Ground improvement body and construction method of ground improvement body

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 technology]

[0002] One type of ground improvement body, which is constructed under the foundation of a building and formed by improving the surface layer below the ground surface of soft ground, is formed by excavating the surface layer into a specified shape with a backhoe or the like, adding and mixing a solidification material such as a cement-based solidification material while mixing, and compacting with heavy machinery and rollers, etc. (For example, see Patent Document 1.) This type of ground improvement body is applicable even when the soft layer is very deep, and does not cause the phenomenon of the ground rising up because it sinks together with the surrounding ground subsidence.

[0003] Meanwhile, in a lattice-like ground improvement column wall constructed by excavating the ground with an auger, mixing and stirring local soil and cement milk to construct a cylindrical ground improvement body, and lapping adjacent outer surfaces of the body to construct a continuous wall, there is a method in which reinforcing fibers are mixed into the intersections where two ground improvement column walls intersect, thereby increasing the toughness of the intersections and suppressing deformation of the ground improvement column walls (see, for example, Patent Document 2). The reinforcing fibers have the required mechanical properties, such as polypropylene fibers.

[0004] On the other hand, it is widely known that spreading bamboo chips made from crushed bamboo on the ground makes it difficult for weeds to grow, and there are ground improvement materials using bamboo chips that cover and protect the ground in gardens, parks, etc., improving the ground and suppressing weeds (see, for example, Patent Document 3). The bamboo chips are made by crushing bamboo into fibers. The ground improvement material using the bamboo chips has appropriate hardness and softness, suppresses weeds, does not get 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] JP 2008-260905 A Summary of the Invention [Problem to be solved by the invention]

[0006] The ground improvement body of Patent Document 1 is produced by mixing and stirring local soil with cement-based solidification materials and the like, and then compacting the mixture, and is therefore excellent in the effect of increasing bearing capacity (compressive strength).

[0007] When a ground improvement body constructed under the foundation of a building reaches the supporting layer, the ground improvement body only needs to bear the compressive force. However, a ground improvement body formed by improving the surface layer below the ground surface of a soft ground, such as the ground improvement body in Patent Document 1, does not reach the supporting layer and therefore allows subsidence.

[0008] The inventor of the present application noticed that the ground improvement body has excellent compressive strength, but is weak in tension and bending, similar to the characteristics of concrete. That is, the inventor of the present application noticed that when a tensile force or bending moment acts on the ground improvement body and a tensile stress or bending stress is generated inside the ground improvement body, the ground improvement body shows brittle fracture behavior.

[0009] Ground improvement bodies formed by improving the surface layer below the ground surface of soft ground may be subject to tensile forces or bending moments acting on them, depending on their shape (for example, when the slenderness ratio is large), or depending on the conditions of horizontal forces during earthquakes, etc., and tensile stresses or bending stresses may occur inside the ground improvement body.

[0010] Therefore, it is desirable to improve the toughness of the ground improvement body so as to prevent brittle fracture when tensile stress or bending stress occurs inside the ground improvement body.

[0011] The polypropylene fiber used as the 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 unenvironmentally friendly.

[0012] The bamboo chips used in the ground improvement material of Patent Document 3 are made by crushing bamboo into fibers, and are therefore naturally derived and environmentally friendly. However, the ground improvement material using bamboo chips in Patent Document 3 is intended for paving the ground, and does not require improved toughness, as is the case with ground improvement bodies that are constructed under the foundations of buildings and are formed 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 formed by improving the surface layer below the ground surface of soft ground, which is constructed under the foundation of a building, by using naturally occurring reinforcing materials.

[0014] The inventors of the present application focused on mixing a large number of rod-shaped bamboo pieces of a required shape 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 has excellent mechanical properties. The inventors of the present application then conducted extensive research into the shape and amount of the rod-shaped bamboo pieces to be mixed, and carried out test evaluations to advance the realization of the invention, which led to the completion of the present invention.

[0015] The gist of the present invention is as follows.

[0016] [1] A ground improvement body formed by improving the surface layer below the ground surface of a soft ground, Built under the foundations of buildings, The soil of the surface layer, a solidification material, and a large number of rod-shaped bamboo pieces are included, The mixing ratio of the rod-shaped bamboo pieces is 0.5 to 3% by volume. Ground improvement body.

[0017] [2] The cross-sectional shape of the rod-shaped bamboo piece is circular or rectangular, The cross-sectional diameter or side length of the rod-shaped bamboo pieces is 1 to 5 mm; The length of the rod-shaped bamboo pieces is 20 to 100 mm. The ground improvement body described in [1].

