Excavator for soil cement diaphragm wall and construction method using the same

Abstract

To provide an excavator for soil cement underground continuous walls and a construction method using the same, capable of reducing the construction costs by improving the construction efficiency of soil cement underground continuous walls using a horizontal multi-spindle excavator and capable of improving the quality of soil cement underground continuous walls.SOLUTION: An excavator comprises a plurality of rotary cutters having a horizontal rotation axis at the lowest part of the excavator and excavates a ground downward by rotating the rotary cutters while in contact with the ground. The excavator comprises: an injection pipe for discharging an excavation injection material and / or a solidification material near the outer periphery of the middle part of the plurality of rotary cutters; a mud feeding pump having an upper port and a lower port and capable of transferring mixed soil that is a mixture of excavated soil excavated by the rotary cutter and the excavation injection material and / or the solidification material; and a mud feeding pipe connected to the lower port of the mud feeding pump and having a lower end near a top of the rotary cutter.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an excavator for a soil cement diaphragm wall and a construction method using the same. [Background technology]

[0002] BACKGROUND ART A soil cement diaphragm wall construction method has been known as a construction method for earth retaining walls and cut-off walls for preventing the diffusion of pollutants.

[0003] This soil cement underground diaphragm wall construction method is carried out using a soil cement construction machine.In this construction method, the soil cement construction machine is first moved and set up as an excavation and mixing process, and cement slurry is added from the tip of the excavator as an excavation and injection material to create a mixture of excavated soil and cement slurry.This mixed soil maintains the stability of the trench wall, and excavation is continued to the bottom of the excavation while maintaining appropriate fluidity.

[0004] Next, in the solidification process, a soil cement construction machine excavates down to the bottom of the excavation, and then adds an appropriate amount of cement slurry or other solidification agent to the mixed soil created in the excavation and mixing process, while mixing and stirring it and pulling it up, creating soil cement that is soft enough for inserting the core material in the next process. Next, in the core material insertion process, a crawler crane or similar tool is used to insert core material such as H-beams into the created soil cement. By repeating this sequence without any gaps between each process, a continuous soil cement solidification wall is constructed.

[0005] Examples of construction machinery used to construct the soil cement underground continuous wall include auger stirring excavators, cutter chain excavators, and horizontal multi-axis excavators. However, when an auger stirring excavator or cutter chain excavator is used in the excavation and mixing process, due to the mechanism of these excavators, the mixed soil of the excavated soil and excavation grouting material is prepared outside the excavator, and therefore excavation is carried out while the mixed soil is left at the excavation position.

[0006] On the other hand, for example, in a horizontal multi-spindle excavator such as that used in the soil cement wall construction method of Patent Document 1, the mixed soil is prepared inside the excavator. Therefore, even if the mixed soil is softened, the rotary cutter, hydraulic equipment for the attitude control machine, control panel, piping, etc. are installed inside the horizontal multi-spindle excavator, and the area through which the mixed soil passes is narrow compared to the excavation area, so when excavation is performed continuously, the prepared mixed soil remains below the excavator, causing a problem of a significant decrease in the excavation speed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-221764 Summary of the Invention [Problem to be solved by the invention]

[0008] Furthermore, during the solidification process, in which the mixed soil and cement slurry are mixed with a rotary cutter while the horizontal multi-axis excavator is being raised, to create soil cement, the mixed soil at the top of the excavator does not easily fall into the rotary cutter, and if it is raised too quickly, the mixing ratio of the mixed soil and cement slurry becomes unstable, resulting in poor quality. Therefore, the excavator must be raised slowly, which increases construction time and costs.

[0009] Furthermore, when excavating gravel, for example, using cement slurry, which has traditionally been used as an excavation injection material, there have been problems such as the mixture of gravel and cement slurry easily separating, and the separated gravel tends to remain between the rotary cutter and the excavation surface, extremely slowing down the excavation speed.

[0010] Furthermore, when cement slurry is used on a highly permeable gravel layer, there is a problem in that the walls of the trench are prone to collapse due to lost circulation.

[0011] Furthermore, when bentonite slurry is added to the cement slurry to reduce the amount of lost circulation, a layer of the cement-bentonite mixture forms on the inner wall of the excavation trench, narrowing the trench, and it has been confirmed that when the horizontal multi-axis excavator is pulled up, the excavator gets caught in the narrow part and cannot be pulled up.

