Cast-in-place piling method and lost circulation preventing material containing adsorbent

Abstract

To provide a cast-in-place pile construction method and a lost circulation preventing material containing an adsorbent, capable of reducing or preventing diffusion of soil contamination without soil improvement, reducing an addition amount of the adsorbent, and preventing contamination of a support layer due to lost circulation.SOLUTION: An upper excavation process S1 and a lower excavation process S2 are provided. In the upper excavation process S1, the pile hole 4 is filled with a stabilizing liquid ST containing no adsorbent A for adsorbing the contaminants X, and the pile hole 4 is excavated from the surface layer to the impermeable layer 2. In the lower excavation process S2, a lost circulation preventing material C containing an adsorbent in which fine particles of the adsorbent A are dispersed and carried is added only to the stable liquid at the bottom of the pile hole 4, and the pile hole 4 is excavated from the impermeable layer 2 to the bearing layer. The lost circulation preventing material C containing an adsorbent contains an adsorbent A for adsorbing and insolubilizing arsenic, fluorine or lead and a lost circulation preventing material B containing water-insoluble fibers, and the adsorbent A is dispersed and blended in the water-insoluble fibers.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a cast-in-place pile construction method for preventing the spread of soil contamination and to an absorbent-containing lost circulation prevention material used in this construction method. [Background technology]

[0002] Most of Japan's major cities are built on relatively soft alluvial deposits, making piles necessary for the construction of mid- to high-rise apartment buildings in urban areas. Piles penetrate the soft alluvial deposits to reach the supporting layer and support the buildings above, but if there is ground contamination in this alluvial deposit, the spread of ground contamination due to pile construction can become a problem. In other words, some kind of measure is needed to prevent the construction of piles from causing contaminated soil and groundwater in the alluvial deposits to infiltrate the supporting layer, the lower aquifer, and spread the contamination.

[0003] It is known that the alluvial deposits in urban areas of Japan, including the Osaka Plain, contain soil containing naturally occurring heavy metals. Until now, soil containing naturally occurring heavy metals was not subject to the Soil Contamination Countermeasures Act, but a 2009 amendment to the law stipulated that it be treated as subject to the law in the same way as artificially contaminated soil. Therefore, in the future, establishing a pile construction method that can install piles without dispersing heavy metals in ground where soil containing naturally occurring heavy metals exists is an urgent issue for pile construction in apartment buildings.

[0004] Therefore, Patent Documents 1 to 3 have proposed methods for constructing piles while preventing the spread of soil contamination.

[0005] The "pile construction method" of Patent Document 1 includes an upper permeable layer ground replacement process in which the upper permeable layer ground within the pile construction area is replaced using a replacement material to prevent the infiltration of pollutants into the center of the pile construction area, and a pile driving process in which piles are driven through the pile construction area to a predetermined depth.

[0006] In the "pile construction method" of Patent Document 2, a vertical hole is excavated in an excavation step from the contaminated layer at the surface of the ground to the position of an impermeable layer deeper than the boundary between the contaminated layer and the impermeable layer. Next, in an injection step, a filler material is injected into the vertical hole from the position of the impermeable layer to the position of the contaminated layer. Next, in an insertion step, a casing tube is inserted to the position of the impermeable layer before the filler material hardens, and the filler material is filled between the outer surface of the casing tube and the inner wall of the vertical hole. Next, in a pile construction step, after the filler material hardens, a pile is constructed through the casing tube, penetrating the permeable layer below the impermeable layer, down to the bearing layer.

[0007] In the "Vertical Hole Drilling Method and Vertical Hole Drilling Apparatus" of Patent Document 3, a vertical hole is formed by excavating ground having an upper permeable layer located above the impermeable layer and a lower permeable layer located below the impermeable layer. This vertical hole drilling method comprises a first excavation step, a replacement step, a layer formation step, and a second excavation step. In the first excavation step, a vertical hole is excavated up to the middle of the impermeable layer. In the replacement step, the soil excavated in the first excavation step is replaced with bentonite mud. In the layer formation step, a layer formation material is sprayed in the bentonite mud onto an area including the boundary between the upper permeable layer and the impermeable layer to form a sealing layer. In the second excavation step, a vertical hole is excavated from the middle of the impermeable layer to the lower permeable layer.

[0008] The means for constructing piles while preventing the spread of the above-mentioned soil contamination require ground improvement methods that differ from conventional cast-in-place pile construction methods, such as an upper permeable layer ground replacement process (Patent Document 1), filler injection and casing tube insertion (Patent Document 2), and a sealing layer formation process (Patent Document 3). Therefore, conventional methods require a long time for ground improvement, and the process is complicated and requires a great deal of cost.

