Ground improvement method

Abstract

To provide a ground improvement method capable of controlling stress which each pile bears.SOLUTION: A ground improvement method is used through assembly of a pile foundation. The ground improvement method carries out steps of: inspecting a ground property by dividing a ground improvement area into a plurality of zones and / or layers; determining an additive amount of improvement material considering the ground property of each of the zones and the layers; excavating the ground improvement area by a target depth by each of the zones and the layers; adding the improvement material to excavated soil for each of the zones and the layers and mixing and stirring the same; and compacting layer by layer refilled improvement soil where the improvement material has been added to the excavated soil.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] A known method for improving soft ground is to use a cement-based solidification material to solidify it (see, for example, Patent Document 1). In the ground improvement method described in Patent Document 1, the ground surface is excavated with a backhoe, the excavated soil is temporarily placed around the excavation site, an improvement material is spread on the bottom of the excavation, and a predetermined amount of the excavated soil is backfilled with the backhoe. The excavated soil and improvement material are mixed and stirred with the backhoe or the like, and the improved soil is compacted with a vibrating roller or the like to form improved ground of a predetermined thickness. The ground is strengthened by repeatedly backfilling the excavated soil, mixing and stirring the excavated soil with the improvement material, and compacting the improved soil. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-313314 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the ground improvement method described in Patent Document 1, the ground is improved by adding the same amount of improvement material as if the ground were a single layer of the same strength, which causes variations in the strength of the improved ground depending on the ground properties. For this reason, when pile foundations and ground improvement are used together, it is difficult to ensure that each pile bears an appropriate stress when subjected to horizontal forces such as those caused by an earthquake.

[0005] The present invention has been made in view of the above points, and an object of the present invention is to provide a ground improvement method that can control the stress borne by piles. [Means for solving the problem]

[0006] One embodiment of the ground improvement method of the present invention is a ground improvement method used in combination with pile foundations, and includes the steps of dividing the ground improvement area into multiple sections and / or layers and investigating the ground properties, determining the amount of improvement material to be added for each section and / or layer taking into account the ground properties, excavating the ground improvement area to a target depth by dividing it into sections and / or layers, adding improvement material to the excavated soil for each section and / or layer and mixing and stirring it, and compacting the improved soil that has been added to the excavated soil and backfilled, layer by layer. [Effects of the Invention]

[0007] In one aspect of the ground improvement method of the present invention, improvement materials are added to each section and / or layer according to the ground properties, allowing the strength of the improved ground to be set arbitrarily in the horizontal and / or depth directions, thereby controlling the horizontal force borne by each pile. When subjected to horizontal forces such as earthquakes, each pile in the pile foundation can bear an appropriate horizontal force. In addition, excessive addition of improvement materials can be prevented, reducing waste of improvement materials. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 10 is a plan view showing an example of ground improvement performed using a comparative ground improvement method. [Figure 2] FIG. 10 is a cross-sectional view showing an example of ground improvement performed using a comparative ground improvement method. [Figure 3] FIG. 1 is a plan view showing an example of ground improvement using the ground improvement method of this embodiment. [Figure 4] This is a cross-sectional view showing an example of ground improvement using the ground improvement method of this embodiment. [Figure 5] This figure shows the results of a pile stress analysis due to ground deformation during an earthquake, taking into account the effects of liquefaction before ground improvement. [Figure 6] This figure shows the results of a pile stress analysis due to ground deformation during an earthquake after ground improvement. [Figure 7] FIG. 2 is a flowchart showing the ground improvement method of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Before describing the ground improvement method of this embodiment, a ground improvement method of a comparative example will be described with reference to Figures 1 and 2. Figure 1 is a plan view showing an example of ground improvement performed using the ground improvement method of the comparative example. Figure 2 is a cross-sectional view showing an example of ground improvement performed using the ground improvement method of the comparative example.

[0010] As shown in Figure 1, most of the ground improvement area before ground improvement is composed of soft ground made up of organic soil with a water content of 150%, and part of the ground improvement area is composed of relatively hard ground made up of clayey soil with a water content of 40%. In the ground improvement method of the comparative example, 230 kg / m of improvement material is applied to the entire ground improvement area. 3 ] is added to improve the ground uniformly. As a result, the unconfined compressive strength of the soft ground is increased to 750 [kN / m 2 ], and in places where the ground was relatively hard, the unconfined compressive strength was increased to 3000 [kN / m 2 ] has been raised, causing variations in the improved ground.

