Ground improvement methods for existing structures

Abstract

To provide a method for improving the ground under an existing structure, which can improve the ground while preventing both leakage of sewage, etc. inside the existing structure into the ground, and infiltration of groundwater into the existing structure.SOLUTION: A ground improvement method for improving the ground G1 below an existing structure C installed in a water area comprises an upper slab penetration step of penetrating a first penetration rod R1 into an upper slab S1, an upper slab drilling step of forming a first through hole H1 in the upper slab S1 with a first drilling rod R2, a middle slab penetration step in which the first drilling rod R2 is used as a second penetration rod and the second penetration rod R2 is penetrated into the middle slab S2, a middle slab drilling step in which a second through hole H1 is formed in the middle slab S2 using a third drilling rod R3, a lower slab penetration step in which the third drilling rod R3 is used as a third penetration rod and the third penetration rod R3 is penetrated into the lower slab S3, a lower slab drilling step of forming a third through hole H3 in the lower slab S3 with the third drilling rod R4, and a ground improvement step for improving ground G1 with an improvement rod Ra.SELECTED DRAWING: Figure 14

Description

Technical Field

[0001] The present invention relates to a ground improvement method under an existing structure.

Background Art

[0002] There are cases where ground improvement is carried out below an existing structure existing in a river, sea area, ground under the groundwater level, etc. (in this specification, these regions are collectively referred to as "water areas"). For example, in a box culvert that forms a main line for taking in and flowing rainwater and sewage, when a new structure is constructed above the box culvert, it is necessary to enhance the ground strength under the box culvert. Therefore, ground improvement will be constructed under the box culvert while supplying the main line of rainwater and sewage. When constructing ground improvement under an existing structure in a water area like this, when the width of the existing structure is long, there is a limit to the method of inserting improvement rods obliquely from the side of the existing structure, and there is a risk of an area that cannot be improved. Therefore, construction can be carried out by forming through holes in the upper floor slab and lower floor slab constituting the existing structure, and inserting improvement rods into the ground under the existing structure through each through hole to perform ground improvement.

[0003] In this construction method, since it is ground improvement under an existing structure in a water area, when forming through holes in the upper floor slab and lower floor slab of the existing structure, water stop measures are essential to prevent groundwater from entering the main line or, conversely, to prevent sewage, etc. from leaking into the ground. However, a technique for inserting improvement rods into the ground under an existing structure through through holes and performing ground improvement while preventing the intrusion of groundwater and the leakage of sewage, etc. through the through holes has not been established.

[0004] Here, in Patent Document 1, a method for improving the confined ground directly under an existing structure is proposed, in which groundwater, etc. directly under the foundation slab concrete is not water-stopped and discharged, and ground improvement is carried out from above the foundation slab concrete. Specifically, a lower watertight member, in which a shutter plate supported by a support plate can slide to close, is installed on the foundation of an existing structure on ground compressed by groundwater. An upper watertight member, in which multiple watertight rubber packings with insertion holes smaller in diameter than the diameter of the excavation pipe are housed in a stacked state with washers in between, is installed on top of the lower watertight member. Next, the excavation pipe is inserted into the insertion hole, and a through-hole is formed in the foundation by the excavation pipe in a watertight state with the watertight rubber packing. After excavating the ground, an injection material is injected to improve the ground up to the foundation. After that, the excavation pipe is raised and the shutter plate slides to close the through-hole. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-102477 [Overview of the project] [Problems that the invention aims to solve]

[0006] According to the method for improving confined ground directly beneath an existing structure described in Patent Document 1, ground improvement can be carried out from above the existing structure to below the existing structure while stopping the groundwater flow directly beneath the existing structure. However, as mentioned above, the existing structures are main lines for rainwater and sewage, and there is no disclosure of means to prevent both leakage of sewage into the ground and infiltration of groundwater into these main lines.

[0007] The present invention aims to provide a method for improving the ground beneath an existing structure, which involves forming through holes in the floor slab that constitutes the existing structure, and which can improve the ground while preventing both the leakage of sewage and other contents from the existing structure into the ground and the intrusion of groundwater into the existing structure. [Means for solving the problem]

[0008] To achieve the above objective, one embodiment of the ground improvement method for existing structures according to the present invention is: A method for improving the ground beneath an existing concrete structure, comprising at least an upper deck, a lower deck, and side walls surrounding a hollow space, and installed in water or underground in a body of water, wherein the existing structure is located in water or underground, and the ground beneath it is improved. The upper floor slab penetration process involves inserting a first penetration rod from above the upper floor slab to a point midway through the thickness of the upper floor slab, The process involves arranging a first drilling rod inside the first penetration rod in the upper deck slab, drilling through the upper deck slab to form a first through-hole, and The lower slab penetration process involves using the first drilling rod as a second penetration rod, or arranging the second penetration rod inside the first drilling rod, and penetrating the lower slab from above to a point midway through its thickness. A second drilling rod is placed inside the second penetration rod, and the lower slab is drilled through to form a second through-hole, a lower slab penetration step, The present invention is characterized by having a ground improvement step, in which an improvement rod constituting a ground improvement device is inserted into the ground beneath the existing structure from above the upper deck slab through the first and second through holes to perform ground improvement.

[0009] According to this embodiment, when performing ground improvement by forming a first through-hole and a second through-hole in the upper and lower slabs of an existing structure, and inserting an improvement rod under the existing structure through these through-holes, a penetration rod with a larger diameter than the through-hole is driven into the slab to an intermediate position before forming the through-hole in each slab. By stopping water leakage through the penetration of this penetration rod, a drilling rod with a relatively smaller diameter is placed inside to form the through-hole. This makes it possible to perform ground improvement under the existing structure while preventing both leakage of sewage and other contents from the existing structure to the outside and infiltration of groundwater into the existing structure. In other words, this embodiment involves performing a set of steps—a floor slab penetration process using a penetration rod and a floor slab penetration process using a drilling rod—starting from the upper floor slab and proceeding sequentially down to the lower floor slabs, thereby forming corresponding through-holes in each floor slab, and inserting the improvement rod into the ground beneath the existing structure through these through-holes. In this context, existing structures in the water include box culverts that form main lines such as rainwater and sewer lines. For example, a box culvert can be configured with an upper slab, a lower slab, and side walls, and with partition walls inside, to form multiple main lines, which are used for rainwater and sewer lines. In addition to rainwater and sewer lines, maintenance walkways and other access points are also provided. For example, in situations where a linear existing structure is buried beneath the ground in a body of water, support piles such as steel pipe piles are constructed on either side of the existing structure, and a work platform is formed above the water surface above the existing structure, supported by these piles. Drilling equipment such as boring machines can then be installed on this work platform, allowing for the penetration of penetration rods into the deck slab and the drilling of drilling rods through the deck slab. Various ground improvement methods can be applied to the ground improvement method using the improvement rods applied in this embodiment, such as high-pressure injection mixing methods, chemical injection methods, and methods that combine these methods.

