Design method for ground reinforcement structure, design system for ground reinforcement structure, and design program for ground reinforcement structure

Abstract

We provide a design method, design system, and design program for ground reinforcement structures that are specialized in the characteristics of the support structure of ground reinforcement structures. [Solution] The design method includes a bearing capacity review step and a settlement review step. In the bearing capacity review step, the bearing capacity is determined to meet the criteria if the allowable vertical bearing capacity is equal to or greater than the design load level, and the allowable vertical bearing capacity is calculated based on the ultimate bearing capacity of the ground below the surface improvement body, the improvement rate of the surface improvement body, the ultimate bearing capacity and improvement rate of the columnar improvement body, and a safety factor. The design system includes a bearing capacity review section and a settlement review section. The bearing capacity review section determines that the bearing capacity meets the criteria if the allowable vertical bearing capacity is equal to or greater than the design load level, and calculates the allowable vertical bearing capacity based on the ultimate bearing capacity of the ground below the surface improvement body, the improvement rate of the surface improvement body, the ultimate bearing capacity and improvement rate of the columnar improvement body, and a safety factor. The design program causes an information processing device to execute the design method.

Description

[Technical Field]

[0001] The present invention relates to a design method for a ground reinforcement structure, a design system for a ground reinforcement structure, and a design program for a ground reinforcement structure, and in particular to a design method for a ground reinforcement structure, a design system for a ground reinforcement structure, and a design program for a ground reinforcement structure that are specialized in the characteristics of the support structure of the ground reinforcement structure. [Background technology]

[0002] When the ground on which a house, commercial building, or other property lies is weak, ground reinforcement work is carried out to improve the ground and increase its strength by applying artificial treatment to the ground. One known method used in ground reinforcement work is a columnar ground reinforcement structure design method in which a rod with an agitator attached to its bottom end is rotated and driven into the ground while a solidifying material (cement slurry) is discharged from the agitator, and the excavated soil and the solidifying material are stirred and mixed to create a cylindrical improved body, thereby increasing the allowable bearing capacity of soft ground (Patent Document 1).Another known method is a small-diameter steel pipe pile construction method in which small-diameter steel pipe piles are driven into the bearing layer using a small rotary driving device, and the load of a building is supported by multiple small-diameter steel pipe piles. However, these ground reinforcement techniques have some inherent problems. First, piles such as columnar improvement bodies and steel pipe piles are placed in a scattered manner according to the foundation shape and structure of the building, making them difficult to reuse when rebuilding a building and, as a rule, requiring their removal. This removal work is extremely time-consuming; in the case of columnar improvement bodies, the entire length must be crushed and recovered, and in the case of steel pipe piles, the heads must be excavated and pulled out. These tasks require considerable effort and, in some cases, can cost several times more than the cost of ground reinforcement work. Furthermore, when removing a steel pipe pile, the head must be grasped accurately, and if the pile is deteriorated, the removal work becomes extremely difficult, significantly increasing the risk in construction. In addition, removing the steel pipe piles and columnar improvement bodies significantly disturbs the ground, leaving a cavity in the ground after removal. This requires restoration measures such as filling with liquefied treated soil and ground improvement, which increases costs. Furthermore, if restoration measures are not carried out, additional measures will be required, such as setting longer pile lengths and improvement lengths, assuming the ground is loose. Given this background, there are concerns that rebuilding on sites where ground reinforcement has been performed will require restoration obligations and corresponding costs, which could result in potential risks to the ground and a decrease in the asset value of the site. In particular, if the improved ground cannot be reused and ground reinforcement must be carried out again, the impact on the environment cannot be ignored. For example, if we assume that the number of housing starts per year is 800,000, of which approximately 70% will undergo ground reinforcement and another 30% will use the columnar improvement method, then the number of housing units using the columnar improvement method will be approximately 168,000 per year. In this case, if 10 tons of solidification material is used per house, the total amount of solidification material used will reach 1.68 million tons. Assuming that carbon dioxide emissions per ton are 0.4 tons, this will result in a total of approximately 672,000 tons of carbon dioxide being emitted. Furthermore, a large amount of carbon dioxide is also generated when burning the fuel used when removing and reinstalling the piles. Furthermore, the removed piles become a huge amount of industrial waste. Furthermore, when removing existing piles, the ground may become loose, creating a risk of heavy machinery tipping over, and may have a negative impact on the adjacent ground, potentially causing damage to surrounding buildings and retaining walls. Additionally, when rebuilding a building, there are often many buildings nearby, making the lot narrow. In such narrow spaces, the use of large heavy machinery is restricted, significantly reducing workability and raising concerns about work safety. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-040499 Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, the inventor of the present invention has invented a new ground reinforcement structure consisting of a combination of a surface improvement body and a columnar improvement body. The ground reinforcement structure of the present invention is rationally designed by combining a surface improvement body that extends in a plate-like manner from the ground surface to a predetermined depth and multiple columnar improvement bodies that extend in a columnar manner from the bottom of the surface improvement body into the ground, and has many advantages such as the reusability of the columnar improvement bodies, economic efficiency, environmental performance, high design freedom, and reduced impact on the surrounding area. However, the ground reinforcement structure of the present invention is not a structure that transfers the building load directly to the columnar improvement body as in conventional technology, but rather consists of a novel support structure in which the load is widely distributed through the surface improvement body while the columnar improvement body functions to suppress deformation of the surface improvement body, and therefore design methods related to conventional ground reinforcement technology cannot be applied as is. Based on the above, the present invention aims to provide a design method for a ground reinforcement structure, a design system for a ground reinforcement structure, and a design program for a ground reinforcement structure that are specialized for the characteristics of the support structure of the ground reinforcement structure. [Means for solving the problem]

[0005] The design method of the ground reinforcement structure of the present invention is a design method of a ground reinforcement structure which is installed on the foundation ground of a building and comprises a surface improvement body extending in a plate-like shape from the ground surface to a predetermined depth, and a plurality of columnar improvement bodies extending in a columnar shape from the bottom surface of the surface improvement body toward the ground, and comprises a bearing capacity examination step of examining the bearing capacity of the ground reinforcement structure, and a subsidence amount examination step of examining the subsidence amount of the ground reinforcement structure, and in the bearing capacity examination step, the allowable vertical bearing capacity (kN / m 2 ) is the design load (kN / m 2 ) or more, the bearing capacity is judged to satisfy the specified standard, and the allowable vertical bearing capacity is calculated by multiplying the ultimate bearing capacity (kN / m 2 ), the improvement rate of the surface improvement body, and the ultimate bearing capacity of the columnar improvement body (kN / m 2 ) and the improvement rate of the columnar improved body, and the safety factor.

