JP6949549B2 - Method of estimating the strength of the root compaction - Google Patents

Description

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

Conventionally, as a method of constructing a foundation pile, there is a method of excavating a pile hole up to the support layer and installing a ready-made pile or a reinforced cage in the pile hole to construct a foundation pile. In this method, the root-consolidating liquid is injected into the bottom of the pile hole and solidified to form the root-consolidating portion. Since the formation of the root compaction is performed deep in the ground, it is difficult to measure the strength. Therefore, a method of estimating the strength of the rooted portion has been proposed (see, for example, Patent Document 1). In this strength estimation method, the N value and ground properties of the construction site are measured in advance, and a correspondence table of specific gravity-compressive strength is created. Then, a sample is taken from the root-consolidated portion before solidification, and the specific gravity is measured. Then, the compressive strength after solidification of the root compaction portion is obtained from this specific gravity and the correspondence table.

JP-A-2010-222799

When determining the compressive strength from the specific gravity, it is necessary that the ground material is 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. Moreover, the amount of ground material contained in the sample may change depending on the sampling location, and there is a problem that it is difficult to estimate a stable strength.

The present invention has been made in view of the above, and an object of the present invention is to provide a stable method for estimating the strength of a rooted portion regardless of the amount of ground material contained in the sample.

In order to solve the above-mentioned problems and achieve the object, the method for estimating the strength of the cemented portion according to the present invention is formed by injecting and solidifying a liquid containing cement milk into the bottom of a pile hole excavated from the ground. A method of estimating the strength of a cemented portion, the first step of collecting the constituents of the layer as a first sample from the layer on which the cemented portion of the ground is formed, and the first step. Multiple types of cement milk containing a sample as an aggregate are generated and solidified, and the cement water ratio of the cement milk containing the first sample as an aggregate is based on the cement water ratio of the cement milk and the compressive strength after solidification. The second step of obtaining the relational expression between the cement milk and the compressive strength, and the third step of injecting cement milk into the bottom of the excavated pile hole and collecting the mixture of the cement milk and the excavated earth and sand after the injection as the second sample. Steps, a fourth step of removing the constituents of the layer from the second sample, and a cement water ratio of the second sample from the second sample from which the constituents of the layer were removed. It has a fifth step to be obtained, and a sixth step of estimating the compressive strength of the solidified portion from the cement water ratio of the second sample and the relational expression calculated in the second step. It is characterized by.

In the method for estimating the strength of the root compaction according to the present invention, a sieve having a step of obtaining the particle size distribution of the first sample and a sieve capable of separating the second sample into aggregate and cement milk is used. It has a step of selecting from the particle size distribution, and in the fourth step, the sieve may be used to remove the constituents of the layer.

According to the above configuration, the compressive strength of the root compaction is estimated from the relationship between the cement water ratio and the compression strength. Therefore, the compression of the root compaction 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 cemented portion can be estimated more accurately.

FIG. 1 is a vertical cross-sectional view showing a foundation pile according to an embodiment of the present invention. FIG. 2 is a vertical sectional view showing a construction procedure according to an 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 flowchart showing a part of the construction procedure of the method for estimating the strength of the root compaction portion according to the embodiment of the present invention.

Hereinafter, a preferred embodiment of the method for estimating the strength of the rooted portion according to the present invention will be described in detail with reference to the accompanying drawings with reference to FIGS. 1 to 4. This method for estimating the strength of the solidified portion is a method for estimating the strength of the solidified portion formed by injecting a liquid containing cement milk into the bottom of the excavated pile hole at the time of construction of the foundation pile. In the present embodiment, as shown in FIG. 1, in the ground 11, a foundation pile 31 is arranged in the pile hole 1 after a consolidation portion is constructed at the bottom of the pile hole 1 excavated from the ground surface to the support layer 12. In this case, a method of estimating the strength of the solidified portion before arranging the foundation pile 31 will be illustrated. As shown in FIG. 2A, the excavator used when excavating the pile hole 1 is provided with an excavation head 3 at the tip of the excavation rod 2. 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 opposite direction, the excavated teeth expand and expanded digging is possible.

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

Second step: Obtain the particle size distribution of the first sample. The particle size distribution may be determined using a particle size distribution measuring device, a sieve, or the like. A sieve having an opening that allows the components of the support layer 12 to be separated from the cement milk containing the components of the support layer 12 is selected based on the particle size distribution of the first sample and the cement. A sieve having eyes that can separate cement milk containing the constituents of the support layer 12 as an aggregate into cement milk and the aggregate is selected based on the first sample and the particle size distribution of the cement. As a selection criterion, a sieve having the largest opening that can separate the components of the support layer 12 is selected. This is to prevent clogging. A first sample such as a confirmation experiment described later, in which the density after sieving cement milk containing the constituents of the support layer 12 as an aggregate is equivalent to that of cement milk containing no aggregate. It may be obtained from an experiment using.

