JP5012405B2 - Underground purification structure and construction method - Google Patents

Description

  The present invention relates to a wall-like purification structure installed in the ground, which is used for in-situ groundwater purification, and a construction method thereof. In particular, the present invention is a wall-like structure that is buried in the ground and that purifies groundwater contaminated with organochlorine compounds or heavy metals, and in particular, a structure in which a purification unit included in the structure is configured to be replaceable and the structure thereof. Concerning construction method.

  Conventionally, as a method for purifying groundwater contaminated with harmful substances, a method for creating a water-permeable purification wall in the ground is known. For example, Patent Document 1 discloses a method of purifying contaminated groundwater by passing through a purification wall made of a metal body such as iron powder. Such a purification structure that allows contaminated groundwater to permeate is called a permeable purification wall (PRB). Some PRBs are provided with a purifying section having a purifying action inside a water-permeable hollow wall body, and it is also known that the purifying section is configured to be replaceable (for example, Patent Document 2 and Patent Document 3). ).

  The following can be cited as a method for creating PRB in the ground. The first method is to create a PRB by excavating underground with steel sheet piles as retaining walls. In this construction method, two rows of steel sheet piles are arranged in the horizontal direction so that the side edges are in contact with each other to form a wall, and two rows are placed in the ground so that the surfaces face each other. And the ground of the area | region pinched | interposed into the row | line | column of this opposite steel sheet pile is excavated, the purification material is filled and backfilled, and it is set as PRB. The steel sheet pile is then pulled out to allow the groundwater to pass through the purification material filled in the excavation hole, and purification is performed in the process.

  As a second construction method, H-section steel is used instead of placing steel sheet piles. In this construction method, a region where the purification wall is formed is surrounded by a plurality of H-shaped steels arranged at regular intervals, and the ground in the region surrounded by the H-shaped steel is excavated. And when excavating to a certain depth, a wooden board is passed between a pair of adjacent H-shaped steels, and the excavation wall is covered with a wooden sheet pile so that the excavation wall does not collapse. After excavating to the lower end position of the purification material in this way, the space generated by excavation is filled with the purification material and backfilled, and the wood sheet pile is pulled out. In this method, the H-shaped steel material is pulled out last.

  Since this method does not drive a sheet pile into the ground prior to excavation, there is an advantage that an inexpensive wooden sheet pile can be used as a sheet pile for retaining earth, although it is inferior in strength to a steel sheet pile. In addition, a relatively small wooden sheet pile is fixed between the H-shaped steel materials and drilled. When the purification material is backfilled, the wooden sheet piles are sequentially pulled out, making it easier to pull out the larger steel sheet piles at once. It also has the advantage of being.

As a third construction method, a hollow casing is penetrated into the ground, the inside of the casing is excavated, and then the excavation hole is backfilled with a purification material, and the casing is pulled out to form a columnar purification section. Next, the casing is newly penetrated so as to be adjacent to the purification section, and the above-described excavation, purification material filling, and casing extraction are repeated, and a purification wall is formed by continuously forming the adjacent columnar purification section ( For example, Patent Document 3).
Japanese Patent No. 3079109 Japanese Examined Patent Publication No. 6-104975 JP 2006-272158 A

  In the PRB construction method described above, during excavation of the ground, the wall is covered with a sheet pile in order to prevent the excavation wall from collapsing. In the method of building a building in the basement, since the inflow of water into the part where the underground building was built after excavation is rather undesirable, the backfilling is performed without pulling out the sheet pile used to prevent the excavation wall from collapsing. However, when creating a PRB, it is necessary to allow groundwater to flow into and out of the PRB. Therefore, it is necessary to draw out the sheet pile that hinders the flow of water at the time of backfilling the purification material or after backfilling. Similarly, in the method using the casing, the casing must be pulled out after the purification material is filled. For this reason, in the said prior art, a construction period becomes long by the part for which a drawing-out process is required.

  On the other hand, in order to replace the PRB purifying section (part composed of the purifying material), it is necessary to newly install a sheet pile or the like in the ground as in the PRB creation. In this way, the initial installation work and replacement work of the PRB had been overwhelmed with long-term work.

