JP7406408B2 - Pile strength estimation method - Google Patents

Description

The present invention relates to a method for estimating pile strength.

Patent Document 1 listed below describes a method for collecting pile hole filling material, in which soil cement is injected into a pile hole and soil cement mixed with the soil cement is collected in an unconsolidated state.

Japanese Patent Application Publication No. 2010-59619

In the method for collecting pile hole fillers in Patent Document 1, after the pile hole fillers are pulled up to the ground and solidified, a compressive strength test is conducted to confirm the strength of the foot protection part. With this method, it is difficult to proceed with the pile construction work during the curing period until the pile hole filler that has been brought up to the ground solidifies.

The present invention takes the above facts into consideration and aims to provide a method for estimating pile strength that can estimate the strength of soil cement in an unconsolidated state.

The method for estimating pile strength according to claim 1 includes the steps of: injecting cement milk into a pile hole; collecting an unconsolidated sample of soil cement in which the cement milk and soil are mixed from the pile hole; A step of measuring the calcium content of a consolidated sample using a fluorescent X-ray analyzer, a correlation between the measured value by the fluorescent X-ray analyzer, the calcium content derived from a plurality of samples, and the compressive strength of soil cement. and a step of estimating compressive strength when the unconsolidated sample is consolidated from the data.

In the pile strength estimation method of claim 1, the calcium content of an unconsolidated sample of soil cement collected from a pile hole is measured using a fluorescent X-ray analyzer. On the other hand, the compressive strength when an unconsolidated sample is consolidated can be estimated from correlation data between calcium content and compressive strength derived from a plurality of samples. In other words, the compressive strength of the soil cement can be estimated in an unconsolidated state.

The method for estimating pile strength according to claim 2 is the method for estimating pile strength according to claim 1, in which a soil sample is collected from the ground where the pile hole is formed and the calcium content is measured, and the calcium content of the cement sample is measured. measuring the content, calculating a theoretical value of the calcium content of the mixed sample according to the mixing ratio of the soil sample and the cement sample, and forming a plurality of the mixed samples with different mixing ratios. The unconfined compressive strength is measured, and the relationship between the theoretical value and the unconfined compressive strength is derived as the correlation data .

In the pile strength estimation method of claim 2, a correlation between calcium content and strength is derived from a sample using soil and cement milk collected from a site where a pile hole is formed. Therefore, the strength of soil cement can be estimated more accurately than when soil collected from other sites is used.

In the pile strength estimation method according to claim 3, in the pile strength estimation method according to claim 1 or 2, the calcium content of the unconsolidated sample is measured, and the measured value is determined from the mixing ratio and the theoretical value. An approximation line is created that associates the value with the theoretical value, and the compressive strength is estimated by correcting the measured value to the theoretical value using the approximation line .

Cement particles generally have a higher specific gravity than soil particles, so in an unconsolidated sample that is a mixture of soil (aggregate of soil particles) and cement (aggregate of cement particles) milk, the lower part of the unconsolidated sample is The proportion of cement on the sides is greater compared to the upper side. In such a case, when the calcium content of the unconsolidated sample is measured by irradiating fluorescent X-rays from below the unconsolidated sample, the measured calcium content is larger than the actual content.
In the pile strength estimation method of claim 3, a theoretical value of calcium content corresponding to the mixing ratio of soil and cement milk is calculated in advance. Then, the measured value obtained by the fluorescent X-ray spectrometer is corrected based on this theoretical value. This makes it possible to accurately estimate the strength of soil cement even when the sample is unconsolidated.

According to the pile strength estimation method of the present invention, the strength can be estimated in an unconsolidated state of soil cement.

