JP2014080750A - Method for recovering impervious performance of impervious wall - Google Patents

Abstract

PROBLEM TO BE SOLVED: To close a crack of an impervious wall constructed from a soil improvement body, by supplying carbon dioxide through the use of a flow of water.SOLUTION: A method for recovering impervious performance of an impervious wall 10 includes a step of injecting carbon dioxide into a section with a higher ground water level on the inside or outside of the impervious wall 10 constructed from a soil improvement body.

Description

  The present invention relates to a method for restoring the water shielding performance of a water shielding wall.

In recent years, the water-blocking function of ground improvement bodies whose soil has been improved with cement has attracted attention. For example, the containment of water-impervious walls constructed with ground improvement bodies, such as containment of pollutants (contaminated soil, contaminated water) buried in the ground Needs are increasing. However, there is still a possibility of partial cracks in the impermeable walls due to the earthquake, and there is a demand for countermeasures against cracks in the impermeable walls built in the ground.
Therefore, a technique for self-repairing the shielding function using underground microorganisms has been proposed (Patent Document 1).
Patent Document 1 describes a technique for making a boring hole in a surrounding rock mass from a cavity provided in the ground to contain radioactive waste. At this time, carbon dioxide is injected by applying pressure to the crack generated in the rock during the drilling of the borehole, and the crack is repaired by utilizing the propagation of microorganisms at the crack position.

Japanese Patent No. 4632998

However, the method of Patent Document 1 targets cracks in natural rock where microorganisms exist, and the presence of microorganisms cannot be expected from artificially constructed ground improvement bodies.
In the method of Patent Document 1, carbon dioxide is injected by applying pressure to the crack position after grasping the position of the crack. However, it is actually difficult to grasp the crack position of the impermeable wall built in the ground and inject carbon dioxide by applying pressure to the crack position.
In view of the above-described facts, the present invention aims to provide a method for recovering the water shielding performance by supplying carbon dioxide using the flow of water and closing the cracks of the water shielding wall constructed by the ground improvement body. .

  The method for recovering water-impervious performance of a water-impervious wall according to claim 1 has a step of injecting carbon dioxide into a higher groundwater level inside or outside the water-impervious wall constructed of a ground improvement body. It is characterized by.

According to the first aspect of the present invention, carbon dioxide injected (mixed) into the groundwater side having a high water level infiltrates from the crack into the impermeable wall together with the groundwater due to the water level difference.
Thereby, as shown by the following chemical reaction formula, CO ₃ ²⁻ dissolved in water attracts Ca ²⁺ in the cement paste to form calcium carbonate crystals, which adhere to the cement paste and the like. When calcium carbonate crystals adhere, Ca ²⁺ moves from the inside of the concrete and further binds to CO ₃ ²⁻ so as to compensate for the decrease in calcium ions in the water. Such a reaction is repeated, and calcium carbonate crystals are generated one after another, which adheres and settles on cement paste and the like, and the cracks in the impermeable wall are gradually repaired.

H ₂ O + CO ₂ ⇔ H ₂ CO ₃ ⇔ H ⁺ + HCO ₃ ⁻ ⇔ 2H ⁺ + CO ₃ ²⁻
Ca ²⁺ + CO ₃ ²⁻ ⇔ CaCO ₃ (pH _WATER > 8)
Ca ²⁺ + HCO ₃ ^{− −} CaCO ₃ + H ⁺ (7.5 <pH _WATER <8)

  That is, by utilizing the flow of water that flows into the crack, the crack is blocked inside the impermeable wall and the impermeable performance of the impermeable wall is recovered without specifying the position of the crack.

  According to a second aspect of the present invention, in the method for recovering the water shielding performance of the impermeable wall according to the first aspect, the impermeable wall is constructed in a lattice shape, and water is placed inside or outside the lattice-shaped impermeable wall. Injecting or pumping water and generating a difference in height in the groundwater level.

