JP2005213804A - Construction method for countermeasure against spread of contamination - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a construction method for a countermeasure against the spread of contamination upon construction work like the excavation of the ground by which secondary contamination caused by ground water existing in a contaminated aquifer is prevented. <P>SOLUTION: Upon excavating or drilling work piercing through a contaminated aquifer 61 and reaching a clean-water aquifer 63 being work for a cast-in-place pile or a boring exploration, for example, a chemical is grouted in the contaminated aquifer 61 of a construction place of the cast-in-place pile or the boring in advance to move the contaminated ground water out of the construction place. The excavation work or the like is carried out in a state that the ground water is prevented from flowing out to the lower layer through a gap between a casing tube of the cast-in-place pile and the natural ground, or through a hole drilled by a boring machine. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pollution diffusion countermeasure method, and more specifically, it prevents the contaminated groundwater from flowing out from the contaminated aquifer where groundwater contamination has been confirmed during construction of cast-in-place piles or drilling of soil surveys. The present invention relates to a pollution diffusion countermeasure method in which excavation is performed in a state where it has been excavated.

  In the ground where permeable layers and impermeable layers are alternately stacked, for example, the upper permeable layer close to the ground surface is an aquifer with groundwater contaminated by industrial activities, etc. The layer may be an aquifer with clean groundwater. And the clean groundwater which a lower aquifer (permeable layer) has may be used for domestic water and other uses.

  In such a ground, when excavation or drilling that penetrates the upper aquifer and reaches the lower aquifer, such as cast-in-place pile construction or boring survey, contamination of the upper aquifer There is a risk that the discharged groundwater will flow into the lower aquifer. When contaminated groundwater flows into the lower aquifer, the contamination of the groundwater extends to the lower aquifer.

  The specific mechanism of expansion of groundwater contamination by cast-in-place piles is as follows. For example, in the construction of cast-in-place piles by the all-casing method, there is a step of rocking and pressing a cylindrical casing tube into the ground. A cutting edge for excavating the ground is attached to the tip of the casing tube. This cutting edge is mounted in a form projecting radially outward from the outer peripheral surface of the casing tube, and excavates a hole having a diameter larger than the outer diameter of the casing tube. This is because a gap is formed between the outer peripheral surface of the casing tube and the natural ground during press-fitting to reduce the frictional force, and the casing tube is press-fit smoothly. Here, when the tip of the casing tube reaches the lower aquifer through the aquifer and the impermeable layer having the contaminated groundwater in the upper part, through the gap between the outer surface of the casing tube and the natural ground, Contaminated groundwater flows into the lower aquifer. This extends the groundwater contamination to the lower aquifer.

  As a method of preventing the spread of such groundwater contamination, steel sheet piles are pressed in to surround the place where the cast-in-place piles are to be constructed, and the groundwater remaining in the enclosed area is pumped up and purified. The method of discharging is widely used. According to this method, since cast-in-place piles can be constructed in the absence of contaminated groundwater, the contamination of groundwater does not increase.

Japanese Patent Laid-Open No. 11-336060 Japanese Patent Laid-Open No. 11-336073 JP 2002-159932 A

  However, in the method of pumping contaminated groundwater by pumping it up and purifying it, there are some that are difficult to purify depending on the type of pollutant. In addition, if the amount of groundwater to be pumped is enormous, it may require a large amount of money to purify it.

  In view of the above situation, the problem to be solved by the present invention is excavation that penetrates an aquifer having contaminated groundwater, such as cast-in-place piles or boring, and an aquifer containing clean groundwater. Another object is to provide a pollution diffusion countermeasure method that prevents the spread of groundwater contamination due to the contaminated groundwater flowing into the uncontaminated aquifer when construction including drilling is performed.

  In order to solve such problems, when excavating the aquifer through the groundwater contaminated aquifer and reaching the uncontaminated aquifer, chemical contamination is applied to the contaminated aquifer from the groundwater at the excavation site in advance. The gist is that excavation is performed in a state in which groundwater is pushed outward from the excavation site and the outflow of groundwater from the excavation site to the lower layer is prevented.

