JP2018193729A - Strength estimation method for foot protection part - Google Patents

Abstract

To provide a strength estimation method for a foot protection part, the method being stable regardless of an amount of ground material.SOLUTION: An estimation method for a foot protection part includes: a first step of collecting a first sample from a support layer 12; a second step of obtaining a density of the first sample; a third step of forming and solidifying plural types of cement milk containing the first sample as aggregate, and from cement-water ratio and compression strength after solidification for the plural types of cement milk, obtaining a relational expression between the cement-water ratio and the compression strength for the cement milk containing the first sample as the aggregate; a fourth step of injecting cement milk on a bottom part of a drilled pile hole 1 and collecting the injected cement milk as a second sample; a fifth step of preparing a test body from the second sample and obtaining volume and mass of the test body; a sixth step of measuring electric conductivity of the second sample; a seventh step of obtaining the cement-water ratio of the second sample; and an eighth step of estimating the compression strength of a foot protection part 32 from the cement-water ratio of the second sample and the relational expression calculated in the third step.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for estimating the strength of a root consolidation portion of a pile.

  Conventionally, as a method of constructing a foundation pile, there is a method of excavating a pile hole up to a support layer and constructing a foundation pile by installing a ready-made pile or a reinforcing bar in the pile hole. In this method, a root hardening liquid is poured into the bottom of the pile hole and solidified to form a root hardening part. Since the formation of the root consolidation is performed deep in the ground, it is difficult to measure the strength. Therefore, a method for estimating the strength of the root-solidified portion has been proposed (for example, see Patent Document 1). In this strength estimation method, the N value and ground properties at the construction site are measured in advance, and a correspondence table of specific gravity and compressive strength is created. And a sample is extract | collected from the root consolidation part before solidifying, and specific gravity is measured. Then, the compressive strength after solidification of the rooted portion is obtained from the specific gravity and the correspondence table.

JP 2010-222799 A

  In order to obtain the compressive strength from the specific gravity, the ground material needs to be uniformly mixed in the sample. That is, since the specific gravity of the sample changes according to the amount of the ground material contained in the sample, the compressive strength obtained from the correspondence table is also affected. However, it is difficult to confirm whether or not the ground material is uniformly mixed at the bottom of the pile hole. In addition, there is a possibility that the amount of ground material contained in the sample may change depending on the location of sampling, and there is a problem that it is difficult to estimate stable strength.

  This invention is made | formed in view of the above, Comprising: It aims at providing the strength estimation method of the stable solidified part irrespective of the quantity of the ground material contained in a sample.

  In order to solve the above-mentioned problems and achieve the object, the root-strengthening-strength estimation method according to the present invention is formed by injecting and solidifying a liquid containing cement milk at the bottom of a pile hole excavated from the ground. A method of estimating the strength of a root consolidation part, wherein a first step of collecting a constituent of the layer as a first sample from a layer in which the root consolidation part of the ground is formed; From the second step of determining the density of the sample, and producing and solidifying a plurality of types of cement milk containing the first sample as an aggregate, from the cement water ratio of the cement milk and the compressive strength after solidification, A third step of obtaining a relational expression between the cement water ratio of the cement milk containing the first sample as an aggregate and the compressive strength; injecting the cement milk into the bottom of the excavated pile hole; Mixing with excavated soil A fourth step of collecting an object as a second sample, a fifth step of creating a test body from the second sample collected in the fourth step, and determining the volume and mass of the test body; A sixth step of measuring the electrical conductivity of the second sample; the mass of the specimen obtained in the fifth step; and the electrical conductivity of the second sample obtained in the sixth step. From the degree, the mass of water contained in the specimen is obtained, and the mass of the water, the mass of the specimen obtained in the fifth step, the volume, and the first obtained in the second step. From the density of the second sample, the seventh step of determining the cement water ratio of the second sample, and the cement water ratio of the second sample and the relational expression calculated in the third step, the rooting And an eighth step of estimating the compressive strength of the part.

  According to the above configuration, since the compressive strength of the root consolidation part is estimated from the relationship between the cement water ratio and the compressive strength, the compression of the root consolidation part is performed regardless of the amount of ground material contained in the second sample. The strength can be estimated, and the compressive strength of the root consolidation portion can be estimated more accurately.

