Method for constructing soil cement improved bodies
By measuring and predicting compressive strength in real-time during construction, the method ensures the quality and performance of soil-cement improved bodies, addressing the challenge of ensuring structural integrity and reducing costs and risks.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- TAISEI CORP
- Filing Date
- 2025-01-17
- Publication Date
- 2026-07-30
AI Technical Summary
Existing methods for constructing soil-cement improved bodies lack a reliable and efficient way to ensure the quality and performance of the improved body, particularly in terms of compressive strength, which is crucial for supporting structures like underground buildings.
A method involving real-time measurement of compressive strength at multiple ages during construction, generating a compressive strength estimation formula, and adjusting the cement milk mix or injection amount based on estimated values to ensure the compressive strength meets predetermined thresholds.
Ensures the quality of the soil-cement improved body by accurately predicting and adjusting the compressive strength, reducing material costs and carbon emissions, and minimizing construction risks such as cracking.
Smart Images
Figure 2026123738000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method for constructing a soil-cement improved body by mixing cement milk into soil and sand in the ground.
Background Art
[0002] Conventionally, when performing ground improvement methods or pile methods, it has been practiced to construct a soil-cement improved body by mixing cement into soil and sand in the ground. In this case, since it is important to control the compressive strength of the soil-cement, methods for estimating the compressive strength of the soil-cement have been proposed. (See Patent Documents 1 and 2).
[0003] Patent Document 1 discloses a method for estimating the strength of soil-cement. Specifically, this method for estimating the strength of soil-cement includes a step of drying an unconsolidated sample of soil-cement formed by mixing cement milk and on-site generated soil to measure the water content of the unconsolidated sample, a step of pulverizing the dried unconsolidated sample and using a fluorescent X-ray analyzer to measure the content of a predetermined element in the unconsolidated sample, a step of calculating the content of the predetermined element of cement in the unconsolidated sample using the content of the predetermined element in the unconsolidated sample and the content of the predetermined element in the on-site generated soil, a step of calculating the effective cement water ratio of the unconsolidated sample using the water content of the unconsolidated sample and the content of cement calculated from the content of the predetermined element of cement, and a step of estimating the compressive strength of the soil-cement from the correlation data between the effective cement water ratio and the compressive strength.
[0004] Patent Document 2 describes a method for estimating the compressive strength of soil cement. Specifically, this method for estimating the compressive strength of soil cement involves setting construction conditions defined by the physical properties of the soil particles contained in the soil cement, the mixing ratio of the cement milk contained in the soil cement, and the constituent materials of the cement milk contained in the soil cement, calculating a relationship formula between the cement-water ratio of the soil cement under these construction conditions and the compressive strength of the soil cement at a predetermined age, calculating the cement-water ratio of the soil cement from the measured density of the soil cement, and substituting this calculated cement-water ratio into the aforementioned relationship formula to estimate the compressive strength of the soil cement at a predetermined age. [Prior art documents] [Patent Documents]
[0005] [Patent Document 1] Japanese Patent Publication No. 2022-110876 [Patent Document 2] Japanese Patent Publication No. 2015-59325 [Overview of the Initiative] [Problems that the invention aims to solve]
[0006] The object of this invention is to provide a method for constructing a soil-cement improved body that can ensure the quality of the improved body. [Means for solving the problem]
[0007] The inventors have discovered that, as a method for constructing soil-cement improved bodies, instead of conducting a compressive strength test on soil-cement at 28 days of age and changing the cement milk mix or injection amount based on whether the 28-day compressive strength falls below the target strength, the quality and performance of the soil-cement improved body can be ensured by measuring the compressive strength of the soil-cement in near real-time, estimating the compressive strength at 28 days of age and over the long term, and then changing the cement milk mix or injection amount based on these estimated values. The first invention is a method for constructing a soil-cement improved body by mixing cement milk with soil in the ground (for example, ground 2 described later) to construct a soil-cement improved body (for example, soil-cement improved body 3 described later), comprising the steps of: constructing the soil-cement improved body by mixing cement milk with soil in the ground while taking a test specimen from the soil-cement improved body under construction (for example, step S2 described later); measuring the compressive strength of the test specimen at an early stage and at multiple ages (for example, 3 days and 7 days); and determining the age and compressive strength of the test specimen based on the measured early compressive strength. The method is characterized by comprising: generating a compressive strength estimation formula (for example, the compressive strength estimation formula p1 described later) that represents the correlation of compressive strengths, and estimating the compressive strength of the soil cement constituting the soil cement improved body at 28 days of age based on the compressive strength estimation formula (for example, step S3 described later); and determining whether the estimated compressive strength at 28 days of age exceeds a predetermined threshold, and if this determination is negative, adjusting the cement milk mixture and / or injection amount, and constructing the soil cement improved body again (for example, steps S4 and S5 described later).
