JP2021038294A - Soil modifying method and soil modifier used therefor, and modified soil - Google Patents

Abstract

To provide a soil modifying method that does not invite complicated processes, has a small impact on the environment, and has a high ability to reduce liquefaction while enabling reversible use of the ground, and to provide a soil modifier used therefor, and to provide a modified soil.SOLUTION: A microorganism, a nutrient source and a cellulose source are added to the target soil 11 whose main component is earth and sand. The microorganism produces the calcium compound 22 by metabolism. The nutrient source contains at least a calcium and a component used by the microorganism in metabolism. The cellulose source is mainly composed of the cellulose fiber 21, and is entangled to the particle 12 of the earth and sand constituting the modified soil 11 and is precipitated with the calcium compound 22 produced by the microorganism.SELECTED DRAWING: Figure 1

Description

The present invention relates to a soil reforming method, a soil modifier used therein, and modified soil.

With the frequent occurrence of earthquakes all over the country, liquefaction of the ground has become a major problem. In particular, the 2011 off the Pacific coast of Tohoku Earthquake caused frequent liquefaction not only in the Tohoku region near the epicenter but also in the coastal areas of the Kanto region such as Chiba prefecture. For this reason, liquefaction of the ground has become a major social problem as a disaster caused by an earthquake. The ground where liquefaction is likely to occur is said to be a layer formed mainly by filling the gaps between the particles constituting the earth and sand with groundwater and loosely packing the particles of the earth and sand having a uniform particle size. When strong vibrations such as earthquakes occur in such ground, the pore water pressure between the particles of earth and sand rises. When this water pressure exceeds the meshing force due to the frictional force between the sand particles, the sand particles are in a state of floating in the groundwater, and the solid ground is liquefied.
Therefore, for example, the SCP (Sand Compaction Pile) method is known as a countermeasure against liquefaction by reforming the ground (see Patent Document 1). In this SCP method, a casing is driven into the ground, and sand piles are press-fitted while replenishing sand in the casing. As a result, the density of the ground can be increased and the shear strength can be increased.

However, the conventional construction method such as the SCP construction method has a problem that it is difficult to shorten the construction construction period without requiring a complicated process. Further, the construction method other than the SCP construction method also has a problem that the load on the environment is large because, for example, a chemical is used. Furthermore, these construction methods are often irreversible, and there is a problem that they hinder the reuse of the ground.

Japanese Unexamined Patent Publication No. 2014-109179

Therefore, a soil reforming method having a high ability to reduce liquefaction while having a small impact on the environment and enabling reversible use of the ground without inviting a complicated process, and a soil modifier used for this, as well as The purpose is to provide modified soil.

In one embodiment, a cellulose source is added. Cellulose sources include cellulose fibers. When this cellulose fiber is added to the target soil, it is intricately entangled between the particles of the earth and sand constituting the target soil. As a result, the cellulose fibers are intricately stretched between the particles constituting the target soil, and the particles and the fibers form a complicated fine structure. In addition, the microorganisms added to the target soil settle on the cellulose fibers added to the target soil, and using the nutrient source added together, a calcium compound such as calcium carbonate is produced by metabolism. Calcium compounds produced by microorganisms connect the particles of earth and sand that make up the target soil and strengthen the target soil. That is, by adding the cellulose source to the target soil, the fine structure of the earth and sand particles constituting the target soil is maintained. At the same time, the microorganisms colonized in this cellulose source precipitate calcium compounds starting from the cellulose fibers stretched between the particles of earth and sand. Therefore, a strong calcium compound structure along a complicated microstructure is formed between the earth and sand particles constituting the target soil. As a result, the space between the earth and sand particles constituting the target soil is filled with the calcium compound, the voids through which the groundwater permeates are reduced, and the strength between the earth and sand particles is improved. All of these cellulose sources, nutrient sources and microorganisms are naturally occurring. Therefore, it does not contaminate the target soil. Therefore, it is possible to enhance the ability to reduce liquefaction without inviting a complicated process and without imposing a load on the environment.