[0006] In the design method of the ground reinforcement structure of the present invention, in the bearing capacity examination step, if the target ground does not include new embankment, or if the target ground includes new embankment and the thickness of the new embankment is equal to or less than the thickness from the ground surface to the bottom surface of the surface improvement body, the design load intensity is calculated based on the load intensity of the building (kN / m 2 ) and the load of the surface improvement body (kN / m 2 ) and if the target ground includes new fill and the thickness of the new fill is greater than the thickness from the ground surface to the bottom of the surface improvement body, the design load intensity is calculated based on the load intensity of the building (kN / m 2 ) and the load intensity of the new embankment (kN / m 2 ) may be calculated based on

[0007] In the design method of the ground reinforcement structure of the present invention, in the bearing capacity examination step, when the target ground does not include new embankment, the allowable vertical bearing capacity (q a ) is the following (Equation 1), and the ultimate bearing capacity of the ground below the surface improvement body in (Equation 1) (q d ) may be represented by the following formula (2): TIFF0007761242000002.tif20150 TIFF0007761242000003.tif20150

[0008] In the design method of the ground reinforcement structure of the present invention, in the bearing capacity examination step, if the target ground includes a new embankment and the thickness of the new embankment is equal to or less than the thickness from the ground surface to the bottom surface of the surface improvement body, the allowable vertical bearing capacity (q a ) is the following (Equation 1), and the ultimate bearing capacity of the ground below the surface improvement body in (Equation 1) (q d ) may be represented by the following formula (3): TIFF0007761242000004.tif20150 TIFF0007761242000005.tif20150

[0009] In the design method of the ground reinforcement structure of the present invention, in the bearing capacity examination step, if the target ground includes a new embankment and the thickness of the new embankment is greater than the thickness from the ground surface to the bottom of the surface improvement body, the allowable vertical bearing capacity (q a ) may be represented by the following (Equation 4): TIFF0007761242000006.tif20150

[0010] In the design method of the ground reinforcement structure of the present invention, in the bearing capacity consideration step, when the target ground includes new embankment and the thickness of the new embankment is greater than the thickness from the ground surface to the bottom of the surface improvement body, the design load intensity (σ1) is given by the following (Equation 5), and the time reduction coefficient in Equation 5 may be a coefficient whose value gradually decreases with the passage of time since the construction of the new embankment, and whose value gradually decreases as the thickness of the consolidation target layer that continues directly below the new embankment becomes smaller. TIFF0007761242000007.tif13150

[0011] In the design method for a ground reinforcement structure of the present invention, in the subsidence amount consideration step, it is confirmed that the estimated subsidence amount (m) of the ground reinforcement structure in the target ground is below an allowable value, and the estimated subsidence amount (S) may be determined as follows (Equation 6): TIFF0007761242000008.tif13150

[0012] In the design method of the ground reinforcement structure of the present invention, in the settlement amount examination step, when the target ground includes a new embankment, the calculation formula for the settlement amount of the ground reinforcement structure includes the new embankment load level (kN / m 2 ) and new embankment load intensity (σ E ) may be formed by the following (Equation 7), and the time-dependent reduction coefficient in Equation 7 may be a coefficient whose value gradually decreases as time passes since the construction of the new embankment, and whose value gradually decreases as the thickness of the consolidation target layer that continues directly below the new embankment decreases. TIFF0007761242000009.tif13150

[0013] The design system for a ground reinforcement structure of the present invention is a design system for a ground reinforcement structure that is installed on the foundation ground of a building and comprises a surface improvement body that extends in a plate-like shape from the ground surface to a predetermined depth, and a plurality of columnar improvement bodies that extend in a columnar shape from the bottom of the surface improvement body into the ground, and comprises a bearing capacity evaluation unit that evaluates the bearing capacity of the ground reinforcement structure, and a subsidence amount evaluation unit that evaluates the subsidence amount of the ground reinforcement structure, and the bearing capacity evaluation unit evaluates the allowable vertical bearing capacity (kN / m 2 ) is the design load (kN / m 2 ) or more, the bearing capacity is judged to satisfy the specified standard, and the allowable vertical bearing capacity is calculated by multiplying the ultimate bearing capacity (kN / m 2 ), the improvement rate of the surface improvement body, and the ultimate bearing capacity of the columnar improvement body (kN / m 2 ), the improvement rate of the columnar improvement body, and the safety factor, and the settlement amount examination section confirms that the estimated settlement amount (m) of the ground reinforcement structure in the target ground is within the allowable value.

[0014] The design program for a ground reinforcement structure of the present invention is characterized by causing an information processing device to execute a design method for a ground reinforcement structure. [Effects of the Invention]

[0015] The design method, design system, and design program for a ground reinforcement structure of the present invention can provide a design method specialized for the characteristics of the support structure of the ground reinforcement structure.

[0016] The ground reinforcement structure of the present invention is configured to support the building load via a surface improvement body constructed on top of a columnar improvement body, so the piles can be reused when rebuilding a building, eliminating the need for removal work as in the past. This eliminates the costs and labor burden of restoring the ground to its original state and the risk of damaging the asset value of the site. Furthermore, because the piles do not need to be removed, there is no risk of loosening the ground and adversely affecting the surrounding ground. Furthermore, since the existing columnar improvement bodies can be reused when rebuilding, it is possible to eliminate the construction and resource consumption associated with both restoration and new ground reinforcement. This also contributes to the prevention of global warming by reducing carbon dioxide emissions associated with the use of solidification materials and the operation of heavy machinery. In addition, since the surface improvement body supports the building load while the columnar improvement body is primarily responsible for suppressing deformation of the surface improvement body, it is possible to significantly reduce the number of pile bodies compared to conventional columnar improvement methods, and even when the construction costs of the surface improvement body are added, the overall construction costs are cheaper. In addition, because the surface improvement body is placed between the building foundation and the columnar improvement body, there is a high degree of flexibility in the placement of the piles, and a wide range of allowable placement is possible. As a result, a high degree of freedom in design is possible according to the shape of the site and the properties of the ground. [Brief explanation of the drawings]