[0009] In order to solve the above-mentioned problems, the inventors of the present invention have previously proposed Patent Document 4. The "cast-in-place pile construction method" of Patent Document 4 is a cast-in-place pile construction method in which pile holes are filled with stabilizing liquid and excavated in ground containing contaminated soil and groundwater containing naturally occurring heavy metal pollutants. The method includes a stabilizing liquid preparation step and a pile hole excavation step. In the stabilizing liquid preparation step, an adsorbent that adsorbs heavy metal pollutants is added to the stabilizing liquid to prepare an added stabilizing liquid. In the pile hole excavation step, the pile hole is filled with the added stabilizing liquid and then excavated. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 3367042 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-241471 [Patent Document 3] Patent No. 6006138 [Patent Document 4] Patent No. 6884527 Summary of the Invention [Problem to be solved by the invention]

[0011] The cast-in-place pile construction method of Patent Document 4 can significantly reduce or prevent the spread of soil contamination without ground improvement. However, this cast-in-place pile construction method has the following problems.

[0012] (1) The adsorbent is added to the stabilizing solution at a plant on land, and once the required concentration is reached, it is pumped into the excavation area. Therefore, the adsorbent must be distributed throughout the stabilizing solution. As a result, a large amount of adsorbent must be added. (2) It is not possible to prevent the stabilizing solution from penetrating into the underlying aquifer. Therefore, if there is water loss, the supporting layer may be contaminated by heavy metal contaminants in the stabilizing solution.

[0013] The present invention has been devised to solve the above-mentioned problems. That is, the object of the present invention is to provide a cast-in-place pile construction method and a lost circulation prevention material containing an adsorbent that can reduce or prevent the diffusion of soil contamination without ground improvement, reduce the amount of adsorbent added, and prevent contamination of the support layer due to lost circulation (lost water). [Means for solving the problem]

[0014] According to the present invention, in a cast-in-place pile construction method in which a pile hole is filled with a stabilizing solution and excavated from the surface to a ground having a contaminated layer containing naturally occurring heavy metal pollutants, an impermeable layer, and a bearing layer in which an aquifer exists, an upper excavation step of filling the pile hole with the stabilizing liquid that does not contain an adsorbent that adsorbs and insolubilizes the heavy metal contaminants, and excavating the pile hole from the surface layer to the impermeable layer; and a bottom excavation step of adding an adsorbent-containing lost circulation prevention material, in which the adsorbent is dispersed and supported, only to the stabilizing liquid at the bottom of the pile hole, and excavating the pile hole from the impermeable layer to the supporting layer.

[0015] According to the present invention, a lost circulation prevention material containing an adsorbent that adsorbs and insolubilizes arsenic, fluorine, or lead and a water-insoluble fiber is provided. The adsorbent is dispersed in the water-insoluble fibers to provide an adsorbent-containing lost circulation prevention material. [Effects of the Invention]

[0016] According to the present invention, in the upper excavation step, a stabilizing solution that does not contain an adsorbent that adsorbs heavy metal pollutants (hereinafter referred to as "pollutants") is filled into the pile hole, and the pile hole is excavated from the surface layer to the impermeable layer (e.g., clay layer). In this step, since the stabilizing solution does not contain an adsorbent, the pollutants contained in the contaminated layer penetrate into the stabilizing solution, but the impermeable layer prevents the pollutants from diffusing into the supporting layer.

[0017] In the lower excavation step, a lost circulation prevention material containing an adsorbent dispersed and supported thereon is added only to the stabilizing solution at the bottom of the pile hole. This lost circulation prevention material contains an adsorbent that adsorbs and insolubilizes heavy metal pollutants and a lost circulation prevention material containing water-insoluble fibers, and the adsorbent is dispersed in the water-insoluble fibers. Therefore, the adsorbent in the stabilizing solution in the support layer adsorbs the contaminants diffusing from the top of the pile hole, preventing the intrusion of the contaminants into the support layer where the underlying aquifer is located.

[0018] In addition, since the lost circulation prevention material containing adsorbent is added to the stabilizing liquid at the bottom, the water-insoluble fibers contained in the lost circulation prevention material with adsorbent can form a water-stopping mud film on the inner surface of the pile hole in the support layer, thereby reducing the intrusion of the stabilizing liquid into the lower aquifer. In addition, since the adsorbent is dispersed and supported (blended) on the water-insoluble fibers, the adsorbent that has adsorbed the pollutants remains inside the water-insoluble fibers, preventing the pollutants from leaking into the support layer.

[0019] In addition, a stabilizing solution containing no adsorbent is used in the upper excavation process, and an adsorbent-containing lost circulation prevention material is added only to the stabilizing solution at the bottom in the lower excavation process, so even if the adsorbent addition rate in the stabilizing solution in the support layer is set high, the total amount of adsorbent added can be reduced.

