KR20060136325A - Solidification method of dredged soils - Google Patents

Abstract

The present invention relates to a dredged soil solidification method, comprising: obtaining a dough of a mixture consisting of dredged soil, a hardening agent and coal ash; It characterized in that it comprises the step of curing the dough of the mixture. As a result, by making the dredged soil difficult to be treated and the unrecycled coal ash to be used as civil engineering materials of economical and improved performance, it is possible to recycle resources and contribute to environmental conservation.

Description

Dredged soil solidification method {SOLIDIFICATION METHOD OF DREDGED SOILS}

The present invention relates to a dredged soil solidification method, and more particularly, to a dredged soil solidification method that can be used as a civil engineering material, such as landfill material, roadbed material, road substrate material and backfill material by solidifying the dredged soil together with coal ash. .

In general, coal-fired power plants using coal as a raw material are pulverized to a predetermined size, that is, to produce pulverized coal, in order to increase the combustion effect of coal. After producing high pressure steam, the steam is generated by supplying the steam to the steam turbine.

When pulverized coal is supplied to the boiler, 10 to 20% of the pulverized coal is ash, which is generated as coal ash during the combustion of coal. About 20% of coal ash is melted by high temperature combustion heat, and various particles are condensed and discharged to the bottom of the boiler. About 80% is burned by each particle and scattered according to the flow of combustion gas. Is collected on the device.

On the other hand, coal ash discharged to the lower part of the boiler is called bottom ash, and its particle diameter is widely distributed in the range of about 100 μm to several centimeters, and large chunks are shredded below 1 centimeter and transported to the landfill along with the seawater to landfill. do. In addition, coal ash scattered from the boiler and collected and discharged from the electrostatic precipitator is called fly ash. Such fly ash has an average particle diameter of approximately 20 μm to 60 μm, a maximum particle diameter of 100 μm or less, and a landfill with flooring material. Is transferred to.

Coal ash buried in the vicinity of domestic power plants is about 30 million tons, and the expansion of power plants is expected to be inevitable due to the increase in economic scale.

However, despite the fact that the landfilled coal ash is a material that can be recycled as general waste, there is almost no recycling, and some attempts to recycle it, but due to the characteristics of the landfill coal ash, very small amount (0.03% of landfill amount) is recycled. It is becoming.

The reason why the landfill coal ash, which is an inorganic combustor, cannot be recycled as aggregate is the construction material. First, the landfill coal ash contains a large amount of chloride (salin), which corrodes the reinforcing steel of the concrete. It is difficult to recycle as concrete aggregate due to its weak strength as well as its high absorption rate.

As a result, there is almost no recycling of landfill coal ash, and each plant has landfilled coal ash (mostly floor ash and some mixed ash) at landfill sites. Not only that, but they are also struggling with environmental management.

On the other hand, dredged soils generated by dredging and river dredging due to port development are generated in large quantities every year, and until recently, most dredged soils have been treated by ocean dumping in the open sea, but the 1996 London Dumping Convention and related protocols entered into the sea Recycling of dredged soil is urgently needed due to the strengthening of dumping conditions and the ban on direct landfilling.

However, in Korea, dredged soil treatment and recycling, which occurs enormously, remain at the beginning stage, and most of them are dumped and disposed of in a dredged soil dumping site.

At present, some dredged soil treatments are attempting to improve the soft ground by mixing and consolidating most of the clay materials. However, the results are insignificant due to the severe shortage of the clay materials and long-term improvement period, and stability problems after construction.

Another treatment method is to improve dredged soil by natural drainage and artificial drainage method. Also, after the development and stabilization of pests due to long-term improvement period, stability problems due to the lack of strength have not been cleared to date. There is a situation.

Meanwhile, the government is planning and implementing various national projects, such as coastal new towns and ports construction, to balance the country's balanced development and leap to advanced countries, but it is hampered by severe shortage of landfill materials. In order to solve this problem, the government is taking various measures through cutting of cutting and construction wastes, but it is difficult to secure landfill materials due to environmental damage and huge logistics costs.

In particular, the method of recycling waste into sedimentary materials using dredged soil is considered, but it is difficult to recycle due to stability problems, long-term improvement period and economical efficiency. Suffer.

