Method for estimating soil-cement strength

Abstract

To provide a strength estimation method of soil cement with which strength estimation is possible without securing curing period until the soil cement hardens.SOLUTION: A strength estimation method of soil cement includes a process to measure moisture content of the unconsolidated sample by drying an unconsolidated sample of soil cement formed by mixing cement milk and in situ soil, a process of pulverizing the dried unconsolidated sample and measuring the content of predetermined element in the unconsolidated sample using fluorescent X-ray analyzer, a process to calculate content of given element in unconsolidated sample using predetermined element content of the unconsolidated sample and predetermined element content of the in-situ soil, a process to calculate effective cement-water ratio of the unconsolidated sample using water content of the unconsolidated sample and cement content calculated from the content of predetermined element in the cement and a process of estimating compressive strength of the soil cement from the correlation data between the effective cement water ratio and the compressive strength.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for estimating soil-cement strength. [Background technology]

[0002] The following Patent Document 1 describes a method for collecting pile hole filling material, in which a root-hardening liquid is injected into a pile hole and soil cement mixed with the root-hardening liquid and muddy water is collected in an unconsolidated state. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-59619 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the method for collecting pile-hole fillers described in the above-mentioned Patent Document 1, the pile-hole fillers are pulled up to the ground and hardened, and then a compressive strength test is conducted to confirm the strength of the base-hardening portion. With this method, it is difficult to proceed with the construction of the piles during the curing period until the pile-hole fillers pulled up to the ground harden. This lengthens the construction period.

[0005] In addition, if the compressive strength test is not performed, the injection rate of the root protection liquid (amount of root protection liquid injected / amount of root protection excavated) is set large enough to ensure the strength of the root protection part. In such a case, the material cost increases.

[0006] In consideration of the above, an object of the present invention is to provide a method for estimating the strength of soil cement that can estimate the strength of soil cement without requiring a curing period until the soil cement hardens. [Means for solving the problem]

[0007] The method for estimating soil cement strength according to claim 1 includes drying an unconsolidated sample of soil cement formed by mixing cement milk and on-site generated soil, measuring the water content of the unconsolidated sample, and Calculate the moisture content and crushing the dried unconsolidated sample and measuring the content of a predetermined element in the unconsolidated sample using an X-ray fluorescence analyzer. and calculate the concentration of a given element And a process of calculating a mass ratio of cement to soil particles in the unconsolidated sample from a predetermined element concentration in the cement contained in the unconsolidated sample, a predetermined element concentration in the on-site generated soil contained in the unconsolidated sample, and the predetermined element concentration; The above From the water content, the concentration of the predetermined element, the concentration of the predetermined element in the cement contained in the unconsolidated sample, the concentration of the predetermined element in the on-site generated soil contained in the unconsolidated sample, and the mass ratio, The method includes a step of calculating an effective cement-water ratio of the unconsolidated sample, and a step of estimating the compressive strength of the soil-cement from correlation data between the effective cement-water ratio and compressive strength.

[0008] The strength of soil cement can be estimated from the correlation data between the effective cement-water ratio (C / We) and compressive strength, if the cement and water content contained in the soil cement are known.

[0009] However, soil cement is formed by mixing cement milk (a mixture of cement and water) with soil generated at the site, and it is difficult to grasp the mixture ratio of these two, so it is also difficult to grasp the cement content of the soil cement.

[0010] Here, cement and on-site generated soil each contain various elements. If it is possible to focus on a specific element (a specific element, such as calcium) among these various elements and grasp the content of the specific element in the soil cement and the on-site generated soil, it is possible to calculate the content of cement that constitutes the soil cement.

[0011] Therefore, in the soil cement strength estimation method of claim 1, the content of a specific element in an unconsolidated sample of soil cement is measured using an X-ray fluorescence analyzer. At this time, the unconsolidated sample is dried and crushed, so that the cement component and the on-site generated soil component are mixed uniformly, and the content of the specific element can be measured with high accuracy.

[0012] Then, the measured content of the specified element in the unconsolidated sample and the content of the specified element in the soil generated at the site are used to calculate the content of the specified element in the cement that constitutes the unconsolidated sample.

[0013] Since the content of a specific element in cement is known, the content of this specific element can be determined to determine the cement content in an unconsolidated sample.

[0014] In addition, in the soil cement strength estimation method of this embodiment, the unconsolidated sample is dried and the water content (We [g]) of the unconsolidated sample is measured, whereby the effective cement-water ratio (C / We), which is the weight ratio of cement to water in the unconsolidated sample, can be calculated.