According to the invention described in claim 2, by injecting or pumping water inside or outside the impermeable wall constructed in a lattice shape, a difference in level of groundwater level is generated inside or outside the impermeable wall. Can be made.
Thereby, either the inner side or the outer side of the water-impervious wall is selected, a difference in level is generated in the water level of the groundwater, and carbon dioxide can be injected into the side of the higher water level of the groundwater. Thereby, carbon dioxide is supplied to the inside of the impermeable wall, and repair of cracks in the impermeable wall can be promoted by the flow of water without specifying the position of the crack.

  The invention according to claim 3 is the method of recovering the water shielding performance of the water shielding wall according to claim 1 or 2, wherein a plurality of boring holes provided along the water shielding wall and the adjacent boring holes are provided. A pump for lowering the groundwater level by pumping groundwater from one side, injecting the carbon dioxide from the other of the adjacent boreholes, and generating the carbon dioxide in the groundwater flow generated by the difference in groundwater level Carbon is diffused in the wall surface of the impermeable wall.

According to the third aspect of the present invention, the water level of one of the adjacent boreholes is lowered, and the carbon dioxide in a wide range on the surface including the borehole due to the difference in the groundwater level between the adjacent boreholes. Can be distributed, and carbon dioxide can be injected into the crack regardless of the position of the crack of the impermeable wall.

According to a fourth aspect of the present invention, in the water shielding performance recovery method for a water shielding wall according to any one of the first to third aspects, contaminated soil is enclosed in the interior surrounded by the water shielding wall. It is characterized by having.
As a result, cracks in the impermeable walls that contain contaminated soil can be blocked by the self-repair function of the impermeable walls with the flow of water without specifying the position of the cracks. It is possible to suppress the outflow of contaminated soil and contaminated water.

  According to a fifth aspect of the present invention, in the method for recovering the water-impervious performance of the impermeable wall according to the first aspect, the impermeable wall is a mountain retaining wall, and a borehole is formed from the natural mountain side toward the water leakage position of the mountain retaining wall. And carbon dioxide is injected from the borehole.

When water leakage from the retaining wall to the excavation space is detected in the retaining wall constructed from the ground improvement body, a borehole is provided from the ground wall side of the retaining wall to the leakage position, and carbon dioxide is injected from the borehole. To do.
As a result, the carbon dioxide is carried to the leakage position by the groundwater on the natural ground side, and the mountain retaining wall can be blocked by the self-repair function.

  Since this invention is set as the said structure, a carbon dioxide can be supplied using the flow of water and the crack of the impermeable wall constructed with the ground improvement body can be obstruct | occluded.

It is a top view for demonstrating the water shielding performance recovery method of the water shielding wall which concerns on 1st Embodiment of this invention. It is a top view for demonstrating the water shielding performance recovery method of the water shielding wall which concerns on 1st Embodiment of this invention. It is XX sectional drawing of FIG. 2 for demonstrating the water-blocking performance recovery method of the water-blocking wall which concerns on 1st Embodiment of this invention. It is XX sectional drawing of FIG. 2 for demonstrating the water-blocking performance recovery method of the water-blocking wall which concerns on 2nd Embodiment of this invention. It is XX sectional drawing of FIG. 2 for demonstrating the water-blocking performance recovery method of the water-blocking wall concerning 3rd Embodiment of this invention. It is sectional drawing for demonstrating the water-blocking performance recovery method of the water-blocking wall which concerns on 4th Embodiment of this invention.

(First embodiment)
The water-blocking performance recovery method for the water-blocking wall 10 according to the first embodiment will be described with reference to FIGS. 1 to 3. As shown in the plan views of FIGS. 1 and 2 and the vertical sectional view of FIG. 3, the water shielding wall 10 is a ground improvement body and is constructed in a lattice shape in plan view. In this specification, for the sake of convenience, the entire ground improvement body including not only the outermost peripheral portion 10G but also the lattice-like portion 10N is referred to as a water-impervious wall 10. Contaminated soil (including contaminated water) 12 is contained in the impermeable wall 10.

