JP6889876B2 - Ground repair method and solidifying agent used for it - Google Patents

Description

The present invention relates to a ground repair method and a solidifying agent used therein, and more particularly to a ground repair method for repairing cracks generated in the ground containing Kuroboku soil and a solidifying agent used therein.

The Kumamoto earthquake that occurred in April 2016 has caused cracks that reach the surface of the earth in a wide area including agricultural land in the Kumamoto region. In order to repair cracks in the ground and regenerate it as agricultural land, it is necessary to temporarily remove the soil from the cracks and their surroundings, repair the ground, and then backfill the soil to level the ground. However, repairing a vast agricultural land requires enormous cost and time, and is difficult to realize easily.

Moreover, in the event of repeated aftershocks, cracks may occur again in the repaired area, and the cost of repairs will increase further. Therefore, it is not possible to determine when to repair, and reconstruction will not proceed further. Is causing the problem.

In addition, Portland cement-based solidifying agents are usually used for large-scale ground repairs, but the cement itself is strongly alkaline, and there is concern about the impact on crop growth when used on agricultural land. Ru. Moreover, the soil solidified by the cement-based solidifying agent is crushed into rubble when it is repaired again. For this reason, when repairing, the work of removing the rubble is also involved, and the cost of regenerating agricultural land is further increased.

Furthermore, most of the soil in the Kumamoto region is formed of Kuroboku soil with volcanic ash deposited on it. As shown in Patent Document 1, unlike the case of sandy soil, volcanic ash cohesive soil such as Kuroboku soil cannot sufficiently knead a cement-based solidifying agent, so that the expression strength is low. Therefore, there is also a problem that a large amount of solidifying agent is required.

On the other hand, as a solidifying agent for solidifying soil, magnesia cement has been proposed as shown in Patent Document 2. Magnesium oxide, magnesium sulfate, magnesium chloride and the like are used as raw materials for magnesia cement. Since magnesium sulfate has efflorescence and magnesium chloride has deliquescent property, it is difficult to store the raw material, and magnesium chloride causes salt damage and affects the growth of plants.

Japanese Patent No. 5862911 Japanese Patent No. 5815903

The problem to be solved by the present invention is that the above-mentioned problems can be solved, the farmland with cracks in the ground can be easily repaired, the re-repair is easy even in the event of a subsequent earthquake, and the regenerated farmland is a plant. It is to provide the ground repair method which does not hinder the growth and the solidifying agent used for it.

In order to solve the above-mentioned problems, the ground repair method according to the present invention and the solidifying agent used therein have the following technical features.
(1) For a farmland having cracks, the soil in the cracked portion and its vicinity is removed, and the cross-sectional shape perpendicular to the crack direction of the hole from which the soil is removed is a substantially inverted triangle. In the removed hole, soil kneaded with a solidifying agent containing magnesium oxide as a main component is spread on the bottom of the hole to form a reinforcing layer, and the reinforcing layer is removed by the soil removing step. It is a ground repair method that includes a soil backfilling process to backfill the soil.
(2) For farmland with cracks, a soil removal step of removing the soil in and near the cracked portion and soil in which a solidifying agent containing magnesium oxide as a main component is kneaded into the hole from which the soil has been removed are placed in the hole. A reinforcing layer forming step of laying on the bottom to form a reinforcing layer, and a soil backfilling step of arranging a water-impervious clay layer on the reinforcing layer and backfilling the soil removed in the soil removing step on the reinforcing layer. It is a ground repair method equipped with.
(3) In the ground repair method described in (2) above, the edge of the upper surface of the clay layer of the hole is set to be at the same position as the upper surface of the water-impervious layer of the soil around the hole. It is characterized by being.

( 4 ) In the ground repair method according to any one of (1) to (3) above, the soil is characterized by containing Kuroboku soil.

( 5 ) In the ground repair method according to any one of (1) to (4) above, the raw material of the solidifying agent is characterized by containing magnesium oxide and magnesium sulfate.

