JP2018199935A - Strength determination method of foot protection portion - Google Patents

Abstract

To provide a strength determination method of a foot protection portion which can more accurately determine whether a foot protection portion satisfies required compression strength regardless of an amount of excavated sediment included in a sample.SOLUTION: A strength determination method comprises: a first step of collecting a constituent of a layer 12 as first sample from the layer 12 in which a foot protection portion 32 in a subsoil is formed; a second step of producing and solidifying a plurality of kinds of cement milks including the first sample as an aggregate, and obtaining a relational expression between cement-water ratio and compression strength of the cement milk including the first sample as the aggregate from cement-water ratio and compression strength after solidification of the cement milks; a third step of injecting the cement milk 21 into a bottom portion of an excavated pile hole 1, and collecting the injected cement milk 21 as second sample; a fourth step of obtaining a moisture content of a test body; fifth step of obtaining a cement content to be included in the test body; and a sixth step of determining whether a cement content included in the test body satisfies the cement content obtained in the fifth step.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for determining 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 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. From this specific gravity and the correspondence table, the compression strength after solidification of the rooted portion is obtained.

JP 2010-222799 A

  When the compressive strength is obtained from the specific gravity, it is necessary that the root hardening liquid and the excavated soil are uniformly mixed in the root hardening portion. However, it is difficult to confirm whether or not the excavated soil is uniformly mixed at the bottom of the pile hole. When the excavated soil is not uniformly mixed in the root consolidation part, the amount of excavated sediment contained in the sample varies depending on the location where the sample is collected. Since the specific gravity of the sample varies depending on the amount of excavated sediment contained in the sample, the compressive strength obtained from the specific gravity also varies depending on the sampling location of the sample. Then, the error of intensity estimation becomes large. Therefore, there is a problem that the accuracy is questionable even when it is determined whether or not the rooted portion satisfies the required compressive strength based on the strength estimated by such a method.

  The present invention has been made in view of the above, and the strength of the root-solidified portion that can determine whether the root-solidified portion satisfies the required compressive strength more accurately regardless of the amount of excavated earth and sand contained in the sample. An object is to provide a determination method.

  In order to solve the above-described problems and achieve the object, the root-clamping strength determination 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 for determining the strength of a root-solidifying portion for determining whether the strength of the root-solidifying portion satisfies a necessary compressive strength, wherein the constituent of the layer is a first sample from the layer in which the root-solidifying portion of the ground is formed. A plurality of types of cement milk containing the first sample as an aggregate and solidified, and the cement water ratio of the cement milk and the compressive strength after solidification, A second step of obtaining a relational expression between the cement water ratio and the compressive strength of cement milk containing the above sample as an aggregate, cement milk is injected into the bottom of the excavated pile hole, and the cement milk and the excavated soil after the injection Mixed with A third step of collecting an object as a second sample, a fourth step of creating a test body from the second sample collected in the third step, and determining a moisture content of the test body, When the test body satisfies the required compressive strength from the water content obtained in the fourth step, the required compressive strength of the root-solidified portion, and the relational expression calculated in the second step, the test is performed. A fifth step of determining the amount of cement to be contained in the body, and a sixth step of determining whether the amount of cement contained in the test body satisfies the amount of cement obtained in the fifth step. It is characterized by that.

  In the strength determination method for the root-solidified portion according to the present invention, it is preferable to determine whether or not the amount of cement contained in the specimen satisfies the amount of cement obtained in the fifth step using an acid.

  The strength determination method for a root-solidified portion according to the present invention may include a step of removing an aggregate having a particle size of 1 mm or more when the test body is created.

  According to the above configuration, a test specimen is prepared from the second sample collected from the root before solidification, and the amount of cement to be included in the test specimen at the required compressive strength is determined between the cement water ratio and the compressive strength. The strength of the root-solidified portion is determined by determining whether the amount of cement contained in the test body satisfies the determined amount of cement. Therefore, regardless of the amount of excavated earth and sand contained in the second sample, the strength of the root consolidation portion can be determined, and the strength of the root consolidation portion can be determined 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 compressive strength and the cement water ratio of various ground materials according to the embodiment of the present invention. FIG. 4 is a diagram showing the relationship between the acid dripping amount and the cement amount according to the embodiment of the present invention. FIG. 5 is a diagram showing the relationship between the compressive strength and the cement water ratio in the test according to the embodiment of the present invention. FIG. 6 is a flowchart showing a part of the procedure of the strength determination method for the root-solidifying portion according to the embodiment of the present invention.

