Design support system for ground improvement body

Abstract

To provide a design support system for a ground improvement body, capable of optimally designing a ground improvement body so as to suppress uneven settlement while allowing uniform settlement.SOLUTION: A calculation device 20 of a design support system 1 includes an allowable condition registration unit 21 in which the maximum allowable settlement amount and maximum allowable inclination angle are registered, an improvement determination unit 22 which determines whether ground improvement is possible, a specification candidate setting unit 23 which, if it is determined that ground improvement is possible, sets a ground improvement range and sets multiple specification candidate conditions that satisfy each range of the ground improvement range, a settlement amount / inclination angle calculation unit 25 which calculates the maximum settlement amount and maximum inclination angle of the surface improvement body for each of the multiple specification candidate conditions based on the building conditions and ground survey results, and a specification extraction unit 6 which extracts specification conditions in which the maximum settlement amount and maximum inclination angle fall within the maximum allowable settlement amount and maximum allowable inclination angle from among the multiple specification candidate conditions.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a design support system for a ground improvement body consisting of a surface improvement body and a plurality of columnar improvement bodies below the surface improvement body, for the ground of a site on which a building is to be constructed. [Background technology]

[0002] Conventionally, there has been a construction method in which the thickness of a surface improvement body that supports the entire building is changed according to the building load (see, for example, Patent Document 1). In addition, there is a construction method in which a building is supported by multiple columnar improvement bodies (see, for example, Patent Document 2). It is known that surface improvement bodies and columnar improvement bodies are improvement bodies made by solidifying soil and sand with a cement-based solidification material such as cement milk. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7175054 [Patent Document 2] JP 2020-176381 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when planning the construction of a building using each of the above construction methods, since each method has different advantages and disadvantages, it is difficult to keep the settlement and tilt angle of the building within a specified range even if the ground improvement is designed using each of these construction methods. Therefore, it is possible to combine each of these construction methods, but designers with little knowledge of the ground may be confused about the specifications of the improvement structure and may make a wrong choice. This has many disadvantages, such as the building sinking and tilting in the event of ground subsidence or regional subsidence, and the need for long-term maintenance.

[0005] The present invention has been made in consideration of such problems, and its purpose is to provide a design support system for ground improvement bodies that enables even a designer with little geological knowledge to optimally design a ground improvement body that combines a surface improvement body and a columnar improvement body so as to suppress differential settlement while allowing equal settlement. [Means for solving the problem]

[0006] In consideration of the above problems, the design support system for a ground improvement body according to the present invention is a design support system for a ground improvement body consisting of a surface improvement body and a plurality of columnar improvement bodies below the surface improvement body, for the ground of a site on which a building is to be constructed, the design support system comprising a calculation device, the calculation device including an allowable condition registration section in which an allowable maximum subsidence amount and an allowable maximum inclination angle regarding ground subsidence input according to the building conditions of the building to be constructed are registered, an improvement judgment section which judges whether ground improvement using the surface improvement body is possible based on the results of a ground investigation, and a calculation section which judges whether ground improvement using the surface improvement body is possible based on the results of the ground investigation when it is judged that the ground improvement is possible, the calculation device including an allowable condition registration section which registers ... The system is characterized by comprising a specification candidate setting unit that sets the thickness range of the surface improvement body, the diameter and length range of the columnar improvement body, and the pitch range of the columnar improvement body as a ground improvement range based on the result, and sets a plurality of specification candidate conditions that satisfy each range of the ground improvement range; a subsidence / inclination angle calculation unit that calculates the maximum subsidence and maximum inclination angle of the surface improvement body based on the building conditions and the ground survey results for each of the plurality of specification candidate conditions; and a specification extraction unit that extracts specification conditions from the plurality of specification candidate conditions in which the maximum subsidence and the maximum inclination angle fall within the maximum allowable subsidence and the maximum allowable inclination angle.

[0007] According to the present invention, for each of a plurality of specification candidate conditions, based on the maximum subsidence and maximum inclination angle of the surface improvement body calculated by the subsidence amount / inclination angle calculation unit, specification conditions in which the maximum subsidence and maximum inclination angle are within the allowable maximum subsidence and maximum inclination angle, respectively, can be extracted from a plurality of specification candidate conditions. As a result, specification conditions for a ground improvement body that combines a surface improvement body and a columnar improvement body are extracted so as to suppress uneven subsidence while allowing a certain degree of uniform subsidence, even a designer who is not familiar with geotechnical knowledge can select from the plurality of extracted specification conditions and optimally design a ground improvement body.