[0011] In addition, pile foundations have been constructed in the ground improvement area, with piles 10a-10l, such as PHC (Prestressed High-strength Concrete) piles, installed vertically and horizontally in the ground improvement area. Piles 10a-10f and 10h-10l have a diameter of 600 mm, and pile 10g has a diameter of 1200 mm. The areas around piles 10a-10i, 10k, and 10l are made up of improved ground made of soft ground, while the area around pile 10j is made up of improved ground made of relatively hard ground. Thus, of piles 10a-10l, pile 10g is formed to be the thickest, and the improved ground strength around pile 10j is the highest.

[0012] When a horizontal force acts on the ground improvement area due to an earthquake or other reason, the horizontal force is borne by piles 10a-10l. At this time, the larger the pile diameter, the higher the horizontal rigidity of the pile, and the greater the horizontal force acting on the pile. Also, the harder the ground is, the stronger the resistance it has to deformation, so the horizontal rigidity of the pile increases, and the greater the horizontal force acting on the pile. Pile 10g, which has a larger diameter than the other piles, bears a greater horizontal force, and even pile 10j, which is installed in an area where the improved ground is stronger than the other piles, bears a greater horizontal force because the improved ground is relatively hard (due to its large deformation coefficient). Conversely, piles 10a-10f, 10h, 10i, 10k, and 10l bear a smaller horizontal force. Generally, the strength of the improved ground (q u ) and deformation modulus (E 50 ) is a proportional relationship (e.g., E 50 =100q u ) and it is known that the greater the strength, the greater the deformation modulus (harder).

[0013] For example, if a horizontal force of 5,000 kN acts on the ground improvement area, pile 10g will bear 736 kN of horizontal force, and pile 10j will bear 940 kN of horizontal force. The remaining piles 10a-10f, 10h, 10i, 10k, and 10l will each bear 332 kN of horizontal force. While the horizontal force burden on piles 10a-10f, 10h, 10i, 10k, and 10l may be reduced depending on the pile diameter and the strength of the improved ground, the horizontal force may be concentrated on specific piles 10g and 10j. Furthermore, with uniform ground improvement, even if piles with high or sufficient bearing capacity exist, these piles will not be able to bear a large amount of horizontal force.

[0014] As shown in Figure 2, the ground improvement method of the comparative example improves the ground uniformly in the depth direction. Before ground improvement, layers 11a, 11b, and 11d consist of soft clayey soil with a water content of 80%, while layers 11c, 11e, and 11f consist of hard sand with a water content of 25%. With the ground improvement method of the comparative example, the uniaxial compressive strength of all layers 11a-11f is increased to 500 kN / m 2 ] or more, all layers 11a-11f are provided with 150 [kg / m 3] is added to uniformly improve the ground. As a result, the unconfined compressive strength of layers 11a, 11b, and 11d is 500 [kN / m 2 ], but the uniaxial compressive strength of layers 11c, 11e, and 11f is 3000 [kN / m 2 ] can be increased to.

[0015] The uniaxial compressive strength of all layers 11a-11f is 500 [kN / m 2 ], but the strength of layers 11c, 11e, and 11f is excessive, resulting in waste of improvement material when considering the required performance. As described above, in the ground improvement method of the comparative example, the entire ground improvement area is uniformly improved in the depth direction, so each pile cannot bear an appropriate horizontal force, and excessive addition of improvement material results in waste. Therefore, in the ground improvement method of this embodiment, the ground improvement area is divided into sections and layers and the amount of improvement material added is changed, thereby controlling the horizontal force borne by each pile and reducing waste of improvement material.

[0016] The ground improvement method of this embodiment will be described below with reference to Figures 3 and 4. Figure 3 is a plan view showing an example of ground improvement using the ground improvement method of this embodiment. Figure 4 is a cross-sectional view showing an example of ground improvement using the ground improvement method of this embodiment.