[0008] According to this invention, test specimens are taken from a soil-cement improved body during construction, and the compressive strength of the specimens is measured at an early stage and at multiple ages. Next, a compressive strength estimation formula is generated that represents the correlation between age and compressive strength based on the compressive strength measured at multiple ages. Then, the compressive strength of the soil-cement at 28 days is estimated based on this compressive strength estimation formula. Finally, it is determined whether the estimated compressive strength at 28 days exceeds a predetermined threshold, and if this determination is negative, the mixture composition, such as the amount of solidifying agent and water in the cement grout, and the amount of cement grout injected into the ground are adjusted, and the soil-cement improved body is constructed further. Therefore, since the compressive strength of soil cement at 28 days of age can be determined in near real-time, the quality of the soil cement improved material can be ensured.
[0009] The method for constructing a soil-cement improved body of the second invention is characterized in that the solidifying agent of the cement milk is blast furnace cement, and the blast furnace cement is such that, when the total content of ordinary Portland cement and blast furnace slag is set to 100% by mass, the content of ordinary Portland cement is 40% by mass or less, and the content of blast furnace slag is 40% by mass or more and 90% by mass or less.
[0010] According to this invention, the solidifying agent for cement milk is blast furnace cement, the content of ordinary Portland cement in this blast furnace cement is 40% by mass or less, and the blast furnace slag content is 40% by mass or more and 90% by mass or less. As a result, the amount of ordinary Portland cement used can be reduced, and carbon dioxide emissions can be reduced. Furthermore, since blast furnace slag is less expensive than ordinary Portland cement, increasing the proportion of blast furnace slag used can reduce material costs. This, in turn, can lower overall construction costs. Furthermore, blast furnace slag has a low heat output during hydration reactions, which helps suppress the temperature rise of soil-cement improved bodies during large-scale construction. This reduces the risk of cracking in soil-cement improved bodies and improves their quality.
[0011] The third invention provides a method for constructing a soil-cement improved body, comprising: measuring the compressive strength of the specimen at 28 days of age; generating a compressive strength estimation formula for ages after 28 days (for example, the compressive strength estimation formula p2 described later) that represents the correlation between age and compressive strength, based on the compressive strength at 28 days of age in addition to the compressive strength at an earlier age measured; estimating the compressive strength of the soil-cement after 28 days of age based on the compressive strength estimation formula (for example, step S8 described later); and determining whether the estimated compressive strength at a specific age after 28 days of age exceeds a predetermined threshold; and if this determination is negative, adjusting the cement milk mix and / or injection amount (for example, steps S9 and S12 described later).
