JP2004183364A - Underground continuous cut off wall structure in land - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an underground continuous cut off wall structure in land improving the durability, withstanding a strong external force in an earthquake without damage, bringing no crack by the ground movement, impairing no water sealability, and forming land at a low cost as compared with the in-situ solidified wall or a continuous underground wall. <P>SOLUTION: The underground continuous cut off wall in land is constituted by filling a filler 33 made by modifying to a gelatinous condition by adding clay minerals and a gelatinizer into a clay-suspension with an adjusted moisture content and mixing an impervious material having a deformation following nature with sand or aggregate such as crushed stones into a continuous underground ditch 30 formed in the depth down to the underground impervious layer 22. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an underground continuous impermeable wall structure on land installed to prevent the contamination from spreading around the contaminated ground when the ground is contaminated with harmful substances.
[0002]
[Prior art]
Conventionally, when the ground has been contaminated with harmful substances in factories, refuse incineration facilities, or existing waste disposal sites (inappropriate disposal sites), a method of preventing the contamination from spreading around the contaminated ground As a method, a method is adopted in which the surroundings of the contaminated ground are surrounded by a water stop wall or continuous underground wall made of a sheet pile to block water.
[0003]
Conventionally, as this water shielding method, there is a water shielding method using a steel sheet pile, an in-situ solidified wall, a continuous underground wall, or the like.
[0004]
As shown in FIG. 4, the method using the inner steel sheet piles is such that U-shaped steel sheet piles 1, 1... The joint 1a is filled with a water-swellable water-stopping material 3 in advance to form a continuous water-stop wall made of steel sheet pile having a structure capable of blocking water flow.
[0005]
In the method using the solidified wall at the current position, as shown in FIG. 5, the earth and sand agitating blade 5 is inserted while being swirled to a depth reaching the impermeable layer 2 under the ground, and the solidified material is injected into the soil and agitated. By doing so, the in-situ solidified wall 6 reaching the impermeable layer 2 underground is continuously formed.
[0006]
Further, in the method using the continuous underground wall, as shown in FIG. 6, a continuous underground trench 7 having a depth reaching the impermeable layer 2 underground is excavated by a grab bucket or the like for trenching, and the continuous underground trench is used. A reinforcing steel bar 8 and concrete 9 are cast in the inside 7 to form a continuous underground wall 10 made of concrete.
[0007]
[Problems to be solved by the invention]
The seepage around the ground contaminated by harmful substances prevents the outflow of pollutants from the contaminated ground to the surrounding ground. If broken, the contaminants will flow back into the surroundings, causing the contamination to spread. Therefore, it is required that such a structure has a structure that ensures the required water shielding over a long period of time and that is sufficiently safe against ground deformation such as an earthquake or immovable settlement. Can be
[0008]
However, the method using steel sheet piles among the above-mentioned conventional methods can be performed at a relatively low cost, but it is difficult to completely perform water shielding at the joint between the steel sheet piles, and However, there is a problem that corrosion of steel sheet piles may occur depending on the type of contaminants.
[0009]
Further, the above-described method using the in-situ solidified wall described above can be expected to have relatively high water blocking performance, but has a problem that the cost is high and that there is a high possibility that cracks will occur due to ground changes due to an earthquake or the like.
[0010]
Furthermore, in the method using the continuous underground wall described above, higher water stopping performance can be expected than the in-situ solidified wall, and the strength is higher than the in-situ solidified wall, but the cost is high, and the There is a problem that the possibility of cracking cannot be denied.
[0011]
In view of such conventional problems, the present invention is excellent in durability, is not damaged even by strong external force such as at the time of an earthquake, does not crack even by ground deformation, does not impair water shielding, and The purpose of the present invention is to provide an underground continuous impermeable wall structure on land that can be constructed at a lower cost than an in-situ solidified wall or a continuous underground wall.
[0012]
[Means for Solving the Problems]
The feature of the invention according to claim 1 for solving the conventional problems as described above and achieving the intended purpose is that the water content ratio is adjusted in a continuous underground trench formed at a depth reaching an impermeable layer underground. The present invention is to fill a filler obtained by adding a clay material and a gelling agent to a modified clay suspension to form a gel, and mixing a water-blocking material having deformability and an aggregate such as sand or crushed stone.
