JP7402836B2 - Method for producing aerated cement milk - Google Patents

Description

The present invention relates to a method for producing aerated cement milk.

At construction sites, pillar piles are used to construct earth retaining walls to prevent soil from collapsing from adjacent land to the construction site during ground excavation work, and to support buildings. Support piles are formed for this purpose. As a construction method for this pile, for example, there is a method shown in Patent Document 1 below. In this construction method, cement, water, and cement milk, whose main ingredients are bentonite, are poured into an excavated hole in the ground, and the excavated soil produced during the excavation is mixed with the cement milk. Forms columns made of cement. Then, before this soil cement solidifies, a core material such as an H-shaped steel is inserted into the excavated hole to construct a columnar body in which the core material is buried (paragraphs 0017 to 0037 of Patent Document 1, Figure 1 (See Figure 3, etc.)

Japanese Patent Application Publication No. 2012-107444

In the method for constructing an earth retaining wall according to Patent Document 1, moisture in cement milk is absorbed into the inner wall of the excavated hole, which tends to loosen the inner wall, and a part of the wall may collapse toward the columnar body. When this collapse occurs, the strength of the columnar body may be insufficient after the soil cement has solidified, or the collapsed earth and sand may accumulate at the bottom of the excavation hole, making it difficult to insert the core material into the excavation hole. problems may arise.

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

In order to solve the above-mentioned problems, the present invention includes an excavation process of forming an excavation hole of a predetermined depth in the ground, and an excavation step in which aerated cement milk containing air bubbles generated by a foaming agent is injected into the excavation hole. a columnar body forming step of forming a columnar body made of soil cement containing air bubbles by stirring and mixing with the excavated soil generated in the process, and causing the internal pressure of the air bubbles to act on the inner wall of the excavation hole. Thus, a pile construction method was constructed that prevented the inner wall of the excavated hole from collapsing toward the columnar body.

The smaller the diameter of the air bubbles introduced into the soil cement, the more stable the internal pressure (gauge pressure) relative to the surrounding pressure of the air bubbles can be maintained. The inner wall of the excavated hole is pressed radially outward by the internal pressure of the bubble in contact with the inner wall. Therefore, it is possible to prevent the inner wall of the excavated hole from collapsing toward the columnar body due to this pressing force.

In the above configuration, it is preferable that the diameter of the bubbles is in a range of 20 μm or more and 500 μm or less.

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

Further, in this invention, a bubble generation step of generating bubbles using a compressed gas having a pressure higher than atmospheric pressure and a foaming agent, a first micronization step of passing the bubbles through a micronization means and micronization, and a second refining step in which the bubbles are ruptured by their internal pressure to become even finer bubbles; and a mixing step in which the air bubbles refined in the second refining step are mixed with cement milk. A method for producing containing cement milk was constructed.

In the above pile construction method, as described above, the smaller the diameter of the bubbles, the more stable the internal pressure of the bubbles can be maintained, but it is not easy to form fine bubbles. Therefore, by sequentially performing the two steps of the first micronization step and the second micronization step and then mixing the cement milk, cement milk mixed with fine air bubbles can be easily formed.

In the above structure, it is preferable that the diameter of the bubbles after the second refinement step is in the range of 20 μm or more and 500 μm or less.

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

Further, the present invention has a columnar body made by stirring and mixing aerated cement milk containing air bubbles generated by a foaming agent and excavated soil generated by excavating the ground, and the diameter of the air bubbles is 20 μm or more and 500 μm or more. A pile with the following range was constructed.

By doing this, the inner wall of the excavated hole will not collapse during the construction of this pile, and a columnar body made of homogeneous soil cement can be constructed all the way to the bottom of the excavated hole, so that the sufficient strength of this pile can be maintained. can be secured.

The present invention provides a pile construction method that includes an excavation step of forming an excavation hole of a predetermined depth in the ground, and a step of injecting aerated cement milk containing air bubbles generated by a foaming agent into the excavation step. a columnar body forming step of forming a columnar body made of soil cement containing air bubbles by stirring and mixing with the excavated soil produced by Since the inner wall of the excavated hole is prevented from collapsing toward the columnar body, the inner wall of the excavated hole is prevented from collapsing toward the columnar body due to outward pressure in the radial direction by the air bubbles introduced into the soil cement. be able to.

