JP2007175674A - Treatment system in site of improved surplus soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment system in site of improved surplus soil capable of easily treating the improved surplus soil produced in ground improvement work in the site of a building with simple composition at a low cost. <P>SOLUTION: This treatment system in site treats improved surplus soil 13 produced in ground improvement work in the site of a building 11 using cement or cement-based solidifier, and is provided with a burying treatment facility 14 in the ground under the foundation 11a of the building 11. The facility 14 is constituted by laying a water permeable sheet material 16 on the bottom face of recessed part 15 formed by excavating the ground, providing a heavy metal adsorbing layer 17 constituted of a heavy metal adsorbing insolubilization agent, while inhibiting flow loss of the agent to the lower ground by the water permeable sheet material 16, providing an intermediate soil covering layer 18 having an alkali reducing function to the strong alkaline permeating water on the heavy metal adsorbing layer 17, and uniformly laying the improved surplus soil on the intermediate soil covering layer 18. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an in-situ treatment system for improved residual soil that treats improved residual soil generated by ground improvement work using cement or cement-based solidifying material in a site of a building.

  For example, hexavalent chromium as a heavy metal exists in nature, and when it is contained in the soil within a range not exceeding the soil environmental standard, it is considered that it does not affect the environment.

  In addition, cement or cement-based solidifying materials used for ground improvement such as columnar improvement methods and surface layer improvement methods contain heavy metals such as hexavalent chromium. In the process of mixing soil and solidified material, it is fixed to sentiment hydrate. However, depending on the type of soil to be mixed with the solidifying material, the hydration reaction is hindered by adsorption of clay minerals and organic substances contained in the soil, such as Ca ions necessary for hydrate formation. For this reason, it is thought that some hexavalent chromium etc. which are not fixed to sentiment hydrate elute from sentiment improved soil. On the other hand, hexavalent chromium itself is known to be reduced to chemically stable trivalent chromium by reducing substances, and sentiment-improved soils include solidified materials and soils containing reducing substances such as blast furnace slag. Is mixed, it is difficult to elute heavy metals such as hexavalent chromium (see Non-Patent Document 1, for example).

On the other hand, regarding the use of cement and cement-based solidification material for ground improvement work and the reuse of improved soil, the large-scale construction work under the jurisdiction of the Ministry of Land, Infrastructure, Transport and Tourism, including the repair work of the government office, was targeted as of March 2000. On March 24, a notification was issued by the Ministry of Construction at the time. The main content of this is that hexavalent chromium may be eluted from the improved soil using cement or cement-based solidifying material at a concentration exceeding the soil environmental standards depending on the conditions. Conduct leaching test of chromium chromodium, take soil environment standards into consideration, take appropriate measures such as changing the composition design of solidifying material and changing the construction method, and use cement or cement-based solidifying material When the improved soil is reused, a hexavalent chromium elution test is carried out, and the elution amount of hexavalent chromium is required to be below the soil environmental standard.
"Soil and Foundation" 2003.11 Vol.51 No.11 Ser.NO.550 "Characteristics of Hexavalent Chromium Elution Caused by Cement Improved Soil"

  The above notification from the Ministry of Construction is intended for large-scale civil engineering works under the jurisdiction of the Ministry of Land, Infrastructure, Transport and Tourism. For example, private small-scale building works such as residential buildings are Although it was considered that there was almost no influence of leaching of chromium, it was not included in the project, but it is expected that appropriate measures will be taken in general private works after understanding the contents of the above notification. It was.

  On the other hand, for example, in the case of a small-scale ground improvement work for a residential building, it is extremely uneconomical in terms of cost and time to carry out the elution test for hexavalent chromium described above. In addition to using blast furnace slag and other materials that are difficult to elute hexavalent chromium, the improved residual soil including the latency of the pile head portion in the columnar improvement method, and the improved residual soil such as shavings on the surface portion in the surface layer improvement method are hexavalent. A method of collecting and treating it as an industrial waste has been adopted, considering chromium as a residual soil in which chromium is difficult to be fixed to sentiment hydrate and hexavalent chromium is easily eluted.

  However, due to the shortage of waste disposal sites in recent years, processing costs are considerable and it is not easy to secure a waste disposal site. Appropriate handling is desired. As a method for treating the improved residual soil in the building site, a known heavy metal adsorption / insolubilizer is mixed and stirred well with the improved residual soil pulverized or slurried, and the strength that constitutes the foundation of the building is high. Methods such as sandwiching improved residual soil between concrete slabs can be considered, but these methods all require large-scale facilities and labor-related work, and the scale of construction work such as residential buildings In comparison, it was not balanced. Moreover, heavy metals such as hexavalent chromium exist in nature, and it may be desirable to return them to the ground at an appropriate concentration that does not exceed the soil environmental standards.