  With reference to the accompanying drawings, a preferred embodiment of a strength determination method for a rooting portion according to the present invention will be described below in detail with reference to FIGS. This strength determination method of root consolidation part determines whether the root consolidation part formed by injecting a liquid containing cement milk into the bottom of the excavated pile hole satisfies the required compressive strength after solidification when constructing the foundation pile To do. 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 the root 32 is constructed at the bottom of the pile hole 1 excavated from the ground surface to the support layer 12. In this case, an example of a method for determining the strength of the root consolidation part 32 before the foundation pile 31 is disposed will be described. 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 determining 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 32 is formed. When collecting a sample, for example, it may be performed by boring.

  Second step: The first sample is obtained by generating a plurality of types of cement milk containing the sample collected in the first step as an aggregate, and measuring the cement water ratio and the compressive strength of the solidified product. The relational expression between the cement water ratio and the compressive strength of cement milk containing as the aggregate is calculated. More specifically, cement milk as a test body including the first sample as an aggregate is changed to, for example, 12 patterns (at least 2) by changing the amount of aggregate, the amount of cement, and the amount of water. Pattern), and the cement water ratio thereof 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 case where the first sample was gravel sand (FIG. 3A), the sand mixed clay (FIG. 3B), the sand clay (FIG. 3C), and the sand mixed gravel (FIG. 3D). It shows an example of the relationship between the cement water ratio and the compressive strength of cement milk containing the first sample as an aggregate. 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.

  3rd process: As shown to FIG. 2A, the pile hole 1 is excavated with the excavation rod 2, injecting water (excavation liquid) in the construction site of a foundation pile. 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 the injected water and excavated soil (ground material) 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 1A, and the mud 13 and the excavated earth and sand are stirred and mixed. The cement milk becomes soil cement 21. After the cement milk is filled, the excavation rod 2 is pulled up from the pile hole 1 and, in the state of FIG. 2D, before the soil cement 21 is solidified, a sample (second sample) is obtained from the soil cement 21 (cement milk containing excavated earth and sand). ) Is collected (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. The amount of sample collected may be about 100 g. In addition, before taking the second sample, the cement milk, the muddy water 13 and the excavated earth and sand are agitated and mixed by the excavating rod 2 of the excavator, but may not be agitated.

  Here, it is preferable to grasp the dissolution rate of the first sample with respect to the acid, which will be described later, and the effect on the pH of the first sample (step S102). Understanding the effect of the first sample on the pH means, for example, that a sufficient amount of acid to neutralize a predetermined amount of cement with sufficient water is added to a predetermined amount of cement and sufficient water. It is to determine the pH value when placed in a liquid consisting of a first sample for quantification. Further, grasping the influence of the first sample on the pH may be measuring the pH of the first sample with sufficient water added.

  Fourth step: A test specimen is prepared from the second sample collected in the third process, and the moisture content of the test specimen is determined. When preparing the test body, the second sample is passed through a sieve having an opening of 1 mm, and aggregates having a particle diameter of 1 mm or more are removed (step S103). A predetermined amount, for example, 5 g is taken out from the second sample that has been sieved to obtain a test specimen. The moisture content of the test body is measured (step S104). Methods for measuring the moisture content of the specimen include, for example, a method of dissipating moisture using an infrared moisture meter or a microwave oven, a method of dissipating moisture by heating with a frying pan, a method of using an organic solvent, etc. Can be used. The moisture content is preferably measured at a temperature of 200 ° C. or lower. This is because clay may be denatured by heat and become a component dissolved in acid.