2 is a cross-sectional view showing the steps of the pile construction method according to the present invention, in which (a) shows a state in which an excavated hole has been formed, and (b) shows a state in which aerated cement milk is injected and stirred and mixed to form a columnar structure made of soil cement. The state in which the body is formed, (c) the state in which the columnar body is completed Enlarged view of section A in Figure 1(c) It is a sectional view showing the process of the pile construction method, (a) is a state in which the first steel sheet pile is being inserted into the columnar body, (b) is a state in which insertion of the first steel sheet pile is completed, (c) shows a state where a new columnar body has been formed next to the first steel sheet pile, (d) shows a state where a second steel sheet pile is being inserted into the newly formed columnar body, and (e) shows a state where a second steel sheet pile is being inserted into the newly formed columnar body. The state in which the second steel sheet pile has been inserted is complete. A schematic diagram showing an apparatus for producing aerated cement milk used in the method for producing aerated cement milk according to the present invention.

Each step of the pile construction method according to the present invention will be explained using FIGS. 1(a) to (c). The main components of this pile construction method are an excavation process and a column formation process.

The excavation process is a process of forming an excavation hole 10 of a predetermined depth in the ground G, as shown in FIG. 1(a). An excavation blade 12 is attached to the lower end side of the auger 11, and when the auger 11 is driven to rotate, the ground G is excavated by the excavation blade 12.

As shown in FIG. 1(b), the columnar body forming process involves injecting a bubble-containing cement milk 14 containing air bubbles 13 from a nozzle provided at the lower end of the excavation blade 12, and repeating the process multiple times while rotating the excavation blade 12. This is a step of stirring and mixing the excavated soil 15 in the excavated hole 10 and the bubble-containing cement milk 14 by moving up and down, thereby forming a columnar body 16 made of soil cement containing bubbles 13.

The cement milk 17 (see FIG. 4) used to generate the aerated cement milk 14 has cement and water as its main components. The blending ratio (blending amount) of the main components is, for example, cement:water=200kg:300kg. At this mixing ratio, the water-cement ratio (water/cement x 100) is 150. For example, about 200 L of air bubbles 13 generated by the foaming agent are introduced into this cement milk 17, and in the case of the above-mentioned blending amount, the total volume of the aerated cement milk 14 including the air 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 (bubble injection rate) is about 0.35, and its specific gravity 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 has a water content adjusted to be lower than that of normal cement milk (for example, water-cement ratio is 250) to accommodate the increase in volume due to the generation of bubbles 13. . Therefore, soil cement produced using this aerated cement milk 14 has a higher viscosity than normal soil cement. In this way, by reducing the amount of water in the bubble-containing cement milk 14, the amount of moisture 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 moisture absorption and the inner wall of the excavated hole 10 from collapsing toward the columnar body 16 made of soil cement is further enhanced.

Additives for stabilizing the generated bubbles 13 may be appropriately added 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 employed.

Note that if the soil has a lot of stones and sand and the inner wall is likely to collapse, it is also permissible to add a small amount of bentonite to the cement milk 17 (for example, 25 kg of bentonite to 200 kg of cement). In this way, when bentonite is added, the clay component penetrates into the inner wall and protects the inner wall, making it possible to more reliably prevent the inner wall from collapsing.

When the columnar body formation process is completed, as shown in FIG. 1(c), the air-filled cement milk 14 and the excavated soil 15 are stirred and mixed in the excavated hole 10, and the air bubbles 13 are evenly introduced into the soil cement. A columnar body 16 is formed.

FIG. 2 shows an enlarged view of section A in FIG. 1(c). Air bubbles 13 are introduced into the interior of the columnar body 16 at a high density. The average diameter of the bubbles 13 can be, for example, about 500 μm. A portion of this bubble 13 is in contact with the inner wall of the excavated hole 10. Although each bubble 13 is shown as an independent bubble in FIG. 2, in reality, a large number of bubbles 13 are often connected to form a continuous cell, and this continuous cell forms the inner wall of the excavation hole 10. are in contact with a wide range of areas.

The bubbles 13 are generated by high-pressure gas (for example, 0.7 MPa (approximately 7 atm)) delivered from a compressed gas delivery device (not shown) connected to a bubble-containing cement milk production device 18 (see FIG. 4), which will be described later. ) is generated by. The volume of this 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 Since there is no leakage of high-pressure gas from the bubble-containing cement milk production device 18, it can be estimated that the internal pressure of the bubbles 13 is approximately the same as the pressure of the original high-pressure gas. In this way, by acting the high internal pressure bubbles 13 on the inner wall of the excavated 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 between the inside and outside of 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 bubble radius.