[0020] The above-described cast-in-place pile construction method of the present invention has the same construction procedure as the conventional cast-in-place pile construction method in which a pile hole is filled with stabilizing fluid and then excavated, and does not require ground improvement work. In addition, the only step added to the conventional construction procedure is the step of adding the adsorbent-containing lost circulation prevention material, which has the adsorbent dispersed and supported, to only the stabilizing liquid at the bottom during the lower excavation process (lost circulation prevention material addition process), which can be carried out in a short time. Therefore, the cast-in-place pile construction method of the present invention can significantly reduce or prevent the spread of soil contamination without ground improvement work. [Brief explanation of the drawings]

[0021] [Figure 1]This is a conceptual diagram of the construction of an apartment building on ground where contaminated materials exist. [Figure 2] FIG. 1 is a process diagram of a conventional earth drill method. [Figure 3] FIG. 1 is an explanatory diagram of a cast-in-place pile construction method according to the present invention. [Figure 4] FIG. 10 is an explanatory diagram of a lost circulation prevention material addition process. [Figure 5] FIG. 1 is a graph showing the relationship between the arsenic concentration in an arsenic-containing liquid and that in a filtrate. [Figure 6] FIG. 10 is a diagram showing the relationship between elapsed time and the amount of water discharged. [Figure 7] These are the results of a column test using φ5mm glass beads. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, common parts in the drawings are given the same reference numerals, and duplicated explanations will be omitted.

[0023] Figure 1 is a conceptual diagram of the construction of an apartment building on ground where contaminated materials exist. As shown in this diagram, when piles are planned in a contaminated layer 1 containing naturally occurring heavy metal pollutants (hereafter referred to as pollutant X) and in ground (bearing layer 3) where groundwater exists, the piles will penetrate the contaminated layer 1 and the impermeable layer 2 below it to reach the bearing layer 3. Construction of such piles may cause heavy metals and other contaminants to diffuse into the bearing layer 3 below the impermeable layer.

[0024] Figure 2 is a process diagram of a conventional earth drill method. The earth drill method is a cast-in-place pile construction method in which a pile hole 4 is filled with stabilizing liquid ST and excavated.The drilling bucket 8 is rotated to excavate the ground and the soil stored inside the bucket is discharged to the surface.

[0025] In this diagram, the earth drilling method includes the following steps, in order: pile centering (1), preliminary drilling (2), casing installation (3), shaft excavation (4), rebar cage installation (5), secondary hole bottom preparation (6), concrete pouring (7), and casing removal (8).

[0026] In the pile centering step (1), the tip of the earth drill is aligned with the core of the pile. In the preliminary excavation process (2), a bucket is attached to the tip of the Kelly bar and excavated to a depth and diameter for pressing in the casing 9. In the casing erection step (3), the casing 9 is press-fitted into the area excavated in the preliminary excavation step (2). In the shaft excavation process (4), the excavation is performed to a predetermined depth in the supporting layer while injecting a stabilizer ST to prevent the excavated hole from collapsing. If necessary, an expanded bottom is excavated in the supporting layer. Furthermore, shavings from the hole wall (excavated hole) are removed (primary slime treatment). In the reinforcing bar cage erection step (5), the reinforcing bar cages 10 are inserted into the hole wall while being connected together. In the secondary hole bottom treatment step (6), a tremie pipe (a pipe through which concrete 11 is poured) is inserted to the hole bottom, and secondary slime treatment is carried out using a pump. In the concrete pouring process (7), a hopper is attached to the tremie pipe, and fresh concrete is poured into the hole from the bottom. In the casing removal process (8), concrete 11 is poured up to the top of the pile, and then the casing 9 is pulled out. Finally, the hole is backfilled and the pile is completed.

[0027] As mentioned above, in the earth drill method, the hole walls are protected by a casing 9 at the surface and by a stabilizing solution ST at deeper depths. After excavation is complete, a reinforcing bar cage 10 made to a specified shape is erected, and concrete 11 is poured using a tremie pipe to construct the pile. Bentonite-based or polymer-based stabilizing solution ST is used depending on the properties of the target ground.

[0028] FIG. 3 is an explanatory diagram of the cast-in-place pile construction method according to the present invention. The cast-in-place pile method of the present invention is a method of drilling a pile hole 4 filled with stabilizing solution ST into ground that has, from the surface, a contaminated layer 1 containing a naturally occurring heavy metal pollutant (pollutant X), an impermeable layer 2, and a bearing layer 3 in which a lower aquifer is present. In this example, the cast-in-place pile construction method of the present invention is an earth drill construction method. The cast-in-place pile construction method of the present invention is not limited to the earth drill construction method, but may also be a reverse construction method or a BH construction method.

[0029] In FIG. 3, the cast-in-place pile construction method of the present invention includes an upper excavation step S1 and a lower excavation step S2. The upper drilling step S1 and the lower drilling step S2 correspond to the shaft drilling step (4) in the earth drill method described above.

[0030] FIG. 3(A) is an explanatory diagram of the upper excavation step S1. In the upper excavation step S1, the pile hole 4 is filled with a stabilizing solution ST that does not contain an adsorbent A that adsorbs the pollutant X, and the pile hole 4 is excavated from the surface layer to the impermeable layer 2. In the upper excavation step S1, the bottom of the pile hole is excavated while the liquid level of the stabilizing solution ST is kept above the groundwater level, and the work of discharging the soil to the ground is repeated.

