Pumping well, and filter material used for the same

Abstract

To suppress infiltration of sand from the surrounding ground into a filter material, in a pumping well that pumps water through a filter material made of granular material packed around a well pipe.SOLUTION: A pumping well 100 comprises: a vertical hole 1 excavated in the ground; a well pipe 2 erected within the vertical hole 1 and equipped with a strainer 22 having a through hole or slit 22b that separates water from granular material and allows the same to pass through; and a filter material 3 made of granular material filled between the well pipe 2 and a surrounding wall of the vertical hole 1. In the pumping well 100, the filter material 3 is made of crushed shells.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pumping well used in a groundwater level lowering method such as root excavation work, and more particularly to a pumping well that pumps up groundwater through a filter material filled with granular material. [Background technology]

[0002] Conventionally, in excavation work involving excavation of the ground, a groundwater level lowering method has been used to pump up groundwater using a pumping well in order to facilitate underground construction work. This groundwater level lowering method is widely used in which a cylindrical strainer that allows water to pass but not soil is installed in a vertical hole in the ground, a filter material made of gravel or silica sand is filled between the strainer and the peripheral wall of the vertical hole, and groundwater is pumped up through this filter material and the strainer (see, for example, Patent Document 1).

[0003] For example, Patent Document 1 discloses a groundwater pumping device in which a groundwater inlet is provided on the peripheral wall of the lower end of an inner pipe erected in a vertical hole, a strainer tube made of wire wound around the inner pipe is attached, and a filter material made of coarse sand, pea gravel, etc. is filled between the strainer tube and the peripheral wall of the vertical hole.

[0004] Moreover, in Figure 11 of Patent Document 1, the so-called deep well method is cited as the prior art at the time of filing. In this deep well method, the lower half of a cylindrical well erected in a vertical hole is used as a strainer, and a filter material made of coarse sand, pea gravel, etc. is filled between the strainer and the inner wall of the vertical hole. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3974851 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when coarse sand or pea gravel is used as the filter material, as in Patent Document 1, there is a problem that if water is pumped over a long period of time, fine soil from the surrounding ground will flow into the gaps in the filter material, causing the filter material to become clogged and reducing its permeability. The present invention has been made in consideration of the above problems, and has an object to provide a pumping well whose pumping capacity is not significantly reduced even when pumping is performed for a long period of time. [Means for solving the problem]

[0007] The invention made to solve the above-mentioned problems is a pumping well comprising a vertical hole excavated in the ground, a well pipe erected in the vertical hole and equipped with a strainer that allows water to pass through a through hole or slit or the like, and a filter material made of granular material filled between the well pipe and the peripheral wall of the vertical hole, wherein the granular material consists of crushed shells.

[0008] Because the pumping well of the present invention uses crushed shells as the filter material, clogging of the filter material by fine soil mixed in from the surrounding area can be suppressed compared to pumping wells that use filter material made of sand or gravel.

[0009] The shells are preferably bivalve shells, which can further prevent the filter material from becoming clogged with sand.

[0010] The shells are preferably scallop shells. This further prevents the filter material from becoming clogged with sand. In addition, in Hokkaido and Tohoku regions, where scallops are produced, there is a problem with disposing of the large amount of scallop shells. By using scallops for the crushed shells, the processing cost of the scallop shells can be reduced.

[0011] The crushed shells preferably contain a basic particle size portion in which the passing mass percentage increases steadily in the particle size range of 4.75 mm to 19 mm, thereby preventing a decrease in the hydraulic conductivity of the filter material due to the inclusion of fine soil in the filter material. Here, "particle size is D1 mm or more and D2 mm or less" means that the metal mesh sieve does not pass through those with openings of D1 mm, but passes through those with openings of D2 mm. "Passing mass percentage at particle size D3mm" means the percentage of the total mass of crushed shells with particle sizes between D1mm and D3mm to the total weight of crushed shells with particle sizes between D1mm and D2mm. Additionally, "increasing steadily in the range of 4.75 mm to 19 mm" means that at least one point between 4.75 mm and 19 mm, the passing mass percentage is greater than 0% and less than 100%.

[0012] The percentage by mass of the fundamental particle size fraction passing through a 9.5 mm sieve is preferably 10% or more and less than 60%. This makes it possible to more effectively prevent a decrease in the hydraulic conductivity of the filter material caused by the incorporation of fine soil into the filter material.

[0013] The crushed shells may include shells having a particle size of 2 mm or more but less than 4.75 mm, and / or greater than 19 mm but less than or equal to 95 mm.

