Excavation method

Abstract

To provide a method that can sufficiently ensure the plastic flow of excavated soil. [Solution] The drilling method includes the steps of: discharging liquid from a rotating cutting section of the drilling device toward the ground to cut the ground; taking in cut soil into the space between a partition wall section dividing the inside of the drilling device and the cutting section; injecting air bubbles into the space where the cut soil has been taken in from a hollow protrusion that extends from the partition wall section toward the cutting section; and stirring and mixing the cut soil taken into the space by the rotation of the cutting section with the injected air bubbles.

Description

[Technical Field]

[0001] The present invention relates to a method for excavating the ground using an excavation device. [Background technology]

[0002] The shield tunneling method is a method of excavating the ground using a shield machine (also simply called a shield) as the excavation device, rotating the cutter head, and immediately constructing a lining at the rear of the excavated tunnel. In such shield tunneling methods, the bubble shield method is known, in which air bubbles are added from the cutter head and mixed with the excavated soil produced at the face of the tunnel to promote the plastic fluidization of the mud (see, for example, Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Hideki Shimizu, et al., "Study on the Applicability of Soil Excavated from Earth Pressure Balance Shield Tunneling to Fluidized Soil," [online], October 2001, Japan Society of Civil Engineers, [Retrieved March 9, 2020], Internet.<URL:http: / / library.jsce.or.jp / jsce / open / 00035 / 2001 / 56-3B / 56-3B-0231.pdf> [Overview of the project] [Problems that the invention aims to solve]

[0004] However, with the conventional techniques described above, when excavating mudstone layers (mudstone layers or consolidated cohesive soil layers), because mudstone layers have a low water content, if air bubbles are added immediately after excavation, the moisture from the air bubbles may be absorbed by the excavated soil, potentially causing the bubbles to burst. This presents a problem in that sufficient plastic fluidization of the excavated soil cannot be ensured. [Means for solving the problem]

[0005] The present invention has been made in view of the above problems, and is a method for excavating the ground using an excavation device, A step in which liquid is discharged from the cutting part of the drilling device, which rotates to cut the ground, toward the ground, The process involves taking in excavated soil into the space between the partition wall section and the cutting section that separates the inside of the excavation device, The process involves injecting air bubbles into the space containing the excavated soil from a hollow protrusion that extends from the partition wall toward the cutting area, The step involves stirring and mixing the excavated soil taken into the space by the rotation of the cutting section with the injected air bubbles. A drilling method is provided, which includes the following: [Effects of the Invention]

[0006] According to the present invention, it is possible to ensure sufficient plastic flow of excavated soil. [Brief explanation of the drawing]

[0007] [Figure 1] A diagram showing an example of the configuration of a drilling machine. [Figure 2] A diagram showing the process of excavating the ground using an excavation device. [Figure 3] A flowchart illustrating the process of excavating the ground using an excavation device. [Figure 4] A diagram showing the configuration of the test apparatus. [Figure 5] A diagram illustrating a method for calculating the amount of bubble rupture from the gas concentration. [Figure 6] A diagram illustrating the properties and characteristics of bubbles during testing. [Figure 7] This figure shows the test results when the foaming solution concentration is fixed and the foaming ratio is varied. [Figure 8] This figure shows the results after correcting the expansion ratio. [Figure 9] This figure shows the test results when the foaming ratio is fixed and the foaming solution concentration is varied. [Figure 10] A flowchart showing the procedure for reproducing the construction conditions. [Figure 11]Figure showing the relationship between the water addition rate, water content ratio, and foam breaking rate. [Figure 12] Figure showing the relationship between the water addition rate, water content ratio, and foam breaking rate when using soap water as the solution. [Figure 13] Figure showing the properties of the sample when the water addition rate is changed.

Mode for Carrying Out the Invention

[0008] For excavating tunnels such as subways and sewers, the shield method using a shield machine as an excavation device is utilized. In the shield method, there is an earth pressure shield method that stirs the cut soil to give it fluidity and applies pressure to the face using the cut soil to achieve the stability of the face. However, in the earth pressure shield method, there is a problem that excavation cannot be carried out due to the adhesion of the cut soil taken into the excavation device.

[0009] Therefore, the foam shield method is adopted as a method of improving the adhesion of the cut soil by using an additive (also called a soil addition material). The foam shield method is a method that uses foam as an additive.

[0010] The foam is in the form of fine shaving cream, enters the gaps between soil particles, imparts a bearing effect that reduces the friction generated between soil particles, and enhances the fluidity of the cut soil. Also, the foam is deformable and elastic, is replaced by the groundwater existing in the gaps between soil particles, and improves the water stopping property of the cut soil.

[0011] Figure 1 shows an example of the configuration of a shield machine as an excavation device. The shield machine has a hollow cylindrical skin plate 10 that resists soil and water pressure, and a rotatable cutting section at one end of the skin plate 10, which is the leading edge in the excavation direction, for cutting the ground. The cutting section is, for example, a cutter head 11. The structure of the cutter head 11 may be spoke-type or faceplate-type. The spoke-type has a structure in which an axle and a ring are connected radially by rod-shaped members, and the faceplate-type has a structure in which one surface is a circular plate with holes in various places. The cutter head 11 is equipped with a bit that cuts in contact with the ground and agitates and fluidizes the cut soil as it rotates.

