JP2016069444A - Soil modifier for wet soil and recovery method of soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soil modifier for wet soil which is available in inexpensive price and can improve efficiency of screening operation and can improve bearing resistance of banking by mixing with wet soil, and a method to recycle wet soil containing debris or other foreign matters to recycled soil for banking by using the soil modifier.SOLUTION: A soil modifier is provided as a mixture of collected dust that dust from a sand processing facility of a foundry is collected by a dust collector and the mean particle diameter is 1-260 μm, and lime. The compound ratio by weight (X/Y) of the collected dust (X) and the lime (Y) is set in the range of 9/1 - 5/5.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a soil modifying material used for regeneration treatment of soil containing a large amount of water (hydrous soil) and a method for regenerating hydrous soil containing debris and other foreign matters into reclaimed soil for embankment.

In connection with the reconstruction work from the Great East Japan Earthquake in March 2011, tsunami deposits (called “tsunami deposits”) are being reclaimed. In general, tsunami sediments contain not only earth and sand but also building debris such as concrete fragments and debris such as driftwood roots and debris. ) And need to be separated. In general, tsunami deposits, residual soils, and the like, when exposed to rain or the like outdoors, contain a large amount of moisture and become sticky or muddy, so the sieving operation cannot be performed smoothly as it is. In addition, it is assumed that soil collected separately by sieving will be reused as backfill soil or embankment soil, but especially for embankment soil, It is necessary to secure the support capacity. Under these circumstances, when treating tsunami deposits, quick lime is mixed with the tsunami deposits by several percent by weight, and then sieving is performed. By the way, quick lime (CaO) reacts with water (H ₂ O) and changes to slaked lime (Ca (OH) ₂ ), thereby removing excess moisture from the sediment and smoothing the sedimentation of the sediment. There is an action to become. In addition, slaked lime converted from quicklime is known to react with silica, which is a component of earth and sand, to produce calcium silicate hydrate, which enhances the ability to bind soil (and thus the soil support capacity). To help.

  Quick lime as a treatment material for tsunami sediments has the advantages of two birds with one stone as described above, but has the disadvantage of high price (for example, it may exceed 30,000 yen per ton). The soil treatment is expensive. Therefore, there is a need for an inexpensive soil modifier that reduces the amount of quicklime used.

  Patent Document 1 is composed of a mixture of dust (including active clay) generated from a factory related to green sand and 20 to 30% by weight of slaked lime (calcium hydroxide), and has a particle size of 1.5. Disclosed is a water purification material / soil improving material having a particle size of ˜20.0 mm and having irregularities formed on the surface (see the claims of the same document). However, since the water purification material and soil improvement material of Patent Document 1 have the purpose and effect of water purification, and the particle size is 1.5 to 20.0 mm, the granular material itself is It is understood that it is a purification / improving material such as water quality that has a certain fastness (in spite of not being baked) and is characterized in that the granular material itself functions as an adsorbent. At least Patent Literature 1 does not allow disclosure of improving the sieving work efficiency of sedimentary soil or improving the characteristics as a banking material.

JP 2004-81993 A

  An object of the present invention is to provide a soil conditioner for hydrous soil that can be obtained at a low cost and can improve the efficiency of sieving by mixing with hydrous soil and can improve the supporting capacity of embankment. It is in. Another object of the present invention is to provide a method for reclaiming hydrous soil containing rubble and other foreign substances into reclaimed soil for embankment using the soil modifier.

  In addition, this invention is the significance of the resource recycling of providing the new use thru | or the reuse method of the dust collection dust (The collective name which collects the dust discharged from a casting process or a raw sand related process) generated in a foundry. It also has.

  The present invention is a soil for hydrous soil, characterized in that it is a mixture of dust collection dust having an average particle diameter of 1 to 260 μm obtained by collecting dust generated by sand treatment equipment in a foundry with a dust collector, and quicklime. It is a modifier.