[0012] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an excavator for soil cement diaphragm walls, which can improve the workability of soil cement diaphragm walls using a horizontal multi-axis excavator, thereby reducing construction costs, and which can improve the quality of the soil cement diaphragm walls, and a construction method using the same. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention has the following features. First, the excavator for a soil cement diaphragm wall of the present invention is provided with a plurality of rotary cutters having horizontal rotation axes at the bottom of the excavator, and excavates the ground downward by rotating the rotary cutters while they are in contact with the ground, an injection pipe for discharging an excavation injection material and / or a solidification material near the outer periphery of the intermediate portions of the plurality of rotary cutters; A mud pump having an upper port and a lower port capable of transporting mixed soil obtained by mixing the excavated soil excavated by the rotary cutter with the excavation grouting material and / or the solidification material; The rotary cutter further includes a mud transport pipe connected to the lower port of the mud transport pump and having a lower end located near the top of the rotary cutter. Secondly, in the excavator for a soil cement diaphragm wall of the first invention, it is preferable to provide an upper mud transport pipe connected to the upper port of the mud transport pump and having an upper end at the top of the excavator. Thirdly, the soil cement diaphragm wall construction method of the present invention is a construction method using the soil cement diaphragm wall excavator of the first or second invention, an excavation and mixing process in which excavation is performed while the excavation and grout material is discharged from the discharge port of the injection pipe near the outer periphery of the intermediate portion of the plurality of rotary cutters, the excavated soil and the excavation and grout material are mixed to form mixed soil, and the mixed soil is sucked through the mud transport pipe connected to the lower port of the mud transport pump and transported to the ground above the excavator; The method is characterized by having a solidification process in which, while the excavator is being raised, the mixed soil above the excavator is sucked in through the mud pump and discharged from the lower end of a mud pipe connected to the lower port of the mud pump, transporting it to the vicinity of the top of the rotary cutter of the excavator, and the solidification material is discharged from the discharge port of the injection pipe, and the solidification material and the mixed soil are mixed and stirred by the rotation of the rotary cutter to create a soil cement wall. Fourth, in the soil cement diaphragm wall construction method of the third invention, the excavation and grouting material preferably contains swelling polymer particles and water, or air bubbles and water. Fifth, in the soil cement diaphragm wall construction method of the third or fourth invention, the solidification material preferably contains cement slurry or cement. Sixth, in the soil cement underground continuous wall construction methods of the third to fifth inventions, it is preferable that in the excavation and mixing process, the rotation direction of the rotary cutter is a rotation direction that guides the mixed soil to the lower end of the mud transport pipe connected to the lower port of the mud transport pump. Seventh, in the soil cement underground continuous wall construction methods of the third to sixth inventions, it is preferable that in the solidification process, the rotation direction of the rotary cutter is a rotation direction that guides downward the mixed soil discharged from the lower end of the mud transport pipe connected to the lower port of the mud transport pump. Eighth, in the soil cement diaphragm wall construction method of the third to seventh inventions, it is preferable to have a core material insertion step of inserting a core material into the constructed soil cement wall after the solidification step. [Effects of the Invention]

[0014] According to the present invention, it is possible to improve the workability of soil cement diaphragm walls using horizontal multi-axis excavators, thereby reducing construction costs and improving the quality of the soil cement diaphragm walls. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic front view showing an embodiment of an excavator for a soil cement diaphragm wall of the present invention. [Figure 2] 1 is a schematic side view showing an embodiment of an excavator for a soil cement diaphragm wall of the present invention. [Figure 3] 1 is a process schematic diagram of the soil cement diaphragm wall construction method of the present invention, in which (A) is an excavation and mixing process, (B) is a solidification process, and (C) is a core material insertion process. [Figure 4] FIG. 10 is a diagram showing the relationship between the filling rate and the TF value. [Figure 5] FIG. 10 is a diagram showing the relationship between the type of excavation grouting material and the permeability coefficient of the trench wall. [Figure 6] This is a graph showing the relationship between filling rate and unconfined compressive strength of soil cement. [Figure 7] FIG. 1 is a graph showing the relationship between electrolyte concentration and the amount of water absorbed by a highly absorbent polymer. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to the drawings. Figure 1 is a schematic front view showing an embodiment of an excavator for a soil cement diaphragm wall of the present invention, and Figure 2 is a schematic side view.

[0017] The excavator 1 for a soil cement diaphragm wall of the present invention (hereinafter simply referred to as the excavator) is equipped with a plurality of rotary cutters 2 with horizontal rotation axes at the bottom of the excavator 1, and excavates the ground downward by rotating the rotary cutters 2 while in contact with the ground, and is equipped with an injection pipe 5 near the outer periphery of the rotary cutters 2 for discharging excavation grout and solidification material, a mud pump 3 with an upper inlet 31 and a lower inlet 32 ​​that can transport a mixed soil obtained by mixing the excavated soil excavated by the rotary cutters 2 with the excavation grout or solidification material, and a mud pipe 4 connected to the lower inlet 32 ​​of the mud pump 3. The excavator 1 is also connected to a wire cable 13 and suspended from a base machine 6, and is provided so that it can be freely moved upward and downward by winding up and down the wire cable 13.

