Method for predicting ground quality after improvement

Abstract

To provide a post-improvement ground quality prediction method capable of predicting the quality of improved ground after construction during the ground improvement construction.SOLUTION: The ground under improvement is injected with a solidifying material and / or, if the ground contains heavy metals, an insolubilizing material for the heavy metals, and then the ground and these materials are agitated and mixed. Before the agitating and mixing is completed, predetermined physical properties of at least one of the solidifying material and the insolubilizing material in the soil discharged by agitating and mixing are measured. Based on the measured values of predetermined physical properties, the quality of the ground after improvement is predicted.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for predicting ground quality after improvement, and in particular to a method for predicting ground quality when the ground is improved by injecting a solidification material and / or a heavy metal immobilization material into the ground and stirring and mixing the ground. [Background technology]

[0002] For example, as described in Patent Document 1 below, when trying to improve the ground by injecting a solidification material such as cement slurry into the ground and mixing it with the soil and sand, if the ground contains heavy metals such as zinc, the solidification of the solidification material is inhibited and the strength of the ground cannot be sufficiently improved. Therefore, a ground improvement method is widely used in which an insolubilizer that reacts with heavy metals in the ground to generate insoluble compounds such as heavy metal hydroxides and heavy metal sulfides to promote the solidification of the solidification material is injected into the ground simultaneously with or before or after the injection of the solidification material.

[0003] In the conventional improvement method for heavy metal-containing ground, which involves injecting solidifying and insolubilizing materials, soil samples are taken by boring at the age when the soil can develop strength after improvement, and it is confirmed whether the required strength has been achieved. In addition, when heavy metals are insolubilized using the above-mentioned sulfides, for example, a soil elution test is conducted after improvement to determine whether the amount of eluted heavy metals is below the national standard value. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-246658 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the conventional method for improving ground containing heavy metals, samples must be taken by boring after construction, and if the strength test results show that the required strength is not obtained, it is necessary to carry out solidification treatment again to improve the solidification of the ground. In addition, when insolubilizing heavy metals, if the amount of heavy metal elution in the improved soil exceeds the national standard value, it is necessary to carry out the insolubilization treatment again. That is, in the conventional method for improving ground containing heavy metals, it was necessary to check after improvement whether the strength of the improved soil was the required strength or whether the amount of heavy metal elution in the improved soil met the national standard value. Therefore, if the quality of the improved soil (strength, amount of heavy metal elution, etc.) was not sufficient, it was necessary to carry out soil improvement treatment again after soil improvement.

[0006] The present invention has been made in consideration of the above-mentioned problems, and its object is to provide a method for predicting improved ground quality, which can predict the quality of improved ground after construction during ground improvement work. [Means for solving the problem]

[0007] In order to achieve the above-mentioned objective, the method of predicting ground quality after improvement of the present invention is characterized in that a solidification material and / or an insolubilization material for heavy metals if heavy metals are present in the ground are injected into the ground to be improved, the solidification material and / or an insolubilization material for the heavy metals are injected into the ground to be improved, the solidification material and / or the insolubilization material for the heavy metals are injected into the ground, the solidification material and / or the insolubilization material are injected into the soil discharged by the stirring and mixing before the stirring and mixing is completed, and the quality of the improved ground is predicted based on the measured values ​​of the specified physical properties.

[0008] According to this configuration, for example, by measuring at least one of the concentration of the solidifying agent and / or the concentration of the insolubilizing agent from the discharged soil of the improved ground discharged during construction, it is possible to detect the amount of the solidifying agent and / or the insolubilizing agent, and based on this, the quality of the improved ground can be predicted, and as a result, if the quality of the improved ground is predicted to be insufficient, correction can be made during the ground improvement construction to inject additional amounts that are considered necessary. In this way, by predicting the construction quality after construction during the ground improvement construction, correction of the injection amount of the solidifying agent and / or the insolubilizing agent to meet the required quality after improvement can be made at the time of construction rather than after construction, making it possible to ensure the specified construction quality and eliminate the trouble of reprocessing after construction.