[0012] According to this invention, the long-term compressive strength after 28 days of age was estimated based on the compressive strength at multiple ages, including 28 days of age. It was then determined whether the estimated long-term compressive strength at a specific age exceeded a predetermined threshold. If the result of this determination was negative, the cement milk mixture was adjusted to continue constructing the soil cement improved body, or the load acting on the SMW was redesigned. Therefore, because the long-term compressive strength of soil cement can be determined early on, the quality of the soil cement improved body can be ensured when it is put into service. [Effects of the Invention]
[0013] According to the present invention, a method for constructing a soil-cement improved body that can ensure the quality of the improved soil-cement body is provided. [Brief explanation of the drawing]
[0014] [Figure 1] This is a longitudinal cross-sectional view of a soil cement improved body constructed by a method for constructing a soil cement improved body according to one embodiment of the present invention. [Figure 2] Figure 1 is a cross-sectional view of SMW II. [Figure 3] This is a longitudinal cross-section of the underground structure of a building constructed using SMW (Single-Mass Web Formation). [Figure 4] This is a flowchart (part 1) of the procedure for constructing the soil cement improved body that makes up the SMW. [Figure 5] This is a flowchart (part 2) of the procedure for constructing the soil cement improved body that makes up the SMW. [Figure 6] This figure shows the compressive strength estimation formula generated based on the uniaxial compressive strength at 3 days and 7 days of age. [Figure 7] This figure shows the compressive strength estimation formula generated based on the uniaxial compressive strength at 3 days, 7 days, and 28 days of age. [Modes for carrying out the invention]
[0015] As a method for constructing a soil-cement improved body, a compressive strength estimation formula is generated based on the compressive strengths of the soil-cement at multiple ages, and the compressive strength at 28 days of age and the long-term compressive strength are estimated according to this compressive strength estimation formula. It is determined whether or not the estimated compressive strength at 28 days of age exceeds a predetermined threshold value. If this determination is No, the blending ratio of the solidifying material (cement) and water is reviewed. Further, it is determined whether or not the estimated long-term (for example, 56 days of age) compressive strength exceeds a predetermined threshold value. If this determination is No, the blending ratio of the solidifying material (cement) and water is reviewed, or the design of the soil-cement improved body is reviewed. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of an SMW (Soil Mixing Wall) 1 constructed by a method for constructing a soil-cement improved body according to an embodiment of the present invention. FIG. 2 is a sectional view taken along line I-I of the SMW 1 in FIG. 1. As shown in FIG. 3, the SMW 1 is provided outside the underground structure 11 of the building 10 and has a function of supporting the earth pressure, and also has a function as a main pile of this underground structure 11 (utilization of the SMW main pile). The SMW 1 includes a plurality of soil-cement improved bodies 3 constructed side by side in the ground 2, and an H-shaped steel 4 inserted inside the soil-cement improved body 3. Each soil-cement improved body 3 is constructed by mixing cement milk with the earth and sand in the ground 2 by an earth auger (not shown). Thus, in the building 10 of the present embodiment, since the SMW 1 is also used as a main pile, the compressive strength of the soil-cement improved body 3 is important.
[0016] The solidifying material of the cement milk is blast furnace cement. When the total content of ordinary Portland cement and blast furnace slag is 100% by mass in blast furnace cement, the content of ordinary Portland cement is 40% by mass or less, and the content of blast furnace slag is 40% by mass or more and 90% by mass or less. For example, the soil-cement improved body is 3 per 1 m of the target soil, 280 kg of the solidifying material (blast furnace cement type B), 10 kg of bentonite, W / C (water-cement ratio) 200%, 560 kg of water, and volume 0.66 m3 This was used as the standard formulation. In this embodiment, at least one of the amounts of solidifying agent and water is adjusted from this standard formulation.
[0017] The procedure for constructing the soil cement improved body 3 described above will be explained below with reference to the flowcharts in Figures 4 and 5. In Step S1, a soil cement mix test is conducted indoors to determine the cement milk mix. In step S2, cement grout is mixed with the soil in the ground to begin the construction of the soil-cement improved body 3, and test specimens are taken from the soil-cement improved body 3 during construction (either unconsolidated specimens or core samples).
[0018] In step S3, the compressive strength of the specimens taken in step S2 is measured at an early stage and at multiple ages (e.g., 3 days and 7 days), and a compressive strength estimation formula p1 representing the correlation between age and compressive strength is generated based on the measured early compressive strength of the specimens. Then, based on the compressive strength estimation formula p1, the compressive strength of the soil cement constituting the soil cement improved body 3 at 28 days is estimated. For example, as shown in Figure 6, a compressive strength estimation formula p1 is generated based on the uniaxial compressive strength at 3 days and 7 days of age.
[0019] Here, if we let σ be the age of the soil cement and q(σ) be the uniaxial compressive strength of the soil cement at this age σ, then with α and β as parameters, the following equation (1) holds. q(σ)=αβσ / (ασ+β) ···(1) Therefore, the values of α and β are determined for the uniaxial compressive strength at 3 days and 7 days of age such that equation (1) holds, and the compressive strength estimation equation p1 is generated.