  Furthermore, the second method of passing a wood sheet pile between H-shaped steels has the above-mentioned advantages, but there is a problem that the excavation wall collapses when the sheet pile is pulled out, and the soil that has fallen into the purification material is mixed. . That is, in this construction method, the sheet pile passed between the H-shaped steel materials during excavation is pulled out by one stage, and the purification material is refilled back to the upper end position of the pulled sheet pile by repeating. When the sheet pile is pulled out, the wall of the excavation hole that has been prevented from collapsing by the pulled sheet pile is likely to collapse. In particular, when a PRB is created on a ground where a lot of sand tends to collapse, the soil that has collapsed in the space filled with the purification material tends to be avalanche. As a result, a portion where the thickness of the PRB is locally thin is formed, causing a short path of groundwater, resulting in a decrease in purification function.

  Moreover, since the conventional PRB is in a state where only the purification material exists in the ground, in the unlikely event of an earthquake, there is a possibility that a horizontal shift may occur depending on the magnitude of the earthquake. If the ground slips laterally, the purification section will be damaged, and there is a risk that the groundwater will not be purified by a short pass from the damaged section.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a PRB structure and a construction method thereof that can form a PRB and exchange a purification material in a short period of time and stably perform a purification function over a long period of time.

  In the present invention, the region (purification part) filled with the purification material is surrounded by a plurality of columnar or plate-shaped strength members arranged at a predetermined interval, and is left as it is. More specifically, the present invention provides the following.

(1) It is a permeable purification structure provided in the ground, and is disposed around the purification unit, which is configured by embedding a purification material in the ground, and is spaced from each other. a plurality of pillars like strength member, permeable purification structures having a lateral sheet pile permeability disposed between the pair of strength members adjacent to each other among the plurality of columnar strength member.
(2 ) The permeable purification structure according to (1 ), wherein each of the plurality of columnar strength members is fixed to another strength member by a fixing member.
(3) spaced apart from each other a plurality of posts like strength member, and Da設into the ground as a whole in a plan view imitates a substantially frame-shaped, drilled region surrounded by the plurality of columnar strength member And arranging a permeable sheet pile between a pair of strength members adjacent to each other among the plurality of columnar strength members, filling a space formed by excavation with a purification material and backfilling to form a purification section, A permeable purification structure construction method in which the purification section is made of a permeable purification structure surrounded by the plurality of purification members without removing a plurality of columnar strength members from the ground.
(4) Before Kiyoko sheet pile by filling the purification material by leaving the ground, permeable purifying structure method according to the ambient is a state of being surrounded by said lateral sheet piles (3) of the purification unit.
( 5 ) The permeability purification structure construction method according to ( 3 ), wherein the plurality of columnar strength members are fixed by a fixing member.

  According to the present invention, a columnar or plate-like strength member such as H-shaped steel is placed around the purification section, and after the PRB is built by excavating the ground, the strength member is left as it is. For this reason, the construction period at the time of replacement | exchange of a purification material can be shortened. Also, by placing a permeable sheet pile between the strength members or connecting the strength members with a fixed member, the strength of the PRB against horizontal strain can be increased, and damage to the PRB when an impact is applied to the ground Can be reduced.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Hereinafter, the same members are denoted by the same reference numerals, and description thereof is omitted or simplified.

  FIG. 1 is a plan view showing a state in which a permeable purification structure (hereinafter “PRB”) 1 according to a first embodiment of the present invention is embedded in the ground, and FIG. 2 is a perspective view. The PRB 1 is substantially wall-shaped, and a pair of oblique water walls 5 are arranged so as to contact a pair of opposing side walls. In the figure, arrows indicate the flow of groundwater. As shown in FIG. 1, the sloping water wall 5 spreads in a fan shape with the PRB 1 in between, and the contaminated groundwater that has passed through the contaminated area flows along the sloping water wall 5 and is collected in the area where the PRB 1 is disposed, and passes through the PRB 1. Discharged as treated water. Hereinafter, the configuration of the PRB 1 will be described by being divided into a substantially wall-like purification unit 11 and a peripheral unit 12 surrounding the purification unit 11. The purification part 11 is comprised with the purification material 21 embed | buried in the water-permeable layer, and the purification material 21 mixes the various substances for purification | cleaning which have sand and gravel and a purification effect. Since sand and gravel have water permeability as a whole aggregated aggregate, they are called water-permeable granular materials. The water-permeable granular material has a particle size of about 0.01 to 10 mm, particularly 0.3 to 5 mm, a particle having a particle size of 1/16 mm or more and less than 2 mm, a gravel (or “gravel”) having a particle size of 2 mm or more, Bean gravel or the like having a particle size exceeding 10 mm is used.

