JP2023005802A - Soil cement dehydration rate estimation method - Google Patents

Abstract

To estimate a dehydration rate of soil cement.SOLUTION: A soil cement dehydration rate estimation method comprises steps of: measuring the water content of an unconsolidated sample of soil cement formed by mixing cement milk and local soil; measuring the content of a predetermined element in the unconsolidated sample using a fluorescent X-ray analyzer; calculating a mass ratio of soil to cement in the soil cement using the content of the predetermined element in the unconsolidated sample, the content of the predetermined element in the local soil, and the content of the predetermined element in the cement used in the cement milk; calculating an effective cement water ratio of the unconsolidated sample using the water content ratio of the unconsolidated sample and the mass ratio; and calculating the dehydration rate of the soil cement from the calculated mass ratio, the water content ratio, the effective cement water ratio, the water content ratio of the local soil, and the water-cement ratio in the cement milk.SELECTED DRAWING: Figure 1

Description

The present invention relates to a soil cement dehydration rate estimation method.

In Patent Document 1 below, an unconsolidated soil cement sample is collected from the ground, the effective cement water ratio of the soil cement sample is calculated, and the effective cement water ratio and the compressive strength of the consolidated soil cement are calculated. A method for estimating the compressive strength of soil cement after consolidation is described from the relationship of

JP 2014-111879 A

As shown in the method for estimating the compressive strength of soil cement in Patent Document 1, the strength of soil cement depends on the effective cement water ratio of the soil cement. However, soil cement can lose moisture in the ground. In particular, in highly permeable sandy ground or gravel ground, the pressure inside the drilled hole is relatively high with respect to the pressure of the surrounding ground, and this pressure difference tends to dehydrate the soil cement.

For example, if the soil cement is dehydrated after the strength of the soil cement is estimated, a discrepancy occurs between the estimated strength and the actual strength. Under such conditions, the strength of soil cement may be underestimated. Therefore, it is necessary to grasp the dehydration rate of soil cement and appropriately manage the strength of soil cement.

An object of the present invention is to estimate the dehydration rate of soil cement in consideration of the above facts.

The method for estimating the soil cement dehydration rate of claim 1 comprises the steps of measuring the water content ratio of an unconsolidated sample of soil cement formed by mixing cement milk and local soil, and using a fluorescent X-ray analyzer, using the predetermined element content of the unconsolidated sample, the predetermined element content of the local soil and the predetermined element content of the cement used in the cement milk; and calculating the effective cement water ratio of the unconsolidated sample by using the step of calculating the mass ratio of soil to cement in the soil cement, the water content ratio of the unconsolidated sample, and the mass ratio. and calculating the dehydration rate of the soil cement from the calculated mass ratio, the water content, the effective cement water ratio, the water content of the local soil, and the water-cement ratio in the cement milk. there is

Soil cement is formed by mixing cement milk (a mixture of cement and water) with local soil (a mixture of soil particles and water). Unsettled soil cement may be dehydrated due to the pressure difference in the surrounding ground. Theoretically, the dehydration rate is calculated by dividing the value obtained by subtracting the volume of water contained in the soil cement after dehydration from the volume of water contained in the soil cement before dehydration by the volume of water before dehydration.

However, it is difficult to grasp the mixing ratio of cement milk and local soil in soil cement. Therefore, it is difficult to directly grasp the amount of water contained in the soil cement before dehydration and the amount of water contained in the soil cement after dehydration. That is, it is difficult to calculate the dehydration rate from the volume of these waters.

Here, cement and local soil each contain various elements. Among these various elements, if we can focus on specific elements (predetermined elements, such as calcium) and grasp the content of predetermined elements in cement, soil cement, and local soil, we can estimate the dehydration rate of soil cement. can be calculated.

Therefore, in the soil cement dehydration rate estimating method of claim 1, the content of a predetermined element in an unsolidified sample of soil cement is measured using a fluorescent X-ray analyzer.

Then, using the measured predetermined element content of the unconsolidated sample, the predetermined element content of the local soil, and the predetermined element content of the cement used in the cement milk, the relationship between the soil and cement in the soil cement Calculate the mass ratio.

