Infiltration and solidification treatment method

Abstract

To provide a seepage solidification treatment method that allows for easy and precise assessment of soil type distribution and enables high-quality ground improvement. [Solution] This permeation solidification treatment method sets a safe permeation injection pressure lower than the limit permeation injection pressure, and measures the change in injection pressure at regular intervals when water is injected into the target ground 1 at a constant injection rate from any injection port 4a to 4f of multiple injection units 3a to 3g,3 within a range below the safe permeation injection pressure, or the change in injection rate at regular intervals when water is injected into the target ground at a constant injection pressure, calculates the permeability coefficient around any injection port 4a to 4f, and estimates the soil distribution based on the permeability coefficient.

Description

[Technical Field]

[0001] This invention relates primarily to a seepage solidification treatment method for preventing liquefaction of sandy ground. [Background technology]

[0002] Conventionally, a known method for preventing liquefaction in sandy ground is the chemical injection method (hereinafter referred to as the permeation solidification treatment method), which involves injecting a chemical solution into the ground at low pressure and allowing the soil solidification chemical solution to permeate into the gaps in the ground to increase the ground strength.

[0003] This infiltration solidification treatment method, considering the properties of the method, is classified as sandy soil in soil classification and evaluated using a permeability coefficient k of 1 × 10⁻⁶. -6 This method is applicable to ground with displacements greater than m / s and is characterized by injecting the chemical solution under injection conditions that minimize ground displacement within that applicable range.

[0004] Generally, the relationship between the injection rate q and the effective injection pressure p is as shown in Figure 5, where a predetermined effective injection pressure (hereinafter referred to as the limiting infiltration injection pressure p) is given. fh Up to this point, the effective injection pressure p increases in proportion to the injection rate q (penetration injection region), and thereafter, the limiting penetration injection pressure p fh As the pressure increases, the effective injection pressure p also increases gradually with increasing injection velocity q (fracture infiltration injection region).

[0005] Then, as the injection rate q increases further and the effective injection pressure p reaches a predetermined pressure (hereinafter referred to as the splitting limit injection pressure), the effective injection pressure decreases sharply from that point onward.

[0006] This phenomenon of a sudden decrease in effective injection pressure is called "fracture," and it is thought that the ground locally fails because it cannot withstand the injection pressure. If injection is carried out at a higher injection rate than when fracture occurred (fracture injection zone), there is a risk of large ground displacement occurring.

[0007] Therefore, in this permeation and solidification treatment method, for a ground having an arbitrary hydraulic conductivity k, it is required to perform the injection work with an optimal injection rate, injection pressure, and injection time within the range where permeation - fracturing permeation injection is established.

[0008] Specifically, several boring tests are carried out in the target ground. As shown in Fig. 6(a), from the results, the strata (soil property distribution in the vertical direction) of the target ground 1 are set as a homogeneous stratum, and a model is created assuming that each layer Bs, Ac, As has a representative single value (for example, the average value) of ground physical properties (N - value, wet unit volume weight γ t , hydraulic conductivity k, etc.).

[0009] Then, based on this model, a critical injection rate test is conducted, the injection rate at which permeation injection is possible and most economical is set, and chemical solution injection is carried out at this injection rate.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] However, in the conventional technology as described above, the target ground is modeled assuming that homogeneous strata are laminated based on the results of boring tests, etc. However, the actual ground is often inhomogeneous. As shown in Fig. 6(b), a clay layer Ac that is outside the scope of application of the method may be deposited thicker than expected, or as shown in Fig. 6(c), a layer Bc with a large amount of clay may be distributed in a lens - shape within the sandy soil layer Bs.

[0012] Therefore, in the prior art, there is a discrepancy between the soil in the design (model) and the actual soil as described above. When injecting chemicals assuming a sand layer as designed for a ground that is actually a clay layer, the injection rate is too fast, resulting in split injection and posing a risk of causing significant ground displacement.

[0013] In particular, the permeation and solidification treatment method is often adopted under conditions with strict displacement constraints, such as the ground under an airport runway. The discrepancy in soil conditions can become a fatal risk in construction.

[0014] On the other hand, if the actual soil distribution can be grasped before construction, the above problems can be avoided. However, at present, a practical method for estimating soil distribution has not been established.

[0015] In addition, as general methods for estimating soil distribution, boring tests and geophysical surveys for two-dimensional (areal) estimation of soil distribution are known, but there are inhibitory requirements in each application.