  Fifth step: From the amount of water obtained in the fourth step, the necessary compressive strength of the root-solidifying part 32 and the relational expression calculated in the second step, the amount of cement to be contained in the specimen at the required compressive strength (first step) (Referred to as one cement amount) (step S105). The necessary compressive strength of the root consolidation part 32 is a compressive strength required when the foundation pile 31 is disposed in the root consolidation part 32 and the root consolidation part 32 is solidified, and the safety factor is considered from the design standard strength. It is good to be. When determining the amount of cement, first, the required compressive strength is substituted into the relational expression calculated in the second step to determine the cement water ratio. Since the cement water ratio = the mass of cement / the mass of water, the mass of cement can be obtained from the obtained cement water ratio and the amount of water obtained in the fourth step. This is the first cement amount.

  Sixth step: It is determined whether the amount of cement contained in the specimen satisfies the first cement amount. As a method for determining this, for example, a method using an acid may be used. Examples of the method using an acid include the following methods. An amount of acid necessary to neutralize the first cement amount of the cement dissolved in water is mixed with the test specimen (step S106). As a result, it is determined whether it is neutralized or alkaline, for example, whether the pH is 7 or more (step S107). At this time, it is desirable to keep the temperature of the solution at 20 ° C. or higher from the viewpoint of keeping the dissolution rate. When neutralized or alkaline (step S107, Yes), it is determined that the first cement amount of cement is included in the test body, and the strength determination of the rooted portion is terminated. At this time, the acid used is preferably an acid that is not a poisonous substance, such as tartaric acid. In addition, for example, an indicator such as a phenolphthalein solution may be used, or a pH test paper may be used to determine whether neutralization has occurred.

  In addition, a method for obtaining an amount of acid necessary to neutralize a first cement amount of cement dissolved in water will be described. The acid adjusted to the predetermined concentration to be used and the cement to be used are dissolved and neutralized, and the ratio of the cement contained in the unit mass sample as shown in FIG. Seeking relationship with. The relationship between the proportion of cement contained in the sample and the amount of acid dropped to neutralization when acid is added to the sample can be expressed by a regression equation as shown in FIG. Therefore, if the amount of the specimen and the amount of cement in the specimen are known, the proportion of cement contained in the sample can be found, and the amount of acid required for neutralization can be determined from the regression equation. When determining the amount of acid necessary for neutralization, the dissolution rate of the first sample with respect to the acid and the effect on the pH of the first sample may be taken into consideration. In this case, for example, the amount of aggregate (first sample) in the test body may be obtained. As a method for determining the amount of aggregate, a method for estimating the mixing ratio of concrete can be used. This includes, for example, a method using hydrochloric acid, a method using sodium gluconate, a method using an inductively coupled plasma emission spectrometer, and the like.

  Moreover, you may determine whether the amount of cement contained in a test body satisfy | fills the amount of 1st cement by calculating | requiring the amount of cement contained in a test body. As a method for obtaining the amount of cement, for example, a method in which a sample after evaporation of water is dissolved in a predetermined amount of hydrochloric acid and titrated with sodium hydroxide, or calculation of heat of dissolution when dissolved in an acid is obtained. Methods such as methods can be used.

  Seventh step: When the mixed solution of the acid and the test specimen is acidic, that is, when it is determined that the root hardening part 32 does not satisfy the necessary compressive strength (Step S107, No), the age of the second sample The X-day strength or the core strength of the root hardening part 32 is measured (step S108). It is determined whether the age X day strength of the second sample or the core strength of the root consolidation part 32 satisfies the design criteria (step S109). When the design standard is satisfied, the strength determination of the rooting portion is terminated (step S109, Yes). On the other hand, when the design standard is not satisfied (No at Step S109), the rooting portion 32 is re-constructed (Step S110). Then, it returns to step S101. When it is determined that the compressive strength of the root consolidation part 32 is sufficient, as shown in FIG. 2E, the pile circumferential fixing liquid 22 is injected to the vicinity of the ground surface into the portion 1B above the enlarged portion 1A in the pile hole 1. . 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, it becomes a root hardening portion 32 after solidification.