Also, using the water content ratio of the unconsolidated sample and the calculated mass ratio, the effective cement water ratio of the unconsolidated sample is calculated.

Further, the dehydration rate of soil cement is calculated from the calculated mass ratio, the water content ratio of the unconsolidated sample, the calculated effective cement water ratio, the water content ratio of the local soil, and the water-cement ratio of the cement milk.

As described above, the soil cement dehydration rate estimating method of this embodiment can estimate the dehydration rate of soil cement.

A method for estimating a soil cement dehydration rate of claim 2 is the method for estimating a soil cement dehydration rate of claim 1, wherein the content of the predetermined element in the local soil is measured using a fluorescent X-ray analyzer.

In the soil cement dehydration rate estimating method of claim 2, the content of the predetermined element in the local soil is measured using a fluorescent X-ray analyzer. As a result, the accuracy of the predetermined element content of the local soil is higher than when the element content of the local soil is not considered or the estimated element content of the local soil based on past data is used.

A method for estimating a soil cement dehydration rate of claim 3 is the method for estimating a soil cement dehydration rate of claim 1 or 2, wherein the soil cement forms a foot protection portion of a pile hole.

In the soil cement dehydration rate estimation method of claim 3, it is possible to estimate the soil cement dehydration rate estimation method for the soil cement that forms the foot protection portion of the pile hole. As a result, it is possible to appropriately manage the strength of the foot protection portion.

According to the invention, the dewatering rate of soil cement can be estimated.

(A) is a vertical cross-sectional view showing a state in which a pile hole is formed for burying a ready-made pile to which the soil cement dehydration rate estimation method of the present invention is applied, and (B) is a foot protection portion in the pile hole. is a vertical cross-sectional view showing a state in which a is formed, (C) is a vertical cross-sectional view showing a state in which the pile circumference fixing liquid is injected while pulling up the excavation rod from the pile hole, (D) is a pile hole It is an elevation cross-sectional view showing a state in which a prefabricated pile is inserted. 1 is a conceptual diagram showing components of soil cement; FIG. 1 is a conceptual diagram showing components of soil cement in a dry state; FIG.

Hereinafter, a method for estimating a soil cement dehydration rate according to an embodiment of the present invention will be described with reference to the drawings. Components shown using the same reference numerals in each drawing mean the same components. However, unless otherwise specified in the specification, each component is not limited to one, and a plurality of components may exist.

In addition, descriptions of configurations and reference numerals that are duplicated in each drawing may be omitted. It should be noted that the present invention is not limited to the following embodiments, and can be carried out with appropriate modifications, 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>
The method for estimating the soil cement dehydration rate according to the embodiment of the present invention is used, as an example, for soil cement forming a hardened foot portion of a pile. Therefore, before explaining the method for estimating the soil cement dehydration rate, an outline of the method for constructing piles using soil cement, which is the target of estimating the dewatering rate, will be described.

FIGS. 1A to 1D show an example of a method of embedding a ready-made pile 10 into the ground G by an embedding method. The prefabricated pile 10 shown in FIG. 1(D) is a concrete pile, which is preliminarily molded 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. In this embodiment, the tip of the pile hole GH reaches the support layer GA in order to use the ready-made pile 10 as the tip support pile. The ground G is a highly permeable ground having a higher water permeability than the cohesive ground, such as sand ground or gravel ground. Note that "soil" in the following description includes sand and gravel.

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 agitating this cement milk, it is mixed with the soil in the ground G to construct the soil cement 12 that forms the hardening part.

Cement milk is formed by kneading cement and water, or by kneading cement, water and various additives. Also, soil cement is a kneaded body of cement milk and soil. In this specification, a mixture of minerals, organic substances, gases, liquids, organisms, etc. that form the "ground G" is referred to as "soil".

At the tip of the pile hole GH, it is preferable to form a foot protection bulb 12A, which is a portion filled with the soil cement 12 and whose diameter is enlarged. When forming the foot protection bulb 12A, the excavation head of the excavation rod 20 has a known structure that can be expanded in diameter. By expanding the diameter of the excavation head at a predetermined depth, the foot protection bulb 12A is formed.