[0012] The shield machine is equipped with a partition wall 12 that separates the tunnel face side, which is the direction of excavation when excavating a tunnel, from the tunnel entrance side, which is the opposite direction. The partition wall 12 is installed at a distance from the cutter head 11 on the tunnel entrance side. The space between the cutter head 11 and the partition wall 12 is called the chamber 13.

[0013] The partition wall section 12 is equipped with a drive device 14 for rotating the cutter head 11, and a discharge device for discharging the cut soil is connected to it. The drive device 14 is a drive motor that rotates a rotating shaft connected to the center of the cutter head 11. The discharge device is a screw conveyor 15 equipped with a screw having a shaft and spiral blades arranged spirally around the shaft inside a pipe. In the case of a spoke-type cutter head 11, the cut soil is taken into the chamber 13 through the gaps between radial rod-shaped members, and in the case of a faceplate-type cutter head, it is taken in through a hole provided in a circular plate.

[0014] The screw conveyor 15 transports the excavated soil in the chamber 13 toward the mine entrance by the rotation of its internal screw. The excavated soil transported by the screw conveyor 15 is then removed from the mine by a belt conveyor or the like.

[0015] The shield machine is equipped with jacks 16 for rotating and advancing the cutter head 11. The shield machine is also equipped with an assembly device (erector) 18 for assembling lining material (segments) 17 that cover the inner wall surface of the tunnel to prevent the excavated tunnel from collapsing. The jacks 16 are positioned between the assembled segments 17 and the bulkhead section 12, and advance the cutter head 11 by moving the bulkhead section 12 based on the fixed segments 17. The shield machine is also equipped with a backfill injection device 19 for backfill injection of mortar or the like. The backfill injection device 19 injects mortar or the like into the back of the segments 17 to prevent the surrounding ground from loosening.

[0016] The shield machine includes a liquid storage tank 20 for storing liquid and a liquid supply device for supplying liquid from the liquid storage tank 20 to the cutter head 11. The liquid supply device is a supply pump 21 that supplies liquid to an inlet provided on the cutter head 11 via a liquid injection pipe and allows it to flow out from the inlet. The liquid is a water-containing liquid that can supply moisture in advance so that the water in the air bubbles injected into the excavated soil is absorbed and does not burst. For example, water or soapy water can be used as the liquid.

[0017] The shield machine includes a foaming agent storage tank 22 for storing foaming agent, a foaming agent supply device (foaming agent supply pump) 23 for supplying foaming agent, a compressor 24 for supplying air, and a foaming device 25 for generating bubbles from the foaming agent and air. The foaming agent can be an aqueous solution of a surfactant dissolved in water. As the surfactant, anionic surfactants such as fatty acid ester salts (soap), alkylbenzene sulfonates, alkyl ether sulfate esters, and phosphate esters can be used. The foaming agent may also contain additives. Examples of additives include thickeners such as polyacrylamide and polyacrylates to improve the stability of the bubbles. The foaming device 25 generates bubbles by, for example, supplying air from the compressor 24 to the stored foaming agent and bubbling it. This is just one example, and bubbles may be generated by other methods.

[0018] The cutter head 11 and the partition wall 12 are provided with protrusions 26 and 27 that project inward into the chamber 13. The protrusion 26 moves circumferentially as the cutter head 11 rotates, and together with the protrusion 27, it has the effect of stirring the excavated soil taken into the chamber 13.

[0019] The protruding portion 26 is rod-shaped, while the protruding portion 27 is rod-shaped and hollow (for example, a short pipe). The bubbles are injected into the excavated soil taken into the chamber 13 through the inside of the hollow protruding portion 27. For this reason, the protruding portion 27 is connected to the foaming device 25 by a pipe or the like.

[0020] Figure 2 shows the process of excavating the ground using a shield machine. In the example shown in Figure 2, there is a fine soil layer 31 above the mudstone layer 30, and the groundwater level is located near the surface of the fine soil layer 31. Here, we will explain using the mudstone layer 30, but it is not limited to the mudstone layer 30, and may also be a consolidated cohesive soil layer, etc. The mudstone layer 30 is a rock layer formed by the deposition and solidification of muddy material with a particle size of less than 1 / 16 mm. The mudstone layer 30 is a geological layer in which groundwater does not easily penetrate. The fine soil layer 31 is a sandy soil layer and is a permeable layer in which groundwater easily penetrates.

[0021] The shield machine excavates the mudstone layer 30 to construct the tunnel. The shield machine excavates by advancing the jacks 16 while rotating the cutter head 11 at its tip. The mudstone layer 30 is composed of clay and silt and has a low water content. Therefore, during excavation, the excavated soil cut by the cutter head 11 adheres to the inner surface of the cutter head 11 and the chamber 13 into which it is taken, making excavation difficult. The water content is the percentage of water contained in the soil, obtained by dividing the weight of water by the weight of the solids in the dry soil.