[0018] The embodiment of the excavator 1 shown in Figures 1 and 2 has two rotary cutters 2 with bits 21 on the outer periphery at its lowest end, a frame 11 that holds the rotary cutters 2 above them, and an equipment storage box 12 within the frame 11, which stores hydraulic equipment, control equipment, etc. for controlling the movement and posture of the rotary cutters 2.

[0019] In addition, near the outer periphery of the intermediate section of the two rotary cutters 2, each having a bit 21 on its periphery, an outlet 51 of the injection pipe 5 extending to the ground is provided, allowing for the discharge of excavation grout, solidification material, air, and other materials supplied from above ground. The solidification material is supplied by a supply pump from a solidification material plant installed above ground, and air is supplied as compressed air from an aboveground compressor from the solidification material injection pipe outlet 51 to the intermediate section of the rotary cutter 2 near the outer periphery. A single supply pipe can be used for both the excavation grout and solidification material, but separate pipes can also be provided for each material. The excavation grout is typically discharged near the outer periphery of the intermediate section of the two rotary cutters 2 during excavation and mixed with the excavated soil to create a mixed soil.

[0020] Furthermore, a mud pump 3 capable of transporting mixed soil obtained by mixing excavated soil excavated by the rotary cutter 2 with an excavation grout material or a solidification material is provided above the rotary cutter 2. The mud pump 3 has an upper port 31 and a lower port 32, and the upper end of a mud pipe 4 is connected to the lower port 32, with the lower end 41 of the mud pipe 4 being disposed so as to be located near the top of the rotary cutter 2. In the embodiment shown in FIG. 1 , the opening of the lower end 41 of the mud pipe 4 is disposed so as to be located near the outer periphery of the middle part of the two rotary cutters 2.

[0021] As shown in Figures 1 and 2, when the mud pump 3 is installed on the top of the excavator 1, the upper port 31 of the mud pump 3 can be used as the discharge port for the mixed soil directly, but depending on the installation position of the mud pump 3, an upper mud pipe can also be connected to the upper port 31 of the mud pump 3. When an upper mud pipe is installed, the upper end of the upper mud pipe only needs to be located underground during excavation, and does not need to be extended to the surface.

[0022] The diameter and length of the mud transport pipe 4 and the upper mud transport pipe connected to the mud transport pump 3 can be determined appropriately depending on the specifications of the mud transport pump 3 and the type of mixed soil to be transported, and are not particularly limited, but if smooth mud transport is considered, it is preferable to use a mud transport pipe 4 with a diameter of approximately 4 inches.

[0023] The performance of the mud pump 3 is not particularly limited as long as it is capable of transporting the mixed soil, but it is generally preferable that it have a mud transport performance of about 400 L / min. An example of a mud pump 3 with this performance is a squeeze pump (OKP-65-ME-L manufactured by Okasan Kiko Co., Ltd.). Furthermore, depending on the characteristics of the mixed soil to be transported and the performance of the mud pump 3, two or more mud pumps 3 can be provided as shown in Figures 1 and 2. By providing multiple mud pumps 3, it becomes possible to transport the mixed soil around the rotary cutter 2 uniformly and efficiently.

[0024] The left and right rotary cutters 2 of the excavator 1 of this embodiment can each rotate forward and backward, and during the excavation and mixing process, the left rotary cutter 2 rotates counterclockwise and the right rotary cutter 2 rotates clockwise to guide the mixed soil upward between the rotary cutters 2. At the same time, the mud pump 3 is operated to suck the guided mixed soil from the opening at the lower end 41 of the mud pipe 4 and discharge it from the upper port 31 of the mud pump 3 or the opening at the upper end of the upper mud pipe, thereby easily transporting the mixed soil to the top of the excavator 1. Furthermore, during the solidification process, the mixed soil above the excavator 1 can be easily transferred to the bottom of the excavator 1 by rotating the left rotary cutter 2 clockwise and the right rotary cutter 2 counterclockwise.

[0025] The following describes a soil cement diaphragm wall construction method of the present invention using the excavator 1 of the above embodiment. Figures 3(A) to 3(C) show schematic diagrams of the steps of the soil cement diaphragm wall construction method of the present invention.

[0026] The soil cement diaphragm wall construction method of the present invention is a construction method using the soil cement diaphragm wall excavator 1 of the present invention, and includes an excavation and mixing process in which excavated soil and excavation and injection material are mixed to create mixed soil, and a solidification process in which the excavator 1 is lifted while mixing and stirring the solidification material and mixed soil to create a soil cement wall.

