Strength estimation method and quality management method of soil cement

Abstract

To provide a strength estimation method and a quality management method of soil cement capable of easily estimating the strength of soil cement containing a solidification material in which a solidification reaction is completed.SOLUTION: A strength estimation method of soil cement comprises the steps of: estimating a shearing wave speed of soil cement of an estimation target material age at a construction place, by applying a shearing wave speed of soil cement of a young material age measured after the elapse of a predetermined time from the actual construction of soil cement to a relation between a material age and a ratio between a shearing wave speed of a consolidated sample of soil cement in which a mass ratio of a cement-based solidification material to soil cement is a predetermined value and the shearing wave speed of the soil cement of the estimation target material age; and estimating compression strength of the soil cement of the estimation target material age at the construction place by applying the estimated shearing wave speed to a relation between the shearing wave speed and compression strength of the consolidated sample of the soil cement in which the mass ratio of the cement-based solidification material to the soil cement is the predetermined value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for estimating strength and a method for quality control of soil cement. [Background technology]

[0002] Traditionally, soil cement is made up of soil, cement, and water, and is used in ground improvement and backfilling works as an intermediate material between ground materials and concrete materials. The quality of soil cement is generally inspected by a compression test aged 28 days using mold specimens taken at the time of pouring, or core specimens taken in situ after the soil cement has solidified. This method ensures high reliability of the data, as specimens are taken from the pouring site. On the other hand, quality inspection is carried out 28 days after the soil cement is poured, so if the quality is not satisfactory, the pouring site must be excavated again, which puts pressure on the process. Furthermore, when coring, it requires coordination with other processes and investigation costs.

[0003] As a technique for solving such problems, a method (C-QUIC) for easily and quickly determining the strength by focusing on the amount of cement contained in the soil cement is known (see, for example, Patent Documents 1 to 4). Also, a method (Vs-QUIC) for determining the strength using the shear wave velocity is known (see, for example, Patent Document 5). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6894244 [Patent Document 2] Patent No. 6979814 [Patent Document 3] Patent Publication No. 2021-059851 [Patent Document 4] JP 2021-156110 A [Patent Document 5] Patent No. 4120809 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when applying the above-mentioned C-QUIC method to the quality inspection of soil cement that contains cement and solidification improvement material components that have completed the solidification reaction in the original soil, such as ground improvement bodies with re-added solidification materials or liquefied soil made from recycled construction soil, there was a problem that estimating the 28-day strength from the cement content of unconsolidated soil cement is technically difficult and the accuracy is reduced.

[0006] For this reason, there was a need for a method that could easily determine the specified age strength of soil cement, such as ground improvement bodies and liquefied treated soil, when newly manufactured and constructed using raw soil containing cement and solidification improvement material components that have undergone the solidification reaction, based on the shear wave velocity Vs in the early stages of the setting and solidification reaction.

[0007] The present invention has been made in consideration of the above, and aims to provide a soil cement strength estimation method and quality control method that can easily estimate the strength of soil cement containing a solidification material that has completed a solidification reaction. [Means for solving the problem]

[0008] In order to solve the above problems and achieve the object, a soil cement strength estimating method according to the present invention is a method for estimating the strength of soil cement obtained by mixing a cement-based solidification material, water, and an earthen material, and is characterized by comprising the steps of: estimating the shear wave velocity of soil cement at an estimated target age at a construction site by applying the shear wave velocity of soil cement at an early age measured a predetermined time after the implementation of soil cement construction to a relationship between the shear wave velocity of a solidified sample of soil cement having a predetermined mass ratio of cement-based solidification material to soil cement and the shear wave velocity of the soil cement at an estimated target age, which is known in advance; and estimating the compressive strength of soil cement at an estimated target age at a construction site by applying the estimated shear wave velocity to the relationship between the compressive strength and shear wave velocity of a solidified sample of soil cement having a predetermined mass ratio of cement-based solidification material to soil cement, which is known in advance.

[0009] Further, another soil cement strength estimating method according to the present invention is characterized in that, in the above-mentioned invention, the soil material includes a solidification material that has completed a solidification reaction.

