Quality control method for liquefied treated soil

Abstract

To provide a quality management method of fluidization treated soil capable of preventing instability in strength.SOLUTION: A quality management method of fluidization treated soil comprises the steps of: adjusting a content percentage of a fine-grained fraction in soil material or an addition amount of cement-based solidification material to adjust viscosity of fluidization treated soil within a specific range in advance; collecting the fluidization treated soil in an unconsolidated state just before installation; measuring the viscosity of the collected fluidization treated soil to determine whether or not the measured viscosity falls within the specific range; estimating the amount of the cement solidification material included in the collected fluidization treated soil or a compound ratio of the cement-base solidification material to water to determine whether or not the estimated cement-base solidification material or compound ratio falls within the specific range set based on design reference strength; and measuring shearing wave velocity of the fluidization treated soil in a consolidated state after installation to determine whether or not the measured shearing wave velocity falls within the specific range set based on the design reference strength.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a quality control method for liquefied treated soil. [Background technology]

[0002] In the past, in redevelopment projects, if the framework or piles of an existing structure are not reused in a new structure, it is common to remove a part of the existing structure that interferes with the new structure in advance and backfill the area. Fluidized treated soil, which is easy to ensure strength development and stability, is often used as a backfill material. Fluidized treated soil is mainly composed of construction waste soil, water, and cement, and has fluidity and self-hardening properties, so it is also used for backfilling, backfilling, and filling work in narrow spaces and places where compaction is difficult. For example, in the removal and backfilling work of existing piles, a casing with a larger diameter than the existing pile diameter is rotary-pressed into the ground, and the inside of the casing is crushed and removed with a hammer club, etc., and then the fluidized treated soil is injected from the bottom of the hole that was removed with a tremie pipe. However, when the removal and backfilling hole length becomes long, there have been reported cases where material separation due to bleeding, etc. occurs in the shallow part of the fluidized treated soil, causing the strength to become unstable (for example, see Non-Patent Document 1).

[0003] The quality of general liquefied treated soil is inspected by the strength of molded specimens taken from the discharge port during production or pouring (see, for example, Patent Document 1). Verification of in-situ strength is limited to "taking undisturbed samples in-situ as necessary to confirm strength" (see, for example, Non-Patent Document 2), and the decision to implement this is left to the operator.

[0004] Meanwhile, methods for determining the strength of soil cement by chemical techniques include, for example, the methods described in Patent Documents 2 to 8 (hereinafter referred to as CW-QUIC). Also, methods for controlling the quality of soil cement using shear wave velocity include, for example, the methods described in Patent Documents 9 and 10 (hereinafter referred to as Vs-QUIC). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] "Quality Investigation of Liquefied Treated Soil Backfilled in Excavated Holes after Removal of Existing Piles", Hirofumi Sakihama, Hironori Horii, Hikaru Yaegashi, Proceedings of the 2014 Annual Meeting of the Architectural Institute of Japan, pp.435-436, 2014 [Non-Patent Document 2] "Technical Manual for the Use of Liquefied Soil," Public Works Research Institute / Comprehensive Management of Liquefied Soil Treatment Methods (ed.), Gihodo Publishing, 2008 [Patent documents]

[0006] [Patent Document 1] JP 2009-161906 A [Patent Document 2] JP 2018-119337 A [Patent Document 3] JP 2018-193716 A [Patent Document 4] JP 2018-199935 A [Patent Document 5] JP 2019-019449 A [Patent Document 6] JP 2019-019471 A [Patent Document 7] JP 2019-105118 A [Patent Document 8] JP 2020-094872 A [Patent Document 9] Patent No. 4120809 [Patent Document 10] Patent application No. 2020-059799 (currently unpublished) Summary of the Invention [Problem to be solved by the invention]

[0007] Two examples of insufficient strength of liquefied treated soil are shown in the figures. Figure 4(1) is from the one described in Non-Patent Document 1 (labeled as site A), and Figure 4(2) is from site B, which was investigated recently. As shown in these figures, the strength of the molded specimens taken from the discharge outlet was 400-450 kPa at site A and 240 kPa at site B, both of which satisfied the design standard strength. However, the in-situ strength of the undisturbed samples taken from boring cores does not satisfy the design standard strength, especially in the shallow areas.