[0014] The present invention provides a filter material for use in a pumping well comprising a vertical hole excavated in the ground, a well pipe erected in the vertical hole and equipped with a strainer that separates water from granular material by means of a through hole or slit and allows water to pass through, and a filter material made of granular material filled between the well pipe and the peripheral wall of the vertical hole, wherein the granular material includes a filter material made of crushed shells. Effect of the Invention

[0015] As described above, the pumping well of the present invention can suppress clogging of the filter material with fine soil. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is a schematic diagram of a pumping well according to the first embodiment of the present invention. [Diagram 2]FIG. 5 is a schematic diagram of a pumping well according to a second embodiment of the present invention. [Diagram 3] FIG. 1 is a schematic diagram of an experimental apparatus used in Experimental Example 1. [Figure 4] FIG. 2 is a schematic diagram of a container loaded into a filter material tank of the experimental device of Experimental Example 1. [Diagram 5] 1 shows the dry density of the sample used in Experimental Example 1. [Figure 6] 1 is a particle size accumulation curve of a sample used in Experimental Example 1. [Figure 7] 1 is a table showing a comparison of the amount of mixed sand, the mixed sand rate, and the mixed sand rate ratio between Example 1 and Comparative Example 1, which were obtained from Experimental Example 1. [Figure 8] FIG. 1 is a graph showing the relationship between the hydraulic conductivity of a filter material and the sand mixing ratio, which was obtained in advance through an experiment in order to estimate the hydraulic conductivity of the filter material. [Figure 9] This is an estimated value of the hydraulic conductivity calculated using the relationship diagram of FIG. 8 based on the sand mixing ratio obtained in Experimental Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Next, an embodiment of a pumping well according to the present invention will be described. However, the present invention is not limited to the following embodiment. In the following description, "sand" is not limited to a specific particle size, but also includes "fine-grained soil." (Embodiment 1) 1 shows a pumping well 100 according to a first embodiment of the present invention. The pumping well 100 mainly comprises a vertical hole 1 excavated in the ground, a well pipe 2 erected in the vertical hole 1, and a filter material 3 filled between the well pipe 2 and the peripheral wall of the vertical hole 1. The pumping well 100 also comprises a pumping pump 4 for pumping up water that has flowed into the well pipe 2, and a vacuum pump 5 for sucking air out of the well pipe 2.

[0018] The pumping well 100 is used for the Ultra Deep Construction Method (registered trademark), and the well pipe 2 includes an inner tube 21 made of a cylindrical steel pipe and a strainer 22 annularly attached to the inner tube 21 .

[0019] The inner cylinder 21 is formed in a cylindrical shape with a lid and a bottom, and is provided with a water passage hole 21a consisting of a circular through hole in the peripheral wall near the lower end. The strainer 22 is formed by winding a metal wire in a spiral shape, and has a spiral slit 22b formed between adjacent spiral rings 22a, 22a. The strainer 22 surrounds the inner tube 21 except for a part of the lower end side and a part of the upper end side of the inner tube 21.

[0020] The filter material 3 is filled into the vertical hole 1 so as to fill the space between the strainer 22 and the peripheral wall of the vertical hole 1, and at a part of the upper end side and a part of the lower end side of the well pipe 2 where there is no strainer, so as to fill the space between the inner tube 21 and the peripheral wall of the vertical hole 1.

[0021] The groundwater W enters the inner cylinder 21 through the filter material 3, the strainer 22, and the water passage hole 21a by gravity and the negative pressure supplied into the inner cylinder 21 by the vacuum pump 5, and is stored in the inner cylinder 21. The groundwater W stored in the inner cylinder 21 is pumped up by the lifting pump 4.

[0022] It is important that the filter material 3 is made of crushed shells. This makes it possible to prevent the filter material 3 from becoming clogged with sand (fine soil) mixed into the filter material 3 from the surrounding area, which would impair the water permeability of the filter material 3, compared to when sand or gravel is used as the filter material 3.

[0023] The shells used for the crushed shells of the filter material 3 are not particularly limited, and may be bivalve shells such as clams, cockles, and scallops, or snail shells such as turban shells, abalone, and cowrie shells, but are preferably bivalve shells, and more preferably scallops. By using crushed shells of bivalve shells, particularly scallops, for the filter material 3, it is possible to effectively prevent sand (fine soil) from entering the filter material 3 compared to using other crushed shells. In particular, about 250,000 tons of scallop shells are generated from Hokkaido to Tohoku, and it is very costly to treat them as industrial waste. By using crushed scallop shells for the filter material, it is possible to reduce the cost of treating the scallop shells.