( 6 ) In the ground repair method described in (5 ) above, in the reinforcing layer forming step, the weight ratio of the soil component to magnesium oxide is in the range of 0.1 to 1 for magnesium oxide when the soil component is 1. It is characterized by being.

( 7 ) In the ground repair method described in (5 ) or ( 6 ) above, the molar ratio of magnesium oxide to magnesium sulfate contained in the solidifying agent is the number of moles of magnesium sulfate, where 5 is the number of moles of magnesium oxide. Is 0.1 to 3.

( 8 ) In the ground repair method according to any one of (1) to ( 7 ) above, soil or crushed stone containing no solidifying agent is arranged under the reinforcing layer arranged in the hole. It is characterized by.

( 9 ) A solidifying agent used in the ground repair method according to any one of (1) to ( 8 ) above, which contains magnesium oxide and magnesium sulfate, and the molar ratio of magnesium oxide to magnesium sulfate is oxidation. Assuming that the number of moles of magnesium is 5, the number of moles of magnesium sulfate is 0.1 to 3.

In the present invention, in a farmland having cracks, a soil removal step of removing the soil in and near the cracked portion and a soil in which a solidifying agent containing magnesium oxide as a main component is kneaded into the hole from which the soil has been removed are formed into the hole. Since it is a ground repair method including a reinforcing layer forming step of laying it on the bottom of the soil to form a reinforcing layer and a soil backfilling step of backfilling the soil removed in the soil removing step on the reinforcing layer, the ground is ground. It is possible to easily repair the farmland with cracks in the soil, to easily repair it even in the event of a subsequent earthquake, and to provide a soil repair method in which the regenerated farmland does not hinder the growth of plants. Moreover, the solidifying agent used in this ground repair method contains magnesium oxide and magnesium sulfate, and the molar ratio of magnesium oxide to magnesium sulfate is 0.1 to 0.1 when the number of moles of magnesium oxide is 5. By setting it to 3, it becomes possible to easily provide it.

It is sectional drawing of the agricultural land containing a crack in the ground. It is a figure (the 1) explaining the process of the ground repair method of this invention. It is a figure (the 2) explaining the process of the ground repair method of this invention. It is a figure (the 3) explaining the process of the ground repair method of this invention. It is a figure explaining the situation when the ground which performed the ground repair method of this invention shifts again. It is a figure explaining the 2nd Example which concerns on the ground repair method of this invention. It is a figure explaining the 3rd Example which concerns on the ground repair method of this invention. It is a figure explaining the 4th Example which concerns on the ground repair method of this invention.

The ground repair method of the present invention and the solidifying agent used therein will be described in detail below.
As shown in FIGS. 1 to 4, the ground repair method of the present invention includes a soil removal step (see FIG. 2) for removing the soil in and around the cracked portion of the farmland having cracks (see FIG. 1). A reinforcing layer forming step (see FIG. 3) in which soil kneaded with a solidifying agent containing magnesium oxide as a main component is spread on the bottom of the hole to form the reinforcing layer 10 in the hole H from which the soil has been removed, and the reinforcing layer. This is a ground repair method including a soil backfilling step (see FIG. 4) for backfilling the soil 20 removed in the soil removing step.

In the ground repair method of the present invention, magnesium oxide is used as a main component as a soil solidifying agent. In addition, magnesium sulfate is used as a component to be combined with magnesium oxide. The reasons for choosing these ingredients are as follows.

Both magnesium oxide and magnesium sulfate are naturally derived components. These magnesiums are typical minerals required for animals and plants, and also have the effect of lowering cholesterol and triglycerides, and magnesium deficiency may induce mild skeleton, heart disease, diabetes, and the like. In addition, both magnesium oxide and magnesium sulfate are contained in gastrointestinal medicines. In particular, magnesium oxide is a component prescribed in hospitals as a laxative for pregnant women, and is safe for animals including the human body. It has been confirmed. In the case of plants, it is indispensable for the formation of chlorophyll necessary for photosynthesis, and if magnesium is insufficient, even if other fertilizers are sufficient, plant growth is not activated, so magnesia-based components are used as top dressing. Further, when magnesium oxide is mixed into the soil, the pH rises, and magnesium sulfate has a function of lowering the pH. Therefore, it is easy to maintain the pH of the soil close to neutral by using magnesium oxide and magnesium sulfate in combination.

