JP2018025055A - Cast-in-place pace construction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cast-in-place pile construction method which can largely reduce or prevent the diffusion of soil contamination without soil improvement.SOLUTION: A cast-in-place pile construction method for excavating a pile hole by filling the pile hole with a stabilizing solution has: a stabilizing solution preparation process for preparing an addition stabilizing solution by adding an adsorbent for adsorbing a heavy metal contamination substance to the stabilizing solution; and a pile hole excavation process for excavating a pile hole by filling the pile hole with the addition stabilizing solution. The heavy metal contamination substance is arsenic, fluorine or zinc. The stabilizing solution is a polymer system stabilizing solution or a bentonite system stabilizing solution. The adsorbent is a magnesium oxide or an aluminum hydroxide. By adding the magnesium oxide or the aluminum hydroxide to the polymer system stabilizing solution and the bentonite system stabilizing solution with respect to arsenic, fluorine and zinc, an elution amount of arsenic, fluorine and zing mixed into the excavated pile hole can be reduced to a value smaller than a reference value.SELECTED DRAWING: Figure 12

Description

  The present invention relates to an in-situ pile method for preventing the spread of soil contamination.

  Since most of the big cities in Japan are developed on relatively soft alluvium, piles are necessary for the construction of middle- and high-rise apartments in urban areas. Pile penetrates the soft alluvium and reaches the lower support layer to support the upper building. When soil contamination exists in this alluvium, diffusion of soil contamination due to pile construction becomes a problem. . In other words, it is necessary to take some measures to prevent contamination of alluvial soil and contaminated groundwater from entering the lower aquifer, which is the lower support layer, and spreading the contamination by pile construction.

  It is known that soil containing heavy metals derived from nature exists in alluvial deposits in urban areas of Japan including the Osaka Plain. So far, soil containing natural heavy metals has not been subject to the Soil Contamination Countermeasures Law, but it was stipulated in the 2009 revision of the law that it should be treated as a law subject as well as anthropogenic contaminated soil. Therefore, in the future, establishment of a pile construction method that provides piles without diffusing heavy metals etc. in the ground where soil containing natural heavy metals etc. exists will be an urgent issue in pile construction of apartment buildings.

  Therefore, Patent Documents 1 to 3 have been proposed as means for carrying out pile construction by preventing diffusion of soil contamination.

  The “pile construction method” of Patent Document 1 uses an upper permeable layer ground replacement to replace the upper permeable layer ground inside the pile construction region, using a replacement material for preventing the entry of contaminants into the center of the pile construction region. A process and a pile driving process of driving a pile through the pile construction area to a predetermined depth.

  In the “pile construction method” of Patent Document 2, a vertical hole is excavated from the contaminated layer on the ground surface to the position of the impermeable layer deeper than the boundary surface between the contaminated layer and the impermeable layer by an excavation process. Next, a filler is injected into the vertical hole from the position of the impermeable layer to the position of the contaminated layer by an injection process. Next, before the filler is cured by the insertion step, the casing tube is inserted to the position of the impermeable layer, and the filler is filled between the outer peripheral surface of the casing tube and the inner peripheral wall of the vertical hole. Next, in the pile construction process, after the filler is cured, the pile is constructed through the casing tube to the lower support layer through the water permeable layer below the impermeable layer.

  In "Vertical hole excavation method and vertical hole excavation apparatus" of Patent Document 3, a ground having an upper permeable layer located above the impermeable layer and a lower permeable layer located below the impermeable layer is excavated vertically. A hole is formed. This vertical hole excavation method includes a first excavation step for excavating a vertical hole to an intermediate portion of an impermeable layer, a replacement step for replacing soil excavated in the first excavation step with bentonite mud water, and an upper portion in bentonite mud water. A layer forming step of forming a sealing layer by spraying a layer forming material on a region including a boundary portion between the water-permeable layer and the water-impermeable layer, and a second excavation step of excavating a vertical hole from a middle portion of the water-impermeable layer to a lower water-permeable layer And.

Japanese Patent No. 3367042 JP 2012-241471 A JP 2014-156752 A

The conventional means for carrying out the pile construction while preventing the diffusion of soil contamination described above forms the upper permeable layer ground replacement step (Patent Document 1), filling material injection and casing tube insertion (Patent Document 2), and a sealing layer. It requires ground improvement that is different from the conventional on-site pile method such as the layer formation process (Patent Document 3).
Therefore, the conventional means requires a long period of time for ground improvement, is complicated in process, and requires a large amount of cost (cost).

  The present invention has been developed to solve the above-described problems. That is, an object of the present invention is to provide an in-situ pile method that can significantly reduce or prevent the spread of soil contamination without ground improvement.

According to the present invention, in the in-situ pile method for excavating the stable liquid in the pile hole,
A stabilizing solution preparation step of preparing an added stabilizing solution by adding an adsorbent that adsorbs heavy metal contaminants to the stabilizing solution;
A pile-hole excavation process is provided, which includes filling a pile hole with the added stabilizing liquid and excavating the pile hole.

As a result of repeating many experiments and studies, the inventors of the present invention have obtained the following new findings.
(1) The stable liquid used in the in-situ pile driving method in which the stable liquid is filled in the pile hole and excavated has a high adsorption function for lead.
(2) By adding an adsorbent to the stabilizing liquid, it is possible to provide an adsorption function for heavy metal contaminants.
(3) If the soil contains naturally-occurring heavy metal contaminants, the elution concentration of heavy metal contaminants is below the standard value by adding an appropriate amount of adsorbent to the stabilizer while maintaining the original performance of the stabilizer. And the diffusion of heavy metal contaminants can be prevented.

The present invention is based on such novel findings. That is, according to the present invention, an adsorbent that adsorbs heavy metal contaminants is added to the stabilizer in the stabilizer preparation step to prepare an added stabilizer. Next, in the pile hole excavation process, the piled hole is excavated by filling the prepared stabilizing liquid in the pile hole.
The above-mentioned in-situ pile method of the present invention has the same construction procedure as the conventional in-situ pile method in which a stabilizing liquid is filled in a pile hole and excavated, and ground improvement is unnecessary.
Moreover, the process added to the conventional construction procedure is only the stabilization liquid preparation process mentioned above etc., and can be implemented in a short time.
Therefore, the on-site pile method of the present invention can significantly reduce or prevent the spread of soil contamination without ground improvement.