[0018] [3] A construction method for a ground improvement body that improves the surface layer below the ground surface of a soft ground, comprising: The ground improvement body is constructed under the foundation of a building, A step of digging down the surface layer into a predetermined shape; A step of backfilling and spreading the soil excavated from the surface layer; A step of spreading a solidification material on the backfilled and evenly spread soil; A step of spreading a required number of rod-shaped bamboo pieces evenly on the solidification material; A process of mixing and stirring the soil, the solidification material, and the rod-shaped bamboo pieces to form a ground improvement body; A step of compacting the ground improvement body; Including, Construction method for ground improvement body.

[0019] [4] A construction method for a ground improvement body that improves the surface layer below the ground surface of a soft ground, comprising: The ground improvement body is constructed under the foundation of a building, A step of digging down the surface layer into a predetermined shape; A step of backfilling and spreading the soil excavated from the surface layer; A step of spreading a required number of rod-shaped bamboo pieces evenly on the backfilled and evenly spread soil; A step of scattering a solidifying material on the rod-shaped bamboo pieces; A process of mixing and stirring the soil, the rod-shaped bamboo pieces, and the solidification material to form a ground improvement body; A step of compacting the ground improvement body; Including, Construction method for ground improvement body.

[0020] [5] The mixing ratio of the rod-shaped bamboo pieces is 0.5 to 3% by volume of the ground improvement body. A method for constructing a ground improvement body according to [3] or [4].

[0021] [6] The cross-sectional shape of the rod-shaped bamboo piece is circular or rectangular, The cross-sectional diameter or side length of the rod-shaped bamboo pieces is 1 to 5 mm; The length of the rod-shaped bamboo pieces is 20 to 100 mm. A method for constructing the ground improvement body described in [5]. Effect of the Invention

[0022] According to the ground improvement body and construction method of the present invention, in a ground improvement body which is constructed under the foundation of a building and formed by improving the surface layer below the ground surface of soft ground, the toughness of the ground improvement body can be efficiently improved by the numerous rod-shaped bamboo pieces contained in the ground improvement body.

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

[0024] Although the mixing ratio of the rod-shaped bamboo pieces is relatively small relative to the amount of the ground improvement body, if they are to be used in the construction of many ground improvement bodies to improve the toughness of the ground improvement body, it is necessary to continue to procure a large amount of the rod-shaped bamboo pieces. However, bamboo grows quickly, has a high regenerative ability, and has a short harvest cycle, so a sufficient supply can be secured continuously at low cost. In addition, bamboo is naturally derived, so it is environmentally friendly, and increasing demand for bamboo will lead to full utilization of bamboo forests, which will also lead to the solution of abandoned bamboo forests. [Brief description of the drawings]

[0025] [Figure 1A] FIG. 2 is a plan view showing an example of a foundation structure of a building including a ground improvement body according to an embodiment of the present invention. [Figure 1B]FIG. 2 is a cross-sectional view taken along the line XX in FIG. 1A. [Figure 1C] FIG. 1C is an enlarged view of a main part of FIG. 1B. [Figure 2A] This is an oblique view showing an example of a rod-shaped bamboo piece contained in a ground improvement body according to an embodiment of the present invention. [Figure 2B] FIG. 2B is a side view of the rod-shaped bamboo piece of FIG. 2A. [Figure 2C] 2C is a cross-sectional view taken along the line Y1-Y1 of FIG. 2B. [Figure 3A] FIG. 2 is a perspective view showing another example of the rod-shaped bamboo piece. [Figure 3B] FIG. 3B is a side view of the rod-shaped bamboo piece of FIG. 3A. [Figure 3C] 3C is a cross-sectional view taken along line Y2-Y2 of FIG. 3B. [Figure 4] 1 is a graph showing the results of bending strength tests on specimens of ground improvement bodies. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0027] [Ground improvement body] Figures 1A and 1B show an example of a foundation structure F of a building 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 the soft ground G, and is constructed under the foundation of the building. The shape of the ground improvement body 1 shown in Figures 1A and 1B is one example, and the ground improvement body 1 can have various shapes.

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

[0029] [Small pieces of stick-shaped bamboo] As shown in Figures 2A, 2B, and 2C, as well as Figures 3A, 3B, and 3C, the cross-sectional shape of the rod-shaped bamboo pieces 2 contained 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 lengths A and B of the sides 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 a machine such as a bamboo skewer manufacturing machine. The bamboo is cut into internodes and shaped into 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 the rod-shaped bamboo pieces 2.