[0022] Therefore, air bubbles can be added from an injection port provided in the cutter head 11, and the excavated soil can be agitated by the rotation of the cutter head 11. However, when air bubbles are injected into excavated soil with a low water content, the water in the bubbles is absorbed by the excavated soil, causing the bubbles to burst. When bubbles burst, the air inside may escape through gaps and cracks between soil particles into the upper fine soil layer 31. The fine soil layer 31 has many voids, and when air escapes into the fine soil layer 31, the pressure decreases and the volume expands. This volume expansion widens the voids, reduces the ground strength, and affects buildings and other structures above.

[0023] This occurs because air bubbles are injected into soil with a low water content; therefore, an appropriate amount of moisture is supplied to the excavated soil, which has a low water content, in advance. Accordingly, a water-containing liquid such as water or soapy water is discharged from the injection port of the cutter head 11.

[0024] After supplying the cut soil with an appropriate amount of moisture, air bubbles can be injected. For this reason, air bubbles can be injected through a hole in the partition wall 12 located behind the cutter head 11. However, when air bubbles are injected through this hole, they move along the surface of the partition wall 12 rather than into the cut soil, and the air bubbles do not reach the inside of the cut soil taken into the chamber 13.

[0025] On the other hand, if a hollow projection is provided in the partition wall 12 that extends close to the cutter head 11, air bubbles injected from the projection may immediately flow out to the working face via the cutter head 11, potentially causing the bubbles to burst.

[0026] Therefore, the protruding length of the projection 27 that extends from the partition wall 12 toward the cutter head 11 can be set to a length of about 1 / 4 to 3 / 4 of the distance from the partition wall 12 toward the cutter head 11. With this length, even if air bubbles are injected from the tip of the projection 27, there is a sufficient thickness of excavated soil on the cutter head 11 side, preventing air bubbles from leaking into the cutting face, and also suppressing the movement of the injected air bubbles along the surface of the partition wall 12. Furthermore, by injecting air bubbles while the cutter head 11 is rotating, excavated soil comes into contact with the vicinity of the injection port one after another as the cutter head 11 rotates, so the air bubbles can be supplied firmly to the excavated soil and will not escape into the cutting face. This effect of preventing air bubbles from leaking into the cutting face is called the plug effect.

[0027] The excavated soil taken into chamber 13 retains an appropriate amount of moisture because it has been supplied with water in advance. Therefore, even if air bubbles are injected into it, the absorption of the water from the air bubbles into the excavated soil is suppressed, and the bursting of air bubbles is greatly reduced. Furthermore, by injecting and stirring an aqueous solution containing the same anionic surfactant as the foaming agent at the face in advance, the cations of the clay minerals in the excavated soil react with the anions in the aqueous solution. Therefore, even if air bubbles are injected into it, the reaction of the anions in the air bubbles with the cations of the clay minerals in the excavated soil is suppressed, and the bursting of air bubbles is greatly reduced. This makes it possible to ensure sufficient plastic flow of the excavated soil. Note that the aqueous solution injected at the face in advance does not have to contain the same surfactant as the foaming agent; it may contain a different anionic surfactant.

[0028] Plastic fluidization is necessary to appropriately control the amount of excavated soil discharged by the screw conveyor 15 and to adjust the amount of excavated soil discharged by the screw conveyor 15. If plastic fluidization is not ensured, ejection or blockage will occur from the screw conveyor 15. Ejection is a phenomenon in which excavated soil is ejected when the gate of the screw conveyor 15 is opened.

[0029] Figure 3 is a flowchart showing the workflow for excavating the ground using a shield machine. The work begins with assembling and setting up the shield machine in the designated location, preparing other equipment such as the foaming device 25, and starting from step 100. In step 101, the cutter head 11 is rotated, and the ground to be excavated is excavated while a liquid containing water is discharged from the cutter head 11. Here, liquid is supplied to the excavation face in advance to provide an appropriate amount of moisture.

[0030] In step 102, cut soil containing an appropriate amount of moisture is taken into the chamber 13. In step 103, air bubbles are injected into the cut soil taken into the chamber 13 from the protruding part 27. Since the cut soil contains an appropriate amount of moisture, it does not absorb moisture from the injected air bubbles, which significantly reduces the bursting of air bubbles and ensures sufficient plastic fluidization. In step 104, the cut soil and air bubbles are mixed and stirred by the rotation of the cutter head 11. The cut soil in the chamber 13 can be mixed and stirred by the rotation of the cutter head 11 alone due to the presence of the protruding part 27, but sufficient mixing and stirring is possible with the presence of the protruding part 26 which rotates together with the cutter head 11.

[0031] Subsequently, in step 105, the material is transported by the screw conveyor 15 to the belt conveyor at the rear, and then transported out of the mine by the belt conveyor.

[0032] In step 106, the cutter head 11 is advanced by the jack 16. In step 107, the segments 17 are assembled using the erector 18 to line the inside of the tunnel. In step 108, it is determined whether to finish the tunnel excavation. If not, the process returns to step 101 and steps 101 to 108 are repeated. If the excavation is finished, the process proceeds to step 109, where finishing work such as paving is done, the shield machine is dismantled, and the work is completed.