It is a conceptual diagram in the case of constructing a housing complex where pollution is kept. It is a flowchart which shows the spot driving pile method by this invention. It is a pile construction construction outline figure by an earth drill method. It is a figure which shows the function and required property of a stabilizer. It is an experiment flowchart. It is a figure which shows the adsorption test result of the stable liquid A. It is a figure which shows the adsorption test result of the stable liquid B. It is a figure which shows the adsorption test result of the stable liquid C. It is a figure which shows the adsorption isotherm of arsenic with respect to the bentonite contained in the stabilizers A, B, and C. FIG. 6 is a relationship diagram between the pH of the stabilizers A, B, and C and the Pb concentration. It is a figure which shows the As adsorption isotherm of the stable liquids A, B, and C. It is a figure which shows the adsorption test result with respect to each heavy metal. It is a figure which shows the excavation procedure by an earth drill construction method. It is a figure which shows the structure of the soil containing a heavy metal etc., and a stabilizer. It is a figure which shows the result of the quality control test (funnel viscosity, filtered water amount, pH) of a stable liquid. It is a figure which shows the relationship between the addition amount of MgO and Al (OH) ₃ which are adsorption agents, and each heavy metal concentration of the stabilizer A. It is a figure which shows the relationship between the addition amount of MgO and Al (OH) ₃ which are adsorption agents, and each heavy metal concentration of the stabilizer B. It is a figure which shows the adsorption isotherm of arsenic. It is a figure which shows the adsorption isotherm of a fluorine. It is a figure which shows an example of the flowchart of a mixing | blending design.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted.

FIG. 1 is a conceptual diagram in the case of constructing an apartment house where pollution remains.
As shown in this figure, when a pile is planned on the ground (bottom support layer 3) where there is contaminated soil 1 containing natural heavy metals and groundwater, the pile penetrates the contaminated soil 1 and the poorly permeable layer 2 below it. Then, the lower support layer 3 is reached. Construction of such a pile may cause heavy metals or the like to diffuse into the lower aquifer 3 (lower support layer 3) below the poorly permeable layer.

FIG. 2 is a flow diagram showing the on-site pile method according to the present invention.
In this figure, the in-situ pile method of the present invention is a in-situ pile method for excavating with a stable liquid filled in a pile hole, and has a stable liquid preparation step S1 and a pile hole excavation step S2.
The in-situ pile method for excavating with a stable liquid filled in a pile hole is, for example, an earth drill method, a reverse method, or a BH method.

In the stabilizing solution preparation step S1, an adsorbent that adsorbs heavy metal contaminants is added to the stabilizing solution to prepare an added stabilizing solution.
In the pile hole excavation step S <b> 2, the prepared stabilization liquid is filled in the pile hole and the pile hole is excavated.

In the present invention, the target heavy metal contaminant is arsenic (As), fluorine (F), or lead (Pb), but may contain other contaminants.
The stabilizer is preferably a polymer stabilizer or a bentonite stabilizer, but may be other stabilizers.
The adsorbent is preferably magnesium oxide or aluminum hydroxide, but may contain other adsorbents.

  Arsenic, fluorine, and lead mixed in the drilling hole by adding magnesium oxide or aluminum hydroxide to the polymer-based stabilizer or bentonite-based stabilizer with respect to arsenic, fluorine, and lead according to examples described later. It was confirmed that the elution amount of can be reduced below the reference value. The “reference value” is preferably a “groundwater environmental reference value”.

  In FIG. 2, the stabilizing solution preparation step S1 has a sampling step S11, a dissolution test step S12, a relationship detection step S13, and an addition rate determination step S14.

In the sampling step S11, the contaminated soil 1 is collected from the ground containing heavy metal contaminants.
In the elution test step S12, the contaminated soil 1 and a plurality of added stabilizing liquids having different adsorbent addition rates are mixed to detect the elution amount of heavy metal contaminants in the liquid.
In the relationship detection step S13, the relationship between the adsorbent addition rate and the elution amount is obtained.
In the addition rate determination step S14, the adsorbent addition rate of the addition stabilizer is determined from the relationship between the adsorbent addition rate and the elution amount.
As will be described later, the adsorbent addition rate and the number n of diversions of the added stabilizing liquid can be determined by this stabilizing liquid preparation step S1.

The pile hole excavation step S2 includes an intermediate confirmation step S21. In the intermediate confirmation step S21, after excavating the ground (contaminated soil 1) containing heavy metal contaminants, excavation is interrupted once before the non-contaminated ground (hardly permeable layer 2), and the liquid phase concentration of the added stable liquid is the reference value Confirm that it is less than
By this intermediate confirmation step S21, it is possible to prevent the heavy metal having a concentration higher than the reference value from diffusing into the lower aquifer 3 in advance.

In FIG. 2, the pile hole excavation step S2 further includes a quality control step S22. In the quality control step S22, the elution amount of heavy metal contaminants contained in the added stabilizing liquid in use is inspected.
In this quality control step S22, if the amount of elution of heavy metals exceeds the reference value as a result of the analysis, the excavation is stopped and measures such as replacement of the stabilizing solution or addition of the adsorbent are performed. The liquid phase concentration can be maintained below the reference value.

In the pile hole excavation step S2, excavation is performed while maintaining the in-hole water level of the added stabilizing liquid at or above the groundwater level.
By keeping the water level in the borehole above the groundwater level, it is possible to prevent the intrusion of heavy metal contaminants from the outside during the excavation process of the soil layer (contaminated soil 1) containing heavy metal contaminants.

  The in-situ pile method is an earth drill method, which is drilled to the planned depth of the surface casing and placed in the surface casing, infused with the added stabilizing liquid, while maintaining the liquid level of the added stabilizing liquid with a drilling bucket. It is preferable to repeat excavation and earth removal work on the ground.

In FIG. 2, the in-situ pile method of the present invention further includes a concrete placing step S3 and a stable liquid recovery step S4.
In the concrete placing step S3, concrete is placed in the pile hole.
In the stable liquid recovery step S4, the added stable liquid replaced with concrete is recovered in the recovery tank.
By discarding the added stabilizing solution recovered in this step with the number of diversions n set in the formulation design, gelation due to the addition of an adsorbent can be avoided.

When the stabilizer is a polymer stabilizer, the adsorbent is preferably 0.5 to 5% magnesium oxide or 0.5 to 5% aluminum hydroxide.
It was confirmed by the examples described later that the amount of arsenic, fluorine and lead mixed in the drilling hole could be reduced below the reference value while ensuring the quality of the stable liquid within this range.