[0010] Furthermore, other embodiments of the ground improvement method for existing structures according to the present invention include: A ground improvement method for an existing structure, comprising at least an upper deck, a middle deck, a lower deck, and side walls surrounding a hollow space, for improving the ground beneath an existing structure located in water or underground in a body of water, The upper floor slab penetration process involves inserting a first penetration rod from above the upper floor slab to a point midway through the thickness of the upper floor slab, The process involves arranging a first drilling rod inside the first penetration rod in the upper deck slab, drilling through the upper deck slab to form a first through-hole, and The intermediate floor slab penetration process involves using the first drilling rod as a second penetration rod, or arranging the second penetration rod inside the first drilling rod, and penetrating the intermediate floor slab from above to a point midway through its thickness. A second drilling rod is placed inside the second penetration rod, and the intermediate deck is drilled through to form a second through-hole, a process of penetrating the intermediate deck, The lower slab penetration process involves using the second drilling rod as a third penetration rod, or arranging the third penetration rod inside the second drilling rod, and penetrating the lower slab from above to a point midway through the thickness of the lower slab. A third drilling rod is placed inside the third penetration rod, and the lower slab is drilled through to form a third through-hole, a lower slab penetration step, The present invention is characterized by having a ground improvement step, in which an improvement rod constituting a ground improvement device is inserted into the ground beneath the existing structure from above the upper deck slab through the first through-hole, the second through-hole, and the third through-hole to perform ground improvement.

[0011] According to this embodiment, even if the existing structure has three deck slabs, an upper deck slab, a middle deck slab, and a lower deck slab, by sequentially performing a set of deck slab penetration process using a penetration rod and deck slab penetration process using a drilling rod for each deck slab in the order of upper deck slab, middle deck slab, and lower deck slab, corresponding through-holes are formed for each deck slab, and the improvement rod is inserted through each through-hole into the ground beneath the existing structure, making it possible to perform ground improvement beneath the existing structure.

[0012] Furthermore, in another embodiment of the ground improvement method for existing structures according to the present invention, In the aforementioned upper deck penetration process, the first penetration rod is fired against the upper deck, and a waterproofing material is filled from the inside of the first penetration rod between the first penetration rod and the upper deck. The lower slab penetration process is characterized by firing the second penetration rod against the lower slab and filling the space between the second penetration rod and the lower slab from the inside of the second penetration rod.

[0013] According to this aspect, in addition to driving the penetration rod into the floor slab and baking it for primary water stop, by further filling the inside of the penetration rod with a water stop material for secondary water stop, the water stop material can be made to flow into the space between the tip of the penetration rod and the penetration groove (the groove into which the penetration rod penetrates) of the floor slab, ensuring an even higher level of water stopping performance. Here, for example, after driving the penetration rod into the floor slab and baking it and filling it with the water stop material, one end of the penetration rod is lifted, the water stop material is made to flow outside the penetration groove formed in the floor slab, and the penetration rod is dropped back into the penetration groove, so that the water stop material can be filled (spread) inside and outside the penetration rod through the penetration groove. Examples of the water stop material include water stop mortar containing non-shrinking mortar, water stop cement, resinous water stop materials containing epoxy resin, and the like.

[0014] In another aspect of the ground improvement method under an existing structure according to the present invention, In the upper floor slab penetration step, the first penetration rod is baked against the upper floor slab, and a water stop material is filled between the first penetration rod and the upper floor slab from the inside of the first penetration rod. In the middle floor slab penetration step, the second penetration rod is baked against the middle floor slab, and a water stop material is filled between the second penetration rod and the middle floor slab from the inside of the second penetration rod. In the lower floor slab penetration step, the third penetration rod is baked against the lower floor slab, and a water stop material is filled between the third penetration rod and the lower floor slab from the inside of the third penetration rod.

[0015] According to this aspect, even when the existing structure has three floor slabs, namely an upper floor slab, a middle floor slab, and a lower floor slab, by filling the water stop material in each penetration step for the upper floor slab, the middle floor slab, and the lower floor slab, the water stopping performance in the penetration area of the penetration rod in each floor slab can be further enhanced.

[0016] In another aspect of the ground improvement method under an existing structure according to the present invention, In the upper floor slab penetration step, a pilot hole is drilled in the upper floor slab, and a part of the fall prevention fixture is extended downward from the upper floor slab through the pilot hole. Support the concrete core generated when the first through-hole is formed with the fall prevention jig, and pull up and recover the concrete core through the first through-hole. The fall prevention jig is a bar, and an expanding member that is rotatably attached to the bar and changes its posture between a reduced-diameter posture and an expanded-diameter posture. When the fall prevention jig is inserted into the pilot hole, the expanding member is in a reduced-diameter posture, and when the expanding member protrudes below the upper floor slab, it changes its posture to an expanded-diameter posture. The formed concrete core is supported by the expanding member in the expanded-diameter posture.

[0017] According to this aspect, when forming a through-hole in the floor slab, the concrete core generated is supported by the fall prevention jig, and the fall prevention jig is pulled up to recover the concrete core above the existing structure, thereby preventing the concrete core from falling inside the existing structure. For example, when the space (such as a main sewer line) formed by the upper floor slab, the lower floor slab, and the side wall is a narrow space where people cannot enter, if the concrete core generated when forming a through-hole in the upper floor slab falls on the lower floor slab, the concrete core cannot be recovered. When forming a through-hole in the upper floor slab that forms such a narrow space, a pilot hole is formed in the floor slab, and the fall prevention jig is projected into the space below the floor slab through the pilot hole to prevent the concrete core from falling onto the lower floor slab, thereby preventing the fallen concrete core from remaining on the lower floor slab.

[0018] Here, the fall prevention jig has an expanding member rotatably attached to the bar, and the expanding member changes its posture between a reduced-diameter posture and an expanded-diameter posture. When the fall prevention jig is inserted into the pilot hole, the expanding member is in a reduced-diameter posture, and when the expanding member protrudes below the upper floor slab, it changes its posture to an expanded-diameter posture. This makes it possible to support a concrete core larger than the hollow of the pilot hole with the fall prevention jig while inserting the fall prevention jig into a pilot hole as small as possible.

[0019] Furthermore, in another embodiment of the ground improvement method for existing structures according to the present invention, In the upper deck penetration process, a pilot hole is drilled in the upper deck, and a part of the fall prevention jig is extended downward through the pilot hole in the upper deck. The concrete core generated when the first through-hole is formed is supported by the fall prevention jig, and the concrete core is pulled up and recovered through the first through-hole. In the intermediate floor slab penetration process, a pre-drilled guide hole is made in the intermediate floor slab, and a part of the fall prevention jig is extended downward through the pre-drilled guide hole. The concrete core generated when the second through-hole is formed is supported by the fall prevention jig, and the concrete core is lifted up and recovered through the second through-hole and the first through-hole. The aforementioned fall prevention jig is Rods and, The rod material is rotatably attached to the aforementioned rod material and has an expanding member that changes its position between a reduced diameter position and an expanded diameter position, When the fall prevention jig is inserted into the preceding guide hole, the diameter-expanding member is in a reduced-diameter position, and changes its position to an expanded-diameter position when the diameter-expanding member protrudes below the upper floor slab. The formed concrete core is supported by the diameter-expanding member in an expanded diameter position.