[0008] In a more preferred embodiment, the specification extraction unit calculates the cost of ground improvement according to each of the extracted specification conditions, and further extracts specification conditions that match preset cost conditions from the extracted specification conditions. According to this embodiment, when there are multiple extracted specification conditions, it is possible to select specification conditions for ground improvement that fall within a predetermined budget.

[0009] In a more preferred embodiment, the calculation device further includes a bearing capacity safety factor calculation unit that calculates, for each of the plurality of candidate specification conditions, from the ground survey results, the allowable bearing capacity per unit area of ​​the lower ground below the ground improvement body, calculates the building load acting from the building per unit area of ​​the lower ground, and calculates the building load relative to the allowable bearing capacity as a bearing capacity safety factor, and the specification extraction unit divides the range of the bearing capacity safety factor according to the building use or ground conditions, and sorts the extracted specification conditions according to each category.

[0010] According to this aspect, the range of the bearing capacity safety factor is divided according to the building use or ground conditions, and the extracted specification conditions are sorted by category, so that a divided specification condition according to the building use or ground conditions can be selected.

[0011] In an even more preferred embodiment, when an embankment is planned to be constructed on the ground on which the ground improvement body is to be placed or when an embankment has already been constructed, the bearing capacity safety factor calculation unit calculates a combined load by multiplying the load of the embankment by a correction coefficient set based on the type of embankment and the elapsed period of construction of the embankment, and adding up the embankment load and the building load, and calculates the combined load relative to the allowable bearing capacity as the bearing capacity safety factor.

[0012] According to this aspect, the bearing capacity safety factor after the construction period can be calculated from the type of embankment and the construction period. This makes it possible to reduce the selection of specification conditions for the ground improvement body with an excessively high bearing capacity safety factor immediately after construction, and to select appropriate specification conditions. Effect of the Invention

[0013] According to the present invention, even a designer with little geological knowledge can optimally design a ground improvement body that combines a surface improvement body and a columnar improvement body so as to suppress differential settlement while allowing equal settlement. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic conceptual diagram of a design support system for a ground improvement body according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a flow diagram of the design support system shown in FIG. [Diagram 3] 2A and 2B are diagrams showing an example of specification candidate conditions set by the specification candidate setting unit shown in FIG. 1; [Figure 4] 2(a) and 2(b) are diagrams for explaining a method of calculating a building load by the bearing capacity safety factor calculation unit shown in FIG. 1. [Diagram 5] 2 is a diagram showing a calculation model by a subsidence amount / tilt angle calculation unit shown in FIG. 1. FIG. [Figure 6] 2 is a table showing the calculation results obtained by the subsidence amount / tilt angle calculation unit shown in FIG. 1. [Figure 7] 2 is a table showing an example of extraction by the specification extraction unit shown in FIG. 1. [Figure 8] FIG. 11 is a diagram for explaining a method of calculating a building load by the bearing capacity safety factor calculation unit shown in FIG. 1 according to a modified example. [Figure 9] (a) is a graph showing the degree of compression of embankments according to the number of years that have passed for each type of embankment, and (b) is a graph showing the safety coefficient (correction coefficient) according to the number of years that have passed for each type of embankment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The design support system 1 for a ground improvement body according to this embodiment will be described below with reference to Figs.

[0016] 1. About ground improvement bodies The design support system 1 in this embodiment is a system that supports the design of a ground improvement body (see, for example, Figure 3, etc.) consisting of a surface improvement body and multiple columnar improvement bodies below the surface improvement body, for the ground of a site where a building is planned to be constructed.

[0017] Here, the surface improvement body is formed by surface ground improvement work, with the aim of increasing the bearing capacity of the soft ground and preventing subsidence. Specifically, surface ground improvement work involves using a backhoe or other tool to mix and stir cement-based solidification material in the ground within 2m of the surface of the planned construction site, and then compacting and solidifying the ground. In plan view, an area slightly larger than the building foundation is improved.

[0018] Columnar improvement bodies are also placed under the surface improvement body to prevent uneven settlement of buildings. Columnar improvement bodies are made by drilling holes while stirring the local soil and solidification material with an auger, and then solidifying the soil into a columnar shape, creating an improvement body called a column in the ground. Unlike piles, columnar improvement bodies do not require a solid supporting layer at the tip, so they can be designed based on the results (data) of ground surveys such as Swedish sounding tests.