[0027] (Excavation and mixing process) In the excavation and mixing process, as shown in Figure 3(A), first, the excavator 1 is suspended from the base machine 6 to be positioned, and the rotary cutter 2 of the excavator 1 is rotated to excavate to a predetermined depth. During this process, the rotary cutter 2 is rotated while excavation grout is discharged from the discharge port 51 of the injection pipe 5 located near the outer periphery of the rotary cutter 2, and the excavated soil and the excavated grout are mixed to create a mixed soil.

[0028] In the excavation and mixing process of this embodiment, the rotary cutters 2 rotate in a direction that guides the excavated soil around the two rotary cutters 2 upward between them, i.e., the left rotary cutter 2 in Fig. 1 rotates counterclockwise, and the right rotary cutter 2 rotates clockwise. As the mixed soil is being created, the mud pump 3 is operated to suck the mixed soil from the opening of the lower end 41 of the mud pipe 4 and transport it above the excavator 1.

[0029] The excavation grout used in excavation is preferably a non-hardening excavation grout, specifically, swollen polymer particles, swollen polymer particle dispersion, air bubbles, or air bubbles and water. The swollen polymer particles and swollen polymer particle dispersion can be prepared by pouring tap water into a water tank equipped with a mixing blade installed on the ground, adding a powdered superabsorbent polymer, and stirring for about 30 minutes.

[0030] For example, when using a superabsorbent polymer with a water absorption rate of 400 times, use 1 m of tap water. 3 When 2.0 kg of superabsorbent polymer is added to the swelled polymer, a dispersion of swollen polymer particles consisting of 800 kg of swollen polymer particles and 200 kg of free water can be prepared. The water absorption capacity in this case is the ratio of the mass of the water absorbed to the mass of the superabsorbent polymer.

[0031] The swollen polymer particle dispersion is delivered to the outer periphery of the rotary cutter 2 through an injection pipe 5 connected to a ground-based squeeze pump and discharged from a discharge port 51. The mixing ratio of the excavated soil and the swelling polymer particles is appropriately determined taking into consideration the physical properties of the excavated soil and the fluidity of the mixed soil. The fluidity of the mixed soil is preferably 150 to 220 mm, more preferably 170 to 200 mm, in terms of table flow value (TF value), considering the pumping of the mixed soil by the mud pump 3 and the need to balance the fluidity of the mixed soil with the stability of the wall. By setting the TF value of the mixed soil within the above range, the mixed soil passes through the internal space of the excavator 1 and can be efficiently pumped to the upper part of the excavator 1 by the mud pump 3, allowing excavation to the desired excavation depth while maintaining the stability of the trench walls.

[0032] As a verification experiment, 700cc of mixed soil was placed in a 1000cc measuring cylinder, shaken, and then left for 4 hours before observing the condition. As a result, no bleeding or separation of the soil and swollen polymer particles was observed, confirming that the mixture was suitable for pumping using the mud pump 3.

[0033] Figure 4 shows a graph of the relationship between packing ratio and TF value, using silica sand No. 7 as the sample soil. The packing ratio refers to the percentage of the volume of the swelling polymer particles relative to the void volume of the excavated soil. This graph shows that the TF value easily increases as the packing ratio of the swelling polymer particles increases. Using this result as an indicator, the TF value can be easily adjusted to a range of 150-220 mm by adjusting the packing ratio of the swelling polymer particles. It can also be seen that a target TF value of 180 mm results in a packing ratio of approximately 80%.

[0034] In addition, if the TF value of the mixed soil is set as above, from the viewpoint of workability and economy, if the excavated soil is gravel soil, and the porosity is 40-45% and the filling rate is 80, then the TF value of 1 m of excavated soil is 3 The swollen polymer particles per 0.35 m 3 , and in the case of clayey soil, swelling polymer particles 0.35 m 3 , water 0.1m 3 The porosity indicates the ratio of the volume of the soil other than soil particles to the total volume of the soil.

[0035] Figure 5 shows a graph of the relationship between excavation grout and hydraulic conductivity. The graph in Figure 5 shows that even with coarse-grained silica sand No. 1, the swelling polymer particles increase the hydraulic conductivity to 1.2E-5 cm / s, forming an impermeable layer and maintaining the stability of the trench walls. The non-hardening excavation grout used in this invention does not harden into a thick layer on the trench walls, even when used in a gravel layer with a large amount of lost circulation, so the excavation trench does not become narrower. In other words, in the solidification process described below, no obstacles are formed that hinder the lifting of the excavator 1, allowing for efficient construction.