[0013]
With this configuration, the contaminated and non-contaminated parts of the ground can be blocked by a water-impervious wall having sufficient water-blocking properties, and furthermore, can be shielded from changes such as earthquakes and immovable settlements. The water wall follows, preventing a significant drop in the water barrier.
[0014]
The invention according to claim 2 is the composition according to claim 1, wherein the clay suspension has a water content of 50 to 300%, and the clay mineral is selected from smectite, kaolin mineral, mica clay mineral, sepiolite, and mixed-layer mineral. The gelling agent is at least one selected from the group consisting of silicates, alkali metal salts, and alkaline earth metal salts.
[0015]
With this configuration, the impermeable wall can obtain sufficient impermeable performance and can be suitably adapted to deformation of the ground due to external force such as an earthquake, immovable settlement, and the like.
[0016]
According to the invention of claim 3, in addition to the structure of claim 1 or 2, the impermeable material comprises a fibrous substance composed of an inorganic material or an organic material, a lime-based or cement-based solidifying agent, and / or a gel retarder. It is characterized by being added.
[0017]
With this configuration, the filler keeps fluidity during construction of the impermeable wall, and exhibits sufficient gel strength after the construction.
[0018]
According to the invention of claim 4, in addition to the constitution of claim 3, the gelling retardant may be an alkali metal borate such as sodium or potassium, an alkali metal lignin sulfonate such as sodium or potassium, sodium, potassium or the like. At least one selected from water-soluble polymers such as alkali metal polycarboxylates, alkali metal polyacrylates such as sodium and potassium, dextrins, fatty acids, sucrose, maltose and alcohols It is characterized by.
[0019]
With this configuration, it is possible to prevent fluidity from being lost during construction, and to obtain suitable workability.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described with reference to FIGS.
[0021]
In the figure, reference numeral 20 denotes an underground continuous impermeable wall embodying the present invention, and the impermeable wall 20 is arranged so as to surround the periphery of the ground 21 contaminated by harmful chemical substances or the like, and impervious water from the ground surface to the underground. It is formed continuously to the depth reaching the layer 22.
[0022]
The construction of the impermeable wall 20 is to excavate and form a continuous underground trench 30 from the ground surface using a grab bucket for trenching. In excavation of the trench, similarly to the excavation formation of the underground trench in the construction of the continuous underground wall, the trench 30 in the middle of excavation is filled with a bentonite liquid to prevent collapse of the inner wall surface of the trench.
[0023]
After excavation of the groove 30, as shown in FIG. 2, in the groove 30 filled with the bentonite liquid 31, a filler material 33 constituting the impermeable wall 20 using the trammy tube 32 is sequentially arranged above the groove bottom. inject.
[0024]
The filler 33 is a mixture of a water-blocking material having deformability and an aggregate such as sand or crushed stone, and is kneaded by a filler adjusting plant using a mixer.
[0025]
The water-blocking material having this deformation-following property is obtained by adding a clay mineral and a gelling agent to a clay suspension having an adjusted water content to modify it into a gel state. = 1.0 × 10 ⁻⁶ (cm / s) or less. Therefore, a sufficient water-blocking performance can be obtained by mixing an aggregate with the water-blocking material and casting it to a required thickness (50 cm or more).
[0026]
Examples of the clay mineral used to reduce the water permeability of the impermeable material include smectite, kaolin mineral, sepiolite, mica clay mineral, and mixed layer mineral, and any of these may be used, but smectite, kaolin mineral, mica It is preferable to use one or more selected from clay minerals.
[0027]
The amount of the clay mineral to be added is appropriately in the range of 5 to 50 parts by weight per 100 parts by volume of the clay suspension having a water content of 50 to 300%. When the addition amount of the clay mineral is 5 parts by weight or less, the gel strength due to the reduction of the water permeability and the addition of the water-soluble inorganic salt is low, and thus the clay mineral may not be suitable as a water barrier material. If the amount is more than 50 parts by weight, the gel strength due to the addition of the water-soluble inorganic salt is too high, and a problem may be caused in construction.
