JP7492846B2 - Reinforcement structure and method for underground cavity - Google Patents

Description

The present invention relates to a reinforcement structure and a reinforcement method for underground cavities.

Cavities in the ground due to deterioration of port or river conservation structures (revetments, quays, embankments) are occurring in various places. In the past, these cavities were filled with crushed stone, etc., but in some cases, liquefied treated soil has been used.

However, if the hole is backfilled with crushed stone or other materials, compaction is difficult, raising concerns that the cavity may reoccur. In addition, backfilling with crushed stone or other materials requires the placement of large heavy machinery and vehicles on the ground that has been weakened by the underground cavity, raising safety concerns.

On the other hand, filling with liquefied treated soil requires identifying the cause of the underground cavity before use, as there is a risk of leakage.

Patent Document 1 describes a method of backfilling underground spaces, such as abandoned mines, mining sites, and tunnels, in which embankments are constructed at a certain distance apart using low-fluidity liquefied treated soil, and high-fluidity liquefied treated soil is repeatedly injected between the embankments.
However, with this method, the embankment is formed in a hill-like shape, making it difficult for the embankment to reach the ceiling of the underground space, and the gap that occurs at the top of the embankment must be sealed by injecting a highly adhesive caulking material.

Patent Document 2 describes a method of closing an underground space by placing a folded bag body, which can be restored to a size sufficient to block the area, in a section to be blocked in an underground space such as a tunnel or an underground mining site, supplying air to the bag to expand it, and then supplying a foamable filler such as a two-part mixture type urethane foam into the bag and filling it to replace the air, thereby forming a bulkhead (partition wall) with the bag body pressed against the area, and filling the area blocked by at least two bulkheads with a filler such as cement, thereby closing the underground space.
However, with this method, there are concerns that the bulkhead made of the bag and urethane foam may not have sufficient strength, especially when used directly under important structures that are subject to dynamic loads, such as revetments, quays, and roads. There are also concerns about the effect of heat generated by the urethane foam on the bag. Furthermore, when the structure is to be renewed, the urethane foam cannot be recycled as soil.

Patent Document 3 describes a method of filling underground cavities containing water, such as underground waterways, abandoned mines, air raid shelters, and natural caves, by filling a first filler made of soil, soil cement, and an accelerator at a predetermined interval to form partitions, and filling the spaces between the partitions with a second filler made of soil and soil cement to fill the underground cavities. It also describes filling the first filler in a state in which it is stored in a cylindrical bag-shaped body made of a flexible material. The cylindrical bag-shaped body serves as a formwork to suppress the fluidity of the first filler, and is a cylindrical bag (which may or may not have a bottom), and it is said that a resin material or steel material formed into a mesh shape, or a rubber material formed into a balloon shape, can be used.
However, in this method, there is a concern that the tubular bag-shaped body may not be expanded properly when the first filler is stored in the tubular bag-shaped body because the viscosity of the first filler is high. There is also a concern that the heat generated by the first filler may affect the bag-shaped body. Furthermore, excavation and removal are difficult when updating the structure.

Japanese Patent Application Laid-Open No. 9-125900 JP 2014-190135 A JP 2008-13910 A

The object of the present invention is to provide a reinforcement structure and method for underground cavities in which the bag body is not easily damaged by liquefied treated soil, the liquefied treated soil does not leak from the bag body, the liquefied treated soil easily expands the bag body, and the underground cavities can be reliably reinforced, and further, the reinforcement structure can be easily excavated and removed when updating the reinforcement structure, and can be recycled as soil.

