Ground improvement structure, and construction method for ground improvement structure

Abstract

To efficiently improve the toughness of a ground improvement body formed by improving a surface layer below the ground surface of soft ground to be constructed under a foundation of a building, by using a naturally derived reinforcing material.SOLUTION: A ground improvement body 1 is formed by improving a surface layer below the ground surface GL of soft ground G. It is constructed under a foundation of a building and contains soil of the surface layer, a solidification material, and a large number of small rod-shaped bamboo pieces, the mixture ratio of which is 0.5-3% by volume. The large number of small rod-shaped bamboo pieces contained in the ground improvement body 1 can efficiently improve the toughness of the ground improvement body 1. The mixture ratio of the small rod-shaped bamboo pieces is 0.5-3% by volume of the ground improvement body 1, so a relatively small amount is required, and construction is easy, so costs are not high.SELECTED DRAWING: Figure 1B

Description

Technical Field

[0001] The present invention relates to a ground improvement body formed by improving the surface layer of soft ground.

Background Art

[0002] As a ground improvement body that is constructed under the foundation of a building and is formed by improving the surface layer below the ground surface of soft ground, there is one that excavates the surface layer into a predetermined shape by a backhoe or the like, and mixes and stirs while adding a solidifying material such as a cement-based solidifying material, and compresses and forms it by a heavy machine, a roller, or the like (see, for example, Patent Document 1). The ground improvement body can be applied even when the soft layer is very deep, and since it sinks together with the surrounding ground subsidence, no uplifting phenomenon occurs.

[0003] On the other hand, in a lattice-shaped ground improvement column wall formed by excavating the ground with an auger, mixing and stirring the in-situ soil and cement milk, and wrapping the adjacent outer peripheral surfaces of the ground improvement bodies constructed in a columnar shape to form a continuous wall shape, by mixing reinforcing fibers at the intersection, which is the part where two ground improvement column walls intersect, the toughness of the intersection is increased and the deformation of the ground improvement column wall is suppressed (see, for example, Patent Document 2). The reinforcing fibers have required mechanical properties, and are, for example, polypropylene fibers.

[0004] On the other hand, it is widely known that by spreading ground bamboo chips obtained by crushing bamboo on the ground, it becomes difficult for weeds to grow. There is a ground improvement material using bamboo chips for covering and protecting the ground of a garden, a park, etc. to improve the ground and suppress weeds (see, for example, Patent Document 3). The bamboo chips are obtained by crushing bamboo into a fibrous shape. The ground improvement material using the bamboo chips has appropriate hardness and softness, suppresses weeds, is not washed away or scattered by rain and wind, and has excellent water permeability and water retention.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Patent No. 3608568 [Patent Document 2] Patent No. 5778968 [Patent Document 3] Japanese Patent Publication No. 2008-260905 [Overview of the project] [Problems that the invention aims to solve]

[0006] The ground improvement body described in Patent Document 1 is made by mixing and stirring cement-based solidifying material and the like with the local soil and compacting it, and is therefore excellent in increasing bearing capacity (compressive strength).

[0007] When a ground improvement structure built beneath the foundation of a building reaches the supporting layer, the ground improvement structure only needs to bear compressive forces. However, a ground improvement structure formed by improving the surface layer below the ground surface of soft ground, such as the ground improvement structure described in Patent Document 1, does not reach the supporting layer and therefore allows for settlement.

[0008] The inventors of this invention focused on the fact that the ground improvement body has excellent compressive strength, but like concrete, it is weak in tension and bending. Specifically, the inventors of this invention focused on the fact that when tensile force or bending moment acts on the ground improvement body, and tensile stress or bending stress is generated inside the ground improvement body, the ground improvement body exhibits brittle fracture behavior.

[0009] In a ground improvement body formed by improving the surface layer below the ground surface of soft ground, depending on the shape of the ground improvement body (e.g., if the slenderness ratio is large) or depending on the application of horizontal forces during an earthquake, tensile forces and bending moments may act on the ground improvement body, causing tensile stress and bending stress to occur inside the ground improvement body.

[0010] Therefore, it is desirable to improve the toughness of the ground improvement body so that it does not undergo brittle fracture when tensile stress or bending stress occurs inside the ground improvement body.