  The invention according to claim 2, in the construction of the cast-in-place pile, injecting a chemical solution in advance to the contaminated aquifer by the groundwater of the cast-in-place pile construction site, and pushing the contaminated groundwater outward from the cast-in-place pile construction site, The gist is that excavation is performed in a state in which the outflow of groundwater from the gap between the casing and the natural ground to the lower layer is prevented during the cast-in-place pile construction.

  In the invention of claim 3, when boring the ground, a chemical solution is injected in advance into the contaminated aquifer by the groundwater at the boring location, and the contaminated groundwater is pushed outward from the boring location. The gist is that excavation is performed in a state in which the outflow of groundwater to the lower layer portion is prevented from the air gap.

  According to the first aspect of the present invention, when excavating through the aquifer having contaminated groundwater, the contaminated groundwater present at the excavation site is pushed out from the location by injecting the chemical solution. As a result, there will be no contaminated groundwater during excavation. Therefore, even if an excavation that penetrates through the aquifer with contaminated groundwater and reaches the aquifer with clean groundwater below, the contaminated groundwater never flows out. Prevents the spread of contamination.

  The invention according to claim 2 is performed prior to the construction of the cast-in-place pile when constructing the cast-in-place pile that penetrates the aquifer having the contaminated groundwater. According to the present invention, when a boring survey is conducted through an aquifer having contaminated groundwater, it is performed prior to the boring survey. Can be prevented.

  The pollution diffusion countermeasure method according to the present invention penetrates an aquifer having contaminated groundwater (hereinafter referred to as “contaminated aquifer”) and has an aquifer having uncontaminated groundwater (hereinafter referred to as “contaminated aquifer”). This will be done prior to the construction that includes processes such as excavation and drilling to reach “clean aquifer”. Examples of such construction include cast-in-place piles and boring surveys. In addition, by conducting the work prior to the construction, the contaminated groundwater in the contaminated aquifer will flow into the clean aquifer and will contaminate the clean aquifer and prevent the contamination of the groundwater. is there.

  That is, first, a chemical solution is injected into a place where excavation or the like of a contaminated aquifer is to be permeated, and contaminated groundwater at the excavation place is pushed out and removed. And the location to excavate etc. is water-blocked by solidifying the chemical | medical solution. In this way, even if excavating through the contaminated aquifer after that, the contaminated groundwater will not flow out from the excavation site, so even if it excavates and reaches the clean aquifer, The clean aquifer is not contaminated.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the pollution diffusion countermeasure method according to the present embodiment may be abbreviated as “main method”.

  The type of chemical solution to be injected and penetrated into the ground is determined by comprehensively judging the characteristics of the ground to be injected, the purpose of construction or the compatibility with the injection method. In this method, it is not necessary to strengthen the ground like general chemical injection, and in consideration of environmental pollution such as groundwater, an inorganic silica sol chemical that is a neutral grout injection is applied. Is preferred.

  And for the purpose of sealing around the lot where the chemical solution is to be injected, or for the purpose of rough filling to fill a large gap in the ground, a short gel time chemical solution is used as the intended chemical solution to penetrate into the ground. It is preferable to use a gel solution. These chemical solutions are composed of a liquid A (main agent) and a liquid B (curing agent), and the liquid B is mixed with the liquid A to be solidified (gelled). Here, short gel time means solidification after several seconds to several minutes after mixing, and long gel time means solidification in several tens of minutes after mixing.

As a specific chemical solution, a short gel time chemical solution is Silica Riser (registered trademark) RMG-L ₃ (trade name), and a long gel time chemical solution is RMG-S ₂ (trade name).

  As a contaminant that can be treated with a silica sol chemical solution by this method, trichloroethylene can be mentioned. It should be noted that other pollutants that are defined as hazardous substances by the Soil Contamination Countermeasures Law can be processed if they do not react with the chemicals to be injected.