[0020] According to this embodiment, even when an existing structure has three floor slabs, an upper slab, a middle slab, and a lower slab, the concrete core can be prevented from falling by constructing a pilot hole and using a fall prevention jig when forming through holes in the upper slab and the middle slab. Furthermore, if the space between the upper and middle floor slabs, or between the middle and lower floor slabs, is a relatively large space that a person can enter, then it is permissible to enter the space and retrieve the concrete core without drilling a pilot hole or using a fall prevention jig. However, even if the space is relatively large, if it is a space that is constantly in use, such as a rainwater main or sewer main, it is difficult for a person to enter and retrieve the concrete core, so drilling a pilot hole and using a fall prevention jig is desirable.

[0021] Furthermore, in another embodiment of the ground improvement method for existing structures according to the present invention, The process further includes a hole-closing step, in which, after the ground improvement step, the second through-hole is filled with a sealing material to close it, and when closing the first through-hole, a bottom cover with a larger planar dimension than the first through-hole is folded and suspended below the first through-hole, then lifted up and in close contact with the lower surface of the upper floor slab, and the first through-hole is filled with sealing material to close it. The bottom cover is, Multiple divided plates that are connected to each other in a way that allows them to be folded, A fixing jig comprising a fixing part fixed to the upper surface of the dividing plate and a rotating part that rotates relative to the fixing part, The device is characterized by having a suspension member attached to one end of the rotating part, or to one end of an intermediate member attached to one end of the rotating part.

[0022] According to this embodiment, when closing a through-hole, a bottom cover with a larger planar dimension than the through-hole is folded and suspended below it through the through-hole, and the bottom cover is pulled up and in close contact with the underside of the floor slab, and the through-hole is closed by filling it with a sealing material. This makes it possible to close a through-hole formed in the floor slab even if the space below the floor slab is a narrow space inaccessible to a person. After filling the sealing material with the bottom cover pulled up and in close contact with the underside of the floor slab, it is preferable to keep the bottom cover suspended from above via a suspension member until the sealing material hardens and achieves a predetermined strength.

[0023] Here, the bottom cover is equipped with multiple segmented plates that are foldable and connected to each other, allowing the planar dimensions of the bottom cover to be adjusted to a size that allows it to pass through the through-hole. Furthermore, as the multiple segmented plates extend out of the through-hole, the entire structure expands laterally, making the planar dimensions of the bottom cover larger than the planar dimensions of the through-hole, and enabling the peripheral area of ​​the bottom cover to be in close contact with the underside of the floor slab. An "intermediate member" is, for example, a steel rod approximately the length of the through-hole. One end of the steel rod is fixed to the rotating part, and one end of the suspension member is fixed to the other end of the steel rod via a nut, including a tall nut. As the sealing material hardens, the intermediate member inside the through-hole is embedded in the sealing material, and the sealing of the through-hole can be completed by removing one end of the suspension member from the tall nut, etc., located above the intermediate member. Although it is possible to omit the intermediate member and fix one end of the suspension member to the rotating part, in this case, the suspension member cannot be removed from the rotating part due to the hardening of the sealing material, and part or all of the suspension member will be left protruding above the floor slab. Therefore, it is preferable to apply an intermediate member having a length approximately equal to the thickness of the first through hole. Here, steel bars or chains can be used as the suspension members. Furthermore, mortar containing non-shrink mortar or concrete can be used as the blocking material.

[0024] Furthermore, by having a fixing jig that includes a fixing part fixed to the upper surface of the divided plate and a rotating part that rotates relative to the fixing part, the divided plate can be rotated relative to the rotating part which is directly or indirectly connected by a suspension member. For example, in a configuration in which the fixing part is fixed to the longitudinal center of the central divided plate of three divided plates, by attaching a counterweight to a position offset to one side from the longitudinal center of this central divided plate, the orientation of the divided plate when passing through the through hole can be made oblique, and the planar dimension through which the divided plate passes can be made even smaller.

[0025] Furthermore, in another embodiment of the ground improvement method for existing structures according to the present invention, The process further includes a through-hole closing step, in which, after the ground improvement step, the third through-hole is filled with a sealing material to close it, and when closing at least one of the first and second through-holes, a bottom cover with a larger planar dimension than the first or second through-hole is folded and suspended below the first or second through-hole, then pulled up and in close contact with the lower surface of the upper or middle floor slab, and the sealing material is filled to close the first or second through-hole. The bottom cover is, Multiple divided plates that are connected to each other in a way that allows them to be folded, A fixing jig comprising a fixing part fixed to the upper surface of the dividing plate and a rotating part that rotates relative to the fixing part, The device is characterized by having a suspension member attached to one end of the rotating part, or to one end of an intermediate member attached to one end of the rotating part.

[0026] According to this embodiment, when an existing structure has three floor slabs, an upper slab, a middle slab, and a lower slab, even if the space below either or both of the upper and middle slabs is a narrow space inaccessible to people, it becomes possible to close the through-holes formed in the upper or middle slab by using a bottom cover. [Effects of the Invention]

[0027] According to the ground improvement method for existing structures of the present invention, in a method of performing ground improvement work for existing structures while forming through holes in the floor slab that constitutes the existing structure, it is possible to perform ground improvement while preventing both the leakage of sewage and other contents from inside the existing structure into the ground and the intrusion of groundwater into the existing structure. [Brief explanation of the drawing]

[0028] [Figure 1] This figure shows an example of an existing structure located in a body of water to which the ground improvement method for existing structures according to the embodiment is applied. [Figure 2] This is a process diagram of an example of a ground improvement method for an existing structure according to the embodiment. [Figure 3] Following Figure 2, this is a process diagram illustrating an example of a ground improvement method for existing structures. [Figure 4] Following Figure 3, this is a process diagram illustrating an example of a ground improvement method for existing structures. [Figure 5] Following Figure 4, this is a process diagram illustrating an example of a ground improvement method for existing structures. [Figure 6]This diagram illustrates an example of a fall prevention jig, showing both the state in which the fall prevention jig passes through a through-hole and the state in which it protrudes from the through-hole. [Figure 7] Following Figure 5, this is a process diagram illustrating an example of a ground improvement method for existing structures. [Figure 8] Following Figure 7, this is a process diagram illustrating an example of a ground improvement method for existing structures. [Figure 9] Following Figure 8, this is a process diagram illustrating an example of a ground improvement method for existing structures. [Figure 10] Following Figure 9, this is a process diagram illustrating an example of a ground improvement method for existing structures. [Figure 11] Following Figure 10, this is a process diagram illustrating an example of a ground improvement method for existing structures. [Figure 12] Following Figure 11, this is a process diagram illustrating an example of a ground improvement method for existing structures. [Figure 13] Following Figure 12, this is a process diagram illustrating an example of a ground improvement method for existing structures. [Figure 14] Following Figure 13, this is a process diagram illustrating an example of a ground improvement method for existing structures. [Figure 15] Following Figure 14, this is a process diagram illustrating an example of a ground improvement method for existing structures. [Figure 16] Following Figure 15, this is a process diagram illustrating an example of a ground improvement method for existing structures. [Figure 17] Following Figure 16, this is a process diagram illustrating an example of a ground improvement method for existing structures. [Figure 18] Following Figure 17, this is a process diagram illustrating an example of a ground improvement method for existing structures. [Figure 19A] This is a perspective view of an example of a bottom cover that closes a through-hole in a floor slab. [Figure 19B] This diagram shows both the state in which the bottom cover passes through the through hole and the state in which it is in close contact with the underside of the floor slab. [Figure 20] Following Figure 18, this is a process diagram illustrating an example of a ground improvement method for existing structures. [Figure 21A] This is a process diagram explaining the test construction. [Figure 21B]Following Figure 21A, this is a process diagram explaining the test construction. [Figure 21C] Following Figure 21B, this is a process diagram explaining the test construction. [Figure 21D] Following Figure 21C, this is a process diagram explaining the test construction. [Figure 21E] Following Figure 21D, this is a process diagram explaining the test construction. [Figure 21F] Following Figure 21E, this is a process diagram explaining the test construction. [Figure 21G] Following Figure 21F, this is a process diagram explaining the test construction. [Figure 21H] Following Figure 21G, this is a process diagram explaining the test construction. [Modes for carrying out the invention]