[0011] The polypropylene fiber used as a reinforcing fiber in Patent Document 2 has excellent mechanical strength. However, since polypropylene is a synthetic resin derived from crude oil, a large amount of CO2 is emitted during the manufacturing process, making it not environmentally friendly.

[0012] The bamboo chips used in the ground improvement material described in Patent Document 3 are naturally derived from bamboo that has been crushed into fibers, making them environmentally friendly. However, the ground improvement material using bamboo chips described in Patent Document 3 is intended for paving the ground and does not require the improvement of toughness, unlike ground improvement bodies that are constructed under the foundation of buildings and form by improving the surface layer below the ground surface of soft ground.

[0013] The present invention aims to efficiently improve the toughness of a ground improvement body, which is constructed beneath the foundation of a building by improving the surface layer below the ground surface of soft ground, by using naturally derived reinforcing materials.

[0014] The inventors of this invention focused on mixing a large number of rod-shaped bamboo fragments into the ground improvement body in order to efficiently improve the toughness of the ground improvement body, while effectively utilizing bamboo, which is naturally derived, environmentally friendly, grows quickly, has high regenerative capacity, and possesses excellent mechanical properties. The inventors of this invention then diligently studied the shape and amount of the rod-shaped bamboo fragments to be mixed, conducted tests and evaluations, and proceeded with the concretization of the invention, thereby completing the present invention.

[0015] The gist of this invention is as follows:

[0016] [1] A ground improvement body formed by improving the surface layer below the ground surface of soft ground, Constructed beneath the foundation of the building, The above-mentioned surface soil, a solidifying agent, and numerous rod-shaped bamboo fragments are included. The mixing ratio of the aforementioned rod-shaped bamboo pieces is 0.5-3% by volume. the law of nature, The cross-sectional shape of the aforementioned rod-shaped bamboo piece is circular or rectangular. The diameter of the cross-section or the length of the side of the aforementioned rod-shaped bamboo piece is 1 to 5 mm. The length of the aforementioned rod-shaped bamboo pieces is 20 to 100 mm. and ground improvement body

[0018] 2 A construction method of a ground improvement body formed by improving the surface layer part below the ground surface of soft ground, the ground improvement body is constructed under the foundation of a building, a step of excavating the surface layer part to a predetermined shape, a step of backfilling and leveling the soil excavated from the surface layer part, a step of spraying a solidifying material on the backfilled and leveled soil, a step of evenly spreading a required number of rod-shaped bamboo pieces on the solidifying material, a step of mixing and stirring the soil, the solidifying material, and the rod-shaped bamboo pieces to form a ground improvement body, a step of compacting the ground improvement body, including fruit, The mixing ratio of the aforementioned rod-shaped bamboo pieces is 0.5 to 3% by volume of the aforementioned ground improvement body. The cross-sectional shape of the aforementioned rod-shaped bamboo piece is circular or rectangular. The diameter of the cross-section or the length of the side of the aforementioned rod-shaped bamboo piece is 1 to 5 mm. The length of the aforementioned rod-shaped bamboo pieces is 20 to 100 mm. , A construction method of a ground improvement body.

[0019] 3 A construction method of a ground improvement body formed by improving the surface layer part below the ground surface of soft ground, the ground improvement body is constructed under the foundation of a building, a step of excavating the surface layer part to a predetermined shape, a step of backfilling and leveling the soil excavated from the surface layer part, a step of evenly spreading a required number of rod-shaped bamboo pieces on the backfilled and leveled soil, a step of spraying a solidifying material on the rod-shaped bamboo pieces, a step of mixing and stirring the soil, the rod-shaped bamboo pieces, and the solidifying material to form a ground improvement body, a step of compacting the ground improvement body, ​​​​Includes fruit, The mixing ratio of the aforementioned rod-shaped bamboo pieces is 0.5 to 3% by volume of the aforementioned ground improvement body. The cross-sectional shape of the aforementioned rod-shaped bamboo piece is circular or rectangular. The diameter of the cross-section or the length of the side of the aforementioned rod-shaped bamboo piece is 1 to 5 mm. The length of the aforementioned rod-shaped bamboo pieces is 20 to 100 mm. , Construction methods for ground improvement structures. [Effects of the Invention]

[0022] According to the ground improvement body and construction method of the present invention, in a ground improvement body formed by improving the surface layer below the ground surface of soft ground, which is constructed beneath the foundation of a building, the ground improvement body contains a large number of The cross-sectional shape is circular or rectangular, the diameter or side length of the cross-section is 1 to 5 mm, and the length is 20 to 100 mm. The toughness of the ground improvement body can be efficiently improved by using rod-shaped bamboo pieces.