Thus, in reusing the dredged soil using a solidifying agent and then reprocessing it into a civil engineering material such as a fill soil, it is possible to secure workability by using a large amount of water to solve the high viscosity. In addition to the difficulty in economic treatment due to the increase, a large amount of alkaline wastewater is generated by a large amount of bibim water used after pouring into the bleeding water. In addition, the organic matter contained in the dredged soil and humic acid (huminic acid, etc.) generated when the organic material is decayed not only makes it difficult to solidify the cement-based solidifying agent, but also reduces the amount of air in the solidified body due to the fine dredged soil particles. There are various problems such as reduction of freeze-thaw resistance and volume reduction and cracking caused by dry shrinkage after solidification of dredged soil.

Accordingly, the present applicant has developed a dredged soil solidification treatment method that can recycle dredged soil solidification treatment, which is difficult to use as fill material, to recycle waste coal and dredged soil as resources, and to solve the problem of severe shortage of soil.

It is therefore an object of the present invention to provide a dredged soil solidification treatment method that can recycle resources and contribute to environmental conservation.

In order to achieve the above object, the present invention provides a dredged soil solidification treatment method comprising the steps of: obtaining a dough of a mixture consisting of dredged soil, hardener and coal ash; It provides a dredged soil solidification method comprising the step of curing the dough of the mixture.

Here, the mixture is preferably composed of 37 to 92% by weight of dredged soil, 3 to 58% by weight of solidifying agent and 5 to 60% by weight of coal ash on a dry basis.

The particle size of the coal ash is in the range of 0.02mm to 25mm corresponding to the fly ash and the bottom ash, the fly ash having a small particle is spherical, and the floor ash having a relatively large grain has a much smaller specific surface area than the dredged soil, and also has the number of particles per unit volume. It is possible to increase the fluidity of highly viscous dredged soil due to the reduction effect of intergranular attraction and friction when using coal ash.

The mixture content of the dough is made on a dry basis and a predetermined amount of water is added to the dry mixed solid so that the hydration reaction necessary for securing the fluidity required for pouring and solidifying occurs. At this time, the amount of water to be added depends on the liquid limit value of the dredged soil to be used. If the liquid limit value is 45% or less, 35 to 60% by weight of water is added to the mixture weight, and the liquid limit value is 45% or more. It is preferable to add 55 to 100% by weight of water to the mixture weight and mix.

The hardener may be made of any one of cement, blast furnace slag cement, slaked lime and gypsum.

The coal ash may be formed of at least one of a floor ash generated from a coal-fired power plant, a floor ash mixed with fly ash generated from a coal-fired power plant, and a floor ash generated from waste incineration.

Hereinafter, the dredged soil solidification treatment method according to the present invention will be described in detail. In addition, it is clear beforehand that% described after this is based on a weight%.

First, 3 to 58 weight% of solidifying agent, 37 to 92 weight% of dredged soil, and 5 to 60 weight% of coal ash are mixed to obtain a dough of the mixture.

Here, the dredged soil is preferably at least one of those occurring in dredging operations such as marine clay, water and sewage sludge, rivers and lakes. In addition, although the dredged soil and coal ash in the mixture usually contains water, the mixing ratio is preferably on a dry basis.

The hardening agent consists of cement, blast furnace slag cement, slaked lime or gypsum.

Coal ash increases the compressive strength during solidification of dredged soil, shortens the consolidation time of the finally solidified mixture, increases freeze-thawing resistance by increasing the air volume of the mixture, and reduces drying shrinkage. It is preferable that the coal ash has a particle size in the range of 0.02 mm to 25 mm. Therefore, the fly ash having a small particle has a spherical shape, and the floor ash having a relatively large particle has a smaller specific surface area than that of dredged soil, and also has a smaller particle size per unit volume. Due to the reduced effect of interfering friction and frictional forces, it is possible to increase the fluidity of highly viscous dredged soil. Particularly, the coal ash is preferably made of at least one of a bottom ash generated in a coal-fired power plant, a fly ash mixed with fly ash generated in a coal-fired power plant, and a floor ash generated in waste incineration.

Further, the dough is added 35 to 60% by weight of water relative to the weight of the mixture when the liquid limit value of the dredged soil is 45% or less, and 55 to 100% by weight of the mixture weight when the liquid limit value is 45% or more. By adding water and mixing, it is possible to increase the strength of the hardened mixture by reducing the ratio of water to cement by drastically reducing the amount of water used in the solidification treatment by mixing more than when the coal ash is not mixed. This leads to a decrease in the number of surplus bibeams generated by the bleeding, so that the treatment of bleeding water, which is a strong alkali, can be reduced.