[0015] The compressive strength of the soil cement is then estimated from the data on the effective cement-water ratio (C / We) and the compressive strength of the sample. This makes it possible to estimate the strength of the soil cement by drying and crushing the soil cement and measuring the content of certain elements without having to wait for a curing period until the soil cement hardens. The soil cement strength estimating method of claim 2 is the soil cement strength estimating method of claim 1, wherein the effective cement-water ratio is R, and the effective cement-water ratio R is calculated using the following formula (A) where ω is the water content, Ca is the predetermined element concentration in the unconsolidated sample, Ca(c) is the predetermined element concentration in the cement contained in the unconsolidated sample, Ca(s) is the predetermined element concentration in the on-site generated soil contained in the unconsolidated sample, and α is the mass ratio of cement to soil particles in the unconsolidated sample. R=Ca / {[α·Ca(s)+Ca(c)]·ω} ···(A) A soil cement strength estimating method according to claim 3 is the soil cement strength estimating method according to claim 2, in which the water content ω is expressed by the following formula (B), where W is the water content contained in the cement constituting the unconsolidated sample, Sw is the water content contained in the soil constituting the unconsolidated sample, C is the dry cement content contained in the unconsolidated sample, and S is the dry soil content contained in the unconsolidated sample. ω = (W + Sw) / (C + S) (B) The soil cement strength estimating method of claim 4 is the soil cement strength estimating method of claim 2, in which the predetermined element concentration Ca of the unconsolidated sample is expressed using the following formula (C), where Cca is the predetermined element content in the cement contained in the unconsolidated sample, Sca is the predetermined element content in the soil contained in the unconsolidated sample, C is the dry cement content in the unconsolidated sample, and S is the dry soil content in the unconsolidated sample. Ca = (Cca + Sca) / (C + S) (C) A soil-cement strength estimating method according to claim 5 is the soil-cement strength estimating method according to claim 2, wherein the mass ratio α is calculated using the following formula (D). α=[Ca(c)-Ca] / [Ca-Ca(s)] ···(D) A soil cement strength estimation method according to claim 6 is the soil cement strength estimation method according to claim 1, wherein the effective cement-water ratio is R, and the effective cement-water ratio R is calculated using the following formula (A) where ω is the water content, Ca is the predetermined element concentration of the unconsolidated sample, Ca(c) is the predetermined element concentration in the cement contained in the unconsolidated sample, Ca(s) is the predetermined element concentration in the on-site generated soil contained in the unconsolidated sample, and α is the mass ratio of cement to soil particles in the unconsolidated sample, and the water content ω is the mass ratio of the soil particles constituting the unconsolidated sample. The water content in the cement contained in the unconsolidated sample is represented by W, the water content in the soil constituting the unconsolidated sample is represented by Sw, the dry cement content in the unconsolidated sample is represented by C, and the dry soil content in the unconsolidated sample is represented by S, and the specified element concentration Ca of the unconsolidated sample is represented by the following formula (C) where the specified element content in the cement contained in the unconsolidated sample is represented by Cca, and the specified element content in the soil contained in the unconsolidated sample is represented by Sca, and the mass ratio α is calculated by the following formula (D). R=Ca / {[α·Ca(s)+Ca(c)]·ω} ···(A) ω = (W + Sw) / (C + S) (B) Ca = (Cca + Sca) / (C + S) (C) α=[Ca(c)-Ca] / [Ca-Ca(s)] ···(D)

[0016] Claim 7 The method for estimating the strength of soil cement according to claim 1 Any one of ~6 In the soil cement strength estimation method described above, the soil cement forms a base reinforcement portion of a pile hole.

[0017] Claim 7 The soil cement strength estimation method described above can estimate the strength of the soil cement forming the base of the pile hole. Therefore, the bearing capacity of the pile can be quickly confirmed.

[0018] Claim 8 The method for estimating the strength of soil cement according to claim 1 Any one of ~7 In the soil cement strength estimation method described above, the content of a specified element in the on-site generated soil is measured by crushing the dried on-site generated soil and using an X-ray fluorescence analyzer.