[0033] As explained above, in this method, water or an aqueous solution containing an anionic surfactant as a water-containing liquid is injected from the cutter head 11 at the tip of the shield machine and mixed and stirred, so that an appropriate amount of moisture can be supplied in advance to the excavated mudstone which has a low water content. Since the air bubbles are injected from a protrusion 26 located behind the cutter head 11, at a certain distance from the face, the air bubbles do not leak to the face due to the plugging effect of the excavated soil in the chamber 13. In particular, by injecting an aqueous solution containing anionic surfactant in advance, an appropriate amount of moisture is supplied, and air bubbles can be injected into the excavated soil, which has reacted with the cations of clay minerals and the anions in the aqueous solution, and mixed and stirred, so that the plastic fluidization of the excavated soil can be sufficiently ensured without the air bubbles bursting. Furthermore, the stability of the air bubbles is increased by adding a thickener to the foaming agent. As a result, the face of the excavated soil is stabilized and the excavated soil can be smoothly discharged.

[0034] To confirm the above effects, we attempted to quantitatively evaluate a method in which the solution is supplied to the cutting face in advance from the cutter head 11, and air bubbles are injected from the protrusion 26 at the rear of the cutter head 11, followed by kneading and stirring, by representing it with elemental tests.

[0035] The element testing was carried out in the following four stages. (1) Physical tests of the target soil (2) Design and manufacture of test equipment and establishment of test methods (3) Test to confirm the state of bubble bursting under pressure (4) Reproduction test of construction conditions

[0036] The physical tests of the target soil described in (1) above are conducted to determine basic physical properties such as water content, and consist of soil sampling and physical testing of the soil. In the physical tests, known methods were used to measure water content, particle size, etc.

[0037] In actual construction, the process involves excavating several tens of meters underground, injecting the solution and air bubbles, and then mixing and stirring. This creates a pressurized state due to the weight of the soil and other materials above. This pressurization is considered to be equivalent to the hydrostatic pressure at the construction depth. Therefore, even when conducting tests, it is impossible to accurately evaluate the actual construction conditions without performing them under pressurized conditions.

[0038] However, currently, there is no test method to evaluate the excavation status of bubble shield tunneling under pressure. Therefore, we designed and manufactured a test apparatus for evaluation under pressure and established a new test method.

[0039] To establish the test method, the injection pressure at the target site for injecting bubbles was set as equivalent to the "hydrostatic pressure + face pressure + pre-pressure (0.02~0.05 MPa)" at the assumed tunnel depth. For example, assuming tunnel excavation to a depth of 30m in a completely self-supporting consolidated ground under conditions of a high groundwater level near the surface, face pressure is almost negligible, but a "hydrostatic pressure + pre-pressure" of 0.3 MPa is assumed, so the injection pressure at the target site for bubbles was set to 0.3 MPa. The foaming agent used to generate bubbles was a special foaming agent (KT-10c) from Tack Co., Ltd., and the foaming ratio was set to 5~10 times (solution concentration of 0.5~1.0% according to the foaming ratio). This special foaming agent is an anionic surfactant whose main component is an alkyl ether sulfate salt. The foaming ratio indicates the ratio (times) of the volume of bubbles to the volume of the foaming solution. For example, if the volume of the foaming solution is 5L and the volume of bubbles generated is 25L, the ratio is 5 times.

[0040] As shown in Figure 4, the test apparatus used a sealed container 40 for conducting the test under pressure. The inner diameter of the container 40 was approximately 15 cm, and the height was approximately 15 cm. To maintain an internal pressure of 0.3 MPa, the container 40 consisted of a circular bottom plate 40a made of steel with a predetermined thickness (approximately 1 cm), hollow cylindrical side plates 40b made of acrylic resin with a predetermined thickness (approximately 1 cm) to allow visual inspection of the internal state, and a circular top plate 40c made of steel with a predetermined thickness (approximately 1 cm). The bottom plate 40a and the top plate 40c were directly fixed using double-threaded shafts and nuts to maintain a sealed state even when the inside of the container 40 was pressurized.

[0041] The top plate 40c is provided with a pressurizing / water injection hole 41 and a bubble injection hole 42. Compressed air is supplied from the pressurizing / water injection hole 41 to pressurize the interior, a solution is supplied to the soil contained inside, and bubbles are injected into the soil contained inside through the bubble injection hole 42. The compressed air was supplied at 0.3 MPa, set in a compressor. Bubbles were supplied from a bubble generator that generates bubbles by foaming a foaming solution of a predetermined concentration at a predetermined foaming ratio. The bubble generator includes a pump for supplying the foaming solution, means for supplying a specific gas, and a container for bubbling the foaming solution and generating bubbles. A commercially available general industrial compressed gas (purity 99.995% or higher) argon gas cylinder was used as the means for supplying the specific gas.

[0042] When supplying a solution after applying air pressure to the container 40 by supplying compressed air from the pressurizing / water injection port 41, or when injecting bubbles from the bubble injection port 42, the internal pressure of the container 40 fluctuates. Therefore, a relief valve 43 is installed and set to a predetermined pressure (for example, 0.3 MPa) to prevent the internal pressure of the container 40 from rising excessively.