[0036] The superabsorbent polymer used in the construction of the soil-cement diaphragm wall of the present invention is a hydrophilic polymer with a cross-linked structure, which typically absorbs water at a rate of 10 to 500 times its own weight and is characterized by its resistance to moisture release even under pressure. Furthermore, the term "swollen polymer particles" used herein means that individual particles maintain a granular shape even after absorbing water and swelling. Therefore, the term "swollen polymer particles" does not include or exclude particles in which multiple water-absorbent polymer molecules do not form independent particles but instead form a paste-like polymer. The water absorption capacity of superabsorbent polymers is defined in JIS K 7223 (1996), and the method for measuring water absorption is also based on the description in JIS K 7223 (1996).

[0037] The type of superabsorbent polymer used in the construction of the soil cement underground continuous wall of the present invention can be used without any particular restriction as long as it satisfies the above conditions, and it is preferable to consider, for example, at least one type selected from the group consisting of starch-based, cellulose-based, and synthetic polymer-based polymers.

[0038] Among the above-mentioned highly water-absorbent polymers, highly water-absorbent polymer particles of synthetic polymer sodium polyacrylate are particularly suitable for use because they are excellent in both performance and cost.

[0039] Sodium polyacrylate superabsorbent polymer is a gel of partially cross-linked acrylic acid polymer sodium salt with a three-dimensional network structure, lightly cross-linked by adding a cross-linking agent to sodium acrylate (CH2=CH-COONa). Conventional cross-linking agents can be used.

[0040] It is known that when the superabsorbent polymer sodium polyacrylate absorbs water, the carboxyl groups dissociate sodium ions into the gel, resulting in a swelling degree of 100 to 1,000 times its own weight in pure water. An example of such a superabsorbent polymer sodium polyacrylate is Geosap (manufactured by Sanyo Chemical Industries, Ltd.). Geosap has a water absorption capacity of approximately 400 times its own weight, and the fluidity of the swelling polymer particles and swelling polymer particle dispersion is good, and it can reliably seal the voids in the gravel layer.

[0041] In addition, when sodium polyacrylate superabsorbent polymer particles are mixed with a large amount of crosslinking agent relative to the sodium acrylate, the resulting gel becomes harder and its water absorption capacity decreases. On the other hand, when the amount of crosslinking agent is reduced, the resulting gel becomes softer and its water absorption capacity increases.

[0042] Furthermore, as a special sodium polyacrylate superabsorbent polymer, a sodium polyacrylate superabsorbent polymer having a dual shell-core structure, in which the surface of superabsorbent polymer particles polymerized with a crosslinking agent is further crosslinked, can be used as an example. In this sodium polyacrylate superabsorbent polymer particle having a dual shell-core structure, the thicker the outer shell, the harder the gel becomes, and the less water it absorbs. On the other hand, a thinner shell results in a softer gel, and the more water it absorbs.

[0043] Furthermore, although the shell and core are usually crosslinked via an ester bond, there are also sodium polyacrylate superabsorbent polymers in which the shell and core are crosslinked via an ether bond, which has excellent alkali resistance and electrolyte resistance. In the present invention, it is more preferable to use a sodium polyacrylate superabsorbent polymer in which the shell and core are crosslinked via an ether bond.

[0044] In addition to the above characteristics, the dissociation of sodium ions in the superabsorbent polymer sodium polyacrylate also depends on the conditions under which the gel is placed, such as pH and electrolyte concentration, so other superabsorbent polymers can be appropriately selected and used depending on the conditions of use.

[0045] Swelling polymer particles or swellable polymer particle dispersions are also expected to be used at great depths, and are pumped under pressure to the construction site. In this case, the swellable polymer particles are exposed to high pressure, so it is necessary to select a highly water-absorbent polymer that has a cross-linked structure that minimizes the loss of water retention due to pressure and that makes the swellable polymer particles themselves less likely to deform. Furthermore, in order to fill the voids in highly permeable coarse gravel layers, it is desirable for the particle size after swelling to be 3 mm or less and for the particle size distribution to be as good as possible.

[0046] In addition, when the excavated layer is a gravel layer, the amount of voids between soil particles in the ground is, for example, 40 to 45%. In the present invention, when a sodium polyacrylate superabsorbent polymer is used as the superabsorbent polymer, any superabsorbent polymer that satisfies the above conditions can be used without particular limitation, but in particular, a sodium polyacrylate superabsorbent polymer having a double structure of a shell and a core adjusted to the above conditions can be preferably used.

[0047] In addition, when using air bubbles or air bubbles and water as the non-hardening excavation grout of this embodiment, the TF value is set within the appropriate range by adding water to the excavated soil 1 m 3 In sandy soil, air bubbles are 0.3m 3 It is preferable to use:

[0048] In addition, when the TF value of the mixed soil is set as above, if the excavated soil is clayey, from the viewpoint of workability and economy, 3 0.3m bubbles per bubble 3 , water 0.3m 3 Conditions of this order are preferred.