[0019] 2. About Design Support System 1 As shown in Fig. 1, the design support system 1 includes an input device 10, a calculation device 20, and an output device 30. The calculation device 20 includes, as hardware, a storage device (not shown) configured with ROM, RAM, etc., and a processing device (not shown) such as a CPU. The input device 10 and the output device 30 are connected to the calculation device 20. In this embodiment, data such as building information is recorded in the storage device via the input device 10. The storage device further stores a program for calculating the maximum settlement amount and maximum inclination angle of the surface improvement body, etc., and this program is executed by the processing device.

[0020] 2. About the arithmetic unit 20 The computing device 20 includes, as software, a condition registration unit 21, an improvement judgment unit 22, a specification candidate setting unit 23, a bearing capacity safety factor calculation unit 24, a settlement amount / inclination angle calculation unit 25, and a specification extraction unit 26. The configuration of the computing device 20 shown in Fig. 1 will be described below with reference to the flow chart shown in Fig. 2.

[0021] 2-1. About the Condition Registration Section 21 The condition registration unit 21 registers the maximum allowable subsidence amount and the maximum allowable inclination angle regarding ground subsidence that are input according to the building conditions of the building to be constructed. In this embodiment, other data and the like are also registered in the condition registration unit 21 by steps S1 to S4 shown in FIG.

[0022] Specifically, in step S1, target performance and calculation conditions are input. Specifically, target performance regarding subsidence is input according to the importance of the building, expected useful life, etc. More specifically, the allowable subsidence amount and allowable inclination angle regarding ground subsidence input according to the building conditions of the building to be constructed, and conditions required for these calculations, etc. are input. As a result, the input conditions are registered in the condition registration unit 21.

[0023] Next, in step S2, building information is input. Specifically, the building information includes the building structure (steel, wood, reinforced concrete), the number of floors (1, 2, 3), foundation specifications (strip footing, slab footing), base width, embedment depth, maximum strip footing interval (only for strip footing), design ground pressure, and design ground line GL. The input conditions are then registered in the condition registration unit 21.

[0024] Next, in step S3, site conditions that will affect the study are input. Specifically, the range of surface improvement, the thickness of the newly developed ground (embankment and backfill soil), and the embankment (separation distance and thickness) of the adjacent land are input as site conditions. The input conditions are then registered in the condition registration unit 21. Here, the following points are checked. When inputting these site conditions, it is checked whether the ground has been loosened when demolishing an existing building, for example by removing a basement, and whether new loads will be generated around the site due to embankments, buildings, etc.

[0025] Next, in step S4, the results of the ground investigation are input. Specifically, the groundwater level, soil quality, and ground strength are input as the results of the ground investigation. The input conditions are then registered in the condition registration unit 21. For example, other than the above, the results of the ground investigation are checked to see if there is a possibility of liquefaction, or if there is a possibility of poor solidification due to the influence of humus. More specifically, in checking the results of the ground investigation, the soil quality and N value are measured for each depth from the ground, and the liquefaction safety factor FL value is calculated to consider the possibility of liquefaction damage. Also, the presence or absence of ground with a high possibility of poor solidification (humus soil, black soil, highly organic soil, peat, peat, etc.) is checked from the boring columnar diagram.

[0026] 2-2. About the improvement determination unit 22 The improvement judgment unit 22 judges whether ground improvement using a surface improvement body is possible based on the results of the ground investigation. Specifically, in step S5, the improvement judgment unit 22 judges from the results of the ground investigation whether there is a possibility of poor solidification due to the influence of humus soil, and whether surface improvement is possible based on the groundwater level (sandy soil). This judgment condition is a general condition, and a detailed explanation will be omitted. If surface improvement cannot be adopted, an alternative construction method is judged.

[0027] Furthermore, the improvement judgment unit 22 judges the liquefaction layer based on the ground survey results. If a liquefaction layer is present, the bearing capacity safety factor calculation unit 24, which will be described later, does not estimate the bearing capacity shallower than the liquefaction layer when considering the short-term bearing capacity.

