Method for predicting mixing ratio of granular soil improvement material and method for improving soft soil

Abstract

To provide an excellent method for predicting a mixing ratio of ground improvement materials with high accuracy using only measured values of simple field experiments.SOLUTION: When using a granular soil improvement material that is expected to have a compaction effect due to granularity improvement, a mixing ratio (volume ratio) of the granular soil improvement material is predicted using hardness of the ground before improvement measured by a Yamanaka soil hardness tester and the CBR required for the improved ground. As the granular soil improvement material, it is preferable to use steel slag. According to the present invention, an appropriate mixing ratio can be obtained using the measured values of a simple test that can be performed on-site.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for predicting the mixing ratio of a granular soil improvement material and a method for improving soft ground using a granular soil improvement material, particularly a granular soil improvement material. [Background technology]

[0002] Methods for improving soft ground include (A) chemical ground improvement, which is expected to cause a hardening reaction between cement-lime and soil particles, and (B) physical ground improvement by compaction using improvement materials that are expected to improve grain size. Of these, (B) ground improvement materials that are expected to improve grain size include natural crushed stone, natural sand, concrete rubble, etc., and in recent years, ground improvement materials made from steel slag have begun to be used in Japan. Although the inventors have developed and sold a product called Geotizer (registered trademark) made from steel slag, it has not yet become widespread nationwide because cement-lime systems are widely used as ground improvement materials in Japan.

[0003] Here, the difference in evaluation indexes is thought to be the reason why it has not been widely adopted nationwide. Cement and lime-based improvement materials are generally evaluated by uniaxial compressive strength, but ground improvement materials that are expected to improve granularity, such as the above-mentioned geotizer, cannot be evaluated by uniaxial compressive strength. Instead, the improvement effect can be evaluated by a different strength index than the conventional ones, such as CBR (California Bearing Ratio: roadbed soil bearing capacity ratio, indicates the relative strength for evaluating the strength of the roadbed or roadbed. Measured by the CBR test specified in JIS A1211) or cone index (a strength index used to determine the strength characteristics of the ground and the drivability of construction machinery. Measured by the cone index test specified in JIS A1228), but it is not well known.

[0004] Therefore, the inventors have been promoting awareness of the evaluation by CBR and cone index in order to promote the use of ground improvement materials using slag. For example, the method disclosed in Patent Document 1 is a method of evaluating the ground improvement materials using molten slag or blast furnace slag with the cone index. However, the above technology is not expected to improve the grain size, but is a method of expecting a solidification effect of the ground using fine powder of molten / blast furnace slag, so the effect is similar to that of the cement-lime system.

[0005] In order to further popularize grain-improved soil improvement materials that use slag, it is necessary for sales representatives to be able to quickly propose quantities and estimates on-site and to eliminate the need for the laborious task of laboratory mix tests. There is therefore a growing demand for a method to predict mix ratios using only the measurements of simple tests that can be performed on-site. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2006-175413 A Summary of the Invention [Problem to be solved by the invention]

[0007] To provide an excellent method for predicting the mixing ratio of a ground improvement material with high accuracy using only the measured values ​​of a simple field experiment, and a method for improving soft ground using this method. [Means for solving the problem]

[0008] In order to solve the above problems, (1) A method for predicting the mixing ratio of particle-improved ground improvement materials, which is characterized by determining the mixing ratio of the particle-improved ground improvement materials using the hardness of the ground before improvement measured with a Yamanaka soil hardness meter and the CBR required for the improved ground when using particle-improved ground improvement materials in the hope of achieving a compaction effect through particle size improvement. (2) A method for predicting the mixing ratio of a grain-size improved ground improvement material described in (1), characterized in that the mixing ratio of the grain-size improved ground improvement material is predicted by the following formula (1). M=α×ln(improved soil CBR)+β-γ×x (1) Here, M is the mixing ratio of the grain-improved ground improvement material (volume %), improved soil CBR is the CBR required after improvement (%), x is the soil hardness measured by the Yamanaka soil hardness meter (mm), and α, β, and γ are coefficients. (3) A method for predicting the mixing ratio of a grain-size-improved ground improvement material according to (1) or (2), characterized in that steel slag is used as the grain-size-improved ground improvement material. (4) A method for predicting the mixing ratio of a grain-improved ground improvement material described in (2), characterized in that the mixing ratio of the grain-improved ground improvement material is calculated from the simplified formula (2) below by determining the CBR required for the improved ground. M(m)=δ-ε×x (2) Here, M(m) is the mixing ratio (%) of the grain-improved ground improvement material when the required CBR is m%, δ, ε are coefficients determined when the required CBR is m%, and x is the soil hardness (mm) measured by the Yamanaka soil hardness meter. (5) A method for predicting a mixing ratio of a grain-size-improved ground improvement material according to claim 4, characterized in that steel slag is used as the grain-size-improved ground improvement material. (6) A method for improving soft ground, comprising mixing a grain-size-improved ground improvement material with the soft ground at a mixing ratio of the improved ground improvement material calculated using a method for predicting the mixing ratio of grain-size-improved ground improvement material according to any one of (1), (2), or (4). (7) A method for improving soft ground according to claim 6, characterized in that iron and steel slag is used as the grain-improved ground improvement material. Effect of the Invention