Further, in one embodiment, the target soil containing the calcium compound is easily broken by applying a large mechanical force while maintaining resistance to liquefaction against vibrations such as earthquakes. For example, when the target soil is modified such as a roadbed or a roadbed and then further maintenance is required for reuse or the like, the structure of the target soil according to the present embodiment is easily broken by heavy machinery or tools. .. Therefore, the target soil can be reversibly reused.

Schematic diagram showing modified soil to which the soil modification method according to one embodiment is applied. Schematic diagram showing an example in which the soil reforming method according to one embodiment is applied to underground piping equipment. It is a schematic diagram which shows the soil modification method by one Embodiment, and is the figure which shows the state which the cellulose fiber is entangled with the particle of earth and sand. It is a schematic diagram which shows the soil modification method by one Embodiment, and is the figure which shows how the calcium compound grows on the cellulose fiber entwined with the particle of earth and sand. It is a schematic diagram which shows the soil modification method by one Embodiment, and is the figure which shows how the calcium compound grows on the cellulose fiber entwined with the particle of earth and sand. Schematic diagram showing an example in which a calcium compound is produced by metabolism by a microorganism used in the soil reforming method according to one embodiment. Schematic diagram showing an example in which a calcium compound is produced by microorganisms dispersed in earth and sand particles of a conventional target soil.

Hereinafter, the soil reforming method according to one embodiment will be described with reference to the drawings.
As shown in FIG. 1, the reformed soil 10 to which the soil reforming method according to one embodiment is applied includes the target soil 11. FIG. 1 is a schematic view showing a part of the target soil 11 to which the modified soil 10 is applied. The target soil 11 is a general soil whose main component is the earth and sand particles 12 to be reformed. The target soil 11 may contain particles having various particle sizes such as gravel, stones, rocks, and some clay, in addition to the earth and sand particles 12 as the main component. The target soil 11 can be arbitrarily used as long as it is soil that may cause liquefaction due to an earthquake or the like. Further, the target soil 11 may be a soil such as a roadbed or a roadbed that is required to be reversibly reused while having an appropriate hardness. The target soil 11 for which reversible reuse is required may be a location that needs to be dug up for future pipe replacement, such as the installation location of the underground pipe 13 as shown in FIG.

The modified soil 10 contains cellulose fibers 21 and calcium compound 22 as shown in FIG. Cellulose fiber 21 is a cellulose source, and contains fibrous cellulose derived from a plant such as pulp or used paper as a main component. The cellulose fiber 21 is not limited to a new pulp fiber obtained by processing wood chips, and a recycled paper fiber made by reusing used paper can be used. Waste paper fibers are obtained, for example, from households and businesses by collecting the paper consumed by them for the purpose of recycling or the like. The used paper fiber used as the cellulose fiber 21 is a fine fibrous material that remains in a crusher or the like when the used paper is crushed, and exhibits an appearance similar to dust. Most of the cellulose fibers 21 are linear fibers having a large aspect ratio, and may include lumpy fibers formed by agglomeration of linear fibers. In each of the drawings including FIG. 1, the hatching is for convenience to distinguish the earth and sand particles 12 and the cellulose fibers 21 which are the constituent elements, and does not show the cross section.

When the cellulose fibers 21 are added to the target soil 11, they are entangled with the earth and sand particles 12 constituting the target soil 11 as shown in FIG. The earth and sand particles 12 constituting the target soil 11 have an irregular structure formed by particles having irregular particle sizes. Note that FIG. 3 shows the earth and sand particles 12 having a regular structure for the sake of simplicity. The cellulose fibers 21 are dispersed between the earth and sand particles 12, and are entwined with the earth and sand particles 12 in a mesh pattern. In this way, the cellulose fibers 21 are complicatedly stretched between the earth and sand particles 12 constituting the target soil 11. As a result, the earth and sand particles 12 and the cellulose fibers 21 form a complicated fine structure.

As shown in FIG. 1, the calcium compound 22 is precipitated so as to connect the earth and sand particles 12 constituting the target soil 11 with the cellulose fibers 21 as a support. Calcium compound 22 is produced by metabolism of microorganisms that settle on cellulose fibers 21. Microorganisms that produce the calcium compound 22 tend to settle on the cellulose fibers 21 relatively easily. Therefore, the calcium compound 22 produced by the metabolism of microorganisms grows using the cellulose fibers 21 entwined between the earth and sand particles 12 as a support as shown in FIGS. 1, 4 and 5. Then, as shown in FIG. 1, the grown calcium compound 22 connects between adjacent earth and sand particles 12 in a state of being crosslinked with the cellulose fibers 21 as a support.