[0010] In addition, the soil cement quality control method of the present invention is a method for controlling the construction quality of soil cement, and is characterized by having a step of estimating the compressive strength of soil cement of an estimated target material age at a construction site using the above-mentioned soil cement strength estimation method, and a step of determining whether the estimated compressive strength satisfies the design conditions. Effect of the Invention

[0011] According to the soil cement strength estimating method of the present invention, there is provided a method for estimating the strength of soil cement obtained by mixing a cement-based solidification material, water, and an earthen material, and the method includes the steps of: estimating the shear wave velocity of soil cement at an estimated target age at a construction site by applying the shear wave velocity of soil cement at an early age measured a predetermined time after the implementation of soil cement construction to the relationship between the ratio of the shear wave velocity of a solidified sample of soil cement having a predetermined mass ratio of cement-based solidification material to soil cement to the shear wave velocity of the soil cement at an estimated target age, which is known in advance, and the material age; and estimating the compressive strength of soil cement at an estimated target age at a construction site by applying the estimated shear wave velocity to the relationship between the compressive strength and shear wave velocity of a solidified sample of soil cement having a predetermined mass ratio of cement-based solidification material to soil cement, which is known in advance,

[0012] In addition, according to another soil cement strength estimating method of the present invention, since the soil material contains a solidification material that has completed a solidification reaction, it has the effect of being able to easily estimate the strength of the soil cement that contains a solidification material that has completed a solidification reaction.

[0013] Furthermore, according to the soil cement quality control method of the present invention, which is a method for controlling the construction quality of soil cement, the method includes a step of estimating the compressive strength of soil cement of an estimated target material age at a construction site using the above-mentioned soil cement strength estimation method, and a step of determining whether the estimated compressive strength satisfies the design conditions, thereby achieving the effect of appropriately controlling the construction quality of the soil cement. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic flow diagram showing an embodiment of a soil-cement strength estimation method and quality control method according to the present invention. [Diagram 2] FIG. 2 is a supplementary explanatory diagram of FIG. [Diagram 3]FIG. 3 is a graph showing an example of the change in normalized shear wave velocity over time. [Figure 4] FIG. 4 is a graph showing an example of the relationship between the unconfined compressive strength and the shear wave velocity. [Diagram 5] FIG. 5 is a diagram showing an example of a time-dependent change in normalized shear wave velocity and a regression equation. [Figure 6] FIG. 6 is a graph showing an example of the relationship between the unconfined compressive strength and the shear wave velocity and a regression equation. [Figure 7] FIG. 7 is a graph showing an example of the change over time in shear wave velocity of soil cement with different amounts of solidification material. [Figure 8] FIG. 8 is a graph showing an example of the change over time of the inverse of the normalized shear wave velocity and a regression equation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, embodiments of the soil cement strength estimation method and quality control method according to the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments.

[0016] This embodiment is a method for easily and quickly estimating the strength of soil cement that contains cement that has already solidified or solidification improvement material components in the original soil, by using the change in shear wave velocity over time (elongation) of the soil cement obtained from laboratory tests before the soil cement is poured, and the relationship between the uniaxial compressive strength and shear wave velocity, and using this method for quality control. A specific implementation procedure of this embodiment will be described below.

[0017] As shown in FIG. 1, in step S1, prior to the actual construction of the soil cement, a soil material that will become the soil cement source soil is collected. The soil material may be in-situ soil at the site (used for ground improvement work or retaining wall work) or construction generated soil in a stockyard (used for backfill work). The soil material contains a solidification material that has undergone a solidification reaction (e.g., cement or solidification improvement material components). However, the soil material of the present invention is not limited to this, and may not contain a solidification material that has undergone a solidification reaction. Next, a laboratory test is performed according to the following steps S2 to S5.

[0018] In step S2, the collected soil material, cement-based solidification material, and water are mixed in a predetermined mass ratio to prepare a soil cement specimen (solidified sample). It is preferable to set multiple amounts of cement-based solidification material (solidification material amount) to be added (for example, about 3 to 4 levels), for example, 100 to 400 kg / m 3 It is desirable to prepare about 30 soil-cement test specimens for each mix.

[0019] In step S3, the measurement of the shear wave velocity Vs of the soil cement specimen and the compression test are performed while changing the material age. For example, it is preferable to perform the measurements at material ages of 8 hours, 12 hours, 24 hours, 2 days, 3 days, 7 days, 14 days, and 28 days, but other material ages are also acceptable. It is preferable to perform the Vs measurement and compression test on 2 to 3 specimens at one material age in order to improve measurement accuracy.