[0009] Another configuration of the present invention is characterized in that, during the stirring and mixing, the solidification material and the insolubilization material are injected, and during the measurement, predetermined physical properties of both the solidification material and the insolubilization material in the discharged soil discharged by the stirring and mixing before the stirring and mixing is completed are measured.

[0010] According to this configuration, for example, by measuring the concentration of the solidifying agent and the concentration of the insolubilizing agent from the discharged soil of the improved ground discharged during construction, the amount of the solidifying agent and the insolubilizing agent can be detected, and the quality of the improved ground can be predicted based on this, and if the quality of the improved ground is predicted to be insufficient as a result, a correction can be made during the ground improvement construction to inject additional amounts that are considered necessary. In this way, by predicting the construction quality after construction during the ground improvement construction, the injection amount of the solidifying agent and the insolubilizing agent to meet the required quality after improvement can be corrected at the time of construction rather than after construction, making it possible to ensure the specified construction quality and eliminate the trouble of reprocessing after construction.

[0011] A further configuration of the present invention is characterized in that, when the solidification material is injected, the specified physical property is the pH of the discharged soil, and the quality of the improved ground is predicted from the concentration of the solidification material in the discharged soil estimated based on the measured pH value.

[0012] According to this configuration, when the solidification material contains a cement composition, the cement composition inherently exhibits an alkaline pH of more than 10. However, if the pH of the discharged soil to which it is added is lower than the pH when the cement composition concentration in the discharged soil is a predetermined concentration (target concentration), this means that the concentration of the cement composition as a solidification material is low. Therefore, the amount of solidification material to be injected can be corrected according to the pH of the discharged soil.

[0013] A further configuration of the present invention is characterized in that, when injecting the solidification material, the specified physical property is the heat of neutralization when acid is added to the discharged soil, and the quality of the improved ground is predicted from the concentration of the solidification material in the discharged soil estimated based on the measured value of the heat of neutralization.

[0014] According to this configuration, when the solidification agent contains a cement composition, the cement composition is inherently alkaline with a pH of over 10, and when acid is added to the waste soil to which it has been added, the temperature rises due to the heat of neutralization. Therefore, the amount of this temperature rise is measured, and if this amount of temperature rise is smaller than the amount of temperature rise when acid is added to waste soil with a cement composition concentration of a predetermined concentration (target concentration), this means that the concentration of the cement composition as a solidification agent is low, and the amount of solidification agent injected can be corrected according to this amount of temperature rise, i.e., the heat of neutralization.

[0015] A further configuration of the present invention is characterized in that, when the insolubilizing agent is injected, the predetermined physical property is the color (RGB code) of sulfides as reaction products in the discharged soil, and the quality of the improved ground is predicted from the concentration of the insolubilizing agent in the discharged soil estimated based on the measured color (RGB code) of the sulfides.

[0016] According to this configuration, when the insolubilizing agent contains sulfides, for example, insoluble compounds of lead sulfide and copper sulfide are black, and insoluble compounds of cadmium sulfide and arsenic sulfide are yellow, the chromaticity (RGB code) varies depending on the heavy metals contained in the soil. In addition, when a cement composition is injected as a solidification agent, the higher the concentration of heavy metals in the discharged soil, the blacker the discharged soil becomes. Therefore, the heavy metal concentration can be estimated from the chromaticity of the discharged soil, and the amount of insolubilizing agent injected can be corrected accordingly.

[0017] A further configuration of the present invention is characterized in that, when the insolubilizing agent is injected, the predetermined physical property is the dissolved sulfide concentration of the discharged soil, and the quality of the improved ground is predicted from the measured dissolved sulfide concentration of the discharged soil.