[0017] As shown in Figure 3, the ground improvement method of this embodiment is used in combination with a pile foundation. The ground improvement area is divided into multiple sections, and the ground properties are investigated. Although not described in detail here, the ground properties include the hardness, density, moisture content, heterogeneity, and geological characteristics of the ground. Before ground improvement, most sections of the ground improvement area consist of soft ground such as organic soil with a water content of 150%, while several sections (10 sections in this embodiment) of the ground improvement area consist of relatively hard ground such as clayey soil with a water content of 40%. Also, as in the comparative example, only certain piles 10g of the pile foundation are formed with a large pile diameter.

[0018] The amount of improvement material added to each section of the ground improvement area is adjusted taking into account the soil characteristics. Each section of soft ground is given 230 kg / m of improvement material.3 ] was added to improve the ground, and 120 [kg / m 3 The unconfined compressive strength of each area, which was previously soft, was increased to 750 [kN / m 2 ], and the unconfined compressive strength of each section 12, which had relatively hard ground, was 750 [kN / m 2 A larger amount of improvement material is added to the sections with soft ground, and a smaller amount of improvement material is added to each section 12 with relatively hard ground, so that each section 12 with relatively hard ground and the section with soft ground are adjusted to have the same strength.

[0019] In addition, the surrounding area of ​​each small diameter pile (10c) is treated with 230 kg / m 3 ] was added to improve the ground, and the surrounding section 13 of the large diameter pile 10g was treated with 150 [kg / m 3 ] is added to improve the ground. The unconfined compressive strength of the surrounding area of ​​each pile is 750 [kN / m 2 ], and the unconfined compressive strength of the surrounding section 13 of the pile 10g is increased to 250 [kN / m 2 A large amount of improvement material is added to the surrounding area of ​​the pile 10c having a small diameter, and a small amount of improvement material is added to the surrounding area 13 of the pile 10g having a large diameter, so that the strength of the surrounding area 13 of the pile 10g is adjusted to be lower than that of the surrounding area of ​​the pile 10c.

[0020] When a horizontal force acts on the ground improvement area due to an earthquake or other event, the horizontal force is borne evenly by piles 10a-10l. Because each section 12 with relatively hard ground is as hard as the section with soft ground, the horizontal force does not bear heavily on pile 10j in each section 12 with relatively hard ground. Pile 10g has the largest pile diameter, but because the surrounding section 13 of pile 10g is softer than the surrounding sections such as pile 10c, the reaction force transmitted from the improved ground to pile 10g is weaker, and pile 10g does not bear a heavy horizontal force. For example, if a horizontal force of 5000 kN acts on the ground improvement area, piles 10a-10l each bear 417 kN.

[0021] As shown in FIG. 4(A), the ground improvement method of this embodiment also allows for ground improvement divided into multiple layers. The ground improvement area is divided into multiple layers and the ground properties are investigated. Before ground improvement, layers 11a, 11b, and 11d are composed of soft clayey soil with a water content of 80%, and layers 11c, 11e, and 11f are composed of hard sand with a water content of 25%. The amount of improvement material added to each layer of the ground improvement area is adjusted taking into account the ground properties. An amount of improvement material of 150 kg / m is added to the soft layers 11a, 11b, and 11d. 3 ] was added to improve the ground, and the hard layers 11c, 11e, and 11f were treated with 60 [kg / m 3 ] is added to improve the ground. The unconfined compressive strength of all layers 11a-11f is 500 [kN / m 2 ] and no waste of improvement material occurs.

[0022] As shown in Figure 4(B), the bending moment acting on the pile 10 increases as it approaches the pile head. Therefore, by increasing the amount of improvement material added to layers 11a and 11b at the pile head height compared to the lower layers, ground improvement can be achieved efficiently. The amount of improvement material added to layers 11a and 11b is increased compared to the amount added to layer 11d, thereby increasing the strength of layers 11a and 11b. Layers 11c, 11e, and 11f, which are already hard, are backfilled without adding improvement material, resulting in a slight decrease in strength. By increasing the amount of improvement material added to layers 11a and 11b at the pile head height, the effect of the bending moment can be reduced, and by reducing the amount of improvement material added to layers 11c-11f below the pile head height, costs can be reduced.