[0008] If the in-situ strength of liquefied treated soil does not meet the design standard strength, problems such as hole bending, collapse of hole walls, and displacement of the pile core may occur when constructing new piles during the work of removing existing piles and backfilling them, which may require a review of the soil properties used in the design of the new piles. To avoid such situations, it is necessary to re-excavate and refill the backfilled area, but this will shorten the construction period and increase the construction and material costs. For this reason, a quality control method that can avoid the instability of the strength of liquefied treated soil was required.

[0009] The present invention has been made in consideration of the above, and aims to provide a quality control method for liquefied treated soil that can avoid strength instability. [Means for solving the problem]

[0010] In order to solve the above problems and achieve the object, the quality control method for liquefied treated soil according to the present invention is a method for controlling the construction quality of liquefied treated soil which contains a soil material, a cement-based solidification material, and water, and is poured into the ground for construction, and is characterized by comprising the steps of: adjusting the fine particle content of the soil material or the amount of cement-based solidification material added when planning the mixture for the liquefied treated soil, thereby adjusting the viscosity of the liquefied treated soil in advance within a predetermined range that enhances material separation resistance; sampling the liquefied treated soil in an unconsolidated state immediately before construction; measuring the viscosity of the sampled liquefied treated soil and determining whether the measured viscosity is within the predetermined range; estimating the amount of cement-based solidification material contained in the sampled liquefied treated soil or the mixture ratio of the cement-based solidification material to water, and determining whether the estimated amount of cement-based solidification material or the mixture ratio is within a predetermined range set based on the design standard strength; and measuring the shear wave velocity of the liquefied treated soil in a solidified state after construction, and determining whether the measured shear wave velocity is within a predetermined range set based on the design standard strength.

[0011] In addition, another quality control method for liquefied treated soil according to the present invention is characterized in that, in the above-mentioned invention, the amount or mixing ratio of cement-based solidification material is estimated by utilizing the time change characteristics of the initial pH when the liquefied treated soil is neutralized with acid.

[0012] Furthermore, another quality control method for liquefied treated soil according to the present invention, in the above-mentioned invention, further comprises a step of conducting a mixing test by mixing soil material, cement-based solidification material, and water prior to the construction of the liquefied treated soil, and this mixing test is characterized by including a step of measuring shear wave velocity and testing compressive strength while changing the amount of cement-based solidification material added and the material age for test specimens of liquefied treated soil, obtaining the relationship between the amount of cement-based solidification material added and the compressive strength, and the relationship between shear wave velocity and compressive strength, and a step of setting the amount of cement-based solidification material added and the shear wave velocity corresponding to a predetermined design standard strength based on the obtained relationship. Effect of the Invention

[0013] The quality control method for liquefied treated soil according to the present invention is a method for controlling the construction quality of liquefied treated soil which contains soil material, cement-based solidification material, and water and is poured into the ground for construction, and includes the steps of: adjusting the fine particle content of the soil material or the amount of cement-based solidification material added when planning the mix proportion of the liquefied treated soil to adjust the viscosity of the liquefied treated soil in advance within a predetermined range that enhances resistance to material separation; sampling the unconsolidated liquefied treated soil immediately before construction; measuring the viscosity of the sampled liquefied treated soil and determining whether the measured viscosity is within the predetermined range; and The method includes the steps of estimating the amount of cement-based solidification material contained in the collected liquefied treated soil or the mixing ratio of the cement-based solidification material to water, and determining whether the estimated amount of cement-based solidification material or mixing ratio is within a predetermined range set based on the design standard strength, and measuring the shear wave velocity of the liquefied treated soil in a solidified state after construction, and determining whether the measured shear wave velocity is within a predetermined range set based on the design standard strength.This has the effect of avoiding strength instability by adjusting the viscosity to increase resistance to material separation when mixing the liquefied treated soil.

[0014] In addition, according to another quality control method for liquefied treated soil of the present invention, the amount or mixing ratio of cement-based solidification material is estimated by utilizing the time change characteristics of the initial pH when the liquefied treated soil is neutralized with acid, thereby achieving the effect of quickly and inexpensively estimating the amount or mixing ratio of cement-based solidification material.

