Ground backfilling method and mixing blade

Abstract

To provide a ground backfilling method capable of making water in a hole from an upper layer to a lower layer be in a uniform state, so as to manage a backfilling material strength simply and correctly.SOLUTION: A ground backfilling method by a backfilling material in which water, soil particles, bentonite and cement are mixed comprises the steps of: excavating a ground 1 in a vertical direction to form a vertical hole 12; injecting bentonite water in which water and bentonite are mixed into the vertical hole; circulating by switching an upper layer 131 and a lower layer 132 of water 13 in a hole in order to mix water in the vertical hole, soil particles and bentonite; determining a cement amount and a water amount in cement milk fed into the vertical hole based on physical properties of the water in the hole after the circulation in the vertical hole; and stirring an inside of the vertical hole while discharging the cement milk from a tip portion 82 of a spiral auger 8 disposed in the vertical hole.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for backfilling ground with a backfill material comprising a mixture of water, soil particles, bentonite, and cement, and to an agitator blade that can be used for the method. [Background technology]

[0002] When removing existing piles buried in the ground or when excavating the ground to construct an underground structure, the cavities formed in the ground are usually backfilled with backfill material to which a solidifying agent such as cement has been added.

[0003] Patent documents 1 and 2 disclose a technique for using liquefied soil produced by mixing construction soil generated by excavation with cement, admixtures, and water as backfill material.

[0004] Backfill materials with added cement, such as liquefied treated soil, may become too hard compared to the surrounding ground if the amount of cement is too large. Therefore, Patent Document 1 describes that various admixtures are used to control the hardening speed, strength properties, elasticity, etc. of the liquefied treated soil.

[0005] Furthermore, as disclosed in Patent Document 3, a control method has been developed that can easily and accurately control the strength of backfill material made of a mixture of water, soil particles, bentonite, and cement, and a backfilling method for ground using this control method. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2008-75342 A [Patent Document 2] JP 2002-371588 A [Patent Document 3] JP 2018-76648 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, the muddy water generated in the vertical hole when excavating the ground is easily lost in sandy or gravel ground with low self-supporting properties, and even in soft clayey ground, there is a risk of the hole wall collapsing if the muddy water level drops when removing existing piles, so there are cases where the water level in the vertical hole must be maintained by refilling it with bentonite water, etc. In such cases, if separation occurs in the water in the vertical hole, causing physical properties such as density to differ between the upper and lower layers, there is a risk that the strength exerted by the cement-based solidification material injected later cannot be accurately controlled.

[0008] Therefore, the present invention aims to provide a method for backfilling ground that can make the water in the hole uniform from the upper layer to the lower layer so that the strength of the backfill material can be easily and accurately controlled, and an agitator blade that can be used for this method. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, the method of backfilling ground of the present invention is a method of backfilling ground with a backfill material comprising a mixture of water, soil particles, bentonite and cement, and is characterized by comprising the steps of: excavating the ground vertically to form a vertical hole; injecting bentonite water comprising a mixture of water and bentonite into the vertical hole; circulating the water in the hole by switching between the upper and lower layers in order to mix the water, soil particles and bentonite in the vertical hole; determining at least the amount of cement and the amount of water in the cement milk to be poured into the vertical hole based on the physical properties of the water in the hole after circulation in the vertical hole; and stirring the vertical hole while ejecting the cement milk from the tip of an injection means having a stirring function and arranged in the vertical hole.

[0010] Here, a pile is buried in the ground before the vertical hole is excavated, and the bentonite water is often injected into the vertical hole when the pile is pulled out from the vertical hole. In addition, in the step of circulating the water in the hole, a configuration can be adopted in which, with an injection means having a stirring function disposed in the vertical hole, the upper layer of the water in the hole is sucked up and the water in the hole is discharged from the tip of the injection means while stirring with the stirring function.

[0011] Furthermore, the step of circulating the water in the hole may be configured to suck up the lower layer of the water in the hole, pass it through a plant outside the hole, and then return it to the upper layer of the water in the hole. The step of circulating the water in the hole may be configured to suck up the lower layer of the water in the hole and discharge it near the mouth of the vertical hole. The discharge amount of the cement milk may be adjusted in the depth direction of the vertical hole.

[0012] In addition, the agitator impeller of the invention is characterized in that it comprises a hollow tube portion which serves as a rotating shaft, a blade portion which protrudes from the circumferential surface of the hollow tube portion, and an outflow pipe which has one end connected to the inner space of the hollow tube portion and is arranged along the blade portion and has a discharge outlet formed therein. Effect of the Invention

[0013] In the method of backfilling ground of the present invention thus configured, after injecting bentonite water into a vertical hole, the water in the hole is circulated by switching between the upper and lower layers in order to mix the water, soil particles, and bentonite in the hole.