[0023] In this way, in the ground improvement method of this embodiment, the ground improvement area is divided into multiple sections and ground improvement is performed for each section, so that each pile can bear an appropriate horizontal force. Also, the ground improvement area is divided into multiple layers and ground improvement is performed for each layer, so excessive addition of improvement material is suppressed. Alternatively, the ground improvement area may be divided into multiple sections and multiple layers, and ground improvement may be performed more finely for each section and each layer. This allows for precise control of the horizontal force acting on the piles and further suppresses excessive addition of improvement material.

[0024] Next, ground improvement of liquefied ground will be explained with reference to Figures 5 and 6. Figure 5 shows the results of a pile stress analysis due to ground deformation during an earthquake, taking into account the effects of liquefaction before ground improvement. Figure 6 shows the results of a pile stress analysis due to ground deformation during an earthquake after ground improvement. Note that Figures 5 and 6 show, from left to right, the N-value, displacement distribution, bending moment distribution, and shear force distribution of the original ground. The left side of the displacement distribution shows the pile displacement, and the right side of the displacement distribution shows the ground displacement.

[0025] As shown in Figure 5, when the ground is viewed in the depth direction, the N-value of the liquefied layer is extremely small. For example, the N-value is 1 in the liquefied layer at a depth of 2-3 m, while the N-value is 10 in the layers above and below the liquefied layer. When there is an extreme difference in the N-values ​​of the liquefied layer and the layers above and below, the bending moment and shear force acting on the piles increases due to the influence of stress due to inertial forces or stress due to the response displacement of the ground. In this case, the maximum bending moment acting on the pile is 2470 kNm, and the maximum shear force acting on the pile is 994 kN.

[0026] As shown in Figure 6, adding a large amount of improvement material to the liquefied layer at a depth of 2-3 m reduces the variation in N-values ​​between the liquefied layer and the layers above and below, thereby suppressing the bending moment and shear force acting on the piles. In the study shown in Figure 6, the liquefied layer is treated as if it has been improved. Here, the maximum bending moment acting on the piles is reduced to 287 kNm, and the maximum shear force acting on the piles is reduced to 71 kN. Thus, it is sufficient to add a large amount of improvement material only to the liquefied layer for ground improvement. It is also possible to improve the ground in other layers by adding less improvement material, or by simply backfilling and compacting.

[0027] The operation procedure of the ground improvement method of this embodiment will be described with reference to Fig. 7. Fig. 7 is a flowchart of the ground improvement method of this embodiment. Note that the order of the steps in the flowchart may be changed as appropriate.

[0028] As shown in Figure 7, the ground improvement area is divided into multiple sections and / or layers, and the ground properties are investigated (step S01). Here, the ground improvement area, ground improvement depth, soil quality, groundwater level, etc. are investigated. Next, the amount of improvement material to be added is determined for each section and / or layer, taking into account the ground properties (step S02). In this case, the amount of improvement material to be added may be reduced for harder sections and / or layers, and increased for softer sections and / or layers. This makes the strength of the improved ground more uniform in the horizontal and depth directions, and reduces the concentration of horizontal forces on specific piles.

[0029] In step S02, the amount of improvement material added may be reduced in a section where a specific pile with a larger diameter than the other piles is to be formed compared to the section where the other piles are to be formed, thereby alleviating the concentration of horizontal force on the specific pile with a larger diameter. Furthermore, the amount of improvement material added may be increased in a section where a specific pile with a higher bearing capacity than the other piles is to be formed, thereby causing the specific pile with the higher bearing capacity to bear the horizontal force, thereby reducing the burden of the horizontal force on the other piles. Furthermore, the amount of improvement material added may be increased in a layer at pile head height compared to lower layers, thereby efficiently suppressing the effects of bending moment.

[0030] Next, the ground improvement area is excavated to the target depth by dividing it into sections and / or layers (step S03). For example, the ground improvement area is divided into multiple sections using band tape or the like, and excavated to the target depth of 3 m, with each layer being 1 m, while staff or the like are checking the excavation depth. The excavated soil dug up from the ground is temporarily stored near the excavation hole. In this case, the excavated soil is temporarily stored divided into sections and / or layers. Next, the bottom half of each layer is backfilled for each section (step S04). In this case, the temporarily stored excavated soil is backfilled by 50 cm, while staff or the like are checking the backfill depth.