  The present invention has been made paying attention to such a conventional problem, and can improve and easily process the improved residual soil generated by the ground improvement work in a building site with a simple configuration. The purpose is to provide an on-site treatment system for improved residual soil.

  The present invention is an in-situ treatment system for improved residual soil generated by ground improvement work using cement or cement-based solidifying material in the site of a building, and the underground in the site of the building The burying treatment facility lays the permeable sheet material on the bottom surface of the recessed portion formed by excavation in the ground, and embeds the improved residual soil into the burying treatment facility. A heavy metal adsorption layer comprising a heavy metal adsorption and insolubilizing agent is provided in a state where flow to the lower ground is prevented, and an intermediate covering layer having an alkali reducing function for strongly alkaline passing water is provided above the heavy metal adsorption layer, The above object is achieved by providing an in-site treatment system for improved residual soil that is constructed by spreading the improved residual soil above an intermediate soil covering layer.

  According to the site processing system of the present invention, it is preferable that the buried processing facility is provided in a lower portion of a building foundation.

  Moreover, according to the site processing system of this invention, when the heavy metal adsorbed by the said heavy metal adsorption layer is hexavalent chromium, it becomes possible to exhibit the function especially effectively.

  Furthermore, according to the site processing system of this invention, it is preferable that the thickness of the said intermediate | middle covering soil layer is 5-50 cm.

  Furthermore, according to the site processing system of this invention, it is preferable that pH of the said intermediate | middle covering soil layer is 5.8-8.6.

  According to the improved residual soil in-situ processing system of the present invention, the improved residual soil generated by the ground improvement work can be easily and inexpensively processed in the site of the building with a simple configuration.

  The in-site processing system 10 according to a preferred embodiment of the present invention shown in FIGS. 1 to 3 firmly supports the residential building part 11 when building the residential building part 11 on a soft ground such as a landfill site. In order to prevent uneven subsidence, etc., a ground improvement work by, for example, a columnar improvement method is preliminarily applied to the soft ground, and the improved residual soil generated by the ground improvement work is applied to the hexagonal chromium in the site of the residential building part 11. In order to make it possible to treat it cheaply and easily by returning it to the ground at a moderate concentration (such as 0.05 mg / L in the case of hexavalent chromium), such as heavy metals such as It has been adopted.

  Here, the columnar improvement method is, for example, inserting a stirring rod with a stirring blade into the ground at a predetermined depth and rotating the stirring rod while spraying cement or cement-based solidifying material to This is a known method for forming the columnar consolidated body 12 in the ground by mixing and stirring. According to the columnar improvement method, in the main body portion of the columnar solid body 12 excluding the pile head portion, heavy metals such as hexavalent chromium eluted from cement or cement-based solidified material are mixed with the earth and sand in the ground. The pile head part that is thought to be fixed to the sentiment hydrate but is scraped off and removed as improved residual soil contains a large amount of latency, and hexavalent chromium and the like are easily fixed without being fixed. It has become. The treatment system of the present embodiment returns the improved residual soil as industrial waste that easily elutes heavy metals such as hexavalent chromium, and returns hexavalent chromium and the like to the ground at an appropriate concentration that does not exceed the soil environmental standards. Thus, it can be appropriately processed within the site of the residential building part 11.

  In addition, in FIGS. 1-3, as the principal part of the site processing system 10 of this embodiment, about the housing building 11, the housing | casing part is abbreviate | omitted and only the foundation 11a is shown. Further, the cement or cement-based solidified material is a solidified material containing cement as a component, and includes ordinary Portland cement, blast furnace cement, cement-based solidified material, lime-based solidified material, and the like. As a solidifying material used for small-scale ground improvement work for residential buildings, for which a hexavalent chromium elution test is not required, blast furnace cement, which is considered to be difficult to elute hexavalent chromium, is preferably used.

  And the site treatment system of this embodiment is processing of the improvement residual soil which processes the improvement residual soil which generate | occur | produces, for example by a columnar improvement method in the site of the residential building 11, as a ground improvement work using a cement or cement-type solidification material. The system includes an embedment processing facility 14 that embeds and processes the improved residual soil 13 in the ground of the residential building 11, and the embedment processing facility 14, as shown in FIG. A permeable sheet material 16 is laid on the bottom surface of the recess 15 formed by excavation, and a heavy metal adsorbing layer 17 made of an adsorbing and insolubilizing agent for heavy metals is provided in a state in which the water permeable sheet material 16 prevents flow out to the lower ground. An intermediate cover layer 18 having a function of reducing alkali with respect to the strongly alkaline passing water is provided above the heavy metal adsorbing layer 17, and the intermediate cover layer 18 is modified above the intermediate cover layer 18. It is constructed by leveling laid residual soil 13.