When magnesium oxide or magnesium sulfate is used as a solidifying agent, even if cracks occur in the same place due to the earthquake again, the solidified soil (reinforcing layer) can be crushed and reused as new soil. Is. For this reason, unlike the case where a cement-based solidifying agent is used, the work of removing foreign substances such as rubble is not required, and soil contamination by cement or the like does not occur, so that it is possible to suppress an increase in the cost for re-repair. It becomes.

The mechanism by which magnesium oxide and magnesium sulfate solidify is as follows.
Magnesium oxide, to form a crystal (magnesium oxysulfate) by hydration reaction in the presence of sulfate ions (SO 4 ^_2-). An example of the reaction is expressed by the following chemical formula.
_{5MgO + MgSO 4 + 8H 2 O} → 5MgOMgSO 4 · 8H 2 O ( Formula 1)

Since these crystals form needle-like or fibrous crystal shapes, they are easily entangled with each other, and as a result, a strong bond can be realized. _{As the ratio of MgO to sulfonyl 4} in the crystal of the above chemical formula, various ratios can be selected, but a molar ratio of 5: 1 is a typical numerical value.
The hydration reaction of magnesium oxide alone shows weak acidity, but when the hydration reaction of magnesium sulfate is also carried out, crystals are formed as described above, so that the pH becomes closer to neutral.

In the following, the soil will be mainly described as Kuroboku soil, but it goes without saying that the soil repair method of the present invention is not limited to Kuroboku soil and can be used for a wide variety of soils.

The following experiments were conducted to investigate the amount of solidifying agent required to solidify the soil.
As the soil to be tested, surface soil (Kuroboku soil) collected in the forest of 25-1, Oaza Kawahara, Nishihara-mura, Aso-gun, Kumamoto Prefecture was used. The Kuroboku soil used was placed in a high-temperature dryer for 24 hours to be in an absolutely dry state.
The solidifying agent, magnesium oxide (MgO, product name: light burned magnesia CWI-120, manufactured by Akokasei Ltd.), magnesium sulfate _(MgSO 4 · _3H 2 O, magnesium sulfate trihydrate, product name: Magnesium sulfate MG- 3K, manufactured by Ako Kasei Co., Ltd.) was used.

(Test Example 1)
In order to investigate the change in properties (hardness) when the amount of the solidifying agent added to the Kuroboku soil was changed, a test was conducted with each compounding amount shown in Table 1.
In the test, the mixture B, which was a mixture of magnesium sulfate and water, was added to the mixture A, which was a mixture of Kuroboku soil and magnesium oxide, and the whole was uniformly mixed. The whole mixture was filled into a 2 L cylindrical cylinder and left for 24 hours.
The test piece after 24 hours was taken out from the cylinder, and the hardness of the test piece was measured with a standard Yamanaka soil hardness tester (Fujiwara Seisakusho Co., Ltd., spring strength 8.0 kg).

The blending ratio of magnesium oxide and magnesium sulfate (magnesium sulfate trihydrate) in Table 1 is set so that the weight ratio is 2: 1. This means that the molar ratio of magnesium oxide (MgO) and magnesium sulfate (Then ₄ ) corresponds to 0.57 when the number of moles of magnesium oxide is 5. In the test, a trihydrate of magnesium sulfate was used, but it goes without saying that it is possible to use an anhydrous salt or a heptahydrate of magnesium sulfate.

