JP5113579B2 - Construction method of low permeability layer - Google Patents

Description

  The present invention relates to a method for constructing a low water permeability layer.

  In final waste disposal sites and radioactive waste disposal facilities, in order to prevent intrusion of groundwater into the pit and outflow of harmful substances from the pit, it is made of bentonite materials around the pit. An artificial barrier (low water permeable layer) may be constructed.

  As a method of constructing a low water permeability layer using a bentonite material, for example, those disclosed in Patent Documents 1 to 3 are known.

  Patent Document 1 discloses a method for constructing a low water-permeable layer by rolling out bentonite-containing granulated material with a predetermined thickness and rolling it. Patent Document 2 discloses the same method as Patent Document 1. In addition to the above method, a method of constructing a low water permeability layer by rolling out a mixture of bentonite-containing granulated material and other soil material at a predetermined thickness and rolling the mixture is disclosed. Further, in Patent Document 3, a lump formed body that is a bentonite-containing granulated product and a bentonite-based fluid (a powder or granule of bentonite-based material) are mixed in advance, and the resulting mixture is placed in a desired space. There are disclosed a method for constructing a low water permeable layer by charging, and a method for constructing a low water permeable layer by alternately charging a massive molded body and a bentonite fluid.

JP 2000-325907 A (see paragraphs [0023] and [0024]) Japanese Patent No. 4036975 (see paragraph [0033]) Japanese Patent No. 3539928 (see paragraphs [0054] to [0056])

  If a large compactor is used to compact the bentonite-containing granulated product, a large lateral pressure is generated, which may affect the surrounding structures. On the other hand, when a compact compactor is used, although the generated side pressure is small, the layer thickness that can be compacted is small, and there is a risk of taking time for the compaction work. In addition, in the method of simply adding bentonite-containing granulated material or the like, there is a possibility that the filling and drying density and the like in the low water permeable layer may vary depending on the input amount and the input height.

  From such a viewpoint, it is an object of the present invention to provide a method for constructing a low water permeable layer that can reduce the influence on peripheral structures and that hardly causes variations in quality.

The first low water permeable layer construction method according to the present invention for solving such a problem is to squeeze an aggregate made of bentonite-containing granulated material to form a loosely packed aggregate of the aggregate, and the loosely packed aggregate A densely packed aggregate is formed by applying vibration to the body, and then granules composed of bentonite-containing granules having a particle size smaller than that of the aggregate are introduced from above the densely packed aggregate. The gap is filled in the aggregate with the granule.

  When the aggregate is squeezed out, a loosely packed aggregate (slowly packed aggregate) with a large gap ratio (= gap volume / aggregate volume) is formed. When added, it changes to a tightly packed aggregate with a small gap ratio (closely packed aggregate), and a homogeneous skeletal structure with little disturbance is formed, so the quality of the low water permeability layer obtained by introducing granules Variations (filling dry density, water permeability coefficient, etc.) are less likely to occur.

  In addition, if the gap ratio of the loosely packed assembly is reduced by force using a large compactor or the like, a large side pressure may be generated and affect the surrounding structure, but the present invention uses vibration energy. Since the gap ratio is reduced, a large side pressure is not generated, and therefore the influence on the surrounding structure is also reduced. By the way, the loosely packed aggregate formed by rolling out only the aggregate is in a state in which the aggregates are in contact with each other, so that the propagation efficiency of vibration is high, and therefore it is in a tightly packed state without applying large vibrations. Can be changed.

Note that vibration may be applied to the loosely packed aggregate while rolling out the aggregate, but vibration may be applied to the loosely packed aggregate after rolling out a predetermined amount of aggregate. That is, squeezing out an aggregate made of bentonite-containing granular material to form a loosely packed aggregate of the aggregate, and applying vibration to the loosely packed aggregate so that the gap ratio is higher than that of the loosely packed aggregate. A main vibration step for forming a small dense aggregate, and granules comprising bentonite-containing granular material having a particle size smaller than that of the aggregate are introduced from the upper side of the dense aggregate, and the granules are filled with the dense aggregate. It is good also as a construction method of the low water permeability layer including the filling process filled up in the inside gap.