[1] Reinforcement structure for underground cavity [1-1] A reinforcement structure for an underground cavity, characterized in that a soil-filled bag body formed by filling an impermeable bag body with liquefied treated soil and hardening it is placed in at least a part of the underground cavity.
[1-2] A reinforcement structure for an underground cavity, characterized in that a soil-filled bag made by filling an impermeable bag with liquefied treated soil and hardening it is placed in the soil outflow area that caused the underground cavity to form, and the remaining part of the underground cavity is filled with filling material.
[1-3] A reinforcement structure for an underground cavity, characterized in that the underground cavity is filled with one or more soil-filled bags formed by filling and hardening a water- impermeable bag with liquefied treated soil containing a solidifying agent and adjusted mud water ^obtained by adding water to soil particles to have a moisture content of 80 to 300 mass % and a density of 1.2 to 1.5 g/cm3.
[1-4] A reinforcement structure for an underground cavity, characterized in that the underground cavity is filled with a plurality of laterally spaced soil-filled bags formed by filling impermeable bags with liquefied treated soil and hardening the bags, and with filler material filled between the bags.

[2] A method for reinforcing an underground cavity, comprising: a through-hole forming step of forming a through-hole in a surface layer of the ground above the underground cavity, the through-hole leading vertically to the underground cavity;
a bag placement step in which an impermeable bag connected to a lower portion of the hose is placed in a folded state in an underground cavity through the through hole;
A soil filling step of filling the bag with liquefied soil sent from a hose;
and a soil hardening step of hardening the liquefied treated soil,
A method for reinforcing an underground cavity, comprising reinforcing at least a portion of the underground cavity with a soil-filled bag formed by filling the bag with liquefied treated soil and hardening the soil.

Here, the soil filling step is a step of filling the bag with fluidized treated soil containing a solidifying material and an adjusted muddy water obtained by adding water to soil particles to have a moisture content of 80 to 300 mass % and a density of 1.2 to 1.5 g/cm3, which is sent from a hose to the bag, and an ^example of a mode in which the entire underground cavity is filled with one or more soil-filled bags to reinforce it can be given.

Another example is a form in which multiple locations in an underground cavity are reinforced with multiple soil-filled bags spaced apart horizontally, and the spaces between them are reinforced with filler material.

It is preferable to include an investigation and measurement step prior to the bag placement step, in which a camera and measuring instrument are placed in the underground cavity through the through hole, and the condition of the underground cavity is investigated using the camera, and the size of the underground cavity is measured using the measuring instrument.

An example of the size of the underground cavity is to measure the height of the underground cavity directly below the hole.

An example of the size of the underground cavity is to measure the height of the underground cavity directly below the through hole and the length of the underground cavity in the lateral direction.

It is preferable that the height of the center of the bag when inflated is 1 to 1.3 times the height of the underground cavity. If it is less than 1 time, it will be difficult for the bag to abut against the ceiling of the underground cavity, and if it exceeds 1.3 times, it will be difficult to inflate the folded bag neatly.

Between the bag placement process and the soil filling process, a bag expansion process can be included in which the bag is inflated with air sent from a hose. When the bag is inflated with air, the bag's weight increases very little, so it tends to move sideways along the bottom of the underground cavity, and it tends to expand to fill almost the entire area of the underground cavity.

However, if there is accumulated water in the underground cavity, the bag will float in the accumulated water during the bag expansion process and will not spread properly to the bottom of the underground cavity. Therefore, it is preferable to omit the bag expansion process and perform the soil filling process, and expand the bag from the bottom of the underground cavity with liquefied treated soil, which is heavier than water.

It is preferable to form a filling confirmation hole in the surface layer of the ground that leads vertically to the underground cavity, separate from the through hole.

[Action]
The filling material for the bag is required to have the following properties:
・It is heavier than water, but the weight of the filling material can reduce the burden on the bag. ・It has the fluidity to push the bag open and ultimately fill the entire underground cavity. ・It generates little hardening heat and has little effect on the bag. ・It has the strength required by the administrator, and can be easily excavated and removed.