Next, as shown in FIG. 1(C), cement milk is injected and stirred above the soil cement 12 while the drilling rod 20 is being pulled out. This forms the soil cement 14 as a pile circumference fixing liquid. The soil cement 14 may be formed using poorly mixed cement milk having a smaller amount of cement per unit volume than the soil cement 12 .

Next, as shown in FIG. 1(D), a 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 foot protection bulb 12A at the tip of the pile hole GH. As a result, the ready-made pile 10 is buried in the ground G.

Note that the soil cement for estimating the dehydration rate in this embodiment may not be the one used for the permanent pile, and may be a soil cement having substantially the same composition as that used for the permanent pile.

In this case, a temporary pile hole is drilled in the same site as the site where the ready-made pile 10 as the permanent pile is provided, and cement milk is poured and stirred. This makes it possible to form soil cement having substantially the same composition as the soil cement 12 used for permanent piles. "Substantially equal" means, for example, that the mixing ratios of cement and soil are substantially equal.

Further, the soil cement for estimating the dehydration rate in this embodiment does not necessarily need to be used for the hardened foot portion of the pile, and may be used for portions other than the hardened foot portion of the pile. Furthermore, the soil cement may be used for earth retaining walls and soil improvement bodies. In the following description, a method for estimating the dehydration rate of soil cement in general including the soil cement 12 used for permanent piles will be described.

<Outline of method for estimating dehydration rate of soil cement>
Soil cement is formed by mixing cement milk with local soil (a mixture of soil particles and water). The unsolidified soil cement may be dehydrated due to the pressure difference in the surrounding ground (ground G). Theoretically, the value obtained by subtracting the volume of water contained in the soil cement after dehydration (volume V2 [cm ³ ] described later) from the volume of water contained in the soil cement before dehydration (volume V1 [cm ³ ] described later). is divided by the volume V1 [cm ³ ] of water before dehydration, the dehydration rate of the soil cement (dehydration rate X to be described later) is calculated.

However, it is difficult to grasp the mixing ratio of cement milk and local soil in soil cement. Therefore, it is difficult to directly grasp the volume V1 [cm ³ ] of water contained in the soil cement before dehydration and the volume V2 [cm ³ ] of water contained in the soil cement after dehydration. That is, it is difficult to calculate the dehydration rate X from the volume of these waters.

Therefore, in the present invention, the volume V1 [cm ³ ] of water contained in the soil cement before dehydration is obtained as a “theoretical value”, and the volume V2 [cm ³ ] of water contained in the soil cement after dehydration is calculated as follows: , the dehydration rate X of the soil cement is calculated from the "measured value" measured by the method described later.

<Volume of water before dehydration>
As shown in FIG. 2 (<before dehydration> on the left side), the cement milk that forms the soil cement is, for example, formed by kneading cement of C [g] and water of C R [g]. ing. R is the water-cement ratio (mass ratio) in the cement milk, and is a known value that can be set arbitrarily.

Also, the local soil, which is the soil to be mixed with the cement milk, contains S[g] soil particles (dry state) and S·ωs[g] water. "ωs" is the water content ratio (mass ratio) of the local soil, and is a value that can be measured by a preliminary survey to be described later.

Also, if the density of water is 1, the volume of water at (C R) [g] is (C R) [cm ³ ], and the volume of water at (S ωs) [g] is (S・ωs) [cm ³ ]. That is, the soil cement before dehydration contains water of volume V1 [cm ³ ] shown by the following formula (1).

V1=C.R+S..omega.s (1)

<Volume of water after dehydration, dehydration rate of soil cement>

Here, the cement and the local soil each contain calcium. If the soil cement, the local soil, and the calcium content of the cement can be grasped, the volume of water after dehydration and the soil cement dehydration rate can be calculated by the following methods. Calcium is an example of the predetermined element in the present invention. The "predetermined element" used in the present invention may be any element contained in cement such as calcium.