[0014] As a result, the water in the hole can be made uniform from the upper to lower layers, and the strength of the backfill material can be easily and accurately controlled. Such circulation of the water in the hole can be efficiently performed by sucking up the upper layer of the water in the hole and stirring it while discharging the sucked up water from the tip of the injection means having a stirring function.

[0015] The water in the hole can also be circulated by pumping up the lower layer of the water in the hole, passing it through a plant outside the hole, and then returning it to the upper layer.Furthermore, the water in the hole can also be circulated by a simple configuration in which the lower layer of the water in the hole is pumped up and discharged near the mouth of the vertical hole.

[0016] In addition, by adjusting the amount of cement milk discharged in the depth direction of the vertical hole, when the ground has different strengths in the depth direction, the strength of the backfill material can be adjusted to match the strength of the surrounding ground.

[0017] On the other hand, the invention of the impeller has an outlet pipe with a discharge port along the blade. By using such an impeller, it becomes easy to effectively disperse the sucked up water in the hole or cement milk to the surroundings as the impeller rotates. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is an explanatory diagram showing a schematic diagram of a circulation process in the method for backfilling ground according to an embodiment of the present invention. [Diagram 2] These are diagrams to explain the problems that occur when the backfill strength varies with depth, where (a) is an explanatory diagram of the effect on excavation of a hole for a newly constructed pile when the strength at the bottom is low, and (b) is an explanatory diagram of the effect on excavation of a hole for a newly constructed pile when the strength at the bottom is high. [Diagram 3] FIG. 13 is a schematic diagram illustrating the process of removing the existing piles. [Figure 4] FIG. 2 is a schematic diagram illustrating the process of injecting cement milk to complete the backfill material. [Diagram 5] FIG. 2 is an explanatory diagram showing a schematic diagram of the circulation process in the method for backfilling ground in Example 1. [Figure 6] FIG. 10 is an explanatory diagram showing a schematic diagram of the circulation process in the method for backfilling ground in Example 2. [Figure 7] FIG. 13 is a diagram for explaining the configuration of the stirring impeller of Example 3, where (a) is a side view and (b) is a cross-sectional view seen in the direction of the arrow AA in (a). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The backfilling material used in the method for backfilling ground according to the present embodiment is a material suitable for backfilling ground that solidifies in a state where water, soil particles, bentonite, and cement are mixed.

[0020] Here, water refers to the water used when drilling the ground, groundwater, and water added as a mix. Also, soil particles mainly refer to construction waste such as excavated soil and sand that mixes with drilling water when excavating the ground. Water containing soil particles generated by drilling the ground is called muddy water.

[0021] On the other hand, bentonite is a type of clay whose main component is montmorillonite, and has a strong affinity with water, and has the property of being highly water-absorbent, absorbing and expanding when soaked in water. It is generally said that bentonite can reduce water by about 300% to 500% of its own mass. The characteristics of bentonite vary depending on the place of production, etc.

[0022] There are also various types of cement, such as blast furnace cement, Portland cement, and fly ash cement, and any type can be added to the backfill material.

[0023] In the method for backfilling ground according to the present embodiment, the backfilling material is prepared with a controlled strength. That is, the type of cement, the amount of cement, the amount of water, etc., injected as a solidification material are adjusted so that the strength of the backfilling material becomes a target strength.

[0024] Figure 2 is a diagram explaining the problems that occur when the strength of the backfill material is not controlled and the strength of the backfill varies with depth. Figure 2(a) shows a case where the strength of the lower part of the backfill is low. For example, when a solidification material is injected from above into a vertical hole after removing a long pile, the muddy water and the solidification material at the bottom do not mix sufficiently and remain unconsolidated, which can result in a low strength at the bottom.

[0025] When a hole for a new pile is drilled adjacent to such backfill with low strength at the bottom, even if the upper part can be excavated straight, the hole may be bent at the bottom as it approaches the backfill with low strength, making it impossible to form a straight hole for the new pile.

[0026] On the other hand, Figure 2(b) shows a case where the strength of the lower part of the backfill is high. For example, if separation occurs in the backfill material, which is a mixture of mud water and solidification material, and most of the solidification material settles to the bottom of the hole, while the solidification material and mud water remain unconsolidated at the top, the backfill will have a high strength at the bottom.

[0027] When a hole for a new pile is drilled adjacent to such backfill with a higher strength at the bottom, the upper part of the hole will penetrate into the backfill, but the lower part will bend away from the stronger backfill, making it impossible to form a straight hole for the new pile.