[0031] In the present invention, the heavy metal pollutant (pollutant X) of interest is arsenic (As), fluorine (F), or lead (Pb), but may include other pollutants. The stabilizer ST is preferably a polymer-based stabilizer or a bentonite-based stabilizer, but may be any other stabilizer.

[0032] FIG. 3(B) is an explanatory diagram of the lower excavation step S2. In the lower excavation process S2, the adsorbent-containing lost circulation prevention material C, which has fine particles of adsorbent A dispersed and supported thereon, is added only to the stabilizing liquid at the bottom of the pile hole 4, and the pile hole 4 is excavated from the impermeable layer 2 to the supporting layer 3. "Only the stabilizing solution at the bottom" means that the lost circulation prevention material C containing adsorbent is added only to the stabilizing solution at the bottom. Therefore, the added lost circulation prevention material C containing adsorbent may be dispersed and diffused to areas other than the bottom of the pile hole 4. In the lower excavation step S2, the bottom of the pile hole is excavated while the liquid level of the stabilizing solution ST is kept above the groundwater level, and the work of discharging the soil to the ground is repeated.

[0033] The lost circulation prevention material C containing an adsorbent of the present invention comprises an adsorbent A that adsorbs and insolubilizes arsenic, fluorine, or lead, and a lost circulation prevention material B that contains water-insoluble fibers, in which the adsorbent A is dispersed in the water-insoluble fibers.

[0034] The adsorbent A preferably contains iron oxide, calcium sulfate (CaSO4), magnesium oxide (MgO), or aluminum hydroxide (Al(OH)3), which have a proven track record in insolubilizing heavy metals.

[0035] It has been confirmed that the amount of arsenic, fluorine, and lead leaching into a borehole can be reduced to below the standard value by adding magnesium oxide or aluminum hydroxide to a polymer-based or bentonite-based stabilizer. The "standard value" is preferably the "groundwater environmental standard value."

[0036] In the examples described below, the adsorbent A is an insolubilizing material mainly composed of iron oxide and calcium sulfate, but may contain other adsorbents. Calcium sulfate is the main component of gypsum. The lost circulation prevention material C containing an adsorbent is preferably a granular solid obtained by mixing the adsorbent A and the lost circulation prevention material B in water containing no adhesive, stirring the mixture, and then drying and solidifying the mixture. The fibers may be fibrous man-made inorganic fibers or natural wood pulp fibers.

[0037] The lower excavation step S2 includes a lost circulation prevention material adding step S21. The lost circulation prevention material adding step S21 has a first step S21a and a second step S21b. In the first step S21a, a vinyl bag 6 containing an absorbent-containing lost circulation prevention material C therein is lowered into the bottom 4a of the pile hole 4 before excavation. In the second step S21b, after the first step S21a, the vinyl bag 6 is dissolved and the lost circulation prevention material C containing the adsorbent inside is added to the stabilizing liquid at the bottom of the pile hole. When adding to the stabilizing solution, the plastic bag 6 is pressed against the bottom of the borehole with a bucket to break the bag and release the contents into the stabilizing solution. "Vinyl" is a type of plastic whose main component is polyvinyl chloride resin (PVC), and is made up of polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), etc.

[0038] The plastic bag 6 can be a commonly used polyethylene bag. It is necessary to ensure that when the plastic bag 6 is torn, the entire bag or fragments of the bag are released into the stabilizing solution and do not remain as foreign matter. To achieve this, the bag must be thick and strong, and a tearing aid line must be provided to assist in tearing the bag. The plastic bag 6 can be made of a water-soluble vinyl material such as polyvinyl alcohol (PVOH), which is highly hydrophilic and soluble in both hot and cold water, and can also be perforated so that the bag tears preferentially at those parts.

[0039] FIG. 4 is an explanatory diagram of the lost circulation prevention material adding step S21. In this example, the cast-in-place pile construction method is an earth drill construction method, and in the first step S21a, a plastic bag 6 is fixed to the underside of the drilling bucket 8 and lowered to the bottom 4a of the pile hole 4. The plastic bag 6 is preferably fixed using, for example, a wire, and tied to, for example, the claws of the drilling bucket 8 so as not to impair its function. In the second step S21b, the drilling bucket 8 is repeatedly rotated idly (turned) and moved up and down in the stabilized solution at the bottom 4a to add the lost circulation prevention material C containing the adsorbent into the stabilized solution.

[0040] The lost circulation prevention material adding step S21 is carried out when the drilling bucket 8 is positioned away from the bottom surface (excavation surface) of the pile hole 4. That is, the bottom 4a of the pile hole 4 means a range of a predetermined distance (depth) from the bottom surface (digging surface) of the pile hole 4. This distance (depth) preferably includes a part or the whole of the drilling bucket 8. When performing the lost circulation prevention material adding step S21, it is preferable that the bottom portion 4a is at least initially surrounded by the impermeable layer 2. Thereafter, it may be surrounded by the support layer 3.