(Calcium concentration of cement and water-cement ratio of cement milk)
As shown in FIG. 3, the calcium content Cca in cement of C[g] is given by the following formula (2). The calcium concentration of cement may be measured using a fluorescent X-ray analyzer.

Cca=C・Ca(c) (2)

Moreover, the water-cement ratio R in the cement milk is a value that can be arbitrarily set as described above. Cement and water are mixed so as to have a predetermined water-cement ratio. For example, the water-cement ratio R of the cement milk injected into the pile hole GH shown in FIG. preferably.

(Preliminary survey - Sampling)
In order to calculate the dehydration rate of soil cement, a preliminary survey will be conducted. As an example of the preliminary survey, first, a sample of local soil is collected from the ground (for example, the ground G shown in FIG. 1). The collection of samples is preferably carried out in conjunction with boring tests for ground investigation. This sample is, for example, the local soil forming the support layer GA shown in FIG. 1 (hereinafter sometimes referred to as "soil sample").

(Preliminary survey - measurement of local soil)
Next, after measuring the mass of the collected soil sample, it is dried and pulverized. Arbitrary equipment such as a heat drying moisture meter and a microwave oven can be used for drying the soil sample. Also, a mill or the like can be used for pulverizing the soil sample. Then, the mass of the dried soil sample is measured.

As a result, the mass S [g] of soil particles (in a dry state) and the water content ratio ωs of the soil sample before drying can be grasped. That is, as shown in FIG. 2 (<before dehydration> on the left side), the soil sample contains S [g] soil particles (dry state) and S·ωs [g] water. .

(Preliminary survey - measurement of calcium content in local soil)
Next, a fluorescent X-ray analyzer is used to measure the calcium concentration in the dried and pulverized soil sample (soil particles). As shown in FIG. 3, when the calcium concentration of soil particles (dry state) is measured as Ca(s) [ppm], the calcium content Sca in soil particles (dry state) of S [g] is It is represented by the following formula (3A).

Sca=S・Ca(s) (3A)

(Measurement of water content ratio of soil cement)
Next, cement milk and local soil are kneaded inside, for example, the pile hole GH shown in FIG. 1 to form soil cement. Then, unconsolidated soil cement is collected as an unconsolidated sample.

It should be noted that at the time the unconsolidated sample is collected, it is considered that the water is dehydrated from the soil cement to the ground G, and in the following explanation, when the term "unconsolidated sample" is used, shall refer to an unconsolidated sample taken from

After the unconsolidated sample is taken, the unconsolidated sample is weighed. The mass W1 of the unconsolidated sample is C + S + W + Sw [g], which is the sum of the masses of cement milk and local soil, as shown in Figure 2 (<after dehydration> on the right) and formula (3-1). .

In the unconsolidated sample, the mass of water derived from cement milk is W [g], and the mass of water derived from local soil is Sw [g]. These masses W[g] and Sw[g] are masses of water after dehydration.

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

The collected unconsolidated sample is then dried and ground. Any equipment such as a heat drying moisture meter, a microwave oven, or the like can be used to dry the unconsolidated sample in the same manner as for the soil sample. A mill or the like can be used for pulverizing the unsolidified sample. The time required for drying, pulverization, and calcium measurement by a microwave oven or the like is about 1 hour (of which, drying with a heat drying moisture meter takes about 30 minutes, and drying with a microwave oven takes about 15 minutes). It is sufficiently short compared to the time (about 3 to 7 days) required for the test and curing of the specimen.

In the present invention, "drying" and "dehydration" are different concepts. "Drying" means intentionally removing water from an unconsolidated sample or soil sample, and "dehydration" means that water in soil cement automatically moves to the ground G.

The dry, unconsolidated sample (ie, dry soil cement) is then weighed. The mass W2 of soil cement in the dry state is the mass of the cement and soil particles (dry state) in the unconsolidated sample, as shown in Fig. 2 (<after dehydration> on the right) and the following formula (3-2). Denoted by C+S[g], which is the sum.

W2=C+S (3-2)

Here, the value W3 calculated from the difference between the mass W1 of the unsolidified sample and the mass W2 of the dry soil cement is shown in FIG. , indicates the water content W+Sw [g] of the unconsolidated sample.