[0016] For example, in the case of a boring test, in order to obtain a highly accurate soil distribution, the number of boring points must be increased. The presence of many boring holes within the improvement range of the target ground increases the risk of leakage of the injected chemicals and adversely affects the quality of the improved ground. Also, increasing the number of boring points poses a problem of increased costs both in terms of time and economy.

[0017] In geophysical surveys, methods such as resistivity tomography and acoustic tomography are available for distinguishing between sand and clay, but there is a problem that they cannot be applied depending on the ground conditions (salt concentration and saturation). Also, geophysical surveys for two-dimensional (areal) estimation of soil distribution have a problem of lower soil estimation accuracy compared to boring tests, and there is also a problem that it is costly both in terms of time and economy when implemented three-dimensionally.

[0018] Therefore, in view of these conventional problems, the present invention aims to provide a seepage solidification treatment method that allows for easy and precise determination of soil type distribution and enables high-quality ground improvement. [Means for solving the problem]

[0019] The invention described in claim 1, which solves the conventional problems described above, is a permeation solidification treatment method in which an injection unit is inserted into a plurality of insertion holes formed in the target ground and a chemical solution is injected into the target ground from a plurality of injection ports formed on the outer surface of each injection unit, wherein a safe permeation injection pressure lower than the theoretical limit permeation injection pressure based on design values ​​is set, the change in injection pressure at regular intervals when water is injected into the target ground at a regular injection rate from any injection port of the plurality of injection units within a range below the safe permeation injection pressure, or the change in injection rate at regular intervals when water is injected into the target ground at a regular injection pressure is measured, the permeability coefficient around the arbitrary injection port is calculated from the relationship between the measured injection pressure and injection rate, the soil distribution is estimated based on the permeability coefficient, and then the chemical solution injection work is performed based on the permeability coefficient and the estimated soil distribution.

[0020] The feature of the invention described in claim 2 is that, in addition to the configuration of claim 1, the injection unit has multiple injection ports provided at intervals in the axial direction, and the pitch between the injection ports in the axial direction is set to be narrower on the side closer to the clay layer.

[0021] The features of the invention described in claim 3 are, in addition to the configuration of claim 1 or 2, that after calculating the permeability coefficient around the arbitrary injection port, a limit injection velocity test is performed based on the permeability coefficient and the estimated soil distribution, and the chemical solution is injected from the injection port at the determined limit injection velocity.

[0022] The feature of the invention described in claim 4 is that, in addition to the configuration of claim 1 or 2, if the permeability coefficient around any of the inlets is less than or equal to a predetermined value, the injection of the chemical solution from the inlet is stopped.

[0023] The feature of the invention described in claim 5 is that, in addition to the configuration of claim 1 or 2, if the permeability coefficient around any inlet is less than or equal to a predetermined value, the chemical solution is injected from the inlet at a pressure less than the safe permeation injection pressure. [Effects of the Invention]

[0024] The permeable solidification treatment method according to the present invention, by having the configuration described in claim 1, makes it possible to grasp the actual distribution of the permeability coefficient (soil type) of the target ground before the chemical injection work, and reduces the risk of ground uplift due to cracking, etc.

[0025] Furthermore, by incorporating the configuration described in claim 2, the present invention enables precise ground improvement in accordance with the actual permeability coefficient and soil distribution.

[0026] Furthermore, by providing the configuration described in claim 3 of the present invention, the limit injection velocity test can be performed with a detailed understanding of the distribution of the permeability coefficient (soil type) of the target ground, thereby preventing significant ground displacement due to the limit injection velocity test.

[0027] Furthermore, by incorporating the configuration described in claim 4 of the present invention, it is possible to avoid ground outside the scope of application of the seepage solidification treatment method and prevent significant ground displacement.

[0028] Furthermore, by incorporating the configuration described in claim 5, the present invention makes it possible to safely perform ground improvement while preventing cracking even in areas of soil with a low permeability coefficient. [Brief explanation of the drawing]

[0029] [Figure 1] This is a schematic cross-sectional view showing an embodiment of the infiltration solidification treatment method according to the present invention. [Figure 2] This is a plan view of the same as above. [Figure 3] This is a partially enlarged cross-sectional view of the injection unit for drug solution injection shown above. [Figure 4]This is a schematic cross-sectional view showing an embodiment of the permeability test described above. [Figure 5] This graph shows the relationship between injection pressure and injection speed in the infiltration solidification treatment method. [Figure 6] (a) is a cross-sectional view showing the soil distribution of the modeled target ground, (b) is a cross-sectional view showing an example of the actual soil distribution, and (c) is a cross-sectional view showing yet another example. [Modes for carrying out the invention]

[0030] Next, embodiments of the infiltration solidification treatment method according to the present invention will be described based on the examples shown in Figures 1 to 6. Components similar to those in the conventional example described above will be denoted by the same reference numerals, and in the figures, reference numeral 1 represents the target ground.