[0029] The following describes a ground improvement method for existing structures according to the embodiment, with reference to the attached drawings. In this specification and the drawings, substantially identical components are denoted by the same reference numerals to avoid redundant explanations.

[0030] [Ground improvement method under an existing structure according to an embodiment] Referring to Figures 1 to 20, an example of a ground improvement method beneath an existing structure according to this embodiment will be described, along with the fall prevention jig and bottom cover used in this construction. Here, Figure 1 is a diagram showing an example of an existing structure located in a body of water to which the ground improvement method for existing structures according to the embodiment is applied, and Figures 2 to 5, 7 to 18, and 20 are, in order, process diagrams of an example of the ground improvement method for existing structures according to the embodiment. Figure 6 is a diagram illustrating an example of a fall prevention jig, showing both the state in which the fall prevention jig passes through the through hole and the state in which it protrudes from the through hole. Furthermore, Figure 19A is a perspective view of an example of a bottom cover that closes the through hole of the deck slab, and Figure 19B shows both the state in which the bottom cover passes through the through hole and the state in which it is in close contact with the underside of the deck slab.

[0031] The existing structure C, which is the target of the ground improvement work shown in Figure 1, is a linear, reinforced concrete box culvert embedded in the ground G beneath the riverbed. This box culvert C has an upper slab S1, a lower slab S3, and left and right side walls W1, and an internal partition wall W2, with an intermediate slab S2 further located in the right-hand area of ​​the partition wall W2.

[0032] The space (hollow) between the upper slab S1 and the middle slab S2 is the sewer main space C1, the space between the middle slab S2 and the lower slab S3 is the management space C2, and the space in the left region of the partition wall W2 is the rainwater main space C3.

[0033] Furthermore, the sewer main space C1 is a narrow space inaccessible to people, and sewer water flows through it at all times. On the other hand, the management space C2 is accessible to administrators and is used for managing the sewer and rainwater main lines. The method for performing ground improvement on the ground G1 below this box culvert C will be explained below.

[0034] In detail, the ground G1 below the rainwater main space C3 and the ground below the management space C2 will be improved separately, but the following explanation will focus on the method of improving the ground G1 below the management space C2. The ground improvement of the ground G1 below the rainwater main space C3 will be carried out using substantially the same method. Note that the existing structure whose ground below is subject to improvement is not limited to the box culvert shown in the illustration, but can include various concrete structures. In addition, the body of water where the ground to be constructed is located may be a river as shown in the illustration, or it may be a sea area. Furthermore, the existing structure may be an underwater structure that protrudes into the water, and the ground below it may be subject to improvement.

[0035] In Figures 2 and beyond, only the right-hand region of the bulkhead W2 under construction is shown. Furthermore, to facilitate understanding of the drawings, the sewer lines in the sewer main space C1 are omitted from the illustration. Additionally, a work platform exists above the river in the box culvert C. Drilling equipment such as boring machines are installed on this work platform to perform rotary press-in of the first penetration rod R1, and similarly, ground improvement is carried out using ground improvement equipment installed on the work platform. However, the illustrations of this work platform, drilling equipment, and ground improvement equipment are omitted.

[0036] As shown in Figure 2, the first penetration rod R1 is driven in the X2 direction while rotating in the X1 direction from above the upper slab S1 to a point midway through the thickness of the upper slab S1. As an example, a φ406 mm casing can be applied to the first penetration rod R1.

[0037] By rotating and pressing the first penetration rod R1 into the upper slab S1 to an intermediate position without water and then curing it, a watertight structure (primary watertight structure) is formed between the first penetration rod R1 and the upper slab S1. For example, if the thickness of the upper slab S1 is about 500 mm, the first penetration rod R1 is driven in about 50 mm.

[0038] Next, as shown in Figure 3, non-shrink mortar M1 (an example of a waterproofing material) is filled into the interior of the first penetration rod R1. After filling with non-shrink mortar M1, the first penetration rod R1 is slightly pulled up, causing the non-shrink mortar M1 to spread outward through the penetration groove formed by the first penetration rod R1. Subsequently, by lowering the first penetration rod R1 and returning its tip to the penetration groove, a waterproofing structure (secondary waterproofing structure) is formed, as shown in Figure 3, in which the areas inside and outside the first penetration rod R1 are waterproofed with non-shrink mortar M1.

[0039] In this way, by forming a watertight structure (secondary watertight structure) using non-shrink mortar M1, the intrusion of groundwater into the interior of the first penetration rod R1 can be suppressed in combination with the primary watertight structure described above (the above describes the upper deck penetration process).

[0040] Next, as shown in Figure 4, a relatively small-diameter single pipe P is inserted into the first penetration rod R1 in the X3 direction, and a pilot hole Ha is formed by drilling through the upper deck slab S1.

[0041] As shown in Figure 5, a fall prevention jig 10 is inserted into the pre-hole Ha in the X4 direction, and its lower part is extended out through the pre-hole Ha into the sewer main space C1.

[0042] Here, with reference to Figure 6, the structure and operation of the fall prevention jig 10 will be explained. The fall prevention jig 10 is a jig that prevents the concrete core CO generated when forming a through hole (first through hole H1 shown in Figure 7) in the upper floor slab S1 from falling onto the upper surface of the middle floor slab S2.

[0043] The fall prevention jig 10 includes, for example, a metal rod 11 and a plurality of metal diameter-expanding members 15 that are rotatably attached to the rod 11.

[0044] The rod 11 is formed from a hollow pipe, and three storage grooves 11a are provided at the left and right positions along its longitudinal direction. The lower ends of two diameter-expanding members 15 are rotatably mounted on a pivot shaft 13 located inside the rod 11, and each diameter-expanding member 15 is constantly biased to expand relative to the rod 11 via an elastic material 16 such as a coil spring.

[0045] In the illustrated example of the fall prevention jig 10, a pair of diameter-expanding members 15 are rotatably attached to three locations along the longitudinal direction of the rod 11.