[0043] The supply of solution (water) into container 40 can be done from the pressurized / water-injection hole 41, and the method of water addition can be selected in accordance with the actual shield construction method. When water addition and air bubble injection are performed simultaneously from the cutter at the face during shield excavation, the construction can be simulated by adding water from the pressurized / water-injection hole 41 while simultaneously injecting air bubbles from the air bubble injection hole 42. On the other hand, when the construction method involves adding water from the cutter at the face and injecting air bubbles from the protruding part 27 on the bulkhead side, the air bubbles will be injected and mixed with a delay after sufficient moisture has been added to the excavated soil from the face. For this reason, in the test simulating this construction method, water or solution was added to the sample before the sample was placed in container 40.

[0044] When the solution or bubbles are injected from the pressurizing / water injection holes 41 and the bubble injection holes 42, which are located away from the soil inside the container 40, it is difficult for the solution or bubbles to penetrate into the soil. Therefore, pipes 44 and 45 that extend close to the surface of the soil are installed at the pressurizing / water injection holes 41 and the bubble injection holes 42. Ideally, the pipes 44 and 45 should extend into the soil, but since there are stirring blades inside and on the surface of the soil, and there is a possibility of damage due to contact with the stirring blades, they are limited to close to the surface of the soil. Because centrifugal force acts on the soil inside the container 40 due to the rotation of the stirring blades, if the solution or bubbles are injected near the side plate 40b, they will move to the side plate 40b and will not mix well with the soil near the center of the container 40. Therefore, in order to ensure proper mixing with the soil near the center of the container 40, the positions of the tips (discharge ports) of the pipes 44 and 45 are set close to the center of the container 40. Furthermore, since air bubbles can only reach the upper part of the soil through the air bubble injection holes 42 in the top plate 40c, air bubble injection holes 42 are also provided in the bottom plate 40a to ensure that air bubbles reach the lower part of the soil as well.

[0045] A predetermined amount of solution is injected into the container 40 relative to the amount of soil contained within. The amount of solution to be injected is determined by a predetermined amount in a separately provided cylindrical water tank and injected by air pressure. A predetermined amount of bubbles is also injected relative to the amount of soil. Since the container 40 is under pressurized conditions, the amount of bubbles injected is determined from the relationship between the injection rate (amount of bubbles injected per unit time), which was measured in advance, and the set time.

[0046] The top plate 40c is provided with a bearing 47 that rotatably supports the rotating shaft 46 while keeping the interior sealed. A handle 48 is provided on the upper part of the bearing 47, and multiple rod-shaped stirring blades 49 are provided on the lower part of the rotating shaft 46 for stirring the soil contained in the container 40. The stirring blades 49 simulate a rotating cutter head 11. The shape of the stirring blades was selected according to the properties of the soil. After mixing the soil and air bubbles, the stirring blades were also used to calculate the shear resistance force to examine the fluidity of the mixed soil.

[0047] One method for quantitatively evaluating the effects of injecting air bubbles into soil and then mixing and stirring is to measure the percentage of injected air bubbles that burst (bubble burst rate) and calculate how many air bubbles remain in the soil based on the measured burst rate. Under atmospheric pressure, the amount of air bubbles can be measured using the NEXCO test method (Test method for air content of fresh air-bubble mixed weighed soil (Test method 128-2015)). However, since it is difficult to perform this test in a pressurized container 40, an alternative method is needed.

[0048] Normally, bubbles are created using air, but this experiment involved creating bubbles using a specific gas other than air (such as carbon dioxide or argon gas), and calculating the amount of burst bubbles by utilizing the increase in the concentration of the specific gas in container 40 when the bubbles burst. For nitrogen and oxygen, which are abundant in air, the change in volume when these gases burst is negligible compared to the total volume, requiring considerable precision for measurement. On the other hand, for gases that are absent from air or present only in trace amounts, the change is larger and easier to detect. For example, carbon dioxide makes up 0.041% of air, but because it is highly soluble in water, it bursts more easily than bubbles created with air. Argon gas is a naturally occurring gas that makes up 0.934% of air. It is poorly soluble in water, resulting in stable bubbles with low reactivity, and possesses properties similar to bubbles created with air. A sample hole 50 for extracting gas from the container 40 was provided in the upper plate 40c, and a gas concentration meter 51 for measuring the concentration of a specific gas in the gas extracted from the sample hole 50 was connected via a sample pipe 52. The gas concentration meter 51 was an ultrasonic gas concentration meter that utilizes the fact that the speed of sound changes with changes in gas concentration. An information processing device such as a PC was connected to the gas concentration meter 51, and the amount of foaming and the foaming rate were calculated from the gas concentration measured by the information processing device.

[0049] An air filter 53 for removing impurities from the gas and a regulator 54 for adjusting the flow rate and pressure of the gas supplied to the gas concentration meter 51 were connected to the sample piping 52. The gas was supplied to the gas concentration meter 51 at a pressure of 0.005 MPa and a flow rate of 1.0 L / min by the regulator 54. The relief valve 43 mentioned above was connected to a cross pipe that led to the sample hole 50, along with the pressure gauge 55 and the sample piping 52.

