JP2021080776A - Pile construction method, and pile - Google Patents

Abstract

To provide a pile construction method capable of preventing an inner wall of an excavated hole from collapsing to a columnar body side.SOLUTION: A pile construction method includes: an excavation step of forming an excavated hole 10 with a predetermined depth in a ground G; and a columnar body forming step of injecting air bubble-containing cement milk 14 which contains air bubble 13 generated by a foaming agent into the excavated hole 10, and stirring to mix it with excavated soil 15 generated by the excavation step, to form a columnar body 16 composed of soil cement containing the air bubble 13. Inner pressure of the air bubble 13 is applied to an inner wall of the excavated hole 10, to prevent the inner wall of the excavated hole 10 from collapsing to the columnar body 16 side.SELECTED DRAWING: Figure 1

Description

The present invention relates to a pile construction method for constructing a pile at a construction site, a method for producing bubble-containing cement milk used in the pile construction method, and a pile constructed by the pile construction method.

At construction sites such as construction works, support pillar-row piles and buildings for constructing earth retaining walls to prevent sediment from collapsing from the adjacent land side of the construction site to the construction site side during ground excavation work. Support piles are formed. As a method of constructing this pile, for example, there is a method shown in Patent Document 1 below. In this construction method, cement, water, and cement milk containing bentonite as the main components are injected into the excavation hole excavated in the ground, and the excavated soil generated by the excavation and cement milk are mixed by stirring. Form a columnar body made of cement. Then, before the soil cement solidifies, a core material such as H-shaped steel is inserted into the excavation hole to construct a columnar body in which the core material is embedded (paragraphs 0017 to 0037 of Patent Document 1, FIG. 1). ~ See Fig. 3 etc.).

Japanese Unexamined Patent Publication No. 2012-107444

In the method for constructing a retaining wall according to Patent Document 1, the water in the cement milk is absorbed by the inner wall of the excavation hole, so that the inner wall is easily loosened, and a part of the inner wall may collapse to the columnar side. When this collapse occurs, the strength of the columnar body after the soil cement solidifies becomes insufficient, and the collapsed earth and sand accumulates at the bottom of the excavation hole, making it difficult to insert the core material into the excavation hole. Problems can occur.

Therefore, it is an object of the present invention to prevent the inner wall of the excavation hole from collapsing toward the columnar body side.

In order to solve the above problems, the present invention comprises an excavation step of forming an excavation hole of a predetermined depth in the ground, and the excavation while injecting bubble-containing cement milk containing air bubbles generated by a foaming agent into the excavation hole. It has a columnar body forming step of forming a columnar body made of soil cement containing the bubbles by stirring and mixing with the excavated soil generated in the process, and the internal pressure of the bubbles acts on the inner wall of the excavated hole. Therefore, a pile construction method for preventing the inner wall of the excavation hole from collapsing toward the columnar body was constructed.

The smaller the diameter of the bubbles introduced into the soil cement, the more stable the internal pressure (gauge pressure) with respect to the pressure around the bubbles can be maintained. The inner wall of the excavation hole is pressed outward in the radial direction by the internal pressure of air bubbles in contact with the inner wall. Therefore, it is possible to prevent the inner wall of the excavation hole from collapsing toward the columnar body side due to this pressing.

In the above configuration, the diameter of the bubbles is preferably in the range of 20 μm or more and 500 μm or less.

In this way, the pressing force required to prevent the inner wall of the excavation hole from collapsing can be applied from the bubbles toward the inner wall.

Further, in the present invention, there are a bubble generation step of generating bubbles by a compressed gas having a pressure higher than atmospheric pressure and a foaming agent, a first miniaturization step of micronizing the bubbles through a micronization means, and miniaturization. Bubbles having a second miniaturization step of bursting the bubbles with the internal pressure to make finer bubbles, and a mixing step of mixing the bubbles refined by the second miniaturization step with cement milk. A method for producing the contained cement milk was constructed.