When the stabilizer is a bentonite stabilizer, the adsorbent is preferably 0.5 to 2% magnesium oxide or 0.5 to 5% aluminum hydroxide.
It was confirmed by the examples described later that the amount of arsenic, fluorine and lead mixed in the drilling hole could be reduced below the reference value while ensuring the quality of the stable liquid within this range.

  As described above, according to the present invention, an adsorbent that adsorbs heavy metal contaminants is added to the stabilizer in the stabilizer preparation step S1 to prepare an added stabilizer. Next, in the pile hole excavation step S2, the prepared addition stabilizing liquid is filled in the pile hole and the pile hole is excavated. Thereby, the diffusion of soil contamination can be significantly reduced or prevented without adsorbing the ground by adsorbing heavy metal contaminants to the added stabilizing liquid.

  Examples of the present invention will be described below. In the following description, “heavy metal contaminant” is simply referred to as “heavy metal etc.” or “pollutant”. In addition, “stabilizing liquid” and “added stabilizing liquid” are simply referred to as “stabilizing liquid” unless it is necessary to distinguish them. The “adsorbent addition rate” is simply referred to as “addition rate”.

(Verification of adsorption function of stable liquid such as heavy metals)
1. Fig. 3 is a diagram of pile construction work by the earth drill method.
The earth drill method is one of the on-site pile methods that excavate by filling the pile hole with a stable liquid. The ground drill method rotates the drilling bucket to excavate the ground, and discharges the earth and sand stored in the bucket to the ground. . For the hole wall, a surface casing is used at the surface layer, and the depth is protected by a stabilizing liquid. After excavation is completed, a steel bar made in a predetermined shape is built, and concrete is cast with a tremy pipe to build a pile. For the stabilizer, bentonite or polymer is used according to the properties of the target ground.

FIG. 4 is a diagram showing the function and necessary properties of the stabilizer.
When excavating the ground with the earth drill method, the water head difference of 1 to 2 m or more is always maintained to prevent the hole wall from collapsing. Therefore, in the excavation process of the soil layer containing heavy metal or the like, it is difficult to consider the intrusion of heavy metal or the like from the outside, but harmful substances contained in the excavated soil (contaminated soil 1) are mixed in the stable liquid. When excavation is continued using this stabilizing liquid and the clay layer (the poorly permeable layer 2) is penetrated, heavy metals and the like may leak into the aquifer under the clay layer (the lower aquifer 3).

2. Experimental Method FIG. 5 is an experimental flowchart. As shown in this figure, in order to verify the adsorption function of the stabilizer for arsenic (As), fluorine (F), and lead (Pb), a batch adsorption test and an API standard (American Petroleum Institute) pressure filtration tester were used. A filtration test was performed. The filtration test simulates the filtration effect of the mud membrane. In addition, in order to confirm the change in the properties of the stable solution due to the mixing of heavy metals, a quality control test of the stable solution was conducted at the same time. The experimental procedure is shown below.

  (1) Stabilizers are commonly used polymer stabilizers (hereinafter “Stabilizer A”), bentonite stabilizers (hereinafter “Stabilizer B”), and sites sampled during construction in Osaka city. Three types of collection stabilizers (hereinafter referred to as “stable fluid C”) were used. Stabilizers A and B were cured for 24 hours after liquid preparation. Table 1 shows the composition of the stabilizers A, B, and C. The unit is% by weight.

(2) The target heavy metals and the like (As, F, Pb) are 1000 mg / L standard solution for atomic absorption analysis (As ₂ O ₃ , F ⁻ , Pb (NO ₃ ) ₂ , all manufactured by Wako Pure Chemical Industries, Ltd.). It added so that it might become a 3 level density | concentration of 1, 5, and 20 mg / L, and it shaked for 1 minute. In order to confirm the interaction of each substance, two kinds of mixed solutions (As + F, As + Pb, F + Pb) and three kinds of mixed solutions (As + F + Pb) were also prepared.

  (3) Two days after the shaking of the stable solution, centrifugation (3000 rpm, 20 min) and filtration with a 0.45 μm membrane filter were performed, and the As, F, and Pb concentrations of the obtained filtrate a were measured. The preparation method of the test solution and the concentration measurement method are shown in FIG.

  (4) Immediately after shaking the stable liquid, perform a filtration test (filtration pressure 0.5 MPa, retained particle diameter of filter paper 1 μm) using a pressure filtration tester, and the concentration of As, F, and Pb in the obtained filtrate b Was measured.

  (5) In the quality control test of the stable liquid, viscosity, wall-forming property and pH were confirmed. Viscosity was measured by using an API standard funnel viscometer to measure the time (s) required for 500 ml of the stable liquid to completely flow out. For the wall-forming property, a filtration test (filtration pressure 0.3 MPa, 30 minutes, retention particle diameter of filter paper 1 μm) was performed with a pressure filtration tester, and the amount of filtrate water (ml) obtained was measured.

3. Experimental results and discussion Tables 2, 3 and 4 show the experimental results, and FIGS. 6, 7 and 8 show the adsorption test results for each heavy metal and the like.
A significant reduction in the Pb concentration was confirmed in each of the A, B, and C stabilizers. Since the filtrate concentration cannot be displayed on the linear axis, the logarithmic axis was used only for the graph of Pb concentration.
The concentration of arsenic was reduced to about 10 to 50%.
Regarding fluorine, almost no reduction in concentration was observed. In addition, no significant change was observed in the properties of the stabilizer (funnel viscosity, pH, filtered water amount) due to the mixing of heavy metals and the like.

(1) Arsenic FIG. 9 shows adsorption isotherms of arsenic (CASE A1-3, B1-3, C1-3) for bentonite contained in the stabilizers A, B, and C. The amount of adsorption was determined by dividing the difference between the initial concentration and the filtrate a by the amount of bentonite. When an approximate straight line is drawn with the adsorption characteristic as the Henry type, since the slopes (distribution coefficients) of the straight lines show relatively close values for the stabilizers A, B, and C, it is considered that arsenic was adsorbed by bentonite.

The arsenic adsorption by bentonite is considered as follows. The pH of the stabilizing solution takes a value of approximately 9 to 12. At this time, arsenic is an anion such as arsenite ion (H ₂ AsO ₃ ⁻ ) or arsenate ion (HAsO ₄ ²⁻ , AsO ₄ ³⁻ ). Present in the stable liquid in the form. Therefore, ion exchange with the layered silicate mineral, which is the main component of bentonite, and ion adsorption reaction at the crystal end face hardly occur. However, the bentonite used in the experiment contains magnetite as an accompanying mineral, which may have adsorbed arsenite ions.