[0031] For example, the target ground 1 is sandy soil in terms of soil classification on top of a clay layer Ac, and its permeability coefficient k is 1 × 10 -6 A layer of sandy soil Bs with a density greater than m / s is stacked, and the upper layer Bs, which consists of this sandy soil, is targeted for ground improvement using the infiltration solidification treatment method.

[0032] As shown in Figures 1 and 2, this permeation solidification treatment method involves inserting injection units 3a, 3ga, and 3g into multiple insertion holes 2, 2… formed in the target ground 1, injecting chemical solution 5 into the target ground 1 through injection ports 4a to 4f formed on the outer surface of each injection unit 3a, 3ga, and 3g, and increasing the ground strength by allowing the ground solidification chemical solution 5 to permeate into the gaps in the ground.

[0033] Furthermore, the infiltration solidification treatment method according to the present invention has a limiting infiltration injection pressure p fh Lower safe infiltration injection pressure p max Set the safe infiltration injection pressure p max A permeability test is conducted within the following range (pressure level), and the soil distribution is estimated based on the permeability coefficient k obtained from the test. Based on the permeability coefficient and the estimated soil distribution, the injection of chemical solution 5 is then carried out.

[0034] The specific procedure of the infiltration solidification treatment method according to the present invention is described in detail below.

[0035] First, as shown in Figure 6(a), boring tests are conducted at several locations within or near the target ground 1, and a design soil distribution model is established based on the test results. Note that the symbol 6 in the figure represents a boring hole.

[0036] The soil distribution is modeled assuming that each layer of the target ground 1 is homogeneous and consists of a single soil type, and that the ground properties (N-value, wet unit weight γ, permeability coefficient k, etc.) are represented by a single representative value, such as an average value.

[0037] Next, a drilling machine (not shown) is placed at a predetermined position on the surface of the target ground 1, and drills are made to a predetermined depth in the target ground 1, down to the lower end of the sandy soil layer Bs, to form multiple insertion holes 2,2…, and injection units 3a to 3g are inserted into the insertion holes 2,2….

[0038] Each injection unit 3a to 3g comprises, for example, a long cylindrical injection outer tube 10 that is installed inside the insertion holes 2, 2..., and a drug solution injection body 11 that can be inserted through the injection outer tube 10.

[0039] As shown in Figure 3, the injection outer tube 10 is formed by connecting unit tubes in the axial direction, and a plurality of injection ports 4a to 4f are formed at predetermined positions in the longitudinal direction of the outer circumference, spaced apart in the circumferential direction, and communicating with the interior.

[0040] The injection ports 4a to 4f are inserted close to the clay layer Ac. The pitch of the lower injection ports 4a to 4d is narrower than the pitch between the upper injection ports 4d-4e and 4e-4f, and is about half the pitch between the upper injection ports 4d-4e and 4e-4f. For example, while the pitch between injection ports 4d-4e and 4e-4f is similar to that of a typical injection outer pipe used in the infiltration solidification treatment method (approximately 2m), the pitch of injection ports 4a to 4d is half that, at 1m.

[0041] Furthermore, although the pitch between the upper end inlet ports 4d-4e and 4e-4f was exemplified as approximately 2m in the above example, this pitch is not limited to this, and any pitch can be adopted.

[0042] Furthermore, the pitch of the inlet ports 4a to 4d on the lower end is not limited to approximately half the pitch between the inlet ports 4d-4e and 4e-4f on the upper end; any pitch can be adopted as long as it is narrower than the pitch between the inlet ports 4d-4e and 4e-4f on the upper end.

[0043] Furthermore, the injection outer tube 10 is equipped with sleeve packers 12, 12 on both sides in the longitudinal direction, flanking each injection port 4a to 4f. By expanding the sleeve packers 12, 12 and sealing the gaps between them and the insertion holes 2, 2... on both sides in the longitudinal direction of each injection port 4a to 4f, the leakage of water or chemical solution 5 can be prevented.