Next, by curing the dough of the mixture, it becomes possible to solidify the dredged soil. Here, the dough of the mixture can be poured and cured, or it can be poured into a predetermined mold and hardened to a predetermined shape.

Meanwhile, in order to clarify the gist of the present invention, various experimental results of the mixture prepared by the dredged soil solidification method according to the present invention will be described.

First, the experimental data showing the correlation of fluidity according to the mixing ratio of dredged soil, cement as a solidifying agent, and coal ash, that is, the increase of fluidity (flow) of the mixture in the unsolidified state according to the coal ash mixing ratio of each sample as shown in <Table 1>. Is disclosed below.

<Table 1 Mixture Mix Ratio, Dredged Soil Limit 34.6%>

The dredged soil liquid limit is a water content of the time when the dredged soil is converted from the liquid phase to a solid phase, and there is a significant difference depending on the source of dredged soil. It is common practice that as the liquid limit of dredged soils increases, more bibeam water is required to achieve the desired fluidity. In Table 1, the test was carried out with dredged soil having a liquid limit of 34.6%. 34.6% of liquid limit means dredged soil which shows the behavior of liquid when water content is 34.6% or more.

When curing each sample disclosed in <Table 1>, the water required for securing fluidity was mixed and kneaded in a weight ratio of 100: 65 (mixture: water) in the same ratio, and then a flow meter having a diameter of 80 mm and a height of 80 mm having both inlets opened. When the measuring device was removed after filling in, the spread of the sample was measured.

The amount of water required for fluidity was estimated by the amount of water required based on 20 ± 2cm of flow, which is the proper fluidity required for pouring work, through preliminary mixing tests using only dredged soil and hardener.

<Table 2 Flow Measurement Results>

<Graph 1 flow measurement result>

In <graph 1>, the flow increases with increasing coal ash mixing ratio, but shows that the flow decreases with coal ash mixing ratio of 50% or more. This indicates that the coal ash mixing ratio for improving the fluidity is limited to about 50 to 60%, and when the coal ash is mixed in pouring the mixture of the dredged soil using the dredged soil, the flow rate is much higher than the flow rate of 20 ± 2 cm. In addition, the mixing of coal ash is expected to reduce the amount of water as non-beam water.

Therefore, as the coal ash mixing ratio for securing maximum fluidity is about 35 to 50%, the amount of water needed to secure the flow 20 ± 2 cm necessary for pouring the mixture as the fill material is adjusted by adjusting the coal ash mixing ratio to 40%. The experimental data calculated on the basis of 1㎥ of landfill material by usage is shown below.

<Table 3 Amount of water required to secure 20 ± 2cm of flow, 1m3 of fill material, 100% of hardening agent and dredged soil, 33.6% of dredged soil liquid limit>

<Table 4 Amount of water required to secure 20 ± 2cm of flow, 1m3 of fill material, solidified material + 60% of dredged soil, 40% of coal ash, 33.6% of dredged soil liquid limit>

The test shows that the amount of water required to secure the same fluidity is significantly reduced in the case of coal ash mixing than in the case of using only dredged soil, which can reduce the amount of solidifying agent (cement) by reducing the amount of water required for kneading the mixture. Can serve as a basis. The data of <Table 3> and <Table 4> are summarized as the ratio of water consumption to the mixture (cement + dredged soil + coal ash) as follows.

<Table 5 Non dredged soil liquid limit of 33.6% of water use compared to the mixture in 1㎥ of dough of the uncured mixture>

In the data of <Table 5>, the sample using only dredged soil having a liquid limit of 33.6% showed a water / mixture ratio of about 65 to 70% in order to secure a flow of 20 ± 2 cm necessary to secure the curing workability of the mixture dough, while the total solid content was When 40% of the mixture was tested with coal ash, it was found to be about 47.8-50%. Although there were some differences depending on the increase and decrease of cement usage in 1 m 3 of the mixture dough, the water consumption was reduced by approximately 17.2 to 20%.

In addition, in order to obtain the result value according to the type of dredged soil, it was tested using dredged soil having a liquid limit of 59.6%.

<Table 6 Ratio of water use compared to mixture in 1㎥ of dough of uncured mixture, 59.5% of dredged soil liquid limit>

In the data of <Table 6>, a sample using only dredged soil having a liquid limit of 59.5% showed water / mixture ratio of about 104.4 to 110.0% in order to secure a flow of 20 ± 2 cm necessary for securing curing workability of the mixture dough, while total solid content When 40% of the mixture was tested by mixing with coal ash, it appeared to be about 77.0 to 80.0%. Although there were some differences according to the increase and decrease of cement usage in 1 m 3 of the mixture dough, the water / mixture ratio of about 27.4-30% was reduced.