[0020] In step S4, the elongation rate of the shear wave velocity of the soil cement (see FIG. 2(1)) and the relationship between the unconfined compressive strength (compressive strength) and the shear wave velocity (see FIG. 2(2)) are obtained. The elongation rate of the shear wave velocity can be expressed as the change in normalized shear wave velocity over time. The change in normalized shear wave velocity over time corresponds to the relationship between the ratio of the shear wave velocity of the present invention to the shear wave velocity of the estimated target material age and the material age. FIG. 3 shows an example of the change in normalized shear wave velocity over time. The vertical axis of FIG. 3 is the ratio of the shear wave velocity at an arbitrary material age normalized to the shear wave velocity at the material age of 28 days (estimated material age) (normalized shear wave velocity). FIG. 4 shows an example of the relationship between the unconfined compressive strength and the shear wave velocity. Although FIG. 3 and FIG. 4 show the results of using multiple amounts of solidification material, it may be obtained only for a predetermined amount of solidification material.

[0021] In step S5, a regression equation showing the elongation rate and the relationship is determined from the elongation rate and the relationship. The regression equation may be a regression line equation or a regression curve equation. In the example of FIG. 5, the regression line equation of a semi-logarithmic graph with the horizontal axis being logarithmic is determined for a solidification amount of 150 kg / m 3 However, since the initial (~20 hours) shear wave velocity extension rate differs depending on the amount of solidified material (see Figure 7), a regression curve may be used. In the example of Figure 6, the amount of solidified material is 150 kg / m 3 The equation for the regression curve is shown in FIG.

[0022] In the next step S6, the soil cement is poured in situ (implementation work). In this case, for example, the cement-based solidification material and water are added to the in-situ ground in a planned ratio, and the mixture is mixed and stirred to pour the soil cement.

[0023] In the next step S7, the shear wave velocity Vs,arb of the early soil cement is measured several hours t,arb (arb stands for arbitrary) after the soil cement has been poured. The time t,arb is usually 3 to 5 hours after the soil cement has been poured and constructed, when it begins to set and harden, but this is not essential. To measure the shear wave velocity, the bender element method or the like can be used on a molded specimen taken in an unconsolidated state from the construction site immediately after pouring.

[0024] In the next step S8, the elongation rate of the shear wave velocity is calculated from the regression equation of the elongation rate and the time t,arb elapsed since the soil cement was poured, and the shear wave velocity Vs,est (est: short for estimate) at 28 days (target material age) is estimated (see Figure 2(3)). For example, in step S7, when the amount of solidification material is 150 kg / m 3 Consider the case where the shear wave velocity measured 8 hours (=t,arb) after the soil cement was poured is 106m / s (=Vs,arb). According to the regression equation shown in Figure 5 (normalized shear wave velocity = 0.428 × log(hour)-0.185), the normalized shear wave velocity (elongation) is about 0.2. Therefore, the shear wave velocity at 28 days can be estimated as 106m / s÷0.2=530m / s (=Vs,est). In order to estimate the shear wave velocity at 28 days, Vs,est, the vertical axis of Figure 5 or Figure 2(3) can be inversely scaled, so that it is possible to directly read how many times the shear wave velocity measured several hours later should be multiplied (see Figure 8 or Figure 2(4)).

[0025] In the next step S9, the unconfined compressive strength qu,est of the soil cement at 28 days is estimated from the regression equation of the above relationship and the shear wave velocity Vs,est at 28 days estimated in step S8 above (see Figure 2 (5)). For example, consider the case where the shear wave velocity at 28 days estimated in step S8 above is 530 m / s (= Vs,est). According to the regression equation shown in Figure 6 (unconfined compressive strength = 0.0147 x {exp(0.0105 x Vs)-1}), the unconfined compressive strength of the soil cement at 28 days can be estimated to be approximately 3.8 MPa.

[0026] In the next step S10, it is determined whether the unconfined compressive strength qu,est of the soil cement at 28 days estimated in step S9 above satisfies the design standard strength (design conditions). If it does, it is determined that the construction quality is satisfied, the quality confirmation process is terminated, and the process proceeds to the next step, such as quality confirmation of other areas (Yes in step S10). On the other hand, if it does not satisfy (No in step S10), it is determined that the specified construction quality is not satisfied, and the soil cement pouring area is excavated as a poured area that has insufficient strength (step S11). After that, the soil cement mix is ​​reviewed (step S12), the process returns to step S2, and the process is repeated. Alternatively, the manufacturing method and pouring method of the soil cement are reviewed (step S13), and the process proceeds to step S6.

[0027] According to this embodiment, the strength of soil cement containing cement and solidification improvement material components that have already undergone the solidification reaction can be easily estimated based on (1) the change in shear wave velocity over time (elongation), which is a soil cement-specific property obtained in a laboratory test before the soil cement is poured, and (2) the relationship between the uniaxial compressive strength and shear wave velocity.

