JPH08253924A - Chemical injection method - Google Patents

Abstract

PURPOSE: To distribute a chemical over a wide area by installing an infection pipe made of a conductive material on both sides of a site intended for ground improvement, and applying DC voltage thereto and injecting a specified amount of chemical at least from an anode based on an electroosmosis. CONSTITUTION: Prior to the application of ground improvement so as to improve the strength of a ground directly under an existing structure 1 or enhance a waterstop ability, electrodes 12a and 12b, which are provided with a pair of chemical infection holes, are installed on both sides. While DC voltage is being applied, a specified chemical is injected at least from the electrodes 12a and 12b. In this case, an infection pipe is arranged to serve as an electrode. In addition to that, the injection pipe and the electrode are separated from each other. The injection pipe may be made of a plastic material or the like. The chemical comprises a mixed liquid of water glass and calcium chloride. The gel time of the chemical is controlled by adjusting the amount of calcium chloride. The electroosmosis range 21 of the chemical is not limited to the peripheral sides of the electrode but the chemical should be distributed all over the wide areas. This construction makes it possible to improve the desired ground with higher efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical injection method for improving ground.

[0002]

2. Description of the Related Art The chemical solution injection method is a method that can improve the ground strength and the water stopping ability by injecting a predetermined chemical solution into the ground through an injection pipe installed in the ground. Widely used as a simple ground improvement method.

[0003]

However, in such a chemical liquid injection method, it is not possible to grasp the permeation state of the injected chemical liquid or control the permeation range thereof, which causes some problems. .

That is, an unnecessarily large amount of chemical liquid may be injected, and the chemical liquid may escape to an unexpected range to cause groundwater pollution. In addition, in order to prevent such chemical liquid escape, The gel time had to be shortened, and as a result, the range of solidification of the injected drug solution was limited to the periphery of the injection pipe, and it was difficult to improve the ground over a wide range.

In order to improve a wide range of ground in such a situation, the pitch of the injection pipe is shortened, for example, 1
It is necessary to set every m, and in the ground where the excavation efficiency is low, the work of excavating the injection hole has been a factor of high cost.

Further, in the case of improving the ground just below the existing structure, as shown in FIG. 6, the existing structure 1 becomes an obstacle, and the injection pipe 2 is inserted into the ground 3 from the side thereof. There is nothing. Therefore, it was practically impossible to sufficiently inject the chemical liquid just below the existing structure.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a chemical liquid injection method capable of distributing a chemical liquid in the widest possible range and controlling the distribution range.

[0008]

In order to achieve the above object, the chemical solution injection method of the present invention, as described in claim 1, applies a DC voltage between a pair of electrodes arranged in the ground, A predetermined chemical solution is injected from at least the vicinity of the anode among the electrodes.

Further, the chemical liquid injecting method of the present invention is described in claim 1.
The chemical solution of is composed of a mixed solution of water glass and calcium chloride.

Further, the chemical liquid injection method of the present invention is defined in claim 1.
The electrode is formed of a hollow tube having a predetermined liquid medicine injection hole, and the liquid medicine is injected into the ground through the liquid medicine injection hole.

[0011]

In the chemical liquid injecting method of the present invention, a pair of electrodes are arranged, for example, facing each other in the ground so as to sandwich a desired region in the ground, and a DC voltage is applied between the electrodes, while a pair of electrodes are applied from near the anode. Inject the prescribed drug solution. The injected chemical solution moves to the cathode side by the electroosmosis phenomenon without staying at the injection site or moving downward due to gravity, and forms a solidified body over a wide area.

Here, when the electrode is formed of a hollow tube provided with a predetermined chemical solution injection hole, the hollow tube also serves as an electrode and injection tube.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the chemical liquid injection method of the present invention will be described below with reference to the accompanying drawings. It should be noted that parts and the like which are substantially the same as those of the conventional technique are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 is a schematic diagram for explaining a case where the chemical solution injection method of this embodiment is applied to the ground improvement directly below the existing structure 1. As can be seen from the figure, in the chemical liquid injection method of this embodiment, a pair of injection pipes 12a, 12b made of hollow pipes provided with a large number of chemical liquid injection holes 11 are arranged in the ground 3 so as to face each other. Ground 3 through injection hole 11
The drug solution can be injected inside.

The injection tubes 12a and 12b are made of a conductive material such as metal and are connected to a DC power source 13 to form a pair of electrodes. In this embodiment, the injection tube 12a is a positive electrode, The injection tube 12b serves as a negative electrode.

The chemicals include water glass-based chemicals containing water glass and a curing agent as main components, urethane-based, acrylic-based chemicals,
A high-molecular-weight chemical such as a urea-based chemical can be used, but it is preferably composed of a mixed solution of water glass and calcium chloride, for example.