Further, the second low water permeable layer construction method according to the present invention for solving the above-mentioned problem is to scrape an aggregate made of bentonite-containing granulated material to form a loosely packed aggregate of the aggregate, and Vibration is applied to the aggregate to form a dense aggregate, and then granules comprising a bentonite-containing granulated product having a particle size smaller than that of the aggregate are introduced from above the dense aggregate. Is filled in a gap in the densely packed assembly, and vibration is applied to the densely packed assembly.

  When the granules are introduced from the upper side of the densely packed aggregate (skeleton structure), the granules are filled into the gaps in the densely packed aggregate by the action of gravity. If vibration is applied, the packing density of the granules is increased, so that it is possible to increase the packing dry density of the obtained low water permeability layer.

  Note that vibration may be applied to the densely packed aggregate while the granules are being charged, but vibration may be applied to the densely packed aggregate after the predetermined amount of granules have been charged. That is, it is good also as a construction method of a low water-permeable layer including the finishing vibration process which adds a vibration again to the said densely packed aggregate which passed through the said filling process.

  In addition, the particle size ratio of the aggregate and the granule in the low water permeability layer to be constructed, the weight percentage of the aggregate, and the weight percentage of the granule are set in a preliminary test, and the grain set in the preliminary test is set. It is desirable to construct so as to have a diameter ratio and a weight percentage.

  According to the construction method of the low water permeable layer according to the present invention, it is possible to reduce the influence on the surrounding structure, and the quality of the obtained low water permeable layer is less likely to vary.

The best mode for carrying out the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram for easily explaining the construction method of the low water permeability layer. As shown in this figure, the construction method of the low water permeability layer according to the present embodiment scoops out the aggregate 1 made of bentonite-containing granulated material to form a loosely packed aggregate S1 of the aggregate 1 (in FIG. 1). (See (a)), the loosely packed aggregate S1 is vibrated to form a densely packed aggregate S2 (see (b) and (c) of FIG. 1), and then granule 2 made of bentonite-containing granulated product Is injected from the upper side of the densely packed aggregate S2 so that the granules 2 are filled in the gaps in the densely packed aggregate S2 (see FIG. 1 (d)), and vibration is applied to the densely packed aggregate S2. (Refer to (e) of FIG. 1), a low water-permeable layer S3 (see (f) of FIG. 1) is constructed.

  That is, the low water-permeable layer construction method according to the present embodiment is a low water-permeable layer using a large particle size bentonite-containing granule (aggregate 1) and a small particle size bentonite-containing granule (granule 2). The construction method includes a step of squeezing the aggregate 1 to form a loosely packed aggregate S1 of the aggregate 1, and applying vibration to the loosely packed aggregate S1 so that the gap ratio is higher than that of the loosely packed aggregate S1. A main oscillating step for forming a small densely packed aggregate S2, a filling step for charging the granules 2 into the gaps in the densely packed aggregate S2 by charging the granules 2 from above the densely packed aggregate S2, and a filling step And a finishing vibration step for applying vibration to the densely packed aggregate S2.

  The bentonite-containing granulated product is a granulated product containing bentonite. Bentonite is a kind of clay mainly composed of montmorillonite, and has a property of absorbing water and swelling and ion exchange.

The size of the particle size of the aggregate 1 is not particularly limited as long as it is a size that can be divided into gravel (2 mm or more), but is desirably 16 mm or more. Further, the shape of the aggregate 1 is not limited, but is preferably spherical. Incidentally, the particle size of the aggregate 1 is 1 (particle size _{D 10} corresponding to the particle size _{D 60} / pressurized product mass ratio 10% corresponding to = pressurized product weight ratio 60%) uniformity coefficient _U C _<U C _<5 It is desirable to adjust so that.

  The granule 2 has a particle size and shape that can be filled in the gaps in the densely packed aggregate S2, and is made of bentonite granulated material having a particle size smaller than that of the aggregate 1. When the average particle size of the aggregate 1 is about 16 mm, the average particle size of the granules 2 is preferably about 0.5 to 0.7 mm.