The impermeable wall 10 surrounds the contaminated soil 12 with the outermost peripheral portion 10G constructed with a complete lap, and the plan view is constructed in a lattice shape with the internal improved body 10N constructed within the outermost peripheral portion 10G. As an example, a description will be given of a water shielding wall 10 in which one side of the outermost peripheral portion 10G is a square of L1 and is divided into 16 squares of L2 with an internal improvement body 10N.
The impermeable wall 10 is constructed to a depth that penetrates the upper sand layer 18 from the ground surface 32 to reach the clay layer 20 below the sand layer 18, and the lower end of the impermeable wall 10 is embedded in the clay layer 20. ing. Thereby, the movement of groundwater is prohibited between the inside and the outside of the impermeable wall 10, and the contaminated soil 12 and the contaminated water can be contained inside the impermeable wall 10.

Further, the internal ground of the impermeable wall 10 is an internal improvement body 10N constructed in a lattice shape, and is divided into 16 squares each having L2. Thereby, the liquefaction of the internal ground of the impermeable wall 10 is suppressed, and the earthquake resistance of the building can be ensured and the function of containing the contaminated soil 12 can be improved.
In addition, 16 internal grounds divided into squares with one side being L2 are divided according to their positions, and portions where at least one side is in contact with the outermost peripheral part 10G are referred to as outer grounds 42A to 42L. The portion surrounded by 42L is referred to as inner ground 44A to 44D (see FIG. 2).

Although the water-impervious wall 10 is soil-improved with cement and has high water-impervious performance, cracks may occur due to an earthquake. If a crack occurs in the water-impervious wall 10, the water-impervious performance of the water-impervious wall 10 decreases. In particular, when the water shielding performance of the outermost peripheral portion 10 </ b> G of the water shielding wall 10 is deteriorated, the contained contaminated soil 12 and the contaminated water may leak out of the water shielding wall 10.
In the present embodiment, as a means for repairing cracks in the impermeable wall 10 built in the ground, a method of self-repairing concrete cracks using a chemical reaction generated by calcium carbonate crystals is used. Specifically, the water shielding performance of the outermost peripheral part 10G is recovered by the following method.
In order to ensure calcium carbonate crystals, carbon dioxide (not shown) was mixed in the groundwater. Thereby, the crack of the outermost peripheral part 10G can be closed using the flow of groundwater.

That is, carbon dioxide injected into the groundwater side having a high water level infiltrates into the water-impervious wall from the crack in the outermost peripheral portion 10G together with the groundwater due to the difference in water level. Thereby, as shown by the following chemical reaction formula, CO ₃ ²⁻ dissolved in water attracts Ca ²⁺ in the cement paste to form calcium carbonate crystals, which adhere to the cement paste and the like. When calcium carbonate crystals adhere, Ca ²⁺ moves from the inside of the concrete and further binds to CO ₃ ²⁻ so as to compensate for the decrease in calcium ions in the water. Such a reaction is repeated, and calcium carbonate crystals are generated one after another, which adheres and settles on cement paste and the like, and the cracks in the impermeable wall are gradually repaired.

H ₂ O + CO ₂ ⇔ H ₂ CO ₃ ⇔ H ⁺ + HCO ₃ ⁻ ⇔ 2H ⁺ + CO ₃ ²⁻
Ca ²⁺ + CO ₃ ²⁻ ⇔ CaCO ₃ (pH _WATER > 8)
Ca ²⁺ + HCO ₃ ^{− −} CaCO ₃ + H ⁺ (7.5 <pH _WATER <8)

  As described above, by utilizing the flow of groundwater flowing into the crack, the crack is blocked inside the impermeable wall and the impermeable performance of the impermeable wall can be recovered without specifying the position of the crack. . In addition, since the crack of the impermeable wall 10 is randomly distributed over a wide range on the surface of the impermeable wall 10, the outermost peripheral portion 10G of the impermeable wall 10 is widened by adopting the following configuration that effectively uses groundwater. Can be self-healing in range.

