JP2024045574A - Method for producing modified soil of high water content mud - Google Patents

Abstract

[Problem] To provide a manufacturing method for modified soil of high water content mud that can modify high water content mud, suppress material separation of mixed steelmaking slag, and increase the manifested strength. [Solution] This manufacturing method for modified soil of high water content mud is a method for manufacturing modified soil by modifying high water content mud, and includes a step of adding and mixing a water-absorbent additive material to mud with a water content of at least 2.0 x wL, and a step of mixing steelmaking slag, in which the step of mixing the additive material is carried out after the step of mixing the steelmaking slag, or the step of mixing the additive material and the step of mixing the steelmaking slag are carried out simultaneously, where wL is the liquid limit of the mud. [Selected Figure] Figure 1

Description

The present invention relates to a method for producing modified soil by modifying high water content mud.

A material made by mixing dredged soil with converter steelmaking slag (calcia modified soil) is known from, for example, Patent Document 1 and Non-Patent Document 1, and has characteristics such as strength development, turbidity suppression, and alkali suppression. , was developed as a technology to effectively utilize dredged soil generated during dredging work for navigation channels and anchorages, and converter steelmaking slag generated as a byproduct in the steel production process, and is used as reclamation material, base material for shallow areas and tidal flats, and seaweed bed creation. It is widely used as backfill material for deep excavation sites, etc.

Generally, the dredged soil used in calcia modified soil has a water content of 1.2 to 2 times the liquid limit (wL) of the dredged soil, and the higher the water content of the dredged soil, the higher the water content of the dredged soil. It is known that the strength decreases (Non-Patent Document 1, Appendices 2-2 to 2-3).

JP 2009-121167 A JP 2016-215191 A

“Technical Manual for the Use of Calcia Modified Soil in Ports, Airports, Coasts, etc.” (Coastal Technology Research Center, published in February 2017)

In the case of calcia modified soil with a volumetric mixing ratio of steelmaking slag to dredged soil of 20 to 30 vol%, if the water content ratio of the dredged soil exceeds twice the liquid limit, steelmaking slag with a high specific gravity will be mixed in the mixed material. There is a risk of sedimentation and further reduction of expression intensity. Furthermore, when mixing calcia-modified soil using an earth carrier and a backhoe, the dredged soil has a high water content, and the steelmaking slag that has been put in will settle in the soil tank, making it difficult to mix thoroughly. Furthermore, when constructing dredged soil at sea, it is difficult to drain the dredged soil, so the dredged soil may remain at a high water content, so calcia-amended soil made from dredged soil with such a high water content is used as ground material, etc. However, if a target intensity is set, a decrease in expression intensity becomes a quality control problem.

There is also a method of temporarily placing dredged soil with a high water content and removing water floating on the surface to lower the water content, but this requires a certain period of standing, which reduces construction efficiency, and this makes it difficult to carry out large-scale construction. becomes difficult to apply.

In addition, in order to compensate for the lack of strength, there is a method of adding pulverized blast furnace slag powder in an amount of 1 to 3% of the weight of dredged soil in addition to steelmaking slag (Non-Patent Document 1, Appendix 2-11). However, although this method is effective when using dredged soil or steelmaking slag that is difficult to develop strength, the effect of improving viscosity on dredged soil with a high moisture content is small, and it is not expected to suppress material separation or improve workability. Can not.

While the amount of steelmaking slag mixed in general calcia modified soil is 20 to 30vol%, there is a method to compensate for the lack of strength by increasing the amount of steelmaking slag mixed to 40vol% or 50vol% (Non-patent Document 1, Appendix 2-7). However, when the volumetric mixing ratio of steelmaking slag is increased, since steelmaking slag is highly alkaline, when mixed with dredged soil with a high water content ratio, the amount of soil particles that have a pH buffering effect decreases, resulting in an increase in pH. It becomes easier. For this reason, problems such as pH exceeding the wastewater standard pH 9 in the pH test method using artificial seawater as a solvent (Non-Patent Document 1, Annex 1 to 2) and the generation of white precipitate (magnesium hydroxide) when entering the sea area have arisen. It ends up.

Patent Document 2 discloses a method of adding gypsum for the purpose of increasing the strength of calcia modified soil, but the water content ratio of the dredged soil in Examples (Tables 1 and 2) is 1.4 × wL and 1.3 × wL. Yes, but it is not intended for dredged soil with a high moisture content.

In view of the problems of the conventional technology as described above, the present invention aims to provide a method for producing modified high-moisture mud that can modify high-moisture mud, suppress material separation of the mixed steelmaking slag, and increase the manifested strength.

