JP2020148037A - Ground modification method - Google Patents

Abstract

To provide a ground modification method capable of preventing floating of a pipe buried in the ground even when the ground becomes liquefied while keeping the environmental load small.SOLUTION: The ground modification method in which the ground around the buried pipe 3 arranged in the liquefaction layer 11 of the ground 10 contains the ground modifier. The ground modifier contains urea. Urea is decomposed by urease activity possessed by microorganisms existing in the liquefaction layer 11. As a result, the liquefaction layer 11 is modified.SELECTED DRAWING: Figure 2

Description

The present invention relates to a ground modification method.

Pipelines and manholes for water and gas are buried in the ground. When constructing these, it is completed by arranging pipes after excavating the ground and backfilling the excavated soil on it.

However, since these pipes have cavities inside, the specific density of the pipes as a whole may be smaller than that of water. If the ground around the pipe is liquefied due to a large earthquake or the like, it is assumed that the pipe will float and the pipe will be damaged and muddy water will invade the inside and cause great damage. Therefore, it is desirable to take measures to prevent liquefaction of the backfill soil when backfilling the pipe (for example, Patent Document 1).

Published by the Japan Sewerage Association, "Guidelines and Explanations for Earthquake-Resistant Measures for Sewerage Facilities 2014 Edition", pp. 203-214

Various liquefaction prevention methods can be mentioned as countermeasures. For example, when backfilling soil is compacted, the pipes and the like are configured to have a curved surface, so compaction near the curved surface may not be sufficient. Cheap. In addition, when backfilled with crushed stone, on-site waste soil treatment is required, which tends to place a burden on the environment and costs. Further, when the backfill soil is solidified with a cement-based solidifying material, an environmental load is generated.

Therefore, the present invention provides a ground reforming method capable of preventing the pipes buried in the ground from floating even when the ground is liquefied while keeping the environmental load small. The purpose.

The present invention provides a ground reforming method in which a ground modifier is contained in the ground around a buried pipe arranged in a liquefied layer of the ground, and the ground modifier contains urea.

When urea is used as a ground modifier, urea is decomposed by urease activity of microorganisms existing in the ground to reform the ground. More specifically, carbonic acid generated by decomposition of urea combines with calcium in the ground to form calcium carbonate, which binds soil particles to each other to solidify the ground. As a result, the liquefied layer becomes difficult to liquefy. Therefore, according to the present invention, the ground around the buried pipe is prevented from being liquefied, and the buried pipe is prevented from floating.

In the present invention, the ground modifier and soil may be mixed to prepare a mixed soil, and the buried pipe may be buried so that the mixed soil is brought into contact with the buried pipe exposed in the liquefaction layer. In this case, the ground modifier can be handled as a powder, and can be reliably mixed with the soil.

Further, in the present invention, the ground may contain the ground modifier by injecting a liquid containing the ground modifier into the ground around the buried pipe. This method is particularly suitable when targeting an existing buried pipe.

The ground modifier preferably further comprises at least one selected from the group consisting of microorganisms having urease activity, microbial nutrient sources, and calcium sources. When these elements are scarce in the ground, by adding the scarce elements together, the microorganisms in the ground can be further activated and the solidification of the ground can be promoted.

According to the present invention, it is provided a ground reforming method capable of preventing the pipes buried in the ground from floating even when the ground is liquefied while keeping the environmental load small. Can be done.

Both (A) and (B) are diagrams showing the ground reforming method of the first embodiment. Both (A) and (B) are diagrams showing the ground reforming method of the first embodiment. It is a figure which shows the modification of 1st Embodiment. It is a figure which shows the ground reforming method of 2nd Embodiment.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same parts or corresponding parts are designated by the same reference numerals, and duplicate description will be omitted. In addition, in this invention, a "buried pipe" means a pipe to be buried in the ground, and it does not matter whether it is exposed to the outside or buried in the ground. Manholes are also considered buried pipes.

Further, in the ground reforming method of the present invention, liquefaction measures are taken for the liquefied layer of the ground in order to prevent the ground from liquefying due to a large earthquake or the like. Here, the "liquefied layer" refers to a layer of the ground that is presumed to be relatively easy to liquefy. Whether or not it is easy to liquefy can be estimated by investigating the soil quality of the ground, particle size distribution, N value based on boring, etc. in advance. Further, a layer estimated to have a small risk of liquefaction is called a "non-liquefied layer".