[0017] [Figure 1] Illustration of the design method for ground reinforcement structures [Figure 2] Flowchart of design method for ground reinforcement structure [Figure 3] Diagram of the ground reinforcement structure [Figure 4] Illustration of ground reinforcement structure (with restraining ribs) [Figure 5] Illustrative diagram of the range of underground stress dispersion [Figure 6] Explaining the reduction coefficient over time [Figure 7] Illustrative diagram of increasing underground stress [Figure 8] Illustrative diagram of the increased underground stress when the target ground includes new embankment [Figure 9] Illustrative diagram of increased underground stress when the adjacent land includes new fill DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, the design method for a ground reinforcement structure, the design system for a ground reinforcement structure, and the design program for a ground reinforcement structure of the present invention will be described in detail with reference to the drawings. [Example]

[0019] <1> Design method for ground reinforcement structures (Figures 1 and 2) The design method for a ground reinforcement structure of the present invention is a design method for installing an effective ground reinforcement structure A that is suited to ground conditions. The design method for a ground reinforcement structure includes a ground survey step S1, a specification setting step S2, a bearing capacity consideration step S3, and a subsidence consideration step S4. In the ground investigation step S1, the target ground on which the ground reinforcement structure A is to be installed (hereinafter referred to as "target ground") is investigated. In the specification setting step S2, the specifications of the ground reinforcement structure A are set based on the survey results. In the bearing capacity examination step S3, the allowable vertical bearing capacity of the target ground is examined based on the set specifications. If it is determined that the bearing capacity does not satisfy the predetermined standard value, the process returns to the specification setting step S2 and resets the specifications so that the standard value is satisfied. If it is determined that the bearing capacity satisfies the predetermined standard value, the process proceeds to the settlement amount examination step S4. In the subsidence amount examination step S4, the subsidence amount of the target ground is examined based on the set specifications. If the examination determines that the subsidence amount exceeds a predetermined allowable value, the process returns to the specification setting step S2 and resets the specifications so that the subsidence amount is equal to or less than the allowable value. If the subsidence amount is determined to be equal to or less than the predetermined allowable value, the examination is terminated and the specifications are finalized.

[0020] <1.1> Scope of application The scope of application of the design method for a ground reinforcement structure of the present invention can be set arbitrarily. In this example, the scope of application is as follows: [Applicable buildings] Floor: 3rd floor or below Design ground pressure of foundation: 100kN / m 2 below Foundation type: slab foundation, strip foundation Uses: Residential, apartment complexes, stores, offices, etc. [Applicable ground] Clayey soil and sandy soil (including gravelly soil) [Non-applicable ground and how to deal with it] Humus soil, acidic soil pH ≦ 4: Conduct a mix test to confirm the design standard strength, and replace the soil. Rock mass, boulders, gravel ground: soil replacement Ground where groundwater continues to be supplied: Implementing water-stopping measures

[0021] <1.2> Ground reinforcement structure (Fig. 3) The ground reinforcement structure A is a newly designed structure that can be reused semi-permanently when rebuilding a building without removing the improved body from the ground. The ground reinforcement structure A comprises at least a surface improvement body A2 extending in a plate-like shape from the ground surface to a predetermined depth, and a plurality of columnar improvement bodies A1 extending in a columnar shape from the bottom surface of the surface improvement body A2 toward the ground. The ground reinforcement structure A is structured so that the load of the building is supported mainly by the surface improvement body A2 that solidifies the entire ground, and the deformation of the surface improvement body A2 is suppressed by multiple columnar improvement bodies A1. Therefore, compared to the conventional columnar improvement method, the number of columnar improvement bodies and / or their diameters can be reduced, making construction less costly. Furthermore, since the bottom surface of the surface improvement body A2 is supported by multiple columnar improvement bodies A1, the surface improvement body A2 does not need to be directly supported on the supporting layer, and it can be applied even when the bottom surface of the surface improvement body A2 is located at a depth shallower than the supporting layer or when the groundwater level is high.

[0022] <1.3> Restraining rib (Fig. 4) The ground reinforcement structure A may be provided with restraining ribs A21 that protrude downward from the outer periphery of the surface improvement body A2. The restraining ribs A21 may be provided in a square shape when viewed from the bottom, surrounding the entire periphery of the bottom of the surface improvement body A2, or may be provided only on two opposing side edges of the bottom of the surface improvement body A2, or may be provided only on one side edge. By providing restraining ribs A21 on the bottom surface of the surface improvement body A2 and restraining the ground at the bottom of the surface improvement body A2 between the restraining ribs A21, it is possible to achieve the same embedment effect as a ground reinforcement structure A in which the entire surface has been improved, and to improve the bearing capacity of the entire ground reinforcement structure A. This makes it possible to reduce the amount of solidification material used and reduce carbon dioxide emissions compared to improving the entire structure.

[0023] <1.4> Function of ground reinforcement structure The ground reinforcement structure A exhibits a remarkable ground reinforcement effect due to the synergistic effect of the columnar improvement body A1 and the surface improvement body A2. In detail, by extending the surface improvement body A2 outward from the building foundation, the load of the building is distributed, the center of gravity of the building is moved closer to the center of the surface improvement body A2, and the outer periphery has reserve capacity for deformation and bearing capacity, thereby improving resistance to differential settlement. Furthermore, by supporting the bottom surface of the surface improvement body A2 with multiple columnar improvement bodies A1 through peripheral friction force, deformation of the surface improvement body A2 is prevented and the uneven subsidence prevention force of the surface improvement body A2 can be maintained.

[0024] <1.5> Construction method of ground reinforcement structure The ground reinforcement structure A is constructed, for example, in the following manner. (1) A columnar improvement device is placed at the position where the columnar improvement body A1 is to be formed, and the mixing device is rotated and pressed into the ground from the ground surface to excavate the ground to a predetermined excavation depth. (2) While rotating the mixing device, a cement-based solidification material is injected below the depth of the dry excavation and mixed with the excavated soil, forming columnar improved bodies A1 of a predetermined length in the ground using cylindrical improved soil. The pitch of the columnar improved bodies A1 should preferably be within six times the diameter of the columnar improved bodies A1. (3) Using heavy machinery such as a backhoe, the ground is excavated to a specified depth, and the bottom surface is flattened using the backhoe bucket. (4) Spread cement-based solidification material on the excavated soil and mix it with the backhoe bucket, taking care to avoid unevenness, to produce improved soil. At this time, the improved soil at the top of the columnar improved body A1 is mixed with the excavated soil. (5) Compact the improved soil with a compaction roller. Compaction is generally performed every 30 cm of the improved soil thickness, and mixing, stirring, and compaction are repeated a predetermined number of times depending on the thickness of the surface improvement body A2.

