Ground improvement method and ground in which water-absorbing swelling agent is placed by the ground improvement method

Abstract

To inexpensively and easily achieve prevention of liquefaction and soil improvement near the ground surface.SOLUTION: A ground improvement method includes a step of arranging a water-absorbing expansion agent at an arrangement place including at least a ground surface of an object ground.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a ground improvement method and ground in which a water-absorbing expanding agent has been placed by the ground improvement method. [Background technology]

[0002] For the purpose of preventing ground subsidence and reducing noise and vibration, a technology has been proposed in which a casing pipe is pressed vertically downward into the ground, fill material is poured into the internal space of the casing pipe, and then the fill material is pressed down by the pressure of air blown into the casing pipe, while the casing pipe is pulled upward by the amount of fill material poured in (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2014-148884 Summary of the Invention [Problem to be solved by the invention]

[0004] Ground liquefaction is a phenomenon in which loosely deposited soil such as sand becomes liquid when subjected to seismic motion. Conventional technologies for preventing liquefaction include density-increasing methods such as the Sand Compaction Pile Method (SCP Method) and Compaction Grouting Method (CPG Method), solidification methods such as deep mixing treatment methods, and groundwater level lowering methods such as deep wells and well points. In particular, the technology described in Patent Document 1 places a water-absorbent expansive material in the borehole, preventing ground subsidence and reducing noise and vibration while also taking into consideration the soil pH environment.

[0005] However, all of these technologies increase the density of the soil relatively deep underground or lower the groundwater level near residential areas. While these methods are effective in preventing liquefaction itself, they have the problem of doing little to improve the soil near the surface. Furthermore, all of these methods require large-scale construction equipment, which is costly and time-consuming.

[0006] The technology disclosed herein has been developed in light of these circumstances, and its purpose is to prevent liquefaction and improve the ground near the surface inexpensively and easily. [Means for solving the problem]

[0007] In order to solve the above problems, a ground improvement method according to one aspect of the present invention includes a step of placing a water-absorbing swelling agent at a placement location that includes at least the ground surface of a target ground.

[0008] Any combination of the above components, and conversion of the present disclosure into a method, device, system, recording medium, computer program, etc., are also valid aspects of the present disclosure. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to prevent liquefaction and improve the ground near the surface inexpensively and easily. [Brief explanation of the drawings]

[0010] [Figure 1] This is a photograph of the experimental system used in the liquefaction simulation experiment. [Figure 2] 10 is a graph showing the amount of subsidence of the ground and the amount of rise in the surface water level when the duration of vibration application is changed. [Figure 3] This is a graph showing the tilt of a miniature building when vibration is applied with different amounts of water added to the sand. [Figure 4] 3 is a flowchart showing the processing flow of the ground improvement method according to the first embodiment of the present disclosure. [Figure 5] 10 is a flowchart showing the processing flow of a ground improvement method according to a second embodiment of the present disclosure. [Figure 6] 10 is a flowchart showing the processing flow of a ground improvement method according to a third embodiment of the present disclosure. [Figure 7] 1 is a photograph (side view) showing the setup of a validation experiment. [Figure 8] 1 is a photograph (top view) showing the setup of the validation experiment. [Figure 9] 10 is a photograph showing the state after vibration is applied to a plurality of water-absorbing swelling agents. [Figure 10] FIG. 1 is a schematic diagram showing the mechanism of ground improvement using the technology of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments will be described below with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing will be designated by the same reference numerals, and redundant descriptions will be omitted where appropriate. Furthermore, the embodiments are merely examples and do not limit the invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0012] In addition, the dimensions (thickness, length, width, etc.) of each component shown in the drawings may be enlarged or reduced as appropriate for ease of understanding. Furthermore, the dimensions of multiple components do not necessarily represent their relative sizes, and even if a component A is depicted as being thicker than another component B in the drawings, it is possible that component A is thinner than component B.

[0013] [Causes of liquefaction] The causes of liquefaction include the following factors related to the sandy ground: (1) Groundwater level (2) Ground density As an incentive (3) Duration of earthquake shaking In other words, the higher the groundwater level, the lower the density of the ground, and the longer the shaking lasts, the more likely liquefaction is to occur. The technology disclosed herein focuses on the above factors (1) and (2) and prevents liquefaction by lowering the groundwater level and increasing the ground density.