  Since this method mixes and injects solution A and solution B, it is preferable to apply the double tube strainer method, and since two types of chemical solutions with different gel times are injected, of the double tube strainer method It is preferable to apply the Multi riser (registered trademark) method. Therefore, in this construction method, construction is performed using a general chemical solution injection facility for injecting a chemical solution by the Multi-Riser (registered trademark) method. The double tube strainer method is a method in which the liquid A and the liquid B are fed into the ground by a double pipe lot, mixed in the ground, and injected and penetrated. The Multi riser (registered trademark) method is a method capable of injecting a chemical solution having a short gel time and a chemical solution having a long gel time in the same process.

  FIG. 1 schematically shows the configuration of a chemical solution injection facility used in the present construction method, and shows the facility in the case of the Multi-Riser (registered trademark) construction method. As shown in the figure, the chemical solution injection equipment used in this construction method includes a chemical solution supply source 4 (for example, an injection material production mixer), an injection pump 3 that pumps the chemical solution from the supply source 4, and an amount of the chemical solution to be injected. A flow meter for monitoring and adjusting the flow rate and a flow rate adjusting valve 2 (illustrated integrally) and a boring machine 1 for injecting a chemical solution by drilling an injection hole for injecting the chemical solution. In the figure, arrow A indicates the flow of liquid A, and arrow B indicates the flow of liquid B. This boring machine 1 has a double pipe lot 11, and this double pipe lot 11 can cut the injection hole 5, and feeds A liquid and B liquid from the base end part to the injection hole 5. Can be mixed and injected into the ground. In addition, since these facilities are the same as the chemical | medical solution injection equipment used with the conventional multi riser (trademark) construction method, detailed description is abbreviate | omitted.

  Next, the construction procedure of this construction method will be described. In the following description, this construction method is used as an example in which the construction method is applied to the construction work of cast-in-place piles by the all casing construction method. FIG. 2 is an underground sectional view schematically showing the process of the present method and the subsequent construction process of cast-in-place piles. As shown in the figure, the target ground to which the present construction method is applied has a substantially horizontal impermeable layer 62 in the ground, and a contaminated aquifer 61 exists above the impermeable layer 62. Then, a structure in which the clean aquifer 63 exists on the lower side is used as an example.

  This construction method is performed in the order of (1) drilling step and (2) chemical solution injection step after the preparatory work, and after the completion of the construction method, cast-in-place piles are constructed. In the preparatory work, marking is performed on one or two or more locations (that is, drilling locations of the injection holes) where chemicals are injected based on the plan, and the boring machine 1 is disposed at the marked positions to determine the drilling angle and direction. Confirm. In addition, in the preparatory work, in addition to this, installation of observation wells, loading of equipment, setup of injection equipment, etc. are performed, but since these are the same as the preparatory work in general chemical injection, the details are omitted.

  In the drilling step (1), the injection hole 5 for inserting and injecting the double tube lot 11 is drilled at the position where the chemical solution is injected (FIG. 2A). The injection hole 5 has a depth that penetrates through the contaminated aquifer 61 into which the chemical solution is injected and reaches the inside of the impermeable layer 62 below the contaminated aquifer 61. Specifically, it is preferable that the depth reaches the inside of the impermeable layer 62 from the boundary between the contaminated aquifer 61 and the impermeable layer 62 to about 500 mm. After the injection hole 5 is drilled, the drilling depth is confirmed. Since the lower end of the injection hole 5 has not reached the clean aquifer 63 at the time of completion of the drilling, the contaminated groundwater oozed from the contaminated aquifer 61 flows into the clean aquifer 63 through the injection hole 5. There is nothing.