The manufacturing method of modified soil made of high water content mud to achieve the above-mentioned objective is a method for manufacturing modified soil by modifying high water content mud, and includes a step of adding and mixing a water-absorbent additive material to mud having a water content of at least 2.0×wL, and a step of mixing steelmaking slag, in which the step of mixing the steelmaking slag is carried out after the step of mixing the additive material, or the step of mixing the additive material and the step of mixing the steelmaking slag are carried out simultaneously. Here, wL is the liquid limit of the mud.

According to this manufacturing method for modified high-moisture mud, by adding and mixing a water-absorbent additive to mud with a moisture content of at least 2.0×wL, the flow value of the material can be reduced and material separation of the mixed steelmaking slag can be suppressed. This allows high-moisture mud with a moisture content of at least 2.0×wL to be modified and its manifestation strength to be increased.

In the method for producing modified soil of high water content mud, the additive material is preferably any one of paper sludge incineration ash, coal ash, and gypsum. By adding these materials, the flow value of high water content mud can be reduced. These materials are also preferable because they are less likely to cause an increase in pH than cement.

Further, it is preferable to add the papermaking sludge incineration ash, the coal ash, or the gypsum in an amount of 25 to 100 kg per 1 m ³ of the mud.

Further, it is preferable that the steelmaking slag is mixed such that the volumetric mixing ratio of the steelmaking slag in the mixture of the mud and the steelmaking slag is within a range of 10 to 30 vol%. Further, it is preferable that the water content ratio of the mud is 2.9×wL or less.

The method for manufacturing modified high-moisture mud of the present invention can modify high-moisture mud, suppress material separation of the mixed steelmaking slag, and increase the expressed strength.

1 is a flowchart for explaining main steps S01 to S04 of a method for producing improved soil of high water content mud according to the present embodiment. 1 is a graph showing the results of a primary compression test (age 28 days) of the improved soil in Example 1. 1 is a graph showing the results of a flow test (immediately after mixing) and a uniaxial compression test (28 days old) of the improved soil in Example 1. 1 is a graph showing the results of a flow test (immediately after mixing) of modified soil in Example 2 when the amount of steelmaking slag mixed was 20 vol% (a) and 30 vol% (b). It is a graph showing the results of a uniaxial compression test (28 days old) of modified soil when the mixed amount of steelmaking slag was 20 vol% (a) and 30 vol% (b) in Example 2. 13 is a graph showing the test results of the pH (a), flow value (b), and unconfined compressive strength (c) of the improved soil when the type of added material in Example 3 was changed (none, paper sludge incineration ash, gypsum, high molecular weight polymer).

The following describes an embodiment of the present invention with reference to the drawings. Figure 1 is a flow chart for explaining the main steps S01 to S04 of the manufacturing method for modified high water content mud soil according to this embodiment.

The manufacturing method of modified soil made from high water content mud according to this embodiment produces modified soil by modifying high water content mud as shown in Figure 1. First, the high water content mud is thawed (S01). Here, high water content mud refers to mud with a water content in the range of 2.0 to 2.9 x wL, where wL is the liquid limit of the mud.

Next, papermaking sludge incineration ash is added to the mud and mixed (S02). In this mixing method, for example, paper sludge incineration ash is thrown into muddy soil with a high moisture content inside an earth carrier and mixed using a backhoe. Paper sludge incineration ash has water absorption properties and improves the flow value of mud with high water content, and is added in the range of 25 to 100 kg per 1 m ³ of mud. Incidentally, instead of the papermaking sludge incineration ash, coal ash or gypsum having similar water absorption properties may be added. Paper sludge incineration ash, coal ash, and gypsum are also preferable because they are less likely to cause an increase in the pH of the material than cement.

Next, paper sludge incineration ash is added to the mud, and steel slag is mixed into the resulting material (S03). This mixing method may be pipe mixing using an air pressure conveyor, drop mixing using a reclaimer ship, or mixing with a backhoe. The steel slag is mixed so that the volumetric mixing ratio of the steel slag in the mud and steel slag mixture is within the range of 10 to 30 vol%.

As described above, the mud with a high water content is modified, the flow value of the material is reduced, and the modified soil is obtained which suppresses material separation of steelmaking slag and increases developed strength (S04). Such modified soil can be used, for example, as a reclamation material, a base material for shallow areas and tidal flats, a seaweed bed creation material, a backfill material for deep excavation sites, and the like.

Conventionally, especially when dredged soil is to be constructed at sea, it has been necessary to use dredged soil with a high water content because it is difficult to drain the dredged soil, and there has been no effective solidification measure when mixing steelmaking slag with such dredged soil with high water content to produce calcia-modified soil. In contrast, according to this embodiment, by adding and mixing additive materials such as paper sludge incineration ash before or at the same time as mixing the dredged soil with steelmaking slag, it becomes possible to process dredged soil with a high water content that was difficult to solidify with conventional calcia-modified soil.