FIG. 1 is a longitudinal sectional view showing a foundation pile in an embodiment of the present invention. FIG. 2 is a longitudinal sectional view showing a construction procedure in the embodiment of the present invention. FIG. 3 is a diagram showing the relationship between the cement water ratio and the compressive strength of various ground materials according to the embodiment of the present invention. FIG. 4 is a diagram showing the relationship between the electrical conductivity and the amount of water according to the embodiment of the present invention. FIG. 5 is a diagram showing the relationship between the electrical conductivity and the amount of water when the clay component is substituted for the sand according to the embodiment of the present invention. FIG. 6 is a flowchart showing a part of the construction procedure of the method for estimating the strength of the root hardening portion according to the embodiment of the present invention.

  With reference to the accompanying drawings, a preferred embodiment of a method for estimating the strength of a rooting portion according to the present invention will be described below in detail with reference to FIGS. This strength-estimating method of the root-solidified portion is a strength-estimating method for the root-solidified portion formed by injecting a liquid containing cement milk into the bottom of the excavated pile hole when the foundation pile is constructed. In the present embodiment, as shown in FIG. 1, in the ground 11, a foundation pile 31 is disposed in the pile hole 1 after constructing a rooted portion at the bottom of the pile hole 1 excavated from the ground surface to the support layer 12. In the case, a method for estimating the strength of the root consolidation portion before disposing the foundation pile 31 will be illustrated. The excavator used when excavating the pile hole 1 has an excavation head 3 at the tip of an excavation rod 2 as shown in FIG. 2A. When the excavation head 3 is rotated in the forward direction, the excavation teeth are closed. On the other hand, when it is rotated in the reverse direction, the excavating teeth spread and an expanded excavation can be performed.

  First step: In this method for estimating the strength of the root-solidified portion, first, the component is collected as a sample (first sample) from the support layer 12 on which the root-solidified portion is formed. When collecting a sample, for example, it may be performed by boring.

  Second step: The density of the first sample collected in the first step is determined. The density at this time may be the density at 105 ° C. drying (absolute drying). A density measurement device may be used for the density measurement.

  Third step: Producing a plurality of types of cement milk containing the first sample collected in the first step as an aggregate, and measuring the cement water ratio and the compression strength of the solidified product, A relational expression between the cement water ratio and the compressive strength of cement milk containing one sample as an aggregate is calculated. More specifically, cement milk as a test body containing the first sample as an aggregate is generated by changing the amount of aggregate, the amount of cement, and the amount of water, and generating a plurality of patterns. The cement water ratio is calculated, and they are solidified, and the compressive strength at the age of 28 days is measured. From the result, as shown in FIG. 3, a relational expression (regression formula) between the cement water ratio and the compressive strength is calculated. The regression equation is a straight line. The square of R represents the coefficient of determination. FIG. 3 shows the cement water ratio and compressive strength of cement milk containing the first sample as an aggregate when the first sample is gravel sand (FIG. 3A) and when the sand is mixed with gravel (FIG. 3B). An example of the relationship is shown. As shown in FIG. 3, the relational expression between the cement water ratio and the compressive strength differs depending on the material of the first sample.

  4th process: As shown to FIG. 2A, the pile hole 1 is excavated with the excavation rod 2 in the construction site of the foundation pile 31, injecting water (excavation liquid). When excavating the pile hole 1, it is preferable to excavate the side wall of the pile hole 1 with the kneading drum 4 as shown in FIG. 2B. The excavated pile hole 1 is filled with muddy water 13 in which injected water and ground material such as excavated earth and sand are mixed. When excavation is performed until the support layer 12 is reached, the excavation rod 2 is reversed and the excavation head 3 that is the tip of the excavation rod 2 is expanded. In this state, as shown in FIG. 2B, the excavation rod 2 performs the excavation of the support layer 12 with a larger diameter than the other part of the pile hole 1 to form the enlarged portion 1A. Thereafter, as shown in FIG. 2C, cement milk (root-setting liquid) is injected into the enlarged portion 1 </ b> A, and the mixture is stirred and mixed with muddy water 13 and ground materials such as excavated earth and sand, mainly the components of the support layer 12. The cement milk becomes a soil cement 21 mainly including the constituents of the support layer 12 as an aggregate. After filling with cement milk, the excavation rod 2 is pulled up from the pile hole 1. In the state of FIG. 2D, before the soil cement 21 is solidified, a sample (second sample) is taken from the soil cement 21 (a mixture of cement milk and excavated earth and sand) containing the constituents of the support layer 12 as an aggregate. (Step S101). As a method for collecting a sample, for example, a sampler is attached to the tip of the excavation rod 2 and thereby a sample is collected. In addition, before taking the second sample, the cement milk, the muddy water 13 and the ground material are stirred and mixed by the excavating rod 2 of the excavator, but the stirring may not be performed.