Fluidized treated soil satisfies the above-mentioned performance requirements and is the best choice as a filling material for bags for the following reasons (1) to (4).
(1) The unit weight of liquefied treated soil is equivalent to that of the ground. (Reference) Unit weight of candidate filling materials: Urethane foam, air mortar, air milk < water (10 kN/m ³ ) < liquefied treated soil (13-18 kN/m ³ ) < mortar, concrete (23 kN/m ³ )
When the filling material is poured into the bag, it spreads from the bottom, pushing the bag apart. It is then filled into the top of the bag while applying pressure to the sides. When pressure is applied to the sides, downward tension is applied to the hose, which may cause the bag to tear and become damaged. The bag is made of a thin material and is folded compactly, making it difficult to reinforce it with a strong material. From this perspective, it is better for the filling material to be lighter than heavy materials such as concrete or mortar.
Also, if there is standing water in the underground cavity, it is necessary to fill the bag with a material that is heavier than water in order to expand the bag from the bottom.
Therefore, liquefied treated soil is the best option as it is lighter than concrete or mortar, heavier than water, and has a unit weight equivalent to that of ground.

(2) Fluidized treated soil has high fluidity and filling properties, and does not require compaction. The filling material must be placed inside the bag and then spread throughout the entire underground cavity. Concrete and mortar require the use of a vibrator or other device to fill them, but there is no space to attach a vibrator. Fluidized treated soil is a highly fluid material that does not require compaction, and there is a long track record of filling underground cavities (without using bags).
Therefore, liquefied treated soil is the best filler for expanding the bag throughout the entire underground cavity.

(3) The hardening heat of liquefied soil is low. (Reference) Hardening heat of filler candidate materials: liquefied soil (outside temperature + 5°C) < aerated milk, aerated mortar, mortar, concrete (thermally insulated, 40°C to 80°C) < foamed urethane (may rise to 80°C or higher)
Many bags made of thin materials have low heat resistance. The lower the hardening heat of the filling, the smaller the impact on the bag.
Therefore, liquefied treated soil is also the best in terms of hardening heat.

(4) The strength of liquefied treated soil can be controlled and it can also be recycled.
After construction, the filler must be able to exhibit the required strength to reinforce the underground cavity, and must be able to be easily excavated and removed when the reinforcing structure is to be renewed.
Concrete and mortar are strong but difficult to remove. Air mortar, air milk, and foamed urethane can be physically removed, but they become construction by-products or are disposed of as waste.
Therefore, liquefied treated soil, which allows for strength control and can also be recycled as soil, is the best option.

Fluidized treated soil is moderate in weight and therefore unlikely to damage the bag body, has high fluidity and therefore excellent filling ability into the bag body, has low hardening heat and therefore little impact on the bag body, strength can be controlled, and it can be recycled. Therefore, according to the present invention, the bag body is unlikely to be damaged by the fluidized treated soil, so the fluidized treated soil does not leak from the bag body and can effectively expand the bag body, reliably reinforcing underground cavities, and furthermore, when renewing the reinforcing structure, it can be easily excavated and removed, and can be recycled as soil.

FIG. 1 shows a method for reinforcing an underground cavity according to a first embodiment, in which (a) is a cross-sectional view showing a through-hole forming step and a part of an investigation and measurement step, and (b) is a cross-sectional view showing another part of the investigation and measurement step. FIG. 2 is a plan view showing the size and shape of the through hole, filling confirmation hole, and underground cavity. 3A is a perspective view of a bag selected in the bag arrangement step, FIG. 3B is a front view of the bag folded and inserted into a pipe, and FIG. 3C is a front view of the bag after insertion. FIG. 4A is a cross-sectional view of the bag when it is inserted into the through-hole in the bag placement step, and FIG. 4B is a cross-sectional view of the bag when it is placed in the underground cavity. FIG. 5A is a cross-sectional view of the bag when it starts to be inflated in the bag inflation step, and FIG. 5B is a cross-sectional view of the bag when it is inflated. FIG. 6A is a cross-sectional view of the bag when the liquefied treated soil begins to be injected into the bag during the soil filling process, and FIG. 6B is a cross-sectional view of the bag when it is filled. FIG. 7(a) is a cross-sectional view of a reinforcement structure for an underground cavity that has been completed by sealing the through holes and filling confirmation holes and hardening the liquefied treated soil. FIG. 8 is a cross-sectional view showing a reinforcement structure and a reinforcement method for an underground cavity according to a second embodiment. FIG. 9 is a cross-sectional view of the completed reinforcement structure for an underground cavity. FIG. 10 shows the reinforcement structure and reinforcement method for an underground cavity of Example 3, where (a) is a cross-sectional view when injection of liquefied treated soil into the bag body begins, and (b) is a cross-sectional view after injection has progressed. Figure 11 shows the reinforcement structure and reinforcement method for an underground cavity of Example 4, where (a) is a cross-sectional view when injection of liquefied treated soil into the bag body begins, and (b) is a cross-sectional view of the completed reinforcement structure for an underground cavity. FIG. 12 is a cross-sectional view showing a bag arrangement step of the underground cavity reinforcing method of the fifth embodiment. FIG. 13 shows the completed reinforcement structure for an underground cavity, (a) being a cross-sectional view and (b) being a plan view.