[0028]
As the gelling agent, at least one or more of water-soluble alkali metal salts, alkaline earth metal salts, and silicates (hereinafter, also referred to as water-soluble inorganic salts) is used.
[0029]
The addition amount of the gelling agent is appropriately in the range of 0.05 to 10 parts by weight per 100 parts by volume of the above-mentioned clay suspension. May not be suitable as material. On the other hand, when the amount is 10 parts by weight or more, the gel strength due to the addition of the water-soluble inorganic salt is too high, and there may be a problem in construction.
[0030]
The clay mineral and the water-soluble inorganic salt used in the present invention may be added as a powder mixture or powder separately, or may be previously suspended or dissolved in water used to adjust the water content of the clay. May be added. The water-soluble inorganic salt may be a liquid product.
[0031]
Further, in this water shielding material, the fibrous substance and / or the solidifying agent are used in combination with the clay mineral and the water-soluble inorganic salt to improve the gel strength.
[0032]
Examples of the fibrous substance include mineral fibers as natural fibers such as asbestos, inorganic fibers as chemical fibers such as rock wool, and synthetic fibers as chemical fibers such as polypropylene.
[0033]
The addition amount of the fibrous substance to be used in combination is appropriately in the range of 0 to 5 parts by weight per 100 parts by volume of the above-mentioned clay suspension. The amount of the solidifying agent to be added is appropriately in the range of 0 to less than 5 parts by weight, and in the range of more than 0 to 5 parts by weight, the gel strength may be too strong or a solidification reaction may occur, which may be inappropriate.
[0034]
Portland cements such as slaked lime, quicklime, lime-based solidifying agents, anhydrous gypsum, hemihydrate gypsum, cement-based solidifying agents, ordinary Portland cement, early-strength Portland cement, ultra-high-strength Portland cement, and moderately heated Portland cement , Blast furnace cement, fly ash cement and so on.
[0035]
It should be noted that a gel retarder may be used in combination with the water-blocking material so that the fluidity is not lost during construction and the workability is not deteriorated.
[0036]
Examples of the gelling retardant include borates of alkali metals such as sodium and potassium, ligninsulfonates of alkali metals such as sodium and potassium, polycarboxylates of alkali metals such as sodium and potassium, and sodium and potassium. And water-soluble polymers such as alkali metal polyacrylates, dextrins, fatty acids, sucrose, maltose and alcohols.
[0037]
The addition amount of the gelation retarding substance to be used in combination is appropriately in the range of 0 to 3 parts by weight per 100 parts by volume of the above-mentioned clay suspension, but in the range more than that, the gelation is suppressed and the appropriate amount is suppressed. Gel strength may not be exhibited.
[0038]
In this water-blocking material, fresh water is added in advance to clay having a water content of about 50 to 150% obtained by general port dredging, and the suspension is increased to a water content of about 50 to 300%. When clay mineral is added, clay mineral particles fill the pores of the clay particles and cause gelation at the same time, have a uniform and fluidity, and have a property of easily separating foreign substances.
[0039]
However, since the clay suspension in this state has a low gel strength, there is a possibility that the material separation becomes large during casting in water. Therefore, by adding water-soluble alkali metal salts, alkaline earth metal salts, and silicates to this clay suspension, the metal cations react with the clay mineral and the clay component in the clay mineral, and the clay particles become electrically conductive. The water impermeable material has a deformability following property by forming a lump and exhibiting a gelling phenomenon.
[0040]
Incidentally, by measuring the vane shear value and managing it within a certain range, the magnitude of deformation followability can be known. The appropriate range of the vane shear value of the water impermeable material of the present invention is 0. a ^{.3 (kN / mm 2) ~6.0} (kN / mm 2).
[0041]
As the aggregate, sand, gravel, crushed stone, slag, or the like having a particle size of about 0.075 mm to 50 mm is used, and is mixed at a ratio of 5 to 50 parts by volume with respect to 100 parts by volume of the impermeable material.
[0042]
Next, a method for producing the filler will be described.
[0043]
As shown in FIG. 3, in the demulsification process, water is added to the clay 41, which is the raw material soil contained in the demulsification tank 40, to loosen the slurry into a slurry state, and at the same time, large rubs and dust contained in the clay are removed.