  As shown in FIG. 1, the outer periphery 10G of the outermost peripheral portion 10G of the impermeable wall 10 surrounds the outermost peripheral portion 10G and is parallel to the outermost peripheral portion 10G (range surrounded by broken lines R1 to R4). A plurality of drilling holes are drilled. The boreholes are divided into two types, eight pumping holes 16A to 16H for pumping groundwater and eight injection holes 14A to 14H for mixing carbon dioxide into the groundwater depending on the application.

  Here, the injection holes 14A to 14H and the pumping holes 16A to 16H are excavated in a line alternately at positions separated by a predetermined distance L3 from the outermost peripheral portion 10G. The injection holes 14A to 14H are formed on each side. It arrange | positions at both ends and a center part, and the pumping holes 16A-16H are each arrange | positioned between the injection holes 14A-14H.

  Pumping pumps (not shown) are respectively attached to the pumping holes 16A to 16H, and the groundwater can be pumped from the pumping holes 16A to 16H by the pumping pump to lower the groundwater level (groundwater level). As a result, there is a difference in level between the groundwater levels of the pumping holes 16A to 16H that pump up the groundwater with the pumping pump and the groundwater levels of the injection holes 14A to 14H that do not pump up the groundwater. In this state, carbon dioxide is mixed into the groundwater from the injection holes 14A to 14H. Thereby, using the flow of groundwater, carbon dioxide can be distributed over a wide range in the groundwater in the range surrounded by broken lines R1 to R4 in which the injection holes 14A to 14H and the pumping holes 16A to 16H are excavated. .

As shown in FIG. 3, which is a plan view of FIG. 2 and a cross-sectional view taken along line XX of FIG. 2, a building 22 is built on the water-impervious wall 10, Are provided with two water tanks 24 </ b> A and 24 </ b> B for temporarily storing groundwater, and the groundwater flows under the groundwater level 26 of the sand layer 18.
Moreover, between the water tank 24A or the water tank 24B and the outer ground 42A to 42L, the oblique holes 28 excavated by the oblique boring are respectively provided, and the ground water is pumped from the outer ground 42A to 42L to the water tank 24A or the water tank 24B. be able to. Moreover, between the water tank 24A or the water tank 24B and the inner ground 44A to 44D, the oblique holes 30 excavated by oblique boring are respectively provided, and the ground water is poured from the water tank 24A or the water tank 24B to the inner ground 44A to 44D. be able to.

Thereby, the groundwater level of the outer ground 42A-42L can be pumped out using the diagonal hole 28, and the groundwater level 27 can be lowered | hung. At this time, the groundwater pumped out is temporarily stored in the water tank 24A or the water tank 24B. In order to make the water tank 24A or the water tank 24B as small as possible, the groundwater pumped out is moved to the inner ground 44A to 44D and stored in the inner ground 44A to 44D.
As other methods, there are a method of temporarily storing all groundwater in the water tanks 24A and 24B and returning them to the basement after repairing cracks, or a method of purifying and disposing of the pumped-up groundwater. However, both of these methods have problems such as the storage water tanks 24A and 24B becoming large and costly, and the cost of purifying water becomes high.

  Here, the oblique holes 28 and 30 are excavated above the shallow water level 26 (shallow position). In order to stabilize the wall surfaces of the oblique holes 28 and 30, a casing is inserted into the oblique holes 28 and 30. Yes. In addition, a water hose is secured in the slanted holes 28 and 30 by inserting a flexible hose into the slanted holes 28 and 30 and flowing water into the flexible hose.

  In this structure, the diagonal holes 28 and 30 are the structures which penetrate the outermost peripheral part 10G and the internal improvement body 10N. However, since the penetration position is above the shallow water level 26 (shallow position), the inner ground of the impermeable wall 10 is not liquefied. In addition, leakage of the contaminated soil 12 and contaminated water to the outside does not occur. Further, as will be described later, after the repair of the crack is completed, the slant holes 28 and 30 are closed with cement milk, so that liquefaction and leakage of contaminants do not occur for a long time.