[0018] According to this configuration, when the insolubilizing agent contains sulfide, the concentration of dissolved sulfides such as sulfide ions increases the less heavy metals (not including insoluble compounds) are present in the discharged soil and the higher the pH of the discharged soil is. Therefore, when a cement composition exhibiting an alkaline pH of more than 10 is injected as a solidification agent, if the dissolved sulfide concentration of the discharged soil is smaller than the dissolved sulfide concentration when the sulfide concentration in the discharged soil is a predetermined concentration (target concentration), this means that the sulfide concentration as the insolubilizing agent is low, and the amount of insolubilizing agent injected can be corrected according to this dissolved sulfide concentration. Effect of the Invention

[0019] As described above, according to the present invention, the addition of solidification materials and / or insolubilization materials to meet the required quality after improvement can be carried out at the time of construction rather than after construction, thereby ensuring the specified construction quality and eliminating the need for reprocessing after construction. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is an explanatory diagram showing an embodiment of a ground improvement method to which the improved ground quality prediction method of the present invention is applied. [Diagram 2] FIG. 2 is an explanatory diagram showing the relationship between the sulfide ion concentration and pH in discharged soil. [Diagram 3] 1 is a graph showing the relationship between the detector tube reading and the amount of NaHS added. [Figure 4] 1 is a graph showing the relationship between soil depth and runoff concentration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] An embodiment of the method for predicting ground quality after improvement according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is an explanatory diagram of a ground improvement method to which the method for predicting ground quality after improvement according to this embodiment is applied. The ground improvement method brings about various effects such as preventing liquefaction and increasing bearing capacity for soft ground. The ground improvement method shown in FIG. 1 is a relative mixing type deep mixing method. This ground improvement method rotates the inner and outer blades in opposite directions while penetrating the ground with relative mixing blades 3 having different rotation directions and rotation speeds (angular speeds), and excavates and mixes while discharging a slurry-like solidification material from the excavation head 2 at the tip. This method can mix and mix the ground and solidification material three-dimensionally while avoiding co-rotation or co-rotation of the target soil, and creates homogeneous improved soil.

[0022] In this ground improvement method, as shown in Figure 1(a), the excavation head 2 attached to the tip of the stirring rod 4 is set at the pile core of the original ground, and then the solidification material is discharged from the center of the excavation head 2 as described above, while the excavation head 2 and the opposing stirring blades 3 are rotated as shown in Figure 1(b) to penetrate into the original ground, and the ground and the solidification material are simultaneously stirred and mixed. After this ground penetration, when the excavation head 2 reaches a specified depth, it performs static mixing for a specified time at the bottom position as shown in Figure 1(c). Then, as shown in Figure 1(d), the excavation head 2 is pulled out and stirring and mixing is performed again by the opposing stirring blades 3, and the excavation head 2 is pulled out of the ground as shown in Figure 1(e) to complete the construction. The solidification material is injected in the form of a slurry of powder such as cement with water. If heavy metals are present in the ground, an insolubilizing agent that insolubilizes the heavy metals is injected together with the solidification material. Insolubilizing agents are generally in liquid form and are diluted with water before injection.

[0023] In this ground improvement method, the improved excess soil from the depth reached by the excavation head 2 is discharged (discharged) to the ground through the gaps in the ground improvement machine 1. That is, during the penetration mixing and mixing in Fig. 1 above, excess soil is generated by the insertion of the excavation head 2, the opposing mixing blades 3, and the mixing rod 4 and the injection of the improvement material (solidification material, insolubilization material). The improvement material has smaller particles than the soil, and since the soil under mixing and mixing is a clay-based material containing water, it moves upward with the vibration of the ground improvement machine 1 according to Stokes' law and is discharged to the ground. This excess soil is discharged with pore water through the gaps between the mixing rod 4 and the improved soil, so it has been confirmed that the excess soil (discharged) discharged to the ground near the mixing rod 4 reflects the improvement situation at a depth approximately the same as the improvement depth. Therefore, in this embodiment, for example, the concentrations of the solidification material and the insolubilization material in the removed soil at the depth reached by the drilling head 2 during the penetration mixing and stirring shown in Figure 1(b) are measured, and the shortfall is corrected by additional injection at the corresponding depth during the withdrawal mixing and stirring as shown in Figure 1(d).

[0024] As mentioned above, the original ground that needs to be improved is soft ground, and a solidifying agent such as cement slurry is injected into the soft ground, and the mixed ground with the solidifying agent is solidified to improve the ground strength. On the other hand, the original ground may contain heavy metals that inhibit the development of strength due to the solidification of the cement slurry. Examples of such heavy metals include zinc, lead, and copper. The necessity of insolubilizing these heavy metals with an insolubilizing agent and the insolubilization process are explained below.