  Examples of the substance for purification include granular materials having a catalytic action and an adsorption action, such as metal reductants such as iron powder, activated carbon, ion exchange resins, and microorganism-supporting carriers. When iron powder is used, the particle diameter is preferably about 0.1 to 2 mm in consideration of the balance between the surface area and water permeability. The types of the purification substance and the water-permeable granular material, and the mixing ratio of both are appropriately selected according to the purification target. When iron powder and sand are mixed, the ratio of iron powder: sand is preferably in the range of 10:90 to 80:20 in terms of weight ratio from the viewpoints of ensuring a purification effect and water permeability and reducing costs.

  In the PRB 1 according to the first embodiment, a plurality of H-section steels 22 as strength members are driven perpendicular to the horizontal plane so as to surround the purification unit 11. When the PRB 1 is formed or when the purification material 21 is replaced, one sheet pile 23 is fitted between the two adjacent H-section steels 22. In this PRB 1, the lateral sheet pile 23 is formed of a net body having a size that can prevent the opening from being sanded, and is disposed in the ground without being pulled out even after the purification material 21 is filled. Such a horizontal sheet pile 23 is comprised by what expanded nets, (synthetic) resin net | networks, net bodies, such as a geotextile, or what made shape steel and bar steel into the shape of a net or a fence.

  The columnar or plate-shaped strength member surrounding the purification unit 11 is not limited in its material and shape as long as it is a member made of a material having strength that can withstand placement. The H-shaped steel and the lateral sheet pile as the strength member may be rust-proofed. Further, the mesh of the permeable sheet piles is not particularly limited as long as it can temporarily stop a large amount of earth and sand from flowing into the excavation space from the excavation surface.

  Hereinafter, the construction method for creating the PRB 1 will be described with reference to FIG. FIG. 3 is a schematic diagram for explaining the flow of the construction method for creating the PRB 1. First, in the land where contaminated groundwater flows, a region where the purification unit 11 is built is determined, and a plurality of H-section steels 22 are placed in the ground so as to surround this region. The H-section steel 22 is placed so as to have a constant interval between the other adjacent H-section steels 22. The interval between the H-section steels 22 is preferably 1000 to 2000 mm. If the interval between the H-shaped steels 22 is about 1000 to 2000 mm, it is suitable for sandwiching a general-purpose sized sheet pile 23 between them, and the H-shaped steels are fixed to each other as in the second embodiment to be described later. It is convenient to fix with.

  Thus, the area surrounded by the H-section steel 22 is excavated to a certain depth. When a predetermined depth (here, the length of the horizontal sheet pile 23) is reached, the horizontal sheet piles 23 are fitted one by one between two adjacent H-shaped steels 22 and fixed to the H-shaped steel 22 ( (See FIG. 3 (a)). In this way, the walls of the space generated by excavation are covered with a plurality of (the number obtained by subtracting 1 from the number of H-section steel) horizontal sheet piles 23 to prevent the excavated walls from being buried because the earth and sand collapsed. .

  After covering the surrounding wall of the space generated by excavation with the lateral sheet pile 23, the excavation is resumed to excavate to a predetermined depth (the length of the lateral sheet pile 23), and the excavated wall is covered with the lateral sheet pile. The operation is repeated (see FIG. 3B). Thereby, as shown in FIG.3 (c), excavation to the target depth (for example, vicinity of the boundary of the aquifer 6 and the impermeable layer 7) is performed, and excavation is complete | finished.

  In the present embodiment, since a permeable plate that allows water to pass is used as the lateral sheet pile 23, the purification material 21 is introduced into the excavated space while the lateral sheet pile 23 is fixed to the H-section steel 22. After the purification material 21 is filled to a predetermined depth (for example, the upper end position of the aquifer), the backfilling is completed using soil for backfilling as necessary.

  In the PRB 1 of this embodiment, the plurality of H-section steel plates 22 and the lateral sheet piles 23 arranged around the purification unit 11 constituted by the purification material 21 are not pulled out. Therefore, the construction period of the PRB 1 can be shortened by the amount that is not necessary for drawing out when using a water shielding wall (such as a steel sheet pile or casing) in order to prevent the excavation wall from collapsing. Further, when the purification material 21 constituting the purification unit 11 is replaced, it is not necessary to arrange a sheet pile again to prevent the excavation wall from collapsing, so that the replacement work period of the purification material 21 can be shortened.

