Ground improvement method and ground improvement body

Abstract

To reduce the amount of cement-based solidification material used in the soil improvement body and reduce the construction cost.SOLUTION: A ground improvement method for improving a ground G in which at least two strata out of strata consisting of volcanic ash soil, cohesive soil, sandy soil, and gravel soil are stacked comprises a step of excavating clay G1 and gravel G2 in an area to be improved and temporarily placing them on each ground, a step of refilling an excavated hole 11 with the clay G1 and the gravel G2 temporarily placed in an appropriate ratio and mixing and agitating, or mixing and agitating outside the excavated hole 11 and refilling the excavated hole 11, and a step of injecting a cement-based solidifying material K into the mixed soil G10 created in the excavated hole 11.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a ground improvement method and a ground improvement body. [Background technology]

[0002] Conventionally, a known method of ground improvement using columnar ground improvement involves moving a horizontal mixing blade attached to a vertical rod vertically, injecting a solidifying material such as cement milk into the excavated ground for each layer, and stirring and mixing the material (see, for example, Patent Document 1).

[0003] In addition, in the ground improvement method using block-shaped ground improvement, the target ground is excavated, the excavated soil is temporarily placed around the excavation site, and then the temporarily placed excavated soil is backfilled into the excavated hole while injecting, stirring, and mixing ground improvement materials such as cement milk. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-217820 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the conventional ground improvement methods described above have the following problems. That is, in the above-mentioned ground improvement method, for example, in the case of a layered stratum consisting of a clay layer and a gravel layer, in order to develop a predetermined strength of the improved ground, the amount of cement-based solidification material added is injected into all layers so that the clay layer, which has a low developed strength, can reach the target strength. In other words, because the same amount of cement-based solidification material is injected into the gravel layer, which has a higher developed strength than the clay layer, as into the clay layer, it is uneconomical and there is room for improvement in this regard.

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a ground improvement method and a ground improvement body that can reduce the amount of cement-based solidification material used in the ground improvement body and thereby reduce construction costs. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides a ground improvement method for improving ground consisting of at least two layers of soil with different soil strengths, which includes excavating the soil of the plurality of layers in an improvement area. Drilling holes are made, A process of temporarily placing each piece of ground, A process of determining the optimum mixing ratio of the plurality of ground layers to be used as the mixed soil to be returned to the excavation hole from the depth and properties of each of the plurality of layers, and determining the amount of cement-based solidification material to be added, which is made of liquid cement milk, based on the strength obtained by performing a strength test based on the mixing amount of the mixed soil; The multiple pieces of ground that are temporarily placed Proportion based on the optimum mixing ratio A process of preparing a mixed soil in a state where the ground is backfilled in the excavated hole as it is and mixed and stirred, or a mixed soil in a state where the ground is backfilled in the excavated hole as it is and mixed and stirred outside the excavated hole; Inside the drilled hole and injecting a predetermined amount of the cement-based solidification material into the mixed soil that has been backfilled in the hole.

[0008] Further, the ground improvement body according to the present invention is a ground improvement body constructed by the above-mentioned ground improvement method, and the mixed soil backfilled in the excavated hole is provided in the excavated hole. multiple of The aforementioned It is prepared by mixing and stirring the soil of the stratum, and is characterized in that a predetermined amount of the cement-based solidification material is injected into the mixed soil.

[0009] In the present invention, by mixing at least two strata with different ground strengths to create a mixed soil, it is possible to increase the strength developed when a cement-based solidification material is mixed into the mixed soil compared to the strength developed when a cement-based solidification material is mixed into the ground with the lowest ground strength. Therefore, the amount of cement-based solidification material injected into the mixed soil can be reduced compared to the amount of cement-based solidification material injected only into the ground with the lowest developed strength. As a result, in the present invention, the amount of cement-based solidification material used in the ground improvement body can be reduced, thereby reducing construction costs. Furthermore, the present invention allows the optimum mixing ratio and amount of cement-based solidification material to be set in advance for the multiple grounds to be improved.The multiple grounds are then mixed based on the set optimum mixing ratio to create a mixed soil, and the cement-based solidification material is then injected into the mixed soil based on the preset amount of cement-based solidification material to form a ground improvement body with optimal strength.

[0010] Furthermore, the ground improvement method according to the present invention may be characterized in that the ground is made up of a stack of at least two strata selected from strata consisting of volcanic ash soil, clayey soil, sandy soil, and gravelly soil.