  Fifth step: A specimen is prepared from the second sample, and its mass and volume are determined (step S102). As the method, for example, a second sample is injected into a container whose volume is known until the container is filled, and a test specimen is prepared. And the mass of the test body is calculated | required. Since the volume of the container is the volume of the specimen, the density of the second sample can be calculated from this volume and the obtained mass of the specimen.

  Sixth step: The electrical conductivity of the second sample is measured (step S103). Electrical conductivity is measured using an electrical conductivity meter. What is necessary is just to measure the electrical conductivity of a test body for electrical conductivity.

Seventh step: The cement water ratio of the second sample is obtained (step S104). From the measured electric conductivity of the second sample and the mass of the specimen, the mass of water contained in the specimen is determined. As shown in FIG. 4, there is a correlation between the electrical conductivity of the test specimen and the amount of water contained in the test specimen. For example, the water quantity of the test specimen can be obtained from the regression equation shown in the figure. . This method is preferably used when the clay content is 20% or less, as shown in FIG. Using the mass of water, the mass of the specimen, the volume of the specimen and the density of the first sample, the mass of cement and the mass of aggregate in the specimen are obtained from the following mass equation and volume equation. The cement water ratio of the second sample is determined from the amount of water contained in the test body and the amount of cement.
W _C + W _W + W _S = W ₀ (1) Mass equation
W _C / ρ _C + W _W / ρ _W + W _S / ρ _S = V ₀ (2) Volume equation where W _C : mass of cement, W _W : mass of water, W _S : mass of aggregate , W ₀ : mass of the specimen,
ρ _C : Cement density (≈3.15), ρ _W : Water density (≈1.0), ρ _S : Aggregate density (first sample density), V ₀ : Specimen volume

  Eighth step: Based on the cement water ratio of the second sample and the above-described relational expression (strength evaluation formula), the compressive strength of the root hardening portion 32 is estimated (step S105).

  Ninth step: It is determined whether the estimated strength satisfies the design criteria (step S106). If the design standard is satisfied, the strength estimation of the root-solidified portion is terminated (step S106, Yes). On the other hand, when the design standard is not satisfied (step S106, No), the age X day strength of the second sample or the core strength of the root hardening portion 32 is measured (step S107). It is determined whether the age X day strength of the second sample or the core strength of the root hardening part 32 satisfies the design criteria (step S108). If the design standard is satisfied, the strength estimation of the rooting portion is finished (step S108, Yes). On the other hand, when the design standard is not satisfied (step S108, No), the re-construction of the root hardening portion 32 is performed (step S109). Then, it returns to step S101. When it is estimated that the compressive strength of the root consolidation part 32 is sufficient, as shown to FIG. 2E, the pile periphery fixing liquid 22 is inject | poured to the part 1B above the expansion part 1A in the pile hole 1 to the ground surface vicinity. . At that time, the muddy water 13 overflowing on the ground may be solidified by adding, for example, a cement-based solidifying material, and may be disposed as industrial waste with a viscosity that can be transported by truck. Then, as shown to FIG. 2F, the foundation pile 31 is sunk until it reaches the enlarged part 1A. When the soil cement 21 of the enlarged portion 1A is hardened, a root hardening portion 32 is obtained.

  As described above, a relational expression between a cement water ratio of cement milk in which a sample is collected in advance from the portion to be the support layer 12 of the foundation pile 31 and the sample is used as an aggregate, and the compression strength of the solidified product. Ask for. Then, a sample is taken from the cement milk (soil cement 21) before solidification injected into the enlarged portion 1A when constructing the root hardening portion 32, the cement water ratio of the sample is obtained, and the compressive strength is obtained from the above-mentioned relational expression. Asking for. The cement water ratio is an amount determined only from the amount of cement and the amount of water. Therefore, the compressive strength can be estimated regardless of the amount of aggregate (ground material) contained in the sample.