[0019] Claim 8 In the soil cement strength estimation method, the content of a specific element in the on-site generated soil is measured by drying and crushing the soil and using an X-ray fluorescence analyzer. This allows the content of a specific element in the on-site generated soil to be measured with high accuracy. Effect of the Invention

[0020] According to the present invention, the strength of soil cement can be estimated without ensuring a curing period until the soil cement hardens. [Brief description of the drawings]

[0021] [Figure 1] (A) is an elevational section showing the state of forming a pile hole in which a precast pile to which the soil cement strength estimation method of the present invention is applied is buried, (B) is an elevational section showing the state of forming a foot protection portion in the pile hole, (C) is an elevational section showing the state of pulling up the drilling rod from the pile hole, and (D) is an elevational section showing the state of inserting a precast pile into the pile hole. [Diagram 2] FIG. 1 is a conceptual diagram showing the components of soil cement. [Diagram 3] 1 is a graph showing correlation data between effective cement-water ratio (C / We) and compressive strength of soil cement. [Figure 4] FIG. 1 is a conceptual diagram showing the components of soil cement in a dry state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, a soil cement strength estimation method according to an embodiment of the present invention will be described with reference to the drawings. Components indicated by the same reference numerals in each drawing are the same components. However, unless otherwise specified in the specification, each component is not limited to one, and may be present in multiple numbers. In addition, explanations of configurations and reference numerals that are duplicated in each drawing may be omitted. Note that the present invention is not limited to the following embodiments, and may be implemented by making appropriate modifications, such as omitting a configuration or replacing it with a different configuration, within the scope of the purpose of the present invention.

[0023] <Pile construction method> The soil cement strength estimation method according to the embodiment of the present invention is used for the soil cement forming the base of a pile, as an example. Therefore, prior to the explanation of the soil cement strength estimation method, an outline of a pile construction method using the soil cement for estimating strength will be explained.

[0024] 1(A) to 1(D) show an example of a method for embedding a precast pile 10 in ground G by an embedding method. The precast pile 10 shown in Fig. 1(D) is a concrete pile that is cast in advance in a factory or the like and then transported to a construction site.

[0025] In order to bury the precast pile 10 in the ground G, first, as shown in Fig. 1 (A), the ground G is excavated while injecting drilling fluid using a drilling rod 20 to form a pile hole GH. In this embodiment, in order to make the precast pile 10 a tip-support pile, the tip of the pile hole GH is made to reach the supporting layer GA.

[0026] Next, as shown in FIG. 1(B), cement milk is injected from the drilling rod 20 to the tip (bottom) of the pile hole GH. By stirring this cement milk, it is mixed with the soil in the ground G to form the soil cement 12 that forms the foot protection part.

[0027] Cement milk is formed by mixing cement and water, or by mixing cement, water and various additives. Soil cement is a mixture of cement milk and soil. In this specification, the mixture of minerals, organic matter, gas, liquid, and living organisms that form the "ground G" is called "soil".

[0028] At the tip of the pile hole GH, it is preferable to form a root-stabilizing bulb 12A, which is a portion where the diameter of the pile hole GH is expanded and filled with soil cement 12. When forming the root-stabilizing bulb 12A, the drilling head of the drilling rod 20 is made to have a known structure capable of expanding the diameter. Then, the drilling head is expanded at a predetermined depth to form the root-stabilizing bulb 12A.

[0029] Next, as shown in Fig. 1(C), while the drilling rod 20 is being withdrawn, cement milk is injected and stirred above the soil cement 12. This forms soil cement 14 as a fixing liquid around the pile. The soil cement 14 may be formed using lean cement milk that has a smaller amount of cement per unit volume compared to the soil cement 12.

[0030] Next, as shown in FIG. 1(D), the prefabricated pile 10 is inserted into the pile hole GH. At this time, the tip of the prefabricated pile 10 is depressed into the root-hardening bulb 12A at the tip of the pile hole GH. As a result, the prefabricated pile 10 is buried in the ground G.

[0031] <Pile strength estimation method> The soil cement strength estimation method according to the embodiment of the present invention is a method for estimating the strength of soil cement 12, which is the base protection portion of a precast pile 10, for example, after hardening.

[0032] The reason for estimating the strength of the soil cement 12 after solidification is that the bearing capacity of the precast pile 10 is affected by the strength of the soil cement 12. Specifically, the soil cement 12 integrates the tip portion of the precast pile 10 with the bearing layer GA, and resists the pressing force acting on the precast pile 10. For this reason, when evaluating the bearing capacity of the precast pile 10, it is preferable to estimate the strength of the soil cement 12 in addition to the strength of the precast pile 10 itself.