It can be seen that as the liquid limit value of dredged soil increases, the water / mixture usage ratio for securing a certain fluidity increases regardless of coal ash mixing. However, water / mixture is mixed when coal ash is not mixed. It can be seen that the phenomenon of decreasing rain is the same regardless of the dredged liquid limit value.

Therefore, the water / mixture usage ratio should be different according to the difference in liquid limit according to the type of dredged soil, and when the mixing standard of solids is mixed with dredged soil 37-92 wt%, solidifying agent 3 ~ 58 wt% and coal ash 5 ~ 60 wt% When the dredged soil having a liquid limit of dredged soil of 45% or less is used, the water use ratio of the mixture is 35 to 60% by weight. If the dredged soil has a liquid limit of 45% or more, the water used ratio of the dredged soil is 55 to 100%. It is preferable to set it as%.

This can improve the strength of the hardened mixture by reducing the ratio of water to cement by drastically reducing the amount of water used when solidifying the dredged soil and using it as a fill material. This can lead to a reduction in the excess number of bibeams generated by the bleeding after the fill process, thereby reducing the treatment of the bleeding water, which is a strong alkali.

Thus, in order to confirm the strength increase of the mixture by reducing the amount of water used per 1 m 3 of the mixture, a specimen 100 mm in diameter and 200 mm in height was prepared on the basis of the mixing tables of <Table 3> and <Table 4> for 7 days at 20 ± 2 ° C. The test results of 28 days of wet curing to measure compressive strength are shown below.

<Table 7 Compressive Strength Measurement Results>

<Graph 2 compressive strength measurement results, as of 28 days>

<Table 8 Compressive Strength Enhancement Rate of 40% of Coal Ash Mixed with 100% of Dredged Soil>

Although the compressive strength test shows a slight difference depending on the increase and decrease of the amount of cement mixture per 1m 3 of the mixture, the increase rate of compressive strength for each cement usage is increased by about 150 to 260%. This drastically reduces the amount of solidifying agent, which is the biggest obstacle in using dredged soil as a fill material, and can economically process it using coal ash in dredged soil solidification treatment, thus cured mixture without resource recycling and damage to natural environment. As a result, it is possible to prevent the delay of large-scale national projects, preserve the environment, and recycle resources.

In addition, when the coal ash is mixed with the dredged soil, the condensation speed is significantly increased when the coal ash is mixed with the dredged soil and recycled as the sedimentary soil. Therefore, the condensation speed is significantly increased. The enormous economic benefit can be obtained.

Therefore, in order to confirm the difference in the setting rate, as shown in <Table 9>, a sample using 170 kg of cement per m3 of the mixture and no coal ash and a 40% coal ash was replaced with 20 ± 2 cm using the same slump. The results of measuring penetration resistance after blending are shown below.

<Table 9 Cement Usage 170kg / ㎥, Slump 20 ± 2cm Standard Mix Table, Dredged Soil Limit 33.6%>

<Table 10 Penetration Resistance Measurement Results>

<Graph 3 Penetration Resistance Measurement Results>

As a result of the measurement of penetration resistance, when the coal ash is mixed in the dredged soil, the condensation speed is remarkably faster, and thus the long-term defect, which is the biggest shortcoming of the soft ground improvement method, is possible due to the early entry of construction equipment for the subsequent process. The construction period can be significantly shortened, which is another factor of economic treatment along with the reduction of cement (cement) during dredged soil solidification treatment.

As a result of the significant increase in compressive strength and penetration resistance, firstly, due to the increase of fluidity due to coal ash mixing, it is caused by the increase of cement concentration in the mixture due to the decrease of water consumption. The third reason for the reduction of the bonding area due to the reduction of the total surface area of the mixture by the replacement of coal ash and the third reason for the increase is mainly the organic matter contained in the dredged soil and the humic acid produced by the decay of the organic matter (huminic acid, etc.). ) Is a cause of reduction in compressive strength due to the formation of complexing compounds with cements, which impedes the solidification of cement.However, when the mixture of dredged soil and coal ash is used, porosity of coal ash acts like activated carbon. Adsorption of organic matter and humic acid to reduce the concentration of humic acid in the mixture solution. As well as the skill, coal ash may be the organic material is almost not dredged by the total organic matter and humic acid content of the mixture decreased by an amount replacing the coal ash on combustion, because at a high temperature of about 1,450 ℃ reduce the degree of disturbance of the solidified mixture.