[0023] The mixing ratio of the aforementioned rod-shaped bamboo pieces is 0.5 to 3% by volume of the ground improvement body, which is a relatively small amount, and the construction is easy, so the cost does not increase.

[0024] Although the amount of the aforementioned rod-shaped bamboo fragments mixed with the ground improvement body is relatively small, if the ground improvement body is to be used in the construction of many such bodies in order to improve its toughness, it will be necessary to continue to procure large quantities of these rod-shaped bamboo fragments. However, since bamboo grows quickly, has a high regenerative capacity, and has a short harvest cycle, a sufficient supply can be continuously secured at a low cost. In addition, since bamboo is a natural product, it is environmentally friendly, and an increase in the demand for bamboo will lead to the full utilization of bamboo forests and contribute to solving the problem of neglected bamboo forests. [Brief explanation of the drawing]

[0025] [Figure 1A] This is a plan view showing an example of a building foundation structure including a ground improvement body according to an embodiment of the present invention. [Figure 1B] This is a cross-sectional view taken along the arrow XX in Figure 1A. [Figure 1C] This is an enlarged view of the main part of Figure 1B. [Figure 2A]This is a perspective view showing an example of rod-shaped bamboo pieces included in a ground improvement body according to an embodiment of the present invention. [Figure 2B] Figure 2A is a side view of the rod-shaped bamboo piece. [Figure 2C] This is a cross-sectional view taken along the line Y1-Y1 in Figure 2B. [Figure 3A] This is a perspective view showing another example of the aforementioned rod-shaped bamboo piece. [Figure 3B] Figure 3A is a side view of the rod-shaped bamboo piece. [Figure 3C] This is a cross-sectional view taken along the line Y2-Y2 in Figure 3B. [Figure 4] This graph shows the results of the bending strength test on specimens of the ground improvement structure. [Modes for carrying out the invention]

[0026] Embodiments of the present invention will be described below with reference to the drawings.

[0027] [Ground improvement structure] Figures 1A and 1B show an example of a building foundation structure F including a ground improvement body 1 according to an embodiment of the present invention. The ground improvement body 1 is formed by improving the surface layer below the ground surface GL of soft ground G and is constructed beneath the foundation of the building. The shape of the ground improvement body 1 shown in Figures 1A and 1B is just one example, and the ground improvement body 1 can have various shapes.

[0028] The ground improvement body 1 contains the surface soil, a solidifying agent, and a large number of rod-shaped bamboo pieces 2, for example, as shown in Figures 2A to 2C or Figures 3A to 3C. The desired effect cannot be obtained if the amount of rod-shaped bamboo pieces 2 in the ground improvement body 1 is too much or too little. The mixing ratio of rod-shaped bamboo pieces 2 is 0.5 to 3% by volume of the ground improvement body 1. There is also a range in the shape and size of the rod-shaped bamboo pieces 2 to obtain the desired effect.

[0029] [Small pieces of stick-shaped bamboo] As shown in Figures 2A, 2B, and 2C, and Figures 3A, 3B, and 3C, the cross-sectional shape of the rod-shaped bamboo pieces 2 included in the ground improvement body 1 according to the embodiment of the present invention is, for example, circular or rectangular. The diameter D in Figure 2C is 1 to 5 mm (1 mm ≤ D ≤ 5 mm). The side lengths A and B in Figure 3C are 1 to 5 mm (1 mm ≤ A ≤ 5 mm, 1 mm ≤ B ≤ 5 mm). The length L in Figures 2B and 3B is 20 to 100 mm (20 mm ≤ L ≤ 100 mm).

[0030] The rod-shaped bamboo pieces 2 can be manufactured, for example, mainly using machinery such as a bamboo skewer manufacturing machine. The internodes obtained by cutting bamboo are used to form rods of the required cross-sectional shape and size using a machine such as a bamboo skewer manufacturing machine. The rod-shaped bamboo material is then cut to the required length L to produce rod-shaped bamboo pieces 2.