  With the configuration described above, the groundwater is pumped up to the water tank 24A or the water tank 24B from the outer ground 42A to 42L of the impermeable wall 10 constructed in a lattice shape, and the water tank 24A or the water tank 24B installed on the ground. The groundwater can be moved to the inner ground 44A to 44D due to the water level difference. Thereby, the inside of the outermost peripheral part 10G can be made lower than the outside, and a water level difference can be generated. Carbon dioxide is injected into the groundwater on the outside with a high water level, and the flow of groundwater generated due to the difference in level of the groundwater level. Thus, carbon dioxide can be infiltrated into the crack in the outermost peripheral portion 10G.

  Moreover, by pumping up the groundwater from the pumping holes 16A to 16H outside the impermeable wall 10 with the pump, it is possible to generate a height difference in the groundwater level 26 outside the outermost peripheral part 10G. In this state, carbon dioxide can be injected from the injection holes 14 </ b> A to 14 </ b> H having a high groundwater level, and the carbon dioxide can be diffused throughout the wall of the impermeable wall by the flow of groundwater generated by the difference in the groundwater level.

  Thereby, carbon dioxide can be injected to the outside of the outermost peripheral portion 10G where the groundwater level 26 is high. As a result, carbon dioxide is supplied to the inside of the outermost peripheral portion 10G, and repair of cracks in the outermost peripheral portion 10G can be promoted by the flow of groundwater without specifying the position of the crack.

An example of trial calculation of the amount of movement of the groundwater, the moving speed, etc. in the present embodiment will be shown below.
The gradient of the groundwater level 26 is 1/1000, the one side L1 of the outermost peripheral part 10G of the impermeable wall 10 is 50 m, and the division dimension L2 of the internal ground is 12.5 m. In this case, the change of the groundwater level 26 is 5 cm at 50 m. Further, the predetermined distance L3 between the injection holes 14A to 14H and the pumping holes 16A to 16H and the outermost peripheral part 10G is set to 50 cm. Originally, it is desirable that the predetermined distance L3 is as short as possible. Therefore, the minimum value is set to 50 cm due to restrictions on the installation of the boring machine.

  In the 12 blocks (outer grounds 42A to 42L) of the outermost peripheral portion of the inner ground of the impermeable wall 10, the groundwater level 27 was lowered by 10 cm using a submersible pump installed in the oblique hole 28. The pumped-up groundwater was once stored in the water tank 24A or the water tank 24B and injected into the four blocks (inner grounds 44A to 44D) of the inner ground of the impermeable wall 10. As a result, the groundwater level 25 of the inner grounds 44A to 44D rises by 30 cm from the volume ratio with the outer grounds 42A to 42L, respectively.

In addition, it is assumed that the hydraulic conductivity of the outermost peripheral portion 10G has decreased from 10 ⁻⁶ cm / s to 10 ⁻⁴ cm / s due to a crack generated during the earthquake. Furthermore, when the groundwater level 26 is 2 m below the ground surface 32 (GL-2.0 m), the amount Q1 of groundwater that enters the outermost peripheral portion 10G per day is as follows.
Q1 = A × v × t
= 800 cm × 5000 cm × 4 × 10 ⁻⁴ cm / s × 10 cm / 50 cm
× 86400s
= 27,648,000 cm ³ / day

In addition, the amount of groundwater Q2 between the injection holes 14A to 14H and the pumping holes 16A to 16H and the outermost periphery 10G is as follows assuming that the predetermined distance L3 is 50 cm and the gap ratio is 0.3.
Q2 = 50 cm × 800 cm × 5000 cm × 4 × 0.3
= 240,000,000 cm ³
The amount of groundwater Q2 all flows into the outermost peripheral portion 10G, and the time t required for carbon dioxide in the groundwater to contact the impermeable wall is:
t = 240,000,000 ÷ 27,648,000
≒ 9 days. That is, from the 9th day, CO ₃ ²⁻ generated by carbon dioxide mixed in the groundwater reacts with Ca ²⁺ from the cement component of the outermost peripheral portion 10G to produce calcium carbonate CaCO _3. The closing of cracks in the outer peripheral portion 10G is started.