In the above-mentioned pile construction method, as described above, the smaller the diameter of the bubble, the higher the internal pressure of the bubble can be stably held, but it is not easy to form fine bubbles. Therefore, by sequentially performing the two steps of the first miniaturization step and the second miniaturization step and then mixing the cement milk, the cement milk in which the fine bubbles are mixed can be easily formed.

In the above configuration, the diameter of the bubbles after the second miniaturization step is preferably in the range of 20 μm or more and 500 μm or less.

In this way, as described above, the pressing force required to prevent the inner wall of the excavation hole from collapsing can be applied from the bubbles toward the inner wall.

Further, in the present invention, it has a columnar body obtained by stirring and mixing bubble-containing cement milk containing bubbles generated by a foaming agent and excavated soil generated by excavation of the ground, and the diameter of the bubbles is 20 μm or more and 500 μm. The piles in the following range were constructed.

In this way, the inner wall of the excavation hole does not collapse during the construction of this pile, and a columnar body made of homogeneous soil cement can be constructed up to the bottom of the excavation hole. Can be secured.

In the present invention, the pile construction method is accompanied by an excavation step of forming an excavation hole of a predetermined depth in the ground and the excavation step while injecting bubble-containing cement milk containing air bubbles generated by a foaming agent into the excavation hole. It has a columnar body forming step of forming a columnar body made of soil cement containing the air bubbles by stirring and mixing with the excavated soil generated in the above, and the internal pressure of the air bubbles is applied to the inner wall of the excavation hole to form the columnar body. Since the inner wall of the excavation hole is prevented from collapsing toward the columnar body side, it is possible to prevent the inner wall of the excavation hole from collapsing toward the columnar body side due to the radial outward pressing by the air bubbles introduced in the soil cement. be able to.

It is sectional drawing which shows the process of the pile construction method which concerns on this invention. FIG. The state where the body is formed, (c) is the state where the columnar body is completed. Enlarged view of part A in FIG. 1 (c) It is a cross-sectional view which shows the process of a pile construction method, (a) is a state which the 1st steel sheet pile is being inserted into a columnar body, (b) is a state which the insertion of the 1st steel sheet pile is completed, (C) is a state in which a newly formed columnar body is formed next to the first steel sheet pile, and (d) is a state in which a second steel sheet pile is being inserted into the newly formed columnar body, (e). Is the state where the insertion of the second steel sheet pile is completed The schematic diagram which shows the bubble-containing cement milk generation apparatus used in the bubble-containing cement milk generation method which concerns on this invention.

Each step of the pile construction method according to the present invention will be described with reference to FIGS. 1 (a) to 1 (c). The main components of this pile construction method are the excavation process and the columnar body formation process.

As shown in FIG. 1A, the excavation step is a step of forming an excavation hole 10 having a predetermined depth in the ground G. An excavation blade 12 is attached to the lower end side of the auger 11, and when the auger 11 is rotationally driven, the ground G is excavated by the excavation blade 12.

In the columnar body forming step, as shown in FIG. 1 (b), the bubble-containing cement milk 14 containing the bubbles 13 is injected from a nozzle provided at the lower end of the excavation blade 12, and the excavation blade 12 is rotated a plurality of times. By moving up and down, the excavated soil 15 in the excavation hole 10 and the bubble-containing cement milk 14 are stirred and mixed to form a columnar body 16 made of soil cement containing the bubbles 13.

The cement milk 17 (see FIG. 4) used for producing the bubble-containing cement milk 14 contains cement and water as main components. The blending ratio (blending amount) of this main component is, for example, cement: water = 200 kg: 300 kg. At this blending ratio, the water-cement ratio (water / cement x 100) is 150. For example, about 200 L of bubbles 13 generated by the foaming agent is introduced into the cement milk 17, and in the case of the above-mentioned blending amount, the total volume of the bubble-containing cement milk 14 including the bubbles 13 is about 550 to 600 L. At this time, the ratio of the bubbles 13 to the total volume of the bubble-containing cement milk 14 (air bubble injection rate) is about 0.35, and its specific weight is about 0.91. In this embodiment, a surfactant (trade name: Emar (manufactured by Kao Corporation)) was used as a foaming agent.