[0025] The cement slurry contains cement, water, and optionally other additives. Cement is an inorganic bonding material that exhibits hardening properties when mixed with water, and hydraulic cement is used in the present invention. As the hydraulic cement, a plain cement such as Portland cement, hydraulic lime, Roman cement, or natural cement may be used, or a mixed cement such as lime-mixed cement or mixed Portland cement may be used. If the original ground has sufficient moisture, a mixture of cement and optionally other additives may be used instead of the cement slurry. As the additive, existing additives may be used.

[0026] Here, we explain the case where the heavy metal in the original ground is zinc and the insolubilizing agent contains NaHS (sodium hydrosulfide).

[0027] i) Reaction of zinc ions with cement inhibits hardening of cement When the cement slurry is mixed with the original soil, the Zn in the original soil 2+ In an alkaline environment, hydroxide ions (OH - ) to form a precipitate of Zn(OH)2 (zinc hydroxide). Note that Ca(OH)2 is also present in the cement slurry, but since Ca has a greater tendency to ionize than Zn, the solubility of Zn(OH)2 is less than that of Ca(OH)2, and the reaction shown in formula (I) below proceeds.

[0028] Zinc 2+ + OH - → Zn(OH)2↓ (I) This Zn(OH)2 reacts with Ca(OH)2 attached to the surface of the CSH (calcium silicate hydrate) gel produced by cement solidification to produce CaZn2(OH)6·6H2O (calcium zincate).

[0029] Ca(OH)2+ 6H2O + 2Zn(OH)2 → CaZn2(OH)6·6H2O↓ (II) The compound CaZn2(OH)6·6H2O is also insoluble in water and is produced to cover the surface of the CSH gel produced in the initial cement hydration reaction, preventing further hydration reactions. As a result, the solidification of the cement slurry is inhibited by the zinc in the original ground.

[0030] ii) Reaction of zinc with sodium hydrosulfide As shown in the following formula (III), zinc ions in the original soil react with sodium hydrogen sulfide in an alkaline environment to precipitate zinc sulfide.

[0031] 2Zn 2+ + 2NaHS + H2O → 2ZnS↓ + 2NaOH (III) Even if the reaction of formula (I) precedes the formation of Zn(OH)2 in the original ground, zinc sulfide will precipitate via the reaction of formula (IV) below.

[0032] Zn(OH)2+ NaHS → ZnS↓ + Na(OH) + H2O (IV) Zinc sulfide is less soluble than zinc hydroxide, so it does not affect the hydration of cement, and calcium does not produce sulfides at room temperature or at the level of heat generated by cement hydration, so sodium hydrosulfide is not involved in the solidification of cement.

[0033] Therefore, by using sodium hydrogen sulfide as an insolubilizing agent to be added to the cement slurry, the Zn in the cement slurry, the original ground, and the mixture can be prevented from being dissolved. 2+ It is believed that this causes Zn(OH)2 to precipitate as ZnS, inhibiting the reaction of formula (II) above, thereby allowing the cement to develop sufficient strength.

[0034] The insolubilizer may be added when the powder is mixed or when kneaded. The concentration of NaHS added to the insolubilizer may be any amount that can insolubilize heavy metals that inhibit the development of strength in the improved ground and alleviate the inhibition, but when added to the original ground, it is sufficient that the molar ratio of NaHS to heavy metals in the original ground (NaHS / heavy metals) is 0.02 or more, preferably 0.03 or more, and particularly preferably 0.09 or more.

[0035] In addition, although zinc has been described as an example of a heavy metal contained in the original ground that inhibits the development of strength in the improved ground, this heavy metal is not limited to zinc. Any heavy metal may be used as long as it has a smaller tendency to ionize than Ca, generates hydroxides in the cement slurry like zinc, and reacts with NaHS to generate sulfides. For example, nickel, tin, lead, copper, cadmium, cobalt, manganese, etc. are examples of heavy metals that inhibit the development of strength in the improved ground. In addition, when the heavy metal is hexavalent chromium, a reducing agent serves as the insolubilizing agent. An example of a reducing agent is ferrous sulfate (FeSO4). Hexavalent chromium is available in the form of chromate and dichromate, which are yellow and orange (red), respectively.