[0033] Furthermore, "estimating" the strength of the soil cement 12 after it has solidified means evaluating the strength of the soil cement 12 before it has solidified. In this case, compared to "measuring" the strength of the soil cement 12 after it has solidified, there is no need to secure a curing period until the soil cement 12 has solidified. This makes it possible to shorten the construction period.

[0034] In this embodiment, the soil cement for estimating the strength does not have to be that used for permanent piles, and may be soil cement with approximately the same composition as that used for permanent piles.

[0035] In this case, a temporary pile hole is drilled on the same site as the site where the precast pile 10 as the permanent pile will be installed, and cement milk is injected and stirred. This makes it possible to form soil cement with approximately the same composition as the soil cement 12 used for the permanent pile. "Approximately the same" means, for example, that the mixture ratio of cement and soil is approximately the same.

[0036] In addition, the soil cement for which the strength is estimated in this embodiment does not necessarily have to be used in the base of the pile, and may be used in a portion other than the base of the pile. Furthermore, the soil cement may be used in a ground improvement body. In the following explanation, a method for estimating the strength of soil cement in general, including the soil cement 12 used in the permanent pile, will be explained.

[0037] (Outline of soil-cement strength estimation method) As shown in Figure 2, the cement milk that forms the soil cement is formed by mixing, for example, C[g] of cement and W[g] of water. The on-site generated soil that is mixed with the cement milk contains S[g] of soil particles (in a dry state) and Sw[g] of water.

[0038] The strength of soil cement can be estimated from the correlation data between the effective cement-water ratio (C / We) and compressive strength, if the cement content (C[g]) and water content (We=W+Sw[g]) in the soil cement are known. Effective cement-water ratio (C / We) and compressive strength (uniaxial compressive strength qu[N / mm 2 ]) can be obtained as known information, for example as shown in FIG.

[0039] In Figure 3, the unconfined compressive strengths of multiple samples with various effective cement-water ratios (C / We) are plotted. These plotted points are shown as an approximation line C1, which is a linear approximation of the plotted points. The unconfined compressive strengths corresponding to the effective cement-water ratios of the samples are derived in a one-to-one correspondence from the approximation line C1.

[0040] However, since it is difficult to grasp the mixing ratio of cement milk and on-site generated soil in soil cement, it is also difficult to grasp the cement content C [g] in the soil cement.

[0041] Here, both the cement and the on-site generated soil contain calcium. If the calcium content of the soil cement and the on-site generated soil can be ascertained, the cement content and effective cement-water ratio (C / We) constituting the soil cement can be calculated by the method shown below. Note that calcium is an example of a specified element in the present invention. The "specified element" used in the present invention may be any element that is contained in cement, such as calcium.

[0042] (Calcium concentration of cement) The calcium concentration Ca(c) [ppm] of the cement used in soil cement is known information. For example, as shown in Figure 4, the calcium content Cca in cement C [g] is expressed by the following formula (1). The calcium concentration of cement may be measured using an X-ray fluorescence analyzer.

[0043] Cca = C·Ca(c) ···(1)

[0044] (Preliminary survey - sample collection) In order to estimate the strength of soil cement, a preliminary investigation is carried out. As an example of the preliminary investigation, first, a sample of on-site generated soil is collected from the ground (for example, ground G shown in FIG. 1). It is preferable to collect the sample in conjunction with a boring test for a ground investigation. This sample is, for example, the on-site generated soil (hereinafter sometimes referred to as "soil sample") that forms the bearing layer GA shown in FIG. 1, and contains S[g] soil particles (in a dry state) and Sw[g] water, as shown in FIG. 2.

[0045] (Preliminary survey - Measurement of calcium content in on-site soil) Next, the collected soil sample is dried and crushed. Any equipment such as a microwave oven can be used to dry the soil sample. A mill or the like can be used to crush the soil sample.

[0046] Next, the calcium concentration in the dried and crushed soil sample (soil particles) is measured using an X-ray fluorescence analyzer. When the calcium concentration in the soil particles (in a dry state) is measured as Ca(s) [ppm] as shown in Figure 4, the calcium content Sca in the soil particles (in a dry state) of S [g] is expressed by the following formula (2).