Until this reaction starts, the groundwater that has entered the outermost peripheral part 10G is pumped up by a pump and moved to the inner ground 44A to 44D. The water level rise amount H1 of the inner grounds 44A to 44D rising by the movement is as follows.
H1 = 0.5m × 8m × 50m × 4 ÷ 25m ÷ 25m
= 1.28m
When the total water level rise of 30 cm is added, the groundwater level 25 is 1.58 m.

It is assumed that carbon dioxide penetrates into the crack of the outermost peripheral part 10G, precipitates calcium carbonate, and the water permeability coefficient of the outermost peripheral part 10G recovers from 10 ⁻⁴ cm / s to 10 ⁻⁶ cm / s. If it takes 20 days to recover, assuming that the hydraulic conductivity during this period is -5th power, which is the average value of -4th power and -6th power, the amount of groundwater Q3 flowing into the outermost periphery 10G can be obtained by the following calculation. it can.
Q3 = A ・ v ・ t
= 800 cm × 5000 cm × 4 × 10 ⁻⁵ cm / s × 10 cm / 50 cm
× 1,728,000s
= 55,296,000 cm ³

Since the groundwater amount Q3 is moved to the inner grounds 44A to 44D, the amount of increase H2 of the groundwater level 25 of the inner grounds 44A to 44D is as follows.
H2 = 55.296m ³ ÷ 25m ÷ 25m ÷ 0.3 (gap ratio)
= 0.29m
The groundwater level 25 is 1.87 m when combined with 1.58 m. From this result, it can be seen that there is a margin of 13 cm compared to the initial groundwater level (GL-2.0) m. After 20 days, cement milk is filled in the boring hole, the boring hole is closed, and the operation ends.

In addition, in the limestone ground (the ground mainly composed of calcium) and the ground where calcium is dispersed as a fertilizer in agricultural land or the like, the above-described chemical reaction occurs in the ground, and the hydraulic conductivity of the ground is lowered. As a result, there may be a case where CO ₃ ²⁻ does not reach the water-impervious wall, so care must be taken in application.

As described above, in the present embodiment, CO ₃ ²⁻ dissolved in the ground water attracts Ca ²⁺ in the cement paste, becomes calcium carbonate crystals, and adheres to the cement paste and the like. When calcium carbonate crystals adhere, Ca ²⁺ moves from the inside of the concrete and further binds to CO ₃ ²⁻ so as to compensate for the decrease in calcium ions in the water. Such a reaction is repeated, and calcium carbonate crystals are generated one after another, which adheres and settles on cement paste and the like, and the cracks in the impermeable wall are gradually repaired.

  As a result, by supplying carbon dioxide using the flow of groundwater, it is possible to close the cracks in the impermeable wall 10 constructed with the ground improvement body. Moreover, in this embodiment, since a boring cost accounts for most construction costs, it becomes cheaper than the method by the chemical | medical solution injection | pouring which is a prior art, and the re-construction of a water-impervious wall. Furthermore, it also has the effect of fixing carbon dioxide, a global warming substance.

  In the present embodiment, the impermeable wall 10 has been described as a square having a side L1. However, the present invention is not limited to this, and the planar view of the impermeable wall 10 may be a rectangle or a combination of a square and a rectangle. Good. Further, when the groundwater contains a predetermined amount or more of carbon dioxide, it is not necessary to mix carbon dioxide into the groundwater.

(Second Embodiment)
With reference to FIG. 4, a water shielding performance recovery method for the water shielding wall 40 according to the second embodiment will be described.
As shown in the vertical sectional view of FIG. 4, the impermeable wall 40 is different from the impermeable wall 10 according to the first embodiment in that it is a method of excavating boring holes 34 and 36 vertically downward from the building 22. . The difference will be mainly described.