[0011] In this case, by mixing at least two strata consisting of volcanic ash soil, clayey soil, sandy soil, and gravelly soil to create mixed soil, the strength exerted when a cement-based solidification material is mixed into the mixed soil can be made higher than the strength exerted when a cement-based solidification material is mixed into ground with the lowest ground strength.

[0014] In addition, in the ground improvement method according to the present invention, it is preferable that the mixed soil prepared in the excavation hole is poured in multiple batches at each predetermined height.

[0015] In the present invention, by constructing the ground improvement body in multiple steps, the mixed soil to be backfilled in the entire excavated hole can be efficiently mixed. [Effects of the Invention]

[0016] According to the ground improvement method and ground improvement body of the present invention, the amount of cement-based solidification material used in the ground improvement body can be reduced, thereby reducing construction costs. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is a longitudinal cross-sectional view showing the configuration of a ground improvement body according to an embodiment of the present invention. [Figure 2] FIG. 1 is a flow chart showing the construction procedure of the ground improvement method. [Figure 3] FIG. 1 is a graph showing the relationship between the amount of cement-based solidification material added and unconfined compressive strength. [Figure 4] (a) and (b) are diagrams showing the construction procedure of the ground improvement method. [Figure 5] 4(a) to 4(c) are diagrams showing the construction procedure of the ground improvement method following FIG. 4(b). DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, a ground improvement method and a ground improvement body according to an embodiment of the present invention will be described with reference to the drawings.

[0019] As shown in Figure 1, the ground improvement body 1 of this embodiment has been improved by a ground improvement method for improving ground G, which is composed of at least two layers of soil layers, for example, volcanic ash soil, clayey soil, sandy soil, and gravelly soil.

[0020] In this embodiment, the stratum to be improved consists of two layers, with clay G1 (clay soil) in the upper layer and gravel G2 (sandy soil, gravel soil) in the lower layer. The supporting ground G3 is placed below the gravel G2. Clay G1 has small particle size and is highly fluid, but is less likely to develop strength than gravel G2. Gravel G2 has the advantage of being less fluid than general aggregates, but still capable of developing strength.

[0021] In this embodiment, the gravel G2 is a mixture of sandy soil and gravel soil. The clay G1, gravel G2, and supporting ground G3 are collectively referred to as ground G, and the mixture of the excavated clay G1 and gravel G2 is referred to as mixed soil G10.

[0022] The ground improvement body 1 is formed by excavating clay G1 and gravel G2 until the supporting ground G3 is exposed, backfilling the excavated hole 11 with excavated soil (mixed soil G10), and mixing and stirring the mixed soil G10 with a soil improvement material, for example, a liquid cement-based solidification material K such as cement milk. The ground improvement body 1 is formed into a square with the same length and width dimensions when viewed from above, for example.

[0023] The ground improvement body 1 is formed using a ground mixing device 2 (see FIG. 5(a)). The ground mixing device 2 for mixing used when constructing the ground improvement body 1 is, for example, 0.5 m 3 Class and 0.8m 3The ground mixing device 2 is attached as an attachment to the end of the arm of a work machine such as a backhoe. The ground mixing device 2 has a mixing blade 22 inside a bucket 21, and by rotating the mixing blade 22 and moving it appropriately within the mixed soil G10, the cement-based solidification material K is added to the mixed soil G10, and the mixed soil G10 is mixed.

[0024] Next, a construction method (ground improvement method) for the ground improvement body 1 will be specifically explained using the construction flow chart of FIG. 2 and the like. As shown in Figure 2, the ground improvement method according to this embodiment includes the steps of excavating multiple (here, two) layers of ground G (clay G1, gravel G2) in the improvement area and temporarily storing each layer of ground G1, G2, mixing and stirring the temporarily stored multiple layers of ground G1, G2 in an appropriate ratio outside the excavation hole 11 and backfilling the excavation hole 11, and injecting cement-based solidification material K into the mixed soil G10 prepared inside the excavation hole 11.

[0025] First, in step S1, the ground G to be improved is sampled and a pre-mixing test is performed. In the pre-mixing test, the type of strata of the ground G and the thickness (height) of each strata are confirmed, and based on the sampled ground G, the optimal mixing ratio of the multiple grounds (clay G1 and gravel G2 in this embodiment) to be used as the mixed soil G10 to be returned to the excavation hole 11 and the amount of cement-based solidification material K to be added are determined from the depth and properties of each of the multiple strata (step S2). In the mix test, strength tests are conducted based on the mix amount of mixed soil G10 for each ground G1 and G2 to determine the amount of cement-based solidification material K to be added.