The present invention is also a method for reclaiming hydrous soil containing rubble and other foreign matter into reclaimed soil for embankment,
A modifier preparation step of preparing a soil modifier, which is a mixture of dust collection dust having an average particle size of 1 to 260 μm, which is obtained by collecting dust generated in sand processing equipment of a foundry with a dust collector, and quick lime;
A mixing step of mixing the soil modifier with a mixing ratio of 0.5 to 20% by weight with respect to the hydrous soil containing rubble and other foreign matters,
A mixture step of the hydrous soil obtained in the mixing step and the soil modifying material is passed through a sieving device, and a separation step of separating into soil and sand having a predetermined threshold grain size or less and other foreign matters,
The soil regeneration method is characterized in that the earth and sand having a size equal to or smaller than the threshold grain size obtained in the sorting step is collected as reclaimed soil for embankment.

  Further preferred aspects and additional constituent elements of the present invention will be described in the “Mode for Carrying Out the Invention” section below.

  According to the soil-improving material for hydrous soil of the present invention, not only is it available at low cost by using relatively cheap dust collection dust in combination with quick lime, but also the soil-modifying material is mixed with the hydrous soil. As a result, the efficiency of the sieving operation can be improved and the supporting force (compactability) of the embankment can be improved. Moreover, according to the soil regeneration method of the present invention, it is possible to regenerate hydrous soil containing rubble and other foreign matters into reclaimed soil for embankment using the soil modifier.

The figure which shows the outline | summary of the processing system regarding a series of processes until it regenerates tsunami deposit soil into embankment material. It is a conceptual diagram for demonstrating the force which acts between soil particles, (A) is a schematic diagram of the situation of the soil particle in the raw soil before adding a soil modifier, (B) is the raw soil The schematic diagram of the condition of the soil particle after adding a soil modifier.

  Hereinafter, details and preferred embodiments of the present invention will be described.

[About soil modifier]
The soil modifying material for hydrous soil of the present invention is a mixture obtained by mixing quick lime with dust collection dust generated as waste in a foundry.

  Specifically, the dust collection dust is a collection of dust generated in a sand processing facility of a foundry with a dust collector. The sand treatment equipment includes all facilities related to various processes for handling sand in the foundry such as preparation of foundry sand, molding of cast sand into molds, crushing of sand mold after pouring, and recovery of crushed sand. means. A dust collector is generally installed in such a sand treatment facility, and this dust collector prevents the scattering of fine particle components that are apt to be released into the factory and keeps the work environment clear. The dust collected by the dust collector during the operation of the foundry is “dust collection dust” which is the main raw material of the present invention.

The dust collection collected by the dust collector of the sand treatment facility has a component composition close to foundry sand. That is, the dust collection dust used in the present invention is preferably in the total amount (100% by mass),
67 to 71% by weight of _SiO 2,
10-14 wt% _Al 2 _O 3,
5-12 mass% FeO,
In addition to these, inorganic oxides such as CaO, MgO, Na ₂ O, and K ₂ O are also included. Moreover, a part (for example, 30-40 mass%) of the inorganic components of the dust collection dust constitutes an active clay component such as bentonite.

  The average particle size (preferably, the volume-based average particle size in laser diffraction scattering type particle size distribution measurement) of the dust collection dust used in the present invention is in the range of 1 to 260 μm, more preferably 40 to 200 μm. If the average particle size of the dust collection dust is less than 1 μm, the particles are too fine, which hinders handling. On the other hand, when the average particle size of the dust collection dust exceeds 260 μm, it becomes difficult to form a fine powder coating (see FIG. 2 (B)) by adhering to the surface of the soil particles of the hydrous soil. There is a risk that the separation workability cannot be improved.

  In the present invention, quick lime is used in combination with dust collection dust. When using commercially available quicklime, it is preferable to use a thing with high CaO purity.