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

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

[0033] (Primary improvement process) The soil excavated in the digging process is backfilled and spread evenly in the "mouth" shaped portion of the lower part 1L (Fig. 1C) of the ground improvement body 1 using a backhoe or similar tool. A solidification material such as a cement-based solidification material is spread on top of the backfilled and spread evenly. The required number of rod-shaped bamboo pieces 2 are spread evenly on top of the solidification material. The soil, solidification material, and rod-shaped bamboo pieces 2 are mixed and stirred using a backhoe or similar tool fitted with a mixing fork as an attachment, and then compacted using heavy machinery and rollers to form the lower part 1L of the ground improvement body 1.

[0034] (Secondary improvement process) The soil excavated in the digging process is backfilled and spread evenly in the upper part 1H (Fig. 1C) of the ground improvement body 1 above the lower part 1L of the ground improvement body 1 using a backhoe or the like. A solidification material such as a cement-based solidification material is spread on the backfilled and spread evenly soil. The required number of rod-shaped bamboo pieces 2 are spread evenly on top of the solidification material. The soil, solidification material, and rod-shaped bamboo pieces 2 are mixed and stirred using a backhoe or the like equipped with a mixing fork 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 process and the secondary improvement process, the order of the process of scattering the solidification material and the process of spreading the rod-shaped bamboo pieces 2 evenly may be reversed.

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

[0037] <Foundation pouring process> 1C is poured. The column base anchor bolts for fixing the steel column 4 are fixed to the basing concrete 6, the foundation reinforcement is arranged, and the foundation concrete 3 is poured. The steel column 4 is installed, and the floor concrete 5 is poured.

[0038] The above steps complete the construction of the foundation structure F of the building, including the foundation ground improvement body 1.

[0039] [Construction method of ground improvement body] As in the ground improvement process in the construction process of the foundation structure F of the building as described above, the construction method of the ground improvement body 1 includes the steps of digging down the surface layer below the ground surface GL of the soft ground G into a predetermined shape, backfilling the soil excavated from the surface layer and spreading it evenly, scattering solidification material on the soil that has been backfilled and spread evenly, scattering and spreading the required number of rod-shaped bamboo pieces 2 on the solidification material, mixing and stirring the soil, the solidification material, and the rod-shaped bamboo pieces to form the ground improvement body 1, and compacting the ground improvement body 1.

[0040] Alternatively, a construction method of the ground improvement body 1 includes the steps of digging down the surface layer below the ground surface GL of the soft ground G into a predetermined shape, backfilling and spreading evenly the soil excavated from the surface layer, scattering and spreading evenly a required number of rod-shaped bamboo pieces 2 on the backfilled and spread evenly soil, scattering a solidification material on the rod-shaped bamboo pieces 2, mixing and stirring the soil, the rod-shaped bamboo pieces 2 and the solidification material to form the ground improvement body 1, and compacting the ground improvement body 1.

[0041] [Bending strength test] <Test Method> Prepare test specimens of a ground improvement body including rod-shaped bamboo pieces 2 (Example 1, Example 2) and a test specimen of a ground improvement body not including rod-shaped bamboo pieces 2 (Comparative Example). After a curing period of 28 days, a three-point bending test is performed on the test specimens based on JIS A 1106:2018 "Test method for bending strength of concrete" using the central point loading method with a support distance of 300 mm, and the relationship between bending stress and displacement of the load point is obtained.

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

[0043] <Soil and solidification material contained in the test specimen> The soil contained in the test specimen was sandy soil from the local area, and the solidification material contained in the test specimen was Geoset 200, a cement-based solidification material for ground improvement, manufactured by Taiheiyo Cement Corporation. The mixing ratio of the solidification material was 100 kg / m 3 It was decided.

[0044] <Size and mixing ratio of small bamboo rods> The rod-shaped bamboo pieces 2 were prepared by cutting bamboo skewers (diameter 2 mm, length 30 cm) with product number ZQ3020, sold by Anhui Yezilin Electronics Business Co., Ltd. and manufactured by Nanling County Jinruizhu Manufacturing Factory, to lengths of 3 cm for Example 1 and 5 cm for Example 2. The mixing ratio of the rod-shaped bamboo pieces 2 was 1.5% by volume of the specimens of Examples 1 and 2.

[0045] <Mixing and stirring> In Examples 1 and 2, the required amount of sandy soil is placed in a mixer, the solidification material is added in the above-mentioned mixing ratio, and the rod-shaped bamboo pieces 2 are added in the above-mentioned mixing ratio, and then mixed and stirred in the mixer. In the Comparative Example, the required amount of sandy soil is placed in a mixer, the solidification material is added in the above-mentioned mixing ratio, and then mixed and stirred in the mixer.

[0046] <Forming of specimen> The mixed and stirred ground improvement body is placed into a formwork and shaped into a size of 100mm x 100mm x 400mm to prepare the test specimen.