[0046] When the fall prevention jig 10 passes through the pre-hole Ha made of the single pipe P, as shown in Figure 6, at least a portion of each enlarged diameter member 15 is housed in the housing groove 11a of the rod member 11, becoming the fall prevention jig 10A in a reduced diameter position, and is inserted through the inside of the single pipe P in the downward direction X4.

[0047] On the other hand, when the lower part of the fall prevention jig 10 extends below the single pipe P (below the upper floor slab S1), the diameter-expanding member 15, which is constantly biased to expand by the elastic material 16, rotates in the X5 direction via the pivot axis 13 and expands outward, and the pair of diameter-expanding members 15 expand to a larger diameter than the preceding guide hole Ha, resulting in the fall prevention jig 10B in an expanded diameter position.

[0048] Thus, when the fall prevention jig 10 is inserted into the preceding guide hole Ha, it is in a reduced diameter position as the fall prevention jig 10A, and when it extends below the upper floor slab S1, it changes its position to an expanded diameter position as the fall prevention jig 10B.

[0049] Here, a pair of diameter-expanding members 15 are rotatably provided at multiple different positions (three in the illustrated example) along the longitudinal direction (height direction) of the rod 11. For example, if the pair of diameter-expanding members 15 at the top malfunction and fail to expand, the pair of diameter-expanding members 15 in the center can expand and support the falling concrete core CO. Also, if the pair of diameter-expanding members 15 in the center are damaged or otherwise fail to expand during use, the pair of diameter-expanding members 15 at the bottom can expand and support the falling concrete core CO.

[0050] In this way, by providing multiple sets of diameter-expanding members 15 rotatably at different height positions on the rod member 11, even if some of the diameter-expanding members 15 malfunction or break, the concrete core CO can be reliably supported by the other sets of diameter-expanding members 15.

[0051] Furthermore, the process of preparing this fall prevention jig 10 is a preparation process (fall prevention jig preparation process), and the process of forming the pre-hole Ha in the upper floor slab S1 is a pre-hole formation process.

[0052] Figure 5 shows the state in which the lower part of the fall prevention jig 10 protrudes into the sewer main space C1, resulting in the fall prevention jig 10B in an expanded diameter position.

[0053] Next, as shown in Figure 7, the first drilling rod R2 is positioned inside the first penetration rod R1 in the upper slab S1, and the first drilling rod R2 is rotated in the X6 direction while drilling through in the X7 direction. As an example, a φ355 mm casing can be applied to the first drilling rod R2.

[0054] By drilling a first drilling rod R2 through the upper slab S1, a first through-hole H1 is formed in the upper slab S1, and a concrete core CO is generated during the formation of the first through-hole H1. By supporting the generated concrete core CO with an expanded-diameter fall prevention jig 10B, it is possible to prevent the concrete core CO from falling onto the upper surface of the middle slab S2. Thus, the process of forming the first through-hole H1 and supporting and recovering the concrete core CO with the expanded-diameter fall prevention jig 10B constitutes the through-hole formation process.

[0055] As previously mentioned, the sewer main space C1 is a narrow space inaccessible to people, making it impossible to recover the concrete core CO if it falls onto the upper surface of the intermediate slab S2. Thus, the fall prevention jig 10 is effective when forming a through hole in the slab (upper slab S1) above a narrow space inaccessible to people.

[0056] Furthermore, by forming the preliminary guide hole Ha with the smallest possible diameter, the first drilling rod R2 can be positioned between the pipe P forming the preliminary guide hole Ha and the first penetration rod R1 to form the first through hole H1. Even when a pipe P forming a small-diameter preliminary guide hole Ha is used, the fall prevention jig 10 can pass through the inside of the small-diameter pipe P by changing its orientation to a reduced-diameter fall prevention jig 10A (the above describes the upper slab penetration process).

[0057] Next, as shown in Figure 8, the first drilling rod R2 is used as the second penetration rod, and the second penetration rod R2 is driven in the X9 direction while rotating it in the X8 direction from above the subfloor slab S2 to a position midway through the thickness of the subfloor slab S2. Here, as shown in the illustrated example, instead of using the first drilling rod R2 as the second penetration rod, a second penetration rod different from the first drilling rod R2 may be used.

[0058] By rotating and pressing the second penetration rod R2 into the intermediate slab S2 in a waterless state up to an intermediate position and then curing it, a watertight structure (primary watertight structure) is formed between the second penetration rod R2 and the intermediate slab S2. For example, if the thickness of the intermediate slab S2 is about 500 mm, the second penetration rod R2 is driven in about 50 mm.

[0059] Next, as shown in Figure 9, non-shrink mortar M2 (an example of a waterproofing material) is filled into the interior of the second penetration rod R2. After filling with non-shrink mortar M2, the second penetration rod R2 is slightly lifted, causing the non-shrink mortar M2 to spread outward through the penetration groove formed by the second penetration rod R2. Subsequently, by lowering the second penetration rod R2 and returning its tip to the penetration groove, a waterproofing structure (secondary waterproofing structure) is formed, as shown in Figure 9, where the areas inside and outside the second penetration rod R2 are waterproofed with non-shrink mortar M2. Note that since sewage is present in the sewer main space C1, if it is not possible to slightly lift the second penetration rod R2 in this manner, it is not necessary to lift the second penetration rod R2.

[0060] In this way, by forming a watertight structure (secondary watertight structure) using non-shrink mortar M2, the intrusion of sewage into the interior of the second penetration rod R2 can be suppressed in combination with the primary watertight structure described above (the above describes the intermediate floor slab penetration process).

[0061] Next, as shown in Figure 10, a second drilling rod R3 is placed inside the second penetration rod R2 in the subfloor slab S2, and the second drilling rod R3 is rotated in the X10 direction while drilling through in the X11 direction. As an example, a φ318 mm casing can be applied to the second drilling rod R3.

[0062] By drilling through the intermediate slab S2 with the second drilling rod R3, a second through-hole H2 is formed in the intermediate slab S2, and concrete core CO is generated during the formation of the second through-hole H2. The generated concrete core CO falls onto the upper surface of the lower slab S3. However, since the management space C2 is large enough for a person to enter, the fallen concrete core CO can be collected by a worker.

[0063] If it is desired to prevent the concrete core CO from falling, a preliminary guide hole can be formed in the sub-slab S2 before the second drilling rod R3 is drilled through, using the same method as in Figures 4 and 5, and the fall prevention jig 10 can be applied (this completes the sub-slab penetration process).

[0064] Next, as shown in Figure 11, the second drilling rod R3 is used as the third penetration rod and is driven in the X13 direction from above the lower slab S3 to a point midway through the thickness of the lower slab S3 while rotating the third penetration rod R3 in the X12 direction. Here, as shown in the illustrated example, instead of using the second drilling rod R3 as the third penetration rod, a third penetration rod different from the second drilling rod R3 may be used.

[0065] By rotating and pressing the third penetration rod R3 into the lower slab S3 in a waterless state up to an intermediate position and then curing it, a watertight structure (primary watertight structure) is formed between the third penetration rod R3 and the lower slab S3. For example, the third penetration rod R3 is driven in about 50 mm.