[0028] In particular, the shear wave velocity at 28 days can be estimated based on the measurement results of shear wave velocity at any early age from soil-cement pouring and (1) the change over time in shear wave velocity obtained from laboratory tests. In addition, the unconfined compressive strength at 28 days can be estimated based on the estimated shear wave velocity at 28 days and (2) the relationship between unconfined compressive strength and shear wave velocity obtained from laboratory tests.

[0029] Furthermore, the quality of construction can be judged at any time (for example, several hours) after the soil cement has been poured. Although it depends on the amount of solidifying agent, for example, the quality of construction can be judged 3 to 5 hours after the soil cement has been poured and laid, when it begins to set and harden. Therefore, compared to conventional compression tests on molded specimens at the age of 28 days, the amount of measurement work is reduced and the time required for quality inspection can be significantly shortened, allowing the quality of construction to be judged at an earlier stage.

[0030] Furthermore, even if it is found that the strength of the soil cement does not meet the design standard strength, the manufacturing method and mix plan can be immediately revised, making it possible to re-apply the soil cement, for example, the next day.

[0031] In the above embodiment, the case where the age to be estimated is 28 days has been described as an example, but the age to be estimated in the present invention is not limited to this, and other ages may be used.

[0032] As described above, the soil cement strength estimating method of the present invention is a method for estimating the strength of soil cement obtained by mixing a cement-based solidification material, water, and an earthen material, and includes the steps of estimating the shear wave velocity of soil cement at an estimated target age at a construction site by applying the shear wave velocity of soil cement at an early age measured a predetermined time after the implementation of soil cement construction to the relationship between the ratio of the shear wave velocity of a solidified sample of soil cement having a predetermined mass ratio of cement-based solidification material to soil cement to the shear wave velocity of the soil cement at an estimated target age and the material age, which are known in advance, and estimating the compressive strength of soil cement at an estimated target age at a construction site by applying the estimated shear wave velocity to the relationship between the compressive strength and shear wave velocity of a solidified sample of soil cement having a predetermined mass ratio of cement-based solidification material to soil cement, which are known in advance,

[0033] In addition, according to another soil cement strength estimation method of the present invention, since the soil material contains a solidification material that has completed a solidification reaction, the strength of the soil cement containing the solidification material that has completed a solidification reaction can be easily estimated.

[0034] Furthermore, according to the soil cement quality control method of the present invention, which is a method for controlling the construction quality of soil cement, the method includes a step of estimating the compressive strength of soil cement of an estimated target material age at a construction site using the above-mentioned soil cement strength estimation method, and a step of determining whether the estimated compressive strength satisfies the design conditions, thereby making it possible to appropriately control the construction quality of the soil cement.

[0035] The "Sustainable Development Goals (SDGs)" are 17 international goals that were adopted at the United Nations Summit in September 2015. The soil cement strength estimation method and quality control method according to the present embodiment can contribute to the achievement of, for example, "12. Responsible Consumption and Production" among the 17 SDGs. [Industrial Applicability]

[0036] As described above, the soil cement strength estimation method and quality control method of the present invention are useful for estimating the strength and controlling the quality of soil cement, and are particularly suitable for easily estimating the strength of soil cement that contains solidification material that has completed the solidification reaction in the original soil.

Claims

1. A method for estimating the strength of soil cement obtained by mixing a cement-based solidification material, water, and a soil material, comprising: a step of estimating the shear wave velocity of soil cement of the estimated target age at the construction site by applying the shear wave velocity of soil cement of an early age measured a predetermined time after the soil cement construction work was carried out to the ratio of the shear wave velocity of a solidified soil cement sample having a predetermined mass ratio of cement-based solidification material to soil cement to the shear wave velocity of the estimated target age, which is known in advance, and the relationship with the age of the soil cement; A method for estimating soil cement strength, comprising the step of estimating the compressive strength of soil cement of an estimated target material age at a construction site by applying an estimated shear wave velocity to a relationship between the compressive strength and shear wave velocity of a solidified soil cement sample having a predetermined mass ratio of cement-based solidification material to soil cement.

2. The method for estimating soil cement strength according to claim 1, characterized in that the soil material includes a solidification material that has completed a solidification reaction.

3. A method for controlling the quality of soil cement construction, comprising: A step of estimating the compressive strength of soil cement at an estimated target age at a construction site by the soil cement strength estimation method according to claim 1 or 2; A soil cement quality control method comprising a step of determining whether the estimated compressive strength satisfies design conditions.

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