[0031] [Construction process for building foundations, including ground improvement structures] The foundation structure F of the building, which includes the ground improvement body 1 shown in Figures 1A to 1C, is constructed, for example, as follows.

[0032] <Soil improvement process> (Excavation process) The surface layer of the soft ground G below the ground surface GL, as shown in Figures 1B and 1C, is excavated to the required shape of the ground improvement body 1, for example, by shoveling with a backhoe.

[0033] (Primary improvement process) The soil excavated in the aforementioned excavation process is backfilled and leveled using a backhoe or the like into the "square" shaped portion of the lower 1L (Figure 1C) of the ground improvement body 1. A solidifying agent such as a cement-based solidifying agent is scattered on top of the backfilled and leveled soil. The required number of rod-shaped bamboo pieces 2 are scattered and leveled on top of the solidifying agent. The soil, the solidifying agent, and the rod-shaped bamboo pieces 2 are mixed and stirred using a backhoe or the like equipped with a mixing fork as an attachment, and then compacted using heavy machinery and rollers to form the lower 1L of the ground improvement body 1.

[0034] (Secondary improvement process) The soil excavated in the aforementioned excavation process is backfilled and leveled using a backhoe or the like in the upper part 1H (Figure 1C) of the ground improvement body 1, above the lower part 1L of the ground improvement body 1. A solidifying agent such as a cement-based solidifying agent is scattered on top of the backfilled and leveled soil. The required number of rod-shaped bamboo pieces 2 are scattered and leveled on top of the solidifying agent. The soil, the solidifying agent, and the rod-shaped bamboo pieces 2 are mixed and stirred using a backhoe or the like equipped with a mixing fork as an attachment, and then compacted using heavy machinery and rollers to form the upper part 1H of the ground improvement body 1.

[0035] In addition, in the primary improvement step and the secondary improvement step, the order of the step of scattering the solidifying agent and the step of scattering the rod-shaped bamboo pieces 2 may be reversed.

[0036] <Foundation excavation process> In the ground improvement process described above, the upper part of the ground improvement body 1 located below the above-ground portion of the steel column 4 is excavated in a rectangular parallelepiped shape to a predetermined depth using a backhoe or the like.

[0037] <Foundation pouring process> Pour the lean concrete 6 shown in Figure 1C. Fix the column base anchor bolts for fixing the steel column 4 to the lean concrete 6, perform the foundation reinforcement and pour the foundation concrete 3. Install the steel column 4 and pour the floor concrete 5.

[0038] The construction of the building's foundation structure F, including the improved foundation ground 1, is completed through the above process.

[0039] [Construction methods for ground improvement structures] As described above, the ground improvement process in the construction process of the foundation structure F of the building includes the following steps for constructing the ground improvement body 1: excavating the surface layer below the ground surface GL of the soft ground G into a predetermined shape; backfilling and leveling the excavated soil from the surface layer; scattering a solidifying agent on the backfilled and leveled soil; scattering a required number of rod-shaped bamboo pieces 2 on the solidifying agent; mixing and stirring the soil, the solidifying agent, and the rod-shaped bamboo pieces to form the ground improvement body 1; and compacting the ground improvement body 1.

[0040] Alternatively, the construction method for the ground improvement body 1 includes the steps of: excavating the surface layer below the ground surface GL of the soft ground G into a predetermined shape; backfilling and leveling the excavated soil from the surface layer; scattering a required number of rod-shaped bamboo pieces 2 on top of the backfilled and leveled soil; scattering a solidifying agent on top of the rod-shaped bamboo pieces 2; mixing and stirring the soil, the rod-shaped bamboo pieces 2, and the solidifying agent to form the ground improvement body 1; and compacting the ground improvement body 1.

[0041] [Bending strength test] <Testing Method> Test specimens of ground improvement bodies containing rod-shaped bamboo pieces 2 (Examples 1 and 2) and test specimens of ground improvement bodies without rod-shaped bamboo pieces 2 (Comparative Example) are prepared. After a curing period of 28 days, a three-point bending test is performed on the test specimens using the central point loading method with a support distance of 300 mm, based on JIS A 1106:2018 "Test Method for Bending Strength of Concrete," and the relationship between bending stress and displacement at the load point is determined.