[0049] On the other hand, increasing the amount of foam added improves fluidity, but reduces the specific gravity of the mixed soil. Therefore, when considering the stability of the wall, the specific gravity needs to be 1.05 or more, and the amount of foam injected to achieve this is approximately 0.8 m 3 / m 3 It is necessary to keep the following:

[0050] Furthermore, a foaming agent can be used to generate the desired bubbles. While known surfactants can be used as foaming agents, a foaming agent that is resistant to foaming itself, even when mixed with excavated soil, has excellent chemical stability against acids and alkalis, and has excellent foaming ability is particularly desirable. For example, an alkyl sulfate surfactant can be preferably used. Specifically, an alkyl sulfate surfactant WTM foaming agent (a solution of Flolic's WTM foaming agent diluted 20 times with clean water) can be preferably foamed 25 times to a specific gravity of 0.04 and a mode of about 100 μm.

[0051] The swollen polymer particles produced in the aboveground plant are transported to the excavator 1 via a flexible injection pipe 5 along a suspension cable 13, and then passed through the inside of the frame 11 of the excavator 1 and discharged from a discharge outlet 51 located near the outer periphery of the middle part of the two rotary cutters 2.

[0052] <Solidification process> The solidification process follows the excavation and mixing process. In the solidification process, as shown in Figure 3(B), the excavator 1 is raised, and the mixed soil above the excavator 1 is sucked in through the upper port 31 of the mud pump 3 or the upper end opening of the upper mud pipe, and discharged through the lower end opening 41 of the mud pipe 4 via the mud pump 3. The solidification material is then passed through the gaps in the excavator 1 and discharged from the discharge port 51 of the injection pipe 5. The solidification material and the mixed soil are then mixed to form a soil cement wall.

[0053] When the mud pump 3 transfers the mixed soil below the excavator 1, the rotation direction of the rotary cutter 2 is set to be opposite to the rotation direction of the rotary cutter 2 during the excavation and mixing process. That is, in the diagram shown in Figure 3(B), the left rotary cutter 2 is rotated clockwise, and the right rotary cutter 2 is rotated counterclockwise. This allows the mixed soil and solidification material to be moved below the excavator 1 while being mixed.

[0054] As the solidification material used in the present invention, cement slurry or powdered cement can be suitably used. Furthermore, a liquid antifoaming agent can be added to the cement slurry, and a powder antifoaming agent can be added to the cement. In the solidification process, the strength of the solidified region can be increased by adding an antifoaming agent to eliminate the air bubbles in the mixed soil created in the excavation and mixing process. The antifoaming agent can be selected appropriately depending on the foaming agent used, etc. Furthermore, in the solidification process, the fluidity of the excavated region immediately after the excavator 1 is lifted is preferably 170 mm or more in terms of TF value, taking into account the core material insertion process described below.

[0055] In addition, the filling rate of the swelling polymer particles used as the excavation and injection material during the excavation and mixing process should be calculated from the TF value of the mixed soil obtained by collecting excavated soil from the construction site in advance and mixing it with swelling polymer particles, and the amount of solidification material to be added during the solidification process should be determined by adding and mixing cement slurry or cement as the solidification material to the mixed soil at the filling rate used in the excavation and mixing process, measuring the uniaxial compressive strength, and determining the amount of solidification material, water-cement ratio (W / C), etc. that will satisfy the required strength.

[0056] In addition, the solidification material can be supplied through an injection pipe 5 that transports the excavation injection material, but if cement, which is a powder solidification material, is used, it is preferable to provide a separate injection pipe 5 for the solidification material.

[0057] <Core Insertion Process> In the soil cement diaphragm wall construction method of this embodiment, a core material insertion step can be performed after the solidification step, if necessary, to insert a core material 8. FIG. 3(C) shows the core material insertion step of this embodiment. In this core material insertion step, the core material 8 is inserted using a core material insertion crane 7, such as a crawler crane. The inserted core material 8 can be a core material 8 that is generally used to reinforce the solidified region, and specific examples include steel materials such as H-shaped steel, precast concrete walls, or steel walls. By inserting the core material 8 into the solidified region, a soil cement diaphragm wall with excellent bending strength properties can be constructed.

[0058] When the core material insertion process is carried out, the solidification reaction begins when the mixed soil and solidification material slurry are mixed in the solidification process, so it is preferable to insert the core material 8 at a stage when the solidification reaction of the solidification material slurry has not progressed as much as possible, i.e., immediately after the solidification process. [Example]

[0059] The conditions for the excavation grout used in the excavator of the present invention will be explained below with reference to examples, but the present invention is not limited to the following examples in any way.