[0028] 2-3. About specification candidate setting section 23 When the improvement judgment unit 22 judges that ground improvement is possible, the specification candidate setting unit 23 sets the range of thickness of the surface improvement body, the range of diameter and length of the columnar improvement body, and the range of pitch of the columnar improvement body as the ground improvement range based on the site conditions and the results of the ground investigation. Specifically, in steps S1 and S7, the specification candidate setting unit 23 sets the range of thickness of the surface improvement body to about 600 mm to 1800 mm, the range of diameter of the columnar improvement body to 400 mm to 600 mm, the range of length of the columnar improvement body to 2 m to 10 m, and the range of pitch of the columnar improvement body to 1700 mm to 4100 mm, for example.

[0029] The specification candidate setting unit 23 sets a plurality of specification candidate conditions that satisfy each range of the ground improvement range set by the specification candidate setting unit 23. Figures 3(a) and (b) show an example of the specification candidate conditions. Specifically, in step S7 and steps S10 and S11 described later, the specification candidate setting unit 23 sets these specification candidate conditions. For example, the specification candidate setting unit 23 sets the thickness of the surface improvement body (surface improvement thickness) to 600 mm, 900 mm, 1200 mm, 1500 mm, and 1800 mm. The diameter of the columnar improvement body (columnar improvement diameter) is set to 400 mm, 500 mm, and 600 mm, and the length of the columnar improvement body (columnar improvement length) is set to the values ​​in the table shown in Figure 6.

[0030] 2-4. Bearing capacity safety factor calculation section 24 The bearing capacity safety factor calculation unit 24 calculates the building load q' acting on the underlying ground per unit area from the building information (see FIG. 4(a)). Here, the area S on which the underlying ground receives the load is calculated using the foundation type, foundation width B, foundation length L, embedded depth Df, building weight q, depth H from the ground surface to the underlying ground, angle θ at which the building weight is distributed to the underlying ground, etc. At this time, if the foundation is a strip footing, punching fracture strength may be calculated.

[0031] On the other hand, the bearing capacity safety factor calculation unit 24 calculates the allowable bearing capacity per unit area of ​​the lower ground below the ground improvement body (allowable bearing capacity of the lower ground) qa from the ground investigation results for each of the multiple specification candidate conditions (see Figure 4 (b)). The allowable bearing capacity per unit area of ​​the lower ground (vertical bearing capacity) can be calculated by a general method using the formulas etc. published in "(2018 Edition, Design and Quality Control Guidelines for Improved Ground for Buildings - Deep and Shallow Mixing Treatment Method Using Cement-Based Solidification Material)" (Reference 1) etc., so a detailed explanation of the calculation method will be omitted. Finally, the bearing capacity safety factor calculation unit 24 calculates the building load q' for the allowable bearing capacity as the bearing capacity safety factor.

[0032] Specifically, in step S8, the bearing capacity safety factor calculation unit 24 calculates the building load q' that the surface improvement body acts on the underlying ground due to the building weight, etc., and the allowable bearing capacity qa of the underlying ground from the results of the ground investigation. Next, in step S9, the bearing capacity safety factor calculation unit 24 determines whether the allowable bearing capacity qa ≥ building load q', and if this condition is met, proceeds to step S15, and if not, proceeds to step S10.

[0033] In step S10, the specification candidate setting unit 23 calculates the pitch of the columnar improved bodies from the thickness of the surface layer improved bodies, the width and length of the surface layer improved bodies, and the maximum spacing between the slabs by using a general method. In this way, the pitch shown in Figures 3(a) and (b) can be calculated. The specification candidate setting unit 23 may set the pitch of the columnar improved bodies from a value input in advance.

[0034] Next, in step S11, the specification candidate setting unit 23 sets the length of the columnar improved body. The length of the columnar improved body (columnar improved length) is set in increments of 0.1 m from about 1 m to about 8 m. This setting may be performed in step S1 or step S7.

[0035] In step S12, the bearing capacity safety factor calculation unit 24 calculates the allowable bearing capacity Ra per columnar improvement body, calculates the allowable bearing capacity qa' by dividing it by the bearing area per columnar improvement body, and adds it to the allowable bearing capacity qa calculated in step S8. The allowable bearing capacity (qa+qa') thus added is what is referred to in this invention as "the allowable bearing capacity per unit area of ​​the lower ground below the ground improvement body calculated from the ground survey results." The allowable bearing capacity qa' can be calculated by a general calculation method described in the above-mentioned Reference 1, etc.