Furthermore, by mixing additive materials such as paper sludge incineration ash and steelmaking slag with high water content mud, it is possible to improve the flow value (improve the workability of mixing work) and increase the strength.

Furthermore, when using paper sludge incineration ash alone to improve muddy soil with a high moisture content, an addition amount of about 200 to ³⁰⁰ kg/m3 is required, but when paper sludge incineration ash is added before mixing with steel slag, an addition amount of about 50 kg/ ^m3 is sufficient. Furthermore, the addition of paper sludge incineration ash does not cause a significant rise in pH or an increase in the amount of eluted heavy metals.

Paper sludge incineration ash refers to the incineration ash produced when paper sludge (PS), which is generated as industrial waste in the paper industry, is incinerated to reduce its volume, and is also called PS ash. PS Ash” may be used. Coal ash is industrial waste generated when coal is burned in thermal power plants, etc., and includes fly ash, clinker ash, etc. By using paper sludge incineration ash or coal ash as the additive material in this embodiment, it is possible to effectively utilize industrial waste.

The volume mixing ratio α (vol%) of steelmaking slag to mud is calculated using the following formula, using the mud volume Vs and the actual volume Vc of the steelmaking slag (volume excluding voids).
α＝{Vc/(Vc＋Vs)}×100

Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
Paper sludge incineration ash (PS ash) was added as an additive material to mud (moisture content ratio 2.0 x wL, liquid limit wL = 91.3%) at 0 kg/m ³ , 50 kg/m ³ , 100 kg/m ³ (to 1 m ³ of mud) Flow tests (NEXCO Test Methods Test Method 313) and uniaxial compression tests (JIS A1216: 2009) were conducted on materials made by mixing steelmaking slag (maximum grain size 10 mm) at 10, 20, and 30 vol%. .

FIG. 2 shows the results of the uniaxial compression test when the amount of PS ash added was varied by changing the amount of steelmaking slag mixed in Example 1 to 10 vol%, 20 vol%, and 30 vol% (28 days old). From FIG. 2, it can be seen that the unconfined compressive strength increases as the amount of PS ash added increases for any steelmaking slag mixing amount. In addition, a material with a mixed amount of steelmaking slag of 10 vol% and an added amount of PS ash of 0 kg/m ³ did not solidify and could not be measured.

Results of the flow test immediately after mixing and after 28 days of curing when the mixed amount of steelmaking slag in Example 1 was 30 vol% and the added amount of PS ash was 0 kg/m ³ , 50 kg/m ³ , and 100 kg/m ³ The results of the uniaxial compression test (28 days old) are shown in Figure 3. Figure 3 shows that by adding PS ash in addition to steelmaking slag, the unconfined compressive strength increases significantly while the flow value decreases.

Example 2
The mud (liquid limit wL = 76.7%) had a water content of 2.3×wL, 2.6×wL, and 2.9×wL. Paper sludge incineration ash (PS ash) was added at 0kg/ ^m3 , 25kg/ ^m3 , 50kg/ ^m3 , and 100kg/ ^m3 (per ^1m3 of mud) and steel slag (maximum particle size 25mm) was added at 20vol% and 30vol%. pH tests (Iron Federation method), flow tests (NEXCO test method 313), and uniaxial compression tests (JIS A1216:2009) were conducted using artificial seawater as a solvent. The effects of adding gypsum and polymers as additives were also confirmed.

In Example 2, the mixed amount of steelmaking slag in the mixture of mud and steelmaking slag with water content ratios of 2.3×wL, 2.6×wL, and 2.9×wL was 20vol% and 30vol%, and the amount of PS ash added was 0kg Figures 4 (a) and (b) show the results of the flow test immediately after mixing at 25 kg/m ³ , 25 kg/m ³ , 50 kg/m ³ , and 100 kg/m ³ , and the uniaxial compression test after 28 days of curing ( Figures 5(a) and 5(b) show the results for 28 days of wood age). From Figures 4 and 5, it can be seen that by adding PS ash to each mud with a higher water content than in Example 1, the flow value tends to decrease, and the unconfined compressive strength at 28 days of age increases. I can confirm that.

Note that the required strength varies depending on the use of the material, but if the indoor compound strength is, for example, 100 kN/m ² in unconfined compressive strength, the conditions are that the water content of mud is 2.9 x wL and the amount of steelmaking slag mixed is 30 vol%. Now, from FIG. 5(b), it can be seen that the amount of PS ash added is 25 kg/m ³ or more.