The Young-Laplace equation indicates that the larger the surface tension γ or the smaller the bubble radius R, the higher the pressure difference Δp between the inside and outside of the bubble 13. For example, if the surface tension γ of the foaming agent (surfactant) is 50 mN/m, the pressure difference Δp will be approximately 400 Pa (0.004 atm) when the bubble radius R is 250 μm (diameter is 500 μm). This pressure difference Δp is very small compared to the pressure of 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 that of the foaming agent, making it possible to maintain the bubbles 13 at a high internal pressure. Conceivable.

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

A core material 19 is embedded in the columnar body 16 made of soil cement, as shown in FIGS. 3(a) to 3(e). In this embodiment, steel sheet piles are used as the core material 19. First, the first steel sheet pile 19a is inserted into the unsolidified columnar body 16 until it reaches the bottom of the excavated hole 10a (see FIGS. 3(a) and 3(b)). After inserting the first steel sheet pile 19a, an excavated hole 10b adjacent to the steel sheet pile 19a is formed, and a new columnar body 16 is formed in the excavated hole 10b (see FIG. 3(c)). 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 in the width direction of each steel sheet pile 19a, 19b (see FIGS. 3(d) and (e)). By repeating the operations shown in FIGS. 3(c) to 3(e), an earth retaining wall 20 in which the required number of steel sheet piles (core material 19) are connected is constructed.

The pile (earth retaining wall 20) constructed in this way contains air bubbles 13 with 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 air bubbles 13 causes the excavation. The inner walls of the holes 10 (10a, 10b) are pressed radially outward. Therefore, during the construction of the pile, the inner wall of the excavated hole 10 (10a, 10b) does not collapse, and a homogeneous columnar body 16 can be constructed to the bottom of the excavated hole 10 (10a, 10b). sufficient strength can be ensured.

Although the earth retaining wall 20 using steel sheet piles 19a and 19b has been described here as an example, the present invention can also be applied to ground improvement piles for buildings, etc. 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.

In this way, by introducing the air bubbles 13 into the soil cement, the frictional force between the columnar body 16 and the core material 19 inserted into the columnar body 16 is reduced. Therefore, there is 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 earth retaining wall 20 is used up.

Aerated cement milk 14 is produced by the method for producing aerated cement milk described below. This method for producing aerated cement milk includes a foaming step, a first refining step, a second refining step, and a mixing step.

The bubble generation process is a process of generating bubbles 13 using compressed gas at a pressure higher than atmospheric pressure and a foaming agent. In this bubble generation process, the process is controlled so that the total volume of the high-pressure compressed gas and the bubbles 13 are approximately the same, and the internal pressure of the bubbles 13 is estimated to be approximately 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 0.3 MPa or more and 0.9 MPa or less, and 0.5 MPa or more and 0.8 MPa or less. More preferably, it is within this range. Various gases such as compressed air and compressed nitrogen can be used as this compressed gas.

The first pulverization step is a step in which the bubbles 13 generated by the foaming agent are passed through a pulverization means to be pulverized. Among the bubbles 13 generated by the mixing process, there are also large bubbles with a diameter of several mm or more. Since the internal pressure of such large bubbles 13 cannot be increased very much, the effect of pressing against the inner wall of the excavated hole 10 is low. Therefore, by refining the large bubbles 13 in the first refining step, the bubbles 13 with high internal pressure are formed at a high density and can effectively press the inner wall of the excavated hole 10.

The second refinement process is a process in which the bubbles 13 made fine by the first refinement process are made to self-rupture to become even finer bubbles 13 . Although most of the bubbles 13 are refined by the first refinement step, some of the bubbles 13 may not be refined enough. At this time, the internal pressure of the bubbles 13, which have not been sufficiently miniaturized, is excessive and unstable considering their diameter. If these unrefined air bubbles 13 are left for a while, they will self-rupture due to their internal pressure, thereby generating fine air bubbles 13 at a high density. The total volume of the bubbles 13 obtained by the second refinement step is approximately the same as the volume of the high-pressure compressed gas used in the bubble generation step. Therefore, the internal pressure of this bubble 13 is also estimated to be approximately 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. This mixing process produces aerated cement milk 14 in which air bubbles 13 are incorporated. The volume of this bubble-containing cement milk 14 is approximately the same as the total volume of the cement milk 17 and the bubbles 13 obtained in the second refinement step. Therefore, the internal pressure of the bubbles 13 in the bubble-containing cement milk 14 is estimated to be approximately the same as the pressure of the compressed gas.