In addition, the "step of measuring the water content of the unconsolidated sample" in the present invention includes measuring the weight W1 of the unsolidified sample and the weight W2 of the dry soil cement, and determining the content of the unsolidified sample. This includes calculating the amount of water (the mass of water contained in the soil cement after dehydration) W3.

W3=W+Sw (3-3)

From the above formulas (3-1) to (3-3), the water content ratio of the unconsolidated sample (the water content ratio of the soil cement after dehydration) "ωsc" is calculated as shown in the following formula (3B). .

ωsc=W3/W2=(W+Sw)/(C+S) (3B)

(Measurement of calcium content in soil cement)
Next, an X-ray fluorescence spectrometer is used to measure the calcium concentration in the dried and ground unconsolidated sample (ie, dry soil cement). At this time, since the unconsolidated sample is dried and pulverized, the cement component and the local soil component are uniformly mixed, and the calcium content can be measured with high accuracy.

As shown in FIG. 3, when the calcium concentration of soil cement (dry state) is measured as Ca(sc) [ppm], the calcium content Cca + Sca in this soil cement (dry state) is given by the following (4) is shown by the formula

Cca + Sca = (C + S) · Ca (sc) (4)

(Mass ratio of cement and soil particles (dry state) in soil cement)
As shown in FIG. 4, when the mass ratio C:S between cement and soil particles (dry state) in soil cement is 1:α, this coefficient α (hereinafter referred to as mass ratio α) is given by the following ( 5-1) is represented by the formula.

α=S/C (5-1)

Also, the calcium concentration Ca(sc) in soil cement is expressed by the following formula (5-2) from formulas (2), (3A) and (4).

Ca(sc)=[C・Ca(c)+S・Ca(s)]/(C+S) (5-2)

From these equations (5-1) and (5-2), the mass ratio α is calculated by the following equation (5).

α=[Ca(c)-Ca(sc)]/[Ca(sc)-Ca(s)] (5)

Here, in soil cement, the ratio β of cement to water (hereinafter referred to as effective cement water ratio β) is calculated using the mass C [g] of cement in the unconsolidated sample and the mass W3 [g] of water. , is represented by the following equation (6-1).

β=C/W3 (6-1)

By modifying the formula (6-1), the mass W3 [g] of water contained in the non-solidified sample is expressed by the following formula (6-2).

W3=C/β (6-2)

Assuming that the density of water is 1, the volume V2 [cm ³ ] of water contained in the soil cement after dehydration can be calculated using the mass W3 [g] of water contained in the unconsolidated sample as follows (7 ).

V2=W3 (7)

Furthermore, using the above formulas (1) to (5) and (6-1), the effective cement water ratio β is calculated by the following formula (8).

β=Ca(sc)/{[α・Ca(s)+Ca(c)]・ωsc} (8)

(Calculation of dehydration rate of soil cement)
The dehydration rate X of the soil cement is obtained by the following formula (9-1) using the volume V1 [cm ³ ] of water before dehydration and the volume V2 [cm ³ ] of water contained in the soil cement after dehydration. is indicated by

X=(V1-V2)/V1 (9-1)

This formula (9-1) can be transformed into the following formula (9-2) using formulas (1) and (7).

X=(C・R+S・ωs−W3)/(C・R+S・ωs) (9-2)

Furthermore, this formula (9-2) can be transformed into the following formula (9) using formulas (5-1) and (6-2).

X={R+α·ωs−(1/β)}/(R+α·ωs) (9)

Here, as described above, R, which constitutes the formula (9), is the water-cement ratio (mass ratio) in cement milk, α is the mass ratio of soil to cement in soil cement, and ωs is the water content ratio (mass ratio) of the local soil. ratio), and β is the effective cement-water ratio of the soil cement. These values can be obtained by calculation or measurement. Therefore, the dehydration rate X of the soil cement can also be calculated.

(Action and effect)
Thus, according to the present invention, the dehydration rate of soil cement can be estimated. By dehydrating the soil cement, the ratio of cement contained in the soil cement increases, and the effective cement water ratio increases. Therefore, the strength is increased.