[0031] Next, one layer of improvement material is spread on each section (Step S05). Before spreading the improvement material, the amount of improvement material to be added is confirmed for each section, and the improvement material is spread using a backhoe in a flexible container bag. Next, the top half of one layer is backfilled for each section (Step S06). In this case, the backfill depth is checked by staff, and 50 cm of the temporarily placed excavated soil is backfilled. Next, one layer of excavated soil and improvement material are mixed and stirred (Step S07). Using a skeleton bucket, etc., the excavated soil and improvement material are mixed uniformly at a rate of 1.5 min / m 3 ] and then mixed and stirred.

[0032] Next, one layer of improved soil after mixing and stirring is compacted (step S08). In this case, the improved soil is leveled using a leveling machine, and then compacted using a roller. Steps S04 to S08 are repeated until the required number of layers of ground improvement (three layers in this embodiment) are completed (step S09). In this way, half of one layer of excavated soil is backfilled and improvement material is spread, and the remaining half of one layer of excavated soil is backfilled, and improvement material is added to the excavated soil for each section and / or layer, and the improved soil is mixed and stirred, and compacted one layer at a time.

[0033] Next, once the required number of layers of ground improvement have been completed, the improved ground is cured (step S10), and after the curing period has elapsed, construction of pile foundations is carried out (step S11). In this case, the pile positions in the improved ground are pre-cut using an all-casing method, a rock auger method, or the like. Note that it is not necessary to spray improvement material at the pile positions during ground improvement, and a retarder may be used to make it difficult for the ground strength to develop. Furthermore, in this embodiment, the excavated soil is backfilled and mixed with the improvement material, but it may also be mixed and mixed with the improvement material in the location where the excavated soil is temporarily stored and then backfilled.

[0034] As described above, according to the ground improvement method of this embodiment, improvement materials are added to each section and / or layer according to the ground properties, and the strength of the improved ground is set arbitrarily in the horizontal and depth directions, thereby controlling the horizontal force borne by each pile. When subjected to horizontal forces such as earthquakes, each pile in the pile foundation can bear an appropriate horizontal force. In addition, excessive addition of improvement materials can be prevented, reducing waste of improvement materials.

[0035] The improvement material may be any material that can be used for ground improvement, such as a cement-based solidification material. Also, a powder improvement material or a slurry improvement material may be used.

[0036] Furthermore, the number of sections can be set arbitrarily, but may be set according to, for example, the area controlled by the pile, the physical properties of the ground, and the physical properties of the pile.

[0037] Furthermore, the number of layers can be set arbitrarily, but may be set according to, for example, the performance of the backhoe, the physical properties of the ground, and the physical properties of the piles.

[0038] In addition, ground improvement may be carried out only in the areas surrounding some of the piles.

[0039] Alternatively, the original ground may be excavated and backfilled without adding improvement material to reduce its strength. In other words, ground improvement does not only involve increasing the strength of the ground, but also involves decreasing its strength.

[0040] As described above, the first aspect is a ground improvement method used in combination with pile foundations, comprising the steps of: dividing the ground improvement area into multiple sections and / or layers and investigating the ground properties; determining the amount of improvement material to be added for each section and / or layer, taking the ground properties into consideration; excavating the ground improvement area to a target depth for each section and / or layer; adding improvement material to the excavated soil for each section and / or layer and mixing and stirring it; and compacting the improved soil, layer by layer, that has been backfilled with the added improvement material. According to this configuration, by adding improvement material for each section and / or layer according to the ground properties, the strength of the improved ground can be arbitrarily set in the horizontal and depth directions, thereby controlling the horizontal force borne by each pile. When subjected to horizontal forces such as earthquakes, each pile in the pile foundation can be made to bear an appropriate horizontal force. Furthermore, excessive addition of improvement material can be prevented, thereby minimizing waste of improvement material.

[0041] In the second aspect, in the first aspect, in the mixing and stirring step, half of the excavated soil of one layer is backfilled and an improvement material is spread, and the remaining half of the excavated soil of one layer is backfilled and mixed and stirred, and the mixing and stirring step and the compaction step are repeated for the target number of layers. With this configuration, the excavated soil and improvement material are well mixed and stirred, and improved ground is formed layer by layer according to the ground properties.