Third step: By 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 compressive strength of the solidified product, the first step is performed. Calculate the relational expression between the cement water ratio and the compressive strength of cement milk containing one sample as an aggregate. More specifically, cement milk as a test body containing the first sample as an aggregate was produced by changing the amount of aggregate, the amount of cement, and the amount of water, and the cement-water ratio thereof. And solidify them, and measure the compressive strength at 28 days of age. From the result, as shown in FIG. 3, the relational expression (regression expression) 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), sand-mixed clay (FIG. 3B), sandy clay (FIG. 3C), and sand-mixed gravel (FIG. 3D). An example of the relationship between the cement water ratio and the compressive strength of cement milk containing the first sample as an aggregate 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.

Fourth step: As shown in FIG. 2A, the pile hole 1 is excavated by the excavation rod 2 while injecting water (excavation liquid) at the construction site of the foundation pile 31. When excavating the pile hole 1, as shown in FIG. 2B, it is preferable to excavate while leveling the side wall of the pile hole 1 with the kneading drum 4. The excavated pile hole 1 will be filled with muddy water 13 in which the injected water and the ground material such as excavated earth and sand are mixed. After excavating until the support layer 12 is reached, the excavation rod 2 is reversed and the excavation head 3 which is the tip of the excavation rod 2 is expanded. In that state, as shown in FIG. 2B, the support layer 12 is expanded and excavated by the excavation rod 2 with a diameter larger than that of the other portion of the pile hole 1 to form the enlarged portion 1A. Then, as shown in FIG. 2C, cement milk (root hardening liquid) is injected into the enlarged portion 1A, and the muddy water 13 and the ground material such as excavated earth and sand, mainly the constituents of the support layer 12, are stirred and mixed. The cement milk is mainly soil cement 21 containing 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, a sample (second sample) is taken from the soil cement 21 (mixture of cement milk and excavated earth and sand) containing the constituents of the support layer 12 as an aggregate before the soil cement 21 solidifies. (Step S101). As a method for collecting a sample, for example, a sampler is attached to the tip of the excavation rod 2 to collect a sample. Before collecting the second sample, the cement milk, the muddy water 13, and the ground material were stirred and mixed by the excavator rod 2 of the excavator, but it is not necessary to stir and mix.

Fifth step: The aggregate is removed from the second sample (step S102). The aggregate is considered to be mainly a constituent of the support layer 12. As a method for removing the aggregate, it is preferable to use the sieve selected in the second step. Further, a sieve having a mesh opening of 0.15 mm may be used.

Sixth step: Determine the cement water ratio of the second sample. A test piece is prepared from the second sample from which the aggregate has been removed, and its mass and volume are determined (step S103). As a method, for example, a second sample from which the aggregate has been removed is injected into a container having a known volume until the container is filled, and a test piece is prepared. Then, the mass of the test piece is obtained. The volume of the test piece is the volume of the container. From the following mass equation and volume equation, the mass of cement and the mass of water in the test piece are obtained. From the mass of cement and the mass of water in the test piece, the cement-water ratio of the second sample is obtained (step S104).
W _C + W _W = W ₀ (1) Mass equation
W _C / ρ _C + W _W / ρ _W = V ₀ (2) Volume equation
W _C : Cement mass, W _W : Water mass, W ₀ : Specimen mass, ρ _C : Cement density (≈3.15), ρ _W : Water density (≈1.0), V ₀ : Specimen volume

Seventh step: The compressive strength of the root compaction portion 32 is estimated from the cement water ratio of the second sample and the above-mentioned relational expression (strength evaluation expression) (step S105).

Eighth step: Determining whether the estimated strength meets the design criteria (step S106). When the design criteria are satisfied, the strength estimation of the root compaction portion is completed (step S106, Yes). On the other hand, when the design criteria are not satisfied (steps S106, No), the material age X-day strength of the second sample or the core strength of the root consolidation portion 32 is measured (step S107). It is determined whether the material age X-day strength of the second sample or the core strength of the root consolidation portion 32 satisfies the design criteria (step S108). When the design criteria are satisfied, the strength estimation of the root compaction portion is completed (step S108, Yes). On the other hand, when the design criteria are not satisfied (steps S108 and No), the root consolidation portion 32 is reconstructed (step S109). Then, the process returns to step S101. When it is estimated that the compressive strength of the root consolidation portion 32 is sufficient, as shown in FIG. 2E, the pile circumference fixing liquid 22 is injected into the portion 1B above the enlarged portion 1A in the pile hole 1 to near the ground surface. .. At that time, the muddy water 13 overflowing to the ground may be solidified by adding, for example, a cement-based solidifying material, and disposed of as industrial waste having a viscosity sufficient to be transported by truck. After that, as shown in FIG. 2F, the foundation pile 31 is sunk until it reaches the enlarged portion 1A. When the soil cement 21 of the enlarged portion 1A hardens, it becomes the root hardening portion 32.

As described above, a relational expression between the cement water ratio of cement milk containing the sample as an aggregate and the compressive strength of the solidified product after collecting a sample from the part serving as the support layer 12 of the foundation pile 31 in advance. Ask for. Then, a sample is taken from the cement milk (soil cement 21) before solidification injected into the enlarged portion 1A when the root hardening portion 32 is constructed, the cement water ratio of the sample is obtained, and the compressive strength is obtained from the above relational expression. I try to ask for. The cement water ratio is an amount determined only by 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.