  The injection step (2) is a step of injecting a chemical solution into the ground from the double tube lot 11 inserted into the injection hole 5. The injection process is divided into the following steps. (I) The double tube lot 11 is installed so that the tip of the double tube lot 11 is located at the bottom of the injection hole 5. (Ii) The chemical solution 15 having a short gel time is injected from the tip of the installed double tube lot 11. As a result, the periphery of the double tube lot 11 is sealed to prevent the chemical solution from escaping (FIG. 2B). (Iii) A chemical solution having a short gel time is further injected to roughly fill the gap in the ground (FIG. 2 (c)). An arrow Z schematically shows the flow of the chemical solution 15 having a short gel time. (Iv) A chemical solution having a long gel time is injected to infiltrate the ground and push out contaminated groundwater, and water is blocked by the solidified chemical solution (FIG. 2 (d)). In the figure, a portion 7 indicated by a mesh is a range where the chemical solution is injected and penetrated. (V) After the injection of the chemical solution is completed, the double tube lot 11 is raised by a predetermined distance, for example, 25 to 50 cm. Thereafter, the steps (iii) to (v) are repeated (FIG. 2 (e)).

  In this way, the injection of the chemical solution is started from the bottom of the injection hole 5, the injection of the chemical solution and the rise of the double pipe lot 11 are repeated, and when the injection is completed over the entire height of the contaminated aquifer 61, The injection process is complete. Thereafter, the other injection holes 5 are similarly injected.

  When the chemical solution is injected, the contaminated groundwater is pushed in a substantially horizontal direction within the contaminated aquifer by the chemical solution. And in the range 7 into which the chemical solution is injected, the contaminated groundwater is replaced with the chemical solution. For this reason, the contaminated groundwater does not exist within a predetermined range from the insertion hole 5. Thereafter, when the injected chemical solution is solidified, the groundwater cannot penetrate into the solidified range (within the range 7 into which the chemical solution is injected) and is blocked.

  After completion of the construction method, cast-in-place piles will be constructed. The casing tube 8 is press-fitted at a certain depth into the portion 7 where the chemical solution is injected, the earth and sand in the casing tube 8 is removed by a clam bucket (not shown), and the casing tube 8 is press-fitted. Thereafter, this operation is repeated to press-fit the casing tube 8 to a predetermined depth. Here, even if the casing tube 8 reaches the contaminated aquifer 62 (FIG. 2 (f)), after the construction method is applied, only the solidified chemical solution and earth and sand are present, and the solidified chemical solution is present. As a result, the contaminated groundwater does not exude. For this reason, even if the casing tube 8 is further press-fitted and the tip reaches the clean aquifer 63 (FIG. 2G), the contaminated groundwater does not flow into the clean aquifer 63 and the contamination is expanded. Can be prevented.

  After the casing tube 8 is press-fitted to a predetermined depth, a reinforcing bar 81 is placed in the casing tube 8, and concrete 82 is placed while the casing tube 8 is pulled out (FIG. 2 (h)). When the concrete 82 is placed, there is no gap between the surface of the concrete 82 (that is, the surface of the cast-in-place pile 80) and the aquifers 61, 63 and the impermeable layer 62. After construction (FIG. 2 (h)), the contamination of groundwater does not expand.

  In addition, although the figure has shown the structure which inject | pours a chemical | medical solution only from one injection hole in order to construct one cast-in-place pile typically, in fact, several injection | pouring is carried out with respect to one pile. A chemical solution may be injected from the hole.

  Next, the injection sequence when the chemical solution is injected into the plurality of injection holes 5 will be described. FIG. 3A is a schematic plan view of the construction site where the chemical solution is injected into the plurality of injection holes 5 as viewed from above. Specifically, in order to construct a footing 83 that serves as a foundation for a bridge pier, etc., it is a construction example when a plurality of cast-in-place piles 80 are arranged in a matrix, and the construction position of the cast-in-place pile 80, chemical solution The injection hole 5 and the injection range 7 are schematically shown.