[0028] Furthermore, backfilling that is too strong may cause problems such as making excavation impossible. On the other hand, backfilling that is too weak may easily cause the hole walls to collapse, hindering subsequent excavation.

[0029] Therefore, in the method for backfilling ground according to the present embodiment, the strength of the backfilling material is precisely controlled, so that even when excavation is required to construct new piles after the backfilling, the construction can be carried out efficiently without interrupting the construction.

[0030] First, the excavation to be backfilled will be described with reference to FIG. For example, when constructing a new building or condominium on a site where an existing building has been demolished, the piles that form the foundation of the existing building (existing piles 2) may lack bearing capacity or may have deteriorated, making it necessary to reconstruct a new pile foundation.

[0031] In such a case, the existing pile 2 is first removed from the ground 1, and the cavity left behind by the removal is backfilled. For example, if an existing reinforced concrete pile 2 is buried in the ground 1, the removal work involves excavating a concave shape near the head of the existing pile 2 to provide a boiler pit 11, as shown in Figure 3(a).

[0032] Next, a casing 3 with an inner diameter larger than the outer diameter of the existing pile 2 is used, and high-pressure water 31 is sprayed from the tip of the casing 3 to cut the ground 1 near the outer periphery of the existing pile 2 to perform edge cutting. The casing 3 is rotated in both forward and reverse directions and is pushed into the ground 1 so as to accommodate the existing pile 2 inside.

[0033] When the casing 3 is pushed into the ground 1 in this manner, a vertical hole 12 is formed around the existing pile 2, as shown in Figure 3(b), and inside it is stored muddy water 4, a mixture of high-pressure water 31, groundwater, and other water, as well as soil particles from the excavated ground 1.

[0034] When the casing 3 used for cutting and the existing pile 2 are pulled out from the vertical hole 12 formed by vertical excavation in this way, the water level of the muddy water 4 drops accordingly, so liquid is injected to maintain the water level in the vertical hole 12. In this embodiment, bentonite water 5, which is a mixture of water and bentonite, is injected into the vertical hole 12.

[0035] When the ground 1 has high hole wall stability or the piles to be removed are short, the bentonite water 5 may be injected all at once after the piles are removed, but when the ground 1 has low hole wall stability or the existing piles 2 are long, the bentonite water 5 is injected from the hole mouth while the existing pile 2 is pulled out, as shown in Figure 3(c). That is, a supply pipe 51 is laid up to the hole mouth of the vertical hole 12, and the existing pile 2 is gradually pulled up while the bentonite water 5 is injected.

[0036] Here, the bentonite water 5 to be injected later into the vertical hole 12 and the muddy water 4 accumulated in the vertical hole 12 do not mix simply by the force of injecting the bentonite water 5, but usually separate. Figure 3(d) shows a state in which the muddy water 4 has settled in the lower layer 132 of the vertical hole 12 and the bentonite water 5 has accumulated in the upper layer 131.

[0037] Therefore, in the method for backfilling ground according to the present embodiment, a circulation process is carried out to eliminate the separated state of the water 13 in the vertical hole 12 and to make the water uniform in the depth direction before adding the cement-based solidification material. In other words, if the muddy water 4 and the bentonite water 5 are separated, it becomes impossible to accurately measure the density to determine the mixture of the cement milk 6 to be injected in the subsequent process. Furthermore, if a difference in strength occurs in the depth direction of the backfill due to separation, there is a possibility that the problems described above with reference to FIG. 2 will occur, so a circulation process is carried out to prevent such a state.

[0038] 1 is an explanatory diagram showing a schematic diagram of the circulation process in the method for backfilling ground according to the present embodiment. In this embodiment, in order to circulate the water 13 in the hole, a spiral auger 8 serving as an injection means having a stirring function, a submersible pump 41, and a plant 42 installed outside the vertical hole 12 are used. This circulation process using the spiral auger 8 is applied, for example, when the ground 1 is a clayey soil ground.

[0039] Spiral auger 8 includes hollow rod 81 serving as a rotation axis, blade portion 821 provided at tip portion 82 of rod 81, and discharge port 822 for spraying liquid sent to tip portion 82 through the inner space of rod 81. In other words, blade portion 821 formed in a spiral shape or the like performs a stirring function, and rod 81 and discharge port 822 constitute an injection means.

[0040] A sand pump that sucks up a fluid by suction force can be used as the submersible pump 41. A conveying pipe 411 or a conveying hose is connected to the submersible pump 41. A filter is attached to the suction port of the submersible pump 41 to prevent clogging of the conveying pipe 411.