The impermeable wall 40 does not require oblique boring from the outside to the inside of the impermeable wall 40, and is constructed by excavating boring holes 34 and 36 vertically downward from the inside of the building 22.
That is, the boring holes 34 are excavated in the outer grounds 42A to 42L vertically downward from the inside of the building 22, respectively. Further, a bored hole 36 is excavated vertically downward from the inside of the building 22 in the inner ground 44A to 44D.

  The outer grounds 42 </ b> A to 42 </ b> L and the water tank 24 are connected by a pipe 35, and groundwater pumped up by the pump is stored in the water tank 24 through the pipe 35. The water tank 24 and the inner ground 44A to 44D are connected by a pipe 37, and the groundwater stored in the water tank 24 passes through the pipe 37 and is injected into the inner ground 44A to 44D. In addition, the quantity and speed of the groundwater moved by this embodiment are the same as 1st Embodiment.

  By adopting this configuration, similarly to the impermeable wall 10 according to the first embodiment, the groundwater of the outer grounds 42A to 42L is pumped up, and the groundwater is moved to the inner grounds 44A to 44D using the pipe 35. Can do. As a result, the groundwater level 27 of the outer grounds 42A to 42L can be made lower than the groundwater level 26 of the sand layer 18, and a difference in height can be generated in the groundwater level inside and outside the outermost peripheral part 10G. Thereby, the flow of the groundwater generated by the difference in level of the groundwater level can be generated inside the outermost peripheral portion 10G, and self-repair with carbon dioxide is possible.

  Further, in this configuration, since boring is performed vertically downward in the impermeable wall 40, the boring distance to be excavated can be shortened compared to oblique boring, and the excavation can be performed economically and inexpensively. However, it takes time and labor to install the pipes 35 and 37 inside the building 22, and it is necessary to drill through the building 22 (pressure board, etc.), which may cut the building rebar. . The cutting of the rod rebars reduces the strength of the rods, so a thorough study is necessary. Other configurations are the same as those of the first embodiment, and a description thereof will be omitted.

(Third embodiment)
With reference to FIG. 5, a water shielding performance recovery method for the water shielding wall 50 according to the third embodiment will be described.
As shown in the vertical sectional view of FIG. 5, the impermeable wall 50 excavates a boring hole 54 vertically downward from the building 22 to the outer grounds 42 </ b> A to 42 </ b> L, and further excavates a boring hole 56 to the outside of the impermeable wall 50. Is the method. An oblique boring hole is unnecessary, and the position of the boring hole 56 is different from that of the second embodiment. The difference will be mainly described.

  Unlike the first embodiment and the second embodiment, the impermeable wall 50 according to the third embodiment makes the groundwater level 27 of the outer grounds 42A to 42L of the impermeable wall 50 higher than the underground water level 26 of the sand layer 18. Is the method. For this reason, after the groundwater pumped up by the pumping pump from the pumping hole 56 provided outside the impermeable wall 50 is stored in the water tank 24 using the pipe 57, the outer ground 42 </ b> A is formed from the water injection hole 54 using the pipe 55. It is the structure which pours water into -42L. Thereby, the groundwater level 27 of the outer grounds 42 </ b> A to 42 </ b> L can be made higher than the groundwater level 26 outside the impermeable wall 50. In addition, excavation of the boring hole to inner side ground 44A-44D is unnecessary.

  Thereby, a water level difference can be provided between the inner side and the outer side of the outermost peripheral part 10G in a state where the inner ground water level 27 is higher than the outer ground water level 26. That is, the carbon dioxide mixed in the outer grounds 42A to 42L can be supplied to the outermost peripheral part 10G by the difference in water level between the inner side and the outer side of the outermost peripheral part 10G. In addition, although illustration is abbreviate | omitted, in order to make carbon dioxide permeate into the outermost periphery part 50G over the wide range of the outermost periphery part 50G, a pumping hole is provided along with the water injection hole 54 in each outer ground 42A-42L. It is desirable that the water is pumped by a pump and a water level difference is generated between the water injection hole 54 and the water pumping hole to create a water flow.