1. Underground Cavities There are no particular limitations on underground cavities, but examples include underground cavities that have developed near port or river conservation structures (revetments, quays, embankments) due to deterioration, underground cavities below road surfaces, abandoned mines, mineral mining sites, underground pits, and unused buried pipes.
When there is a surface layer of ground above an underground cavity, the surface layer of ground is not particularly limited, but examples thereof include a concrete plate, an asphalt pavement layer, and a soil layer.

2. Impermeable bag The material of the impermeable bag is not particularly limited, but examples thereof include resin, fiber-reinforced resin, cloth, etc. Examples of cloth include those made impermeable by surface coating, inter-thread impregnation, etc. Flexible materials that can be folded to a size that can pass through the through holes are preferable. Needless to say, materials that are as strong as possible are also preferable. The thickness of the bag is appropriately selected so that it can be folded to a size that can pass through the through holes while maintaining strength.

The number of bags used can be determined appropriately depending on the size and shape of the underground cavity, for example as follows.
(a) If the average length of the underground cavity is less than 4 m, one bag shall be used, and if the average is 4 m or more, multiple bags shall be used.
(i) When the ratio of the longest to shortest lengths of the underground cavity is less than 2 (i.e., the planar shape of the underground cavity is close to a circle), one bag body is used, and when the ratio is 2 or more, multiple bags are used.

3. Fluidized treated soil Fluidized treated soil contains mud (adjusted mud made by adding water to soil particles) and a solidifying material, and the mixture is not particularly limited.
The particle size composition of the soil particles is not particularly limited, but it is preferable that the clay and silt content is 10 to 100 mass %.
The water content of the muddy water is not particularly limited, but is preferably 80 to 300 mass %.
The density of the muddy water is not particularly limited, but is preferably 1.2 to 1.5 g/cm ³ .
The solidification material is not particularly limited, but examples thereof include cement, cement-based solidification material, lime-based solidification material, steel slag and alkaline irritant, etc.

4. Through holes The number of through holes may be one or more and can be determined depending on the size, shape, etc. of the underground cavity.
The through hole may serve both as a hole for passing the bag body and as a hole for passing the camera and measuring instrument, or may be dedicated to each purpose.
The method for forming the through holes is not particularly limited, but examples thereof include boring and core drilling.
The diameter of the through hole is not particularly limited, but is preferably 100 to 200 mm. This is because a large hole cannot be drilled directly above the underground cavity for safety reasons, and drilling a large hole is also difficult from the viewpoints of the selection of construction machinery and costs.

5. Survey and Measurement It is preferable to use a digital camera, and the captured image data can be sent to the ground and monitored and recorded as video or as still images.
The measuring instrument is not particularly limited, but examples thereof include a laser range finder, a laser scanner, etc. The measuring instrument for measuring the height of the underground cavity may be a tape measure.