[0042] <Size of the test specimen> Based on JIS A 1132:2020 "Method for preparing test specimens for concrete strength testing," the cross-sectional dimensions of the test specimen were set to 100 mm x 100 mm, and the length of the test specimen was set to 400 mm.

[0043] <Soil containing the test specimen, solidification material containing the test specimen> The soil contained in the aforementioned test specimens was local sandy soil, and the solidifying agent contained in the aforementioned test specimens was GeoSet 200, a cement-based solidifying agent for ground improvement manufactured by Taiheiyo Cement Corporation. The mixing ratio of the solidifying agent was 100 kg / m³. 3 That's what I decided.

[0044] <Size and mixing ratio of stick-shaped bamboo pieces> The rod-shaped bamboo pieces 2 were obtained by cutting bamboo skewers (2 mm in diameter, 30 cm in length) with product number ZQ3020, sold by Anhui Province Yezhurin Electronic Trading Co., Ltd. and manufactured by Nanling County Jinrui Bamboo Products Processing Plant. Example 1 was made by cutting the skewers to a length of 3 cm, and Example 2 was made by cutting the skewers to a length of 5 cm. The mixing ratio of the rod-shaped bamboo pieces 2 was 1.5% by volume of the test specimens in Example 1 and Example 2.

[0045] <Mixing and stirring> In Examples 1 and 2, the required amount of sandy soil is placed in the mixer, the solidifying agent in the specified mixing ratio is added, and the rod-shaped bamboo pieces 2 in the specified mixing ratio are added, and then the mixture is stirred in the mixer. In the comparative example, the required amount of sandy soil is placed in the mixer, the solidifying agent in the specified mixing ratio is added, and then the mixture is stirred in the mixer.

[0046] <Molding of the test specimen> The mixed and stirred soil improvement material is placed in a mold and shaped to 100 mm x 100 mm x 400 mm to form the test specimen.

[0047] <Summary of Examples and Comparative Examples> (1) The test specimen of the ground improvement body in Example 1 consisted of the sandy soil and the solidification material (100 kg / m³ 3 ), and a large number of the aforementioned rod-shaped bamboo pieces 2. The rod-shaped bamboo pieces 2 have the shape shown in Figures 2A to 2C, with D=2mm and L=3cm, and the mixing ratio of the rod-shaped bamboo pieces 2 is 1.5% by volume of the specimen. (2) The test specimens of the ground improvement body in Example 2 consisted of the sandy soil and the solidification material (100 kg / m³). 3 ), and a large number of the aforementioned rod-shaped bamboo pieces 2. The rod-shaped bamboo pieces 2 have the shape shown in Figures 2A to 2C, with D=2mm and L=5cm, and the mixing ratio of the rod-shaped bamboo pieces 2 is 1.5% by volume of the specimen. (3) The test specimens of the comparative example ground improvement body consisted of the sandy soil and the solidification agent (100 kg / m³). 3 ) consists of (excluding the aforementioned rod-shaped bamboo pieces 2).

[0048] <Test Results> In the graph of Figure 4, which shows the relationship between bending stress and displacement of the load points in the three-point bending test of the aforementioned specimen, the comparative specimen (without rod-shaped bamboo pieces) exhibits brittle fracture with a sudden decrease in yield strength. In contrast, the specimen of Example 1 (with rod-shaped bamboo pieces (1.5 vol%), D=2 mm, L=3 cm) and the specimen of Example 2 (with rod-shaped bamboo pieces (1.5 vol%), D=2 mm, L=5 cm) exhibit tough fracture without a sudden decrease in yield strength.

[0049] In other words, as in Examples 1 and 2, by mixing a large number of the aforementioned rod-shaped bamboo pieces 2 (Example 1: D=2mm, L=3cm; Example 2: D=2mm, L=5cm), which are relatively small in volume relative to the entire ground improvement body, at a ratio of about 1.5%, into the ground improvement body, it is possible to efficiently improve the toughness of the ground improvement body.

[0050] [Effects and Effects] According to the ground improvement body and construction method of the ground improvement body according to the embodiment of the present invention, in a ground improvement body 1 formed by improving the surface layer below the ground surface GL of soft ground G to be constructed under the foundation of a building, the toughness of the ground improvement body 1 can be efficiently improved by the numerous rod-shaped bamboo pieces 2 included in the ground improvement body 1.