In addition, when the dredged soil is solidified and used as a fill material, there is a high possibility of frostbite due to freezing and thawing due to the lack of air in the solid due to the fine particle composition of the dredged soil. The countermeasure is solved by adding an air emulsifier (AE agent), which is an expensive chemical admixture, but acts as a factor to reduce the economic efficiency of the solidification treatment. This drawback can also reduce the damage to frostbite caused by freezing and thawing through the use of coal ash. To demonstrate this, data as measured in <Table 11> and measuring the amount of air in the mixture are shown.

<Table 11 Air Volume Measurement Results>

<Graph 4 measurement result of air volume>

In the air amount measurement result, it can be seen that, in the case of the sample using the coal ash, the increase rate of the air amount in the mixture is increased by 185.7% compared to the sample not using the coal ash. This suggests that when used as a civil engineering material after curing due to an increase in the amount of air in the mixture, the entrained air contained in the mixture can significantly improve the buffering effect against shrinkage and expansion due to freeze-thawing. It is possible to increase the resistance by freezing and thawing without addition, thereby enabling economic solidification treatment.

In addition, when the mixture cured only by dredged soil is used as a fill material, there is a risk of cracking and ground subsidence of the fill material when it is used for a long time with a volume reduction of about 9% due to shrinkage caused by drying. It is solved by mixing gypsum, which is an expensive expansion material.

However, when mixed dredged soil and coal ash are mixed, salt in seawater and salt in dredged soil, which is used as a transfer means of coal ash disposal in power plants, react with the active silica component of coal ash to make sodium silicate compound and expand and harden the mixture. Filling the voids to strengthen the strength of the fill material, as well as to compensate for the dry shrinkage of the cured mixture to suppress ground subsidence and cracking after the fill.

Therefore, to confirm this, as shown in Table 12, the contents of dredged soil and coal ash were changed on the basis of the same amount of cement, and then the specimens having a diameter of 10 mm and a height of 20 mm were manufactured, and the degree of expansion after wet curing at 20 ± 2 ° C. for 150 days was measured. Tested.

＜ Table 12 Coal Ash Mixing Rate, Crack Test Formulation Table, Based on 1㎥ of Landfill Material, 33.6% of Dredged Soil Limit

As a result of the test, there was no cracking of the specimen until the mixing ratio of coal ash was 50%, and cracking was observed at 60%. It is estimated that excessive mixing of coal ash caused detrimental clay and salts in coal ash to react with activated silica of coal ash, resulting in excessive sodium silicate compound, causing the specimen to be cracked. The optimum mixing ratio of coal ash to compensate for phosphorus dry shrinkage and to prevent cracking is calculated by the following formula: coal ash weight / (cement weight + dredged soil weight + coal ash weight) × 100.

As can be seen from the above test, in solidifying the existing dredged soil and recycling it as a landfill material as a civil engineering material, a large amount of water is required to secure workability required for high viscosity dredged soil placing work, which is mostly clay material. In addition, it is not only an inhibitory factor in the expression of compressive strength of the fill material, but also an organic compound contained in the dredged soil and humic acid generated when the organic material is corroded to form a complexing compound with Ca ++ ions eluted during the solidifying hydration reaction. There is a difficulty in securing a predetermined strength because it surrounds the hydrate reaction of the solidifying agent. As a way to solve this problem, by mixing a certain amount of coal ash during solidification of dredged soil, the target fluidity can be satisfied even if a small amount of water per unit m3 of landfill material is used compared to the existing method, thereby increasing the cement concentration in the solidified reactant. The organic matter contained in the adsorbed organic matter is absorbed by the coal ash to reduce the concentration of organic matter in the solidified reactant bibim water, and there is almost no organic content due to the characteristics of coal ash. It can significantly improve the compressive strength of landfill materials by reducing the hydration inhibitory factor of the groundwater, and can increase the freezing and thawing resistance by increasing the amount of entrained air in the landfill materials, and compensate for dry shrinkage of landfill materials by using sodium silicate compounds. By reducing the bleeding number after solidification It is possible to reduce the generation of waste water alkaline.