  Moreover, when calculating | requiring a cement water ratio, since electrical conductivity is measured and the quantity of water is calculated, the quantity of cement can be calculated by calculation and a cement water ratio can be calculated | required easily.

  In addition, water is more likely to mix with cement milk evenly compared to the ground material, and the change in the cement water ratio depending on the sampling location is considered to be small compared to the change in the amount of ground material depending on the sampling location. It is done. Therefore, the present method for obtaining the compressive strength from the cement water ratio can estimate the compressive strength with less error than the case of obtaining the compressive strength from the specific gravity of the sample.

  Moreover, since the number of days required for estimating the compressive strength can be within one day after placing the cement milk on the enlarged portion 1A, the root portion 32 can be repaired at an early stage.

(Confirmation experiment)
-Materials used: Portland cement (C) was used as the cement, and tap water (W) was used as the water. As the soil samples, Narita sand (hereinafter referred to as sand / S) and Tokyo gravel (hereinafter referred to as gravel / R) collected in the suburbs of Tokyo were used to simulate the aggregate of the support layer. The material properties of the material are shown in Table 1. Tables 2 and 3 show the formulations of the prepared specimens. As shown in Tables 2 and 3, specimens simulating root solid liquids having various compositions were prepared.

Measurement of weight and electrical conductivity The materials were mixed according to JIS R 5201. The kneaded material was poured into a tin cylindrical mold having a diameter of 50 mm and a height of 100 mm (volume: 196.3 cm ³ ) so that bubbles did not enter as much as possible.

After measuring the weight, the measurement part of the electric conductivity meter was inserted into the same container, and the electric conductivity was measured. The conductivity (mS / cm milli Siemens / centimeter), between the water of the specimen, as shown in FIG. 4, there is a correlation, the amount of water simply tested body from the regression equation (W _W) You can ask for it. In addition, when the content of clay in the support layer material is changed by substituting 5,10,15,20,100% for sand / S, the results of separately taking the relationship between electrical conductivity and water content are shown in FIG. Shown in As shown in FIG. 5, the clay content is preferably 20% or less from the viewpoint of variation in data.

  In the above-described embodiment, the bottom portion of the pile hole 1 is enlarged and formed to form the enlarged portion 1A. However, the enlarged portion 1A is not formed, and the bottom portion of the pile hole 1 having the same diameter as the other portions is cemented. Milk may be injected to form a root. Although the cement water ratio is used in the above-described embodiment, a water cement ratio may be used. Any ratio between the amount of cement and the amount of water may be used. The order of the steps in the above-described embodiment is not limited to the order described. For example, the second step may be before the seventh step or may be performed simultaneously with the seventh step.

DESCRIPTION OF SYMBOLS 1 Pile hole 1A Expansion part 11 Ground 12 Support layer 21 Soil cement 31 Foundation pile 32 Root consolidation part

Claims (1)

A method for estimating the strength of a root-solidified part formed by injecting and solidifying a liquid containing cement milk at the bottom of a pile hole excavated in the ground,
A first step of collecting a constituent of the layer as a first sample from a layer in which the solidified portion of the ground is formed;
A second step of determining the density of the first sample;
Cement milk containing the first sample as an aggregate from the cement water ratio of the cement milk and the compressive strength after solidification of the cement milk containing the first sample as an aggregate. A third step for obtaining a relational expression between the cement water ratio and the compressive strength of
A fourth step of injecting cement milk into the bottom of the excavated pile hole and collecting a mixture of the cement milk and the excavated earth and sand after the injection as a second sample;
Creating a test specimen from the second sample collected in the fourth step, and determining the volume and mass of the test specimen;
A sixth step of measuring the electrical conductivity of the second sample;
The mass of water contained in the specimen is obtained from the mass of the specimen obtained in the fifth step and the electrical conductivity of the second sample obtained in the sixth step. The cement water ratio of the second sample is obtained from the mass, the mass of the specimen obtained in the fifth step, the volume, and the density of the first sample obtained in the second step. The seventh step;
From the cement water ratio of the second sample and the relational expression calculated in the third step, an eighth step of estimating the compressive strength of the root-solidified portion,
A strength estimation method for a root-solidified portion, characterized by comprising:

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