[0047] Sca = S·Ca(s) ··· (2)

[0048] (Measurement of water content of soil cement) Next, for example, the cement milk and the on-site generated soil are mixed inside the pile hole GH shown in Figure 1 to form soil cement. The unconsolidated soil cement is then collected as an unconsolidated sample and its weight is measured. The weight W1 of the unconsolidated sample is expressed as C+S+W+Sw [g], which is the total weight of the cement milk and the on-site generated soil, as shown in Figure 2 and formula (3-1).

[0049] W1 = C + S + W + Sw (3-1)

[0050] Next, the collected unconsolidated sample is dried and pulverized. As with soil samples, any equipment such as a microwave oven can be used to dry the unconsolidated sample. A mill or the like can be used to pulverize the unconsolidated sample. The time required for drying, pulverization, and calcium measurement using a microwave oven or the like is approximately 1 hour, which is sufficiently short compared to the time required for testing and curing the specimen for the uniaxial compression test (approximately 3 to 7 days).

[0051] Then, measure the weight of the dried unconsolidated sample (i.e., the soil-cement in a dry state). The weight of the dry soil-cement, W2, is expressed as C+S [g], which is the total weight of the cement and soil particles (in a dry state) in the unconsolidated sample, as shown in Figure 2 and the following formula (3-2).

[0052] W2 = C + S (3-2)

[0053] Here, the value W3 calculated from the difference between the weight W1 of the unconsolidated sample and the weight W2 of the dry soil-cement indicates the moisture content W+Sw (=We) [g] of the unconsolidated sample, as shown in Figure 2 and the following equation (3-3).

[0054] In addition, the "step of measuring the moisture content of the unconsolidated sample" in the present invention includes measuring the weight W1 of the unconsolidated sample and the weight W2 of the dry soil cement, and calculating the moisture content W3 of the unconsolidated sample.

[0055] W3 = W + Sw (3-3)

[0056] From the above formulas (3-1) to (3-3), the water content ω of the unconsolidated sample is calculated as shown in the following formula (3).

[0057] ω=W3 / W2=(W+Sw) / (C+S) ···(3)

[0058] (Measurement of calcium content in soil cement) Next, the calcium concentration in the dried and crushed unconsolidated sample (i.e., dry soil cement) is measured using an X-ray fluorescence analyzer. Since the unconsolidated sample is dried and crushed, the cement component and the on-site generated soil component are mixed uniformly, allowing the calcium content to be measured with high accuracy.

[0059] As shown in Figure 4, when the calcium concentration of soil cement (dry state) is measured as Ca [ppm], the calcium content Cca+Sca in this soil cement (dry state) is expressed by the following equation (4).

[0060] Cca+Sca=(C+S)·Ca·(4)

[0061] (Mass ratio of cement to soil particles (dry state) in soil cement) As shown in FIG. 4, if the mass ratio C:S of cement to soil particles (in a dry state) in soil cement is 1:α, then this coefficient α (hereinafter referred to as the mass ratio α) is expressed by the following equation (5-1).

[0062] α = S / C (5-1)

[0063] In addition, the calcium concentration Ca in soil cement is expressed by the following equation (5-2) from equations (1), (2), and (4).

[0064] Ca=[C·Ca(c)+S·Ca(s)] / (C+S) ···(5-2)

[0065] From these equations (5-1) and (5-2), the mass ratio α is calculated as shown in the following equation (5).

[0066] α=[Ca(c)-Ca] / [Ca-Ca(s)] ···(5)

[0067] Furthermore, using the above formulas (1) to (5), the cement content constituting the soil cement and the available water-cement ratio (C / We) are calculated as shown in the following formula (6).

[0068] C / We=Ca / {[α·Ca(s)+Ca(c)]·ω} ···(6)

[0069] (Estimation of soil-cement strength) Next, the soil cement strength (unconfined compressive strength) is estimated from the correlation data between the effective water-cement ratio (C / We) and compressive strength shown in Figure 3. Specifically, the unconfined compressive strength value corresponding to the calculated effective water-cement ratio (C / We) on the approximation line C1 is estimated as the soil cement strength. This allows the unconfined compressive strength of the unconsolidated soil cement sample to be estimated when it has solidified.

[0070] In this way, according to the soil cement strength estimation method of this embodiment, the strength can be estimated without ensuring the curing period until the soil cement hardens.