Urea-degrading bacteria can be applied as the microorganism that produces the calcium compound 22. By providing a calcium source, the urea-degrading bacterium produces calcium compound 22, such as calcium _{carbonate (CaCO 3), by biological metabolism as shown in FIG.} The generated calcium compound 22 grows using the cellulose fibers 21 entwined between the earth and sand particles 12 as a support as described above. The microorganism that produces the calcium compound 22 is not limited to the above-mentioned urea-degrading bacterium, and may be any other bacterium as long as it is a microorganism that produces a calcium compound. For example, photosynthetic bacteria, denitrifying bacteria, ammonia-producing bacteria, sulfur-reducing bacteria, methane-oxidizing bacteria, etc. are considered to be applicable.

When microorganisms are simply added to the target soil 11, the added microorganisms are dispersed throughout the target soil 11 and do not settle in a specific range. Therefore, in the target soil 11 that does not contain the cellulose fibers 21, the calcium compound 22 is produced in the entire target soil 11 as shown in FIG. 7. As a result, the soil containing no cellulose fibers 21 does not form a structure in which the calcium compound 22 crosslinks between the particles 12, and the soil has a structure in which the calcium compound 22 is merely precipitated as a whole.

On the other hand, by adding the cellulose fiber 21 to the target soil 11 as in the present embodiment, the microorganisms added to the target soil 11 are selectively fixed to the cellulose fiber 21. Therefore, the calcium compound 22 produced by the metabolism of microorganisms selectively grows using the cellulose fibers 21 entwined with the earth and sand particles 12 constituting the target soil 11 as a support, and bridges between the earth and sand particles 12. Connect like this. As a result, the calcium compound 22 can selectively reinforce the space between the earth and sand particles 12.

The target soil 11 containing such a calcium compound 22 improves resistance to liquefaction against vibrations such as earthquakes. On the other hand, when a large mechanical force is applied by, for example, a heavy machine or a tool, the material is easily broken. That is, when the calcium compound 22 is contained, the earth and sand particles 12 constituting the target soil 11 are ensured with sufficient resistance to liquefaction by the calcium compound 22 produced by the metabolism of microorganisms. On the other hand, the earth and sand particles 12 connected by the calcium compound 22 are easily broken when a large mechanical force is applied. Therefore, the modified soil 10 can be treated in the same manner as ordinary soil when a force is applied by a heavy machine or the like. As a result, the modified soil 10 can be reversibly reused.

Next, a soil reforming method, which is a procedure for reforming soil, will be described.
As described above, the target soil 11 contains particles having various particle sizes such as gravel and stone in the earth and sand particles 12. When the soil is modified, microorganisms, nutrient sources, and cellulose fibers as a cellulose source are added to the target soil 11. The microorganism produces calcium compound 22 by metabolism as described above. The nutrient source contains components used in the metabolism of microorganisms. The nutrient source contains a calcium source that provides calcium ions such as calcium chloride and calcium oxide. In addition, the nutrient source contains components used in metabolism by the microorganisms, depending on the microorganisms to which they are applied. In this case, the nutrient sources are, for example, environmental regulators, pH regulators and organic matter. As an example, when urea-degrading bacteria are used as microorganisms, the nutrient source preferably contains urea, ammonium chloride, sodium hydrogen carbonate, nutrient broth and the like. Urea is a carbon dioxide source used by urea-degrading bacteria during metabolism. Ammonium chloride is an environmental conditioner for providing an environment in which microorganisms can easily grow. Sodium bicarbonate is a pH regulator for adjusting the pH of soil. Nutrient broth is a component that serves as a culture medium for providing organic substances and minerals used by microorganisms during metabolism. These microorganisms, nutrient sources and cellulose sources are produced as soil modifiers.