(A) is an elevational sectional view showing a state in which a pile hole is formed in which a ready-made pile is buried, to which the pile strength estimation method of the present invention is applied, and (B) is a vertical sectional view showing a state in which a foot protection part is formed in the pile hole. (C) is an elevational sectional view showing the state in which the drilling rod is being pulled up from the pile hole, and (D) is an elevational sectional view showing the state in which the ready-made pile is inserted into the pile hole. It is. It is a graph showing the relationship between the calcium content of soil cement and the unconfined compressive strength derived from a preliminary investigation. FIG. 3 is a cross-sectional view showing the time of fluorescent X-ray measurement of an unconsolidated sample of soil cement collected from a pile hole. (A) is a graph plotting the correspondence between the measured value and the theoretical value of the calcium content in the unconsolidated sample, and (B) is the measurement of the calcium content in the unconsolidated sample derived from (A). This is a graph depicting the correspondence between values and theoretical values using approximate lines.

Hereinafter, a pile strength estimation method according to an embodiment of the present invention will be described with reference to the drawings. Components indicated using the same reference numerals in each drawing mean the same components. Unless otherwise specified in this specification, each component is not limited to one, and a plurality of components may exist. Furthermore, descriptions of overlapping structures and symbols in each drawing may be omitted. Note that the present invention is not limited to the following embodiments, and can be implemented with appropriate changes, such as omitting the configuration or replacing it with a different configuration, within the scope of the purpose of the present invention.

<Pile construction method>
Prior to explaining the pile strength estimation method according to the embodiment of the present invention, the outline of the pile construction method for estimating the strength according to the present invention will be explained.

FIGS. 1A to 1D show an example of a method for embedding ready-made piles 10 in the ground G using the embedding method. The ready-made pile 10 shown in FIG. 1(D) is a concrete pile, and is molded in advance in a factory or the like and then transported to a construction site.

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

Next, as shown in FIG. 1(B), cement milk is injected from the drilling rod 20 into the tip (bottom) of the pile hole GH. By stirring this cement milk, it is mixed with the soil in the ground G to construct soil cement 12 that forms a foot hardening section. Note that cement milk is formed by kneading cement and water, or by kneading cement, water, and various additives. Moreover, soil cement is a mixture of cement milk and soil. In this specification, the mixture of minerals, organic substances, gases, liquids, living organisms, etc. that forms the "ground G" is referred to as "soil."

It is preferable that the diameter of the pile hole GH is expanded and a hardening bulb 12A, which is a portion filled with soil cement 12, is formed at the tip of the pile hole GH. In addition, when forming the hardening bulb 12A, the excavation head of the excavation rod 20 has a known structure that can be expanded in diameter. Then, by expanding the diameter of the excavation head at a predetermined depth, the root hardening bulb 12A is formed.

Next, as shown in FIG. 1(C), cement milk is injected and stirred above the soil cement 12 while pulling out the drilling rod 20. This forms soil cement 14 as a pile circumference fixing fluid. Soil cement 14 may be formed using poorly blended cement milk that has a smaller amount of cement per unit volume than soil cement 12.

Next, as shown in FIG. 1(D), the ready-made pile 10 is inserted into the pile hole GH. At this time, the tip of the ready-made pile 10 is invaginated into the root hardening bulb 12A at the tip of the pile hole GH. Thereby, the ready-made pile 10 is buried in the ground G.

<Pile strength estimation method>
The pile strength estimation method according to the embodiment of the present invention is a method of estimating the strength of the soil cement 12, which is the hardening part of the ready-made pile 10, after solidification, rather than the strength of the ready-made pile 10 itself.

The reason for estimating the strength of the soil cement 12 after solidification is that the bearing capacity of the ready-made pile 10 is affected by the strength of the soil cement 12. Specifically, the soil cement 12 integrates the tip portion of the ready-made pile 10 and the support layer GA, and resists the pushing force acting on the ready-made pile 10. Therefore, when evaluating the bearing capacity of the ready-made pile 10, it is preferable to estimate not only the strength of the ready-made pile 10 itself but also the strength of the soil cement 12.

Moreover, "estimate" the strength of the soil cement 12 after consolidation means to evaluate the strength of the soil cement 12 after consolidation "before consolidation." Thereby, the time can be shortened compared to "measuring" the strength of the soil cement 12 after solidification.

(Preliminary investigation - sample collection)
In order to estimate the strength of the soil cement 12, a preliminary investigation is conducted. As an example of the preliminary investigation, first, a plurality of samples are collected from the ground G prior to forming the pile hole GH. Preferably, sample collection is performed in conjunction with a boring test for soil investigation. This sample is soil that forms the support layer GA (hereinafter sometimes referred to as "soil sample").