[0026] Figure 3 shows the amount of cement-based solidification material K added (kg / m) for each of the grounds G1, G2, and G10. 3 ) and unconfined compressive strength qu (kN / m 2 ) is an example showing the relationship between the strength and the concrete strength. Mixed soil G10 is a mixture of clay G1 and gravel G2 with a mixing ratio of 6 (clay G1):4 (gravel G2). The line with symbol P in Figure 3 shows the strength of 2867 kN / m 2 The amount of cement-based solidification material K to be added to reach the target strength P using only clay G1 is 364 kg / m 3In contrast, in the case of mixed soil G10, the amount of cement-based solidification material K added to reach the target strength P is 258 kg / m 3 In this case, by using the mixed soil G10, the amount of cement-based solidification material K to be added can be reduced by approximately 30%.

[0027] As shown in FIG. 4(a), in parallel with the calculation of the optimal mixing ratio and the amount of cement-based solidification material K to be added in steps S1 and S2, the ground G to be improved is excavated (step S3) and temporarily stored around the excavation hole 11 after being separated into layers (clay G1, gravel G2) (step S4). The ground G can be excavated using a shovel 3. The excavation depth is set to a depth at which all of the clay G1 and gravel G2 have been excavated and the supporting ground G3 is exposed. The temporary storage positions of the excavated ground G1 and G2 can be set as desired.

[0028] Next, in step S5, as shown in Fig. 4(b), clay G1 and gravel G2 are mixed in a ratio based on the optimal mixing ratio calculated in advance to create mixed soil G10. Here, clay G1 and gravel G2 temporarily placed around the excavation hole 11 are used and mixed on the spot in a ratio of, for example, 6:4 to create mixed soil G10.

[0029] Next, in step S6, as shown in Fig. 5(a), the prepared mixed soil G10 is backfilled into the excavated hole 11 to a predetermined height. Then, the mixed soil G10 is backfilled into the excavated hole 11, and a previously determined amount of cement-based solidification material K is poured into the mixed soil G10, followed by stirring and mixing (step S7). The stirring and mixing work is carried out by moving the ground stirring device 2 attached as an attachment to the work machine with the mixed soil G10, which is stirred by the stirring blades 22, and the cement-based solidification material K is mixed into the mixed soil G10.

[0030] The mixed soil G10 to be backfilled into the excavated hole 11 is poured in multiple batches (three batches in FIG. 5) at predetermined heights as shown in FIGS. 5(a) to 5(c). As shown in Figure 5(c), after backfilling with the third mixed soil G10, the formation of the ground improvement body 1 is completed by confirming that all backfill soil (improved soil) has reached the target strength.

[0031] Next, the above-mentioned ground improvement method and the action of the ground improvement body will be described in detail with reference to the drawings. In this embodiment, by mixing multiple types of clayey soil, sandy soil, and gravelly soil ground G to create mixed soil G10, it is possible to increase the strength developed when the cement-based solidification material K is mixed into the mixed soil G10 compared to the strength developed when the cement-based solidification material K is mixed into the ground with the lowest ground strength (clay G1 in this embodiment). Therefore, the amount of cement-based solidification material K injected into the mixed soil G10 can be reduced compared to the amount of cement-based solidification material K injected only into the ground G with the lowest strength developed (clay G1). As a result, in this embodiment, the amount of cement-based solidification material K used in the ground improvement body 1 can be reduced, and construction costs can be reduced.

[0032] Furthermore, in this embodiment, it is possible to set in advance the optimum mixing ratio and the amount of cement-based solidification material K to be added for the multiple grounds G to be improved. Then, the multiple grounds G are mixed based on the set optimum mixing ratio to create mixed soil G10, and further, the cement-based solidification material K is injected into the mixed soil G10 based on the preset amount of cement-based solidification material K to be added, thereby forming a ground improvement body 1 with optimal strength.

[0033] In addition, in this embodiment, the mixed soil G10 created in the excavation hole 11 is poured in multiple batches at predetermined heights, and the ground improvement body 1 is constructed in multiple batches, so that the mixed soil G10 that is backfilled throughout the entire excavation hole 11 can be mixed efficiently.

[0034] As described above, in the ground improvement method and ground improvement body 1 according to this embodiment, the amount of cement-based solidification material K used in the ground improvement body 1 can be reduced, and construction costs can be reduced.

[0035] The above describes embodiments of the ground improvement method and ground improvement body according to the present invention, but the present invention is not limited to the above embodiments and can be modified as appropriate within the scope of the spirit thereof.