[0041] The plant 42 is formed in a box shape capable of temporarily storing a fluid. The borehole water 13 pumped up by the submersible pump 41 is discharged to the plant 42 through a transport pipe 411. If necessary, a filter can also be installed near the discharge port of the transport pipe 411. This filter is installed to reduce the accumulation of sediment in the plant 42 and to prevent clogging of the pressure pump 43 and the transport pipe 431.

[0042] The borehole water 13 temporarily stored in the plant 42 is discharged to the outside of the plant 42 by a pressure pump 43. To the pressure pump 43, a conveying pipe 431 or a conveying hose, one end of which is connected to the upper end of the rod 81 of the spiral auger 8, or the other end of which is connected.

[0043] In the circulation process, a submersible pump 41 is placed in the upper layer 131 of the borehole water 13, and mainly the bentonite water 5 accumulated in the upper layer 131 is pumped up. The bentonite water 5 sucked into the submersible pump 41 rises through a transport pipe 411 and is discharged to a plant 42.

[0044] The borehole water 13 accumulated in the plant 42 is sent to the transport pipe 431 by the pressure pump 43, and is transported to the upper end of the rod 81 of the spiral auger 8, which serves as an injection means having a stirring function. The borehole water 13 that has flowed into the rod 81 in this manner hangs down inside the rod 81 and is sprayed again into the vertical hole 12 from the discharge port 822.

[0045] The tip 82 of the spiral auger 8 is disposed near the bottom of the vertical hole 12. For example, in the stirring range of the illustrated lower layer 132, the tip 82 is moved up and down while the rod 81 is rotated.

[0046] At this time, the water 13 in the hole in the upper layer 131 that has been sucked up by the submersible pump 41 is sprayed from the discharge port 822, and the water 13 in the hole in the upper layer 131 is supplied from the discharge port 822 to the lower layer 132 in which the muddy water 4 had mainly settled before the circulation started, and is stirred by the blade portion 821.

[0047] In short, in the circulation process of this embodiment, the borehole water 13 in the upper layer 131 is replaced by being sent to the lower layer 132, and the borehole water 13 is stirred by the blades 821 of the spiral auger 8. When this circulation process is continued for a set time, the muddy water 4 and the bentonite water 5 that were separated before the circulation are mixed, and the borehole water 13 becomes uniform in the depth direction.

[0048] As shown in Fig. 4(a), a sample 130 is collected from the borehole water 13, which is a homogeneous mixture of the muddy water 4 and the bentonite water 5 obtained by the circulation process, in order to examine the physical properties of the water. The density, water content, grain size, pH, viscosity, etc. of the collected sample 130 are examined.

[0049] The sample 130 can be examined as needed or continuously during the circulation process. By observing the changes in density and pH of the sample 130, it can be confirmed that the borehole water 13 has been mixed uniformly by checking that the physical properties have stabilized. The density can be easily measured using a mud balance.

[0050] Cement milk 6 is added to the water in the hole 13 as a solidification agent for imparting a desired strength to the backfill material 7. The composition of the cement milk 6 to be finally injected into the vertical hole 12 is determined by the physical properties of the sample 130 collected.

[0051] The strength of the backfill material 7 is determined by the amount of cement, the amount of water, and the amount of bentonite. The amount of bentonite can be controlled by knowing the amount of bentonite water 5 injected into the vertical hole 12 when the existing pile 2 is removed. The amount of water before the injection of the cement milk 6 can be obtained from the physical properties of the sample 130, such as the density.

[0052] Furthermore, the effect on the strength exhibited per unit cement content can be estimated depending on the pH of the sample 130. For example, it is known that acidity has an effect in the direction of decreasing the strength of the backfill material 7.

[0053] In short, in order to achieve the desired strength of the backfill material 7 filled in the vertical hole 12, the amount of cement and water that should be injected into the uniformly mixed hole water 13 is calculated, and the cement milk 6 is formulated.

[0054] In addition to cement and water, bentonite, thickeners, water reducers, anti-gelling agents, set retarders, etc. can be added to the cement milk 6. Some of these additives, such as bentonite, affect the strength of the backfill material 7, while others are added to solve various problems in construction. For example, if the strength of the backfill material 7 is 0.2 - 1.0 (N / mm 2 The composition is adjusted so that the content falls within the range of

[0055] Here, the volume V of the vertical hole 12 can be easily calculated from the penetration length of the pulled-out casing 3 and the inner diameter of the vertical hole 12 (the outer diameter of the casing 3). In addition, by measuring the water level of the water in the hole 13, the volume V of the water in the hole 13 can be easily calculated. m On the other hand, the volume V of the cavity above the water 13 in the vertical hole 12 can be calculated easily. v V v =VV m It becomes.