  The As concentration of the filtrate a was lower by about 20% on the average in the stable liquid A and about 10% on the average in the stable liquids B and C than the As concentration in the filtrate b. The reason is considered as follows. The reaction between arsenite ions and iron oxides and hydroxides as described above is not completed instantaneously like the cation exchange reaction. Arsenite ions and bentonite are separated by filtration using a pressure filtration tester immediately after shaking, but the centrifugation and filtration of filtrate a were carried out after about 2 days. It is considered that the elution concentration decreased due to the progress of the adsorption reaction. Moreover, it is thought that the difference between the membrane filter (pore diameter 0.45 mm) used in filtration according to the notice 46 method and the qualitative filter paper (retained particle diameter 1 μm) used in the pressure filtration test according to the API standard is also considered to be affected.

(2) Fluorine For all of the stabilizers A, B, and C, the F concentration was slightly reduced. This is considered to be caused by the fact that fluorine does not coprecipitate very much with the layered silicate mineral or iron hydroxide in the alkaline region. The F concentration of the filtrate b was about 20% higher than the F concentration of the filtrate a. The reason for this is considered to be due to the difference in the type of the filter as in the case of arsenic.

(3) Lead The Pb concentration of filtrate a is <0.01 to 0.78 mg / L for stabilizer A, <0.01 to 0.18 mg / L for stabilizer B, and <0.01 for stabilizer C. It was -0.10 mg / L. In the stable liquid C, the Pb concentration of the filtrate b was all below the groundwater environmental standard value (0.01 mg / L), and a significant decrease in the concentration was observed. Since the pH of the stabilizer is about 8 to 12 and alkaline, lead is present in the stabilizer in the form of an anion of Pb (OH) ₃ ⁻ , so that the layered silicate which is the main component of bentonite There is no ion exchange with minerals or ion adsorption reactions at the crystal edges. Therefore, it is thought that lead produced | generated the deposit of the hardly soluble hydroxide. FIG. 10 shows the relationship between the pH of the stabilizers A, B, and C and the Pb concentration. In each case, a negative correlation was observed between the pH and the lead concentration.

  In the stable solutions B and C, the Pb concentration of the filtrate b was lower than the Pb concentration of the filtrate a except for CASE B15. The reaction time of the ion exchange reaction of lead and the formation reaction of hydroxide is on the order of ms to min, and these reactions are completed before the filtration test, and thereafter no new adsorption reaction can occur before the elution test. Furthermore, it is considered that the filtration function by the mud membrane was exhibited that the Pb concentration of the filtrate a> the Pb concentration of the filtrate b despite the difference in the filter diameters described above.

(4) Effect of coexistence with heavy metals, etc. The interaction with coexistence with other heavy metals, etc., tends to suppress the amount of arsenic adsorbed in the presence of fluorine and lead in both stabilizers A, B, and C. (FIG. 11). On the other hand, with respect to Pb and F, no influence on the amount of adsorption by coexisting heavy metals was observed.

(Examination of applicability of adsorbent)
1. Evaluation of Adsorbent Performance In Example 1, it was clarified that the stabilizing liquid generally used in the earth drill method has an adsorption function for arsenic and lead. In particular, lead has a high adsorption function (including precipitation of hydroxide), and if the initial concentration is about 1 mg / L, the concentration can be reduced to several times the soil elution standard value. It became clear that it was possible. Furthermore, it was found that a certain concentration reduction can be expected by the filtration function of the mud membrane.

In Example 2, an adsorbent for reducing the concentration of arsenic, fluorine, and lead added to the stabilizer was studied. Select from five types of adsorbents: ferrous sulfate (FeSO ₄ ), magnesium oxide (MgO), calcium carbonate (CaCO ₃ ), zeolite, and aluminum hydroxide (Al (OH) ₃ ) that have a proven track record in insolubilizing heavy metals. The adsorption performance was evaluated. In addition, the effect of the addition of these adsorbents on the original function (wall-forming property, viscosity, pH) of the stable liquid was also verified.

2. Experimental Method In order to verify the adsorption function of the adsorbent with respect to three kinds (As, F, Pb) such as heavy metals, a batch adsorption test was conducted. In addition, a quality control test of the stabilizer was also conducted to confirm whether the original function of the stabilizer was degraded due to the addition of the adsorbent. The experimental procedure is shown below.

(1) A bentonite stabilizer was used as the stabilizer. Table 5 shows the composition at the time of preparation of the stabilizing liquid (before addition of the adsorbent).

(2) After curing the stabilizing solution for 24 hours, 1% by weight of the adsorbent was added. Adsorbents are ferrous sulfate (powder, main component FeSO ₄ · 7H ₂ O), magnesium oxide (fine powder, main component MgO), calcium carbonate (fine powder, main component CaCO ₃ ), zeolite (granular, main component) SiO ₂ ) and amorphous aluminum hydroxide (powder, main component Al (OH) ₃ ).

(3) The target heavy metals were As, F, and Pb, and 1000 mg / L standard solution for atomic absorption analysis was mixed with the stabilizing solution to a concentration of 5 mg / L, and shaken for 1 minute. . A mixture of heavy metal and a stabilizing solution was used as the following sample.
(4) The sample was subjected to a quality control test of the stabilizer, and when the “quality control standard value of the stabilizer” shown in Table 6 was not satisfied, the properties were corrected with a dispersant or the like.

  (5) The sample was centrifuged and filtered according to the Circular 46 method, and the As, F, and Pb concentrations of the filtrate were measured. As the concentration measurement method, As and Pb were ICP mass spectrometry, and F was a flow analysis method.

3. Experimental Results and Discussion FIG. 12 shows the adsorption test results for each heavy metal.

When ferrous sulfate was added to the stabilizer and stirred, it gelled markedly. This is presumably because bentonite in the stable liquid became agglomerated by mixing iron ions (Fe ²⁺ ). Since there was no effect of correction with a dispersant or the like, it was judged that it could not be applied as an admixture for a stabilizer.

Zeolite had a high cation exchange capacity and expected to adsorb lead, but no adsorption effect was seen compared to the case of only the stabilizer.
Although calcium carbonate was expected to adsorb lead, arsenic, and fluorine, the adsorption effect was not seen as compared to the case of using only a stable solution as in the case of zeolite.

  Magnesium oxide adsorbs all of arsenic, fluorine and lead well, and the concentration of fluorine and lead satisfied the groundwater environmental standard value. The funnel viscosity regained fluidity by shaking again after the heavy metal was mixed. In addition, the pH of the stabilizing solution to which magnesium oxide was added increased by about 2 compared to the other cases.