[0024] The crushed shells of the filter material 3 preferably have a particle size of 4.75 mm or more and 19 mm or less, and include a basic particle size portion in which the passing mass percentage increases steadily within that range. This can suppress deterioration of the hydraulic conductivity caused by sand (fine soil) being mixed into the filter material 3. The passing mass percentage of only this basic particle size portion at a particle size of 9.5 mm is preferably 10% or more and less than 60%, more preferably 20% or more and less than 50%, and particularly preferably 30% or more and less than 40%. This can more effectively suppress a decrease in the hydraulic conductivity of the filter material 3. Furthermore, it is preferable that the filter material 3 has less than 10% of the total mass of granular matter with a particle size of less than 4.75 mm. This can increase the hydraulic conductivity of the filter material.

[0025] The crushed shells of the filter material 3 may include shells having a particle size of 2 mm or more and less than 4.75 mm, and may also include crushed shells having a particle size of more than 19 mm and less than 95 mm.

[0026] Second embodiment 2 shows a pumping well 200 according to a second embodiment of the present invention. The pumping well 200 mainly comprises a vertical hole 1 provided by excavating the ground, a well pipe 202 erected in the vertical hole 1, and a filter material 3 filled between the well pipe 202 and the peripheral wall of the vertical hole 1, as well as a pumping pump 4 for pumping up water that has flowed into the well pipe 202. In the second embodiment, components common to the first embodiment are designated by the same reference numerals as in the first embodiment, and description thereof will be omitted.

[0027] The pumping well 200 according to the second embodiment is a pumping well used in the so-called deep well method, and the well pipe 202 is cylindrical with an open top and bottom, and includes an upper part 221 made of a cylindrical steel pipe, and a strainer 222 formed by winding a linear member in approximately the same shape as the upper part. The filter material 3 is filled between the well pipe 202 and the peripheral wall of the shaft 1.

[0028] <Experimental Example 1 - Penetration test> Next, a description will be given of a penetration test for measuring the amount of sand mixed into the filter materials according to Example 1 of the present invention and Comparative Example 1. However, the present invention is not limited to the following examples.

[0029] As shown in FIG. 3, a small soil tank 300 formed into a rectangular parallelepiped shape using 10 mm thick acrylic plates was used as the experimental equipment used in the infiltration test. The small soil tank 300 imitates the pumping well of the present invention. The small soil tank 300 had inner dimensions of 430 mm wide, 198 mm deep, and 450 mm high. The inside of the small soil tank 300 was divided into three equal parts in the width direction by removable acrylic plates, which were a sand tank 301, a filter material tank 302, and a well tank 303 from the left side of the figure. A box-shaped container 304 shown in FIG. 4 was loaded into the filter material tank 302. The box-shaped container 304 had the front and back side walls and bottom wall formed of acrylic plates in FIG. 3 and FIG. 4, and the left and right side walls formed of geotextile, and had a depth of 400 mm, width of 90 mm, and depth of 195 mm. A water supply tank 305 was provided on the outside of the sand tank 301 (left side in Fig. 3), and the water supply tank 305 and the sand tank 301 were connected via a water supply pipe 306 provided near the lower part of the outer surface of the sand tank 301. A drain outlet 307 was provided at the lower part of the outer surface of the well tank 303 (right side in Fig. 3).

[0030] Example 1 After filling the container 304 with crushed scallop shells as test specimens, Toyoura sand with a relative density of D was poured into the sand tank 301. r = 50%. The well tank 303 was filled with water to a depth of 50 mm with the drain outlet 307 closed. The dry density and particle size normal curves of the crushed shells and Toyoura sand used here are shown in Figures 5 and 6. Next, water was poured into the sand tank 301 from the water supply tank 305 until the water level reached the surface of the Toyoura sand over a sufficient period of time. After confirming that the water level had stabilized on the surface of the Toyoura sand and the water level difference with the well tank 303 had reached 200 mm, the acrylic plate 301a between the sand tank 301 and the filter material tank 302 was slowly pulled out. Then, the water was drained until no water came out of the drain outlet 307, and the container 304 was removed. The test specimen thus obtained, containing sand, was oven-dried for 24 hours, sieved, and the amount of sand mixed in was measured.

[0031] Comparative Example 1 The penetration test was carried out in the same manner as in Example 1, except that the test specimen was crushed stone having the dry density and particle size accumulation curves shown in Figures 5 and 6, and the amount of sand mixed in was measured. As shown in Figure 6, the crushed shells in Example 1 and the crushed stone in Comparative Example 1 had roughly the same particle size accumulation curves. In addition, the passing mass percentages (%) of both the crushed stone and the crushed shells through a 9.5 mm sieve were approximately 35% (30% to 40%).