[0056] Next, an injection process will be described in which cement milk 6 in an amount corresponding to the cavity of the vertical hole 12 is injected and mixed with the hole water 13 to form the backfill material 7. The cement milk 6, the composition of which is determined based on the physical properties of the collected sample 130, is injected into the vertical hole 12 using a spiral auger 8, which serves as an injection means having a stirring function, as shown in Fig. 4(b). For example, the cement milk 6 is charged into the plant 42 used in the circulation process, and the cement milk 6 sent to a conveying pipe 431 by a pressure pump 43 is made to flow into a rod 81 and discharged from a discharge port 822.

[0057] The tip 82 of the spiral auger 8 is initially submerged near the bottom of the vertical hole 12, and the blades 821 are rotated to stir the cement milk 6 while it is injected from an outlet 822 located at the lowest injection point 61.

[0058] After a predetermined amount of cement milk 6 has been discharged at the lowest injection point 61, the spiral auger 8 is pulled up while rotating the blade portion 821, as shown in Figure 4 (c), so that the discharge outlet 822 is positioned at the position of the next injection point 61.

[0059] At the second injection point 61 from the bottom, the cement milk 6 is injected and stirred by rotating the blades 821. By repeating the movement to the injection point 61 and the injection and stirring of the cement milk 6 in this manner, the entire vertical hole 12 is filled with a uniform backfill material 7 (see FIG. 4(d)).

[0060] Here, when creating a backfilling material 7 having uniform strength in the depth direction, the intervals between the injection points 61 may be made constant, and the amount of cement milk 6 discharged from each injection point 61 may be made constant.

[0061] On the other hand, the ground 1 often has multiple geological layers stacked in the depth direction, and the strength may vary depending on the depth even in the area to be backfilled with the backfill material 7. The problem described above with reference to Figure 2 is merely an example of a case where the area to be backfilled is a ground of uniform strength, and it is preferable that the strength of the backfill material 7 is close to the strength of the original ground around it.

[0062] Therefore, if it is found from the results of ground investigations such as standard penetration tests, uniaxial or triaxial compression tests, and borehole horizontal loading tests that the strength of the ground 1 varies greatly in the depth direction, the strength of the backfill material 7 can be changed in the depth direction.

[0063] When changing the strength of the backfilling material 7 in the depth direction, for example, the above-mentioned steps are followed until the mixture of cement milk 6 is determined, and adjustment is made in the step of injecting the cement milk 6. In short, since the strength of the backfilling material 7 changes depending on the amount of cement milk 6 added, the strength is adjusted by adjusting the amount of cement milk 6 added in the range in which the strength is to be adjusted.

[0064] For example, by shortening the interval (injection interval) between the injection points 61, 61, the amount of cement milk 6 added in that range can be increased. Also, the amount added can be adjusted by increasing the discharge amount of the injection points 61 in the range where strength is desired to be increased and decreasing it in the range where strength is desired to be decreased. Furthermore, by shortening the interval between the injection points 61, 61 and increasing the discharge amount at each injection point 61, the strength of a specific range of the backfill material 7 can be further increased.

[0065] By using the above-mentioned method or by changing the composition of the cement milk 6, it is possible to perform backfilling with, for example, three or four different strength zones in the depth direction. When controlling the injection interval to change the strength, the length can be controlled to about 1 to 2 m.

[0066] Next, the operation of the method for backfilling ground according to this embodiment will be described. In the method for backfilling the ground according to the present embodiment configured as described above, after the bentonite water 5 is injected into the vertical hole 12, the water in the hole 12 is circulated by forcibly sending the upper layer 131 of the water 13 to the lower layer 132 in order to mix the water, soil particles, and bentonite in the vertical hole 12.

[0067] As a result, the borehole water 13 can be made uniform from the upper layer 131 to the lower layer 132, and the strength of the backfill material 7 can be easily and accurately controlled. In short, circulation of the borehole water 13 can be efficiently carried out by sucking up the upper layer 131 of the borehole water 13 with the submersible pump 41 and discharging the sucked up borehole water 13 from the tip 82 of the spiral auger 8.

[0068] In addition, almost all of the muddy water 4 generated when removing the existing piles 2 can be used as material for the backfill material 7, thereby reducing the burden of treating waste soil and drainage such as the muddy water 4 as industrial waste, etc.

[0069] Furthermore, if only a small-scale plant 42 is installed outside the vertical hole 12, it can be easily implemented even in a site with a small lot. In addition, since the cement milk 6, which is the solidification material, is injected in the final process after the borehole water 13 is sufficiently mixed, it is possible to prevent the occurrence of a situation in which solidification starts at an unintended timing even if the work takes a long time.