(Preliminary investigation - measurement of calcium content)
Next, the calcium content in the plurality of collected soil samples is measured using a fluorescent X-ray analyzer. The calcium content is shown, for example, by the weight of calcium (mass percent concentration: [wt%]) in the total weight per unit volume of the sample. Here, the calcium content of the soil sample is expressed as Ws [%].

In addition, using a fluorescent X-ray analyzer, the calcium content in the cement milk (cement milk that is not mixed with soil) that forms the soil cement 12 is measured (hereinafter, the cement milk to be measured is referred to as "cement milk"). (sometimes referred to as "sample"). Here, the calcium content of the cement sample is expressed as Wc [%].

(Preliminary investigation - Calculation of calcium content)
By measuring the calcium content Wc [%] of the cement sample and the calcium content Ws [%] of the soil sample, the calcium content of soil cement formed by mixing cement milk and soil can be determined. Calculated.

For example, if the mixing ratio of cement milk and soil in soil cement is {α:(1-α)}, the calcium content in this soil cement is:
W(α)={αWc+(1-α)Ws}...Calculated as equation (1-1).

(Preliminary investigation - unconfined compressive strength test)
Next, cement milk and soil are mixed in a predetermined ratio to form soil cement. Soil cement is made by forming multiple types of cement milk and soil with different mixing ratios. After these soil cements are solidified, an unconfined compressive strength test is conducted to measure the unconfined compressive strength (hereinafter, the solidified soil cement to be measured may be referred to as a "mixed sample").

Here, the calcium content in each mixed sample is calculated by equation (1-1). Thereby, as shown in FIG. 2, the relationship between the calcium content W [%] and the unconfined compressive strength qu [kN/m ² ] of the mixed sample is derived. That is, the relationship between the calcium content of soil cement in the ground G and the unconfined compressive strength is derived. This unconfined compressive strength qu is the strength when soil cement is solidified. Further, the relationship between the calcium content W [%] of soil cement and the unconfined compressive strength qu [kN/m ² ] is expressed, for example, by an approximate straight line Cx.

In addition, in this embodiment, the calcium content of the soil sample collected from "the ground G forming the pile hole GH" is measured as a preliminary investigation, but the embodiment of the present invention is not limited to this. For example, the calcium content of a soil sample taken from the ground ``other than'' ground G that forms the pile hole GH is measured, and from this measured value, the relationship between the calcium content of soil cement in ground G and the unconfined compressive strength is determined. may be inferred.

However, in this case, soil samples are collected from various locations and the calcium content of each soil sample is measured. We will also quantitatively analyze the correlation between various soil types and calcium content. Furthermore, these measurement results and analysis results are accumulated. Using the statistical knowledge obtained from the accumulated data, we calculated the relationship between the calcium content of soil cement in ground G and the unconfined compressive strength based on the calcium content of soil samples collected from ground ``other than ground G''. relationships can be inferred.

(Collection of unconsolidated samples)
After preliminary investigation, the strength of soil cement 12 will be estimated at the main construction stage. In order to estimate the strength of the soil cement 12, an unconsolidated sample 12S (see FIG. 3) of the soil cement 12 is collected from the pile hole GH shown in FIG. 1(B). Note that the pile hole GH for collecting the unconsolidated sample 12S may be a pile hole in which a permanent pile is buried, or a pile hole in which a test pile is buried.

The collected unconsolidated sample 12S contains cement milk and the soil of the support layer GA mixed in a predetermined ratio. This ratio depends on the pile diameter of the pile hole GH, the excavation depth, the amount of drilling fluid injected into the pile hole GH, the amount of cement milk, etc., but the constructor shall know this ratio in advance. . For example, if the mixing ratio of cement milk and soil in the unconsolidated sample 12S is {α ₁ :(1−α ₁ )}, the “theoretical value” of the calcium content in the unconsolidated sample 12S is (1− 1) Using the formula,
W(α ₁ )={α ₁ Wc+(1−α ₁ )Ws} (1-2) is calculated.