FIG. 4 shows an example of an aerated cement milk production device 18 that implements the above series of methods for producing aerated cement milk. This bubble-containing cement milk generation device 18 includes a plurality of bubble generating sections 21, a connecting pipe 22 that connects the bubble generating sections 21 to each other, and a gas introduction tube connected to the upstream side of the bubble generating section 21 on the most upstream side. 23 and a foaming agent introduction pipe 24, a discharge pipe 25 connected to the downstream side of the foam generating section 21 on the most downstream side, and a mixer 26 provided downstream of the discharge pipe 25.

The bubble generating section 21 has a tubular shape that allows fluid to flow in one direction. The bubble generating section 21 is filled with a spherical (bead-shaped) stirring member 27, and furthermore, a plurality of filters 28 are installed spaced apart from each other perpendicular to the fluid flow direction. . The stirring member 27 and the filter 28 correspond to the aforementioned micronization 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 . A high-pressure compressed gas (compressed air in this embodiment) passes through the foaming agent introduction pipe 24, and the foaming agent is fed into the bubble generation section 21 on the most upstream side.

Bubbles 13 are generated as the compressed gas and the foaming agent are mixed, and the bubbles 13 are made fine as they pass through the gap between the stirring members 27 and the filter 28 (first atomization step). . By arranging a 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 filters 28, the number of filters, and the like are changed as appropriate depending on the diameter of the bubbles 13 after micronization. Further, the number of connected bubble generating units 21 can also be changed as appropriate. The bubbles 13 made fine by the first making process are sent to the discharge pipe 25 from the downstream side of the bubble generation section 21 on the most downstream side.

Although the bubble generating unit 21 of the bubble-containing cement milk generating device 18 shown in FIG. 4 uses both the stirring member 27 and the filter 28, it may be possible to employ only one of them. Further, in place of the stirring member 27 and the filter 28, other micronization means may be adopted. Further, in this configuration, four bubble generating units 21 are arranged in series, but this number can be increased or decreased as appropriate.

The discharge pipe 25 is a flexible hose with a length of several meters to about 20 meters. It takes several seconds to several tens of seconds for the bubble-containing cement milk 14 sent out from the bubble generating section 21 to pass through the discharge pipe 25. Then, during the passage, the bubbles 13 that were not sufficiently refined while passing through the bubble generation section 21 are self-ruptured by their internal pressure to generate fine bubbles 13 (second refinement step). As a result, most of the bubbles 13 are sufficiently miniaturized, and the high internal pressure p of the bubbles 13 presses the inner wall of the excavated hole 10 radially outward, thereby preventing the inner wall from collapsing.

The mixer 26 is a container for producing and temporarily storing the aerated cement milk 14. This mixer 26 is filled with a small amount of cement milk 17 in advance, and the tip of the discharge pipe 25 is inserted into this cement milk 17. When the air bubbles 13 are supplied from the discharge pipe 25, the air bubbles 13 are taken into the cement milk 17, its volume increases (see the white arrow in FIG. 4), and the air bubble-containing cement milk 14 is produced.

The pile construction method, the method for producing aerated cement milk, and the pile shown in the above embodiments are merely examples, and this invention prevents the inner wall of the excavated hole 10 from collapsing toward the columnar body 16 side. As long as the problem can be solved, it is possible to make changes to part of the steps of the pile construction method and the method of producing aerated cement milk, and to part of the structure of the pile.

10 (10a, 10b) Drilled hole 11 Auger 12 Drilling blade 13 Bubbles 14 Bubbles-containing cement milk 15 Excavated soil 16 Column 17 Cement milk 18 Bubbles-containing cement milk generating device 19 Core material 19a, 19b Steel sheet pile 20 Earth retaining wall 21 Bubbles generating section 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 (2)

a bubble generation step of generating bubbles (13) using compressed gas at a pressure higher than atmospheric pressure and a foaming agent;
a first refining step of passing the bubbles (13) through a refining means;
a second micronization step of bursting the micronized air bubbles (13) with their internal pressure to form even smaller air bubbles (13);
a mixing step of mixing the air bubbles (13) refined by the second refinement step with cement milk (17);
has
A method for producing aerated cement milk, wherein the atomization means is constituted by a spherical stirring member (27) and a plurality of filters (28) installed spaced apart from each other perpendicular to the flow direction of the fluid. The method for producing aerated cement milk according to claim 1, wherein the diameter of the air bubbles (13) after the second refinement step is in the range of 20 μm or more and 500 μm or less.

Images