[0036] In this embodiment, as described above, for example, the concentration of the solidification material and the concentration of the insolubilization material in the discharged soil are measured when the soil improvement machine 1 penetrates and mixes the original ground. The following measurement methods can be used for each measurement.

[0037] 1) Measure the concentration of the solidification material from the pH of the discharged soil.

[0038] When the solidification material is a cement slurry, the cement composition is inherently alkaline with a pH of more than 10, but if the pH of the waste soil to which it is added is lower than the pH when the cement composition concentration in the waste soil is at a specified concentration, the amount of solidification material to make up for the pH deficiency can be used as the correction amount for the injection amount.

[0039] 2) The concentration of the solidification material is measured from the heat of neutralization when acid is added to the discharged soil.

[0040] When the solidification material is a cement slurry, adding acid to the waste soil to which it has been added will cause a temperature rise due to heat of neutralization, and if the amount of temperature rise is smaller than the amount of temperature rise when acid is added to waste soil with a specified cement composition concentration in the waste soil, the amount of solidification material to make up for the shortage of this temperature rise can be used as the correction amount for the injection amount. Specifically, for example, 10 mL of 1% hydrochloric acid is added to 100 g of waste soil, and the heat generation curve when stirred and mixed is measured with a plug-in thermometer, and the content (concentration) of the solidification material is calculated using a calibration curve created in advance from the maximum temperature and the time it takes to reach the maximum temperature.

[0041] 3) The concentration of the insolubilizing material is measured from the color (RGB code) of sulfides, which are reaction products in the discharged soil.

[0042] When the insolubilizing agent contains sulfides, the chromaticity (RGB code) differs depending on the heavy metals contained in the soil, such as insoluble compounds of lead sulfide and copper sulfide being black, and insoluble compounds of cadmium sulfide and arsenic sulfide being yellow. In addition, when a cement composition is injected as a solidification agent, the higher the concentration of heavy metals in the discharged soil, the blacker the discharged soil becomes, so that the concentration of heavy metals can be estimated from the chromaticity (RGB code) of the discharged soil, and the injection amount of the insolubilizing agent can be corrected based on this.

[0043] 4) Measure the concentration of insolubilizing materials from the dissolved sulfide concentration of the discharged soil.

[0044] The concentration of dissolved sulfides such as sulfide ions increases with the amount of heavy metals in the discharged soil and the pH of the discharged soil. Therefore, when cement slurry is injected as a solidification material, if the dissolved sulfide concentration in the discharged soil is lower than the dissolved sulfide concentration when the sulfide concentration in the discharged soil is a specified concentration, the amount of insolubilizing material to make up for the shortfall in the dissolved sulfide concentration can be used as the correction amount for the amount of insolubilizing material injected.

[0045] Specifically, when the insolubilizing agent is NaHS, H2S is generated by hydrolysis as shown in the following formula (V).

[0046] NaHS+H2O→Na + +2OH - +H2S (V) H2S is ionized into ions according to the following formula (VI) depending on the pH, as shown in FIG. 2, which is an explanatory diagram showing the relationship between the sulfide ion concentration in the waste soil and pH.

[0047] H2S⇔H + +HS - ⇔2H + +S 2- (VI) As is clear from Fig. 2, S 2-When the pH is high, the concentration increases along with the pH, so this correlation can be used to detect the pH, and the amount of NaHS that compensates for this pH deficiency becomes the correction amount for the injection amount.

[0048] Dissolved sulfide (S 2- ) concentration can be measured using a simple method that uses a commercially available liquid detector tube, a simple method in which sulfuric acid is added to the sample to generate hydrogen sulfide gas and then measured with a hydrogen sulfide gas detector tube, the methylene blue spectrophotometric method in which the absorbance of methylene blue produced when sulfide ions react with N,N'-dimethyl-p-phenylenediamine in the presence of iron(III) chloride is measured, and the iodometric method in which the sample is acidified with sulfuric acid, the hydrogen sulfide generated is absorbed in an aqueous zinc acetate solution, and the zinc sulfide produced is measured by titrating it with iodine and sodium thiosulfate solutions.