[0036] In step S13, the bearing capacity safety factor calculation unit 24 judges whether the bearing capacity of the ground improvement body (consisting of the surface improvement body and the columnar improvement body) is acceptable. Specifically, the bearing capacity safety factor calculation unit 24 judges whether the allowable bearing capacity (qa+qa') is equal to or greater than the building load q'. At this time, the bearing capacity safety factor [(qa+qa') / q'], which is the building load q' relative to the allowable bearing capacity (qa+qa'), is calculated. If this condition is satisfied, the process proceeds to step S14, and if not, the process returns to step S11 and the length of the columnar improvement body is increased by 0.1 m. Note that here, instead of the above-mentioned judgment, in step S13, the process may return to step S11 until the bearing capacity safety factor is calculated for all conditions in which the length is changed by 0.1 m increments within the range of the length of the columnar improvement body, and then the process proceeds to step S14 after the calculation of the bearing capacity safety factor for all conditions is completed.

[0037] In step S14, the bearing capacity safety factor calculation unit 24 calculates the improvement body strength Fc2 (columnar improvement Fc2) at which the bearing capacity Ra per columnar improvement acts on the improvement body without destroying it. In step S15, the bearing capacity safety factor calculation unit 24 calculates the improvement body strength Fc1 (surface improvement Fc1) at which the surface improvement body is not destroyed by the load acting on the surface improvement from the bottom surface of the foundation and punching.

[0038] 2-5. Subsidence amount and inclination angle calculation unit 25 The settlement amount / inclination angle calculation unit 25 calculates the maximum settlement amount and maximum inclination angle of the surface layer improvement body for each of a plurality of specification candidate conditions based on the building conditions and the ground investigation results. Specifically, in step S16, as shown in the model in Fig. 5, the stress dispersion method from the virtual ground surface is used to calculate the settlement amount of each part when the surface layer improvement body is viewed in plan, and the maximum settlement amount is extracted from among them. The maximum inclination angle can be calculated from the difference between the maximum settlement amount and the minimum settlement amount of these calculated settlement amounts, and the distance of the section where the maximum settlement amount and the minimum settlement amount occurred when the surface layer improvement body is viewed in plan.

[0039] When calculating the amount of settlement, the thickness of the newly developed ground (banking and fill soil) and the banking soil (distance and thickness) of the neighboring land may be taken into consideration, as shown in Fig. 8, etc., which will be described later. The calculation of the amount of settlement can be performed by a generally known method disclosed in the above-mentioned Reference 1, etc., and therefore a detailed explanation thereof will be omitted.

[0040] 2-6. About specification extraction part 26 The specification extraction unit 26 extracts specification conditions in which the maximum subsidence amount and maximum tilt angle calculated by the subsidence amount / tilt angle calculation unit 25 fall within the allowable maximum subsidence amount and maximum allowable tilt angle from the multiple specification candidate conditions.

[0041] The specification extraction unit 26 determines whether the calculated maximum subsidence and maximum inclination angle are less than the maximum allowable subsidence and maximum allowable inclination angle set in step S16, and if this determination condition is met, proceeds to step S17, and if not, returns to step S10, and the subsidence / inclination calculation unit 25 changes the pitch of the columnar improvement body and performs a series of recalculations.

[0042] Although such a judgment is made in step S16, for example, in step S16, the specification extraction unit 26 may repeat steps S10 to S14 without making a judgment on subsidence, etc., until the maximum subsidence amount and maximum inclination angle are calculated for all specification candidate conditions with different pitches of the columnar improvement body. Furthermore, the specification extraction unit 26 may extract specification conditions from all specification candidate conditions such that the calculated maximum subsidence amount and maximum inclination angle for all specification candidate conditions fall within the maximum allowable subsidence amount and maximum allowable inclination angle. In this case, the result shown in FIG. 6 can be obtained.

[0043] The specification extraction unit 26 may calculate the cost of ground improvement work according to each of the extracted specification conditions. Specifically, in step S17, the specification extraction unit 26 calculates the estimated material cost and construction cost according to the specifications of the surface improvement body and the columnar improvement body.

[0044] In step S18, the specification extraction unit 26 determines whether a series of calculations has been performed for all the specification candidate conditions set in step S7, and if not, returns to step S7, and if completed, proceeds to step S19.

[0045] In step S19, the specification extraction unit 26 outputs the examination results of the specification candidate conditions as a list. Specifically, the output information includes the surface improvement thickness (thickness of the surface improvement body), surface improvement Fc1 (strength of the surface improvement body), columnar improvement diameter (diameter of the columnar improvement body), columnar improvement length (length of the columnar improvement body), columnar improvement pitch (pitch of the columnar improvement body), columnar improvement Fc2 (strength Fc2 of the columnar improvement body), safety factor of bearing capacity, maximum settlement, maximum inclination angle, and estimated cost, as shown in Fig. 6.