[0032] <Results and Considerations of Experimental Example 1>

[0033] (Sand mixing ratio) The amount of sand (g), sand content (%), and sand content ratio obtained from the permeation test in Experimental Example 1 (Example 1 and Comparative Example 1) are shown in Figure 7. The sand content (%) is calculated based on the pore volume (cm) of the filter material. 3 ) vs. the volume of sand mixed in the filter material (cm 3 ) and the sand mixing ratio indicates the ratio of the sand mixing ratio of the crushed shells (Example 1) to the sand mixing ratio of the crushed stone (Comparative Example 1).

[0034] As shown in Figure 7, when comparing the amount of sand mixed in crushed stone and crushed shells, it can be seen that the amount of sand mixed in crushed stone is less. On the other hand, crushed shells have a large porosity, so when comparing the sand mixing rates of crushed stone and crushed shells, it can be seen that the sand mixing rate of crushed shells is less. In addition, since the sand mixing rate ratio of crushed shells to the sand purchase rate of crushed stone is 0.7, it can be seen that by using crushed shells as the filter material, the sand mixing rate can be reduced to about 70% compared to when crushed stone is used as the filter material.

[0035] (Permeability coefficient) Fig. 8 is a graph showing the relationship between the sand mixing rate (%) and the hydraulic conductivity (m / s) obtained by the inventors in separate experiments for crushed stone and crushed shells. In the table shown in Fig. 9, the initial hydraulic conductivity (%) is the hydraulic conductivity without sand mixing, and the hydraulic conductivity (%) taking into account the mixing of sand is the hydraulic conductivity (m / s) at the sand mixing rate (%) of the crushed shells of Example 1 and the crushed stone of Comparative Example 1 shown in Fig. 7, which was read using the graph in Fig. 8. In the table in Fig. 9, the hydraulic conductivity reduction rate (%) indicates the reduction rate of the hydraulic conductivity (%) taking into account the mixing of sand from the initial hydraulic conductivity (%).

[0036] As shown in Figure 9, the rate of decrease in hydraulic conductivity due to the inclusion of sand was smaller for the crushed shells of Example 1 than for the crushed stone of Comparative Example 1. This indicates that the decrease in hydraulic conductivity due to the inclusion of sand can be suppressed by using crushed shells instead of crushed stone.

[0037] As described above, the pumping well according to the present invention is not limited to the above-mentioned embodiment. For example, the strainer may have through holes or slits that suppress the passage of the filter material and allow water to pass through, and may not be a metal wire wound in a spiral shape. The shells used for the crushed shells do not have to be scallop shells or bivalve shells. The crushed shells may include shells with a particle size of less than 2 mm or more than 95 mm. The pumping well according to the present invention can also be used as a water injection well for injecting water into the ground. [Explanation of symbols]

[0038] 100 Pumping well 1 Pit 22b Slit 22 Strainer 2. Well pipes 3. Filter material

Claims

1. A pumping well comprising: a vertical hole excavated in the ground; a well pipe provided with a strainer that is erected in the vertical hole and has a through hole or a slit that separates water from granular matter and allows water to pass through; and a filter material made of granular matter that is filled between the well pipe and the peripheral wall of the vertical hole, A pumping well, characterized in that the granular material consists of crushed shells.

2. The pumping well of claim 1 , wherein the shells are bivalve shells.

3. The pumping well of claim 1 , wherein the shells are scallop shells.

4. The pumping well according to claim 1, wherein the crushed shells include a basic particle size portion in which the passing mass percentage increases steadily in the particle size range of 4.75 mm or more and 19 mm or less.

5. The pumping well according to claim 4, wherein the basic particle size fraction has a passing mass percentage at a sieve opening of 9.5 mm of 10% or more and less than 60%.

6. The pumping well of claim 4, wherein the crushed shells include shells having a particle size of 2 mm or more but less than 4.75 mm, and / or greater than 19 mm and less than 95 mm.

7. A filter material for use in a pumping well, comprising: a vertical hole excavated in the ground; a well pipe provided with a strainer that is erected in the vertical hole and has a through hole or a slit that separates water from granular matter and allows water to pass through; and a filter material made of granular matter that is filled between the well pipe and the peripheral wall of the vertical hole, The filter material, wherein the particulate matter is crushed seashells.

Images