[0014] Below, we will show the results of inducing liquefaction using a miniature (approximately 1 / 250) shaking table that simulates the ground, and verifying the above-mentioned factors. Figure 1 is a photograph of the experimental system used in this simulation experiment. A transparent container was placed on the shaking table, and 1,100 g of sand (Mikawa silica sand No. 6) that simulated the ground was piled inside. When 340 ml of water was poured into this, the sand became saturated with water, with no puddles on the surface. Hereafter, this state will be referred to as the standard state. This sand was subjected to vibrations with a strength equivalent to a seismic intensity of 5 and a period of 0.4 seconds, and observations were made to see if liquefaction would occur.

[0015] Figure 2 is a graph showing the amount of ground subsidence and the amount of rise in surface water level when the duration of vibration is varied between 0, 30, 60, and 120 seconds. When the duration is 30 seconds or longer, the water level rises above the ground surface. Furthermore, the longer the duration, the greater the amount of ground subsidence and the amount of rise in surface water level. These results show that the longer the duration of shaking, the more likely liquefaction is to occur.

[0016] Figure 3 is a graph showing the tilt of a miniature building when vibrations are applied with different amounts of water added to the sand. The amount of water was changed so that the difference from the standard state was -10g, -5g, 0g, and +5g. Liquefaction occurred at the standard state of -5g. Furthermore, the tilt of the building generally increases the more water there is (i.e., the higher the groundwater level). These results show that the higher the groundwater level, the more likely liquefaction is to occur.

[0017] [First embodiment] 4 is a flowchart showing the flow of processing in the ground improvement method according to the first embodiment of the present disclosure. This ground treatment method includes step S1 of placing a water-absorbing swelling agent in a placement location that includes at least the ground surface of the target ground.

[0018] The target ground is the ground to be improved. This may include ground to be prevented from liquefaction, as well as, for example, a muddy ground surface over which people or vehicles pass and which is to be dried or hardened.

[0019] The placement location is a location where the water-absorbing swelling agent is placed. The placement location includes at least the ground surface. As long as it includes the ground surface, the placement location may be almost the ground surface alone, may be a series of depth regions extending from the ground surface to the interior of the ground, or may include the ground surface and several discontinuous regions within the ground.

[0020] The water-absorbent swelling agent may be placed at the placement location by any suitable method. For example, the water-absorbent swelling agent may be spread on the ground surface. Alternatively, soil may be excavated from the ground surface to a predetermined depth, the water-absorbent swelling agent may be mixed with the excavated soil, and then the excavated soil may be returned to the ground surface. Alternatively, a borehole may be formed from the ground surface to a predetermined depth and filled with the water-absorbent swelling agent. Alternatively, the water-absorbent swelling agent and soil may be alternately deposited in the formed borehole.

[0021] As a more specific example, the water-absorbing swelling agent may be placed using a casing pipe whose tip is closed when pressed downward and opened when withdrawn upward. Such a casing pipe may be, for example, a casing pipe used in a sand compaction pile construction method. This casing pipe is pressed vertically downward into the ground at the placement location. This forms a borehole such that the hole wall is protected by the casing pipe. After a sufficient amount of water-absorbing swelling agent is poured into the internal space of the casing pipe, the casing pipe is withdrawn upward, thereby placing the water-absorbing swelling agent in a series of depth regions extending from the ground surface to the interior of the ground.

[0022] The water-absorbing swelling agent may be a material capable of expanding against a reaction force from the surroundings when absorbing water. For example, the water-absorbing swelling agent may be a superabsorbent polymer containing a material containing a water-absorbing polymer. Such superabsorbent polymers are commercially available and relatively easy and inexpensive to obtain. Such water-absorbing swelling agents absorb moisture from the surrounding ground, expanding and hardening. When such a water-absorbing swelling agent is placed at a location, the density of the surrounding ground area increases and compacts, and the water in the ground is absorbed, lowering the groundwater level. As a result, liquefaction can be prevented without adverse effects such as land subsidence. Furthermore, by placing the water-absorbing swelling agent in an area including the ground surface, for example, the muddy ground surface can be improved, resulting in a dry and hardened ground surface.