  Moreover, in this embodiment, the burying processing facility 14 is provided in the lower part of the foundation 11 a of the residential building 11, and the crushed stone layer 19 covering the improved residual soil 13 is placed above the burying processing facility 14. For example, it is provided with a thickness T1 of about 10 to 20 cm by applying rolling pressure. Furthermore, the foundation 11a of the residential building 11 is constructed above the crushed stone layer 19 by placing concrete after assembling the formwork and reinforcing bars.

  According to the present embodiment, the recess 15 for providing the buried processing facility 14 in the ground preferably has a depth D of about 50 to 100 cm, and does not overlap with the formed columnar solid bodies 12. Thus, while being arrange | positioned in these space | interval parts, in the area | region of the foundation 11a of the residential building 11, it is excavated by the plane rectangular shape, and multiple are provided. Note that the size and number of the recesses 15 can be appropriately set according to the amount of the improved residual soil 12 calculated in advance according to the number of the columnar consolidated bodies 12. 12 can be disposed at any position that does not overlap.

  The water-permeable sheet material 16 laid on the bottom surface of the concave portion 15 allows water passing through the upper improved residual soil 13 and the intermediate cover soil layer 18 to permeate and flow down to the lower ground, while allowing soil particles to pass upward. A sheet material having a function that can be held, such as a non-woven cloth such as a nonwoven fabric, a woven cloth, or a resin, provided with a slit or a mesh for a transmission portion, or the like can be used. Moreover, the structure which prevents the adsorption | suction insolubilizer which forms the heavy metal adsorption layer 17 by the water-permeable sheet material 16 from flowing down to the lower ground is, for example, a granular or slurry adsorption / insolubilizer above the water-permeable sheet material 15. In addition to the laid configuration, the permeable sheet material 15 is impregnated with or infiltrated with an adsorption insolubilizing agent, so that the permeable sheet material 15 holds the adsorption insolubilizing agent and forms the heavy metal adsorption layer 17. It is.

  As the adsorption insolubilizer that prevents the flow to the lower ground by the water permeable sheet material 15 and forms the heavy metal adsorption layer 17, various known adsorption insolubilizers can be used as the heavy metal adsorption insolubilizer. More specifically, for example, trade name “Acedra” (registered trademark) (manufactured by Nippon Sheet Glass Co., Ltd.), which is an inorganic metal adsorbent, can be preferably used. Such an inorganic metal adsorbent effectively adsorbs various heavy metals such as chromium, arsenic, selenium, lead, fluorine, cadmium and anions, is easy to handle, and is made of all inorganic materials. It exhibits excellent adsorption performance and has a high heavy metal fixing ability. In addition, the usage-amount of an adsorption | suction insolubilizing agent can be suitably set according to the generation amount etc. of the improvement residual soil 13 which should be processed.

  On the other hand, it is known that such an inorganic metal adsorbent does not sufficiently exhibit heavy metal adsorption performance and fixing ability in a strong alkali region having a pH of, for example, 8.5 or more. Because it contains cement or cement-based solidified material, rainwater or other water that enters the improved residual soil 13 and leaches out from the improved residual soil 13 is a highly alkaline leaching. May be water. For this reason, in the present embodiment, an intermediate soil covering layer 18 that exhibits an alkali reducing function with respect to strongly alkaline passing water is provided above the heavy metal adsorption layer 17, and the intermediate soil covering layer 18 elutes components such as hexavalent chromium. After reducing the pH of the leachate containing, for example, to a neutral range of about 5.8 to 8.6, heavy metals such as hexavalent chromium are adsorbed and fixed by the heavy metal adsorption layer 17. In addition, the intermediate soil covering layer 18 can reduce hexavalent chromium contained in the leachate passing therethrough to non-toxic trivalent chromium by a general soil reducing function.

Here, as the earth and sand forming the intermediate soil covering layer 18, it has water permeability that allows the leachate from the improved residual soil 13 to pass downward, and has a pH that can relax strong alkalinity, for example, a pH of 8.6 or less. Although it can select and use, it is preferable that the pH of the intermediate | middle covering soil layer 18 shall be 5.8-8.6 which is a neutral region. By setting the pH of the intermediate covering layer 18 to 5.8 to 8.6, there is an advantage that the pH of the strong alkaline leachate can be more effectively reduced. Further, the thickness T2 of the intermediate covering layer 18 is preferably about 5 to 50 cm. By setting the thickness T2 of the intermediate covering layer 18 to about 5 to 50 cm, there is an advantage that the function of reducing the hexavalent chromium to the trivalent chromium and rendering it harmless is more effectively exhibited. It should be noted that sodium zinc borate (Na (ClO ₂ )) or bleaching powder (Ca (ClO) ₂ · nCa (OH) ₂ ) or the like is laid on the surface of the intermediate cover layer 18 or in the middle, or immersed in the water-permeable sheet material 15. It is possible to more effectively exert the function of neutralizing the leachate.