[0066] Next, as shown in Figure 12, non-shrink mortar M3 (an example of a waterproofing material) is filled into the interior of the third penetration rod R3. After filling with non-shrink mortar M3, the third penetration rod R3 is slightly pulled up, causing the non-shrink mortar M3 to spread outward through the penetration groove formed by the third penetration rod R3. Subsequently, by lowering the third penetration rod R3 and returning its tip to the penetration groove, a waterproofing structure (secondary waterproofing structure) is formed, as shown in Figure 12, in which the areas inside and outside the third penetration rod R3 are waterproofed with non-shrink mortar M3.

[0067] In this way, by forming a watertight structure (secondary watertight structure) using non-shrink mortar M3, in combination with the primary watertight structure described above, it is possible to prevent groundwater that has seeped in from below the lower slab S3 from entering the management space C2 when a through hole (third through hole) is formed in the lower slab S3 (this concludes the lower slab penetration process).

[0068] Next, as shown in Figure 13, the third drilling rod R4 is positioned inside the third penetration rod R3 in the lower slab S3, and the third drilling rod R4 is rotated in the X14 direction while drilling through in the X15 direction. As an example, a φ267mm casing can be applied to the third drilling rod R4.

[0069] By drilling through the lower slab S3 with the third drilling rod R4, a third through-hole H3 is formed in the lower slab S3. If it is desired to recover the concrete core generated during the formation of the third through-hole H3, a preliminary guide hole can be formed in the lower slab S3 before drilling through with the third drilling rod R4, using the same method as in Figures 4 and 5, and the fall prevention jig 10 can be inserted into the ground G1 below (this concludes the lower slab penetration process).

[0070] By sequentially executing the above steps, the first through-hole H1, the second through-hole H2, and the third through-hole H3 are formed at vertically corresponding positions in the upper slab S1, the middle slab S2, and the lower slab S3.

[0071] Next, a wing bit of, for example, φ250 mm is inserted into the ground G1 below the box culvert C through the first through-hole H1, the second through-hole H2, and the third through-hole H3 from above, and by excavating to the ground improvement depth, an installation hole Hg for installing the improvement rod Ra is created, as shown in Figure 14.

[0072] Next, as shown in Figure 14, while lifting and removing the third drilling rod R4, the improvement rod Ra is inserted in the X16 direction to the installation hole Hg, and the improvement rod Ra is installed at the ground improvement depth. Then, while rotating the improvement rod Ra, a slurry of (ultra) high pressure and (large) flow rate is injected laterally in the X17 direction from its tip, performing a (ultra) large-diameter high-pressure injection mixing method (an example of ground improvement).

[0073] This high-pressure injection mixing method creates, for example, a large-diameter pile ground improvement body GI in the ground G1 below the lower slab S3 in the right-hand region of the bulkhead W2 of the box culvert C, as shown in Figure 15.

[0074] Here, in addition to the illustrated example, other ground improvement methods such as chemical grouting methods that can be used to perform ground improvement by applying the improvement rod Ra may also be applied (ground improvement process).

[0075] After constructing the ground improvement body GI, a φ250mm wing bit or similar is reinserted into the third through-hole H3, and the ground improvement body that has entered the third through-hole H3 is re-drilled to clean the inside of the hole.

[0076] Next, a fiberscope is inserted into the third through-hole H1 to check the construction status of the ground improvement body GI. Then, as shown in Figure 16, the second drilling rod R3 is withdrawn and removed, and non-shrink mortar M4 (an example of a sealing material) is filled into the third through-hole H3 of the lower slab S3. The top cover L1 is then placed on the upper surface of the lower slab S3 to seal the non-shrink mortar M4, and the top cover L1 is fixed to the lower slab S3 with anchor bolts A. Here, although not shown in the illustration, it is desirable to ensure watertightness by interposing a packing between the upper surface of the lower slab S3 and the top cover L1.

[0077] Next, the second through-hole H2 on the underside of the intermediate floor slab S2 is closed with the lower cover L2, and the lower cover L2 is fixed to the intermediate floor slab S2 with anchor bolts A. The lower cover L2 can be attached to the underside of the intermediate floor slab S2 by a worker from inside the management space C2. Here, although not shown in the diagram, it is desirable to ensure watertightness by interposing a packing between the underside of the intermediate floor slab S3 and the lower cover L2.

[0078] Next, as shown in Figure 17, while the first drilling rod R2 is withdrawn and removed, non-shrink mortar M5 (an example of a sealing material) is filled into the second through-hole H2 through the filling hole provided in the lower cover L2, thereby sealing the second through-hole H2.

[0079] Next, when closing the first through-hole H1 of the upper slab S1, workers cannot enter the sewer main space C1 and attach the bottom cover to the underside of the upper slab S1. Therefore, by applying the bottom cover 20 shown in Figures 19A and 19B, the area below the first through-hole H1 of the upper slab S1 is closed, as shown in Figure 18.

[0080] As shown in Figure 19A, the bottom cover 20 has a plurality (three in the illustrated example) of dividing plates 21A, 21B that are connected to each other in a foldable manner, a fixing jig 23 fixed to the upper surface of the central dividing plate 21A, and a suspension member 33 attached to the fixing jig 23 via an intermediate member 31. Here, the number of dividing plates may be two or four or more.

[0081] The fixing jig 23 comprises a fixing part 23a fixed to the central dividing plate 21A and a rotating part 23b that rotates relative to the fixing part 23a, with one end of the intermediate member 31 fixed to one end of the rotating part 23b. The fixing part 23a and the rotating part 23b can be formed by a knuckle joint.

[0082] For example, the upper end of the rotating part 23b has a screw groove, and one end of an intermediate member 31 of a predetermined length (for example, the length of the first through hole H1), made of, for example, a steel bar, is screwed into this screw groove. The other end of the intermediate member 31 is screwed into one end of a high nut 32, and one end of a suspension member 33, made of, for example, a steel bar, is screwed into the other end of the high nut 32. This suspension member 33 is suspended from a work platform or the like above the box culvert C.

[0083] The divided plates 21A and 21B are connected to each other by multiple hinges 22 (two in the illustrated example), and the left and right divided plates 21B rotate upward in the Y1 direction relative to the central divided plate 21A.

[0084] Furthermore, the three divided plates 21A and 21B have a circular shape in plan view, and the fixing part 23a is fixed to the centroid position T of the three divided plates 21A and 21B. Because the shape in plan view is circular, in the illustrated example, the fixing part 23a is fixed to the center of the circle.

[0085] On the other hand, in the illustrated example of the bottom cover 20, a counterweight 27 is attached to one side of the back surface of the divided plate 21A at an offset position. As shown in Figure 19B, when the bottom cover 20 is inserted through the first through hole H1, the left and right divided plates 21B come into contact with the wall surface of the first through hole H1 and rotate, rising towards the central divided plate 21A, and furthermore, the counterweight 27 rotates the entire three divided plates 21A and 21B around the rotating part 23b in the Y2 direction, resulting in an oblique position.

[0086] These measures make it possible to minimize the planar area of ​​the three divided plates 21A and 21B as they pass through the first through-hole H1, thereby facilitating their passage through the first through-hole H1.