[0023] Such water-absorbing swelling agents may be, for example, soil improvement agents that contain a water-absorbing polymer as the main component and a viscous polymer or inorganic mineral as a blend. When such water-absorbing swelling agents are applied to mud, they disperse among the soil particles. The water-absorbing swelling agent then absorbs moisture in the mud, causing the polymer to expand and the viscous components to dissolve. Over time, for example, due to rainfall, the water-absorbing swelling agent absorbs more moisture and expands significantly. As a result, the density of the ground increases.

[0024] More preferably, the water-absorbing swelling agent is made of a material that has little impact on the environment, such as a material that has a pH in the neutral range, is below the standard value of soil environmental standards, and is highly safe for living organisms.

[0025] As described above, according to this embodiment, it is possible to prevent liquefaction and improve the ground near the surface at low cost and easily.

[0026] The water-absorbing swelling agent may be disposed in one location within a surrounded area, but preferably in multiple locations. The multiple locations may be spaced apart in a grid pattern when viewed from above, or may be randomly spaced apart when viewed from above.

[0027] By providing multiple placement locations, it is possible to more effectively prevent liquefaction and improve the ground near the surface.

[0028] The ground density of the placement location may be lower than a predetermined value. Ground with low density and gaps between the soil particles that make up the ground is considered to be at a higher risk of liquefaction. By applying the technology of the present disclosure to such ground, liquefaction can be more effectively prevented. In other words, the ground at the placement location may contain more gaps than a predetermined value, resulting in a ground density lower than the predetermined value.

[0029] The ground where the agent is to be placed may contain moisture that allows the agent to absorb and expand. If the ground where the agent is to be placed does not contain moisture, the agent must wait for the ground to absorb moisture through rainfall or the inflow of surrounding groundwater, or must be artificially moistened. In contrast, by applying the technology of the present disclosure to moist ground, the agent can immediately absorb moisture and expand. This allows for more rapid prevention of liquefaction and ground improvement near the surface.

[0030] [Second embodiment] 5 is a flowchart showing the flow of processing in a ground improvement method according to a second embodiment of the present disclosure. This ground treatment method includes step S2 of adding moisture to the placement location in addition to step S1 of the ground improvement method shown in FIG.

[0031] Moisture may be applied to the placement site in any suitable manner, for example, by spraying water onto the placement site from above, or by running a pipe underground that points to the placement site and supplying water to the placement site through the pipe.

[0032] According to this embodiment, even if there is not enough moisture at the placement location, by adding moisture, the water-absorbing expanding agent can expand, preventing liquefaction and improving the ground near the surface.

[0033] [Third embodiment] Fig. 6 is a flowchart showing the processing flow of a ground improvement method according to a third embodiment of the present disclosure. This ground treatment method includes step S3 of scraping off the mounded water-absorbent swelling agent in addition to step S1 of the ground improvement method shown in Fig. 4. As a result, the portion where the water-absorbent swelling agent is placed may be at the same height as the ground surface, lower than the ground surface, or may be at a height not exceeding a predetermined height above the ground surface.

[0034] The placed water-absorbing swelling agent may swell after absorbing water, causing it to rise above the ground surface. In this case, unevenness occurs on the ground surface, which should be flat. According to this embodiment, by scraping off the raised water-absorbing swelling agent in step S3, the surface can be returned to a flatter shape after the ground improvement.

[0035] [Fourth embodiment] The fourth embodiment is a ground in which a water-absorbing swelling agent is placed in an arrangement location that includes at least the ground surface, and is real estate.

[0036] The water-absorbing swelling agent placed in the ground in this embodiment may be a material that can expand while resisting a reaction force from the surroundings when absorbing water.

[0037] In the ground of this embodiment, the water-absorbing swelling agent may be disposed at a plurality of locations.

[0038] In the ground of this embodiment, the density of the soil at the location where the water-absorbing swelling agent is disposed may be lower than a predetermined value.

[0039] According to this embodiment, ground with the surface layer improved to prevent liquefaction can be provided inexpensively and easily.