  As for aluminum hydroxide, the concentration of fluorine and lead satisfied the groundwater environmental standards. As for the properties of the stable liquid, although the viscosity and the amount of filtered water increased slightly, the pH was good with no change compared to the initial value.

  Based on the above, by adding magnesium oxide or aluminum hydroxide to the stabilizer at an appropriate concentration, the amount of arsenic, fluorine, and lead mixed in the drilling hole can be used as a standard without impairing the original function of the stabilizer. It has been shown that it can be reduced below the value.

(Examination of composition design method of stabilizer)
1. Examination of application to ground containing natural heavy metals, etc. In Example 2, by adding adsorbents (magnesium oxide, aluminum hydroxide) to the stable liquid, the elution amount of lead and fluorine with an initial concentration of 5 mg / L was reduced to groundwater. It was shown that the concentration of arsenic can be reduced to several times the groundwater environmental standard value below the environmental standard value. Therefore, in Example 3, effective blending of the adsorbent added to the stabilizing liquid was examined for soil containing naturally-derived heavy metals and the like, that is, about 10 times the elution amount standard.

2. Concentration of heavy metals eluting in the stable liquid Earth drilling method excavates while maintaining the water level in the hole of the stable liquid at the groundwater level plus 1 to 2 m or higher, so soil and groundwater containing external heavy metals etc. will not enter the hole. Very Hard to think. Therefore, it is considered that only the heavy metals eluted from the excavated soil are mixed in the stabilizing liquid. Therefore, we examine the mixing of heavy metals from excavated soil into the stable liquid.

  FIG. 13 shows a drilling procedure by the earth drill method. First, the surface casing is excavated to the expected depth (about 3 m) (FIG. 13 (a)), and after the surface casing is stowed, a stabilizing liquid is injected (FIG. 13 (b)). Thereafter, the operation of excavating with a drilling bucket and discharging to the ground while keeping the liquid level of the stable liquid constant is repeated (FIG. 13C). Therefore, the soil deeper than the surface casing comes into contact with the stabilizing liquid in the excavation and earth removal processes, and the volume ratio is considered to be approximately 1: 1 although it depends on the pile length.

FIG. 14 is a diagram illustrating a configuration of soil (a) containing a heavy metal or the like and a stabilizing solution (b). The dry mass m _{s of} soil particles, the mass m _{w of} interstitial water, and the mass m _wsl of water in the stabilizing liquid can be shown as follows.

m _s = ρ _s · V _s (1)
m _w = ρ _w · V _w = ρ _w · eV _s (2)
m _wsl = ρ _sl · V (1−α) = ρ _sl · V _s (1 + e) (1−α) (3)
Here, N is defined as the ratio between the mass sum of the pore water and the water in the stabilizing liquid (m _w + m _wsl ) and the mass m _{s of the} soil particles.
N = (m _w + m _wsl ) / m _s = {ρ _w · e + ρ _sl · (1 + e) (1−α)} / ρ _s (4)
It becomes.

Here, V: volume of soil, V _s : volume of solid phase, V _w : volume of liquid phase, m _w : mass of pore water, m _s : dry mass of soil particles, m _wsl : contained in stable liquid Mass of water, m _b : dry mass of bentonite, etc., m _sl : mass of stabilizer, α: blending ratio of bentonite etc. = m _b / m _sl , ρ _s : density of soil particles, ρ _sl : density of stabilizer , E: gap ratio = V _w / V _s .

The elution amount of soil containing heavy metals (measured at a liquid-solid ratio of 10 in accordance with the Environmental Agency Notification No. 46 method) is c ₀ (mg / L). Is constant, the liquid phase concentration c of the stable liquid satisfies the following equation. It is assumed that there is no groundwater contamination.
10 · c ₀ = N · c (5)
c = 10c ₀ · ρ _s / {ρ _w · e + ρ _sl · (1 + e) (1-α)} (4.6)

For example, excavating a soil layer containing heavy metals with c ₀ = 0.10 mg / L, e = 1.0, ρ _s = 2.65 t / m ³ , using a stable liquid with ρ _sl = 1.05 t / m ³ In this case, the liquid phase concentration of the stable liquid at the completion of excavation is c = 0.89 mg / L at the maximum. This is approximately 10 times the elution amount value c ₀ of the original soil.

3. Experimental Method Table 7 shows the experimental conditions for the batch adsorption test. The target heavy metals were four kinds including three kinds of mixed solutions in three kinds of arsenic, fluorine and lead. The concentration of each heavy metal was 100 times the soil elution standard value. This is because the elution value of soil containing naturally-derived heavy metals etc. is generally within 10 times the standard value of soil elution, and when the ground containing this soil is excavated by the earth drill method, the liquid phase concentration of the stable liquid is maximum. Is assumed to be about 100 times the soil elution standard value.

From the experimental results of Example 2, the adsorbent was selected from two types of magnesium oxide and aluminum hydroxide. The amount of addition is 3 levels of 0.5, 1.0, 2.0% when the target heavy metal is arsenic alone or lead alone, and 1.0, 2.0, 5 for cases containing fluorine. Three levels of 0.0% were set.
There were two types of stabilizers, the polymer stabilizer (stable solution A) and the bentonite stabilizer (stable solution B) shown in Table 1. In the experiment of Example 3, neither the stabilizers A nor B added clay. In addition, in order to confirm whether or not the function of the stabilizing solution was deteriorated due to the admixture of adsorbents, heavy metals, etc., a “stabilizing solution quality control test” shown in Table 6 was also carried out. As the concentration measurement method, As and Pb were ICP mass spectrometry, and F was a flow analysis method.

4). Experimental Results and Discussion (1) Quality Control Test of Stabilizing Liquid The results of the quality control tests (funnel viscosity, filtered water volume, pH) of the stabilizing liquid for CASE A-1 to 24 and CASE B-1 to 24 shown in Table 7. As shown in FIG.
In this figure, (a) is the funnel viscosity, (b) is the amount of filtered water, and (c) is the pH. The horizontal axis is the CASE number, the broken line in the figure is an example of the control reference value, the circle mark is the stabilizer A (polymer stabilizer), and the triangle is the stabilizer B (bentonite stabilizer).
The experimental results and considerations for each quality control item are described below.