  The said embodiment can be suitably employ | adopted when the geology of contaminated land is sandy and an excavation part tends to collapse. That is, in the above-described conventional technique, the purification material is filled after removing the wood sheet pile fitted between the H-shaped steels, so that the excavation wall of the portion where the wood sheet pile is removed collapses, and the collapsed earth and sand fall in the purification material filling space. There was a risk of mixing. On the other hand, in this embodiment, the fall of the purification material content rate by mixing of collapsed earth and sand can be reduced.

  Moreover, in the construction method according to the above-described embodiment, the H-shaped steel is first placed, and the transverse sheet pile is fixed therebetween. Therefore, unlike the case where the sheet pile itself is placed in the ground, the sheet pile itself can withstand the placement. There is no need for strength. For this reason, a member such as a permeable net body can be used as a sheet pile, and even if the sheet pile is buried in the ground, the inflow and outflow of contaminated groundwater to the purification unit 11 is not hindered.

  Furthermore, since the purification | cleaning part 11 is enclosed by the H-section steel 22 and the cross sheet pile 23, even when a shift | offset | difference arises in the ground by an earthquake etc., the peripheral part 12 acts so that the shape of the purification | cleaning part 11 may be maintained, Damage to the purification unit 11 can be prevented or reduced. Moreover, since the peripheral part 12 which covers the purification | cleaning part 11 is comprised with the several member (The several H-section steel 22 and the cross sheet pile 23) which can be removed separately, the repair of the peripheral part 12 is also easy.

  Next, the PRB 2 according to the second embodiment of the present invention will be described with reference to FIG. The PRB 2 of the second embodiment differs from the PRB 1 of the first embodiment in that the peripheral portion 12B is configured by an H-section steel 22 and a fixing member 25 that connects and fixes adjacent H-section steels 22 to each other.

  Here, a reinforcing bar is used as the fixing member 25, and the reinforcing bar and the H-shaped steel are welded. The present invention is not limited to the above-mentioned means using a steel bar such as a reinforcing bar for fixing the H-shaped steels, but is configured so that a plurality of H-shaped steels 22 can be welded or fixed with bolts and nuts via a fixing member. Anything is acceptable. The H-shaped steels 22 may be fixed together during excavation or after completion of excavation and before the purification material 21 is backfilled. The PRB 2 of the second embodiment can be suitably used for slightly clayey soil in which walls are not easily collapsed during excavation.

  In order to achieve this object, the present invention makes it unnecessary to pull out the H-section steel and shortens the construction period by eliminating the need to place the H-section steel when the purification section is replaced. The H-section steels 22 do not necessarily have to be connected and fixed to each other. That is, in order to prevent the movement of water with respect to the purification unit from being disturbed even if the columnar or plate-like member is left, members such as H-shaped steel are placed around the purification unit at regular intervals during PRB creation. In this way, it is possible to eliminate the need to pull out the member.

  However, if the strength members are connected and fixed, the strength members that are connected and fixed act as a frame that surrounds the purification portion and maintains this shape. it can. Further, when any of the plurality of strength members moves or bends and needs repair, it can be repaired easily.

  The method for fixing the strength members to each other is not limited to the above-described mode. For example, the lateral sheet pile 23 of the first embodiment may be used as the fixing member. That is, in the first embodiment, the H-section steel 22 is made to function as a rail that is fixed with the cross sheet pile 23 interposed therebetween. However, the cross-sheet pile 23 is connected to the H-section steel member 22 and fixed to connect and fix the H-section steel pieces 22 to each other. You may use the horizontal sheet pile 23 as a member.

[Example 1]
PRB was created on a hard ground with an N value exceeding 50 according to the standard penetration test defined in Japanese Industrial Standard JIS A1219, and the contaminated groundwater was purified for a certain period without extracting the H-section steel. The PRB has the same configuration as the PRB 2 shown in FIG. 4 except that the H-shaped steels are not fixed to each other by a fixing member. The horizontal width W is 2 m, the length L is 200 m, and the lower end is 8 m underground. Located in. The purification unit 11 is constructed so that the horizontal width W and length L are the same as those of the PRB 2, the vertical height H with respect to the ground is 3 m, the lower end is 5 m underground, and the upper end is located 2 m underground. Yes. A total of 40 H-sections 22 are placed at a depth of 8 m underground so as to surround the purification section 11. The H-section steel 22 has a width of 350 mm and a length of 8 m, and the interval between adjacent H-section steels 22 is 1.5 m.