The bubble-containing cement milk 14 used in this embodiment is adjusted to have a smaller water content than normal cement milk (for example, a water-cement ratio of 250) in response to the increase in volume accompanying the generation of bubbles 13. .. Therefore, the soil cement produced by using the bubble-containing cement milk 14 has a higher viscosity than the ordinary soil cement. By reducing the amount of water in the bubble-containing cement milk 14 in this way, the amount of water absorbed from the bubble-containing cement milk 14 into the ground G is reduced. Therefore, the effect of preventing the ground G from loosening due to the absorption of water and the inner wall of the excavation hole 10 from collapsing toward the columnar body 16 side made of soil cement is further enhanced.

It is permissible to appropriately add an additive for stabilizing the generated bubbles 13 to the foaming agent. As this additive, for example, a polymer compound that increases the viscosity of the bubble-containing cement milk 14 can be adopted.

In the case of soil with a large amount of stones and sand and the inner wall easily collapsing, it is permissible to add a small amount of bentonite (for example, 25 kg of bentonite to 200 kg of cement) to the cement milk 17. As described above, when bentonite is added, the clay component permeates the inner wall and protects the inner wall, so that the collapse of the inner wall can be prevented more reliably.

When the columnar body forming step is completed, as shown in FIG. 1 (c), the air bubble-containing cement milk 14 and the excavated soil 15 are agitated and mixed in the excavation hole 10, and the air bubbles 13 are evenly introduced into the soil cement. A columnar body 16 made of the material is formed.

An enlarged view of part A in FIG. 1 (c) is shown in FIG. Bubbles 13 are introduced at high density inside the columnar body 16. The average diameter of the bubbles 13 can be, for example, about 500 μm. A part of the bubble 13 is in contact with the inner wall of the excavation hole 10. In FIG. 2, each bubble 13 is shown as a closed cell, but in reality, it is often an open cell in which a large number of bubbles 13 are connected, and the open cell is the inner wall of the excavation hole 10. Is in contact over a wide area.

The bubbles 13 are high-pressure gases (for example, 0.7 MPa (about 7 atm)) sent from a compressed gas delivery device (not shown) connected to a bubble-containing cement milk generation device 18 (see FIG. 4) described later. ). The volume of the high-pressure gas and the volume increase of the bubble-containing cement milk 14 (volume difference between the bubble-containing cement milk 14 and the original cement milk 17; see ΔV in FIG. 4) are almost the same and are substantially the same. Since there is no leakage of the high-pressure gas from the bubble-containing cement milk generator 18, it can be estimated that the internal pressure of the bubbles 13 is about the same as the pressure of the original high-pressure gas. In this way, by allowing the bubbles 13 having a high internal pressure to act on the inner wall of the excavation hole 10 (see FIG. 2), it is possible to prevent the inner wall from collapsing toward the columnar body 16.

Generally, the pressure difference Δp inside and outside the bubble 13 is derived from the Young-Laplace equation shown below.
Δp = pp'= 2γ / R
Here, p is the pressure inside the bubble, p'is the pressure outside the bubble, γ is the surface tension, and R is the radius of the bubble.

The Young-Laplace equation shows that the larger the surface tension γ or the smaller the bubble radius R, the higher the pressure difference Δp inside and outside the bubble 13. For example, assuming that the surface tension γ of the foaming agent (surfactant) is 50 mN / m, the pressure difference Δp is about 400 Pa (0.004 atm) when the bubble radius R is 250 μm (diameter is 500 μm). This pressure difference Δp is very small as compared with the pressure of the high-pressure gas (for example, 0.7 MPa) delivered from the compressed gas delivery device. The reason for this is not clear, but for example, the apparent surface tension of the cement milk 17 is much larger than the surface tension of the foaming agent, and the bubbles 13 having a high internal pressure can be maintained. Conceivable.