[0047] <Summary of Examples and Comparative Examples> (1) The test specimen of the ground improvement body of Example 1 was made of the above sandy soil, the above solidification material (100 kg / m 3 ) and a number of the rod-shaped bamboo pieces 2. The rod-shaped bamboo pieces 2 have the shape shown in Figures 2A to 2C, with D = 2 mm and L = 3 cm, and the mixture ratio of the rod-shaped bamboo pieces 2 is 1.5% by volume of the specimen. (2) The test specimen of the ground improvement body of Example 2 was made of the above sandy soil, the above solidification material (100 kg / m 3 ) and a number of the rod-shaped bamboo pieces 2. The rod-shaped bamboo pieces 2 have the shape shown in Figures 2A to 2C, with D = 2 mm and L = 5 cm, and the mixture ratio of the rod-shaped bamboo pieces 2 is 1.5% by volume of the specimen. (3) The specimen of the ground improvement body of the comparative example was made of the above sandy soil and the above solidification material (100 kg / m 3 ) (not including the 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 point in the three-point bending test of the specimen, the specimen of the comparative example (without rod-shaped bamboo pieces) shows a brittle fracture with a sudden drop 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) show a tough fracture without a sudden drop in yield strength.

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

[0050] [Effects] According to the ground improvement body of the embodiment of the present invention and the construction method of said ground improvement body, in the 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 contained in the ground improvement body 1.

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

[0052] Although the mixing ratio of the rod-shaped bamboo pieces 2 to the ground improvement body 1 is relatively small, if they are to be used in the construction of many ground improvement bodies 1 to improve the toughness of the ground improvement body 1, it will be necessary to continue to procure large quantities of the rod-shaped bamboo pieces 2. However, bamboo grows quickly, has a high regenerative capacity, and has a short harvest cycle, so a sufficient supply can be secured continuously at low cost. In addition, since bamboo is naturally derived, it is environmentally friendly, and increasing demand for bamboo will allow bamboo forests to be fully utilized, which will also help solve the problem of abandoned bamboo forests.

[0053] The above description of the embodiments is given by way of example only and is not intended to be limiting, and 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 Lower 2 small bamboo sticks 3. Foundation concrete 4. Steel columns 5. Concrete floor 6. Waste concrete Length of sides A and B D diameter F. Foundation of the building 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 a soft ground, Built under the foundations of buildings, The soil of the surface layer, a solidification material, and a large number of rod-shaped bamboo pieces are included, The mixing ratio of the rod-shaped bamboo pieces is 0.5 to 3% by volume. Ground improvement body.

2. The cross-sectional shape of the rod-shaped bamboo piece is circular or rectangular, The cross-sectional diameter or side length of the rod-shaped bamboo piece is 1 to 5 mm; The length of the rod-shaped bamboo pieces is 20 to 100 mm. The ground improvement body according to claim 1.

3. A construction method for a ground improvement body that improves the surface layer below the ground surface of a soft ground, comprising: The ground improvement body is constructed under the foundation of a building, A step of digging down the surface layer into a predetermined shape; A step of backfilling and spreading the soil excavated from the surface layer; A step of spreading a solidification material on the backfilled and evenly spread soil; A step of spreading a required number of rod-shaped bamboo pieces evenly on the solidification material; A process of mixing and stirring the soil, the solidification material, and the rod-shaped bamboo pieces to form a ground improvement body; A step of compacting the ground improvement body; Including, Construction method for ground improvement body.

4. A construction method for a ground improvement body that improves the surface layer below the ground surface of a soft ground, comprising: The ground improvement body is constructed under the foundation of a building, A step of digging down the surface layer into a predetermined shape; A step of backfilling and spreading the soil excavated from the surface layer; A step of spreading a required number of rod-shaped bamboo pieces evenly on the backfilled and evenly spread soil; A step of scattering a solidifying material on the rod-shaped bamboo pieces; A process of mixing and stirring the soil, the rod-shaped bamboo pieces, and the solidification material to form a ground improvement body; A step of compacting the ground improvement body; Including, Construction method for ground improvement body.

5. The mixing ratio of the rod-shaped bamboo pieces is 0.5 to 3% by volume of the ground improvement body. A method for constructing the ground improvement body according to claim 3 or 4.

6. The cross-sectional shape of the rod-shaped bamboo piece is circular or rectangular, The cross-sectional diameter or side length of the rod-shaped bamboo piece is 1 to 5 mm; The length of the rod-shaped bamboo pieces is 20 to 100 mm. A method for constructing the ground improvement body according to claim 5.

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