Basically, magnesium oxide alone exerts a curing action, but it is possible to further increase the strength of the cured product by forming needle-shaped or fibrous crystals represented by the above chemical formula in the cured product. Therefore, it is preferable to use magnesium sulfate together.
The molar ratio of magnesium oxide and magnesium sulfate, when 5 moles of magnesium oxide (MgO), the number of moles of magnesium sulfate (MgSO ₄₎ is preferably in a range of 0.1 to 3. When the number of moles of the magnesium sulfate is less than 0.1, can not be significant change is expected in the cured strength, when it exceeds 3, the necessary oxidation to form crystals of the chemical formula (5MgOMgSO ₄ · _8H 2 O) The molar ratio of magnesium to magnesium sulfate greatly exceeds 5: 1, and magnesium sulfate, which is a water-soluble salt, becomes surplus, hindering the solidification reaction itself, and after solidification due to the mixture of magnesium sulfate, which is an unreacted water-soluble component. The strength of the cured product is also reduced.

Tap water was used as the water, and in each test sample, water was added so that the mass ratio of magnesium sulfate to water was 1: 3.

For each test piece in Table 1, the hardness index (mm) measured by the soil hardness tester showed a gradual increasing tendency as the amount of the solidifying agent for Kuroboku soil increased from sample 01 to sample 10. Specifically, the hardness index of sample 01 was 7.0 mm, that of sample 06 was 10.5 mm, and that of sample 10 was 31.8 mm. For example, in the hardness index of 10.5 mm of KMK06, the conversion ground of the long-term allowable bearing capacity is 0.15 MPa, which is a value in the range of about 7 to 15 when converted to the N value (standard penetration test). This N value of 7 falls into the category of "hard" ground in clay ground.

Even when the hardness index of sample 01 is 7.0 mm, it can be used as a reinforcing layer. Therefore, the weight ratio of the soil component and magnesium oxide to the soil component Kuroboku soil may be 0.1 or more, assuming that the soil component is 1. If a large amount of magnesium oxide is used, the cost of construction will increase. Therefore, in reality, it is preferable to use magnesium oxide in the range of 0.1 to 1 with respect to soil component 1.

In Table 1, the hardness of the test piece was measured 24 hours after the mixture was placed in the cylinder, but at the actual work site, the solidification action starts in an elapsed time of about 30 to 60 minutes in consideration of the working time. Is preferable. To adjust the start time of the solidifying action, adjust the amount of solidifying agent added, such as the amount of magnesium oxide added, the amount of water added, and the mixing ratio of magnesium oxide and magnesium sulfate. It is possible to do. In addition, the method of adding water mixed with magnesium sulfate to the kneaded soil and magnesium oxide is relatively more suitable for adjusting the start time of the solidifying action than the case of mixing magnesium oxide and magnesium sulfate at the same time. It is valid.

Next, the ground repair method using the above-mentioned solidifying agent will be described.
The ground repair method of the present invention will be described with reference to FIGS. 1 to 4.
FIG. 1 is a cross-sectional view of a farmland where cracks (faults) have occurred.
a1 (a2) is the surface layer and is mainly composed of Kuroboku soil. b1 (b2) and c1 (c2) differ depending on whether the farmland is a field or a paddy field. For example, in the case of a field, it is gravel or crushed stone such as pebbles or sand, and in the case of a paddy field, b1 (b2) is clay. It is an impermeable layer such as a layer, and c1 (c2) is gravel or crushed stone. d1 (d2) indicates a solid ground. Naturally, the properties of each layer differ depending on the location of the agricultural land, but the surface layer (for example, a1 (a2)) is still mainly soil of Kuroboku soil.

In FIG. 1, a vertically displaced fault is shown, but in addition to the laterally displaced fault and a crack in the ground generated by moving the ground so as to be separated in the horizontal direction, in the present invention, the “crack” is also used. ".

(Soil removal process)
First, the crack portion and the soil in the vicinity thereof are removed as shown in FIG. 2 to form a hole H. The shape of the hole (the cross-sectional shape perpendicular to the crack direction of the hole (shape in FIG. 2)) is preferably formed by a substantially inverted triangle including an inverted triangle. The substantially inverted triangle is not only an upside-down triangle such as an isosceles triangle or a right triangle, but also a trapezoid in which the length of the lower base is shorter than the length of the upper base.