The diameter of the bubble 13 is not particularly limited, but is preferably in the range of 20 μm or more and 500 μm or less. It is difficult to generate bubbles 13 having a diameter smaller than 20 μm, which is not preferable because there is a risk of increasing the working cost. Further, the bubble 13 having a diameter larger than 500 μm is not preferable because it is difficult to maintain a sufficient internal pressure p that can prevent the inner wall of the excavation hole 10 from collapsing. The diameter of the bubble 13 is more preferably in the range of 100 μm or more and 500 μm or less.

As shown in FIGS. 3A to 3E, the core material 19 is embedded in the columnar body 16 made of soil cement. In this embodiment, a steel sheet pile is used as the core material 19. First, the first steel sheet pile 19a is inserted into the unsolidified columnar body 16 up to the bottom of the excavation hole 10a (see FIGS. 3A and 3B). After inserting the first steel sheet pile 19a, an excavation hole 10b adjacent to the steel sheet pile 19a is formed, and a new columnar body 16 is formed in the excavation hole 10b (see FIG. 3C). Then, the second steel sheet pile 19b is inserted into the newly formed columnar body 16. The first steel sheet pile 19a and the second steel sheet pile 19b are connected to each other by joints formed at both ends of the steel sheet piles 19a and 19b in the lateral width direction (see FIGS. 3 (d) and 3 (e)). By repeating the operations shown in FIGS. 3 (c) to 3 (e), the earth retaining wall 20 connecting the required number of steel sheet piles (core material 19) is constructed.

The pile (retaining wall 20) constructed in this way contains bubbles 13 having a diameter in the range of 20 μm or more and 500 μm or less inside the columnar body 16, and the high internal pressure p of the bubbles 13 is excavated. The inner wall of the hole 10 (10a, 10b) is pressed outward in the radial direction. Therefore, the inner wall of the excavation hole 10 (10a, 10b) does not collapse during the construction of the pile, and a homogeneous columnar body 16 can be constructed up to the bottom of the excavation hole 10 (10a, 10b). Sufficient strength can be secured.

Here, the earth retaining wall 20 using the steel sheet piles 19a and 19b has been described as an example, but the present invention can also be applied to a ground improvement pile of a building or the like. Further, the core material 19 is not limited to the steel sheet piles 19a and 19b, and other shapes such as H-shaped steel can also be adopted.

By introducing the air bubbles 13 into the soil cement in this way, the frictional force between the columnar body 16 and the core material 19 inserted into the columnar body 16 is reduced. Therefore, there is also an advantage that the core material 19 can be smoothly inserted into the columnar body 16 and the core material 19 can be smoothly pulled out from the columnar body 16 after the retaining wall 20 is used up.

The bubble-containing cement milk 14 is produced by the method for producing bubble-containing cement milk described below. The method for producing the bubble-containing cement milk includes a bubble generation step, a first miniaturization step, a second miniaturization step, and a mixing step.

The bubble generation step is a step of generating bubbles 13 by using a compressed gas having a pressure higher than atmospheric pressure and a foaming agent. In this bubble generation step, the process is controlled so that the total volumes of the high-pressure compressed gas and the bubbles 13 are substantially the same, and the internal pressure of the bubbles 13 is estimated to be substantially the same as the pressure of the compressed gas. The pressure of the compressed gas is preferably in the range of 0.1 MPa or more and 1.0 MPa or less, more preferably in the range of 0.3 MPa or more and 0.9 MPa or less, and 0.5 MPa or more and 0.8 MPa or less. It is more preferable to keep it within the range. As this compressed gas, various gases such as compressed air and compressed nitrogen can be adopted.