In order to improve the ground by using the chemical solution injection method of this embodiment, first, the electrodes 12a and 12b are arranged so as to face each other in the ground 3 so as to sandwich the region directly below the existing structure 1, and the electrodes 12a and 12b are opposed to each other. DC voltage between the electrodes (less than 50 V)
While applying, the above-mentioned chemicals are injected via the electrodes 12a and 12b, which are injection tubes. The gel time of the drug solution is set longer than usual by reducing the amount of calcium chloride, for example, and is set between 2 hours and 50 hours.

Here, since a predetermined potential difference is generated between the electrodes 12a and 12b, the chemical liquid injected from the electrode 12a does not stay in the injection site or moves downward due to gravity, and thus the electric liquid is not generated. Cathode 12 due to penetration phenomenon
Move to b. Then, it becomes integral with the chemical liquid injected from the cathode 12b, and thus the chemical liquid injected from each electrode is widely distributed over the region 21 as shown in FIG.
A solid is formed in the region through gelation. When a mixed solution of water glass and calcium chloride is used as a chemical solution, water glass Na ₂ O.SiO ₂ reacts with calcium Ca,
Calcium silicate CaSiO _3, which is a solid, is formed.

Next, an indoor experiment and an on-site demonstration test were conducted on the chemical liquid injection method of the present embodiment. The outline and results thereof will be described.

FIG. 3 (a) shows an outline of the apparatus used for the laboratory experiment. An acrylic container 31 is filled with sand (silica sand No. 6) 32, and this is water-tightened to construct the ground. Then, the injection pipes 33a, 33 similar to the injection pipes 12a, 12b are used.
b was placed facing each other, and a mixed solution of sodium silicate (JIS No. 3) and calcium chloride (gel time 3 hours) was injected from the injection tubes 33a and 33b. At the same time, direct current electricity was supplied by using the injection tube 33a as an anode and the injection tube 33b as a cathode. The injection conditions and energization conditions at that time are shown in Table 1.

[0021]

[Table 1] In the experiment, as shown in the same table, when the chemical solution was injected without energization (case 1), when the chemical solution was injected only from the injection pipe 33a while energizing (case 2), and when injection was performed with the injection tube 33a while energizing The procedure was performed for three cases in which the drug solution was injected from both tubes 33b (case 3).

Next, after the injection was performed under the conditions shown in Table 1, the apparatus was disassembled two days later, and the consolidating volume was measured, and at three positions near the anode, at the intermediate position and near the cathode. Each of the samples was sampled and the chemical components (Si, Ca) and the like were measured by chemical analysis to grasp the distribution status.

Table 2 shows the current value during energization, the volume ratio of the solidified body to the amount of the injected chemical, and Si per unit weight of the solidified body.
It shows the weight ratio of O ₂ component and CaO component.

[0024]

[Table 2] Further, a graph in which the weight ratio of these components is plotted for each sampling position is shown in FIG. 3 (b), and a sketch for observing the solidification state is shown in FIG.

From these results, first, in case 2 and case 3, it is understood that the current amount increases with the progress of the injection of the chemical solution, and becomes maximum after 2 to 3 hours and then decreases. (Table 2). This is considered to be due to the decrease in conductivity due to the gelation of the drug solution.

Further, it can be seen that the volume of the solidified body injected with the chemical solution is considerably larger when the current is applied (case 2 and case 3) than when the current is not applied (case 1) (Table 2). In the case 1 which is not energized, the solid body spreads vertically downward due to gravity, and its distribution range is limited to a narrow triangular region, while in case 2 which is energized.
In case 3 and case 3, it can be seen that the consolidation range is expanded and widely distributed between the electrodes (FIG. 4). This suggests that the chemical solution moved to the cathode side by energization, and as a result, the chemical solution penetrated into a wide range.

The weight ratio of the SiO ₂ component to the CaO component in the solidified body is almost the same in the case 1 where no current is applied, depending on the sampling position. It can be seen that the ratio of the SiO ₂ component increases on the side and the ratio of the CaO component increases on the cathode side (FIG. 3 (b), Table 2). This suggests that a so-called electrophoretic phenomenon occurs in which the drug solution having a long gel time easily moves in the ground, and calcium as a cation moves to the cathode and silicic acid as an anion moves to the anode. It is a thing.

Next, a field verification test will be described. In this verification test, a mixed solution of water glass and calcium chloride (gel time 4.5 hours, specific gravity) was applied to sand ground (D ₅₀ = 0.15, hydraulic conductivity 1.3 × 10 ^-3 cm / sec) with a small amount of fine grains in the alluvium.
1.26) was injected at a rate of 1.6 liters per minute for a total of 900 liters. At that time, 0.25 V / cm using the injection tube as an electrode
Direct current was applied with a potential gradient of, and after 7 hours, the electrode was inverted.

FIGS. 5 (a) and 5 (b) are a plan view and a cross-sectional view showing the arrangement of the injection pipes.
Injecting pipes 41a and 41b similar to 33b are arranged in two rows,
They are used as a negative electrode and a positive electrode, respectively. In addition, in FIG.
Reference numeral 2 shows the chemical liquid penetration range (target range).