[0020] In step S4, it is determined whether the estimated compressive strength at 28 days of age exceeds a predetermined threshold. This predetermined threshold is the compressive strength sufficient to support the underground structure 11. If the determination is No, the process proceeds to step S5; if the determination is Yes, the process proceeds to step S6. In step S5, since the compressive strength of the soil cement at 28 days is not expected to be sufficient, the mixture and injection amount of cement milk, such as the amount of solidifying agent and water, are adjusted, and the process proceeds to step S2. In step S6, since the compressive strength of the soil cement at 28 days is expected to be sufficient, construction of the soil cement improved body 3 is continued.
[0021] In other words, according to steps S1 to S6, the compressive strength of the soil cement at 28 days is estimated based on the compressive strength of the specimen (step S3), and the mixture and injection amount of cement milk, such as the amount of solidifying agent and water, are adjusted until this estimated compressive strength at 28 days exceeds a predetermined threshold.
[0022] In step S7, after the soil cement has reached 28 days of age, the compressive strength of the 28-day-old specimen is measured, and it is determined whether this actual 28-day-old compressive strength exceeds a predetermined threshold. If the determination is Yes, the examination of the compressive strength of the soil cement is completed; if the determination is No, the process proceeds to step S8.
[0023] In step S8, a long-term (after 28 days of age) compressive strength estimation formula p2 is generated, which represents the correlation between age and compressive strength, based on the compressive strength at 28 days of age, in addition to the compressive strength at earlier ages (e.g., 3 days and 7 days of age) that have already been measured. Then, based on this long-term compressive strength estimation formula p2, the compressive strength of the soil-cement improved body 3 at the time of service (i.e., at the time of construction of the underground structure 11) is estimated. The long-term compressive strength estimation formula p2 is generated by finding α and β that satisfy equation (1), as described above. For example, as shown in Figure 7, the compressive strength estimation formula p2 is generated based on the uniaxial compressive strength at 3 days, 7 days, and 28 days of age.
[0024] In step S9, it is determined whether the estimated compressive strength during operation exceeds a predetermined threshold. If the determination is Yes, the process proceeds to step S10; otherwise, the process proceeds to step S12. In step S10, since the compressive strength of the soil cement at the time of commissioning is expected to be sufficient, the plan is made to construct the underground structure 11 at the time of commissioning. In step S11, the compressive strength of the test specimen is measured during use, and it is determined whether this actual compressive strength during use exceeds a predetermined threshold. If the determination is No, the process moves to step S12; if the determination is Yes, the examination of the compressive strength of the soil cement is completed.
[0025] In step S12, the construction of the soil-cement improved body 3 is continued by adjusting the mixture and injection amount of cement milk, such as the amount of solidifying agent and water, or by changing the design of the underground structure 11.
[0026] This embodiment provides the following effects. (1) Sample specimens are taken from the soil-cement improved body 3 during construction, and the compressive strength of the specimens is measured at 3 days and 7 days of age. Next, based on these measured compressive strengths at multiple ages, a compressive strength estimation formula p1 is generated that represents the correlation between age and compressive strength. Next, based on this compressive strength estimation formula p1, the compressive strength of the soil-cement at 28 days of age is estimated. Then, it is determined whether the estimated compressive strength at 28 days of age exceeds a predetermined threshold. If this determination is negative, the mixture of cement grout, including the amount of solidifying agent and water, and the amount of cement grout injected into the ground are adjusted, and the soil-cement improved body 3 is constructed further. Therefore, since the compressive strength of the soil cement can be confirmed before 28 days of age, the compressive strength of the soil cement at 28 days of age can be grasped in near real time, and the quality of the improved soil cement body 3 can be ensured. In other words, the compressive strength of the soil cement at 28 days is estimated based on the compressive strength of the test specimen, and the mixture and injection amount of cement grout, such as the amount of solidifying agent and water, are adjusted until this estimated compressive strength at 28 days exceeds a predetermined threshold. Therefore, insufficient compressive strength of the soil cement can be quickly corrected, improving construction efficiency and thus reducing construction costs.