[0050] The test apparatus was configured as described above, and the test was actually conducted to measure the gas concentration of the specified gas. To measure the gas concentration, the gas in the pipeline was discharged for 5 seconds, then the gas concentration meter 51 was connected, and the measurement was taken for 30 seconds the first time, and for 45 seconds the second time, and the average value was taken as the gas concentration.

[0051] A method for calculating the amount (rate) of foam breakdown from the obtained gas concentration will be described. First, referring to FIG. 5, the concept will be described. The volume of the soil used as a sample is the volume of soil particles V ss and the amount of moisture V sw intervening between the soil particles, and the amount of air V sa present in the interstitial spaces between the soil particles, combined. When this soil is placed in the container 40, air pressure is applied, and water and bubbles are injected, the total volume inside the container 40 is the volume of the above soil plus the amount of injected moisture V ww the amount of the foaming solution as a foaming agent that constitutes the bubble film V bw and the specific gas amount V ba inside the film, and the amount of air V a in the atmosphere, added together.

[0052] When an operator manually rotates the handle 48 and the rotation of the stirring blade 49 kneads and stirs the soil, water, and bubbles, it is considered that a part of the bubbles breaks down and the specific gas inside the bubble film flows out into the atmosphere. Since the container 40 is a sealed container, there is no entry or exit of soil, air, etc. Therefore, the specific gas amount V ba maintained by being covered with the film of the foaming solution and maintaining the bubbles decreases, and the specific gas V ar flows out into the atmosphere, so the gas concentration of the specific gas in the atmosphere increases. By measuring this gas concentration, it is possible to know how much foaming has occurred and calculate the amount (rate) of foam breakdown.

[0053] A specific calculation method will be described. The water content ratio w of the soil inside the container 40 can be expressed by the following formula 1, assuming the density of water is ρ w and the density of soil particles is ρ s .

[0054]

Equation

[0055] The gas concentration D Gas of the specific gas can be calculated by the following formula 2 when the specific gas is a component present in the air, using the amount of the specific gas originally in the air and the increased gas amount due to foam breakdown.

[0056]

number

[0057] In equation 2 above, α is the normal concentration (%) of the specific gas in the air, and m is the foam rupture rate (%). The specific gas V released after foam rupture. ar This can be expressed using the foam-breaking rate m as shown in equation 3 below.

[0058]

number

[0059] Rearranging equation 2 above for the foam breaking rate m, it can be rewritten as equation 4 below.

[0060]

number

[0061] Furthermore, substituting equation 4 into equation 3 above, it can be rewritten as equation 5 below.

[0062]

number

[0063] Therefore, in physical property tests, the amount of air V present in the gaps between soil particles is sa If we can determine the specific amount of gas V inside the bubble membrane, ba V is the amount of a specific gas used to generate bubbles, and represents the amount of air in the atmosphere. a This is the volume obtained by subtracting the volume of soil from the volume of container 40, and when the specific gas is argon gas, α = 0.934%, so the foaming rate and foaming amount can be calculated.

[0064] The bubble bursting test under pressure described in (3) above was conducted by performing a test to confirm the properties and characteristics of the bubbles alone. In this test, in order to confirm the properties and characteristics of the bubbles alone, the change in the bubbles over time was observed under various conditions under pressurized pressure. To confirm the properties of the bubbles, as shown in Figure 6, air pressure was applied to the container from the pressure hole, and bubbles were injected from the bubble injection hole. As time passed, the bubbles burst, and the height h of the liquid surface that returned to the foamed solution was measured. The cross-sectional area A of the container 40 is known, and since bubbles are generated at a predetermined foaming ratio, the foaming ratio is also known, so the amount of burst bubbles (volume) was calculated as h × A × (foaming ratio - 1).

[0065] Furthermore, since the concentration of a specific gas in the atmosphere increases due to bubble rupture, the amount of bubble rupture (volume) was also calculated by measuring the increase in the concentration of the specific gas. Since these calculation results showed almost the same value, it was confirmed that the amount of bubble rupture can be calculated using Equation 5 above by measuring the gas concentration of the specific gas, and that it can be adequately evaluated by gas concentration measurement.

[0066] In the property and characteristics confirmation tests of bubbles alone, two tests were conducted: one in which the foaming solution concentration was fixed and the foaming ratio was varied, and another in which the foaming ratio was fixed and the foaming solution concentration was varied. In the former test, the foaming solution concentration was fixed at 0.5% and 1.0%, and the foaming ratio was varied between 5 and 12. Figure 7(a) shows the results when the foaming solution concentration was 0.5% and the foaming ratio was varied between 5 and 12, and Figure 7(b) shows the results when the foaming solution concentration was 1.0% and the foaming ratio was varied between 5 and 12.