The first miniaturization step is a step of miniaturizing the bubbles 13 generated by the foaming agent through a miniaturization means. Among the bubbles 13 generated by the mixing step, large bubbles having a diameter of several mm or more are also mixed. Since the internal pressure of such a large bubble 13 cannot be increased so much, the effect of pressing the inner wall of the excavation hole 10 is low. Therefore, by miniaturizing the large bubbles 13 in the first miniaturization step, the bubbles 13 having a high internal pressure are formed at a high density, and the inner wall of the excavation hole 10 can be effectively pressed.

The second miniaturization step is a step of self-rupturing the bubbles 13 miniaturized by the first miniaturization step into finer bubbles 13. Most of the bubbles 13 are miniaturized by the first miniaturization step, but some bubbles 13 may not be sufficiently miniaturized. At this time, the internal pressure of the bubble 13 that has not been sufficiently miniaturized is excessive and unstable in terms of its diameter. If the non-fine bubbles 13 are left for a while, they will self-rupture due to the internal pressure thereof, whereby fine bubbles 13 will be generated at high density. The total volume of the bubbles 13 obtained in the second miniaturization step is substantially the same as the volume of the high-pressure compressed gas used in the bubble generation step. Therefore, it is estimated that the internal pressure of the bubbles 13 is almost the same as the pressure of the compressed gas.

The mixing step is a step of mixing the bubbles 13 generated by the foaming agent and the cement milk 17. By this mixing step, the bubble-containing cement milk 14 in which the bubbles 13 are incorporated is produced. The volume of the bubble-containing cement milk 14 is substantially the same as the total volume of the cement milk 17 and the bubbles 13 obtained in the second miniaturization step. Therefore, it is estimated that the internal pressure of the bubbles 13 in the bubble-containing cement milk 14 is almost the same as the pressure of the compressed gas.

FIG. 4 shows an example of the bubble-containing cement milk generating device 18 that realizes the above-mentioned series of bubble-containing cement milk producing methods. The bubble-containing cement milk generation device 18 includes a plurality of bubble generation units 21, a connection pipe 22 for connecting the bubble generation units 21 to each other, and a gas introduction pipe connected to the upstream side of the bubble generation unit 21 on the most upstream side. It has a foaming agent introduction pipe 24, a discharge pipe 25 connected to the downstream side of the bubble generation unit 21 on the most downstream side, and a mixer 26 provided on the downstream side of the discharge pipe 25.

The bubble generation unit 21 has a tubular shape capable of flowing a fluid in one direction. The inside of the bubble generating portion 21 is filled with a spherical (bead-shaped) stirring member 27, and a plurality of filters 28 are installed so as to be separated from each other perpendicular to the flow direction of the fluid. .. The stirring member 27 and the filter 28 correspond to the above-mentioned miniaturization means. A compressed gas delivery device (not shown) is connected to the gas introduction pipe 23, and a foaming agent tank (not shown) is connected to the foaming agent introduction pipe 24. The gas introduction pipe 23 is connected to the gas introduction pipe 23. A high-pressure compressed gas (compressed air in this embodiment) is sent through the foaming agent introduction pipe 24, and the foaming agent is sent to the bubble generation unit 21 on the most upstream side.

Bubbles 13 are generated by mixing the compressed gas and the foaming agent, and the bubbles 13 are miniaturized when passing through the gap between the stirring members 27 and the filter 28 (first miniaturization step). .. By arranging the plurality of bubble generating units 21 in series, the bubbles 13 can be smoothly miniaturized to a predetermined diameter. The size and filling amount of the stirring member 27, the coarseness of the mesh of the filter 28, the number of sheets, and the like are appropriately changed according to the diameter of the bubbles 13 after miniaturization. Further, the number of connected bubble generation units 21 can be changed as appropriate. The bubbles 13 refined by the first miniaturization step are sent to the discharge pipe 25 from the downstream side of the bubble generation unit 21 on the most downstream side.