  In the present embodiment, the improved residual soil 13 is further introduced into the recess 15 whose inner peripheral surface is covered with the water-permeable sheet material 16 above the intermediate covering layer 18, and has a thickness T3 of, for example, about 10 to 90 cm. It is spread on the floor. In addition, as described above, the crushed stone layer 19 is provided to cover the improved residual soil 13 that has been spread, and the foundation 11a and the residential building 11 are constructed, so that it is buried in the lower part of the foundation 11a of the residential building 11 The in-site processing system of this embodiment provided with the processing facility 14 is formed.

  And according to the site processing system 10 of the present embodiment configured as described above, the improved residual soil 13 generated by the ground improvement work is processed cheaply and easily in the site of the residential building 11 with a simple configuration. be able to. That is, the site processing system 10 of the present embodiment includes an embedded processing facility 14 in the site of the residential building 11, and this embedded processing facility 14 is permeable to the bottom surface of the recess 15 formed by excavation in the ground. A sheet material 16 is laid and held by the water-permeable sheet material 16 to provide a heavy metal adsorbing layer 17, an intermediate covering layer 18 is provided above the heavy metal adsorbing layer 17, and the improved residual soil 13 is laid above and leveled. Therefore, it can be provided at a low cost. Further, the leaching water containing heavy metal such as hexavalent chromium leached from the improved residual soil 13 by the burying treatment facility 14 passes through the intermediate covering soil layer 18 to reduce its alkalinity, and then the heavy metal adsorption layer 17 is adsorbed and insolubilized. After adsorbing a considerable amount of hexavalent chromium, etc. by contact with the agent, it can be discharged to the lower ground in a state where it has been reliably treated as leachate containing heavy metals at an appropriate concentration not exceeding the soil environmental standards. It becomes possible.

  The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, the buried processing facility is not necessarily provided in the lower part of the foundation of the building, and the buried processing facility can be provided by digging up the ground in the site away from the building. In this case, it is preferable to cover the upper part of the improved residual soil thrown into the concave portion with a cover soil having a considerable thickness. In addition to the improved residual soil of the pile head portion in the columnar improvement method, the improved residual soil to be treated is improved residual soil such as shavings on the surface portion in the surface layer improvement method, and other improved soil generated by other ground improvement works. Also good. Furthermore, the heavy metal to be adsorbed by the adsorption insolubilizer of the heavy metal adsorption layer is not limited to hexavalent chromium, and may be other heavy metals such as arsenic, selenium, lead, fluorine, cadmium and the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic perspective view illustrating a configuration of an improved residual soil site processing system according to a preferred embodiment of the present embodiment. It is a schematic plan view explaining the configuration of the on-site treatment system for improved residual soil according to a preferred embodiment of the present embodiment. It is principal part sectional drawing explaining the structure of the site processing system of the improved residual soil which concerns on preferable one Embodiment of this embodiment.

Explanation of symbols

10 On-site disposal system for improved residual soil 11 Residential buildings (buildings)
11a Foundation of a residential building 12 Columnar consolidated body 13 Improved residual soil 14 Embedding treatment facility 15 Recess 16 Permeable sheet material 17 Heavy metal adsorption layer 18 Intermediate cover layer 19 Crushed stone layer

Claims (5)

A site treatment system for improved residual soil that treats improved residual soil generated by ground improvement work using cement or cement-based solidifying material in the site of the building,
It is provided with a burying treatment facility for burying and processing the improved residual soil in the grounds of the building,
The burying treatment facility comprises a heavy metal adsorption and insolubilizer in a state where a water permeable sheet material is laid on the bottom surface of a recess formed by excavation in the ground and the water permeable sheet material prevents the flow to the lower ground. A heavy metal adsorbing layer is provided, an intermediate soil covering layer having a function of reducing alkali against strongly alkaline passing water is provided above the heavy metal adsorbing layer, and the improved residual soil is spread over the intermediate covering layer. On-site processing system for improved residual soil.   The on-site treatment system for improved residual soil according to claim 1, wherein the buried treatment facility is provided in a lower part of a foundation of a building.   The on-site treatment system for improved residual soil according to claim 1 or 2, wherein the heavy metal adsorbed by the heavy metal adsorption layer is hexavalent chromium.   The on-site treatment system for improved residual soil according to any one of claims 1 to 3, wherein the intermediate covering layer has a thickness of 5 to 50 cm. The on-site treatment system for improved residual soil according to any one of claims 1 to 4, wherein the intermediate soil cover layer has a pH of 5.8 to 8.6.

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