[0067] As shown in Figures 7(a) and (b), at all foaming solution concentrations, a higher foaming ratio resulted in a lower bubble burst rate and better foam retention. Furthermore, the initial bubble burst rate immediately after injection was also lower at higher foaming ratios, and this trend did not reverse with elapsed time. In Figure 7(a), at a foaming ratio of 5, the bubble burst rate already exceeds 30% at time 0; however, this is not due to bursting immediately after injection, but rather suggests that the bubbles were not contributing to the foam from the beginning. Therefore, by removing the initial solution content and correcting the foaming ratio, as shown in Figure 8, the bubble burst rate at time 0 becomes 0, and the overall bubble burst rate decreases. At this point, the foaming ratio was 7.3.

[0068] Figure 9 shows the results when the foaming ratio was set to 10 and the foaming solution concentration was changed to 0.5% and 1.0%. At the same foaming ratio, the rate of foam collapse over time remained almost the same even when the foaming solution concentration was changed. This was also true for the initial foam collapse rate immediately after injection.

[0069] From the above, it was found that increasing the foaming ratio is desirable. However, if the foaming ratio is increased too much, the ratio of the amount of specific gas to the amount of foaming solution becomes large, so the foam film becomes thin and easily bursts. For this reason, it was found that even if the foaming ratio is increased, it is desirable to keep it to around 10 to 20 times.

[0070] The reproduction test of the construction conditions described in (4) above was conducted according to the flow shown in Figure 10. The reproduction test simulates the situation in which a bubble shield machine cuts the ground and mixes the bubbles with the excavated soil using element tests, and confirms the properties. For the reproduction test, Yokohama mudstone from the Sagami Group mudstone layer (SLm layer) was used as the sample. Starting from step 200, the water content of the sample was adjusted in step 201. The water content was adjusted to the in-situ water content (approximately 28%). In step 202, the sample was placed in container 40, and in step 203, the container 40 was sealed and pressurized with compressed air. The pressure inside container 40 was set to 0.3 MPa.

[0071] In step 204, solution (water) was injected through the pressurization / water injection port 41, and bubbles were injected through the bubble injection port 42. The concentration of the foaming solution used as a foaming agent to create bubbles was 0.5-1.0%, and the foaming ratio of the bubbles was 5-10 times. The amount of bubbles injected was 20% (volume) of the sample.

[0072] In step 204, the injection of solution and bubbles into the sample was tested by varying the timing of injection of the solution (water) and the bubbles. In the first injection timing, water was added to the sample first, followed by the addition of bubbles (sequential addition). In sequential addition, a curing time of 10 minutes was allowed after adding the water to allow the water to permeate the sample. In the second injection timing, water and bubbles were added to the sample simultaneously (simultaneous addition).

[0073] In step 205, the sample, water, and air bubbles were stirred and mixed by turning the handle 48 by hand to prevent the sample from being crushed. The stirring was performed at a rotation speed of approximately 40 rpm for 30 seconds, determined from the relationship between the diameter of the shield machine and the cutter rotation speed, relative to the diameter of the test apparatus. In step 206, the gas concentration of the specific gas was measured using the gas concentration meter 51, and the amount of bubble rupture was evaluated based on the increase in the gas concentration of the specific gas.

[0074] In step 207, if possible, the stirring torque was measured, the shear strength was calculated from the measured stirring torque, and the fluidity was evaluated. Fluidity was evaluated by methods such as a vane shear test. In step 208, the properties were observed, and in step 209, the test was completed.

[0075] Two different sample sizes were prepared, and tests were conducted on both. One sample consisted of large particles with an average particle size of 9.5 mm to 19 mm, and the other consisted of small particles with an average particle size of 9.5 mm or less. The small particles had a larger specific surface area, so they easily absorbed moisture and turned into mud, and air bubbles easily burst. Judging from the actual cutting depth of the cutter head 11, the cracks in the mudstone, and the soil removal situation, the large particles were closer to reality as simulated cutting soil, and air bubbles did not burst as easily as with the small particles. Therefore, the large particles were used to evaluate the amount of air bubbles bursting, etc.

[0076] Figure 11 shows the relationship between the water addition rate, water content ratio, and the foaming rate. Unlike the water content ratio, the water addition rate is the amount of water V that the soil originally contains. sw Ignoring other factors, this is the ratio of the mass of added water to the mass of soil. Figure 11(a) shows the relationship between the water addition rate and the foaming rate, and Figure 11(b) shows the relationship between the water content and the foaming rate. The sample had a water content of approximately 28%.

[0077] As shown in Figure 11, it was found that a lower water content (hydration ratio) resulted in a higher bubble burst rate, while a higher water content (hydration ratio) resulted in a lower bubble burst rate. Furthermore, a bubble expansion ratio of 10 times resulted in a lower bubble burst rate than a bubble expansion ratio of 5 times. Additionally, a foaming solution concentration of 1.0% resulted in a lower bubble burst rate than a 0.5% concentration. From these findings, it was discovered that a high water content (hydration ratio), a high bubble expansion ratio, and a high foaming solution concentration can keep the bubble burst rate low.

[0078] Furthermore, tests were conducted with a foaming solution concentration of 1.0% and a foaming ratio of 10 times, while varying the injection timing. It was found that sequential addition, the first injection timing, resulted in a lower foam bursting rate. Among the same white circles with the same water content, the one with the lower foam bursting rate represents the result of the first injection timing.