[0025] <1.6> Reuse of ground reinforcement structures If the ground reinforcement structure A satisfies certain conditions, it can be reused even after the building is rebuilt. In order to reuse the ground reinforcement structure A, crushed stone is placed on the surface of the surface improvement body A2 when the foundation of the building is installed, and the foundation is then built on top of the crushed stone. This makes it possible to protect the surface of the surface improvement body A2 from damage when the existing building is demolished before reconstruction. When rebuilding a building, ensure that all of the following conditions (1) to (5) are met. (1) No new earthworks will be carried out. (2) Allowable vertical bearing capacity q a (kN / m 2 ) is the design load σ1 (kN / m 2 ) or above. (3) The planned building must not extend beyond the existing ground reinforcement structure A. (4) There are no problems with the foundation shape (for example, a foundation with an elevator pit or semi-basement). (5) There are no problems with the quality inspection. If any of the conditions are not met, the design will be reconsidered to determine whether it can be reused. For example, in condition (3), if the planned building protrudes outside the existing ground reinforcement structure A, by constructing additional columnar improvement bodies A1 and surface improvement bodies A2 on the outside of the existing ground reinforcement structure A, condition (3) may be met and the ground reinforcement structure A may be able to be reused.

[0026] <2> Ground investigation steps The ground investigation step S1 is a step for investigating the target ground of the ground reinforcement structure A. In the ground investigation step S1, for example, a preliminary investigation S11, a main investigation S12, and an additional investigation S13 are carried out based on an investigation plan. The soil investigation step S1 obtains at least site information and ground information. Site information includes elevation differences (levels) within the site or between adjacent land, the soundness of structures, and the development status. Ground information includes soil quality, groundwater conditions (water level, inflow status, etc.), the status of fill and fill soil (soil quality, degree of compaction, number of years since development, etc.), and the presence or absence of humus soil that may be prone to poor solidification.

[0027] <2.1> Preliminary survey The preliminary survey S11 is a survey conducted prior to the main survey to determine the quality of the ground and any problems. In the preliminary survey S11, information such as the topography and geology of the target ground, the results of nearby ground surveys, and disaster history is obtained from materials such as maps, topographical classification maps, geological classification maps, hazard maps, neighborhood data, development plans, and current status survey maps. The preliminary survey S11 makes it possible to estimate the survey depth and select the survey points, thereby making the survey more efficient and effective. In particular, for developed ground (newly filled land, newly filled land, etc.) that has a high risk of subsidence, it is necessary to collect sufficient data.

[0028] <2.2> Main Survey This survey S12 consists of a field survey of the target ground and a site reconnaissance. In this example, the on-site investigation is carried out using an SWS test (screw weight penetration test). The SWS test is a test that aims to determine the hardness, thickness, and inclination of the stratum. The SWS test is carried out, for example, using the following procedure. (1) Select the measurement points for the test. In principle, four or more measurement points should be set up, and the measurement points should basically be located near the four corners of the building. (2) Level the ground surface at the measurement point and install the screw point of the SWS tester vertically into the ground. The SWS tester may be manual, semi-automatic, or fully automatic. (3) Rotate the screw point and penetrate it into the ground while gradually applying the specified load. (4) The number of revolutions required for penetration is measured, and at the same time the hardness of the soil and the bearing capacity of the ground are evaluated. The test is conducted with Nsw ≥ 150 and a penetration length of 10 m (up to 20 m if there is a continuous soft layer). (5) If penetration becomes impossible or abnormal values ​​are observed, change the measurement point or conduct additional investigations as described below. A site survey is conducted in conjunction with the SWS test. During the site survey, the target ground and surrounding environment are observed, and information is collected on the condition of the structure, the condition of adjacent buildings, the condition of the retaining wall, the thickness and extent of the new fill soil, the thickness and extent of the new fill soil, the number of years since construction, etc.

[0029] <2.3> Additional investigation Additional survey S13 is a survey to confirm the ground conditions that could not be confirmed in the main survey. For example, in S12 of this survey, if the SWS tester cannot penetrate the ground due to rubble or a hard layer, a standard penetration tester or dynamic cone penetration tester will be used to investigate the depths beyond the impenetrable layer. Also, if the presence of organic soil or strongly acidic soil is suspected, samples will be taken using an SPT sampler or similar. Based on these findings, the findings of this study will be supplemented and revised.

[0030] <3> Specification setting steps The specification setting step S2 is a step for setting the specifications of the ground reinforcement structure A. In the specification setting step S2, the specifications of the surface improvement body A2 and the columnar improvement body A1 are set based on the site information and ground information obtained in the ground investigation step S1.

[0031] <3.1> Specifications of the surface improvement body The specifications of the surface improvement body A2 include, for example: (1) Layer thickness: A standard value is set, and the thickness is set based on the standard value, taking into consideration the ground conditions (hardness or softness of the ground, water level, etc.). If a restraining rib A21 is provided, the layer thickness of the restraining rib A21 part and the layer thickness inside the restraining rib are set separately. (2) Design strength: Design ground pressure σ of the foundation e (kN / m 2 ) The lower limit is set taking into consideration the stress distribution between the columnar improvement body and the ground between the columnar improvement body. (3) Amount of solidifying material to be mixed: A lower limit is set to ensure the design standard strength. The lower limit is set separately for each type of soil, such as sandy soil or clayey soil. If there is concern about poor solidification, mixing tests and early strength checks are conducted to manage the construction quality so that the design standard strength can be reliably achieved. (4) Improvement range: The range should be at least the building position (outer edge of the foundation), and should be approximately 1m outward as a standard. The range should also be set taking into consideration the site conditions, the use of vacant land, and the possibility of enlarging the building when it is rebuilt. If there are structures or buildings near the boundary of the site, a distance should be secured between their edge and the edge of the surface improvement work.