(Measurement of calcium content)
The calcium content of the unconsolidated sample 12S is measured using an X-ray fluorescence spectrometer. At this time, as an example, as shown by arrow Lx in FIG. 3, X-rays are irradiated from below the unconsolidated sample 12S.

Here, as shown in FIG. 3, the distribution of components in the unconsolidated sample 12S is not uniform. Specifically, cement particles generally have a higher specific gravity than soil particles, so in an unconsolidated sample that is a mixture of soil and cement milk, the proportion of cement on the lower side of the unconsolidated sample is higher than that on the upper side. They tend to be larger in comparison. Therefore, in the unconsolidated sample 12S, the lower cement concentration is high and the upper cement concentration is low.

Therefore, for example, on the lower surface of the unconsolidated sample 12S, the mixing ratio of cement milk and soil is different from the original mixing ratio. Specifically, on the lower surface of the unconsolidated sample 12S, the mixing ratio of cement is measured to be larger than the actual ratio.

If the mixing ratio of cement milk and soil including this error is {α ₂ :(1-α ₂ )} (α ₂ >α ₁ because the mixing ratio of cement is measured to be larger than the actual value), then this unbalanced The "measured value" of the calcium content in the solidified sample 12S is calculated using the formula (1-1),
W(α ₂ )={α ₂ Wc+(1−α ₂ )Ws} (1-3).

The calcium content Wc [%] of cement milk is generally larger than the calcium content Ws [%] of soil (Wc>Ws). In addition, the mixing ratio α ₂ of the cement milk including the error in the unconsolidated sample 12S is larger than the actual mixing ratio α ₁ of the cement milk. Therefore, the "measured value" W (α ₂ ) of the calcium content in the unconsolidated sample 12S is larger than the “theoretical value” W (α ₁ ).

(Correction of calcium content)
Here, the actual mixing ratio α ₁ of cement milk in the unconsolidated sample 12S, the calcium content Wc [%] of the cement milk, and the calcium content Ws [%] of the soil are known in advance. . Therefore, the "theoretical value" W(α ₁ ) of the calcium content in the unconsolidated sample 12S can be calculated using equation (1-2).

As a result, the "theoretical value" W (α ₁ ) of the calculated calcium content and the "measured value" W (α ₂ ) of the calcium content measured by the X-ray fluorescence spectrometer are understood in association with each other. be able to.

That is, as shown in FIG. 4(A), the relationship between the "measured value" W (α ₂ ) and the "theoretical value" W (α ₁ ) of the calcium content in the unconsolidated sample 12S is plotted on a graph. By doing so, as shown in FIG. 4(B), it is possible to create an approximate line (approximate function Wx) that associates the "measured value" W (α ₂ ) with the "theoretical value" W (α ₁ ). .

By using this approximation function Wx, the "measured value" W1 of the calcium content measured by the X-ray fluorescence spectrometer can be corrected based on the "theoretical value" W2.

(Estimation of compressive strength)
Next, the unconsolidated compressive strength when the unconsolidated sample 12S is consolidated is estimated from the relationship between the calcium content of the soil cement in the ground G obtained by the preliminary investigation and the unconfined compressive strength. Specifically, the "theoretical value" W2 corrected using the approximation line in FIG. 4(B) is taken as the calcium content shown in FIG. 2. Thereby, the unconfined compressive strength when the unconsolidated sample 12S is consolidated is estimated as the estimated strength C2.

<Action and effect>
In the pile strength estimation method according to the embodiment of the present invention, the calcium content of the unconsolidated sample 12S (see FIG. 3) of the soil cement 12 collected from the pile hole GH shown in FIG. 1(B) is determined by fluorescent X-ray analysis. measured by a meter. On the other hand, the unconsolidated compressive strength when the unconsolidated sample 12S is consolidated can be estimated from the correlation data between the calcium content and the unconfined compressive strength derived from a plurality of samples (see FIG. 2). That is, the unconfined compressive strength can be estimated while the soil cement 12 is in an unconsolidated state.