If the dehydration rate of the soil cement is not taken into account, that is, if the fact that the soil cement is dehydrated is not taken into account, it is not possible to grasp that the strength of the soil cement has increased, so there is a risk that the strength will be underestimated. .

Here, the piles may be removed in the future when the use of the building is changed or when the area is redeveloped. If the strength of the soil cement formed by backfilling and improving the ground after removing the piles is underestimated, the strength of the ground that is backfilled after the removal of the piles is also underestimated.

When constructing a new pile on the ground whose strength has been underestimated, it is difficult to excavate a pile hole for installing the new pile in the assumed position and shape. This is because the strength of the backfilled ground is higher than expected, and the excavation rod escapes into the surrounding ground, making it difficult to excavate in the vertical direction, for example.

On the other hand, by grasping the dehydration rate of soil cement and appropriately managing the strength, it is possible to adjust the position of new piles and consider the excavation method according to the strength. Avoid troubles during construction.

Also, by dehydrating the soil cement, the volume of the soil cement becomes smaller than when it is not dehydrated. This also reduces the amount of sludge that is pushed out of the borehole by the cement milk during the formation of soil cement. By grasping the dehydration rate of soil cement, the amount of sludge discharged from the borehole can also be managed.

In this embodiment, as described above, it is assumed that "water has been dehydrated from the soil cement to the ground G at the time when the unconsolidated sample is collected". The unconsolidated sample may be collected immediately after the cement milk is mixed with the soil in the ground G by stirring. Immediately after the cement milk is stirred and mixed with the soil in the ground G, even if no dehydration occurs, the dehydration rate can be calculated by the above method and the presence or absence of dehydration can be confirmed.

Moreover, the timing of collecting the unsolidified sample may be after a predetermined time has passed since the cement milk was stirred. Further, for example, every time a predetermined time elapses (for example, every 3 hours, every 6 hours, etc.), an unconsolidated sample may be collected and the dehydration rate may be calculated for each unconsolidated sample. By grasping the change in the dehydration rate over time by such a method, it is possible to estimate the final dehydration rate.

In addition, the method for estimating the soil cement dehydration rate of the present invention can be applied not only to highly permeable sandy ground and gravel ground, but also to ground made of cohesive soil. By applying the present invention, regardless of the type of ground, it is possible to grasp the water permeability of the ground G, grasp the presence or absence of dehydration from soil cement to the ground G, and further determine the degree of dehydration. can also comprehend.

Furthermore, in the above explanation, the case where the pressure inside the drilled hole becomes higher than the pressure of the surrounding ground and the soil cement is dehydrated is explained. can also be applied when is "hydrated".

The soil cement may be "hydrated" when the pressure inside the borehole becomes "low" relative to the pressure of the surrounding ground, for example in viscous ground with low permeability. Even in such a case, the water content can be calculated by applying the above method. When the dehydration rate calculated by the above formula (9) is a negative value, the water content is the absolute value of the value.

12 soil cement

Claims (3)

measuring the water content of an unconsolidated sample of soil cement formed by mixing cement milk and local soil;
measuring the content of a predetermined element in the unconsolidated sample using a fluorescent X-ray analyzer;
A step of calculating the mass ratio of soil and cement in the soil cement using the content of the predetermined element in the unconsolidated sample, the content of the predetermined element in the local soil, and the content of the predetermined element in the cement used in the cement milk. When,
calculating an effective cement water ratio of the unconsolidated sample using the water content ratio of the unconsolidated sample and the mass ratio;
a step of calculating the dehydration rate of the soil cement from the calculated mass ratio, the water content ratio, the effective cement water ratio, the water content ratio of the local soil, and the water-cement ratio in the cement milk;
method for estimating soil cement dehydration rate. 2. The method for estimating the soil cement dehydration rate according to claim 1, wherein the content of the predetermined element in the local soil is measured using a fluorescent X-ray analyzer. The method for estimating the soil cement dehydration rate according to claim 1 or 2, wherein the soil cement forms a foot protection portion of a pile hole.

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