[0009] The present invention makes it possible to easily predict the mixing ratio of grain-improved ground improvement materials using only the hardness of soft ground, which can be measured by a simple on-site test, and the CBR required for the improved ground, and therefore greatly contributes to improving construction efficiency. [Brief description of the drawings]

[0010] [Figure 1] This figure shows the relationship between soil hardness and CBR of local soil measured with a Yamanaka soil hardness meter. [Diagram 2] This is a diagram showing the relationship between the mixing ratio of geotizer and the CBR of improved soil / CBR of local soil. [Diagram 3] This figure shows the relationship between soil hardness of local soil measured with a Yamanaka soil hardness meter and the mixing ratio for each required improved soil CBR. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The key to solving this problem is that it is possible to predict the mixing ratio of grain-improved ground improvement material required to achieve the CBR required for the improved ground using only the results of simple on-site tests.

[0012] The above idea was considered in two phases: firstly, the relationship between the simple test results (measurements made by Yamanaka soil hardness meter) and CBR for soft soil (hereafter referred to as local soil), and secondly, the relationship between the CBR of the local soil and the CBR and mixing ratio of soil (hereafter referred to as improved soil) in which local soil is mixed with a grain-improved ground improvement material (here, as an example, geotizer manufactured by Nippon Steel Corporation). Here, the mixing ratio of geotizer is determined according to the condition of the local soil, and is usually mixed at around 20% to 50%.

[0013] Regarding the first point, Yoshida et al. (Yoshida, 1983, Proceedings of the Japan Society of Irrigation, Drainage and Reclamation Engineers, Vol. 104, pp. 25-29.) already clarified it in 1983, and it was confirmed that the tendency was similar to the experimental values ​​(local soil hardness measured by Yamanaka soil hardness meter, CBR by CBR test, solid line in Figure 1) that were conducted for this invention using fine sandy soil collected in Kiyosu City, Aichi Prefecture (● in Figure 1). However, as shown in Figure 1, the experimental values ​​tended to have lower CBR values ​​overall compared to the predicted values ​​by Yoshida et al., so for safety reasons, the approximation formula shown in the following formula (3), which was estimated from the experimental values, was adopted. Local soil CBR=0.0807e 0.139x (3) Here, x is the soil hardness (mm) measured by the Yamanaka soil hardness tester.

[0014] Next, the second point will be explained. This is the main point of the present invention, and data on the most representative soil is used here. Assuming that the CBR of the local soil and the CBR of the improved soil can be expressed by a linear equation (CBR of improved soil = α x CBR of local soil), Figure 2 shows the test values ​​for the relationship between the linear coefficient (CBR of improved soil / CBR of local soil) and the mixture ratio. To add, the CBR of the local soil and the CBR of the improved soil here are both measured values ​​obtained by the CBR test specified in JIS A1211.

[0015] The mixing ratio of the geotizer here is the volumetric ratio (%) of the geotizer contained in the improved soil. For example, if the geotizer is 1 part and the local soil is 3 parts, the improved soil is 1 + 3 = 4, and the mixing ratio is 1 / 4 = 25%. The range of the mixing ratio is usually about 20% to 50% (about 1 / 5 to 1 / 2), and the prediction formula according to the present invention is derived using test results within this range, and its validity is verified. Regarding the concept of each volume, since it is necessary to reproduce the state at the time of mixing, it is common to use the volume of the local soil in a state that is not disturbed by excavation, etc., and the volume of the geotizer in a loosely packed state without tamping.