[0049] Therefore, when cement slurry is injected as a solidification material, if the pH of the discharged soil is equal to or higher than the specified pH (e.g. pH 10), or if the heat of neutralization when acid is added to the discharged soil is equal to or higher than 50 kJ, the quality of the improved soil is predicted to be good. Also, when an insolubilizing material for heavy metals is injected, if the concentration of dissolved sulfides in the discharged soil is equal to or higher than 1 ppm, or if the color (RGB code) of sulfides as reaction products in the discharged soil is equal to or lower than R=G=B:200, the heavy metals in the improved soil are insolubilized and there is a surplus of insolubilizing material, so that the quality of the improved soil is predicted to be good without the inhibition of solidification by heavy metals. The quality of the improved soil is considered to be good if the breaking strength of a core obtained by boring a 1-7 day old soil is equal to or higher than the design strength.

[0050] Therefore, the concentration of the solidification material, the pH of the discharged soil, and the heat of neutralization when acid is added to the discharged soil each correspond to the specified physical properties of the solidification material of the present invention, and the concentration of the insolubilization material, the color (RGB code) of the sulfides as reaction products in the discharged soil, and the concentration of dissolved sulfides in the discharged soil each correspond to the specified physical properties of the insolubilization material of the present invention. EXAMPLES

[0051] The present invention will be specifically described below by showing examples, but the present invention is not limited to these examples. [Design example] How to set the injection volume Cement and water are added to the soil, and sodium hydrogen sulfide (NaHS) is added to produce a slurry. Approximately 50 mL of the slurry is then sampled. The sampled slurry is then placed in a syringe and filtered through a 45 μm membrane filter. 1 mL of the filtered liquid is diluted 100 times (100 mL) with water to measure the sulfide ion (S 2- The concentration of sulfide ions is measured by the simplified method using the above-mentioned detector tube for dissolved sulfide liquids, and the pH (solidification material concentration) is measured by a pH meter, and the injection (addition) amount is calculated from the sulfide ion concentration and pH. Specifically, for example, from Figure 2, the ionization of sulfide ions is expressed by the following formula.

[0052] [H + ][S 2- ]=1.2×10 -13 [HS - ] Therefore, the pH and sulfide ions (S 2- By measuring the concentration, it is possible to control whether the addition is being made appropriately.

[0053] The pH and sulfide ion (S) content of cement slurry when the ratio of cement, water, and sodium hydrosulfide (NaHS) was adjusted 2- ) concentrations are shown in Table 1 below.

[0054] [Table 1] Case 4 will be taken as an example below.

[0055] Standard addition amount (mixture amount) for Case 4: 15.0 kg of soil Cement: 120kg / m 3 868g (specific gravity 3.04) ·Water: 120kg / m 3 688g ·NaHS: 0.3% 180g (specific gravity 1.2, 25% aqueous solution) S in cement slurry 2- The concentration of sulfide ions (S 2- ) concentration is calculated using the following formula:

[0056] S 2- =0.25×(180×0.57×106)÷(688180 / 1.2) =30609(mg / L) In the formula, 0.57: weight ratio of sulfide ions S 2- / NaHS.

[0057] In addition, the pH of the cement slurry was 11.80, so [H + ] is 10 -11.80 =1.58×10 -12 It becomes.

[0058] From the above ionization formula, the abundance ratio of sulfide ions and hydrosulfide ions is [S 2- ]=1.2×10 -13 / 1.58×10 -12 [HS - ]=0.076 and S 2- = 30609 × 0.076 = 2318 (mg / L).

[0059] In this measurement, the sample was diluted 100 times to match the scale of the detector tube, and the results were as shown in the converted values ​​in the table.

[0060] Although sulfide ions were detected in greater amounts than the theoretical value, in the cement slurry HS - ⇔H + +S 2- (a) Equilibrium is established, and the following reaction occurs in the detector tube: S 2- +Pb (lead) → PbS↓ (solid) ···(b) S 2-This is because when is consumed, expression a moves to the right (expression c).