[0032] <3.2> Specifications of columnar improved body The specifications of the columnar improved body A1 include, for example, the following: (1) Improved diameter: Set an upper limit, a lower limit, and a standard value, and set the standard value within the range of the upper limit and lower limit. (2) Design standard strength: Design ground pressure σ e (kN / m 2 ) The lower limit is set taking into consideration the stress distribution between the columnar improvement body and the ground between the columnar improvement body. (3) Amount of solidifying material to be mixed: A lower limit is set to ensure the design standard strength. The lower limit is set individually for each type of soil, such as sandy soil, clayey soil, and loam. If there is concern about poor solidification, mix tests and early strength checks are conducted to manage the construction quality so that the design standard strength can be reliably achieved.

[0033] <3.3> Consideration of existing retaining walls If there is an existing retaining wall to the side of the target ground, the specifications can be set based on the structure, location, stability, etc. of the existing retaining wall. For example, if the safety of the existing retaining wall cannot be confirmed, the design will be such that the weight of the building does not act on the existing retaining wall. Also, if the columnar improvement body is eccentric to the inside of the site, a standard foundation will be used if the building fits within an imaginary line 30° outward from the end of the columnar improvement head, but if it does not fit, a cantilever-type foundation reinforcement will be used.

[0034] <4> Bearing capacity examination step The bearing capacity examination step S3 is a step for examining the bearing capacity of the target ground. In the bearing capacity examination step S3, the allowable vertical bearing capacity q of the target ground is calculated. a (kN / m 2 ) is the design load σ1 (kN / m 2 ) or more, the bearing capacity is judged to meet the standard value. In this example, if the target ground includes a new embankment, the settlement of the new embankment may not have converged, and the ground is unstable, so the allowable vertical bearing capacity q aThe impact of new embankments is taken into account when examining the above. Here, "new embankments" refers to embankments that have been constructed within a certain period of time. In this example, embankments that have been constructed less than five years ago are defined as new embankments. In this case, the weight of the new embankment is reflected in the calculation of the design load intensity σ1. Specifically, in this example, the allowable vertical bearing capacity q a and design load intensity σ1 are calculated separately for <4.1> the case where the target ground does not include new embankment, and <4.2> the case where the target ground includes new embankment. In addition, if the target ground includes new embankment, they are divided into <4.2.1> the case where the thickness of the new embankment is equal to or less than a specified thickness, and <4.2.2> the case where the thickness of the new embankment exceeds a specified thickness, and are calculated according to the classification in Table 1 below. The contents of each formula will be explained later.

[0035] [Table 1] However, the present invention is not limited to the above, and for example, a design may be made in which the influence of new embankment is not taken into consideration in the bearing capacity consideration step S3.

[0036] <4.1> When the target ground does not include new fill If the target ground does not contain new fill, the allowable vertical bearing capacity can be calculated by apportioning the ultimate bearing capacity of the ground below the surface improvement body A2 and the ultimate bearing capacity of the columnar improvement body A1 by their respective improvement rates. Therefore, the allowable vertical bearing capacity q a (kN / m 2 ) is calculated using the following formula (1). [Formula 1] TIFF0007761242000011.tif20150 where, q d is the ultimate bearing capacity (kN / m 2 ), R u is the ultimate bearing capacity of columnar improved body A1 (kN), A p is the cross-sectional area of ​​the columnar improved body A1 (m 2 ), a S is the improvement rate of columnar improvement body A1, F s indicates the safety factor, respectively.

[0037] Ultimate bearing capacity q of the lower ground of the surface improvement body A2 d can be calculated using Terzaghi's bearing capacity formula as the sum of the bearing capacity due to the adhesion of the soil, the bearing capacity due to the weight of the ground below the base of the foundation and the width of the foundation, and the bearing capacity due to the thickness of the soil cover at the root section. Therefore, the ultimate bearing capacity q d (kN / m 2 ) is calculated using the following (Equation 2). [Formula 2] TIFF0007761242000012.tif13150where α·β is the shape factor of the foundation, B b is the width of the foundation (m), c is the adhesion strength of the supporting ground (kN / m 2 ), Nc·Nγ·Nq is the bearing capacity coefficient, i c i γ i q is the correction coefficient for the load inclination, γ1 is the unit volume weight of the supporting soil (kN / m 3 ), γ2 is the unit weight of the embedded part (kN / m 3 ), D' f indicates the depth (m) from the ground surface to the bottom of the surface improvement body A2, respectively.

[0038] If the target ground does not contain new fill, the design load intensity σ1 is the load intensity acting on the lower part of the surface improvement body A2, and can be calculated by adding together the load intensity of the building and the load intensity of the surface improvement body A2. Therefore, the design load σ1 (kN / m 2 ) is calculated using the following (Equation 8). [Formula 8] TIFF0007761242000013.tif13150 where σ e is the design contact pressure of the foundation (kN / m 2 ), B is the short side of the foundation (m), L is the long side of the foundation (m), B' is the short side of the underground stress distribution range (m), L' is the long side of the underground stress distribution range (m), γ3 is the unit volume weight of the surface improvement body A2 (kN / m 3 ), D ’ 1 indicates the thickness (m) of the surface improvement body A2, respectively. The range of underground stress distribution in the surface improvement area can be defined by a dispersion angle of 1:2 (approximately 26.7 degrees) (Figure 5).

[0039] <4.2> When the target ground includes new embankment If the target ground includes new embankment, the ground is not stable, so the allowable vertical bearing capacity q of the new embankment a and the effect on the design load intensity σ1 must be considered. Therefore, in this case, it is further examined whether the thickness h (m) of the new embankment exceeds a predetermined thickness. In this example, the predetermined thickness of the new embankment is the depth D from the ground surface to the bottom surface of the surface improvement body A2. ’ f (m) is adopted. Here, the "bottom surface of the surface improved body" refers to the bottom surface of the main body of the surface improved body A2 surrounded by the restraining ribs A21 when the surface improved body A2 is equipped with the restraining ribs A21.