[0016] From FIG. 2, the exponential function formula for predicting the linear coefficient is derived as follows: Y=0.196e 0.122M (4) Here, Y is the linear coefficient, M is the mixture ratio (%) of improved soil and local soil, which is the volume ratio. The CBR of the improved soil is calculated by multiplying equation (4) by the CBR of the local soil, so the CBR of the improved soil is calculated by equation (5). Improved soil CBR=0.196e 0.122M ×Local soil CBR (5)

[0017] Here, for equation (5), the CBR of the local soil can be calculated using equation (3) to obtain the following equation. Improved soil CBR=0.0158e 0.122M+0.139x (6) By resolving the mixture ratio in equation (6), the following equation (7) was derived, which predicts the mixture ratio from the hardness of the local soil and the CBR required for the improved soil. M=8.2×ln(improved soil CBR)+34-1.1×x (7) In the present invention, since the values ​​of the coefficients may vary depending on various conditions, the values ​​of the above formula (7) are expressed as the coefficients α, β, and γ in the following formula (8). M=α×ln(improved soil CBR)+β-γ×x (8)

[0018] Here, in order to further simplify the formula, if the required CBR of the improved soil is set to 3, 10, or 20%, the above formula (7) becomes: M(3%)=43-1.1×x (9) M(10%)=53-1.1×x (10) M(20%)=59-1.1×x (11) and can be organized as shown in Figure 3. The coefficients in formulas (9) to (11) are calculated using test data for a representative field soil, and the coefficient values ​​may vary depending on various conditions, so in the configuration of the present invention, as described above, the values ​​in formulas (9) to (11) are expressed as coefficients σ and ε, and the mixture ratio when the required CBR is m% is M(m), as shown in formula (12) below. M(m)=δ-ε×x (12) In addition, the M(m) calculated above has a ±ζ range because it depends on the local weather such as rain and the properties of the soil. As a guideline, the ζ value is assumed to be 20 to 30.

[0019] It goes without saying that the soft ground will be improved if the mixing ratio of the grading-improved ground improvement material is calculated using the above-mentioned method for predicting the mixing ratio of the grading-improved ground improvement material, and then the grading-improved ground improvement material is mixed into the soft ground at the mixing ratio with a range of ±ζ depending on the situation. Furthermore, there is no problem with the mixing method of the grading-improved ground improvement material in the conventional construction.

[0020] In the above, geotizers have been used as an example in this document, but since ground improvement materials that are expected to improve grain size perform physical (compaction) ground improvement that is not influenced by the chemical properties (ingredients, etc.) of natural crushed stone, natural sand, geotizers, etc., similar effects can be expected with other grain size improvement type ground improvement materials.

Claims

1. A method for predicting the mixing ratio of a granular improvement type ground improvement material, which is characterized by determining the mixing ratio of the granular improvement type ground improvement material using the hardness of the ground before improvement measured with a Yamanaka soil hardness meter and the CBR required for the improved ground, when using a granular improvement type ground improvement material in the hope of achieving a compaction effect through granularity improvement.

2. 2. A method for predicting a mixing ratio of a grain-improved ground improvement material according to claim 1, characterized in that the mixing ratio of the grain-improved ground improvement material is calculated by the following formula (1). M=α×ln(improved soil CBR)+β-γ×x (1) where M is the mixing ratio of the grain-improved ground improvement material (volume %), improved soil CBR is the CBR required after improvement (%), x is the soil hardness measured by the Yamanaka soil hardness meter (mm), and α, β, and γ are coefficients.

3. 3. The method for predicting the mixing ratio of a grain-size-improved ground improvement material according to claim 1 or 2, characterized in that steel slag is used as the grain-size-improved ground improvement material.

4. A method for predicting the mixing ratio of grain-improved ground improvement material as described in claim 2, characterized in that the mixing ratio of the grain-improved ground improvement material is calculated from the simplified formula (2) below by determining the CBR required for the improved ground. M(m)=δ-ε×x (2) Here, M(m) is the mixing ratio (%) of the grain-improved ground improvement material when the required CBR is m%, δ, ε are coefficients determined when the required CBR is m%, and x is the soil hardness (mm) measured by the Yamanaka soil hardness meter.

5. The method for predicting the mixing ratio of a grain-size-improved ground improvement material according to claim 4, characterized in that steel slag is used as the grain-size-improved ground improvement material.

6. A method for improving soft ground, comprising mixing a granular improvement type ground improvement material into soft ground at a mixing ratio of the improved ground improvement material calculated using the method for predicting the mixing ratio of granular improvement type ground improvement material according to any one of claims 1, 2 and 4.

7. 7. The method for improving soft ground according to claim 6, wherein steel slag is used as the grain size-improved ground improvement material.

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