  The aggregate 1 and the granule 2 may have different blending density of bentonite-containing granulated material and bentonite filling dry density contained in the bentonite-containing granulated material, but in this embodiment, they are the same.

Particle size ratio of aggregate 1 and granule 2 to be achieved in the low water permeable layer S3 (average particle size of aggregate 1: average particle size of granule 2), weight percentage of aggregate 1 (= unit volume weight of aggregate 1) / Unit volume weight of the low water permeable layer S3 × 100%), the weight percentage of the granule 2 (= unit volume weight of the aggregate 1 / unit volume weight of the low water permeable layer S3 × 100%) is set by a preliminary test. It is desirable to do. The preliminary test is a test that simulates the above-described steps, and is performed using the same materials as the aggregate 1 and the granules 2 used in the construction work.
In the present embodiment, the particle size ratio between the aggregate 1 and the granules 2 is 16: 0.5 to 16: 0.7, the weight percentage of the aggregate 1 is 70%, and the weight percentage of the granules 2 is 30%. In this embodiment, since the low water permeable layer S3 is formed only by the aggregate 1 and the granule 2, the unit volume weight of the low water permeable layer S3 is the unit volume weight of the granule 2 to the unit volume weight of the aggregate 1. The value obtained by adding.

In addition, what is necessary is just to determine the mixing | blending, filling dry density, etc. of a bentonite containing granulated material so that the target filling dry density in the low water-permeable layer S3 may be satisfied. In this embodiment, the target filling dry density ρ _d of bentonite in the low water permeable layer S3 is set to 1.6 Mg / m ^3, and the bentonite filling dry density in the bentonite-containing granule is set to 2.0 Mg so as to satisfy this. / M ³ or so. Such a bentonite-containing granulated product is, for example, mixed with 3 to 12 parts by weight of water with respect to 100 parts by weight of finely powdered bentonite (particle size of 0.001 to 0.074) to adjust granulation and water content ratio. It is manufactured by adjusting the particle size.

  Next, the construction method of the low water permeability layer according to the present embodiment will be described in more detail by taking as an example the case where an artificial barrier is formed around a pit (structure) of a radioactive waste disposal facility. FIG. 2 is a schematic diagram for explaining the construction method of the low water permeability layer in an easy-to-understand manner. The dimensions and the like of the aggregate 1 and the granules 2 are different from actual ones.

  As shown in FIG. 2, the pit P of the radioactive waste disposal facility is constructed in the tunnel T, and the low water permeable layer S3 serving as an artificial barrier is formed so as to surround the pit P. The low water permeable layer S3 is formed between the invert of the tunnel T and the bottom plate of the pit P, between the side wall constructed in the tunnel T and the side wall of the pit P, and on the top plate of the pit P. In any part, the construction method of the low water permeable layer according to the present embodiment can be applied. Below, the case where the low water-permeable layer S3 is built in the side part of the pit P is illustrated.

(Spreading process)
First, the aggregate 1 is sprinkled on the already constructed low water permeability layer S3 and spread as necessary to form a loosely packed aggregate S1 having a predetermined layer thickness. The overhang thickness may be set within a range of 1 m. There is no limitation on the method of squeezing the aggregate 1, and for example, it may be performed by a dump truck, a bulltozer, etc. . Incidentally, the unwinding device 3 includes a traveling platform 31, a receiving hopper 32, a belt conveyor 33, a supply feeder 34, a chute 35, and the like. When the material 1 is introduced, the material 1 is sprinkled on the existing low water permeable layer S3 through the belt conveyor 33, the supply feeder 34, and the chute 35.