The soil modifier is added to the target soil 11 to be reformed. The soil modifier is, for example, a pile-shaped or pellet-shaped processed cellulose fiber 21 containing microorganisms and nutrient sources. By driving or adding this soil modifier to the target soil 11, the cellulose fibers 21 contained in the soil modifier are diffused into the target soil 11 by the water contained in the target soil 11. At this time, the microorganisms and nutrient sources contained in the soil modifier diffuse into the target soil 11 in a state of being impregnated with the cellulose fibers 21 without being uniformly dispersed in the target soil 11. At this time, the cellulose fibers 21 containing microorganisms and nutrient sources are entangled between the earth and sand particles 12 constituting the target soil 11 while forming a complicated three-dimensional structure as shown in FIG.

The microorganism contained in the cellulose fiber 21 grows using the nutrient source also contained in the cellulose fiber 21, and produces a calcium compound 22 such as calcium carbonate as a metabolite. Microorganisms are mainly settled on the cellulose fiber 21. Therefore, as shown in FIGS. 4 and 5, the calcium compound 22 produced by metabolism grows so as to connect between the earth and sand particles 12 constituting the target soil 11 with the cellulose fibers 21 as a support. As a result, the modified soil 10 as shown in FIG. 1 is generated.

In one embodiment described above, a cellulose source is added to the target soil 11. The cellulose source contains cellulose fibers 21. When the cellulose fibers 21 are added to the target soil 11, they are intricately entangled between the earth and sand particles 12 constituting the target soil 11. As a result, the cellulose fibers 21 are complicatedly stretched between the particles 12 constituting the target soil 11, and the earth and sand particles 12 and the cellulose fibers 21 form a complicated fine structure. Further, the microorganism added to the target soil 11 is fixed on the cellulose fiber 21 added to the target soil 11, and the calcium compound 22 such as calcium carbonate is produced together with the metabolism by using the nutrient source added together. To do. The calcium compound 22 produced by the microorganism connects the earth and sand particles 12 constituting the target soil 11 to strengthen the target soil 11. That is, by adding the cellulose fiber 21 to the target soil 11, the fine structure of the earth and sand particles constituting the target soil 11 is maintained. At the same time, the microorganisms fixed on the cellulose fibers 21 generate the calcium compound 22 starting from the cellulose fibers 21 stretched between the particles 12 of the earth and sand. Therefore, a strong calcium compound 22 structure along a complicated microstructure is formed between the earth and sand particles 12 constituting the target soil 11. As a result, the space between the earth and sand particles 12 constituting the target soil 11 is filled with the calcium compound 22, the voids through which groundwater permeates are reduced, and the strength between the earth and sand particles 12 is increased. All of these cellulose fibers 21, nutrient sources and microorganisms are naturally present. Therefore, the target soil 11 is not contaminated. Therefore, it is possible to enhance the ability to reduce liquefaction without inviting a complicated process and without imposing a load on the environment.

Further, in one embodiment, the target soil 11 containing the calcium compound 22 is easily broken by applying a large mechanical force while maintaining resistance to liquefaction against vibrations such as earthquakes. For example, when the target soil 11 is modified such as a roadbed or a roadbed and then further maintenance is required for reuse or the like, the target soil 11 according to the present embodiment can be easily constructed by a heavy machine or a tool. It will be broken. Therefore, the target soil 11 can be reversibly reused.

The present invention described above is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.

In the drawings, 10 is a modified soil, 11 is a target soil, 12 is a particle, 21 is a cellulose fiber, and 22 is a calcium compound.

Claims (4)

For the target soil whose main component is earth and sand,
Microorganisms that produce calcium compounds by metabolism, nutrient sources containing at least calcium and components used in metabolism by the microorganisms, and the particles of earth and sand that are mainly composed of cellulose fibers and constitute the modified soil are entangled and the microorganisms are produced. A soil modification method for adding a cellulose source from which the calcium compound is precipitated. A soil modifier used in the soil reforming method according to claim 1.
A soil modifier containing the microorganism, the nutrient source, and the cellulose source. The soil modifier according to claim 2, wherein the cellulose source is mainly composed of recycled paper fibers containing linear fibers and agglomerated fibers in which linear fibers are aggregated. Cellulose fibers entwined with earth and sand particles,
A calcium compound that is produced by the metabolism of microorganisms that settle on the cellulose fibers and that connects the particles to each other using the cellulose fibers as a support.
Modified soil with.

Images