The reason why the shape of the hole is formed into a substantially inverted triangle is that the solidifying agent using magnesium oxide or magnesium sulfate expands the volume of the entire mixture when solidified. For this reason, when a reinforcing layer is formed along a hole of a substantially inverted triangle, when the reinforcing layer solidifies and expands in volume, the reinforcing layer adheres to the surrounding soil and the portion that cannot be spread laterally is upward. Since it is lifted, it is expected that the reinforcing layer will be stronger against the load from above.

Furthermore, if the shape of the hole is formed into a substantially inverted triangle, as shown in FIG. 5, even if an earthquake occurs again and the left and right grounds move up and down separately, the height of the surface of the repaired soil (ground) will be , It will be located in the middle of the height position of the surface of the left and right soil (ground). In such a situation, although it depends on the underground condition, for example, it is expected that the current state can be restored and the repair work can be performed extremely easily only by adjusting the surface height of the soil 20.

(Reinforcing layer forming process)
As shown in FIG. 3, the soil in which the soil is removed in the soil removal step is kneaded with a solidifying agent containing magnesium oxide as a main component, and the soil is spread on the bottom of the holes to form a reinforcing layer. The soil used for the reinforcing layer may be the soil removed in the soil removal process, or separately prepared soil (gravel such as pebbles or sand, or volcanic ash such as Kuroboku soil brought in from other land. It may be quality cohesive soil, etc.).

As the solidifying agent to be used, one containing magnesium oxide as a main component and magnesium sulfate added as necessary can be used. Naturally, it is possible to add other additives as long as they do not inhibit the solidification reaction of magnesium oxide or magnesium sulfate. As the compounding ratio of the soil and the solidifying agent, it is possible to use the compounding ratio for Kuroboku soil shown in the above test. If the soil is sandy soil instead of Kuroboku soil, it can be expected that the required hardness can be obtained with a smaller amount of solidifying agent.

The method of kneading the solidifying agent into the soil can be produced by adding magnesium oxide powder, magnesium sulfate powder and water to the soil and kneading the whole, but as explained in the above test, the soil and magnesium oxide can be produced. There is also a method in which the mixture A in which the above is mixed and the mixture B in which magnesium sulfate and water are mixed are separately prepared, and then the two are mixed and kneaded. It is also possible to prepare a mixture of magnesium oxide powder and magnesium sulfate powder in a predetermined compounding ratio in advance as a solidifying agent.

The soil usually contains about 30% of water. Therefore, the amount of water to be added is preferably the amount obtained by subtracting the amount of water contained in the soil.
However, if the land around the soil to be repaired is dry or if there are many gaps such as gravel under the surface soil, the added water will be absorbed by the surrounding soil and ground. In consideration of the above, it is preferable to add a water content larger than a predetermined amount.
In addition, since magnesium sulfate is water-soluble, magnesium sulfate may also flow out from the reinforcing layer to the surroundings as water flows out. In such a case, it is preferable that the total amount of the mixture B to be added is larger than the predetermined amount.

(Soil backfill process)
After the reinforcing layer 10 is formed inside the hole, either after the reinforcing layer is solidified or before the reinforcing layer is solidified, as shown in FIG. 4, the soil 20 removed in the soil removal step is used as the reinforcing layer. Work to backfill on top. In the ground repair method of the present invention, when a solidifying agent containing magnesium oxide as a main component is used, the time required for solidification varies depending on the water content of the soil and the amount of magnesium sulfate added, but it will eventually solidify. I know, and there is no problem as long as I don't use the farmland until then. Therefore, the surface soil can be backfilled even immediately after the reinforcing layer is formed (when uncured). Moreover, since the same or similar soil as the agricultural land is used for the reinforcing layer and the solidifying agent is also a naturally derived component, there is no concern about contaminating the agricultural land.

The above is the first embodiment of the ground repair method of the present invention, but the present invention is not limited thereto.
For example, as shown in FIG. 6, the reinforcing layer can be divided into 11 and 12, and the hardness of the reinforcing layer 11 can be weaker or stronger than that of the reinforcing layer 12. When the pressure from the ground surface is strong, the reinforcing layer 11 can be set to be weaker so that the reinforcing layer 11 does not bite into the ground due to the pressure from above. When the ground c1 (c2) or d1 (d2) is strong, the reinforcing layer 11 is rather strengthened so that it can be integrated with the surrounding ground and the reinforcing layer can be stabilized. ..