[0087] Furthermore, as shown in Figure 19A, a sealing material 25 is provided on the upper surfaces of the three divided plates 21A and 21B to close or surround the lower opening of the first through hole H1 and to adhere tightly to the lower surface of the upper floor slab S1. Here, the sealing material 25 is made of a waterproof rubber sheet or the like.

[0088] Furthermore, on the upper surfaces of the three divided plates 21A and 21B, four alignment pins 26 are provided that protrude upward at multiple locations corresponding to the downward opening of the first through hole H1 (four locations on a virtual circle VC that simulates the downward opening of the first through hole H1).

[0089] As shown in Figure 19B, when the first through-hole H1 is inserted downward in the Y5 direction and the three divided plates 21A and 21B protrude below the lower surface of the upper floor slab S1, two of the divided plates 21B spread out to the sides. Subsequently, when the three divided plates 21A and 21B are lifted by the suspension member 33, the four alignment pins 26 that protrude upward fit into the downward opening of the first through-hole H1, thereby positioning the three divided plates 21A and 21B at predetermined positions on the lower surface of the upper floor slab S1.

[0090] This allows the sealant 25 to adhere tightly to the underside of the upper deck slab S1 while the lower opening of the first through hole H1 is closed by the three divided plates 21A and 21B. The tight adhesion of the sealant 25 to the underside of the upper deck slab S1 ensures watertightness.

[0091] Furthermore, the process of preparing this bottom cover 20 is a preparation process (bottom cover preparation process), and the process of closing the lower opening of the first through hole H1 with the three divided plates 21A and 21B is an opening closing process.

[0092] Following the opening closing process, the first through-hole H1 is filled from above with non-shrink mortar M6 (an example of a sealing material) via the first penetration rod to close it. Figure 20 shows the state after the first through-hole H1 has been closed with non-shrink mortar M6 and the first penetration rod R1 has been pulled up and removed.

[0093] Until the non-shrink mortar M6 achieves its predetermined strength, the three divided plates 21A and 21B are suspended from the work floor by the suspension member 33. As shown in Figure 20, an overcut portion M6a is provided above the non-shrink mortar M6, and as the overcut portion M6a hardens, it locks into the upper surface of the upper deck slab S1. The intermediate member 31 and the high nut 32 are embedded in the non-shrink mortar M6, and the frictional force of these and the locking structure of the overcut portion M6a maintain the close contact position of the three divided plates 21A and 21B with the lower surface of the upper deck slab S1, preventing the bottom cover 20 from falling off.

[0094] The tall nut 32 is located at the upper end of the non-shrink mortar M6, and after the non-shrink mortar M6 has developed its strength, the suspension member 33 can be rotated to remove it from the tall nut 32 and retrieve it. Alternatively, the tall nut 32 may be positioned on the outside of the non-shrink mortar M6, and the suspension member 33 and tall nut 32 may be rotated together to remove them from the intermediate member 31 and retrieve them (this completes the through-hole closing process).

[0095] Thus, in this method of performing ground improvement on the ground G1 below the box culvert while forming through holes in each of the multiple slabs constituting the box culvert C, it becomes possible to perform ground improvement while preventing both the leakage of sewage and other contents into the ground G within the box culvert C and the infiltration of groundwater into the box culvert C.

[0096] [Test construction] Next, the test construction carried out by the inventors will be described with reference to Figures 21A to 21H. Here, Figures 21A to 21H are, in order, process diagrams of the test construction.

[0097] First, as shown in Figure 21A, a concrete slab was fabricated. The fabricated concrete slab was supported by two H-shaped steel beams and raised by 0.3 m. A test pressure box was installed on the top surface of the concrete slab via a packing and secured with anchor bolts.

[0098] Next, as shown in Figure 21B, a work platform was set up around the concrete slab, and a boring machine was installed on it. This work platform simulates an actual work platform.

[0099] Next, as shown in Figure 21C, a φ400 mm casing was attached to the φ90 mm boring rod of the boring machine, and a hole was drilled in the concrete slab.

[0100] Next, as shown in Figure 21D, a φ400 mm casing was inserted into the upper 10 to 15 mm area of ​​a 500 mm thick concrete slab without water and fired, and non-shrink mortar was filled inside the casing.

[0101] Next, as shown in Figure 21E, the test pressure box and lid, and the lid and a φ400mm casing were fixed in place to seal the connection, and pressurized water at 0.2 MPa was supplied from the ball valve section. This simulates the water pressure based on the actual groundwater level in the construction plan area.

[0102] Next, as shown in Figure 21F, a φ350mm casing was inserted into a φ400mm casing, and a hole was drilled through the concrete slab. The water leakage situation at that time was then observed. The observation revealed that no water leakage was detected under the condition of pressurized water at 0.2 MPa.

[0103] As shown in Figure 21G, a retrieval hinge for concrete core retrieval (to prevent it from falling) is attached to the lower inner end of the φ350mm casing, and the concrete core was retrieved simultaneously when the casing was lifted. This retrieval hinge simulates a fall prevention jig.

[0104] Next, as shown in Figure 21H, a steel plate was attached to the underside of the concrete slab to seal the through-hole, non-shrink mortar was filled into the φ400mm casing, and the φ400mm casing was removed to seal the through-hole.

[0105] This series of test constructions verified that, under conditions where a predetermined water pressure is applied, it is possible to achieve a series of construction methods that completely seal through-holes in concrete slabs with non-shrink mortar while preventing water leakage.

[0106] Furthermore, other embodiments may be used in which other components are combined with the configurations listed in the above embodiments, and the present invention is not limited in any way to the configurations shown herein. In this regard, modifications can be made without departing from the spirit of the present invention, and can be appropriately determined according to the application form. [Explanation of symbols]

[0107] 10: Fall prevention jig 10A: Drop prevention jig in reduced diameter position 10B: Fall prevention jig in expanded diameter position 11: Bar material 11a: Storage groove 13: Rotating shaft 15: Diameter-enlarged material 16: Elastic material 20: Bottom lid 21,21A,21B:Dividing plate 22: Hinge 23: Fixing jig 23a: Fixed part 23b: Rotating part 25: Sealant 26: Alignment pin 31: Intermediate member (steel bar) 32: High nut 33: Lifting member (steel bar) C: Existing structure (box culvert) C1: Main sewer space C2: Management space C3: Stormwater main space S1: Upper floor version S2: Middle floor version S3: Lower floor version W1: Exterior wall W2: Bulkhead G: Ground G1: Lower ground (ground beneath existing structures) R1: First penetration rod R2: First drilling rod (second penetration rod) R3: Second drilling rod (third penetration rod) R4: Third drilling rod Ra: Improved rod P: Single tube M1, M2, M3: Water-stopping material (non-shrink mortar) M4, M5, M6: Sealing material (non-shrink mortar) M6a: Overcut section H1: 1st through hole H2: 2nd through hole H3: 3rd through hole Ha: Leading hole Hg: Installation hole CO: Concrete Core GI: Ground improvement body L1: Upper lid L2: Lower lid A: Anchor bolt T: Center of gravity position VC: Virtual Yen