[0046] Furthermore, the specification extraction unit 26 may divide the range of the bearing capacity safety factor according to the building use or ground condition, and sort the extracted specification conditions by category. Specifically, in step S20, a specification selection table shown in FIG. 7 is created from the contents of the examination result list created in step S19. The designer assumes the required level based on the importance of the building and the topographical danger, and selects the specifications in consideration of cost-effectiveness. Then, the determined structural examination document is output. Each specification condition shown in FIG. 7 shows the maximum settlement amount, maximum inclination angle, number of improvement bodies, bearing capacity safety factor, and estimated cost.

[0047] In FIG. 7, the range of bearing capacity safety factors is divided into A to E, with the bearing capacity safety factor increasing from E to A. For example, A is a building whose use is, for example, a hospital or a building that handles precision equipment, and the ground condition is a developed valley land. In such a case, an improved structure with one of the specification conditions classified as A is selected. D is a building whose use is, for example, a house with a construction budget restriction, and the terrain is standard land. In such a case, an improved structure with one of the specification conditions classified as D is selected.

[0048] The specification extraction unit 26 further extracts specification conditions that match the preset cost conditions from the extracted specification conditions. Specifically, the specification extraction unit 26 extracts the cheapest cost conditions for each specific category by marking a circle in the table. For example, in FIG. 7, in category A, a specification condition is extracted in which the thickness of the surface improvement body is 1.2 m, and the diameter, length, and pitch of the columnar improvement body are 500 mm, 8.0 m, and 2.9 m. For example, in category A, a specification condition is extracted in which the thickness of the surface improvement body is 1.2 m, and 12 columnar improvement bodies have a diameter of 500 mm, a length of 8.0 m, and a pitch of 2.9 m. Furthermore, in category D, a specification condition is extracted in which the thickness of the surface improvement body is 0.9 m, and 20 columnar improvement bodies have a diameter of 500 mm, a length of 4.5 m, and a pitch of 2.3 m.

[0049] The specification extraction unit 26 further extracts the usage conditions based on the cost conditions. However, for example, it may be possible to divide the range of the maximum subsidence amount and / or the range of the maximum inclination angle, and extract the specification conditions so as to satisfy each of these divided ranges.

[0050] Thus, according to this embodiment, by inputting the ground conditions, building conditions, and surrounding ground conditions, a composite ground design that ensures safety is automatically performed, so the time required for design can be significantly reduced. Furthermore, as shown in FIG. 7, there is not one correct answer for the design of ground reinforcement, so it may be selected through risk communication with the client. With a specification list divided into areas by level for bearing capacity performance, settlement guideline, and cost, it is possible to select specifications after communicating with the client.

[0051] Many building designers are not familiar with specialized knowledge of the ground (soil quality), so even such people can create appropriate and economical designs. In particular, when designing in areas with thick soft ground, instead of securing bearing capacity and settlement with tip bearing capacity like support piles, the surface improvement body and pile-shaped improvement body are supported in the middle layer by the embedment effect and frictional force, which prevents the ground from slipping out (the building is supported by piles, but the ground sinks).

[0052] By creating an artificial ground with ground improvement bodies consisting of surface layer improvement bodies and columnar improvement bodies, it is possible to easily reuse buildings of the same scale when rebuilding. These surface layer improvement bodies and columnar improvement bodies are made with cement-based solidification materials and have excellent long-term durability. In particular, by completely solidifying the ground directly below the foundation with the surface layer improvement bodies, damage caused by liquefaction can be suppressed.

[0053] Even when constructing a large building during reconstruction, both the surface improvement body and the columnar improvement body can be constructed with a strength below that which would be an obstacle to excavation and pile driving work, making it easy to place the ground improvement body. By making the area of ​​the surface improvement body larger than the building, the impact from the surrounding ground (draw-in settlement due to buildings and embankments) can be reduced.

[0054] As shown in the right diagram of Fig. 8, there are cases where embankment is constructed on the ground on which the ground improvement body is to be placed. In such cases, the ground subsidence and embankment shrinkage of the new embankment load will subside over time, and the ground can be treated as normal. The period until the ground stabilizes (subsidence converges) differs depending on the soil type, so it is necessary to consider the soil type accordingly.