[0040] <4.2.1> When the thickness of the new embankment is less than the specified thickness The thickness h of the new embankment is the depth D from the ground surface to the bottom of the surface improvement body A2. ’ f The impact of new embankments is considered to be limited in the following cases: Therefore, <4.1> As in the case where the target ground does not include new embankment, the allowable vertical bearing capacity q a is calculated using equation (1), and the design load intensity σ1 is calculated using equation (6). However, the ultimate bearing capacity q of the lower ground of the surface improvement body A2 d In this case, the embedment effect corresponding to the thickness of the new embankment cannot be expected, so this is excluded. Therefore, the ultimate bearing capacity q d (kN / m 2 ) is calculated using the following (Equation 3). [Formula 3] TIFF0007761242000014.tif13150where α·β is the shape factor of the foundation, B b is the width of the foundation (m), c is the adhesion strength of the supporting ground (kN / m 2 ), Nc·Nγ·Nq is the bearing capacity coefficient, i c i γ i q is the correction coefficient for the load inclination, γ1 is the unit volume weight of the supporting soil (kN / m 3), γ2 is the unit weight of the embedded part (kN / m 3 ), D' f indicates the depth (m) from the ground surface to the bottom of the surface improvement body A2, and h indicates the thickness (m) of the new fill.

[0041] <4.2.2> When the thickness of the new embankment exceeds the specified thickness The thickness h of the new embankment is the depth D from the ground surface to the bottom of the surface improvement body A2. ’ f If it is larger than this, the bottom surface of the surface improvement body A2 will be supported only by the bearing capacity of the columnar improvement body A1 deeper than the new soft embankment, so the allowable vertical bearing capacity q a From the calculation formula, the ultimate bearing capacity q of the lower ground of the surface improvement body A2 d Exclude. Therefore, the allowable vertical bearing capacity q a (kN / m 2 ) is calculated using the following (Equation 4). [Formula 4] TIFF0007761242000015.tif20150Here, Ru is the ultimate bearing capacity (kN) of columnar improved body A1, and Af is the area (m 2 ), and Fs is the safety factor.

[0042] The thickness h of the new embankment is the depth D from the ground surface to the bottom of the surface improvement body A2. ’ f If it is larger, the design load intensity σ1 will be the load intensity acting on the bottom of the new embankment, and can be calculated by adding up the load intensity of the building and the load intensity of the new embankment. Therefore, the design load σ1 (kN / m 2 ) is calculated using the following (Equation 5). [Formula 5] TIFF0007761242000016.tif13150 where σ e is the design contact pressure of the foundation (kN / m 2 ), γ4 is the unit volume weight of the new embankment (kN / m 3 ), h is the thickness of the new embankment (m), D f indicates the embedded depth of the foundation (m), and η indicates the time-dependent reduction coefficient.

[0043] <4.2.3> Reduction coefficient over time (Fig. 6) The time-dependent reduction coefficient η is a coefficient that reflects the convergence of consolidation settlement over time after the construction of new embankment. New fills undergo gradual consolidation settlement over time after construction, and settlement often converges within 3 to 5 years. The time it takes for consolidation settlement to converge is also greatly affected by the drainage distance of the ground. Drainage distance refers to the distance from a certain point to a permeable layer (gravel layer, ground surface, etc.) when water drains from the ground under pressure. Therefore, the drainage distance differs greatly between ground with a continuous, thick layer of consolidation target deposits and ground with a sand layer deposited in between, and the time it takes for consolidation settlement to converge also differs greatly. Therefore, when calculating the design load intensity σ1, the load intensity of the new embankment is multiplied by a time-dependent reduction coefficient η to reflect the elapsed time since the construction of the new embankment and the drainage distance. Specifically, the time-dependent reduction coefficient η is set to gradually decrease with the passage of time since the construction of the new embankment. Also, the time-dependent reduction coefficient η is set to gradually decrease as the thickness of successive layers to be consolidated decreases. The aging reduction coefficient η can be set, for example, as shown in Table 2 below.

[0044] [Table 2] However, the present invention is not limited to the above, and may be designed, for example, so that the calculation of the design load intensity σ1 does not reflect the time-dependent reduction coefficient η, or so that the time-dependent reduction coefficient η reflects only the time since construction, without reflecting the thickness of successive layers to be consolidated. Note that, as the consolidation characteristics by region are accumulated, a table of time-dependent reduction coefficients η set by region may be created and used.

[0045] <5> Subsidence amount examination step The subsidence amount examining step S4 is a step for examining the amount of subsidence of the target ground. In the subsidence amount examining step S4, it is confirmed that the estimated amount of subsidence S of the ground reinforcement structure in the target ground is equal to or less than the allowable value. In this example, the estimated settlement S is calculated at nine points, including the four corners and middle part of the building, and the maximum inclination angle is calculated based on the estimated settlement S. If the estimated settlement S and maximum inclination angle at each point are each below the allowable values, it is determined that the settlement meets the standards. The design criteria follow the content of the guidelines of the time. The estimated settlement S is the amount of settlement due to consolidation settlement of the ground, and is normally calculated using the Mv method, which is an equivalent load surface method that utilizes the pile group effect. However, it is also possible to conduct laboratory tests and obtain the estimated settlement S using the Cc method, e-logP method, etc. Specifically, the estimated settlement S (m) of the ground reinforcement structure A at each point is calculated using the following (Equation 6). [Formula 6] TIFF0007761242000018.tif13150where m v is the volumetric compressibility coefficient (m 2 / kN), Δσ z is the increased stress in the ground (kN / m 2 ), and H indicates the thickness of the layer to be consolidated (m). However, the present invention is not limited to the above, and for example, a design may be adopted in which the maximum tilt angle is not considered in the subsidence amount consideration step S4.

[0046] <5.1> Increasing underground stress (Fig. 7) The increased stress Δσz (kN / m 2 ) is calculated by dividing the underground stress distribution range of the target ground into areas that share each point using the rectangular division method and adding up the underground incremental stress Δσz in each area. Incremental stress Δσ at depth Z (m) in each area z (kN / m 2 ) is calculated using the following equation (9), which is an integration of the Boussinesq formula. [Formula 9] TIFF0007761242000019.tif26156Here, m is B / Z, n is L / Z, B is the short side of the foundation (m), L is the long side of the foundation (m), and σ3 is the building load acting on the subgrade (kN / m 2 ) are shown respectively.