<First Embodiment>
As shown in FIG. 1 (A), the application target of the ground reforming method of the present embodiment is from the non-liquefied layer 12 and the liquefied layer 11 located above the non-liquefied layer 12 and reaching the ground surface. Of the ground 10, the liquefied layer 11 FIG. 1A shows a state in which the groundwater level is in the liquefaction layer 11 and a state in which the asphalt 13 is laid on the outermost surface of the liquefaction layer 11 assuming the road.

When constructing a new burial pipe, the area where the burial pipe is to be buried is first excavated, and a retaining wall 1 is installed on the excavated surface (FIG. 1 (B)). After excavating to a predetermined depth in the liquefaction layer 11, the foundation gravel 2 is laid on the bottom surface thereof, and the buried pipe 3 is further arranged on the foundation gravel 2 (FIG. 2 (A)).

On the other hand, the powdered ground modifier is mixed with the excavated soil generated by excavation. As the mixing method, an existing mixing method can be appropriately adopted. The following ground modifiers are used.

Here, the ground modifier is a material that activates the activity of microorganisms having urease activity inhabiting the target ground and solidifies the ground. In the present embodiment, the ground modifier contains urea. The ground modifier may further contain a microorganism having urease activity, a nutrient source for the microorganism, a calcium source, and the like. When these elements are scarce in the ground, the addition of the scarce elements together can further activate the microorganisms in the ground and promote the solidification of the ground. The ground modifier is prepared by preparing a composition in which each of the above elements is mixed, and this is mixed with excavated soil for use.

As the microorganism, a microorganism having urease activity is used. The microorganism used may be a culture of a microorganism collected from the target ground (liquefaction layer 11), or may be a microorganism collected or purchased from another place in Japan. Urease is an enzyme produced by the microorganism and catalyzes the reaction of hydrolyzing urea to produce carbonic acid and ammonia.

There is no particular limitation on what is used as a nutrient source for microorganisms, and examples thereof include meat extracts, sugars such as glucose, and polysaccharides such as starch. The amount added to the excavated soil may be 0.3 to 6.5 g or 0.5 to 3.0 g with respect to 1 kg of the dry weight of the excavated soil.

The amount of urea added may be 5 to 30 g or 10 to 15 g with respect to 1 kg of the dry weight of the excavated soil. If the urea content is too high, the movement of microorganisms will be impaired and the ground solidification effect will tend to be reduced.

The calcium source may be any one that dissolves in water and releases calcium ions, and examples thereof include calcium chloride, calcium carbonate, calcium hydroxide, and calcium nitrate. The amount added to the excavated soil may be 10 to 50 g or 15 to 30 g with respect to 1 kg of the dry weight of the excavated soil. If the content of the calcium source is too high, the movement of microorganisms becomes slow and the solidification effect of the ground tends to be small.

The ground modifier may contain various components in addition to the above. For example, ammonium chloride, sodium hydrogen carbonate, air and the like can be mentioned. When the specific gravity of the ground modifier is high, it tends to sink in the groundwater. Therefore, it is possible to prevent the ground modifier from sinking by including air. In addition, the ground modifier may contain a thickener in some cases. Cellulose derivatives are preferable as the thickener, and among them, carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl methyl cellulose are preferable. The content of the thickener is preferably contained so that the viscosity of the ground modifier when mixed with groundwater is 1 to 10 times or 2 to 5 times the viscosity of water.

Using the mixed soil 4 in which the ground modifier is mixed with the excavated soil, the mixed soil 4 is put into the excavation hole so that the mixed soil 4 comes into contact with the buried pipe 3, and the buried pipe 3 is filled while rolling (FIG. 2 (FIG. 2). B)). At this time, as the retaining wall 1 is removed, groundwater infiltrates from the surrounding liquefaction layer 11, so that the ground modifier is dissolved and the effect is easily exhibited. After the mixed soil 4 reaches the uppermost surface of the liquefaction layer 11, the asphalt 13 is laid and the construction is completed.

Urea contained in the ground reformer is decomposed by urease activity possessed by microorganisms into carbonic acid and ammonia. Carbonic acid combines with calcium in the ground (or calcium contained in the ground modifier) to form calcium carbonate, which bonds soil particles together (sementation) to solidify the mixed soil 4 and form a modified region. It becomes 11A. As a result, the liquefied layer 11 has a property of being difficult to liquefy. As the period for solidification, for example, a curing period of several months is required. After the curing period, the liquefied layer 11 becomes difficult to liquefy. Therefore, according to the ground reforming method of the present embodiment, the ground around the buried pipe 3 is prevented from solidifying and liquefying, and the buried pipe 3 is prevented from floating even when a large earthquake occurs. Will be done.