[0055] Therefore, as shown in Figure 9(b), a coefficient ε indicating the stability of the embankment ground is set based on the relationship between the period until consolidation settlement converges and the degree of compaction. Specifically, as shown in Figure 9(a), the degree of compaction changes over time for each type of embankment material, such as clay silt, organic soil, and highly organic soil. Therefore, based on this relationship, an embankment stability coefficient (correction coefficient) ε is set as shown in Figure 9(b).

[0056] Specifically, when construction of an embankment is planned on the ground on which the ground improvement body is to be placed, the bearing capacity safety factor calculation unit 24 calculates a combined load (Pm+P) by adding together the building load P and the embankment load Pm, which is calculated by multiplying the load of the embankment by a correction coefficient ε set based on the type of embankment and the period of time since the construction of the embankment shown in Fig. 9(b). Next, the combined load per unit area of ​​the combined load (q'+qm) relative to the allowable bearing capacity qa is calculated as the bearing capacity safety factor. When the bearing capacity safety factor exceeds 1, in other words, when the allowable bearing capacity qa exceeds the combined load, the safety of the ground reinforcement can be ensured.

[0057] According to this aspect, the bearing capacity safety factor after the construction period can be calculated from the type of embankment and the construction period. This makes it possible to reduce the selection of specification conditions for the ground improvement body with an excessively high bearing capacity safety factor immediately after construction, and to select appropriate specification conditions.

[0058] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various design modifications can be made without departing from the spirit of the present invention as described in the claims. [Explanation of symbols]

[0059] 1: Design support system, 21: Condition registration section (allowable condition registration section), 22: Improvement judgment section, 23: Specification candidate setting section, 24: Bearing capacity safety factor calculation section, 25: Settlement amount / inclination angle calculation section, 26: Specification extraction section

Claims

1. A design support system for a ground improvement body comprising a surface improvement body and a plurality of columnar improvement bodies below the surface improvement body, for a ground on a site where a building is to be constructed, The design support system includes a computing device, The computing device includes: a permissible condition registration section in which a permissible maximum subsidence amount and a permissible maximum inclination angle regarding ground subsidence inputted according to the building conditions of a building to be constructed are registered; an improvement judgment unit that judges whether ground improvement is possible using the surface improvement body based on the results of the ground investigation; a specification candidate setting unit which, when it is determined that the ground improvement is possible, sets the range of thicknesses of the surface improvement bodies, the range of diameters and lengths of the columnar improvement bodies, and the range of pitches of the columnar improvement bodies as a ground improvement range based on the conditions of the site and the results of the ground investigation, and sets a plurality of specification candidate conditions which satisfy each range of the ground improvement range; a subsidence amount / inclination angle calculation unit for calculating a maximum subsidence amount and a maximum inclination angle of the surface improvement body based on the building conditions and the ground investigation results for each of the plurality of specification candidate conditions; A design support system for ground improvement bodies, comprising: a specification extraction unit that extracts specification conditions from the multiple specification candidate conditions in which the maximum subsidence and the maximum inclination angle fall within the maximum allowable subsidence and the maximum allowable inclination angle.

2. The design support system for ground improvement bodies as described in claim 1, characterized in that the specification extraction unit calculates the cost of ground improvement according to each of the extracted specification conditions, and further extracts specification conditions that match predetermined cost conditions from the extracted specification conditions.

3. The computing device includes: Further provided is a bearing capacity safety factor calculation unit which calculates an allowable bearing capacity per unit area of ​​the lower ground below the soil improvement body from the soil investigation results for each of the plurality of specification candidate conditions, calculates a building load acting from the building per unit area of ​​the lower ground, and calculates the building load relative to the allowable bearing capacity as a bearing capacity safety factor; The design support system for ground improvement bodies as described in claim 1, characterized in that the specification extraction unit divides the range of the bearing capacity safety factor according to the building use or ground conditions, and sorts the extracted specification conditions according to each division.

4. When embankment is planned to be constructed on the ground on which the ground improvement body is to be placed or when embankment has already been constructed, The design support system for ground improvement bodies as described in claim 3, characterized in that the bearing capacity safety factor calculation unit calculates a combined load by multiplying the load of the embankment by a correction coefficient set based on the type of embankment and the construction period of the embankment, and adding up the embankment load and the building load, and calculates the combined load relative to the allowable bearing capacity as the bearing capacity safety factor.

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