[Example 1]
A method for reinforcing an underground cavity 5 according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 7. FIG.
The underground cavity 5 to be reinforced in this embodiment occurs in a revetment structure.
The revetment structure before the underground cavity is created consists of a vertical concrete wall 1 facing the sea, soil 2 held back by the concrete wall 1, and a concrete slab as the ground surface layer 3 laid on top of the soil 2. A Hume pipe 4 is buried in the soil 2 from the land toward the sea, and the tip of the Hume pipe 4 penetrates the concrete wall 1 and opens into the sea.
After the underground cavity is formed, soil 2 near the concrete wall 1 of the revetment structure flows out, creating an underground cavity 5 as shown in FIG.

(1) Through-hole forming process Before the through-hole forming process, the underground cavity 5 hidden under the ground surface layer 3 was detected by non-destructive testing (non-destructive testing process). In detail, a radar-type underground cavity exploration device (not shown) was used to irradiate electromagnetic waves from above the ground surface layer 3, and the underground cavity 5 was detected by the reflected waves.
Then, as shown in Figs. 1 and 2, a through hole 6 leading from above ground to the underground cavity 5 was formed above the vicinity of the center of the underground cavity 5 in the ground surface layer 3.
Furthermore, a filling confirmation hole 7 was formed above near the end of the underground cavity 5 in the ground surface layer 3, leading from above ground to the underground cavity 5. It is preferable to form the filling confirmation hole 7 near the end farthest from the center of the underground cavity 5, i.e., near the upper end in Fig. 2, but for convenience of showing it in other cross-sectional views, it is assumed that it is formed near the right end in Fig. 2.

(2) Survey and Measurement Process An apparatus comprising a digital camera 9 and a laser range finder as a measuring instrument 10 attached to the lower end of a rod 8 was placed in the underground cavity 5 through the through hole 6 .
As shown in FIG. 1(a), when the measuring device 10 was positioned at the lower end of the through hole 6, the height of the underground cavity directly below the through hole 6 was measured to be 0.63 m.
As shown in Figure 1(b), the horizontal length of the underground cavity was measured and averaged while rotating the measuring device 10 together with the rod 8 when it was positioned at a height below (0.1 m), in the middle (0.3 m), and above (0.5 m) the bottom of the underground cavity 5. As a result, as shown in Figure 2, the length in the sea-land direction was 1.36 m (= 0.51 m + 0.85 m), and the length in the perpendicular direction was 2.18 m (= 1.10 m + 1.08 m).
From these results, it was found that the shape of the underground cavity 5 was an irregular, roughly elliptical shape, and the volume of the underground cavity 5 was calculated to be approximately 1.4 ^m3 .

As shown in Figure 1(b), the deterioration of the revetment structure was observed while rotating the camera 9 together with the rod 8 when it was positioned 0.3 m above the bottom of the underground cavity 5. As a result, as shown in Figure 2, it was confirmed that the Hume pipe 4 was located in the center of the underground cavity 5, and a bright area was observed in the area circled in Figure 1(b). This bright area is thought to be the damaged area (or loose joint) of the Hume pipe 4, and the soil outflow area R that caused the underground cavity to form. In other words, the mechanism by which the underground cavity formed is thought to be that some of the soil 2 that was originally clogged connected from the soil outflow area R to the Hume pipe 4, and was sucked out by seawater that flows in and out due to the tides, etc.

(3) Bag placement process As shown in Fig. 3(a), a bag 11 made of impermeable and scratch-resistant resin was selected, the size of which when inflated corresponds to the size of the underground cavity 5. The height of the center of the bag 11 when fully inflated is 0.8 m, which is slightly higher than the height of the underground cavity directly below the through hole 6, and the shape of the bag 11 is an octagon with a diameter of 2 m. The bag is connected to the bottom of a hose 12 made of flexible resin, and is closed except for the part connected to the hose.
3(b) and (c), the bag body 11 was folded thinly and inserted into a pipe 13 (e.g., a PVC pipe). The bag body 11 was folded so that it could be accommodated in the pipe 13 and could easily be expanded in the underground cavity.