Further, it is also possible to form the layer of reference numeral 11 in FIG. 6 with gravel, sandy soil, crushed stone or the like instead of the reinforcing layer using the solidifying agent, and use the solidifying agent only for the reinforcing layer 12. This allows the use of solidifying agents to be minimized.

Further, as shown in FIG. 7, it is also possible to arrange the impermeable layer 30 such as a clay layer on the reinforcing layer 10 and arrange the surface soil (Kuroboku soil) 20 on the impermeable layer 30. Such an impermeable layer 30 is suitable for paddy fields and is an indispensable configuration for rice cultivation and lotus root fields.

Further, as shown in FIG. 8, the end portion of the upper surface of the clay layer 30 of the hole is set to be at the same position as the upper surface of the water-impervious layer (b1, b2) of the soil around the hole. .. As a result, when an earthquake occurs again and the surrounding ground moves, even if a crack occurs between the impermeable layer and the surrounding strata (b1, b2), the surroundings will be in the thickness direction of the impermeable layer. As long as the portion overlapping with the water-impervious strata (b1, b2) remains, the gap between the two can be easily filled with the clay layer and repaired.

As described above, according to the present invention, agricultural land with cracks in the ground can be easily repaired, re-repair is easy even in the event of a subsequent earthquake, and the regenerated agricultural land does not hinder the growth of plants. It becomes possible to provide a construction method.

a1 to d2: Strata 10-12: Reinforcing layer 20: Soil (surface soil)
30: Impermeable layer

Claims (9)

For agricultural land with cracks, the soil removal step in which the soil in the cracked portion and its vicinity is removed and the cross-sectional shape perpendicular to the crack direction of the hole from which the soil is removed is approximately an inverted triangle.
A reinforcing layer forming step of forming a reinforcing layer by laying soil in which a solidifying agent containing magnesium oxide as a main component is kneaded into the hole from which the soil has been removed is spread on the bottom of the hole.
A ground repair method including a soil backfilling step of backfilling the soil removed in the soil removing step on the reinforcing layer. For agricultural land with cracks, a soil removal process that removes the soil in and around the cracks,
A reinforcing layer forming step of forming a reinforcing layer by laying soil mixed with a solidifying agent containing magnesium oxide as a main component in the hole from which the soil has been removed at the bottom of the hole.
A ground repair method comprising a soil backfilling step in which a water-impervious clay layer is arranged on the reinforcing layer and the soil removed in the soil removing step is backfilled on the clay layer. In the ground repair method according to claim 2, the end portion of the upper surface of the clay layer of the hole is set to be at the same position as the upper surface of the water-impervious layer of the soil around the hole. The characteristic ground repair method. The ground repair method according to any one of claims 1 to 3, wherein the soil contains Kuroboku soil. The ground repair method according to any one of claims 1 to 4, wherein the raw material of the solidifying agent contains magnesium oxide and magnesium sulfate. In the ground repair method according to claim 5 , in the reinforcing layer forming step, the weight ratio of the soil component and magnesium oxide is in the range of 0.1 to 1 when the soil component is 1. The characteristic ground repair method. In the ground repair method according to claim 5 or 6 , the molar ratio of magnesium oxide to magnesium sulfate contained in the solidifying agent is 0.1 to 3 when the number of moles of magnesium oxide is 5. A ground repair method characterized by being. In the ground repair method according to any one of claims 1 to 7 , the ground repair is characterized in that soil or crushed stone containing no solidifying agent is arranged under the reinforcing layer arranged in the hole. Construction method. A solidifying agent used in the ground repair method according to any one of claims 1 to 8 , which contains magnesium oxide and magnesium sulfate, and the molar ratio of magnesium oxide to magnesium sulfate is such that the number of moles of magnesium oxide is 5. Then, the solidifying agent characterized in that the number of moles of magnesium sulfate is 0.1 to 3.

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