[0041] The amount of adsorbent A contained in the lost circulation prevention material C with adsorbent contained in the vinyl bag 6 is set to an amount sufficient to adsorb and insolubilize the contaminant X diffused from the stabilized liquid ST above when the adsorbent A is added to and mixed with the stabilized liquid filled in the bottom 4a. After the addition of the absorbent-containing lost circulation prevention material is completed, the drilling bucket is temporarily lifted up to retrieve the vinyl bag 6, and then drilling of the bottom of the hole is resumed.

[0042] The lower excavation step S2 further includes a lost circulation measuring step S22. As described above, in the lower excavation step S2, the bottom 4a of the pile hole 4 is excavated while the liquid level of the stabilizer ST is kept above the groundwater level, and the soil discharge work to the ground is repeated. In the lost circulation amount measurement step S22, the supply of the stabilizer ST is stopped, and the lost circulation amount of the stabilizer ST is measured from the change in the liquid level in the hole. Based on the measured amount of lost circulation of the stabilized liquid ST, it is preferable to set the amount of lost circulation prevention material B contained in the adsorbent-containing lost circulation prevention material C to an amount that can suppress lost circulation from the impermeable layer 2 or supporting layer 3 surrounding the bottom 4a.

[0043] In addition, during repeated soil discharge work onto the ground, the stabilizer ST at the bottom 4a may be sampled to measure the adsorbent A in the stabilizer, and the amount of lost circulation prevention material C containing adsorbent to be placed in the vinyl bag 6 may be determined. [Example]

[0044] (Manufacturing method and arsenic adsorption test of absorbent-containing lost circulation prevention material C) (1) Sample Fixall (registered trademark), which is primarily composed of iron oxide and gypsum, was used as adsorbent A. Fixall is commercially available as a heavy metal insolubilizer with a neutral pH range that easily adsorbs and insolubilizes heavy metals contained in soil and groundwater, preventing the spread of contamination. Fixall is composed mainly of iron oxide (Fe2O3·nH2O) and gypsum (CaSO4·nH2O), and the specific surface area of ​​the iron oxide particles is 180m 2 / g or more and is known as an adsorbent for arsenic, selenium, lead, and cadmium.

[0045] Uragomer (registered trademark), which has a proven track record in preventing lost circulation, was used as lost circulation prevention material B. Uragomer is a lost circulation prevention additive whose main component is pulp fiber, made primarily from recycled pulp, and is known to be able to prevent lost circulation even in relatively large gaps due to the filtering effect of the fiber.

[0046] The adhesives used were vinyl acetate and starch glue. Vinyl acetate is a water-soluble adhesive known as wood glue. Starch glue is made from flour and water and is known for its high adhesive strength when bonding paper and cardboard.

[0047] (2) Manufacturing method An adsorbent-containing lost circulation prevention material C carrying adsorbent A was manufactured in the following order.

[0048] First, 100 g of adhesive solution was prepared by adding water at 20° C. to either no adhesive (0 g), vinyl acetate (3 g), or starch paste (15 g). Next, the three types of adhesive solutions were mixed in order with adsorbent A (20 g) and lost circulation prevention material B (30 g) and thoroughly stirred to prepare three types of adsorbent-containing solutions.

[0049] (Appropriate range of weight ratio of absorbent to lost circulation prevention material) The lost circulation prevention material is made of fine fibers, and when it is loosened, its bulk density becomes very small. On the other hand, adsorbent A (Fixall in this example) is a fine powder. The condition for evenly mixing and supporting the adsorbent in the lost circulation prevention material (optimal weight ratio range) is that the amount of adsorbent added to the lost circulation prevention material should be 40% to 80% by weight. If the amount added is too much, it will not be fully supported, and if it is too little, it will not be distributed evenly. The appropriate weight ratio range differs depending on the type of lost circulation prevention material.

[0050] The adsorbent-containing liquid was then dried in an oven at 110°C to obtain three types of granular solids. All three types of granular solids were in the form of particles with an average particle size of about 3 mm.

[0051] (Appropriate size range of adsorbent and lost circulation prevention material (granular solid material) containing adsorbent) The first key point is that the absorbent is adequately supported on the lost circulation prevention material (so that most of it does not separate before or during use), and the second is to prevent as much reduction in the lost circulation prevention effect as possible. In order to achieve the lost circulation prevention effect, the fibers must cover the holes where the lost circulation is occurring, but these holes vary in size depending on the ground conditions. In gravelly ground, there are holes several millimeters or larger, while in sandy ground, there are many holes less than 1 mm. Therefore, it is sometimes better for the granular solid material to have a certain degree of variation in particle size. In standard usage, there are few problems with an average particle size of about 3 mm. However, the particle size can be changed depending on the conditions of the lost circulation layer.