[0040] [Evaluation experiment] The present inventors conducted an evaluation experiment to confirm the effectiveness of the present disclosure. The experiment contents are as follows. 1. Prepare a miniature (approximately 1 / 250) shaking table that simulates the ground (see Figure 1). 2. Pile water-saturated sand 6 cm deep on the vibrating table. 3. Apply vibrations to the sand for 60 seconds, with a period of 0.4 seconds and an intensity equivalent to a seismic intensity of 4-5. Confirm that liquefaction occurs. 4. Remove 0.1 cm of sand from the surface and mix it with the water-absorbing swelling agent. Then, place this back on top of the remaining sand on the vibrating table and vibrate it in the same way as above. 5. Repeat the experiment by changing the depth of the sand into which the water-absorbing swelling agent is mixed to 0.25cm, 0.5cm, 1cm, and 2cm, and subjecting each to the same vibration as above.

[0041] Figures 7 and 8 are side and top views of the setup for this experiment, showing the state when the depth of the sand into which the water-absorbing swelling agent was mixed was 2 cm.

[0042] The results of the experiment showed that no liquefaction occurred when the depth of the sand that was removed and mixed with the water-absorbing swelling agent was 0.1 cm, 0.25 cm, 0.5 cm, 1 cm, or 2 cm. This confirmed the effectiveness of this disclosure at the model level.

[0043] Figure 9 is a photograph showing the condition of multiple water-absorbing swelling agents placed and subjected to vibration. The left image is before water absorption, and the right image is after water absorption. In either case, before or after water absorption, no liquefaction occurred. In particular, the water-absorbing swelling agents after water absorption expanded in volume by more than 10 times compared to before water absorption, which shows that they had sufficiently compacted the ground.

[0044] Figure 10 is a schematic diagram showing the mechanism of ground improvement using the technology disclosed herein. The left diagram shows multiple water-absorbing expansion agents placed at regular intervals from the ground surface into the ground. The right diagram shows the water-absorbing expansion agents absorbing water and expanding. As shown above, by placing the water-absorbing expansion agents in locations including the ground surface, it is clear that liquefaction can be prevented by both lowering the groundwater level and increasing the ground density, and ground improvement at the ground surface can be achieved.

[0045] The present invention has been described above based on the embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of the respective components and treatment processes, and that such modifications are also within the scope of the present invention.

[0046] Any combination of the above-described embodiments and modifications is also useful as an embodiment of the present disclosure. A new embodiment resulting from the combination has the combined effects of the combined embodiments and modifications.

[0047] When understanding the abstract technical ideas of the embodiments, the technical ideas should not be interpreted as being limited to the contents of the embodiments. The above-described embodiments and variations are merely illustrative examples, and many design modifications, such as changes, additions, and deletions of components, are possible. In the embodiments, the contents in which such design modifications are possible are emphasized by adding the notation "embodiment." However, design modifications are also permitted even in contents without such notation. [Industrial Applicability]

[0048] The ground improvement method disclosed herein can be widely used in fields such as civil engineering, building design, architecture, agriculture, and soil improvement. [Explanation of symbols]

[0049] S1: Place the water-absorbing expansive material in the target ground at least at the ground surface. a step of: S2: Adding moisture to the placement location; S3: A step of scraping off the water-absorbing swelling agent that has risen to the surface of the ground.

Claims

1. A ground improvement method comprising the step of placing a water-absorbing swelling agent at a placement location that includes at least the ground surface of a target ground.

2. 2. The method for improving ground according to claim 1, wherein the water-absorbing swelling agent is a material that can expand while resisting a reaction force from the surroundings when absorbing water.

3. The ground improvement method according to claim 1, wherein there are a plurality of said placement locations.

4. 2. The ground improvement method according to claim 1, wherein the density of the ground at the placement location is lower than a predetermined value.

5. 2. The method for improving ground according to claim 1, wherein the ground at the location where the water-absorbing swelling agent is placed contains moisture that can be absorbed by the water-absorbing swelling agent to expand.

6. The method for improving ground according to claim 1, further comprising the step of providing moisture to the placement location.

7. 2. The method for improving ground according to claim 1, further comprising the step of scraping off the water-absorbing swelling agent that has risen to the ground surface.

8. A ground characterized in that a water-absorbing swelling agent is placed in an area including at least the ground surface.

9. 9. The ground according to claim 8, wherein the water-absorbing swelling agent is a material that can expand while resisting a reaction force from the surroundings when absorbing water.

10. The ground according to claim 8, characterized in that there are a plurality of said placement locations.

11. The ground according to claim 8, wherein the density of the ground at the placement location is lower than a predetermined value.

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