[0036] For example, in the above-described embodiment, the clay G1 and gravel G2 temporarily stored outside the excavation hole 11 are mixed and stirred to create the mixed soil G10, and then the mixed soil G10 is backfilled into the excavation hole 11, but the present invention is not limited to this. For example, it is also possible to adopt a procedure in which the clay G1 and gravel G2 temporarily stored are backfilled into the excavation hole 11, and then the clay G1 and gravel G2 are mixed and stirred inside the excavation hole 11 to create the mixed soil G10, and at the same time, the cement-based solidification material K is also injected.

[0037] In addition, the ground G in this embodiment is a two-layer ground consisting of clay G1 and gravel G2, which is a mixture of sandy soil and gravel soil, but this is just one example and the ground conditions are not limited to these. For example, the ground may be made up of four layers of volcanic ash soil, clayey soil, sandy soil, and gravel soil, or two layers of clayey soil and sandy soil, two layers of clayey soil and gravel soil, or three layers of volcanic ash soil, sandy soil, and gravel soil. Furthermore, the ground to be improved is not limited to the four strata of volcanic ash soil, clayey soil, sandy soil, and gravel soil described above, and the present invention is also applicable to strata that do not fall into the four layers of volcanic ash soil, clayey soil, sandy soil, and gravel soil exemplified here.

[0038] In this embodiment, the pre-mixing test involves investigating each layer of the target ground and determining the optimal mixing ratio and amount of cement-based solidification material to be added for the multiple layers of ground to be used as the mixed soil to be returned to the excavation hole based on the depth and properties of each layer, but it is also possible to omit such a pre-mixing test. For example, if the condition of the target ground to be improved is known in advance, the optimal mixing ratio and amount of cement-based solidification material to be added may be determined without conducting the above-mentioned mix testing.

[0039] Furthermore, in this embodiment, the mixed soil G10 prepared in the excavation hole 11 is poured into the excavation hole 11 in multiple batches at predetermined heights, but the pouring height can be set arbitrarily. Also, if the depth of the excavation hole 11 is shallow, all of the mixed soil G10 may be poured into the excavation hole 11 at once, without being poured into multiple batches, and stirred and mixed.

[0040] Furthermore, there are no particular limitations on the specific configuration of the ground mixing device 2 for constructing the ground improvement body 1. It is possible to mix and stir the mixed soil using a general-purpose shovel or machine with a mixing function, without using such a dedicated ground mixing device 2.

[0041] In addition, the components in the above-described embodiments can be replaced with well-known components as appropriate, without departing from the spirit of the present invention. [Explanation of symbols]

[0042] 1 Ground improvement body 2 Ground stirring device 11 Drilling Hole G Ground G1 Clay (Clayey Soil) G2 Gravel (sandy soil, gravelly soil) G10 mixed soil K Cement-based solidification material P target strength

Claims

1. A ground improvement method for improving ground consisting of at least two layers of soil with different ground strengths, a step of excavating the ground of the plurality of strata in the improvement area, creating excavation holes, and temporarily placing each of the ground; A process of determining the optimum mixing ratio of the plurality of ground layers to be used as the mixed soil to be returned to the excavation hole from the depth and properties of each of the plurality of layers, and determining the amount of cement-based solidification material to be added, which is made of liquid cement milk, based on the strength obtained by performing a strength test based on the mixing amount of the mixed soil; A process of preparing a mixed soil in a state where the plurality of temporarily placed soils are backfilled into the excavation hole as they are in a proportion based on the optimal mixing ratio, or a mixed soil in a state where the plurality of soils are backfilled into the excavation hole as they are in a mixed state outside the excavation hole; a step of injecting a predetermined amount of the cement-based solidification material into the mixed soil backfilled in the excavated hole; A ground improvement method comprising the steps of:

2. 2. The ground improvement method according to claim 1, wherein the ground is a layered structure of at least two layers selected from the group consisting of volcanic ash soil, clayey soil, sandy soil, and gravelly soil.

3. 3. The method for improving ground according to claim 1, wherein the mixed soil prepared in the excavated hole is poured in a plurality of times at predetermined heights.

4. A ground improvement body constructed by the ground improvement method according to any one of claims 1 to 3, The mixed soil backfilled in the excavation hole was prepared by mixing and stirring the soil of the plurality of strata provided in the excavation hole, A ground improvement body characterized in that a predetermined amount of the cement-based solidification material is injected into the mixed soil.

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