Claims

1. A method for improving the ground beneath an existing concrete structure, comprising at least an upper deck, a lower deck, and side walls surrounding a hollow space, and installed in water or underground in a body of water, wherein the existing structure is located in water or underground, and the ground beneath it is improved. The upper floor slab penetration process involves inserting a first penetration rod from above the upper floor slab to a point midway through the thickness of the upper floor slab, The process involves arranging a first drilling rod inside the first penetration rod in the upper deck slab, drilling through the upper deck slab to form a first through-hole, and The lower slab penetration process involves using the first drilling rod as a second penetration rod, or arranging the second penetration rod inside the first drilling rod, and penetrating the lower slab from above to a point midway through its thickness. A second drilling rod is placed inside the second penetration rod, and the lower slab is drilled through to form a second through-hole, a lower slab penetration step, The process includes inserting an improvement rod, which constitutes a ground improvement device, into the ground beneath the existing structure from above the upper deck slab through the first and second through-holes to perform ground improvement, and performing ground improvement. In the upper deck penetration process, a pilot hole is drilled in the upper deck, and a part of the fall prevention jig is extended downward through the pilot hole in the upper deck. The concrete core generated when the first through-hole is formed is supported by the fall prevention jig, and the concrete core is pulled up and recovered through the first through-hole. The aforementioned fall prevention jig is Rods and, The rod material is rotatably attached to the aforementioned rod material and has an expanding member that changes its position between a reduced diameter position and an expanded diameter position, When the fall prevention jig is inserted into the preceding guide hole, the diameter-expanding member is in a reduced-diameter position, and changes its position to an expanded-diameter position when the diameter-expanding member protrudes below the upper floor slab. A method for improving the ground beneath an existing structure, characterized in that the formed concrete core is supported by the diameter-enlarging member in an enlarged position.

2. A ground improvement method for an existing structure, comprising at least an upper deck, a middle deck, a lower deck, and side walls surrounding a hollow space, for improving the ground beneath an existing structure located in water or underground in a body of water, The upper floor slab penetration process involves inserting a first penetration rod from above the upper floor slab to a point midway through the thickness of the upper floor slab, The process involves arranging a first drilling rod inside the first penetration rod in the upper deck slab, drilling through the upper deck slab to form a first through-hole, and The intermediate floor slab penetration process involves using the first drilling rod as a second penetration rod, or arranging the second penetration rod inside the first drilling rod, and penetrating the intermediate floor slab from above to a point midway through its thickness. A second drilling rod is placed inside the second penetration rod, and the intermediate floor slab is drilled through to form a second through-hole, a intermediate floor slab penetration process, The lower slab penetration process involves using the second drilling rod as a third penetration rod, or arranging the third penetration rod inside the second drilling rod, and penetrating the lower slab from above to a point midway through the thickness of the lower slab. A third drilling rod is placed inside the third penetration rod, and the lower slab is drilled through to form a third through-hole, a lower slab penetration step, The ground improvement process involves inserting the ground improvement rods, which constitute the ground improvement device, into the ground beneath the existing structure from above the upper deck slab through the first through-hole, the second through-hole, and the third through-hole to perform ground improvement. In the upper deck penetration process, a pilot hole is drilled in the upper deck, and a part of the fall prevention jig is extended downward through the pilot hole in the upper deck. The concrete core generated when the first through-hole is formed is supported by the fall prevention jig, and the concrete core is pulled up and recovered through the first through-hole. In the intermediate floor slab penetration process, a pre-drilled guide hole is made in the intermediate floor slab, and a part of the fall prevention jig is extended downward through the pre-drilled guide hole. The concrete core generated when the second through-hole is formed is supported by the fall prevention jig, and the concrete core is lifted up and recovered through the second through-hole and the first through-hole. The aforementioned fall prevention jig is Rods and, The rod material is rotatably attached to the aforementioned rod material and has an expanding member that changes its position between a reduced diameter position and an expanded diameter position, When the fall prevention jig is inserted into the preceding guide hole, the diameter-expanding member is in a reduced diameter position, and changes its position to an expanded diameter position when the diameter-expanding member protrudes below the upper floor slab and below the middle floor slab. A method for improving the ground beneath an existing structure, characterized in that the formed concrete core is supported by the diameter-enlarging member in an enlarged position.

3. In the upper deck penetration process, the first penetration rod is pressed against the upper deck, and a water-sealing material is filled from the inside of the first penetration rod between the first penetration rod and the upper deck. In the aforementioned lower deck penetration process, the second penetration rod is pressed against the lower deck, and a waterproofing material is filled from the inside of the second penetration rod between the second penetration rod and the lower deck. The method for improving the ground beneath an existing structure according to claim 1, characterized in that the aforementioned firing is performed by fixing the first penetration rod and the second penetration rod to the upper deck slab and the lower deck slab, respectively, by rotating and pressing them in a waterless state.

4. In the upper deck penetration process, the first penetration rod is pressed against the upper deck, and a water-sealing material is filled from the inside of the first penetration rod between the first penetration rod and the upper deck. In the aforementioned intermediate deck penetration process, the second penetration rod is pressed against the intermediate deck, and a waterproofing material is filled between the second penetration rod and the intermediate deck from the inside of the second penetration rod. In the aforementioned lower slab penetration process, the third penetration rod is pressed against the lower slab, and a waterproofing material is filled from the inside of the third penetration rod between the third penetration rod and the lower slab. The method for improving the ground beneath an existing structure according to claim 2, characterized in that the aforementioned firing is fixed by rotating and pressing the first penetration rod, the second penetration rod, and the third penetration rod into the upper deck slab, the middle deck slab, and the lower deck slab, respectively, in a waterless state.

5. The process further includes a through-hole closing step, in which, after the ground improvement step, the second through-hole is filled with a sealing material to close it, and when closing the first through-hole, a bottom cover with a larger planar dimension than the first through-hole is folded and suspended below the first through-hole, then lifted up and in close contact with the lower surface of the upper floor slab, and the first through-hole is filled with sealing material to close it. The bottom cover is, Multiple divided plates that are connected to each other in a way that allows them to be folded, A fixing jig comprising a fixing part fixed to the upper surface of the dividing plate and a rotating part that rotates relative to the fixing part, A ground improvement method for an existing structure according to claim 1, characterized in that it has a suspension member attached to one end of the rotating part, or to one end of an intermediate member attached to one end of the rotating part.

6. The process further includes a through-hole closing step, in which, after the ground improvement step, the third through-hole is filled with a sealing material to close it, and when closing at least one of the first and second through-holes, a bottom cover with a larger planar dimension than the first or second through-hole is folded and suspended below the first or second through-hole, then pulled up and in close contact with the lower surface of the upper or middle floor slab, and the sealing material is filled to close the first or second through-hole. The bottom cover is, Multiple divided plates that are connected to each other in a way that allows them to be folded, A fixing jig comprising a fixing part fixed to the upper surface of the dividing plate and a rotating part that rotates relative to the fixing part, The ground improvement method for an existing structure according to claim 2, characterized in that it has a suspension member attached to one end of the rotating part, or to one end of an intermediate member attached to one end of the rotating part.

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