[0052] (3) Arsenic adsorption test Pressure filtration tests were carried out using the three types of granular solids mentioned above. In the pressure filtration test, four types of arsenic-containing solutions with arsenic concentrations of 0, 0.05, 0.1, and 0.5 ppm were prepared, and after shaking the arsenic-containing solutions, a filtration test (filtration pressure 0.5 MPa, filter paper retention particle size 1 μm) was immediately conducted using a pressure filtration tester, and the As concentration of the obtained filtrate was measured.

[0053] (4) Test results The four arsenic-containing solutions had high fluidity and easily penetrated three types of granular solids as adhesives: no adhesive, vinyl acetate, or starch paste.

[0054] 5 is a graph showing the relationship between the arsenic concentration in the arsenic-containing solution and the filtrate. In this graph, the horizontal axis represents the As concentration in the arsenic-containing solution, and the vertical axis represents the As concentration in the filtrate. From this figure, it can be seen that the As concentration in the filtrate from lost circulation prevention material C containing adsorbent, which was mixed with only water without adhesive, was the lowest, and the arsenic immobilization effect was the highest.

[0055] It is thought that vinyl acetate coated adsorbent A, reducing the amount of arsenic adsorbed. Furthermore, as the amount of starch paste added increases, the viscosity increases, and it becomes difficult for the adsorbent A and the lost circulation prevention material B to mix therewith.

[0056] From the above test results, it can be seen that the lost circulation prevention material C containing adsorbent of the present invention is preferably a granular solid material obtained by mixing adsorbent A and lost circulation prevention material B in water containing no adhesive, stirring the mixture, and then drying and solidifying it. [Example]

[0057] Uragomer and Adsorbent A were bonded with water and air-dried before use. Simulated As-contaminated soil was also mixed with a bentonite-based stabilizing solution that simulated the actual site. The contamination concentration was level 2. These were mixed and filtered to measure the As concentration. In column tests, Case 1 was filtered through 2 mm beads and analyzed for As, and Case 2 was filtered and analyzed for As.

[0058] The test results are shown in Table 1. In the lost circulation prevention material without adsorbent (Test Nos. 1 and 6), the arsenic concentration exceeded the standard by approximately eight times. A stabilizing solution of 40% absorbent and 60% mud escape prevention material is added to 1 m 3 1 to 1.5% or 10 to 15 kg / m 3 In the tests used (test numbers 2 to 5, 7 to 10), the As concentration in the filtrate (permeate) was below the environmental standard.

[0059] [Table 1] [Example]

[0060] (Performance test of stabilized liquid ST with absorbent-containing lost circulation prevention material C added) (1) Sample As the stabilizer ST, a commonly used polymer stabilizer was used.

[0061] As lost circulation prevention material B, commercially available (a) TN fiber, (b) Uragomer, (c) a mixture of Uragomer and Atom Block (weight ratio 1:1), (d) Atom Block, and (e) Kuniforce were used.

[0062] TN fiber is an amorphous artificial inorganic fiber made from several types of ores and processed into thin fibers.It is effective as a plugging agent for permeable layers such as gravel and sand layers, and is stable at high temperatures. As mentioned above, Uragomer (registered trademark) is a lost circulation prevention additive whose main component is pulp fiber made primarily from recycled pulp, and the filtering effect of the fiber allows it to prevent lost circulation even in relatively large gaps. Atom Block is a lost circulation prevention material whose main component is natural wood pulp, and is made by compressing wood pulp fibers into blocks. Kuniforce is a water-stopping material that utilizes the properties of bentonite. Because bentonite is an inorganic clay, it exhibits excellent water-stopping properties without deterioration for a semi-permanent period.

[0063] The above-mentioned Fixall was used as a heavy metal absorbent (adsorbent A), and an adsorbent-containing lost circulation prevention material C was prepared by supporting adsorbent A on lost circulation prevention material B. Hereinafter, the adsorbent-containing lost circulation prevention material C corresponding to "lost circulation prevention material B (a) to (e)" will be referred to as "adsorbent-containing lost circulation prevention material (A) to (E)."

[0064] Glass beads (2 mm in diameter) were used to simulate gravel ground as the ground simulating material.

[0065] (2) Test method The water permeation device was made by gluing a bottom plate to a transparent PVC pipe (inner diameter 50 mm, length 500 mm), providing a water passage hole with a diameter of 10 mm in the center of the bottom plate, and attaching a mesh to the water passage hole to prevent glass beads from leaking out.

[0066] As a gravel layer, glass beads (350 g) were filled up to 100 mm from the bottom plate of the permeable device.

[0067] The lost circulation prevention materials containing adsorbents (A) to (E) were added to 400 mL (414 g) of stabilizing solution ST and stirred and mixed in a sealed container for 1 minute. The amount of the lost circulation prevention materials containing adsorbents (A) to (E) added was 1% by weight of the stabilizing solution ST. Next, the stabilizing solution (400 mL) was poured gently from the top of the permeation device so as not to disturb the surface of the glass beads, and the amount of the stabilizing solution ST drained from the bottom plate was measured.