(A) Viscosity (funnel viscosity)
The change in the funnel viscosity due to the addition of MgO and Al (OH) ₃ to the stabilizing liquid A was stable, and changed around 30 seconds in all cases. On the other hand, the stabilizer B was CASE B-11 (addition amount 2%) and the funnel viscosity exceeded the control standard value of 48 seconds, so the tests of CASE B-6 and B-12 (addition amount 5%) were cancelled. The funnel viscosity of CASE B-24 (added amount 5%) also exceeded the control standard value for 45 seconds. CASE B-11 and CASE B-24 stabilizing solutions were once gelled when allowed to stand for 6 hours after the test, but fluidity was restored by applying vibration.

In Stabilizer B, the viscosity and the amount of filtered water increased as the amount of adsorbent added increased because the stabilizer became agglomerated due to the mixing of metal ions (Mg ²⁺ and Al ³⁺ ) contained in the adsorbent. it is conceivable that. Since the funnel viscosity has exceeded the control standard value, the amount of MgO added to the stabilizer B, that is, the bentonite stabilizer, should be less than 2% and the amount of Al (OH) ₃ added should be less than 5%. On the other hand, polymer-based stabilizers are more resistant to metal ions than bentonite-based stabilizers, and the viscosity and filtered water volume increase as the amount of adsorbent added increases but exceeds the control standard value. I never did.

(B) Wall-forming property Wall-forming property can be grasped by measuring the amount of filtered water. When MgO and Al (OH) ₃ were added in an increased amount, the amount of filtered water tended to increase. From this, it can be said that the smaller the added amount of both MgO and Al (OH) _{3, the} better the wall-forming property. However, when 0.5 to 5% of MgO is added, the amount of filtered water is distributed in 6 to 10 ml, and when 0.5 to 5% of Al (OH) ₃ is added, the amount of filtered water is distributed in 7 to 11 ml. did. Both are good values, and it can be said that the influence on the wall-forming property by the addition of the adsorbent is small under the present experimental conditions.
However, since CASE A-18, in which 5% of Al (OH) ₃ was added to Stabilizer A, showed a sharp increase in the amount of filtered water, the addition of Al (OH) ₃ to Stabilizer A, that is, the polymer stabilizer The amount should be limited to about 5%.

(C) pH
In both of the stabilizers A and B, the change in pH due to the addition of MgO was small and distributed between pH 10-11. On the other hand, the change in pH due to the addition of Al (OH) ₃ is relatively large. In particular, when 5% of Al (OH) ₃ is added to the stabilizer A, that is, the pH is 8 in CASE A-18 and CASE A-24. Near the lower limit of the management standard value.

(2) Adsorbent Addition Amount and Equilibrium Concentration FIG. 16 shows the relationship between the adsorbent addition amounts of MgO and Al (OH) ₃ and the concentration of each heavy metal in the stabilizer A. In this figure, (a) is a relationship diagram of MgO addition amount, As concentration (upper) and F concentration (lower), and (b) is Al (OH) ₃ addition amount and As concentration (upper), F It is a relationship figure with density | concentration (medium) and Pb density | concentration (lower).

Arsenic is less affected by mixing with fluorine and lead, and the addition amount of MgO and Al (OH) ₃ is 0.5% and 5% or more, respectively, to keep the arsenic concentration below the groundwater environmental standard value. it can.

As for fluorine, when MgO is added, there is an influence due to coexistence with arsenic and lead. By adding MgO and Al (OH) _{3 to} 5% or more, the fluorine concentration is kept below the groundwater environmental standard value. be able to.
About lead, when MgO was added, it became less than the groundwater environmental standard value in all cases. When Al (OH) ₃ is added, there is little influence due to coexistence with arsenic and fluorine, and the lead concentration can be suppressed below the groundwater environmental standard value by setting the addition amount to 2% or more.

FIG. 17 shows the relationship between the added amount of MgO and Al (OH) ₃ as adsorbents and the concentration of each heavy metal in the stabilizer B. In this figure, (a) is a relationship diagram of MgO addition amount, As concentration (upper) and F concentration (lower), and (b) is Al (OH) ₃ addition amount and As concentration (upper), F It is a relationship figure with density | concentration (medium) and Pb density | concentration (lower).

Arsenic is less affected by mixing with fluorine and lead, and by adding MgO and Al (OH) _{3 to} 2% and 5% or more respectively, the arsenic concentration can be kept below the groundwater environmental standard value. .

Fluorine is affected by coexistence with arsenic and lead when MgO is added, and can be suppressed to less than the groundwater environmental standard value by setting the addition amount to 2.5% or more. When Al (OH) ₃ was added to fluorine, the influence of coexistence with arsenic and lead was not observed, and the fluorine concentration did not satisfy the groundwater environmental standard value when the addition amount was 5% or less.

When MgO was added to lead, it was less than the groundwater environmental standard value in all cases. When Al (OH) ₃ was added to lead, the influence of coexistence with arsenic and fluorine was observed, and the groundwater environmental standard value was satisfied by setting the addition amount to 2% or more.

(3) Optimal combination of stabilizing solution and adsorbent FIGS. 18 and 19 show adsorption isotherms for arsenic and fluorine, respectively. Both arsenic and fluorine have a higher MgO adsorption function than Al (OH) ₃ . Among them, the case where MgO is added to the stabilizer A has the highest adsorption function. In addition, it was found that the amount of adsorption with respect to lead was larger when MgO was added than with Al (OH) ₃ .

(4) Discussion (a) About adsorption of heavy metal by aluminum hydroxide Al (OH) ₃ has an active surface hydroxyl group, and Pb ²⁺ which is a cation, F ⁻ and H ₂ AsO ₃ ⁻ which are anions, Also adsorb and form a surface complex. Here, the pH of the stabilizer when Al (OH) ₃ is added is 8.1 to 9.6, which is the zero potential point of Al (OH) ₃ except for CASE B-14. .5 to less than 10.0. For this reason, Al (OH) ₃ has a positive charge and is considered to have adsorbed F ⁻ and H ₂ AsO ₃ ⁻ . Compared with Pb concentration in CASE A-19 to 21 and CASE B-19 to 21 and experimental results of Examples (A-7 and B-7 in Table 2), lead concentration reduction by Al (OH) ₃ The fact that the effect is not seen also suggests that lead has produced a slightly soluble hydroxide.

When using a polymer-based stabilizer in the summer, it is necessary to adjust the pH to 9 or more as a measure against bacterial alteration. Therefore, when adding Al (OH) ₃ , limit the amount of addition or consider using an alkaline agent. There is a need to. However, as described above, the potential zero point of Al (OH) ₃ is 9.5, and the adsorption effect of arsenic and fluorine may be lowered by setting the pH to 9 or more. Need attention.