[0061] HS - →H + +S 2- (c) The relationship between the detector tube reading and the amount to be added is shown in Figure 3. If the pH of the cement slurry is less than 11, or if the detector tube reading is below 100 on the graph in Figure 3, it is possible that NaHS is being consumed more than the design value, and treatment such as adding chemicals will be necessary. [Construction example] For an improvement diameter of 1.6 m, according to the above design example, 0.3% NaHS is added: the amount of added slurry is 321 L / m. From experience, the amount of soil discharged is 80% of the amount added, so approximately 257 L is generated per 1 m of depth. To evaluate the amount of improved soil per 1 m, samples of the discharged soil were taken every 1 m of excavation, and the pH was measured with a pH meter and the NaHS concentration was measured with a dissolved sulfide detector tube. Discharged soil was sampled near the rod of the excavation machine (as this reflects the depth conditions). <Condition> Drilling diameter: 1600mmφ Cement dosage = 120kg / m 3 , NaHS 0.3% addition, W / C=100%, injection volume=321L / m ·Drilling speed: 1.5 min / m ·Improved length: 16.35m The measurement results are shown in Table 2 below and FIG.

[0062] [Table 2] In areas where the values ​​did not match those of the control values, additional cement slurry was injected when the rod was pulled up. When strength tests were carried out using cores drilled from the ground three days after the material was in use, the areas where additional slurry had been injected had lower strength than other areas, but still met the design strength.

[0063] The above sampled soil was photographed with a white-balanced camera, and the average chromaticity (RGB code) was calculated in grayscale. The results are shown in Table 3 below, along with Table 2 above. The shading in the table indicates the chromaticity expressed in the RGB code by the shade of the shading. In the above control value deviation area, the chromaticity (RGB code) of the soil exceeded 200 in all cases. Therefore, poor areas of ground improvement work can be managed using the chromaticity (RGB code) as an index.

[0064] [Table 3] Thus, according to the method for predicting the quality of improved ground of the present invention, the amount of solidifying material and insolubilizing material can be detected by measuring the concentration of the solidifying material and the concentration of the insolubilizing material from the discharged soil of the improved ground discharged during construction, and the quality of the improved ground can be predicted based on this. As a result, if the quality of the improved ground is predicted to be insufficient, correction can be made during the ground improvement construction to inject additional amounts of the solidifying material and insolubilizing material that are considered necessary. In this way, by predicting the construction quality after construction during the ground improvement construction, the injection amount of the solidifying material and insolubilizing material to meet the required quality after improvement can be corrected at the time of construction rather than after construction, making it possible to ensure the specified construction quality and eliminate the trouble of reprocessing after construction.

[0065] In addition, when the solidification agent contains a cement composition, the cement composition inherently exhibits an alkaline pH of more than 10. However, if the pH of the discharged soil to which it is added is lower than the pH when the cement composition concentration in the discharged soil is at a specified concentration, this means that the concentration of the cement composition as a solidification agent is low. Therefore, the amount of solidification agent to be injected can be adjusted according to the pH of the discharged soil.

[0066] In addition, when the solidification agent contains a cement composition, which is inherently alkaline with a pH of over 10, adding acid to the waste soil to which it has been added will cause the temperature to rise due to heat of neutralization. Therefore, by measuring the amount of temperature rise, if the amount of temperature rise is smaller than the amount of temperature rise when acid is added to waste soil with a specified concentration of the cement composition in the soil, this means that the concentration of the cement composition as a solidification agent is low, and the amount of solidification agent injected can be corrected according to the amount of temperature rise, i.e., the heat of neutralization.

[0067] Furthermore, when the insolubilizing agent contains sulfides, the chromaticity (RGB code) varies depending on the heavy metals contained in the soil; for example, insoluble compounds of lead sulfide and copper sulfide are black, while insoluble compounds of cadmium sulfide and arsenic sulfide are yellow. Furthermore, when a cement composition is injected as a solidification agent, the higher the concentration of heavy metals in the discharged soil, the blacker the discharged soil becomes. Therefore, the heavy metal concentration can be estimated from the chromaticity (RGB code) of the discharged soil, and the amount of insolubilizing agent injected can be corrected accordingly.