Further, in the present embodiment, since the powdered ground modifier is mixed with the excavated soil, it is possible to surely mix the ground modifier with the excavated soil. Further, in the present embodiment, the liquefaction layer 11 is solidified to the uppermost surface thereof in the construction portion, so that the entire ground area above the buried pipe 3 is solidified, and it is more certain that the buried pipe 3 floats. Is prevented. At the same time, this prevents the buried pipe 3 from being damaged, and keeps the lifeline and the like sound.

The above embodiment can also be applied to manholes. As shown in FIG. 3, when the liquefied layer 11 around the newly installed manhole 3B is backfilled, the buried pipe 3 including the manhole 3B is used by using the mixed soil 4 mixed with the ground modifier. The whole circumference can be solidified.

<Second embodiment>
As the second embodiment, a method of modifying the ground around the existing buried pipe is shown. FIG. 4 shows an existing buried pipe 3, in which the buried pipe 3 includes a flow path portion 3A extending in a substantially horizontal direction in the liquefaction layer 11 and a manhole leading vertically upward from the flow path portion 3A to the ground. It has 3B and.

In this case, the injection pipe 5 is inserted into the construction target portion to reach the vicinity of the buried pipe 3, and the ground modifier is injected into the liquefaction layer 11 around the buried pipe 3. A well may be provided instead of the injection pipe 5 for injection. As the ground modifier, a material having the same composition as that in the first embodiment is mixed with water, and an aqueous solution, a suspension, an emulsion, etc. (hereinafter, these are collectively referred to as "liquid"). There is.) Used as a state.

Here, when preparing a liquid containing a ground modifier, the content (concentration) of each component is preferably as follows. The content of the nutrient source of the microorganism may be 1 to 30 g per liter of water, or 4 to 20 g. The urea content may be 0.1 to 10 mol (mol), 0.2 mol to 5 mol, or 0.3 to 0.7 mol per liter of water. Good. The content of the calcium source may be 0.1-10 mol (mol), 0.2 mol-5 mol, 0.3-0.7 mol, per liter of water. May be good.

The liquid may be injected at all locations over the entire length of the buried pipe 3, or may be injected at a plurality of locations at predetermined intervals from each other as shown in FIG. The predetermined interval may be 1 m to 30 m or 5 m to 10 m. When liquefied, the buoyancy of the manhole 3B portion becomes particularly large, so it is particularly preferable to intensively inject the liquid around the manhole 3B. The injected liquid permeates the ground around the buried pipe 3, and the portion where the liquid permeates (the portion which becomes the mixed soil 4) solidifies after a curing period of several months, for example, and becomes a reformed region 11A.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, in the first embodiment, a mode in which a powdered ground modifier is mixed with excavated soil and used when a new buried pipe is installed has been described, but this method also applies to an existing buried pipe. Can be applied. That is, the area around the existing buried pipe may be excavated to expose the buried pipe, the ground modifier may be mixed with the excavated soil, and the buried pipe may be backfilled with the mixed soil.

Further, in the second embodiment, a mode in which a liquid containing a ground modifier is injected into the ground around an existing buried pipe is shown, but this method is also applied to the case where a new buried pipe is installed. can do. That is, a liquid containing a ground modifier may be injected using an injection pipe immediately after the buried pipe is buried in the ground.

Further, in any of the above embodiments, the ground 10 composed of the non-liquefied layer 12 and the liquefied layer 11 located above the non-liquefied layer 12 and reaching the ground surface is shown, but the composition of the ground is not limited to this. The present invention can be applied when the buried pipe is arranged in the liquefaction layer and when the buried pipe is arranged in the liquefaction layer.

The present invention can be used as a countermeasure against liquefaction of the ground.

1 ... Mountain retaining wall, 2 ... Foundation gravel, 3 ... Buried pipe, 3A ... Flow path, 3B ... Manhole, 4 ... Mixed soil, 5 ... Injection pipe, 10 ... Ground, 11 ... Liquefaction layer, 11A ... Modified area , 12 ... non-liquefied layer, 13 ... asphalt.

Claims (4)

The ground around the buried pipe placed in the liquefaction layer of the ground contains the ground modifier.
The ground reforming material is a ground reforming method containing urea. The ground modifier and soil are mixed to prepare mixed soil.
The ground reforming method according to claim 1, wherein the buried pipe is buried by bringing the mixed soil into contact with the buried pipe exposed in the liquefaction layer. The ground reforming method according to claim 1, wherein a liquid containing the ground modifier is injected into the ground around the buried pipe to contain the ground modifier in the ground. The ground modification according to any one of claims 1 to 3, wherein the ground modifier further comprises at least one selected from the group consisting of a microorganism having urease activity, a nutrient source of the microorganism, and a calcium source. Quality method.

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