[0051] The mixing ratio of the rod-shaped bamboo pieces 2 is 0.5-3% by volume of the ground improvement body 1, which is a relatively small amount, and the construction is easy, so the cost does not increase.

[0052] Although the amount of rod-shaped bamboo fragments 2 mixed with the ground improvement body 1 is relatively small, if the ground improvement body 1 is to be used in the construction of many ground improvement bodies 1 in order to improve its toughness, it will be necessary to continue to procure large quantities of rod-shaped bamboo fragments 2. However, since bamboo grows quickly, has a high regenerative capacity, and has a short harvest cycle, a sufficient supply can be continuously secured at low cost. In addition, since bamboo is a natural product, it is environmentally friendly, and an increase in the demand for bamboo will lead to the full utilization of bamboo forests, which will also contribute to solving the problem of neglected bamboo forests.

[0053] All embodiments described above are illustrative and not limiting. Various improvements and modifications can be made without departing from the scope of the present invention. [Explanation of Symbols]

[0054] 1. Ground improvement body 1H Top 1L bottom 2 small bamboo sticks 3. Foundation concrete 4 Steel columns 5. Concrete floor 6. Waste concrete Lengths of sides A and B D diameter F. Foundation structure of buildings G Soft ground GL ground surface L Length

Claims

1. A ground improvement body formed by improving the surface layer below the ground surface of soft ground, Constructed beneath the foundation of the building, The above-mentioned surface soil, a solidifying agent, and numerous rod-shaped bamboo fragments are included. The mixing ratio of the aforementioned rod-shaped bamboo pieces is 0.5 to 3% by volume. The cross-sectional shape of the aforementioned rod-shaped bamboo piece is circular or rectangular. The diameter of the cross-section or the length of the side of the aforementioned rod-shaped bamboo piece is 1 to 5 mm. The length of the aforementioned rod-shaped bamboo pieces is 20 to 100 mm. Ground improvement structure.

2. A method for constructing a ground improvement body formed by improving the surface layer below the ground surface of soft ground, The aforementioned ground improvement structure is constructed beneath the foundation of the building. The process of excavating the surface portion into a predetermined shape, The process involves backfilling and leveling the soil excavated from the surface layer, The process involves spreading a hardening agent on top of the soil that has been backfilled and leveled, The process involves scattering and leveling the required number of rod-shaped bamboo pieces on top of the solidifying material, A step of mixing and stirring the soil, the solidifying agent, and the rod-shaped bamboo pieces to form a ground improvement body, The process of compacting the aforementioned ground improvement body, Includes, The mixing ratio of the aforementioned rod-shaped bamboo pieces is 0.5 to 3% by volume of the ground improvement body. The cross-sectional shape of the aforementioned rod-shaped bamboo piece is circular or rectangular. The diameter of the cross-section or the length of the side of the aforementioned rod-shaped bamboo piece is 1 to 5 mm. The length of the aforementioned rod-shaped bamboo pieces is 20 to 100 mm. Construction methods for ground improvement structures.

3. A method for constructing a ground improvement body formed by improving the surface layer below the ground surface of soft ground, The aforementioned ground improvement structure is constructed beneath the foundation of the building. The process of excavating the surface portion into a predetermined shape, The process involves backfilling and leveling the soil excavated from the surface layer, The process involves scattering the required number of stick-shaped bamboo pieces on top of the soil that has been backfilled and leveled, The process involves scattering a solidifying agent onto the aforementioned rod-shaped bamboo pieces, The process involves mixing and stirring the soil, the rod-shaped bamboo pieces, and the solidifying agent to form a ground improvement body. The process of compacting the aforementioned ground improvement body, Includes, The mixing ratio of the aforementioned rod-shaped bamboo pieces is 0.5 to 3% by volume of the ground improvement body. The cross-sectional shape of the aforementioned rod-shaped bamboo piece is circular or rectangular. The diameter of the cross-section or the length of the side of the aforementioned rod-shaped bamboo piece is 1 to 5 mm. The length of the aforementioned rod-shaped bamboo pieces is 20 to 100 mm. Construction methods for ground improvement structures.

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