[0044] The chemical injection body 11 is formed in a cylindrical shape with a smaller diameter than the injection outer tube 10, and has discharge ports 13, 13... on its outer surface, as well as double packers 14, 14 positioned on both sides of the discharge ports 13, 13..., and is configured to supply water or chemical solution 5 through the supply pipe 15.

[0045] Then, the chemical injection body 11 is inserted into the injection outer pipe 10 and moved to coincide with the position of any of the injection ports 4a to 4f, and the double packers 14, 14 of the chemical injection body 11 are expanded to fill the gap between the chemical injection body 11 and the injection outer pipe 10, so that the water or chemical solution 5 discharged from the discharge ports 13, 13 can be injected into the target ground 1 through any of the injection ports 4a to 4f.

[0046] Furthermore, the drug injection body 11 is not limited to this embodiment and may be composed of a single tubular body with discharge ports 13, 13 and double packers 14, 14 provided at the tip of the tubular body.

[0047] On the one hand, the actual soil quality distribution is often inhomogeneous. As shown in Fig. 6(b), a clay layer Ac that is not applicable to the construction method may be deposited thicker than expected, or as shown in Fig. 6(c), a layer Bc with a high clay content may be distributed in a lens shape within the buried soil layer. Therefore, the permeability coefficient k and the soil quality distribution at each position of the target ground 1 are estimated using the injection units 3a to 3g for the chemical solution 5 described above.

[0048] Specifically, first, a safe injection pressure p fh lower than the theoretical limit injection pressure p fh based on the design value is set. max is set.

[0049] The limit injection pressure p fh is the effective injection pressure indicating the limit of the region (penetration injection region) where the effective injection pressure also increases in proportion to the injection rate q as shown in Fig. 5, and theoretically, fracturing occurs when the limit injection pressure p fh is exceeded.

[0050] Fracturing is considered a phenomenon in which the ground is locally damaged because it cannot withstand the pressure (effective injection pressure) acting on the injection ports 4a to 4f. From the formula of the hydraulic fracturing phenomenon, the limit injection pressure p fh can be expressed by the following formula.

[0051]

Equation

[0052] Here, p0 is the vertical total stress, σ t is the tensile strength of the soil, and m is a coefficient depending on the fracturing situation, etc., and is set to a value of about 1 to 2.

[0053] The limit injection pressure p fh ​​​​The following pressure levels are considered to be the safety osmosis injection pressure p. max We define it as follows:

[0054]

number

[0055] Safe infiltration injection pressure p max For safety reasons, in equation 1, tensile strength was ignored, and m=1 was assumed to be the only resistance to splitting due to the total vertical stress. Furthermore, considering the uncertainty of the soil properties, a coefficient β was multiplied to correct the total vertical stress.

[0056] The coefficient β can be set, for example, by the difference between the unit weight of soil in the design and the actual unit weight of soil.

[0057] Specifically, before the injection of chemical solution 5, on-site soil samples are collected by boring for mix design testing. From at least one of these collected boring cores, an undisturbed sample is taken from the boring core down to the deepest point of the improvement depth.

[0058] Then, a wet density test was conducted for the entire depth, and the measured wet density ρ obtained from this test was... t From unit volume weight γ t_test Calculate this value and the unit weight γ in the design t_plan Based on this difference, we define the UI (Uncertainty Index) as an index representing the uncertainty of the physical properties of the ground, and set a coefficient β according to the UI.

[0059]

number

[0060] Furthermore, the unit weight γ of the design t_plan If not given, the design unit weight γ t_plan and the measured unit weight γ t_test Let us assume that these two things are in agreement.

[0061] Next, the safe infiltration injection pressure p max Once set, the safe infiltration injection pressure p is set as shown in Figure 4. max The following range (pressure level) is used to measure the change in injection pressure at regular intervals when water is injected into the target ground 1 at a constant injection rate from any injection port 4a to 4f of multiple injection units 3a to 3g, or the change in injection rate at regular intervals when water is injected into the target ground 1 at a constant injection pressure. The permeability coefficient k around any injection port 4a to 4f is then calculated from the relationship between the measured injection pressure p and injection rate q (hereinafter referred to as the permeability test).

[0062] Furthermore, the injection pressure p and injection speed q can be measured by measuring the pump pressure and supply speed when supplying water to the injection units 3a to 3g (chemical injection bodies 11) through the supply pipe 15.