[0068] (3) Test results Figure 6 is a diagram showing the relationship between elapsed time and the amount of water discharged. In this figure, the horizontal axis represents elapsed time and the vertical axis represents the amount of water discharged. Note that (F) is the case where the absorbent-containing lost circulation prevention material C is not included. The amount of displacement simulates the amount of lost circulation, and the smaller the amount of displacement, the greater the effect of preventing lost circulation.

[0069] From FIG. 6, it can be said that in (E) and (F), the amount of water supplied is substantially all drained, and there is almost no effect in preventing lost circulation (water cutoff effect). In addition, it can be seen that the other (A) to (D) have a drainage amount less than the supply amount, and have a lost circulation prevention effect (water cutoff effect).

[0070] The results in Figure 6 show that the lost circulation prevention effect of adsorbent-containing lost circulation prevention material C is greatest in the following order: (A) TN fiber, (B) Uragomer, (C) a mixture of Uragomer and Atom Block, and (D) Atom Block. In addition, (E) Kuniforce lost circulation prevention material C with adsorbent is almost the same as (F) when it does not contain lost circulation prevention material with adsorbent, and it can be said that almost no lost circulation prevention effect can be expected.

[0071] As mentioned above, in this test (Example 3), TN fiber had the greatest effect in preventing lost circulation. The reason for this is presumably that the TN fiber is short, inorganic, and does not easily tangle, allowing it to penetrate into the gaps between the glass beads, narrowing the gaps and allowing bentonite particles to settle there, forming a mud film. Furthermore, when the test sample was disassembled after the test, a mud film was found to have formed not only on the surface but also inside the glass bead layer. This is likely due in part to the fact that the TN fiber length, at 0.2 to 0.6 mm, is significantly shorter than the other fibers. [Example]

[0072] A column test was conducted using φ5mm glass beads. The results are shown in Figure 7. In this figure, the vertical axis shows how many milliliters of lost circulation of approximately 450 mL of stabilized liquid can be stopped by the effect of the lost circulation prevention material. The horizontal axis shows the amount of lost circulation prevention material (containing adsorbent) added relative to the stabilized liquid volume. TN fiber begins to be effective when the amount added is 1.2% or more, but its effectiveness in preventing lost circulation thereafter is also weak. When Uragomer and Atomblock were added at 1.2%, the leakage volume stopped at just under 100 mL. This volume of just under 100 mL contained almost no stabilizing liquid, and consisted mainly of water that had been filled in the gaps between the glass beads and at the bottom of the column during the column test. When the diameter of the glass beads increases and the gaps become larger, Uragomer or Atom Block, which have long fiber lengths, are effective.

[0073] However, when the conditions of the lost circulation layer (especially the grain size composition of the lost circulation layer) change in actual construction, TN fiber is not necessarily a panacea. This is because, when there are large voids, it is necessary to first plug the large holes with a material that forms a block with long fibers, such as Atom Block or Uragomer. In this invention, we have not developed a lost circulation prevention material itself, but have focused on adding the function of an adsorbent to a lost circulation prevention material that is optimal for the conditions at the target site.Since lost circulation prevention measures have a wide variety of ground conditions that cause lost circulation and the on-site factors are very significant, it can be said that we are not yet at the stage where design values ​​can be derived through indoor testing.

[0074] According to the above-described cast-in-place pile construction method of the present invention, in the upper excavation step S1, the pile hole 4 is filled with a stabilizing solution ST that does not contain an adsorbent A that adsorbs heavy metal pollutants X, and the pile hole 4 is excavated from the surface layer to an impermeable layer (e.g., a clay layer). In this step, since the stabilizing solution ST does not contain adsorbent A, the pollutants X contained in the contaminated layer penetrate into the stabilizing solution, but the impermeable layer prevents the pollutants X from diffusing into the supporting layer.

[0075] In the lower excavation step S2, the lost circulation prevention material C containing adsorbent A dispersed and supported thereon is added only to the stabilized liquid at the bottom of the pile hole. This lost circulation prevention material C containing adsorbent A contains adsorbent A that adsorbs and insolubilizes heavy metal pollutant X, and a lost circulation prevention material containing water-insoluble fibers, and the adsorbent A is dispersed in the water-insoluble fibers. Therefore, the contaminant X diffusing from the upper part of the pile hole 4 can be adsorbed by the adsorbent A in the stabilizing solution in the support layer, and the intrusion of the contaminant X into the support layer where the lower aquifer is located can be prevented.

[0076] In addition, since the lost circulation prevention material C containing adsorbent is added to the stabilizing liquid at the bottom 4a, the water-insoluble fibers contained in the lost circulation prevention material C containing adsorbent can form a water-stopping mud film on the inner surface of the pile hole 4 in the supporting layer, thereby reducing the intrusion of the stabilizing liquid ST into the lower aquifer. In addition, since the adsorbent A is dispersed and supported (blended) on the water-insoluble fibers, the adsorbent A that has adsorbed the pollutant X remains inside the water-insoluble fibers, preventing the pollutant X from leaking into the support layer.