  With this configuration, the boring hole 54 can be used both as an injection hole for injecting groundwater and an injection hole for mixing carbon dioxide into the groundwater. However, in this embodiment, since groundwater flows out from the outermost peripheral portion 50G of the impermeable wall 50 to the outside of the impermeable wall 50, the contaminated soil 52 is entirely composed of the inner ground 44A to 44D of the impermeable wall 50. Only if it is inside. In addition, although the boring hole 54 demonstrated the boring of the perpendicular direction as an example, it is not limited to this, Diagonal boring like 1st Embodiment may be sufficient. Other configurations are the same as those of the second embodiment, and a description thereof will be omitted.

(Fourth embodiment)
The water-blocking performance recovery method for the water-blocking wall 60 according to the fourth embodiment will be described with reference to FIG.
As shown in the sectional view of FIG. 6, the impermeable wall 60 is different from the impermeable wall 10 according to the first embodiment in that the impermeable wall 60 is a retaining wall 64 constructed of a ground improvement body. The difference will be mainly described.

The mountain retaining wall 64 used in the construction work constructed with the ground improvement body for the purpose of water shielding is partially constructed with a low water shielding performance due to poor construction or the like, and the water leakage portion 66 from which groundwater flows out is provided. May occur. In this case, groundwater flows from the natural ground part 68 toward the excavation part 70 along with the root cutting.
The ground surface 72 of the excavation part 70 is lowered from the natural ground part 68, and the water leakage part 66 can be visually confirmed. For this reason, it is not necessary to disperse carbon dioxide over a wide range, and it is only necessary to excavate the borehole 62 on the back surface (the ground portion 68) of the water leaking portion 66 and mix carbon dioxide into the groundwater from the borehole 62.

Thereby, the mixed carbon dioxide can be carried to the water leakage part 66 by the groundwater on the ground mountain part 68 side where the water level is high. Due to the presence of carbon dioxide, the self-repairing function of the retaining wall constructed of the ground improvement body is promoted, and the water leakage portion 66 of the retaining wall 64 can be blocked.
As a result, the water leaking portion 66 can be repaired at a lower cost than the current countermeasure method in which the water stop treatment is performed by injecting the chemical solution.

10 Impermeable wall 12 Contaminated soil 14 Injection hole (boring hole)
16 Pumping hole (boring hole)
25 Groundwater level 26 Groundwater level 27 Groundwater level 64 Mountain retaining wall (water-impervious wall)
66 Water leakage part (water leakage position)
68

Claims (5)

A method for recovering the water shielding performance of a water shielding wall, comprising the step of injecting carbon dioxide into a higher groundwater level inside or outside the water shielding wall constructed of a ground improvement body. The impermeable wall is constructed in a lattice shape,
The method for recovering the water shielding performance of the water shielding wall according to claim 1, further comprising a step of injecting or pumping water inside or outside the lattice shaped water shielding wall to generate a difference in height in the groundwater level. A plurality of boring holes provided along the impermeable wall;
A pump for lowering the groundwater level by pumping groundwater from one of the adjacent boreholes;
The carbon dioxide is injected from the other of the adjacent boring holes, and the carbon dioxide is diffused in the wall surface of the water-impervious wall by the flow of the groundwater generated due to a difference in groundwater level. 2. The method for recovering the water shielding performance of the water shielding wall according to 2.   The method for recovering water shielding performance of a water shielding wall according to any one of claims 1 to 3, wherein contaminated soil is enclosed in the interior surrounded by the water shielding wall.   The water shielding performance of the water shielding wall according to claim 1, wherein the water shielding wall is a mountain retaining wall, a borehole is provided from a natural mountain side toward a water leakage position of the mountain retaining wall, and carbon dioxide is injected from the borehole. Method.

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