Therefore, in view of the above test results, the mixing ratio of coal ash when coal ash is mixed and dredged soil solidification is calculated by the formula of coal ash weight / (cement weight + dredging soil weight + coal ash weight) × 100, which is appropriately 5 to 60%. For this reason, when the substitution mixture is mixed at the lower limit of 5% or more, the effect of improving fluidity is visible, and the effect of improving the fluidity is relatively decreased at the substitution mixing ratio of the upper limit of 60% or more, as well as the solidified soil material due to expansion due to excessive generation of sodium silicate hydrate. This is because the crack begins.

In addition, the water consumption during the solidification treatment is calculated by the formula of water weight / (cement weight + dredged soil weight + coal ash) × 100 due to the improvement of fluidity due to coal ash mixing, and is 35 to 60% when the dredged liquid liquid limit value is 45% or less. When the liquidus limit value is 45% or more, 55 to 100% is preferable.

In addition, by mixing coal material when solidifying dredged soil and using it as a fill material, the water cost compared to solids can be reduced by about 15 to 20%. Therefore, the leaching amount of water used as bibim water immediately after the completion of fill is drastically reduced. Alkaline wastewater can be drastically reduced, enabling environmentally friendly processes to work.

As such, when the landfill coal material generated in the coal-fired power plant is mixed at less than 5 to 60% by weight based on the combined weight of the dredged soil (dry basis) and the solidifying agent, the fluidity of the dredged soil with high viscosity is improved due to the drastic reduction in the number of bibides. Reduction of the amount of cement per unit volume in the compressive strength can increase the economics of the dredged soil using dredged soil, and also reduce the amount of alkaline wastewater generated during operation.

In addition, by adsorbing the dredged organic matter and humic acid to the porous coal ash, by reducing the concentration of organic matter in the mixture and by mixing the coal ash with little organic content with the dredged soil, it is possible to reduce the organic matter in the mixture per unit volume corresponding to the mixing rate to promote the solidification reaction. have.

In addition, the use of coal ash may increase the amount of air in the mixture to increase freeze-thaw resistance, and may also dry the solidified civil material by expanding the sodium silicate compound produced by the reaction of dredged soil with salt contained in coal ash and activated silica of coal ash. By compensating for shrinkage, it is economical and eco-friendly, and can be used as a civil engineering material with improved physical properties, which can effectively treat dredged soils and landfills of coal-fired power plants, which are difficult to process, and damage the natural environment by cutting for sedimentary materials. It is possible to reduce the environmental impact and to reduce the environmental load during dredged soil solidification.

Therefore, in the process of dredged soil which occurs enormously every year and recycled to civil materials such as fill material through solidification treatment, due to the economic burden caused by the use of excessive hardening agent and bibim water, it was not smoothly processed. By using the discharged coal ash, the water cost can be reduced, so that the amount of solidifying agent per unit volume can be reduced during solidification of dredged soil of the same target strength, and in addition, the amount of waste water generated after the mixture kneading can be drastically reduced. It is an eco-friendly material that can be used as a civil engineering material that reduces the content of organic matter in the cured mixture to promote the solidification reaction and to increase the condensation speed to shorten the projecting period, as well as to improve freeze-thawing resistance and reduce dry shrinkage. Can provide a formal method.

As described above, according to the present invention, by making the dredged soil difficult to be treated and unrecycled coal ash used as civil engineering material of economical and improved performance, dredged soil which can recycle resources and contribute to environmental conservation A solidification treatment method is provided.

Claims (6)

In the dredge soil solidification method, Obtaining a dough of the mixture consisting of dredged soil, hardener and coal ash; Dredge soil solidification method comprising the step of curing the dough of the mixture. The method of claim 1, The mixture is dredged soil solidification method characterized in that composed of 37 to 92% by weight of dredged soil, 3 to 58% by weight solidifying agent and 5 to 60% by weight of coal ash on a dry basis. The method of claim 1, The grain size of the coal ash is 0.02mm ~ 25mm range dredged soil solidification method characterized in that. The method according to any one of claims 1 to 3, The dough is made by mixing 35 to 60% by weight of water when using dredged soil having a liquid limit value of 45% or less, and 55 to 100% by weight of water when using a dredged soil having a liquid limit value of 45% or more. Dredged soil solidification method characterized in that made by mixing. The method according to any one of claims 1 to 3, The solidifying agent is any one of cement, blast furnace slag cement, slaked lime and gypsum. The method according to any one of claims 1 to 3, The coal ash is dredged soil solidification method characterized in that made of at least one of the bottom ash generated from the coal-fired power plant, the fly ash mixed with the fly ash generated from the coal-fired power plant, and the bottom ash generated when the waste incineration.