(B) About adsorption of heavy metal by magnesium oxide The pH of the stabilizer when MgO is added is 10.5 to 11, and this value is lower than 12.4 which is the potential zero point of MgO. Therefore MgO also has a positive charge F ^- and _H 2 AsO ₃ ^- believed to form an adsorbed surface complexes. It is also considered that fluorine is taken in when MgO reacts with water and changes to Mg (OH) ₂ . For lead, the mechanism of insolubilization by MgO has not been clarified, but the formation of lead hydroxide due to an increase in pH is considered.

  In CASE A-1 to 12, the pH increased by about 1 from the time of experiment (immediately after addition of MgO) to the time of concentration analysis (after 2 days). The reason is considered as follows. As shown in formula (7), MgO dissolves in an aqueous solution and supplies hydroxide ions, so that the pH rises. However, as shown in formula (8), magnesium ions and hydroxides that are supersaturated are then obtained. The ions precipitate as magnesium hydroxide ions.

MgO + H ₂ O⇔Mg ²⁺ + 2OH ⁻ (7)
Mg ²⁺ + 2OH ⁻ ⇔Mg (OH) ₂ (8)

  However, in the presence of smectite, which is the main component of bentonite, the reactions of formulas (7) and (8) depend on the concentration of magnesium oxide, and when magnesium oxide is 10% or less of smectite, formulas (7) and (8) It has been pointed out that no reaction takes place. In addition, it is known that smectite has a pH buffering capacity by ion exchange or the like. From these facts, the stable solution CASE B-1-12 containing a large amount of bentonite has a pH higher than that of CASE A-1-12. The rise is thought to have been suppressed.

  The reactions of formulas (7) and (8) are slow, and the production rate of magnesium hydroxide is reported to be 75% in 3 days and 92% in 28 days. Moreover, the reaction of Formula (7), (8) is reported as about 8 hours. These facts indicate that the curing time after stable liquid preparation may greatly affect the adsorption effect, and caution must be exercised when applying it to the construction work.

5. Verification experiment using naturally-derived arsenic-containing soil The adsorption function of heavy metals, etc., by a stabilizing solution with adsorbent added was verified using soil collected on site. The sample used is naturally-occurring arsenic-containing soil having the properties shown in Table 8. The stabilizing solution was a polymer-based stabilizing solution, the adsorbent was MgO and Al (OH) ₃ , and the addition amount was two levels of 0.5% and 2.0% from the experimental results of FIG. Two days after shaking the stable solution and sample soil at a volume ratio of 1: 1 for 1 minute, centrifugation (3000 rpm, 20 min) and filtration with a 0.45 μm membrane filter were performed, and the As concentration of the obtained filtrate was measured. .

Table 9 shows the experimental results. Even in the soil collected at the site, the adsorption function of MgO was higher than that of Al (OH) ₃ , and the As concentration of the stable solution was reduced to less than the groundwater environmental standard value at an MgO addition amount of 0.5%.

6). In summary, the bentonite-based stabilizer is easily gelled by the addition of an adsorbent, and aluminum hydroxide has a pH of less than 9 and may be degraded by bacteria in the summer. As for the combination of the stabilizer and the adsorbent when applied, it is considered effective to add 0.5 to 5% of MgO as an additive to the polymer stabilizer.

(Study on design method and construction management method of stabilizer)
1. Stabilizing liquid design method (1) Blending design Here, we examine the blending design of the stabilizing liquid that has the effect of preventing diffusion of heavy metals and the like. In Example 3 described above, it was shown that the excavated soil and the stabilizing liquid are in contact with each other at a volume ratio of approximately 1: 1 in excavation by the earth drill method. Therefore, the solid-liquid ratio in the treatability test is 1.

  From the results of Example 3 described above, the stabilizer is a polymer-based stabilizer, the adsorbent is MgO, and the addition rate is set to four levels of 0.5, 1, 2, and 5%. From the dissolution test result, a graph of addition rate-elution amount is created, and the addition rate d1 is calculated. The number of diversions of the stabilizing liquid is n times (1 ≦ n ≦ 4), and dn that satisfies d1 × n ≦ dn is defined as the adsorbent addition rate. Based on the above, an example of a blending design flowchart is shown in FIG.

  As described above, magnesium oxide produces magnesium hydroxide by a hydration reaction, but this reaction rate is slow, and the adsorption effect may vary depending on the number of days of curing after the liquid preparation. Therefore, it is necessary to conduct a treatability test suitable for the working process of the working construction.

(2) Safety factor In the earth drill method, generally, one cycle from drilling to excavation with a drilling bucket is about 10 minutes, and the soil is pulled up to the ground while staying in the drilling bucket. It cannot be said that the soil and the stabilizing liquid are in sufficient contact. Compared with the preparation method in the dissolution test (200 shakes per minute for 6 hours), the contact time is shorter and the contact area is smaller. It is considered small.

  Further, as described above, the mud film between the stabilizing liquid and the ground is considered to have a certain filtration function. Therefore, these two points can be considered as “safety” in design. The designer needs to set a safety factor, such as increasing the adsorbent addition rate, taking these into consideration.

2. Construction Management Method (1) Quality Control of Stabilizing Liquid During construction of the method of the present invention, it is necessary to confirm the concentration of the target heavy metal or the like during the quality control test of the stabilizing liquid. In particular, after excavating the ground containing heavy metals, etc., it is most important to temporarily stop excavation before the uncontaminated ground and confirm that the liquid phase concentration of the stable liquid is below the groundwater environmental standard value. As a result of the analysis, if the concentration of heavy metals or the like is less than the groundwater environmental standard value, the excavation is resumed.

  When confirming the concentration of heavy metals, etc. during construction, it is not realistic to wait for the analysis result by the official method to proceed with construction, and as mentioned above, the concentration may be evaluated low due to the time lag from sampling to filtration Therefore, it is desirable to adopt a rapid determination method.

(2) Disposal of stable liquid After placing concrete, the stable liquid replaced with concrete is temporarily stored in the recovery tank. In general, this stabilizer is subjected to a correction process after a quality control test and is used again for excavation. Dispose of it as an industrial waste that cannot be used again or at the end of construction. However, in the case of the construction method of the present invention, addition of an adsorbent should not be performed as a modification process for the adsorption function because there is a risk of gelation, and at present, it should be disposed of at the number of diversions set in the formulation design. .