(This vibration process)
Next, vibration is applied to the loosely packed aggregate S1. When vibration is applied to the loosely packed aggregate S1, it changes to a densely packed aggregate S2 with a small gap ratio, and a homogeneous skeletal structure with less disturbance is formed. The loosely packed aggregate S1 is in a state in which the aggregates 1, 1,... Are in contact with each other, so that the vibration propagation efficiency is high. Change. Frequency of the vibration applied to the Yurutsume assembly S1, amplitude, vibration causing time etc. per one place, it may be appropriately determined depending on the size of the particle size and target fill dry density [rho _d of the aggregate 1, When the average particle size of the aggregate 1 is 16 mm and the target filling dry density ρ _d is 1.6 Mg / m ³ , the vibration time per location is about 5 to 15 seconds. The vibration method is not limited, and vibration may be applied by a small vibration roller 5 (see FIG. 2B) that can travel on the loosely packed assembly S1, or a narrow portion that has a head limitation, etc. In FIG. 2, vibration may be applied by the plate compactor 6 (see FIG. 2A). Although there is no restriction | limiting also in an excitation direction, It is desirable to vibrate up and down suitably.

(Filling process)
Subsequently, as shown in FIG. 1 (d), the granules 2 are introduced from above the densely packed aggregate S2, and the granules 2 are filled into the gaps in the densely packed aggregate S2 by the action of gravity. There is no restriction | limiting in the injection | throwing-in method of the granule 2, For example, you may carry out with the dump truck provided with the mechanism which pours out equally, a bulltozer, etc., and may carry out with the brewing apparatus 3 (refer FIG. 2). Moreover, although illustration is abbreviate | omitted, piping for powder conveyance may be provided in the tunnel T, and the granule 2 may be powder-transported using the airflow of the said piping. If the granule 2 is used for powder transportation, an environment close to dust-free can be ensured, and the working environment is improved.

(Finish vibration process)
Next, as shown in FIG. 1E, vibration is applied to the densely packed assembly S2 that has undergone the filling process. When vibration is applied to the densely packed aggregate S2, a gap may be generated in the upper layer portion of the densely packed aggregate S2 because the packing density of the granules 2 increases. In this case, the granule 2 may be reintroduced into the gap and vibration may be applied as necessary. The vibration frequency, amplitude, vibration time per location, and the like may be appropriately set according to the particle diameter of the granule 2 and the size of the target filling dry density ρ _d. If you 0.5mm diameter, the target charging dry density [rho _d and 1.6 mg / ^{m 3,} the vibration time per point is approximately 5 to 15 seconds. The vibration method is not limited, and vibration may be applied by a small vibration roller 5 (see FIG. 2B) that can travel on the densely packed assembly S2, or a narrow portion that has a head limitation. For example, vibration may be applied by the plate compactor 6 (see FIG. 2A). Although there is no restriction | limiting also in an excitation direction, It is desirable to vibrate up and down suitably.

  In the present embodiment, 70 parts by weight of the aggregate 1 is squeezed out in the squeezing step so that the weight percentages of the aggregate 1 and the granules 2 are the values set in the preliminary test described above. In the vibration process, 30 parts by weight of granules 2 are charged.

  Through the above steps, the low water permeability layer S3 having a very low water permeability coefficient is formed. Then, an artificial barrier is formed around the pit P by repeating the brewing process to the finishing vibration process.

  According to the construction method of the low water permeability layer according to the present embodiment described above, a homogeneous skeletal structure (densely packed aggregate S2) with less turbulence is formed, and the granules 2 are closest packed. In addition, the quality of the low water permeability layer S3 (filling dry density, water permeability coefficient, etc.) is less likely to vary. In addition, since the construction method is simple, quality control on site is easy, and since reproducibility is high, setting of construction conditions and the like can be performed in a test room.

  In addition, if the gap ratio of the loosely packed assembly S1 is reduced by force using a large compactor or the like, a large lateral pressure may be generated and affect the pit P. However, the construction of the low water permeability layer according to the present embodiment is possible. Since the method uses the vibration energy to reduce the gap ratio, a large side pressure is not generated, and therefore the influence on the pit P is small.

  In addition, according to the present embodiment, existing construction machines and equipment can be used, and a special construction machine or the like is not required, so that the cost can be reduced. In addition, since a large heavy machine is not necessarily required, it is possible to construct a high quality low water permeable layer S3 even in a narrow space.