[0068] Furthermore, when the insolubilizing agent contains sulfide, the concentration of dissolved sulfides such as sulfide ions increases the less heavy metals (not including insoluble compounds) are present in the discharged soil and the higher the pH of the discharged soil is. Therefore, when a cement composition exhibiting an alkaline pH of more than 10 is injected as a solidification agent, if the dissolved sulfide concentration of the discharged soil is lower than the dissolved sulfide concentration when the sulfide concentration in the discharged soil is a specified concentration, this means that the sulfide concentration as the insolubilizing agent is low, and the amount of insolubilizing agent injected can be corrected according to this dissolved sulfide concentration.

[0069] The method for predicting the quality of improved ground according to the embodiment has been described above, but the present invention is not limited to the configuration described in the above embodiment, and various modifications are possible within the scope of the gist of the present invention. For example, in the above embodiment, the concentration of the solidification material and the concentration of the insolubilization material were measured, but in the present invention, only the concentration of the solidification material or only the concentration of the insolubilization material may be measured to predict the quality of the improved ground. Also, as described above, instead of measuring the concentration of the solidification material, the quality of the improved ground may be predicted from the pH of the discharged soil or the heat of neutralization when acid is added to the discharged soil. Similarly, instead of measuring the concentration of the insolubilization material, the quality of the improved ground may be predicted from the color (RGB code) of sulfides as reaction products in the discharged soil or the concentration of dissolved sulfides in the discharged soil. quality may be predicted.

[0070] In the above embodiment, only the relative mixing type deep mixing treatment method is described in detail as a ground improvement method, but the method for predicting ground quality after improvement of the present invention can be applied to other ground improvement methods. Also, it is not limited to the so-called columnar ground improvement method, but can be applied to surface ground improvement methods and other types of ground improvement methods. [Explanation of symbols]

[0071] 1 Ground improvement machine

Claims

1. A solidification material is injected into the ground to be improved, and if heavy metals are present in the ground, an insolubilization material for the heavy metals is injected, and the mixture is stirred and mixed. Before the stirring and mixing is completed, predetermined physical properties of both the solidification material and the insolubilization material in the discharged soil discharged by the stirring and mixing are measured; A method for predicting improved ground quality, characterized in that the quality of the improved ground is predicted from the concentrations of solidification materials and insolubilization materials measured or estimated based on the measured values ​​of the specified physical properties.

2. A method for predicting improved ground quality as described in claim 1, characterized in that the specified physical property is the pH of the discharged soil, and the quality of the improved ground is predicted from the concentration of solidifying material in the discharged soil estimated based on the measured pH value.

3. A method for predicting improved ground quality as described in claim 1, characterized in that the specified physical property is the heat of neutralization when acid is added to the discharged soil, and the quality of the improved ground is predicted from the concentration of solidifying material in the discharged soil estimated based on the measured value of the heat of neutralization.

4. The method for predicting ground quality after improvement as described in claim 1, characterized in that, when the insolubilizing agent is injected, the specified physical property is the chromaticity (RGB code) of sulfides as reaction products in the discharged soil, and the quality of the improved ground is predicted from the concentration of the insolubilizing agent in the discharged soil estimated based on the measured chromaticity (RGB code) of the sulfides.

5. The method for predicting improved ground quality according to claim 1, characterized in that, when the insolubilizing agent is injected, the specified physical property is the dissolved sulfide concentration of the discharged soil, and the quality of the improved ground is predicted from the measured dissolved sulfide concentration of the discharged soil.

6. If heavy metals are present in the ground to be improved, an insolubilizing agent for the heavy metals is injected into the ground and mixed with stirring. Before the stirring and mixing is completed, a predetermined physical property of the insolubilizing material in the discharged soil discharged by the stirring and mixing is measured; A method for predicting improved ground quality, characterized in that the quality of the improved ground is predicted from the concentration of the insolubilizing agent measured or estimated based on the measured value of the specified physical property.

Images