When the mixing weight of the dust collection dust is X and the mixing weight of quick lime is Y, the weight mixing ratio of the dust collection dust and quick lime is preferably in the range of X / Y = 9/1 to 5/5. .
Weight mixing ratio: When X / Y becomes more dust-collecting dust than 9/1, the content of quicklime becomes too small, and support for embankment when reusing soil treated with the soil modifier as embankment It is not preferable because the force may not reach the required level. On the other hand, when the weight mixing ratio: X / Y is richer than quick lime than 5/5, the amount of quick lime used is not drastically reduced compared to the conventional example (use of 100% quick lime). The merit is diluted. Incidentally, the unit price of the soil modifying material used in the present invention is about one tenth of the unit price of quicklime.

[About soil regeneration]
The soil regeneration method of the present invention is a method of reclaiming hydrous soil containing rubble and other foreign substances into reclaimed soil for embankment, and is a method that passes through at least three steps of a modifier preparation step, a mixing step, and a separation step. is there. FIG. 1 shows an example of a processing system suitable for performing a series of steps of the method. The outline of the present method will be described below with an explanation according to FIG.

  The reformer preparation process, which is the first step of the present method, is a dust collection dust having an average particle size of 1 to 260 μm (more preferably 40 to 200 μm) obtained by collecting dust generated in a sand treatment facility of a foundry with a dust collector. And a step of preparing a soil modifying material that is a mixture with quicklime. In the treatment system of FIG. 1, the soil-improving material is produced by mixing dust-collected dust collected from a dust collector (not shown) and quicklime with a mixer 11 for granular materials. The mixing operation by the mixer 11 is preferably performed in a foundry, but may be performed at a hydrous soil treatment site.

  The mixing step, which is the second step of this method, mixes the soil modifying material obtained in the modifying material preparation step with a mixing ratio of 0.5 to 20% by weight with respect to the hydrous soil containing rubble and other foreign matters. It is a process to do. The blending ratio is more preferably 1 to 10% by weight, and further preferably 2 to 5% by weight. Moreover, you may make it remove a (relatively large) foreign material from the hydrous soil containing a foreign material before the mixing process which is a 2nd step.

  In the treatment system of FIG. 1, tsunami deposit soil as a hydrous soil containing foreign substances is stocked in the first silo 12 and soil modifier is stocked in the second silo 13. An amount of tsunami sediment corresponding to 80 to 99.5% by weight is cut out from the first silo 12, and an amount of soil modifier corresponding to 0.5 to 20% by weight is extracted from the second silo 13. Cut out. And the tsunami sediment and the soil modifier provided from both silos are mixed by the mixer 14 for earth and sand. As the earth and sand mixer 14, for example, a screw type conveyor or a kneader can be used.

  The earth and sand containing the soil modifier discharged from the mixer 14 is sent to the sieving device 16 by the conveyor device 15. As the conveyor device 15, for example, a vibration conveyor or a belt conveyor can be used. In the middle of conveying the earth and sand by the conveyor device 15, relatively light foreign matter such as driftwood pieces may be removed (that is, dust removal) by blowing it out of the conveyor device by wind pressure, for example. Moreover, you may remove a metal foreign material with a magnetic separator.

  The separation step, which is the third step of the present method, applies a mixture of the hydrous soil obtained in the mixing step and the soil modifying material to a sieving device, earth and sand below a predetermined threshold grain size, and other than that It is a process of separating into foreign matters. In the processing system of FIG. 1, the earth and sand thrown into the sieving device 16 via the conveyor device 15 is classified or classified into three types according to the grain size. The sieving device 16 shown in FIG. 1 is preferably a vibrating screen 16 for earth or sand or crushed stone, and includes a relatively coarse screen 16a and a relatively fine screen 16b. That is, earth and sand and residual foreign matters having a grain size of 40 mm or more are captured and sieved by the coarse sieve net 16a. Of the earth and sand passing through the coarse sieve net 16a, the earth and sand having a grain size of more than 20 mm and less than 40 mm is captured by the fine sieve net 16b and sieved. And the earth and sand (that is, earth and sand whose grain size is 20 mm or less) that has passed through the fine sieve net 16b is collected as reclaimed earth (banking material) for banking. That is, in the case of FIG. 1, the “threshold grain size” for reclaimed soil sorting is 20 mm.