[0047] Building load acting on the underlying ground σ3 (kN / m 2 ) is distributed to the underground stress distribution range via the columnar improvement body A1, and is calculated using the following equation (10). [Formula 10] TIFF0007761242000020.tif20150Here, B is the short side of the foundation (m), L is the long side of the foundation (m), B' is the short side of the underground stress distribution range (m), L' is the long side of the underground stress distribution range (m), and W is the building load intensity (kN / m 2 ) are shown respectively. The building load intensity W can be the average building load intensity modeled for consolidation settlement studies. In this case, for example, depending on the number of floors in the building, the load intensity for a first-floor building is 10 kN / m 2 , 12kN / m for two-story buildings 2 , 3-storey: 16kN / m 2 It can be divided into the following categories:

[0048] <5.2> When the target ground includes new embankment (Fig. 8) When the target ground includes new embankment, the calculation formula for the settlement of ground reinforcement structure A is z New embankment load σ E can be reflected. Specifically, the building load intensity σ3 in the above equation (9) is calculated by the new embankment load q e and the increased underground stress Δσ due to the new embankment is z Calculate the increased underground stress Δσ due to the building load σ3 z (kN / m 2 ) and the increased underground stress Δσ due to the new embankment z are added together and substituted into the above equation (4) to calculate the estimated subsidence (S). New embankment load q e (kN / m 2 ) is calculated using the following (Equation 7). [Formula 7] TIFF0007761242000021.tif13150Here, h is the thickness of the new embankment (m), γ4 is the unit volume weight of the new embankment (kN / m 3 ), and η are the coefficients of reduction over time. The time-dependent reduction coefficient η is a coefficient that reflects the time that has passed since the construction of the new embankment and the drainage distance, and for example, the values ​​in Table 2 above can be used. However, the present invention is not limited to the above, and may be, for example, a design that does not reflect new embankment load in the calculation of underground increased stress, or a design that does not reflect the time-dependent reduction coefficient η in the calculation of new embankment load.

[0049] <5.3> When the adjacent land includes new fill (Figure 9) If there is a new embankment on the land adjacent to the target ground, the new embankment load σ E (kN / m 2 ) may be reflected in the target ground. In detail, the new embankment load σ of the new embankment on the neighboring land adjacent to the target ground on all four sides E is calculated using the above formula (5), and added to the building load intensity σ3 of the target ground using the rectangular division method to obtain the underground incremental stress Δσ z Calculate the following. Even if there is no new fill on the land adjacent to the target ground, if the adjacent land is low and there is a possibility that new fill will be constructed in the future, the impact of the new fill can be reflected. Furthermore, in the case of newly developed ground where no building has been built until now, the impact of the load of a building to be constructed on the adjacent land can also be reflected.

[0050] <6> Design system for ground reinforcement structures The design system 1 for a ground reinforcement structure is a system for implementing a design method for a ground reinforcement structure. The design system 1 includes at least a specification setting unit 10, a bearing capacity review unit 20, and a settlement amount review unit 30. The design system 1 is comprised of a central processing unit (CPU), storage devices (SSD, HDD, memory, etc.), input devices (keyboard, mouse, touch panel, etc.), output devices (display, printer, etc.), and communication devices (network interface, wireless communication module, etc.). Specifically, among the components constituting the design system 1, for example, the bearing capacity analysis unit 20 and the settlement amount analysis unit 30, perform the necessary calculations using the central processing unit (CPU) and store the calculation process and result data in the storage device (SSD, HDD, etc.). Furthermore, they receive setting information and data from the user through the input device (keyboard, mouse, etc.) and display and output the results through the output device (display, printer, etc.). Data communication with external systems and other computer environments can be performed through the communication device. The design system 1 can also be implemented in a cloud environment, and hybrid operation in combination with an on-premise environment is also possible. These configurations are well known, and therefore will not be described in detail here. The design system 1 may be configured to be implemented by causing a computer to function using a design program stored on a computer-readable storage medium, such as an SSD, HDD, USB flash memory, SD card, Blu-ray (registered trademark) disc, cloud storage, etc. [Explanation of symbols]

[0051] 1 Design System 10 Specification Setting Section 20 Bearing Capacity Analysis Department 30 Subsidence amount examination section A Ground reinforcement structure A1 Columnar improvement body A2 Improved surface layer A21 Restraining rib S1 Ground investigation step S11 Preliminary survey S12 Main Survey S13 Additional investigation S2 Specification Setting Steps S3 Bearing capacity study step S4 Subsidence amount consideration step

Claims

1. A design method for a ground reinforcement structure comprising a surface improvement body that is installed in the ground directly under the foundation of a building, expanding outward from the foundation of the building, and extending in a plate-like shape from the ground surface to a predetermined depth, and a plurality of columnar improvement bodies that extend in a columnar shape from the bottom surface of the surface improvement body into the ground, A bearing capacity examination step for examining the bearing capacity of the ground reinforcement structure, and a subsidence amount examination step for examining the subsidence amount of the ground reinforcement structure, In the supporting capacity examination step, Allowable vertical bearing capacity of the target ground (kN / m ２ ) is the design load (kN / m ２ ) or more, it is determined that the bearing capacity satisfies the specified standard, The allowable vertical bearing capacity is calculated by the ultimate bearing capacity (kN / m ２ ), the improvement rate of the surface improvement body, and the ultimate bearing capacity of the columnar improvement body (kN / m ２ ) Calculated based on the improvement rate and safety factor of the columnar improved body, If the target ground does not include new embankment, or if the target ground includes new embankment and the thickness of the new embankment is equal to or less than the thickness from the ground surface to the bottom of the surface improvement body, the design load intensity is calculated based on the design ground pressure (kN / m 2 ) of the foundation of the building and the load intensity (kN / m 2 ) of the surface improvement body, When the target ground includes new embankment and the thickness of the new embankment is greater than the thickness from the ground surface to the bottom surface of the surface improvement body, the design load intensity (σ 1 ) is calculated based on the following (Equation 5): The time-dependent reduction coefficient in the (Equation 5) is a coefficient whose value gradually decreases with the passage of time from the construction of the new embankment, and whose value gradually decreases as the thickness of the consolidation target layer immediately below the new embankment decreases. Design methods for ground reinforcement structures. (where σ e is the design ground pressure of the foundation (kN / m 2 ), γ 4 is the unit volume weight of the new embankment (kN / m 3 ), h is the thickness of the new embankment (m), D f is the embedded depth of the foundation (m), and η is the time-dependent reduction coefficient.)