[0063] In that case, the permeability test is performed at a safe infiltration injection pressure p max Since the tests are conducted at the following pressure levels, ground failure due to splitting will not occur, allowing for safe testing.

[0064] The theoretically optimal injection rate can be expressed by the following equation, based on the Maag equation, assuming that drug solution 5 is injected in a spherical infiltration manner: The relationship between effective injection pressure and injection rate is as follows.

[0065]

number

[0066] Here, k is the permeability coefficient of the ground, r1 is the radius of the insertion hole, and μ L The viscosity coefficient of the injection material is μ W is the viscosity coefficient of water.

[0067] Therefore, the permeability coefficient can be calculated using the following formula.

number

[0068] While the permeability test can be performed at each inlet 4a to 4f of all injection units 3a to 3g, it is desirable to conduct it within a limited construction period, within a timeframe that does not affect the main construction work. Therefore, it is preferable to clearly define the purpose of the permeability test and limit the locations where it is performed accordingly.

[0069] Furthermore, in the permeability solidification treatment method, the permeability coefficient is 1 × 10 -6 Since it is considered necessary to examine the applicability of the construction method to ground with a permeability coefficient of k = 1 × 10 -6 Using m / s as a threshold, attention must be paid to ground with a permeability coefficient below this threshold.

[0070] For example, if it is suspected that a portion of the clay layer Ac beneath the sandy soil layer Bs shown in Figure 6(b) is thick, then a permeability test is conducted in Figure 4, focusing on injection ports 4a to 4d located near the clay layer Ac, with the aim of understanding the distribution of the clay layer Ac within the improved layer.

[0071] Furthermore, in terms of planar dimensions, the reliability of the ground information is considered to decrease the further away it is from the location of the borehole 6. For example, in Figure 2, a permeability test is first performed on the injection unit 3d near the center of the locations of both boreholes 6, 6, starting from the lowest injection port 4a, and the permeability coefficient k = 1 × 10 -6 We will monitor whether ground conditions with a subsurface depth of m / s or less are detected.

[0072] Next, a permeability test is performed on injection unit 3d and injection unit 3b or 3c near the center of the borehole 6, in that order, and this is repeated until the interval between the positions where the permeability tests are performed reaches a predetermined interval (for example, the pitch between injection units or a fixed distance of 10m).

[0073] Furthermore, among the inlets where the permeability test was performed, the threshold permeability coefficient k = 1 × 10 -6 If an injection port is confirmed to have a permeability of m / s or less, a permeability test will also be conducted on the injection unit located near the midpoint between that port and its adjacent points.

[0074] Then, by conducting permeability tests at arbitrary injection ports 4a to 4f in multiple injection units 3a to 3g, the permeability coefficients around the injection ports 4a to 4f that underwent the permeability tests are calculated, as shown in Figures 1 and 4. From these calculated permeability coefficients, the three-dimensional soil distribution of the target ground 1 can be estimated, and it can be determined whether the area around the injection ports 4a to 4f is suitable for the seepage solidification treatment method, i.e., the permeability coefficient is k = 1 × 10⁻⁶. -6 It can be determined whether the ground pressure is greater than m / s.

[0075] Next, a critical injection velocity test is conducted based on the calculated permeability coefficient and estimated soil distribution to determine the critical injection velocity.

[0076] This limit injection velocity test can be performed using a well-known, existing method. Since the permeability coefficient and soil distribution at the location where the limit injection velocity test is to be performed are known through permeability tests, if the calculated permeability coefficient around any injection port 4a to 4f is below a predetermined value, the test using that injection port 4a to 4f is stopped. This allows the test to be conducted safely by avoiding clay layers such as Ac, which are not suitable for the infiltration solidification treatment method.

[0077] Then, once the critical injection rate is determined, the injection conditions at each injection port 4a to 4f are set based on the calculated permeability coefficient and estimated soil distribution, and the injection of chemical solution 5 is carried out. In the following explanation, the symbols for each injection port will be shown in combination with the respective injection units 3a to 3g as appropriate. For example, injection port 4a of injection unit 3a will be written as injection port 3a4a.

[0078] Specifically, the surrounding permeability coefficient k is a predetermined value (for example, permeability coefficient = 1 × 10⁻⁶). -6 For injection ports 3b4a, 3c4a, 3c4b, 3d4a, 3d4b, 3e4a, 3f4a with a displacement of m / s or less, the control displacement during chemical injection (e.g., ground uplift) is set as the control value, and the safe seepage injection pressure P max The drug solution 5 is injected at a rate less than the control value and at the lower limit of the injection device's capacity, and the injection is immediately stopped when the control value is exceeded.