  In this specification, “grain size” means the mechanical or structural characteristics (for example, the roughness of the sieve screen 16b) of the sieving tool (eg, the sieve screen 16b in the vibration sieve 16) employed by the sieving device. ), And does not necessarily mean the diameter of a grain having an ideal spherical shape.

  In addition, about the earth and sand whose grain size is more than 20 mm and less than 40 mm, and / or earth and sand whose grain size is 40 mm or more, the earth and sand may be crushed and sieved again by inputting into the vibration sieve 16.

  According to this method, since the soil modifier (mixture of dust collection dust and quicklime) is mixed with the hydrous soil in the mixing step prior to the separation step, even when the hydrous soil is passed through a sieving device, Smooth sieving can be performed without causing lumps.

  One of the reasons that the sieving work is facilitated by the addition of the soil modifier is that each of the dust collection dust and quicklime contained in the soil modifier absorbs a part of the water in the hydrous soil, and the soil particles. The purpose is to reduce the amount of interstitial water (so-called free water). Speaking of quick lime, quick lime is known to react with water to produce slaked lime, but consumes moisture during the production of slaked lime. Also, regarding dust collection dust, dust collection dust adheres to the surface of the soil particles by the mixing operation in the above mixing step, but the active clay contained in the dust collection dust that has adhered absorbs moisture on the surface of the soil particles. It works to remove moisture from the surface of the soil particles. As described above, due to the actions of the dust collection dust and quicklime, the water content between the soil particles and the surface of the soil particles is reduced, and the sieving workability is improved.

  The second reason for the smoothing of the sieving operation is that the dust particles, which are fine powder with an average particle size of 1 to 260 μm, cover the surface of the soil particles to increase the surface area of the soil particles, and the surface of the soil particles The apparent water content in the vicinity is reduced. The reason why the sieving workability is improved by the effect of increasing the surface area will be described again in the “Example” section below.

  The earth and sand having a size equal to or smaller than the threshold grain size collected through the sorting step has excellent suitability as a reclaimed soil (banking material) for banking. This is because the reclaimed soil contains quick lime and / or slaked lime converted from quick lime, and these lime components contribute to the improvement of the bearing capacity of the embankment. Note that the soil conditioner used in this method has a relatively low content of quicklime compared to dust collection dust, but even when the recovered reclaimed soil is used for embankment, it is at the required level. It has been confirmed by the CBR test described later that the supporting force can be exhibited.

  Examples 1 and 2 according to the present invention and Comparative Example 1 to be compared will be described below.

[Soil modifying material]
The quicklime used in Examples 1 and 2 and Comparative Example 1 is quicklime made by Ube Materials Co., Ltd. (grain size adjusted to about 2 mm). The purity of CaO in this commercially available quicklime was about 93 wt%.

The dust collection dust used in Examples 1 and 2 is the dust collected by the dust collector installed in the FCD sand treatment facility in the foundry of Aisin Takaoka Tohoku Co., Ltd., which is the subsidiary of the applicant (hereinafter “dust collection”). Called Dust No.11). The composition of dust collection dust was analyzed by requesting the Miyagi Prefectural Industrial Technology Center, and the composition of dust collection dust No. 11 was as follows in terms of oxides.
_{SiO 2: 70.00wt%, Al 2} O 3: 12.67wt%, FeO: 6.97wt%,
CaO: 2.66 wt%, MgO: 2.56 wt%,
Na ₂ O: 2.77 wt%, K ₂ O: 1.11 wt%, other: 1.26 wt%

  The particle size distribution of the dust collection dust No. 11 was measured with a laser diffraction scattering type particle size distribution measuring instrument (manufactured by Seishin Enterprise Co., Ltd .: SK Laser Micron Sizer LMS-2000e was used), and its volume standard average diameter was about 163 μm. there were. Further, when the general characteristics of the dust collection dust No. 11 were measured according to the test method for foundry sand, the water content was 4% and the loss on ignition (ig.loss) was 12%. In addition, according to the measurement of active clay content using a methylene blue solution defined in the JIS foundry sand test method, the active clay content of dust collection dust No. 11 was 35%.