On the other hand, if the unconsolidated compressive strength of the unconsolidated sample 12S is not estimated, it is necessary to conduct an unconfined compressive strength test after the soil cement 12 has consolidated and measure the unconfined compressive strength. be. In this case, it is difficult to proceed to the next step because it is not possible to confirm the strength of the foot hardening portion until the soil cement 12 hardens. This will lengthen the construction period. In addition, in order to avoid prolonging the construction period, a method is adopted in which the amount of cement used to form the soil cement 12 is larger than the designed amount, and the strength is maintained at a high level to form the foot protection section.

Furthermore, in the pile strength estimation method according to the embodiment of the present invention, the correlation between calcium content and unconfined compressive strength shown in Figure 2 is derived from a sample using soil collected from the site where the pile hole GH is formed. be done. Therefore, the strength of the soil cement 12 can be estimated with higher accuracy than when soil collected from other sites is used.

In addition, in the pile strength estimation method according to the embodiment of the present invention, using the calculation formula shown in equation (1-2), calcium Calculate the theoretical value of the content. Then, the measured value obtained by the fluorescent X-ray spectrometer is corrected based on this theoretical value (FIG. 4(B)). Thereby, even if the sample (unconsolidated sample 12S) is unconsolidated, the strength of soil cement can be estimated with high accuracy.

<Other embodiments>
In this embodiment, the "measured value" W1 of calcium content measured by a fluorescent X-ray analyzer is corrected to the "theoretical value" W2, but the embodiment of the present invention is not limited to this. For example, if cement is uniformly distributed in the unconsolidated sample 12S, it is not necessary to correct the "measured value" W1. Alternatively, even if the deviation between the "measured value" W1 and the "theoretical value" W2 is small, it is not necessary to correct the "measured value" W1. That is, the uniaxial compressive strength when the unconsolidated sample 12S is consolidated may be estimated using the "measured value" W1 as the calcium content shown in FIG. 2.

In addition, in this embodiment, the unconfined compressive strength test of the mixed sample is conducted through a preliminary investigation, and the unconsolidated compressive strength when the unconsolidated sample 12S is consolidated is estimated. Not exclusively. For example, instead of the uniaxial compressive strength test, a triaxial compressive strength test may be performed to estimate the triaxial compressive strength when the unconsolidated sample 12S is consolidated.

Further, in this embodiment, the strength of the soil cement 12 forming the foot hardening portion is estimated, but the embodiment of the present invention is not limited to this. For example, the strength of the soil cement 14 in a portion other than the foot protection portion may be estimated using the method described above.

Furthermore, although the embodiment of the present invention is used to estimate the strength of ready-made piles, the embodiment of the present invention is not limited to this. For example, it may be used to estimate the strength of improved piles for ground improvement. Even in this case, it can be used to estimate the strength of soil cement other than the tip of the improved pile. Thus, the present invention can be implemented in various ways.

12 Soil cement 12S unconsolidated sample GH pile hole

Claims (3)

A process of injecting cement milk into the pile hole,
collecting an unconsolidated sample of soil cement mixed with the cement milk and soil from the pile hole;
Measuring the calcium content of the unconsolidated sample with an X-ray fluorescence analyzer;
The compressive strength when the unconsolidated sample is consolidated is estimated from the measured value by the fluorescent X-ray analyzer and the correlation data between the calcium content and the compressive strength of soil cement derived from a plurality of samples. process and
A pile strength estimation method with Collecting a soil sample from the ground where the pile hole is formed and measuring the calcium content, and measuring the calcium content of the cement sample, according to the mixing ratio of the soil sample and the cement sample. Calculate the theoretical value of calcium content of the mixed sample,
forming a plurality of mixed samples with different mixing ratios and measuring unconfined compressive strength;
Deriving a relationship between the theoretical value and the uniaxial compressive strength as the correlation data;
The pile strength estimation method according to claim 1. measuring the calcium content of the unconsolidated sample;
From the mixing ratio and the theoretical value, create an approximation line that associates the measured value with the theoretical value,
correcting the measured value to the theoretical value using the approximate line to estimate the compressive strength;
The pile strength estimation method according to claim 2.