FIG. 5 (c) shows the change over time in the amount of current, showing an increasing tendency for the first 11 hours, and a maximum value of 2.
After taking 4A, it decreased after about 20 hours, and although there is a deviation from the set gel time, it suggests that the entire injection range is solidified.

When a part of the solidified body was excavated and the solidified state was observed, the liquid medicine was evenly distributed in the injection cross section and solidified in a bulb shape or a cylindrical shape around the injection pipe, or at the injection position. The lower part did not solidify. This is considered to be a manifestation of the inducing effect of the drug solution by energization.

Table 3 shows the soil test results of the injection ground.

[0033]

[Table 3] As can be seen from the results of the in-situ permeability test (water injection method) in the same table, the water loss was severely unmeasurable before injection of the chemical solution, but after injection, the order was 10 ^-6 cm / sec. It shows the effect of consolidation due to.

As can be seen from the results of the strength test in the same table, the sand that had poor adhesive strength before injection could not be molded and had a uniaxial compressive strength of 4 kgf / cm ² or more, and there was little variation in strength. It was

As described above, according to the chemical solution injecting method of this embodiment, the chemical solution can be widely penetrated into the ground without being retained in one place, and as a result, the chemical solution can be solidified in a wide area. it can. Therefore, it becomes possible to increase the pitch of the injection holes for inserting the injection pipes, which reduces the work of excavating the injection holes and facilitates the ground improvement such as directly under the existing structure, which was impossible in the past. You will be able to do it.

Further, by distributing the chemical solution in a wide range, it is possible to greatly increase the consolidation volume of the ground, and it is possible to consolidate or stop the water in a wider area with a small amount of the chemical solution.

Further, by appropriately setting the arrangement of the electrodes and the energization conditions, it is possible to control the permeation range of the chemical liquid, and there is no risk of causing the chemical liquid to escape in an unexpected direction to cause groundwater contamination.

In this embodiment, the injection tube and the electrode are used in common. However, this is a separate body, and an electrode made of a metal rod, a metal plate or the like is embedded near the injection tube made of plastic or the like to conduct electricity. You may do it.

Further, in the present embodiment, the chemicals were injected from both the anode and the cathode, but as can be seen in the laboratory experiment, injection of only one of them has a sufficient effect,
Therefore, for example, only the anode may be used also as the injection tube and the chemical solution may be injected from here, and the cathode may be formed as a simple metal rod.

Further, in the present embodiment, a water glass type chemical liquid composed of a mixed liquid of water glass and calcium chloride was used as the chemical liquid, but in addition to this, polymer type chemical liquids such as urethane type, acrylic type and urea type are used. May be used. Even in the case of such a chemical solution, the chemical solution can be distributed over a wide range in the ground by the electroosmosis phenomenon, and the same effect as described above can be obtained. The gel time when using a high-molecular chemical solution may be adjusted by reducing the amount of the catalyst for polymerizing the monomer.

[0041]

As described above, according to the chemical solution injecting method of the present invention, as described in claim 1, at least one of the electrodes is applied while applying a DC voltage between the pair of electrodes arranged in the ground. Since the predetermined chemical solution is injected from the vicinity of the anode, the chemical solution can be distributed in as wide a range as possible and its distribution range can be controlled.

[0042]

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing how a ground is improved immediately below an existing structure by using a chemical liquid injection method according to this embodiment.

FIG. 2 is a diagram showing a permeation range of a chemical liquid when the chemical liquid is injected using the chemical liquid injection method according to the present embodiment.

FIG. 3 (a) is a schematic view of the apparatus used in the indoor experiment, and FIG. 3 (b) is a graph showing the results of the indoor experiment.

FIG. 4 is a schematic view showing a range solidified by an indoor experiment for each case.

FIG. 5 (a) is a plan view showing the arrangement of the injection pipes in the field verification test, FIG. 5 (b) is a cross-sectional view of the same, and FIG. 5 (c) is a graph showing the change over time in the current amount in the field verification test.

FIG. 6 is a cross-sectional view showing how the ground is improved immediately below an existing structure using a chemical liquid injection method according to a conventional technique.

[Explanation of symbols]

 1 Existing Structures 11 Chemical Injection Holes 12a, 12b Electrodes, Injection Pipes 13 DC Power Supply 21 Penetration Range of Chemicals 33a, 33b Electrodes, Injection Pipes 41a, 41b Electrodes, Injection Pipes

Claims (3)

[Claims] 1. A chemical injection method, wherein a predetermined chemical is injected from at least the anode of the electrodes while applying a DC voltage between a pair of electrodes arranged in the ground. 2. The chemical liquid injecting method according to claim 1, wherein the chemical liquid is composed of a mixed liquid of water glass and calcium chloride. 3. The chemical injection method according to claim 1, wherein the electrode is formed of a hollow tube having a predetermined chemical injection hole, and the chemical is injected into the ground through the chemical injection hole.