[Example 1]
The soil modifying material of Example 1 is obtained by mixing dust collection dust No. 11 (X) and quicklime (Y) at a weight mixing ratio X / Y = 7/3. Incidentally, the approximate composition (converted predicted value) of the main components constituting the soil modifying material of Example 1 is as follows. SiO ₂ : 49 wt%, Al ₂ O ₃ : 9 wt%, FeO: 5 wt%, CaO: 28 wt%, others: 9 wt%

[Example 2]
The soil modifying material of Example 2 is obtained by mixing dust collection dust No. 11 (X) and quicklime (Y) at a weight mixing ratio X / Y = 9/1. Incidentally, the approximate composition (converted predicted value) of the main components constituting the soil modifying material of Example 2 is as follows. SiO ₂ : 63 wt%, Al ₂ O ₃ : 12 wt%, FeO: 6 wt%, CaO: 9 wt%, others: 10 wt%

[Comparative Example 1]
The soil modifying material of Comparative Example 1 is made of quick lime (Y) (that is, X / Y = 0/10). By the way, the general composition of the main components constituting the soil modifier of Comparative Example 1 is as follows.
CaO: 93 wt%, others: 7 wt%

[Raw earth used for evaluation test]
Tsunami sediments deposited in Miyagi Prefecture during the Great East Japan Earthquake and then collected in the stockyard (temporary storage location) were used as “raw soil” in the evaluation tests described below.

[Evaluation of sieving workability (water content ratio test)]
Although it is difficult to express numerically whether the sieving workability is good or not, the measured value of how much the moisture content in the sediment has been reduced by adding soil modifier to the raw soil Indirect or alternative evaluation indicators. Specifically, the moisture content of the raw soil before adding the soil modifier, and when 5 wt% of the soil modifier is added to the raw soil (that is, 95 wt% of the soil, the soil modifier 5) % Water content). It can be said that the sieving workability tends to improve as the water content ratio decreases due to the addition of the soil modifier. The water content was measured in accordance with the water content test method of JIS A1203. That is, the moisture content (%) was measured based on the weight of the sample soil before oven drying and the weight of the sample soil after oven drying in a constant temperature air bath at about 105 ° C.

Table 1 shows the measurement results of the water content ratio in each test example.

  In general, it is said that sieving workability can be greatly improved if the water content ratio can be reduced by 3% or more by adding a soil modifier to the raw soil (tsunami sediment). In this respect, the water content ratio in the earth and sand could be reduced by 6% by adding the soil conditioner of Example 1 to the raw soil (Test Example 3). Moreover, the water content ratio in earth and sand was able to be reduced by 5% by adding the soil modifier of Example 2 to the raw soil (Test Example 4). All of them satisfied the demands of soil conditioners.

  Among the mechanisms in which the sieving workability is improved by adding the soil modifying material of Example 1 or 2 to the raw soil, the mechanism in which dust collection dust contributes to the workability improvement is considered as follows. .

  FIG. 2 (A) schematically shows the state of the soil particles constituting the raw soil (tsunami deposited soil) before the soil modifier is added. Since the muddy raw soil contains a lot of moisture, the soil particles are in a state of floating in the water, and excessive surface tension (adhesive force) is generated by moisture intervening between the soil particles. As a result of the surface particles attracting each other and adhering to each other due to this surface tension, lumps are formed, making sieving work difficult. On the other hand, FIG. 2 (B) schematically shows the situation of the soil particles after adding the soil modifier of the present invention. Dust collection dust, which occupies most of the soil modifier, is a micron (μm) sized fine powder, so it adheres to the surface of the soil particle as shown in FIG. Coating). Dust collection dust that covers the surface of each individual soil particle contains active clay such as bentonite, and this active clay absorbs moisture on the surface of the soil particle and removes moisture from the surface of the soil particle. To do. Further, as the surface area of the soil particles increases due to the fine powder coating, the apparent water content near the surface of the soil particles decreases. Such moisture absorption and removal effect and surface area increase effect reduce the surface tension due to moisture that can intervene between the soil particles and weaken the force with which the soil particles adhere to each other, resulting in improved sieving workability. Conceivable.