[0027] (2) The solidifying agent for the cement milk is blast furnace cement, with the content of ordinary Portland cement in this blast furnace cement being 40% by mass or less, and the blast furnace slag being 40% by mass or more and 90% by mass or less. This reduces the amount of ordinary Portland cement used and reduces carbon dioxide emissions. Furthermore, since blast furnace slag is less expensive than ordinary Portland cement, increasing the proportion of blast furnace slag used can reduce material costs. This, in turn, can lower overall construction costs. Furthermore, blast furnace slag has a low heat output during hydration reactions, which helps suppress the temperature rise of soil-cement improved bodies during large-scale construction. This reduces the risk of cracking in soil-cement improved bodies and improves their quality.
[0028] (3) Based on the compressive strength at 3 days, 7 days, and 28 days of age, the long-term compressive strength of the soil-cement improved body 3 at the time of service was estimated. Then, it was determined whether the estimated long-term compressive strength at the time of service exceeded a predetermined threshold, and if the result of this determination was negative, the cement milk mix was adjusted to continue the construction of the soil-cement improved body 3, or the load acting on SMW1, i.e., the structure of the underground structure 11, was redesigned. Thus, since the long-term compressive strength of the soil cement can be determined early, the quality of the soil-cement improved body 3 at the time of service can be ensured. In other words, by estimating the long-term compressive strength after 28 days of age based on compressive strength values at multiple ages prior to 28 days of age, including 28 days of age, it becomes possible to predict the long-term compressive strength. This allows for understanding the long-term performance of the soil-cement improved body at 28 days of age. Furthermore, by estimating the long-term compressive strength using a compressive strength estimation formula and confirming that this estimated long-term compressive strength exceeds a predetermined threshold, the reliability of the design can be improved. In addition, by reviewing the design based on the estimated long-term compressive strength, necessary improvements can be implemented efficiently. This reduces unnecessary rework and saves costs and time.
[0029] Furthermore, the present invention is not limited to the embodiments described above, and any modifications, improvements, etc., that can achieve the objectives of the present invention are included within the scope of the present invention. For example, in this embodiment, a soil-cement improved body was used to construct an SMW (Soil-Cement Continuous Wall), but the invention is not limited to this, and the soil-cement improved body may be in the shape of columns or cubes. [Explanation of Symbols]
[0030] 1…SMW 2…Ground 3…Soil-cement improved body 4…H-beam 10...Building 11...Underground structure
Claims
1. A method for constructing a soil-cement improved body by mixing cement grout with soil and sand in the ground, A procedure for constructing a soil-cement improved body by mixing cement grout with soil in the ground, and for taking test specimens from the soil-cement improved body under construction, The procedure involves measuring the compressive strength of the specimen at an early stage and at multiple ages, generating a compressive strength estimation formula that represents the correlation between age and compressive strength based on the measured early compressive strength of the specimen, and estimating the compressive strength of the soil cement constituting the soil cement improved body at age 28 based on the compressive strength estimation formula. A method for constructing a soil-cement improved body, comprising the steps of: determining whether the estimated compressive strength at 28 days of age exceeds a predetermined threshold; if this determination is negative, adjusting the composition and / or injection amount of the cement milk, and then constructing the soil-cement improved body again.
2. The solidifying agent of the cement milk is blast furnace cement. The method for constructing a soil cement improved body according to claim 1, characterized in that, when the total content of ordinary Portland cement and blast furnace slag is set to 100% by mass, the content of ordinary Portland cement is 40% by mass or less, and the content of blast furnace slag is 40% by mass or more and 90% by mass or less.
3. The procedure involves measuring the compressive strength of the specimen at 28 days of age, generating a compressive strength estimation formula for ages 28 and beyond that represents the correlation between age and compressive strength, based on the compressive strength measured at earlier ages and the compressive strength at 28 days of age, and estimating the compressive strength of the soil cement at ages 28 and beyond based on the compressive strength estimation formula. A method for constructing a soil cement improved body according to claim 1 or 2, comprising the steps of determining whether the compressive strength at a specific age after 28 days of age, as estimated above, exceeds a predetermined threshold, and if this determination is negative, adjusting the composition and / or injection amount of the cement milk.