As shown in FIG. 4(a), the bag body 11 was inserted into the through hole 6 together with the pipe 13, and then, as shown in FIG. 4(b), the bag body 11 was placed in the underground cavity 5 with the bag body 11 protruding from the pipe 13.
The survey and measurement device was then placed in the underground cavity 5 through the filling confirmation hole 7, and the state of the bag body 11 was checked with the camera 9. It was found to be slightly loose, but was mostly folded.

(4) Bag Inflation Process As shown in Fig. 5(a), an air compressor (not shown) was used to start inflating the bag 11 with air sent from a hose 12. When the state of the bag 11 at this time was checked with a camera 9, the bag 11 started to inflate in all directions.
As shown in Fig. 5(b), when the bag 11 is further inflated with air, the bag 11 tends to shift sideways after coming into contact with any side surface of the underground cavity 5 (because there is no filling material), and so the bag 11 inflates to fill almost the entire area of the underground cavity 5. Then, when the inflow of air is stopped after the bag 11 is fully inflated, the bag 11 deflates slightly due to natural air escape, and eventually reaches an intermediate inflated state as shown in Fig. 5(b).

(5) Soil filling process Table 1 below shows the analysis results of the muddy water, which is the soil material, and Table 2 shows the mix proportions and properties of the liquefied treated soil, which is a soil mixture made by mixing the muddy water with a solidifying agent. The mix proportions of the liquefied treated soil were made for filling, with excellent fluidity and packing properties. Blast-furnace cement type B was used as the solidifying agent.

As shown in Figure 6(a), a mortar pump (not shown) was used to start injecting liquefied treated soil 14 sent from a hose 12 into the bag 11 that had been partially inflated as described above. A pressure gauge (not shown) was attached to the hose 12 to monitor the pressure during filling. The state of the bag 11 and liquefied treated soil 14 at this time was confirmed by a camera 9. The liquefied treated soil 14 was injected to replace the air, and spread neatly inside the bag 11.
6(b), when the bag 11 was filled with the liquefied treated soil 14, the bag 11 expanded to its full extent and came into contact with almost the entire circumference of the side surface of the underground cavity 5 as well as the bottom and top surfaces of the underground cavity 5. The camera 9 was removed immediately before this filling.
By visually checking the bag 11 abutting the top surface through the filling confirmation hole 7, it was confirmed that the liquefied treated soil 14 had been filled, and filling was then terminated. Although the final filling check can be made through the filling confirmation hole 7 in this way, it was found that checking with a camera during expansion and filling is effective in that the state and changes during expansion and filling can be visually confirmed and any abnormalities can be immediately detected.
After filling, the bag was left to stand for 30 minutes to confirm that the liquefied treated soil 14 and the bag 11 did not sink or otherwise move.

(6) Soil hardening process As shown in Fig. 7, the through hole 6 and the filling confirmation hole 7 were blocked with non-shrink mortar 16, and then the liquefied treated soil 14 was hardened. In this way, the underground cavity 5 was filled with one of the soil-filled bags 15 formed by filling the bag 11 with liquefied treated soil 14 and hardening it, completing a reinforcement structure for the underground cavity 5.

The reinforcement structure for the underground cavity 5 completed by the above-mentioned method has the following advantages.
(A) The liquefied treated soil 14 is moderate in weight and therefore unlikely to damage the bag body 11, has high fluidity and therefore excellent filling ability into the bag body 11, has low hardening heat and therefore has little effect on the bag body 11, strength control is possible, and it can be recycled. Therefore, the bag body 11 is unlikely to be damaged by the liquefied treated soil 14, so the liquefied treated soil 14 does not leak from the bag body 11 and expands the bag body 11 well. Thus, the underground cavity 5 can be reliably reinforced by the soil-filled bag body 15, and furthermore, it can be easily excavated and removed when updating the reinforcing structure, and can be recycled as soil.