[Evaluation of supporting capacity of embankment material]
Based on the CBR test method (Method of Test for California Bearing Ratio) established as an evaluation method for bearing capacity of paved roads (roadbed and roadbed) in the field of civil engineering, the bearing capacity (compactability) of embankment materials is evaluated. Specifically, the CBR value of the raw soil before the soil modifier is added and the case where 5% by weight of the soil modifier is added to the raw soil (that is, 95% by weight of the soil, the soil modifier 5) % CBR value). It can be evaluated that the supporting force as the embankment material is higher as the CBR value is increased by the addition of the soil modifier.

  The CBR value was measured according to JIS A1211. That is, a columnar specimen (diameter 150 mm) formed by tamping the sample soil using a mold defined in JIS was prepared and cured for 20 days. Using a steel penetrating piston (diameter 50 mm) and a penetrating amount measuring device, the specimen after curing is subjected to a penetrating test specified in JIS, and the CBR (%) relative to the standard load is calculated from the load value at a predetermined penetrating depth. Calculated.

Table 2 shows the measurement result of the CBR value in each test example.

  Although it is inferior to the case where the modifier made of almost CaO is added to the raw soil (Test Example 6), the CBR value is 23% by adding the soil modifier of Example 1 to the raw soil (Test Example 7). Was able to be raised. Moreover, the CBR value could be raised to 21% by adding the soil modifier of Example 2 to the raw soil (Test Example 8). These values sufficiently satisfy the level required by civil engineering contractors (CBR value of 20% or more).

  As described above, the soil conditioner for hydrous soil according to the present invention can be used for the treatment of the tsunami sediment and the regeneration of the embankment, and “it is left as a residual soil for a long time due to quality problems and contains a lot of rainwater. It can be used for the treatment, reforming, or regeneration of soil (including earth and sand and soil) having a relatively high water content such as “construction generated soil” and “mud dredged from the sea or river”.

DESCRIPTION OF SYMBOLS 11 Mixer for granular materials 12 1st silo 13 2nd silo 14 Mixer 15 for earth and sand Conveyor apparatus 16 Vibrating fluid machine (sieving device)
16a Coarse screen, 16b Fine screen

Claims (4)

  A soil modifying material for hydrous soil, characterized in that it is a mixture of dust collection dust having an average particle size of 1 to 260 µm, which is obtained by collecting dust generated in sand processing equipment of a foundry with a dust collector, and quicklime.   2. The hydrous soil according to claim 1, wherein a weight mixing ratio (X / Y) of the dust collection dust (X) and the quicklime (Y) is in a range of 9/1 to 5/5. Soil modifying material. The dust collection dust is
67 to 71% by weight of _SiO 2,
10-14 wt% _Al 2 _O 3,
5-12 mass% FeO,
And comprising CaO, MgO, Na ₂ O and K ₂ O,
The soil modifying material for hydrous soil according to claim 1 or 2. A method for reclaiming hydrous soil containing rubble and other foreign matter into reclaimed soil for embankment,
A modifier preparation step of preparing a soil modifier, which is a mixture of dust collection dust having an average particle size of 1 to 260 μm, which is obtained by collecting dust generated in sand processing equipment of a foundry with a dust collector, and quick lime;
A mixing step of mixing the soil modifier with a mixing ratio of 0.5 to 20% by weight with respect to the hydrous soil containing rubble and other foreign matters,
A mixture step of the hydrous soil obtained in the mixing step and the soil modifying material is passed through a sieving device, and a separation step of separating into soil and sand having a predetermined threshold grain size or less and other foreign matters,
The soil regeneration method is characterized in that the earth and sand having a size equal to or smaller than the threshold grain size obtained in the sorting step is collected as reclaimed soil for embankment.

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