Figures 6(a)-(c) show the test results for pH, flow value, and unconfined compressive strength (28 days old) when the type of added material was changed (none, paper sludge incineration ash (PS ash), gypsum, high molecular weight polymer). Figure 6(a) shows that compared to the case where steelmaking slag was mixed into the mud at 30 vol% (no added material), there was no significant change in pH for any of the materials with PS ash, gypsum, or high molecular weight polymer added. For comparison, the amount of steelmaking slag mixed in was increased to 50 vol%, and the pH increased significantly, exceeding the effluent standard of pH 9.0.

In addition, from Figures 6(b) and (c), it can be seen that the flow value decreases and the uniaxial compressive strength increases by adding additive materials, although the degree of effect varies depending on the type of additive material.

Example 3
Assuming that the modified soil according to this embodiment is used as a landfill material, a heavy metal elution test was conducted on mud and materials with typical blending conditions, and a comparison was made with the soil elution amount standard. Table 1 shows the results of the elution test on heavy metals, etc., for the mud with a water content of 2.6 x wL in Example 2, a material obtained by mixing this mud with 30 vol% steelmaking slag, and a material obtained by adding 50 kg/ ^m3 of paper sludge incineration ash (PS ash) and mixing 30 vol% steelmaking slag. From the results in Table 1, it can be seen that no significant increase in the amount of elution of heavy metals, etc. was observed for the material obtained by mixing 30 vol% steelmaking slag with mud with a water content of 2.6 x wL, and the material obtained by adding 50 kg/ ^m3 of PS ash and mixing 30 vol% steelmaking slag, and that the amount of elution was below the soil elution amount standard.

Although the embodiments for carrying out the present invention have been described above, the present invention is not limited to these, and various modifications are possible within the scope of the technical concept of the present invention. For example, as the additive material in step S02 in Fig. 1, a polymer having a viscosity increasing effect and a pH value of the material that is less likely to increase than that of cement may be used, and the amount of the polymer to be added is preferably within the range of 0.1 to 1.0 kg per ¹ m3 of mud.

In addition, when producing modified soil of high water content mud using a mixing mixer, the process of adding and mixing papermaking sludge incineration ash (S02) and the process of mixing steelmaking slag (S03) are performed. They may be performed at the same time.

The manufacturing method of high water content mud modified soil of the present invention can effectively modify high water content mud, which was not possible with conventional calcia modified soil, and can suppress material separation of the mixed steelmaking slag and increase the expressed strength, so modified soil modified from dredged soil with high water content can be effectively used as landfill material, base material for shallow water and tidal flats, material for creating seaweed beds, backfill material for deep excavation sites, etc.

A method for producing modified soil of high water content mud to achieve the above purpose is a method of producing modified soil by modifying mud with a high water content ratio, and includes mud with a water content ratio of 2.0 to 2.9 × wL. The method includes a step of adding and mixing papermaking sludge incineration ash as a water-absorbing additive material, and a step of mixing steelmaking slag, and the step of mixing the steelmaking slag is performed after the step of mixing the additive material. Or, the mixing process of the additive material and the mixing process of the steelmaking slag are performed simultaneously. However, wL is the liquid limit of the mud.

In the method for producing modified soil of high water content mud, the additive material is paper sludge incineration ash, and by adding this material, the flow value of the high water content mud can be reduced. This material is also preferable because it is less likely to cause an increase in pH than cement.

Further, it is preferable to add the papermaking sludge incineration ash in the range of 25 to 100 kg per 1 m ³ of the mud.

Further, it is preferable that the steelmaking slag is mixed such that the volumetric mixing ratio of the steelmaking slag in the mixture of the mud and the steelmaking slag is within a range of 10 to 30 vol%.

Claims (5)

A method for producing modified soil by modifying mud with a high moisture content, the method comprising:
A step of adding and mixing a water-absorbing additive material to mud with a water content ratio of at least 2.0 x wL, and a step of mixing steelmaking slag,
A method for producing modified soil of high water content mud, comprising performing the steelmaking slag mixing step after the adding material mixing step, or performing the adding material mixing step and the steelmaking slag mixing step simultaneously. However, wL: the liquid limit of the mud The method for producing improved soil from high moisture content mud soil according to claim 1, wherein the additive material is any one of paper sludge incineration ash, coal ash, and gypsum. 3. The method for producing modified soil of high water content mud according to claim 2, wherein the papermaking sludge incineration ash, the coal ash, or the gypsum is added in a range of 25 to 100 kg to 1 m ³ of the mud. The high water content ratio according to any one of claims 1 to 3, wherein the steelmaking slag is mixed so that the volumetric mixing ratio of the steelmaking slag in the mixture of the mud and the steelmaking slag is within a range of 10 to 30 vol%. Method for producing modified mud soil. The method for producing modified soil of high water content mud according to any one of claims 1 to 4, wherein the water content ratio of the mud is 2.9×wL or less.

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