[0070] Furthermore, by adjusting the discharge amount of cement milk 6 in the depth direction of the vertical hole 12, when the ground 1 has different strengths in the depth direction, the strength of the backfill material 7 can be adjusted to match the ground strength at the original location. EXAMPLES

[0071] Hereinafter, a method for backfilling ground that is different from the method for backfilling ground described in the above embodiment will be described with reference to Fig. 5. Note that the same terms or the same reference numerals will be used to describe the same or equivalent parts as those described in the above embodiment.

[0072] In the above embodiment, the circulation process is performed using the spiral auger 8, but in this Example 1, a circulation process using a different method will be described. The circulation process of this Example 1 is applied, for example, to a case where the ground 1 is a sandy ground.

[0073] In this embodiment 1, in order to circulate the borehole water 13, a submersible pump 41, a plant 42 installed outside the vertical hole 12, and a transport pipe 44 that serves as a path for returning the borehole water 13 to the vertical hole 12 are used.

[0074] A conveying pipe 411 or a conveying hose is connected to the submersible pump 41 used in the embodiment 1. Further, a filter is attached to the suction port of the submersible pump 41 to prevent clogging of the conveying pipe 411.

[0075] The borehole water 13 pumped up by the submersible pump 41 and transported through the transport pipe 411 is discharged to the plant 42 and temporarily stored there. If necessary, a filter can also be installed near the discharge port of the transport pipe 411. This filter is installed to reduce the accumulation of sediment in the plant 42 and to prevent clogging of the pressure pump 43 and the transport pipe 44.

[0076] The borehole water 13 temporarily stored in the plant 42 is discharged to the outside of the plant 42 by a pressure pump 43. The pressure pump 43 is connected to an end of a conveying pipe 44 or a conveying hose whose discharge port 441 is disposed near the mouth of the vertical hole 12.

[0077] In the circulation process, a submersible pump 41 is placed in the lower layer 132 of the borehole water 13 near the bottom of the vertical hole 12, and pumps up mainly muddy water 4 that has accumulated in the lower layer 132. The muddy water 4 sucked into the submersible pump 41 rises through a transport pipe 411 and is discharged to a plant 42.

[0078] The borehole water 13 accumulated in the plant 42 is pumped out to the transport pipe 44 by the pressure pump 43, and is sprayed again into the vertical hole 12 from the discharge port 441 of the transport pipe 44. This discharge port 441 is disposed near the mouth of the vertical hole 12.

[0079] The muddy water 4 having a high specific gravity injected from the discharge port 441 sinks down the vertical hole 12 and mixes with the water in the hole 13. That is, the muddy water 4 is pulled up from the lower layer 132 where the muddy water 4 had mainly settled before the start of circulation, and returned from the discharge port 441 to the upper layer 131 where the bentonite water 5 has mainly accumulated, forcibly exchanging the upper layer 131 with the lower layer 132.

[0080] When this circulation process is continued for a set time, the muddy water 4 and the bentonite water 5 that were separated before the circulation are mixed together to become borehole water 13 that is uniform in the depth direction. In this way, the borehole water 13 can be circulated and mixed even in a configuration that does not involve mechanical mixing, in which the lower layer 132 of the borehole water 13 is pumped up, passed through a plant 42 outside the borehole, and then returned to the upper layer 131 of the borehole water 13. Other configurations and effects of the first embodiment are substantially the same as those of the above-described embodiment or other embodiments, and therefore description thereof will be omitted. EXAMPLES

[0081] Hereinafter, an embodiment of the method for backfilling ground, which is different from the embodiment and the embodiment 1 described above, will be described with reference to Fig. 6. Note that the same terms or the same reference numerals will be used to describe the same or equivalent parts as those described in the embodiment or the embodiment 1.

[0082] In the above-mentioned Example 1, a circulation process with a simple configuration in which the borehole water 13 in the lower layer 132 is returned to the upper layer 131 via the plant 42 is described, but in the present Example 2, a circulation process with an even simpler configuration is described. The circulation process of the present Example 2 is applied, for example, when the ground 1 is a sandy ground.

[0083] In this second embodiment, in order to circulate the borehole water 13, a submersible pump 41, a conveying pipe 45 for raising the borehole water 13, and a branching section 451 provided at the upper end of the conveying pipe 45 are used. The branching section 451 has branch pipes extending in two directions approximately perpendicular to the conveying pipe 45 so as to form a T shape when viewed from the front, and each branch pipe has a downward discharge port 452, 452.