[0060] In order to use the excavation grout applied to the excavator of the present invention, i.e., the swollen polymer particles or the swollen polymer particle dispersion, the air bubbles, or the air bubbles and water, under suitable conditions, the physical property conditions thereof are as follows: 1. Even if the excavated soil is a gravel layer, there is little separation between the excavated soil and the excavation grouting material, making it easy to obtain fluidity. 2. The mixed soil of excavated soil and excavated grouting material has good pumpability. 3. The trench walls can be made impermeable and stable even in gravel layers with a high coefficient of permeability. 4. By adding and mixing a solidifying material into a mixture of excavated soil and excavation and injection material, it is possible to create soil cement with a specified strength. Examples include:

[0061] The suitability of the excavation grout material to be applied to the excavator of the present invention was confirmed by an experiment as follows. In this experiment, a sodium polyacrylate superabsorbent polymer (manufactured by Sanyo Chemical Industries, Ltd., trade name: Geosap) having the physical properties shown in Table 1 was used as the superabsorbent polymer.

[0062] [Table 1]

[0063] <1. Fluidity, separation, and pumpability of mixed soil> The fluidity, separability, and pumpability of a mud pump were investigated for a mixture of excavated soil and excavation grout. Fluidity was expressed as a table flow value (hereinafter referred to as TF value) (JIS R 5201:2015). A mixture of swollen polymer particles that had absorbed tap water and expanded was prepared as the sample soil by mixing it with silica sand No. 5.

[0064] In Test 1, 10 types of swelling polymer particles were mixed with No. 5 silica sand with a moisture content of 15% at a loading rate of 25-150%, and the relationship between the loading rate and TF value of the resulting soil mixture was examined. In Test 2, 8 types of swelling polymer particles were mixed with No. 5 silica sand with a moisture content of 20% at a loading rate of 35-150%, and the relationship between the loading rate and TF value of the resulting soil mixture was examined. Here, loading rate refers to the ratio of the volume of swelling polymer particles to the void volume of the soil.

[0065] These results are shown in Figure 4. Figure 4 shows that in both Test 1 and Test 2, there is a proportional relationship between the filling rate and the TF value, and it was confirmed that a TF value of 150 to 220 mm, which is necessary for optimal construction, can be obtained when the filling rate is in the range of 50 to 150%.

[0066] Next, 700 ml of the above-mentioned mixed soil with a TF value of 183 mm (a mixed soil prepared by adjusting the filling rate of swelling polymer particles to 70.2% with silica sand No. 5 with a water content of 20%) was placed in a 1000 ml measuring cylinder and shaken. After 4 hours, the state of the mixed soil was observed. As a result, no separation or bleeding was observed.

[0067] Next, to examine the pumpability of the mixed soil using a mud pump, the mixed soil (TF value 183 mm) was used and pumped through a 4-inch pipe with a horizontal length of 30 m using a mud pump. The soil was pumped without any problems and no separation of the mixed soil was observed after pumping.

[0068] <2. Stability of the groove wall> Constant water level test (water head: 300 kN / m 2 ) silica sands No. 1, 3, 5, and 7 were used as sample soils, and the hydraulic conductivity of a swollen polymer particle dispersion with 30% free water was determined as the excavation grouting material. For comparison, a hydraulic conductivity test was also conducted using water. Specifically, the relationship between time and the amount of water flowing was measured, and the hydraulic conductivity was determined.

[0069] Figure 5 shows the relationship between the type of silica sand and the coefficient of permeability. According to this, regardless of the type of silica sand, the coefficient of permeability with water is 10 -3 The permeability is about 10 cm / s due to the swelling polymer particles. -5 The water permeability was about 1 / 100 of that of the conventional swelled polymer particles, and it was confirmed that the swelled polymer particles could prevent water leakage from the groove walls and stabilize the groove walls.

[0070] In addition, the permeability coefficient when air bubbles are used as the excavation grouting material is shown in Figure 5. The permeability coefficient is 10 -5 It was found that the stability of the trench wall can be maintained even when air bubbles are used as an excavation grouting material.

[0071] <3. Filling ratio and unconfined compressive strength> The compressive strength development of soil cement was investigated by adding and mixing a solidification material into a soil mixture containing excavated soil and excavation grout. The sample soil was Tohoku Silica Sand No. 7 (two types with a water content of 15% and 20%) and a soil mixture with swelling polymer particle filling rates varying between 40% and 80%. Two types of solidification material, cement slurry and cement, were added and mixed, and the unconfined compressive strength (strength after 4 weeks) was measured to investigate the relationship between filling rate and unconfined compressive strength. This relationship is shown in Figure 6. Figure 6 shows that regardless of whether the solidification material was cement slurry or cement, there is a tendency for unconfined compressive strength to decrease as the filling rate increases.