[0044]
Next, the slurry-form clay is transferred to the sludge tank 43 in the sludge preparation step by a transfer means such as the backhoe 42. In this mud conditioning tank 43, a predetermined amount of water is added to the slurry-like clay to remove foreign substances, the water content is adjusted to a target water content (50 to 300%) and the density is adjusted, and the adjusted mud is stored in the adjusted mud storage tank 44. Earn 45.
[0045]
Then, the obtained adjusted mud 45 is sent to a mixer 47 in a plant 46 in a kneading process, and an auxiliary material including a clay mineral, a gelling agent, a fibrous substance, and the like is added from an auxiliary material adding device 48 to water-blocking. A filler is prepared, and an aggregate such as sand or crushed stone is further kneaded to produce a filler.
[0046]
This filler is conveyed to a setting place by a pressure feeding pipe 50 using a pressure feeding pump 49 (pressure feeding step), and is driven into a predetermined position using a tray-me pipe 32 shown in FIG. ).
[0047]
【The invention's effect】
As described above, the underground continuous impermeable wall structure on land according to the present invention uses stone or clay-based impermeable material, which is a natural material, as the impermeable material. Water barrier performance can be maintained.
[0048]
In addition, since a clay-based water-blocking material having deformation-following properties is used, the water-blocking wall follows the ground deformation such as an earthquake or immovable settlement, thereby preventing a significant decrease in water-blocking.
[0049]
Furthermore, even when relatively large external force acts on the impermeable wall due to an earthquake or the installation of a structure near the impermeable wall, the friction of the skeleton by the aggregates will resist and impair the impermeable water. It has sufficient durability against significant impermeable wall deformation.
[0050]
The aggregate is mainly made of stone, and the water-blocking material is mainly made of clay. Therefore, the cost of the material is relatively low, and the clay can be pumped and pumped, so that the workability is good and the work can be performed at low cost.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an underground continuous impermeable wall structure on land according to the present invention.
FIG. 2 is a cross-sectional view showing a step of placing a filler.
FIG. 3 is a side view showing a manufacturing process of the filler.
FIG. 4A is a cross-sectional view showing an example of a conventional impermeable wall structure, and FIG. 4B is a cross-sectional view showing a joint portion of a steel sheet pile used for the impermeable wall structure.
FIG. 5 is a longitudinal sectional view showing another example of the conventional water impermeable wall structure.
FIG. 6 is a longitudinal sectional view showing still another example of the conventional impermeable wall structure.
[Explanation of symbols]
Reference Signs List 20 continuous underground impermeable wall 21 contaminated ground 22 impervious layer 30 underground trench 31 bentonite liquid 32 trammy pipe 33 filling material 40 mud crushing tank 41 clay 42 backhoe 43 mud adjusting tank 44 adjusted mud storage tank 45 adjusted mud 46 plant 47 mixer 48 auxiliary material addition device 49 pressure pump 50 pressure tube

Claims (4)

A water-impregnating material with a deformation-following property obtained by adding a clay mineral and a gelling agent to a clay suspension with an adjusted water content in a continuous underground trench formed to the depth of reaching the impermeable layer under the ground Underground continuous impermeable wall structure on land filled with filler mixed with aggregate such as sand or crushed stone. The clay suspension has a water content of 50 to 300%, and the clay mineral is at least one selected from smectite, kaolin mineral, mica clay mineral, sepiolite, and mixed layer mineral, and the gelling agent is The underground continuous impermeable wall structure on land according to claim 1, which is at least one selected from silicates, alkali metal salts, and alkaline earth metal salts. The underground continuity on land according to claim 1 or 2, wherein a fibrous substance made of an inorganic material or an organic material, a lime-based or cement-based solidifying agent, and / or a gelling retardant are added to the water-blocking material. Impermeable wall structure. Gelling retardants include alkali metal borates such as sodium and potassium, alkali metal lignin sulfonates such as sodium and potassium, alkali metal polycarboxylates such as sodium and potassium, and alkalis such as sodium and potassium. The underground continuous impermeable wall structure on land according to claim 3, which is at least one selected from water-soluble polymers such as metal polyacrylates, dextrins, fatty acids, sucrose, maltose, and alcohols.

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