Further, when the cement water ratio of the second sample is obtained, the cement water ratio is obtained after removing the aggregate, so that the cement water ratio can be easily obtained.

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

Further, since the number of days required for estimating the compressive strength can be set within one day after the cement milk is placed in the enlarged portion 1A, the rooting portion 32 can be repaired at an early stage. When removing the aggregate in the sample, the aggregate in the sample can be confirmed, and it can be confirmed whether or not the pile hole 1 has reached the support layer 12.

(Confirmation experiment)
-Materials used: Portland cement was usually used as the cement, and tap water was used as the water. The prepared test piece is
・ Water cement mass ratio W / C = 0.6,0.8,1.0
・ Sand cement mass ratio S / C = 1.0
-Type of soil Sandy soil and gravel soil were used, and a root consolidation liquid was simulated. The material properties of the materials used are shown in Table 1 and the formulations are shown in Table 2. The aggregate was previously dried in a drying oven at 105 ° C.

・粒度分布
材料の粒度分布を表２に示す。礫、砂は、0.075mm以上で、体積の98%以上を占める。また、セメントの粒子径は、0.075mm以上が体積のわずか4.6%であり、0.15mm以上は1%程度である。このような場合、適切な篩を使用することで、それぞれの材料が分離可能である。

-Particle size distribution Table 2 shows the particle size distribution of the material. The gravel and sand are 0.075 mm or more and occupy 98% or more of the volume. The particle size of cement is 0.075 mm or more, which is only 4.6% of the volume, and 0.15 mm or more, which is about 1%. In such cases, each material can be separated by using an appropriate sieve.

-Separation by sieve and measurement of density Material kneading conforms to JIS R 5201. It was examined whether the mixed material could be separated into aggregates using a sieve. The sieves used were sieves with a mesh size of 1 mm, 0.6 mm, 0.3 mm, 0.15 mm, and 0.075 mm. After passing through the sieve, the sample is driven into a tin cylindrical form with a diameter of 50 mm and a height of 100 mm (volume 196.3 cm ³ ) so that air bubbles do not enter as much as possible, and then the driven surface is smoothed and the mass is measured. The density was calculated. The measurement results of the density after passing through the sieve are shown in Tables 3 and 4. Regardless of the use of sandy soil or gravel soil, when a 0.15 mm sieve is used, the density is almost the same as the density of the paste alone, and it is clear that the aggregate and the paste can be separated.

In addition, since the paste density (cement weight and water weight) can be obtained, the aggregate content can be calculated from the initial density, and the composition of the unconsolidated sample whose material composition is unknown. There is also an effect that can clarify.

In the above-described embodiment, the bottom of the pile hole 1 is expanded and dug to form the enlarged portion 1A, but the enlarged portion 1A is not formed and cement is formed on the bottom of the pile hole 1 having the same diameter as the other portions. Milk may be injected to form a cemented portion. Although the cement-water ratio is used in the above-described embodiment, the water-cement ratio may be used. It may be the ratio of the amount of cement to the amount of water. 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 fifth step.

1 Pile hole 1A Enlarged part 11 Ground 12 Support layer 21 Soil cement 31 Foundation pile 32 Root consolidation part

Claims (2)

It is a method of estimating the strength of the root consolidation part formed by injecting a liquid containing cement milk into the bottom of a pile hole excavated in the ground and solidifying it.
The first step of collecting the constituents of the layer as the first sample from the layer on which the root compaction portion of the ground is formed, and
A plurality of types of cement milk containing the first sample as an aggregate are produced and solidified, and based on the cement water ratio of the cement milk and the compressive strength after solidification, the cement milk containing the first sample as an aggregate is obtained. The second step to find the 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 injected cement milk and the excavated earth and sand as a second sample.
A fourth step of removing the majority of the composition from the second sample,
A test piece was prepared from the second sample from which most of the constituents were removed, and a mass equation and a mass equation using the mass of the test piece, the volume of the test piece, the known density of cement, and the known density of water were used. The mass of the cement of the unknown test piece and the mass of the water of the unknown test piece were obtained using the volume equation, and the cement water ratio of the test piece was obtained using the obtained mass of the cement and the mass of the water. In the fifth step , the obtained cement water ratio is used as the cement water ratio of the second sample.
A sixth step of estimating the compressive strength of the root compaction portion from the cement water ratio of the second sample obtained in the fifth step and the relational expression calculated in the second step.
A method for estimating the strength of a rooted portion, which is characterized by having. The step of obtaining the particle size distribution of the first sample and
Based on the particle size distribution, a sieve for separating most of the constituents having a large particle size from the second sample and most of cement milk containing cement having a small particle size from the second sample is selected. Has a process and
The method for estimating the strength of a rooted portion according to claim 1, wherein in the fourth step, most of the constituents are removed from the second sample using the sieve.

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