  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 cement milk (soil cement) before solidification injected into the enlarged portion 1A when constructing the root hardening portion 32, and the cement in which the root hardening portion 32 satisfies the necessary compressive strength in the sample. It is determined whether or not the first cement amount, which is the amount, is included. The first cement amount is obtained from the relational expression described above. In this way, it is determined whether the root hardening part 32 satisfies the required compressive strength. Therefore, it is possible to determine the strength of the solidified portion regardless of the amount of aggregate (excavated earth and sand) included in the sample.

  In addition, water is more likely to be mixed with cement milk evenly compared to the excavated sediment, 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 excavated sediment depending on the sampling location. It is done. Therefore, this method for determining the amount of first cement, which is the required amount of cement via the cement water ratio, from the required compressive strength is more error than when determining the strength of the solidified part by determining the compressive strength from the specific gravity of the sample. There is little, and the intensity | strength of a root hardening part can be determined.

  Moreover, since the number of days required for the determination of the compressive strength can be within one day after placing the cement milk on the enlarged portion 1A, the rooting portion 32 can be repaired at an early stage. In addition, since the test specimen is prepared after removing coarse aggregate with a sieve, it is possible to prevent the coarse aggregate from being mixed into the test specimen, and to reduce factors that cause errors.

(test)
A test related to the above-described strength determination method of the root hardening portion was performed. It was actually determined whether a solidified portion was formed and the required compressive strength was satisfied. The method is as described above. The judgment intensity was 18 N / mm ² . After the acid was added to the test body, the determination was made using the indicator. As a result, the indicator developed color, and the rooted portion was determined to satisfy the required compressive strength. When pH was measured, it was pH = 8.5. In addition, the dry sample (test body) whose moisture was measured was analyzed, and the strength of the root-solidified portion was estimated. The analysis method is as follows.
(1) The sealed specimen was coarsely pulverized (about 1 mm) and dried in a 105 ° C. drying oven for 2 hours. Mass loss before and after drying was defined as free water dissipation. (Average value of three specimens)
(2) A sample dried at 105 ° C. was finely pulverized and heated to 1000 ° C. by TG-DTA (analyzer), and the loss on ignition from 105 ° C. to 1000 ° C. was defined as the amount of bound water. (Average value of two test specimens) The mass reduction from 600 ° C to 750 ° C was excluded from the amount of bound water as calcium carbonate decarboxylation.
(3) A sample dried at 105 ° C. was finely pulverized, 1 g was measured, and dissolved using hydrochloric acid (1 + 100). The insoluble residue at this time was defined as solids such as clay, dotan, gravel and sand constituting the support layer. (Average value of two specimens)

The results are shown in Table 1. Moreover, the estimation formula of the used intensity | strength is shown in FIG. The estimation formula was created from the strength test results of unconsolidated simulated specimens made with 10% and 25% sand in the laboratory. The estimated compressive strength was 19.5 N / mm ² . Moreover, the compressive strength at the age of 28 days of the unconsolidated sample actually collected was 22.5 N / mm ² . Therefore, it is considered that the determination made by the above-described strength determination method for the root-fixed portion was correct.

  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, ascertaining the dissolution ratio of the first sample with respect to the acid in the third step may be before the sixth 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 (3)

A method for determining the strength of a root-solidified portion that determines whether the strength of a root-solidified portion formed by injecting and solidifying a liquid containing cement milk into a bottom portion of a pile hole excavating the ground satisfies a required compressive strength,
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;
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 second step of obtaining a relational expression between the cement water ratio and the compressive strength of
A third 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 third step, and determining the moisture content of the test specimen;
When the test body satisfies the required compressive strength from the water content obtained in the fourth step, the required compressive strength of the root-solidified portion, and the relational expression calculated in the second step, the test is performed. A fifth step for determining the amount of cement to be contained in the body;
A sixth step of determining whether the amount of cement contained in the specimen satisfies the amount of cement obtained in the fifth step;
A strength determination method for a root-solidified portion, comprising:   2. The method according to claim 1, wherein in the sixth step, it is determined whether an amount of cement contained in the test body satisfies an amount of cement obtained in the fifth step using an acid. Strength determination method for roots.   The strength determination method for a root-solidified portion according to claim 1, further comprising a step of removing an aggregate having a particle size of 1 mm or more when the test body is created.

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