(i) It is sufficient to form through holes 6 etc. in the surface layer 3 of the ground, and no large-scale construction work is required.
(c) By investigating the condition of the underground cavity 5 with a camera 9 inserted through the through hole 6, it is possible to obtain information that is useful for understanding the mechanism of underground hollowing and for determining the effectiveness of applying this reinforcement method.
(e) By measuring the size of the underground cavity 5 with a measuring instrument 10 passed through the through hole 6, one or more bag bodies 11 corresponding to the same size can be selected, thereby avoiding the difficulty in expanding the bag body 11 if it is too large, and the lack of reinforcement if the bag body 11 is too small.
(O) Since there is a bag expansion process in which the bag 11 is inflated with air between the bag placement process and the soil filling process, as described above, the bag 11 tends to inflate nicely so as to fill almost the entire underground cavity 5.

In Example 1, the survey and measurement process can be omitted. This is because the size of the underground cavity 5 can be detected in some cases using the non-destructive testing process described above.

[Example 2]
The reinforcement method and structure for an underground cavity according to the second embodiment are as shown in FIGS. 8 and 9.
In the investigation and measurement process, the size of the underground cavity 5 measured was larger than that in Example 1 (for example, the average length of the underground cavity was 4 to 10 m).
In the bag placement process, a plurality of bags 11 were selected such that the total size of the plurality of bags when inflated corresponds to the size of the underground cavity 5, and each bag 11 was placed in the underground cavity 5 in a folded state through a through hole 6 formed in a position different from the through hole 6 used for the investigation and measurement (the latter through hole 6 was formed in a position of the ground surface layer determined based on a bag placement plan based on the measured size of the underground cavity 5 and the number of bags 11).
The second embodiment is different from the first embodiment in the above point, and the rest is common to the first embodiment.

According to this embodiment, as shown in FIG. 9, a reinforcement structure for the underground cavity 5 is completed by filling the underground cavity 5 with multiple soil-filled bags 15, and the same effects (A) to (E) as those of the first embodiment are obtained.

[Example 3]
The reinforcement method and structure of the underground cavity of the third embodiment are as shown in FIG.
During the investigation and measurement process, it was confirmed that there was water 18 in the underground cavity 5.
- After the bag placement process, the bag expansion process was omitted and the soil filling process was performed, i.e., the bag 11 was filled with liquefied treated soil 14 and the bag 11 was inflated, which is different from the embodiment, but the rest is the same as embodiment 1.

According to this embodiment, the bag 11 can be expanded from the bottom of the underground cavity 5 using the liquefied treated soil 14, which is heavier than water.
In this embodiment as well, a reinforcement structure for an underground cavity 5 similar to that shown in FIG. 6(b) of the first embodiment is finally completed, and the same effects (a) to (d) as those of the first embodiment are obtained.

[Example 4]
The reinforcement method and structure of the underground cavity of the fourth embodiment are as shown in FIG.
In the bag placement process, the bag 11 (having a height at the center when inflated of, for example, 0.3 m, which is lower than the height of the underground cavity, and a diameter of, for example, 0.7 m, which is shorter than the horizontal length of the underground cavity) was placed against the soil outflow portion R that caused the underground cavity 5 to occur, and the bag expansion process was omitted and the bag 11 was filled with liquefied treated soil 14.
- After that, the remaining part of the underground cavity 5 was filled with liquefied treated soil as a filler 17 through the through hole 6;
This embodiment differs from the embodiment in that a hardening process was then carried out, but the rest is the same as embodiment 1.

According to this embodiment, as shown in FIG. 11(b), a soil-filled bag 15 is placed in the soil-flow area R, and the remaining part of the underground cavity 5 is filled with a filler material 17 to complete the reinforcement structure of the underground cavity 5, and the same effects (a) to (c) as those of the first embodiment are obtained.