  In addition, according to the present embodiment, since the aggregate 1 and the granule 2 are formed of bentonite-containing granulated material, the work space is not filled with dust, and a good work space is ensured. It becomes possible.

  Moreover, in this embodiment, since vibration is applied to the densely packed aggregate S2 filled with the granules 2 after the granules 2 are charged, the packing density of the granules 2 is increased, and consequently low water permeability. The filling and drying density of the layer S3 is high.

  Incidentally, the relationship between the bentonite filling dry density ρ in the low water permeable layer S3 and the vibration time is as shown in Table 1.

  As can be seen from Table 1, the filling dry density ρ tends to increase as the excitation time of the main excitation becomes longer. If the excitation time of the main excitation is the same, the excitation time of the final excitation is the same. As the length increases, the filling dry density ρ tends to increase. In addition, even when the excitation time of the main excitation is 5 seconds, it is possible to obtain a low water permeability layer S3 with no variation in quality, but when the excitation time of the main excitation is 10 seconds or more, Since the effect of the finish excitation time on the filling and drying density ρ is small, the low water permeability layer S3 with no further variation in quality can be obtained.

  In the above-described embodiment, the case where vibration is applied to the loosely packed aggregate S1 after the predetermined amount of aggregate 1 has been sprinkled is illustrated. However, while the aggregate 1 is sprinkled, vibration is applied to the loosely packed aggregate S1. May be.

  In the above-described embodiment, the case where vibration is applied to the densely packed aggregate S2 after the predetermined amount of granules 2 is charged is illustrated. However, the granules 2 are charged while being vibrated to the densely packed aggregate S2. Also good. Further, as can be seen from Table 1, finish vibration may be omitted.

(A)-(f) is a schematic diagram for demonstrating the procedure of the construction method of the low water permeability layer which concerns on one Embodiment of this invention. (A) is typical sectional drawing which shows the case where the construction method of the low water permeability layer which concerns on one Embodiment of this invention is applied to the disposal facility of radioactive waste, (b) is AA of (a). It is line sectional drawing.

Explanation of symbols

1 Aggregate 2 Granule S1 Loosely packed aggregate S2 Closely packed aggregate S3 Low water permeability

Claims (5)

The aggregate made of bentonite-containing granulated material is sprinkled to form a loosely packed aggregate of the aggregate, and the loosely packed aggregate is vibrated to form a tightly packed aggregate, and then from the aggregate A method for constructing a low water permeable layer, characterized in that granules comprising bentonite-containing granules having a small particle diameter are introduced from above the densely packed aggregate and the granules are filled in the gaps in the densely packed aggregate . The aggregate made of bentonite-containing granulated material is sprinkled to form a loosely packed aggregate of the aggregate, and the loosely packed aggregate is vibrated to form a tightly packed aggregate, and then from the aggregate A granule made of bentonite-containing granule having a small particle diameter is charged from above the densely packed aggregate to fill the gap in the densely packed aggregate and vibrates with respect to the densely packed aggregate. A method for constructing a low water permeable layer, characterized by comprising: Squeezing out an aggregate composed of bentonite-containing particulates to form a loosely packed aggregate of the aggregate;
Applying the vibration to the loosely packed aggregate to form a tightly packed aggregate having a smaller gap ratio than the loosely packed aggregate; and
Filling a granule made of bentonite-containing granular material having a particle size smaller than that of the aggregate from the upper side of the densely packed aggregate, and filling the granules into the gaps in the densely packed aggregate. A method for constructing a low water permeability layer.   The method for constructing a low water permeability layer according to claim 3, further comprising a finish vibration step for applying vibration to the densely packed aggregate that has undergone the filling step.   The particle size ratio between the aggregate and the granule in the low water permeability layer to be constructed, the weight percentage of the aggregate and the weight percentage of the granule are set in a preliminary test, and the particle size ratio set in the preliminary test is set. The construction method of the low water permeable layer according to any one of claims 1 to 4, wherein the construction is performed so as to be a weight percentage.

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