[0042] In the third aspect, in the step of determining the amount of improvement material to be added in the first or second aspect, the amount of improvement material to be added is reduced for the hard sections (12) and / or layers (11a, 11b, 11d) and increased for the soft sections and / or layers (11c, 11e, 11f). This configuration makes it possible to make the strength of the improved ground nearly uniform in the horizontal and depth directions.

[0043] In a fourth aspect, in any one of the first to third aspects, in the step of determining the amount of improvement material to be added, the amount of improvement material to be added is reduced in a section where a specific pile (10g) having a larger pile diameter than the other piles is to be formed, compared to a section where the other piles are to be formed. This configuration makes it possible to mitigate the concentration of horizontal force on the specific pile with a larger pile diameter.

[0044] A fifth aspect is any one of the first to fourth aspects, wherein in the step of determining the amount of improvement material to be added, the amount of improvement material to be added is increased in a section where a specific pile having a higher bearing strength than the other piles is to be formed compared to a section where the other piles are to be formed. With this configuration, the horizontal force can be borne by the specific pile having a higher bearing strength, thereby reducing the horizontal force burden on the other piles.

[0045] A sixth aspect is any one of the first to fifth aspects, in which, in the step of determining the amount of improvement material to be added, the amount of improvement material added is increased in the layers (11a, 11b) at pile head height compared to the lower layer (11d). With this configuration, since the bending moment acting on the pile increases the closer to the pile head, the effect of the bending moment can be suppressed by increasing the amount of improvement material added in the layer at pile head height. Also, the amount of improvement material added in layers lower than the pile head height can be reduced, thereby reducing costs.

[0046] Although the present embodiment and modifications have been described, other embodiments may be obtained by combining the above-described embodiments and modifications in whole or in part.

[0047] Furthermore, the technology of the present invention is not limited to the above-described embodiments, and may be variously changed, substituted, or modified within the scope of the spirit of the technical idea. Furthermore, if the technical idea can be realized in a different way due to technological advances or other derived technologies, it may be implemented using that method. Therefore, the claims cover all embodiments that may fall within the scope of the technical idea. [Explanation of symbols]

[0048] 10a-10l: Pile 11a-11f: layer 12: Section with hard ground 13: Area surrounding a specific pile

Claims

1. A ground improvement method used in combination with pile foundations, Dividing the ground improvement area into a plurality of sections and / or layers and investigating the ground properties; A step of determining the amount of improvement material to be added in consideration of the ground properties for each section and / or each layer; Excavating the ground improvement area to a target depth by dividing it into sections and / or layers; Adding an improvement material to the excavated soil for each section and / or layer and mixing and stirring; and a step of adding an improvement material to the excavated soil and backfilling the improved soil, and compacting the improved soil layer by layer.

2. In the mixing and stirring step, half of the excavated soil in one layer is backfilled and the improvement material is spread, and the remaining half of the excavated soil in one layer is backfilled and mixed and stirred, 2. The method for improving ground according to claim 1, wherein the mixing and stirring step and the compacting step are repeated for the number of target layers.

3. A ground improvement method as described in claim 1 or claim 2, characterized in that in the step of determining the amount of improvement material to be added, the amount of improvement material to be added is reduced for hard sections and / or layers, and the amount of improvement material to be added is increased for soft sections and / or layers.

4. A ground improvement method as described in claim 1 or claim 2, characterized in that in the step of determining the amount of improvement material to be added, the amount of improvement material to be added is reduced in areas where specific piles with larger pile diameters than other piles are to be formed compared to areas where other piles are to be formed.

5. A ground improvement method as described in claim 1 or claim 2, characterized in that in the step of determining the amount of improvement material to be added, the amount of improvement material to be added is increased in areas where specific piles with higher bearing strength than other piles are to be formed compared to areas where other piles are to be formed.

6. 3. A ground improvement method according to claim 1 or claim 2, characterized in that in the step of determining the amount of improvement material to be added, the amount of improvement material to be added is increased in the layer at pile head height compared to the lower layer.

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