  In this construction method, it is necessary to inject a chemical solution into a predetermined range around the cast-in-place pile 80 to be constructed and to prevent contaminated groundwater from remaining between the injection holes 5. For this reason, the intervals between the injection holes 5 must be such that the permeation ranges of the chemical solution in each injection hole 5 overlap. Several theoretical and empirical formulas have been proposed to determine the penetration range of chemicals, but they all make many assumptions about ground conditions and chemical penetration. For this reason, in determining the permeation range, in addition to the values obtained from these equations, the interval between the injection holes 5 is determined with reference to construction results. In addition, as for the range which inject | pours and osmose | permeates this chemical | medical solution, it is desirable that it is the range of 1500 mm from the surface of a cast-in-place pile, for example. In addition, it is necessary not to leave a residual pressure on the ground in the injection range 7 of the chemical solution and to prevent ground deformation.

  FIG. 3B schematically shows the injection order in the case shown in FIG. As shown in the figure, a water-impervious zone is formed by first injecting in the direction of arrow a upstream of the groundwater flow in the contaminated aquifer. This prevents contaminated groundwater from flowing into the injection area. Thereafter, the injection is performed from the inside to the outside in order from the upstream side, that is, in the order of the arrows b, c,. If the injection is performed in this order, no residual pressure remains on the ground and no contaminated groundwater remains between the injection holes 5, so that the contaminated groundwater is excluded from the injection range and is blocked. be able to.

  The embodiments of the present invention have been described in detail with reference to the drawings. However, the present invention is not limited to the embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say.

  For example, the structure of the ground to which the pollution diffusion countermeasure method according to the present invention is applied is not limited to that shown in the embodiment. That is, in a ground having a laminated structure in which a plurality of impermeable layers and a plurality of permeable layers appear alternately, and one or more of the permeable layers is a contaminated aquifer having contaminated groundwater. Is also applicable. When there are a plurality of contaminated aquifers, the pollution diffusion countermeasure method according to the present invention may be applied to each contaminated aquifer.

  In the above embodiment, the construction to be performed prior to the construction of the cast-in-place pile is shown, but if it is a construction that performs excavation and the like that penetrates the contaminated aquifer and reaches the clean aquifer, It can be applied regardless of the content of the construction.

  In addition, although the form which applies Multi riser (registered trademark) construction method was shown as an injection construction method, the construction purpose, soil condition, construction condition, expectation degree of the injection effect, etc. are judged comprehensively and conform to these conditions. However, the construction method is not limited to the Multi-Riser (registered trademark) construction method.

It is the figure which showed typically the structure of the chemical | medical solution injection equipment used for the pollution diffusion countermeasure construction method concerning embodiment of this invention. It is sectional drawing in the earth which showed typically the process of the pollution diffusion countermeasure construction method concerning an embodiment of the invention. (A) is the figure which showed typically the position of a chemical | medical solution injection hole, a chemical | medical solution injection | pouring range, and a cast-in-place pile, and (b) is the figure which showed typically the order which inject | pours a chemical | medical solution into a some chemical | medical solution injection hole. is there.

Explanation of symbols

7 Range in which chemical solution is injected 11 Double tube lot 15 Chemical solution with short gel time 61 Contaminated aquifer 62 Impervious layer 63 Clean aquifer 80 Cast-in-place pile

Claims (3)

  When excavating through the groundwater contaminated aquifer to reach the uncontaminated aquifer, the groundwater contaminated by the groundwater at the excavation site is pre-injected with chemicals and the contaminated groundwater is moved outward from the excavation site. A pollution diffusion countermeasure method characterized by excavation in a state in which groundwater flow from the excavation site to the lower layer is prevented.   During the construction of cast-in-place piles, a chemical solution is injected into the contaminated aquifer in the groundwater of the cast-in-place piles in advance and the contaminated groundwater is pushed outward from the cast-in-place pile construction site. Contamination diffusion countermeasure method characterized in that excavation is carried out in a state where groundwater outflow is blocked from the gap with the mountain to the lower layer.   When boring the ground, chemical solution is pre-injected into the groundwater contaminated aquifer of the borehole, and the contaminated groundwater is pushed outward from the borehole. Pollution diffusion countermeasure method characterized by excavation in a state where the outflow is blocked.

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