[0084] In the circulation process, a submersible pump 41 is placed in the lower layer 132 of the borehole water 13 near the bottom of the vertical hole 12, and sucks up mainly muddy water 4 that has accumulated in the lower layer 132. The muddy water 4 sucked into the submersible pump 41 rises through a transport pipe 45, and at a branching point 451 near the mouth of the vertical hole 12, it branches into two branch pipes and is discharged from discharge ports 452, 452 toward the water surface of the borehole water 13.

[0085] In this way, even with a very simple configuration in which the lower layer 132 of the borehole water 13 is sucked up and discharged near the mouth of the vertical hole 12, the borehole water 13 can be circulated and mixed. Other configurations and effects of the second embodiment are substantially the same as those of the above-described embodiment or other embodiments, and therefore description thereof will be omitted. EXAMPLES

[0086] Hereinafter, a mixing impeller that can be used in the method for backfilling the ground described in the above embodiment or Examples 1 and 2 will be described with reference to Fig. 7. Note that the same or equivalent parts as those described in the above embodiment or Examples 1 and 2 will be described using the same terms or symbols.

[0087] In this Example 3, as shown in Fig. 7(a), for example, an agitating blade provided at the tip 83 of a spiral auger 8 will be described. This agitating blade may be provided integrally with a rod 81 of the spiral auger 8, or may be attached to the end of the rod 81 as an attachment. Alternatively, it may be provided at the tip of an injection tube.

[0088] The impeller of this Example 3 comprises a hollow tube portion 831 which serves as a rotation shaft, a blade portion 832 which protrudes from the peripheral surface of the hollow tube portion 831, and an outflow pipe 833 one end of which is connected to the inner space of the hollow tube portion 831.

[0089] 7(b), the hollow pipe portion 831 is formed with a pipe 831a that communicates with the hollow portion of the rod 81. That is, when the borehole water 13 or the cement milk 6 described in the above embodiment is supplied from the upper end of the rod 81, it flows into the outflow pipe 833 through the pipe 831a.

[0090] The blade portion can be formed, for example, by a spiral blade or a plurality of plate-shaped blades. In the third embodiment, a configuration including a spiral blade portion 832 that makes two revolutions around a hollow tube portion 831 will be described. An outflow pipe 833 is disposed along the upper surface of the blade portion 832.

[0091] For example, the two outflow pipes 833, 833 each extend in a direction substantially perpendicular to the hollow pipe portion 831. For example, the two outflow pipes 833, 833 preferably extend in directions different from each other by approximately 180° in plan view.

[0092] A connection portion 833c which is one end of the outflow pipe 833 is connected to a pipe line 831a of the hollow pipe portion 831. At least one discharge port is formed in the outflow pipe 833. In the third embodiment, a case where discharge ports 833a, 833b are drilled in the other end and the side surface of the outflow pipe 833 will be described.

[0093] The discharge port 833a provided at the end is perforated on the end face of the outflow pipe 833, and discharges the cement milk 6 flowing down the outflow pipe 833 in the downward direction as it is. The discharge port 833b provided on the side discharges the cement milk 6 flowing inside the outflow pipe 833 by leaking out.

[0094] The outlet ports 833b provided on the side surface can be multiple holes spaced apart in the extension direction of the outflow pipe 833. In this embodiment 3, as shown in Fig. 7(b), one outflow pipe 833 is provided with two outlet ports 833b on each side surface, totaling four outlet ports 833b on the side surfaces.

[0095] The impeller of the third embodiment thus configured has an outlet pipe 833 having a plurality of discharge ports 833a, 833b disposed along the blade portion 832 of the impeller provided at the tip portion 83 of the spiral auger 8.

[0096] In other words, if discharge ports 833a, 833b are drilled in an outflow pipe 833 that extends laterally from the hollow tube portion 831 and is provided along the rotating blade portion 832, the fluid to be discharged, such as cement milk 6, can be sent to the side, away from the hollow tube portion 831, and can be scattered around by centrifugal force.

[0097] Therefore, if such an agitator is provided, when returning the hole water 13 to the vertical hole 12 or when injecting the cement milk 6, it is easy to effectively disperse the cement milk 6 and the like around as the agitator rotates. Other configurations and effects of the third embodiment are substantially the same as those of the above-described embodiment or other embodiments, and therefore description thereof will be omitted.

[0098] Although the embodiments and examples of the present invention have been described in detail above with reference to the drawings, the specific configurations are not limited to these embodiments and examples, and design changes that do not deviate from the gist of the present invention are included in the present invention.

[0099] For example, in the above embodiment, a method for extracting an existing pile 2 using a casing 3 and high-pressure water 31 has been described, but this is not limited to this, and any method for removing the existing pile 2 from the ground 1 may be used.

