment improvement structure.   The bottom sediment improvement method according to claim 5, further comprising a step of digging up bottom mud before dropping the bottom sediment improvement structure.   The bottom sediment improvement method according to claim 5, wherein a plurality of types of bottom sediment improvement structures having different dropping speeds in water are dropped.   Dropping both bottom sediment improvement structures with and without the solid agent coated with a base material that is insoluble or sparingly soluble in water, or a plurality of bottom sediment improvement structures with different coating degrees The method for improving bottom sediment according to claim 5.

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