[0072] Test 1 was a mixture of silica sand No. 7 and swelling polymer particles with a common cement mix of 200 kg / m 3 This is a relationship diagram for a water-cement ratio (W / C) of 80%, but the unconfined compressive strength is 1000kN / m at a filling rate of 70%. 2 It was confirmed that the strength development is comparable to that of the conventional method using cement slurry as the excavation and grouting material.

[0073] In Test 2, powdered cement (W / C = 0%) was mixed with a mixture of silica sand No. 7 and swelling polymer particles, and the unconfined compressive strength was measured. The cement addition amount was 200 kg / m 3 When comparing the unconfined compressive strength of the powdered cement and cement slurry (W / C = 80%), it was found that the powdered cement exhibited a higher degree of strength, and the strength exhibited was consistent with the general understanding that the less water content the higher the unconfined compressive strength, confirming that there is no problem with using powdered cement.

[0074] The swelling polymer particles release most of the absorbed water due to calcium hydroxide produced when the minerals contained in the cement react with water, causing the particles to shrink. Figure 7 shows the relationship between electrolyte concentration and the amount of water absorbed by the superabsorbent polymer. The released water is also used in the hydration reaction with the cement. The decrease in unconfined compressive strength as the filling rate increases is thought to be due to the use of cement slurry with a high water / cement ratio. [Explanation of symbols]

[0075] 1. Soil cement diaphragm wall excavator 11 frames 12 Equipment storage box 13 Cable 2 rotary cutters 21-bit 3 Mud pump 31 Upper Entrance 32 Lower Entrance 4 Mud transport pipe 41 Lower end 5 Injection tube 51 Discharge port 6 Base Machine 7. Crane for inserting core material 8 Core material

Claims

1. An excavator for a soil cement diaphragm wall, comprising two rotary cutters having horizontal rotation axes at the bottom of the excavator, and rotating the rotary cutters in a state of contact with the ground to excavate the ground downward, an injection pipe for discharging an excavation grout and / or a solidification material near the outer periphery of the intermediate portion of the two rotary cutters; A mud pump having an upper port and a lower port capable of transporting mixed soil obtained by mixing the excavated soil excavated by the rotary cutter with the excavation grouting material and / or the solidification material; a mud transport pipe connected to the lower port of the mud transport pump and having a lower end near the upper part of the rotary cutter; The rotary cutter rotates in a direction that guides the excavated soil upward between the two rotary cutters, A soil cement diaphragm wall excavator characterized in that it rotates in a direction that guides the mixed soil downward between the two rotary cutters.

2. 2. The excavator for a soil cement diaphragm wall according to claim 1, further comprising an upper mud feed pipe connected to the upper port of the mud feed pump and having an upper end at the top of the excavator.

3. A construction method using the soil cement diaphragm wall excavator according to claim 1 or 2, an excavation and mixing process in which excavation is performed while the excavation and grout material is discharged from the discharge port of the injection pipe near the outer periphery of the intermediate portion of the two rotary cutters, the excavated soil and the excavation and grout material are mixed to form mixed soil, and the mixed soil is sucked through the mud transport pipe connected to the lower port of the mud transport pump and transported to the ground above the excavator; a solidification step in which, while the excavator is being raised, the mixed soil above the excavator is sucked in through the mud pump, and discharged from the lower end of a mud pipe connected to the lower port of the mud pump, thereby transporting the mixed soil to the vicinity of the upper part of the rotary cutter of the excavator, and the solidification material is discharged from the discharge port of the injection pipe, and the solidification material and the mixed soil are mixed and stirred by the rotation of the rotary cutter to create a soil cement wall; In the excavation and mixing step, the rotation direction of the two rotary cutters is rotated in a direction that guides the mixed soil to the lower end of a mud transport pipe connected to the lower port of a mud transport pump, A soil cement underground continuous wall construction method characterized in that, in the solidification process, the rotation direction of the two rotary cutters is in a direction that guides downward the mixed soil discharged from the lower end of the mud transport pipe connected to the lower port of the mud transport pump.

4. 4. The soil cement diaphragm wall construction method according to claim 3, wherein the excavation and grouting material contains swelling polymer particles and water, or air bubbles and water.

5. 5. The soil cement diaphragm wall construction method according to claim 3, wherein the solidification material contains cement slurry or cement.

6. A soil cement underground continuous wall construction method described in any one of claims 3 to 5, characterized in that after the solidification process, it includes a core material insertion process of inserting a core material into the constructed soil cement wall.

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