[0077] In addition, since a stabilizer ST not containing adsorbent A is used in the upper excavation process S1, and an adsorbent-containing lost circulation prevention material C is added only to the stabilizer at the bottom 4a in the lower excavation process S2, the total amount of adsorbent A added can be reduced.

[0078] The above-mentioned cast-in-place pile construction method of the present invention has the same construction procedure as conventional cast-in-place pile construction methods (e.g., earth drill method, reverse construction method, BH construction method) in which stabilizing liquid ST is filled into the pile hole 4 and then excavated, and no ground improvement work is required. In addition, the only step added to the conventional construction procedure is the step of adding the adsorbent-containing lost circulation prevention material C, which has adsorbent A dispersed and supported thereon, to only the stabilized liquid at the bottom 4a during the lower excavation step S2 (lost circulation prevention material addition step), which can be carried out in a short time. Therefore, the cast-in-place pile construction method of the present invention can significantly reduce or prevent the spread of soil contamination without ground improvement work.

[0079] It should be noted that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. [Explanation of symbols]

[0080] A: Adsorbent, B: Lost circulation prevention material, C: Lost circulation prevention material with adsorbent, ST: Stabilizing liquid, X: Heavy metal pollutant (pollutant), 1: Contaminated layer, 2: Impermeable layer, 3: Supporting layer, 4: Pile hole, 4a: Bottom, 6: Plastic bag, 8: Drilling bucket, 9: Casing, 10: Reinforced concrete cage, 11: Concrete

Claims

1. In this cast-in-place pile construction method, the pile holes are filled with stabilizing fluid and excavated from the surface into ground having a contaminated layer containing naturally occurring heavy metal pollutants, an impermeable layer, and a bearing layer where an aquifer exists. an upper excavation step of filling the pile hole with the stabilizing liquid that does not contain an adsorbent that adsorbs and insolubilizes the heavy metal contaminants, and excavating the pile hole from the surface layer to the impermeable layer; and a bottom excavation step of adding an adsorbent-containing lost circulation prevention material, in which the adsorbent is dispersed and supported, only to the stabilizing liquid at the bottom of the pile hole, and excavating the pile hole from the impermeable layer to the supporting layer.

2. 2. The cast-in-place pile construction method according to claim 1, wherein the lower excavation step includes a lost circulation prevention material addition step, which includes a first step of sinking a plastic bag containing the absorbent-containing lost circulation prevention material to the bottom of the pile hole before excavation, and a second step of dissolving the plastic bag and adding the absorbent-containing lost circulation prevention material contained therein to the stabilizing liquid at the bottom of the pile hole.

3. The cast-in-place pile method is an earth drill method, In the first step, the plastic bag is fixed to the bottom surface of the drilling bucket and allowed to sink to the bottom; 3. The cast-in-place pile construction method according to claim 2, wherein in the second step, the drilling bucket is rotated idly in the stabilizing solution at the bottom, and the absorbent-containing lost circulation prevention material is added to the stabilizing solution.

4. 2. The cast-in-place pile construction method according to claim 1, wherein the lower excavation step includes a lost circulation amount measurement step of interrupting the supply of the stabilizing solution and measuring the lost circulation amount of the stabilizing solution from a change in the solution level in the hole.

5. The in-situ pile construction method according to claim 1, wherein the absorbent-containing lost circulation prevention material is a granular solid obtained by mixing the absorbent and the lost circulation prevention material in water not containing adhesive, stirring the mixture, and drying and solidifying the mixture.

6. the heavy metal contaminant is arsenic, fluorine, or lead; the stabilizing liquid is a polymer-based stabilizing liquid or a bentonite-based stabilizing liquid, The cast-in-place pile construction method according to claim 4 , wherein the lost circulation prevention material comprises fibrous artificial inorganic fibers or natural wood pulp fibers.

7. 3. The cast-in-place pile construction method according to claim 2, wherein in the upper excavation step and the lower excavation step, the bottom of the pile hole is excavated while maintaining the liquid level of the stabilizing liquid above the groundwater level, and the earth removal work to the ground is repeated.

8. The present invention includes an absorbent that adsorbs and insolubilizes arsenic, fluorine, or lead, and a lost circulation prevention material that includes water-insoluble fibers, The absorbent-containing lost circulation prevention material is formed by dispersing the absorbent in the water-insoluble fibers.

9. The lost circulation prevention material containing an adsorbent according to claim 8, which is a granular solid obtained by mixing the adsorbent and the lost circulation prevention material in water containing no adhesive, stirring the mixture, and drying to solidify it.

10. The lost circulation prevention material containing an adsorbent according to claim 8, wherein the fibers are fibrous artificial inorganic fibers or natural wood pulp fibers.

11. The adsorbent is iron oxide, calcium sulfate (CaSO ４ ), magnesium oxide (MgO), or aluminum hydroxide (Al(OH) ３ The lost circulation prevention material containing an adsorbent according to claim 8, comprising:

Images