2. In the supporting capacity examination step, If the target ground does not include new embankment, The above-mentioned allowable vertical support capacity (q ａ ) is expressed by the following (Equation 1), and the ultimate bearing capacity (q ｄ ) is characterized in that it is represented by the following formula (2): A method for designing a ground reinforcement structure according to claim 1. (However, q ｄ is the ultimate bearing capacity of the ground below the surface improvement body (kN / m ２ ), R ｕ is the ultimate bearing capacity of the columnar improved body (kN), A ｐ is the cross-sectional area of ​​the columnar improvement body (m ２ ), a Ｓ is the improvement rate of the columnar improvement body, F ｓ indicates the safety factor, respectively.) (where α and β are the shape coefficients of the foundation, B ｂ is the width of the foundation (m), c is the adhesion strength of the supporting ground (kN / m ２ ), Nc, Nγ, and Nq are bearing capacity coefficients, i ｃ ・i γ ・i ｑ is the correction coefficient for the load inclination, γ １ is the unit volume weight of the supporting soil (kN / m ３ ), γ ２ is the unit weight of the embedded part (kN / m ３ ), D' ｆ indicates the depth (m) from the ground surface to the bottom of the surface improvement body A2.)

3. In the supporting capacity examination step, If the target ground includes new embankment and the thickness of the new embankment is equal to or less than the thickness from the ground surface to the bottom of the surface improvement body, The allowable vertical bearing capacity (qa) is expressed by the following (Equation 1), and the ultimate bearing capacity (q ｄ ) is characterized in that it is represented by the following formula (3): A method for designing a ground reinforcement structure according to claim 1. (However, q ｄ is the ultimate bearing capacity of the ground below the surface improvement body (kN / m ２ ), R ｕ is the ultimate bearing capacity of the columnar improved body (kN), A ｐ is the cross-sectional area of ​​the columnar improvement body (m ２ ), a Ｓ is the improvement rate of the columnar improvement body, F ｓ indicates the safety factor, respectively.) (where α and β are the shape coefficients of the foundation, B ｂ is the width of the foundation (m), c is the adhesion strength of the supporting ground (kN / m ２ ), Nc, Nγ, and Nq are bearing capacity coefficients, i ｃ ・i γ ・i ｑ is the correction coefficient for the load inclination, γ １ is the unit volume weight of the supporting soil (kN / m ３ ), γ ２ is the unit weight of the embedded part (kN / m ３ ), D' ｆ indicates the depth (m) from the ground surface to the bottom of the surface improvement body A2, and h indicates the thickness (m) of the new embankment.

4. In the supporting capacity examination step, If the target ground includes new embankment and the thickness of the new embankment is greater than the thickness from the ground surface to the bottom of the surface improvement body, The above-mentioned allowable vertical support capacity (q ａ ) is characterized in that it is represented by the following (Formula 4): A method for designing a ground reinforcement structure according to claim 1. (However, R ｕ is the ultimate bearing capacity (kN) of the improved column excluding the surface friction force generated in the new embankment. ｆ is the area covered by one columnar improvement body (m ２ ), F ｓ indicates the safety factor, respectively.)

5. In the subsidence amount examination step, Confirm that the estimated settlement (m) of the ground reinforcement structure in the target ground is within the allowable value, The estimated subsidence amount (S) is expressed by the following (Equation 6): A method for designing a ground reinforcement structure according to claim 1. (However, m ｖ is the volume compression coefficient (m ２ / kN), Δσ ｚ is the increased stress in the ground (kN / m ２ ), and H indicates the thickness of the layer to be consolidated (m).

6. In the subsidence amount examination step, If the target ground includes new embankment, In the calculation formula for the amount of settlement of the ground reinforcement structure, the new embankment load level (kN / m ２ ) and The new embankment load level (σ Ｅ ) is represented by the following (Equation 7): The time-dependent reduction coefficient in the formula 7 is a coefficient whose value gradually decreases with the passage of time from the construction of the new embankment, and whose value gradually decreases as the thickness of the consolidation target layer immediately below the new embankment decreases. A method for designing a ground reinforcement structure according to claim 5. (where h is the thickness of the new embankment (m), γ ４ is the unit volume weight of the new embankment (kN / m ３ ), and η is the coefficient of reduction over time.

7. A design system for a ground reinforcement structure comprising a surface improvement body that is installed in the ground directly under the foundation of a building, extending outward from the foundation of the building, and extending in a plate-like shape from the ground surface to a predetermined depth, and a plurality of columnar improvement bodies that extend in a columnar shape from the bottom surface of the surface improvement body into the ground, a bearing capacity review unit that reviews the bearing capacity of the ground reinforcement structure; and a subsidence amount review unit that reviews the subsidence amount of the ground reinforcement structure, The bearing capacity examination unit, Allowable vertical bearing capacity of the target ground (kN / m ２ ) is the design load (kN / m ２ ) or more, it is determined that the bearing capacity satisfies the specified standard, The allowable vertical bearing capacity is calculated by the ultimate bearing capacity (kN / m ２ ), the improvement rate of the surface improvement body, and the ultimate bearing capacity of the columnar improvement body (kN / m ２ ) Calculated based on the improvement rate and safety factor of the columnar improved body, If the target ground does not include new embankment, or if the target ground includes new embankment and the thickness of the new embankment is equal to or less than the thickness from the ground surface to the bottom of the surface improvement body, the design load intensity is calculated based on the design ground pressure (kN / m 2 ) of the foundation of the building and the load intensity (kN / m 2 ) of the surface improvement body, When the target ground includes new embankment and the thickness of the new embankment is greater than the thickness from the ground surface to the bottom surface of the surface improvement body, the design load intensity (σ 1 ) is calculated based on the following (Equation 5): The time-dependent reduction coefficient in the (Equation 5) is a coefficient whose value gradually decreases with the passage of time from the construction of the new embankment, and whose value gradually decreases as the thickness of the consolidation target layer immediately below the new embankment decreases. Design system for ground reinforcement structures. (where σ e is the design ground pressure of the foundation (kN / m 2 ), γ 4 is the unit volume weight of the new embankment (kN / m 3 ), h is the thickness of the new embankment (m), D f is the embedded depth of the foundation (m), and η is the time-dependent reduction coefficient.)

8. A method for causing an information processing device to execute the design method for a ground reinforcement structure according to any one of claims 1 to 6, A design program for ground reinforcement structures.

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