[0079] Figure 11 shows the results when water is added, but a solution such as soapy water may be added instead of water. Therefore, Figure 12 shows the relationship between the water addition rate, water content ratio, and foaming rate when soapy water is added as the solution. For comparison, the results when water is added, with the same foaming ratio of 10 times and the same foaming solution concentration of 1.0%, are also shown.

[0080] Since bubble bursting occurs when the moisture from the bubbles is absorbed by the soil, it is thought that it will be less likely to occur if the soil retains sufficient moisture. Because soil particles are positively charged, a solution containing anions is considered desirable to retain moisture in the soil. Soapy water is a solution containing anionic surfactants, in which the hydrophilic group dissociates into anions when dissolved in water. Referring to the results shown in Figure 12, it was confirmed that the bubble bursting rate was lower when soapy water, a solution containing anions, was added compared to when water was added.

[0081] Figure 13 shows the properties of the sample before and after testing when the foaming solution concentration was 1.0%, the foaming ratio was 10 times, and a large-grained sample was used, while varying the water content. Figure 13(A) shows the properties of the sample under atmospheric pressure after adding water at a water content of 10% and after adding bubbles. Figure 13(B) shows the properties when the water content was 15%, Figure 13(C) shows the properties when the water content was 20%, and Figure 13(D) shows the properties when the water content was 25%. The injection timing of the solution and bubbles was sequential, which is the first injection timing. After adding the foaming solution, it was allowed to cure for 10 minutes, and then the sample was kneaded and stirred while injecting bubbles under pressure. In Figure 13, the left side shows the state after adding water to the sample under atmospheric pressure, and the right side shows the state after injecting bubbles under pressure, kneading and stirring, and then releasing the pressure to return to atmospheric pressure.

[0082] These results confirmed that a higher water content (hydration ratio) resulted in more bubbles remaining unbroken. Furthermore, it was observed that the bubbles expanded and became larger when the pressure was reduced from pressurized to atmospheric pressure.

[0083] The above test results show that by adding water first to the excavated soil and then adding air bubbles later, the rate of foam breakage can be reduced, and by adding a solution containing anions instead of water, the rate of foam breakage can be further reduced. Furthermore, the rate of foam breakage can be reduced for large-grained soil with a particle size similar to that of the actual excavated soil produced by the cutter head 11. From these findings, it has been verified that by adopting this method, sufficient plastic fluidization of the excavated soil can be ensured, enabling face stability due to the excavated soil and smooth excavation of the excavated soil.

[0084] Furthermore, the above test results show that a higher foaming ratio results in better foam retention, and a higher concentration of the foaming solution results in a lower foam bursting rate. Therefore, by increasing the foaming ratio and setting a higher concentration of the foaming solution, the foam bursting rate can be further reduced.

[0085] The drilling method of the present invention has been described in detail with reference to the embodiments shown in the drawings. However, the present invention is not limited to the embodiments described above, and can be modified to include other embodiments, additions, changes, or deletions within the scope that a person skilled in the art can conceive. Any embodiment that achieves the function and effect of the present invention is included within the scope of the present invention. [Explanation of symbols]

[0086] 10... Skin plate 11…Cutter head 12...Partition part 13… Chamber 14…Drive system 15... Screw conveyor 16... Jack 17... Segments 18… Erecta 19…Backfilling injection device 20...Liquid storage tank 21…Supply pump 22… Foaming agent storage tank 23…Foaming agent supply pump 24... Compressor 25... Foaming device 26, 27...Protrusion 30…mudstone layer 31…Fine soil layer 40…Container 40a…bottom plate 40b…Side plate 40cm... Top board 41…Pressurization / water injection port 42…Bubble injection hole 43…Relief valve 44, 45...tube 46…Rotation axis 47... Bearings 48... Handle 49…Agitator blades 50…Sample wells 51...Gas concentration meter 52…Sample piping 53... Air filter 54… Regulator 55... Pressure gauge

Claims

1. A method for excavating a mudstone layer or a consolidated cohesive soil layer beneath a sandy soil layer using an excavation device, The steps include: discharging water or soapy water from the cutting part of the excavation device, which rotates to cut the ground, toward the ground; The steps include: taking the excavated soil into the space between the partition wall section that divides the inside of the excavation device and the cutting section; The step of injecting bubbles generated using a foaming agent, which is a surfactant dissolved in water, from a hollow protrusion that extends from the partition wall toward the cutting portion into the space into which the excavated soil has been taken in, The step of stirring and mixing the excavated soil taken into the space by the rotation of the cutting part with the injected air bubbles. A drilling method, including...

2. The excavation method according to claim 1, wherein the protruding length of the protruding portion is 1 / 4 to 3 / 4 of the distance from the partition wall portion to the cutting portion.

3. The drilling method according to claim 1 or 2, wherein the bubbles are created using a foaming solution in which the concentration of the foaming agent is 0.5 to 1.0%, and the foaming ratio of the bubbles is 5 to 20 times.

4. The drilling method according to any one of claims 1 to 3, wherein the foaming agent comprises a thickening agent.

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