[0100] In the above embodiment, the method of backfilling the cavity formed by removing the existing piles 2 with the backfilling material 7 has been described, but the present invention is not limited to this and can be applied to any case, such as when removing buried objects or filling cavities created by excavation. Furthermore, the ground 1 backfilled with the backfilling material 7 is suitable not only for constructing new piles, but also for driving sheet piles and driving gantry piles vertically.

[0101] Furthermore, in the above embodiment, the spiral auger 8 has been described as the injection means having the stirring function, but the present invention is not limited to this. For example, the injection means may have a mechanical stirring function, such as a plate-shaped blade attached to the tip of the injection pipe. Furthermore, even a high-pressure injection stirring device used in a deep mixing treatment method can be used as the injection means having the stirring function. Furthermore, the injection means having the stirring function may have different configurations for the circulation process and the injection process. [Explanation of symbols]

[0102] 1: Ground 12: Vertical hole 13: Water inside the hole 131: Upper layer 132: Lower layer 2: Existing pile (pile) 4: Muddy water 42: Plant 5: Bentonite water 6: Cement milk 7: Backfill material 8: Spiral auger (injection means with stirring function) 82:Tip 83:Tip 831 :Hollow tube part 832: Wing 833 :Outflow pipe 833a:Discharge port 833b:Discharge port

Claims

1. A method for backfilling ground with a backfill material comprising a mixture of water, soil particles, bentonite, and cement, comprising the steps of: A step of excavating the ground vertically to form a vertical hole; A step of injecting bentonite water, which is a mixture of water and bentonite, into the vertical hole; a step of continuing circulation of the water in the borehole for a predetermined period of time by replacing the upper layer with the lower layer in order to mix the water, soil particles, and bentonite in the borehole and make the water in the borehole uniform in the depth direction; A step of determining at least the amount of cement and the amount of water of the cement milk to be charged into the vertical hole based on the physical properties of the water in the vertical hole after circulation; and a step of stirring the inside of the vertical hole while discharging the cement milk from a tip of an injection means having a stirring function and disposed in the vertical hole, A method for backfilling ground, characterized in that a pile is buried in the ground before the vertical hole is excavated, and the bentonite water is injected into the vertical hole when the pile is pulled out of the vertical hole.

2. The method for backfilling ground as described in claim 1, characterized in that in the step of circulating the water in the hole, with an injection means having a stirring function placed in the vertical hole, the upper layer of the water in the hole is sucked up and the water in the hole is discharged from the tip of the injection means while stirring using the stirring function.

3. A method for backfilling ground with a backfill material comprising a mixture of water, soil particles, bentonite, and cement, comprising the steps of: A step of excavating the ground vertically to form a vertical hole; A step of injecting bentonite water, which is a mixture of water and bentonite, into the vertical hole; a step of continuing circulation of the water in the borehole for a predetermined period of time by replacing the upper layer with the lower layer in order to mix the water, soil particles, and bentonite in the borehole and make the water in the borehole uniform in the depth direction; A step of determining at least the amount of cement and the amount of water of the cement milk to be charged into the vertical hole based on the physical properties of the water in the vertical hole after circulation; and a step of stirring the inside of the vertical hole while discharging the cement milk from a tip of an injection means having a stirring function and disposed in the vertical hole, A method for backfilling ground, characterized in that in the process of circulating the water in the borehole, the lower layer of the water in the borehole is pumped up, passed through a plant outside the borehole, and then returned to the upper layer of the water in the borehole.

4. A method for backfilling ground with a backfill material comprising a mixture of water, soil particles, bentonite, and cement, comprising the steps of: A step of excavating the ground vertically to form a vertical hole; A step of injecting bentonite water, which is a mixture of water and bentonite, into the vertical hole; a step of continuing circulation of the water in the borehole for a predetermined period of time by replacing the upper layer with the lower layer in order to mix the water, soil particles, and bentonite in the borehole and make the water in the borehole uniform in the depth direction; A step of determining at least the amount of cement and the amount of water of the cement milk to be charged into the vertical hole based on the physical properties of the water in the vertical hole after circulation; and a step of stirring the inside of the vertical hole while discharging the cement milk from a tip of an injection means having a stirring function and disposed in the vertical hole, A method for backfilling ground, characterized in that in the step of circulating the water in the hole, a lower layer of the water in the hole is sucked up and discharged near the mouth of the vertical hole.

5. A method for backfilling ground as described in claim 3 or 4, characterized in that a pile is buried in the ground before the vertical hole is excavated, and the bentonite water is injected into the vertical hole when the pile is pulled out of the vertical hole.

6. 6. A method for backfilling ground according to claim 1, characterized in that the amount of cement milk discharged is adjusted in the depth direction of the vertical hole.

Images