[0071] In addition, the amount of cement milk injected into the foot protection section can be reduced compared to the case where the strength of the foot protection section is ensured by sufficiently increasing the injection rate of cement milk (amount of cement milk injected / for example, amount of excavation of the foot protection section), while omitting the compressive strength test. This allows for reduction in material costs. [Explanation of symbols]

[0072] 12 Soil Cement

Claims

1. A step of drying an unconsolidated sample of soil cement formed by mixing the cement milk and the on-site generated soil, measuring the water content of the unconsolidated sample, and calculating the water content ratio; a step of crushing the dried unconsolidated sample, measuring the content of a predetermined element in the unconsolidated sample using an X-ray fluorescence analyzer, and calculating a concentration of the predetermined element; calculating a mass ratio of cement to soil particles in the unconsolidated sample from a predetermined element concentration in the cement contained in the unconsolidated sample, a predetermined element concentration in the on-site generated soil contained in the unconsolidated sample, and the predetermined element concentration; From the water content, the concentration of the predetermined element, the concentration of the predetermined element in the cement contained in the unconsolidated sample, the concentration of the predetermined element in the on-site generated soil contained in the unconsolidated sample, and the mass ratio, Calculating the effective cement-water ratio of the unconsolidated sample; A step of estimating the compressive strength of the soil cement from correlation data between the effective cement-water ratio and compressive strength; A method for estimating soil-cement strength comprising:

2. If the effective cement-water ratio is R, the effective cement-water ratio R is: The water content ratio is ω, The concentration of the predetermined element in the unconsolidated sample is Ca, The concentration of a given element in the cement contained in the unconsolidated sample is Ca(c), The concentration of a given element in the on-site generated soil contained in the unconsolidated sample is Ca(s), The mass ratio of cement to soil particles in the unconsolidated sample is α, Calculate using the following formula (A): A method for estimating soil cement strength as claimed in claim 1. R=Ca / {[α・Ca(s)+Ca(c)]・ω} ...(A)

3. The water content ratio ω is The content of water contained in the cement constituting the unconsolidated sample is W, The water content in the soil constituting the unconsolidated sample is Sw, The content of dry cement in the unconsolidated sample is C; The content of dry soil in the unconsolidated sample is defined as S, Represented by the following formula (B): A method for estimating soil cement strength according to claim 2. ω=(W+Sw) / (C+S)...(B)

4. The predetermined element concentration Ca of the unconsolidated sample is The content of a predetermined element in the cement contained in the unconsolidated sample is Cca, The content of a predetermined element in the soil contained in the unconsolidated sample is Sca, The content of dry cement in the unconsolidated sample is C; The content of dry soil in the unconsolidated sample is defined as S, Represented by the following formula (C): A method for estimating soil cement strength according to claim 2. Ca=(Cca+Sca) / (C+S)...(C)

5. The mass ratio α is Calculate using the following formula (D): A method for estimating soil cement strength according to claim 2. α=[Ca(c)-Ca] / [Ca-Ca(s)]...(D)

6. When the effective cement-water ratio is R, the effective cement-water ratio R is: The water content ratio is ω, The concentration of the predetermined element in the unconsolidated sample is Ca, The concentration of a given element in the cement contained in the unconsolidated sample is Ca(c), The concentration of a given element in the on-site generated soil contained in the unconsolidated sample is Ca(s), The mass ratio of cement to soil particles in the unconsolidated sample is α, Calculate using the following formula (A): The water content ω is The content of water contained in the cement constituting the unconsolidated sample is W, The water content in the soil constituting the unconsolidated sample is Sw, The content of dry cement in the unconsolidated sample is C; The content of dry soil in the unconsolidated sample is defined as S, It is expressed by the following formula (B): The predetermined element concentration Ca of the unconsolidated sample is The content of a predetermined element in the cement contained in the unconsolidated sample is Cca, The content of a predetermined element in the soil contained in the unconsolidated sample is defined as Sca, It is represented by the following formula (C): The mass ratio α is Calculate using the following formula (D): A method for estimating soil cement strength as claimed in claim 1. R=Ca / {[α・Ca(s)+Ca(c)]・ω} ...(A) ω=(W+Sw) / (C+S)...(B) Ca=(Cca+Sca) / (C+S)...(C) α=[Ca(c)-Ca] / [Ca-Ca(s)]...(D)

7. The soil cement strength estimation method according to any one of claims 1 to 6, wherein the soil cement forms a base fixing portion of a pile hole.

8. The soil cement strength estimation method according to any one of claims 1 to 7, wherein the content of the predetermined element in the on-site generated soil is measured by crushing the dried on-site generated soil and using an X-ray fluorescence analyzer.

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