(3) Cost effect Table 10 shows an estimate of the cost effect of the construction method of the present invention. As a model case, pile diameter 2000mm, pile length 30m, soil layer thickness including heavy metals 10m (GL ± 0-10m), hard-permeable layer thickness 7m (GL-10-17m), heavy metals As, F, Pb coexist The elution amount was set to 2, 5, and 10 times the soil elution amount reference value. In addition, based on the experimental results of Example 3, 5% MgO was added to the polymer-based stabilizing solution, and the As, Pb, and F concentrations 10 times the soil elution standard value in one excavation using this stabilizing solution. Was reduced to the soil elution standard value. Regarding the construction cost, the construction cost per pile with no soil contamination countermeasures was taken as 100, and the construction costs for other cases were calculated.

  If the amount of soil elution is about twice the standard value, it will be possible to divert the stabilizer four times in the same way as normal construction, and the increase in construction costs is about 3%. The amount of soil elution is about 5 times the standard value, the diversion of the stabilizer is reduced to 2 times, and the construction cost increase is 12%. Even if the amount of soil elution is about 10 times the standard value and the diversion of the stabilizer is not possible, the construction cost increases by about 30%, which is a significant cost reduction compared to the current ground contamination countermeasures.

  When excavating the contaminated ground with the earth drill method and constructing the on-site pile, heavy metals, etc. (arsenic, fluorine, lead) are mixed in the stable liquid. In the present invention, the adsorption function of heavy metals and the like by the stabilizing liquid at this time was clarified. Next, an experimental study was conducted on a blending design method for adding an adsorbent to the stable liquid and reducing the concentrations of arsenic, fluorine, and lead in the liquid phase below the groundwater environmental standard value. The results obtained are as follows.

  (1) It was found that the stabilizing liquid generally used in the earth drill method has a high adsorption function for lead. The adsorption function is considered to be greatly influenced by the amount of bentonite contained in the stabilizing solution and the pH (8.5 to 12.0) of the stabilizing solution.

(2) By adding an adsorbent to the bentonite-based stabilizer, it is possible to have an adsorption function for arsenic and fluorine. The adsorbent is applicable if it is MgO (addition amount 2% or less), Al (OH) ₃ (addition amount 5% or less).
(3) By adding an adsorbent to the polymer-based stabilizer, it is possible to provide an adsorption function for arsenic and fluorine. The adsorbent is applicable if it is MgO (addition amount 5% or less), Al (OH) ₃ (addition amount 5% or less).

  (4) If the ground (arsenic, fluorine, lead) contains heavy metals, etc. that are naturally derived (within 10 times the soil elution standard value), an appropriate amount of adsorbent is added to the stable liquid, It was suggested that the concentration of heavy metals can be kept below the groundwater environmental standard value while preventing the diffusion of heavy metals.

  (5) The construction cost of the construction method of the present invention varies depending on the amount of adsorbent determined based on the type of the target heavy metal and the like, the amount of elution, and the number of times the stabilizer is used. However, the proportion of the stable liquid in the entire excavation cost of the pile is small, and even if the elution amount of heavy metals etc. is about 10 times the standard value, the increase in the construction cost is about 30%. Compared with the double pipe method, the cost reduction effect is large.

The above-mentioned in-situ pile method of the present invention has the same construction procedure as the conventional in-situ pile method (for example, earth drill method, reverse method, BH method) for excavating by filling the pile hole with a stabilizing liquid, and ground improvement Is unnecessary.
Moreover, the process added to the conventional construction procedure is only the stabilizing liquid preparation process S1, the intermediate confirmation process S21, and the quality control process S22, which can be performed in a short time.
Therefore, the on-site pile method of the present invention can significantly reduce or prevent the spread of soil contamination without ground improvement.

  In addition, this invention is not limited to embodiment mentioned above, Of course, it can change variously, unless it deviates from the summary of this invention.

n Number of diversions of the stabilizer, 1 Contaminated soil (alluvium),
2 Hardly permeable layer, 3 Lower support layer (lower aquifer)

Claims (10)

In the field pile driving method to fill the hole with the stable liquid and excavate,
A stabilizing solution preparation step of preparing an added stabilizing solution by adding an adsorbent that adsorbs heavy metal contaminants to the stabilizing solution;
A pile hole excavation process for excavating the pile hole by filling the pile hole with the added stabilizing liquid. The stabilizing solution preparation step includes
A sampling step of collecting contaminated soil from the ground containing the heavy metal pollutant;
Mixing the contaminated soil and a plurality of the addition stabilizers having different adsorbent addition rates, and detecting an elution amount of the heavy metal contaminants in the solution,
A relationship detection step for obtaining a relationship between the adsorbent addition rate and the elution amount;
An in-situ pile driving method according to claim 1, further comprising: an addition rate determining step for determining the adsorbent addition rate of the added stabilizing liquid from the relationship. The pile hole excavation process includes:
After excavating the ground containing the heavy metal pollutant, the excavation is temporarily interrupted before the non-contaminated ground, and an intermediate confirmation step of confirming that the liquid phase concentration of the added stabilizing liquid is less than a reference value. The on-site pile method described in 1. The heavy metal contaminant is arsenic, fluorine, or lead;
The stabilizer is a polymer stabilizer or a bentonite stabilizer,
The in-situ pile driving method according to claim 1, wherein the adsorbent is magnesium oxide or aluminum hydroxide. The heavy metal contaminant is arsenic, fluorine, or lead;
The stabilizer is a polymer stabilizer,
The on-site pile method according to claim 1, wherein the adsorbent is 0.5 to 5% magnesium oxide or 0.5 to 5% aluminum hydroxide. The heavy metal contaminant is arsenic, fluorine, or lead;
The stabilizer is a bentonite stabilizer.
The in-situ pile method according to claim 1, wherein the adsorbent is 0.5 to 2% magnesium oxide or 0.5 to 5% aluminum hydroxide.   The pile driving method according to claim 1, wherein the pile hole excavation step includes a quality control step of inspecting an elution amount of the heavy metal contaminant contained in the added stabilizing liquid in use. The on-site pile method is an earth drill method,
Drilling up to the expected depth of installation of the surface casing and standing up the surface casing,
Injecting the added stabilizing solution,
The in-situ pile driving method according to claim 1, wherein excavation with a drilling bucket is performed while soil removal to the ground is repeated while keeping the liquid level of the added stabilizing liquid constant.   The in-situ pile driving method according to claim 1, wherein, in the pile hole excavation step, excavation is performed while maintaining an in-hole water level of the added stabilizing liquid at or above a groundwater level. A concrete placing process for placing concrete in the pile hole;
The in-situ pile driving method according to claim 1, further comprising: a stabilizing liquid recovery step of recovering the added stabilizing liquid replaced with the concrete in a recovery tank.