  In Example 1, the purifying unit 11 of the PRB 2 was replaced. Specifically, the area where the PRB 2 is installed is excavated to 5 m underground, all the purifying material 21 constituting the purifying unit 11 is excavated, and the new purifying material 21 is filled again in the excavation hole and purified. The material 21 was changed. The purification material 21 was formed by mixing sand (average particle size: 1 mm) as a water-permeable material and iron powder (average particle size: 1 mm) as a purification material.

  When replacing the purification material 21, it was not necessary to place and pull out the H-section steel 22. As a result, the construction period could be shortened by 30 days compared to the conventional PRB purification section replacement work where the H-section was pulled out after the PRB construction. The construction cost was greatly reduced.

[Experiment 1]
In Experimental Example 1, an artificial ground was prepared by filling an acrylic container having a width of W 15 cm, a length of L 25 cm, and a depth of H 20 cm with glass beads having a particle diameter of 0.4 mm, and fresh water was poured to 1 cm below the simulated ground surface. In an acrylic container filled with glass beads, PRB1 having the same configuration as PRB1 shown in FIG. PRB1 had a width of W15 cm, a length of L5 cm, and a depth of H10 cm.

  The peripheral portion 12 is composed of a steel bar having a thickness of 3 mm as the H-shaped steel 22 and a 1 mm mesh net as the cross sheet pile 23. The steel bar is arranged so as to have the size of PRB1, and the net is stretched between the steel bars. . The peripheral portion 12 thus configured was filled with sand (an average particle size of 1 mm) as the purification material 21.

  This PRB1 was embedded in an acrylic container filled with glass beads so that the centers of the two substantially overlapped. The embedding depth of PRB1 was set so that its lower end was located at a depth of 10 cm from the surface of the glass beads in the acrylic container.

  A simulated earthquake having a horizontal amplitude of 1 cm and a horizontal frequency of 4 Hz was applied to the acrylic container embedded with PRB1. The duration of the simulated earthquake was 20 seconds. PRB1 after applying the simulated earthquake subsided 2 mm, but maintained its original shape and was not destroyed.

[Experiment 2]
In Experimental Example 2, a simulated earthquake was given by performing a test under the same conditions as in Experimental Example 1 except that a strength member (bar) was to be provided around the PRB. After the simulated earthquake, the PRB became a mixture of glass beads and sand non-uniformly due to liquefaction, and a thin part was generated in the PRB.

  From the above experiment, it has been shown that PRB can be prevented from being damaged even when a force causing a shift in the horizontal direction is applied according to the present invention.

  INDUSTRIAL APPLICABILITY The present invention can be used for construction work of structures such as in-situ purification of contaminated groundwater.

The top view which shows the state by which the permeability purification | cleaning structure which concerns on 1st Embodiment of this invention was embed | buried in the ground. The perspective view of the permeability purification | cleaning structure which concerns on the said embodiment. The schematic diagram which shows a part of process of building the said permeable purification | cleaning structure. The perspective view of the permeability purification | cleaning structure which concerns on 2nd Embodiment of this invention.

Explanation of symbols

1, 2 PRB (permeable purification structure)
DESCRIPTION OF SYMBOLS 11 Purification | purification part 12 Peripheral part 21 Purification | cleaning material 22 H-section steel 23 Side sheet pile 25 Fixing member

Claims (5)

A permeable purification structure provided in the ground,
A purification section constructed by embedding a purification material in the ground,
Surrounds the purification unit, and a plurality of pillars like strength members which are spaced apart from each other,
A permeable purification structure having a permeable transverse sheet pile disposed between a pair of adjacent strength members among the plurality of columnar strength members . The permeable purification structure according to claim 1, wherein each of the plurality of strength members is fixed to another strength member by a fixing member. And spaced from one another a plurality of posts like strength member, and Da設into the ground as a whole in a plan view imitates a substantially frame shape,
Excavating a region surrounded by the plurality of columnar strength members,
A permeable sheet pile is disposed between a pair of strength members adjacent to each other among the plurality of columnar strength members,
A space formed by excavation is filled with a purification material and backfilled to form a purification unit, and the purification unit is surrounded by the plurality of columnar strength members without removing the plurality of columnar strength members from the ground. Permeable purification structure construction method for purification structure. Filling the purification material by leaving the pre Kiyoko sheet pile into the ground, permeable purifying structure method of claim 3, state around the purifier is surrounded by the transverse sheet pile. The permeable purification structure construction method according to claim 3 , wherein the plurality of columnar strength members are fixed by a fixing member.

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