[0079] In this case, if the injection volume falls short of the design value, injection will not be stopped from the injection port 3b4a, 3c4a, 3c4b, 3d4a, 3d4b, 3e4a, 3f4a, but will be compensated for by adjusting the injection volume of the drug solution from the adjacent injection ports 3a4a, 3b4b, 3c4c, 3d4c, 3e4b, 3f4b, 3g4a.

[0080] The injection of the drug solution from adjacent inlets 3a4a, 3b4b, 3c4c, 3d4c, 3e4b, 3f4b, and 3g4a shall be carried out at the injection rate q obtained in the limit injection rate test conducted in advance. If the aforementioned control value is exceeded, the injection shall be stopped immediately.

[0081] Furthermore, the surrounding permeability coefficient k is a predetermined value (for example, permeability coefficient = 1 × 10⁻⁶). -6 In injection work on soil areas with a density of m / s or less, the pitch of the lower injection ports 4a-4d, which are inserted close to the clay layer Ac, is narrower than the pitch between the upper injection ports 4d-4e and 4e-4f. This allows for precise control of the chemical injection in accordance with the actual soil distribution.

[0082] On the other hand, the surrounding permeability coefficient k is a predetermined value (for example, permeability coefficient = 1 × 10⁻⁶). -6 Chemical injection operations from inlet sizes larger than m / s can be efficiently performed using the injection rate q obtained from a prior limit injection rate test.

[0083] The infiltration solidification treatment method configured in this way requires a safe infiltration injection pressure p before the limit injection rate test and the injection of chemical solution 5. max By conducting permeability tests at the following pressure levels and understanding the detailed permeability coefficients and soil distribution of each layer of the target ground 1, the risk of ground uplift due to cracking injection can be reduced.

[0084] Furthermore, the permeation solidification treatment method according to the present invention is not limited to the case of vertical drilling described above, but can also be applied to other drilling methods such as oblique drilling, horizontal drilling, and curved drilling.

[0085] Furthermore, the configuration of the injection unit is not limited to the embodiments described above. For example, the axial pitch of the injection port may be uniform, and any injection unit compatible with the infiltration solidification treatment method can be used. [Explanation of Symbols]

[0086] 1. Target ground 2 Insertion holes 3 Injection Unit 4a~4h Inlet 5. Chemical solution 10 Injection tube 11 Drug injection unit 12 Sleeve Packers 13 Outlet 14 Double Packer 15 Supply pipe

Claims

1. In a permeable solidification treatment method in which an injection unit is inserted into multiple insertion holes formed in the target ground, and a chemical solution is injected into the target ground from multiple injection ports formed on the outer surface of each injection unit, Based on the theoretical limit infiltration injection pressure using design values, a safe infiltration injection pressure lower than the limit infiltration injection pressure is set. The change in injection pressure at regular intervals when water is injected into the target ground at a constant injection rate from any injection port of multiple injection units within a range below the safe seepage injection pressure, or the change in injection rate at regular intervals when water is injected into the target ground at a constant injection pressure, is measured. The permeability coefficient around the arbitrary injection port is calculated from the relationship between the measured injection pressure and injection speed, and the soil distribution is estimated based on the said permeability coefficient. The infiltration solidification treatment method is characterized by subsequently performing the injection of the chemical solution based on the permeability coefficient and the estimated soil distribution.

2. The infiltration solidification treatment method according to claim 1, wherein the injection unit has multiple injection ports spaced apart in the axial direction, and the pitch between the injection ports in the axial direction is set to be narrower on the side closer to the clay layer.

3. The permeability coefficient around the aforementioned arbitrary injection port is calculated, a limit injection velocity test is performed based on the permeability coefficient and the estimated soil distribution, and the chemical solution is injected from the injection port at the determined limit injection velocity, according to claim 1 or 2.

4. The permeable solidification treatment method according to claim 1 or 2, wherein if the permeability coefficient around the aforementioned arbitrary inlet is less than or equal to a predetermined value, the injection of the chemical solution from the arbitrary inlet is stopped.

5. The permeable solidification treatment method according to claim 1 or 2, wherein if the permeability coefficient around the arbitrary inlet is less than or equal to a predetermined value, the chemical solution is injected from the arbitrary inlet at a pressure less than the safe permeable injection pressure.

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