The bubble generating section 21 of the bubble-containing cement milk generating device 18 shown in FIG. 4 uses both the stirring member 27 and the filter 28 in combination, but there is a case where only one of them is adopted. Further, in some cases, other miniaturization means can be adopted instead of the stirring member 27 and the filter 28. Further, in this configuration, four bubble generating units 21 are arranged in series, but the number can be increased or decreased as appropriate.

The discharge pipe 25 is a flexible hose having a length of several meters to 20 meters. It takes about several seconds to several tens of seconds for the bubble-containing cement milk 14 delivered from the bubble generation unit 21 to pass through the discharge pipe 25. Then, during the passage, the bubbles 13 that have not been sufficiently miniaturized while passing through the bubble generation unit 21 are self-ruptured by the internal pressure to generate fine bubbles 13 (second miniaturization step). As a result, most of the bubbles 13 are sufficiently miniaturized, and the inner wall of the excavation hole 10 is pressed outward in the radial direction by the high internal pressure p of the bubbles 13 to prevent the inner wall from collapsing.

The mixer 26 is a container for generating the bubble-containing cement milk 14 and temporarily storing it. The mixer 26 is pre-filled with a small amount of cement milk 17, and the tip of the discharge pipe 25 is inserted into the cement milk 17. When the bubble 13 is supplied from the discharge pipe 25, the bubble 13 is taken into the cement milk 17 and its volume increases (see the white arrow in FIG. 4), and the bubble-containing cement milk 14 is generated.

The pile construction method, the bubble-containing cement milk generation method, and the pile shown in the above embodiment are merely examples, and the present invention is to prevent the inner wall of the drilling hole 10 from collapsing toward the columnar body 16. As long as the above problems can be solved, changes can be made to a part of the steps of the pile construction method and the method of producing air-containing cement milk, and a part of the pile composition.

10 (10a, 10b) Drilling hole 11 Auger 12 Drilling blade 13 Bubble 14 Bubble-containing cement milk 15 Drilling soil 16 Columnar body 17 Cement milk 18 Bubble-containing cement milk generator 19 Core material 19a, 19b Steel sheet pile 20 Retaining wall 21 Bubble generation part 22 Connection pipe 23 Gas introduction pipe 24 Foaming agent introduction pipe 25 Discharge pipe 26 Mixer 27 Stirring member 28 Filter G Ground

Claims (5)

An excavation process for forming an excavation hole (10) with a predetermined depth in the ground (G), and
While injecting the bubble-containing cement milk (14) containing the bubbles (13) generated by the foaming agent into the excavation hole (10), the mixture is stirred and mixed with the excavated soil (15) generated in the excavation step to obtain the above. A columnar body forming step of forming a columnar body (16) made of soil cement containing air bubbles (13), and
A pile construction method in which the internal pressure of the bubble (13) is applied to the inner wall of the excavation hole (10) to prevent the inner wall of the excavation hole (10) from collapsing toward the columnar body (16). .. The pile construction method according to claim 1, wherein the diameter of the bubble (13) is in the range of 20 μm or more and 500 μm or less. A bubble generation step in which bubbles (13) are generated by a compressed gas having a pressure higher than atmospheric pressure and a foaming agent.
The first miniaturization step of miniaturizing the bubbles (13) through a miniaturization means, and
A second miniaturization step of bursting the finely divided bubbles (13) with its internal pressure to make finer bubbles (13).
A mixing step of mixing the bubbles (13) refined by the second miniaturization step and the cement milk (17), and
A method for producing bubble-containing cement milk having. The method for producing bubble-containing cement milk according to claim 3, wherein the diameter of the bubbles (13) after the second miniaturization step is in the range of 20 μm or more and 500 μm or less. It has a columnar body (16) in which a bubble-containing cement milk (14) containing bubbles (13) generated by a foaming agent and excavated soil (15) generated by excavation of the ground (G) are mixed by stirring. A pile in which the diameter of the bubble (13) is in the range of 20 μm or more and 500 μm or less.

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