[Example 5]
The reinforcement method and structure of the underground cavity of the fifth embodiment are as shown in Figs. 12 and 13 .
In the investigation and measurement process, the size of the underground cavity 5 measured was larger in the sea-land direction than in Example 1 (for example, 5 to 10 m), but the perpendicular direction was about the same as in Example 1.
In the bag placement process, the two bags 11 were placed in the underground cavity 5 in a folded state through the through holes 6 formed in two positions near the sea and near the land, different from the through holes 6 used for the investigation and measurement.
After the soil filling step, the space between the two soil-filled bags (15) is filled with liquefied soil as a filler 17 through the through hole 6.
This embodiment differs from the embodiment in that a hardening process was then carried out, but the rest is the same as embodiment 1.

According to this embodiment, as shown in FIG. 13, the underground cavity 5 is filled with a plurality of soil-filled bags 15 spaced apart in the lateral direction and with filler material 17 filled between the bags, completing a reinforcement structure for the underground cavity 5, and providing the same effects (A) to (C) as in embodiment 1.

The present invention is not limited to the above examples, and can be modified as appropriate without departing from the spirit of the invention.

REFERENCE SIGNS LIST 1 Concrete wall 2 Soil 3 Ground surface 4 Hume pipe 5 Underground cavity 6 Through hole 7 Filling confirmation hole 8 Rod 9 Camera 10 Measuring instrument 11 Bag 12 Hose 13 Pipe 14 Fluidized treated soil 15 Bag containing soil 16 Non-shrink mortar 17 Filling material 18 Pooled water R Soil runoff area

Claims (8)

The reinforcement structure for an underground cavity is characterized in that the underground cavity (5) is filled with one or more soil-filled bags (15) formed by filling and hardening a water-impermeable bag (11) with liquefied treated soil (14) containing adjusted mud water obtained by adding water to soil particles and having a moisture content of 80 to 300 mass % and a ^density of 1.2 to 1.5 g/cm 3, and a solidifying agent. a through-hole forming step of forming a through-hole (6) in the ground surface layer (3) above the underground cavity (5) so as to vertically communicate with the underground cavity (5);
a bag placement step of placing the water-impermeable bag (11) connected below the hose (12) in a folded state in the underground cavity (5) through the through hole (6);
a soil filling step of filling the bag (11) with liquefied treated soil (14) containing a solidification material and adjusted mud water having a moisture content of 80 to 300 mass % and a density of 1.2 to 1.5 g/cm ^3, which is obtained by adding water to soil particles, sent from a hose (12);
and a soil hardening step of hardening the liquefied treated soil (14),
This method for reinforcing an underground cavity is characterized in that the entire underground cavity is filled with one or more soil-filled bags (15) formed by filling the bags (11) with liquefied treated soil (14) and hardening the bags to reinforce the cavity. A method for reinforcing an underground cavity as described in claim 2, which includes an investigation and measurement step of placing a camera (9) and a measuring instrument (10) in the underground cavity (5) through the through hole (6) prior to the bag placement step, investigating the condition of the underground cavity (5) with the camera (9) and measuring the size of the underground cavity (5) with the measuring instrument ( 10 ). 4. The method for reinforcing an underground cavity according to claim 3 , wherein the size of the underground cavity (5) is determined by measuring the height of the underground cavity directly below the through hole (6). 4. The method for reinforcing an underground cavity according to claim 3 , wherein the size of the underground cavity (5) is determined by measuring the height of the underground cavity directly below the through hole (6) and the lateral length of the underground cavity. 6. The method for reinforcing an underground cavity according to claim 4 or 5 , wherein the height of the center part of the bag body (11) when inflated is 1 to 1.3 times the height of the underground cavity. A method for reinforcing an underground cavity according to any one of claims 2 to 6 , comprising a bag expansion step of inflating the bag (11) with air sent from a hose (12) between the bag placement step and the soil filling step. A method for reinforcing an underground cavity according to any one of claims 2 to 7, comprising forming a filling confirmation hole (7) in the ground surface layer (3) separate from the through hole (6) and leading vertically to the underground cavity (5).

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