[0015] Furthermore, according to another quality control method for liquefied treated soil of the present invention, there is further provided a step of conducting a mixing test by mixing soil material, cement-based solidification material, and water prior to construction of the liquefied treated soil, and this mixing test includes a step of measuring shear wave velocity and testing compressive strength while changing the amount of cement-based solidification material added and the material age of specimens of liquefied treated soil, obtaining the relationship between the amount of cement-based solidification material added and the compressive strength, and the relationship between shear wave velocity and compressive strength, and a step of setting the amount of cement-based solidification material added and the shear wave velocity corresponding to a specified design standard strength based on the obtained relationship, thereby achieving the effect of accurately grasping the amount of cement-based solidification material added and the shear wave velocity required to realize the specified design standard strength. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a flow chart showing an embodiment of a quality control method for liquefied treated soil according to the present invention. [Diagram 2] Figure 2 (1) shows the relationship between the amount of cement added and compressive strength, (2) shows the relationship between shear wave velocity and compressive strength, and (3) is an illustration of when the liquefied treated soil is determined to have sufficient strength. [Diagram 3] Figure 3 is a depth distribution map showing an example of the unconfined compressive strength of liquefied treated soil that satisfies the design standard strength. [Figure 4] Figure 4 is a depth distribution map showing examples of the unconfined compressive strength of conventional liquefied treated soil. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the quality control method for liquefied treated soil according to the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to this embodiment.

[0018] As described above, it is important to have a mix that can ensure the resistance to material separation of the liquefied treated soil. Therefore, in this embodiment, the amount of solidification material to be added and the shear wave velocity corresponding to the design standard strength are determined while the viscosity of the liquefied treated soil is appropriately ensured. Next, the liquefied treated soil to be inspected is sampled in an unconsolidated state as an acceptance inspection, and the strength of the liquefied treated soil is confirmed to be sufficient in the amount of cement to be added for strength development by a method (CW-QUIC) that determines the strength of the liquefied treated soil by a chemical method. After the liquefied treated soil is solidified, a quality inspection method (Vs-QUIC) using shear wave velocity is performed on the surface of the liquefied treated soil to confirm that the in-situ strength satisfies the design standard strength. Note that the present invention is not limited to the application of the liquefied treated soil. A specific implementation procedure of this embodiment will be described below.

[0019] (Indoor blending test) As shown in FIG. 1, prior to the actual construction of the liquefied treated soil, an indoor mix test is conducted according to the following steps S1 to S4. First, in step S1, the target soil material (e.g., construction waste soil) is collected from the stockyard of the liquefied soil manufacturing plant, and the fine particle content is adjusted. This adjustment can be performed by a general grain size adjustment procedure. The fine particle content after adjustment is preferably 5% to 30%, and more preferably 10% to 20%. If the fine particle content of the target soil material at the time of collection is distributed within a predetermined range (e.g., the above range), this step S1 can be omitted. The fine particle content can also be adjusted by adding bentonite, etc., but there is a risk that flow reduction will occur easily. For this reason, in the case of liquefied soil that requires flow retention, it is desirable to adjust the fine particle content by combining the target soil material stored in the stockyard, or to adjust it by using soil material such as construction waste soil that meets the specified fine particle content.

[0020] In the next step S2, the amount of cement-based solidification material added to the target soil material whose grain size has been adjusted in the above step S1 is set to about 3 to 4 levels, and liquefied soil is prepared. The amount of cement-based solidification material added is, for example, 50 kg / m 3~400kg / m 3 However, in order to increase the resistance of the liquefied treated soil to material separation, it is desirable for the viscosity μspe to be between 500 mPa·s and 4000 mPa·s, and it is even more desirable for it to be between 1500 mPa·s and 3000 mPa·s so that bleeding does not occur. The viscosity of liquefied treated soil can be adjusted by the amount of cement-based solidification material added and the fine particle content of the target soil material used. It is desirable to prepare around 30 specimens of liquefied treated soil for each mix.

[0021] In the next step S3, measurements of shear wave velocity Vs and compression tests are carried out using specimens of liquefied treated soil with varying material ages. For example, it is preferable to carry out the tests 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. The number of specimens for Vs measurement and compression tests is preferably 2 to 3 for each material age.

[0022] In the next step S4, the relationship between the amount of cement added and the compressive strength at 28 days, and the relationship between the shear wave velocity Vs and the compressive strength are obtained. Examples of the obtained relationships are shown in Figures 2(1) and (2). Next, based on these relationships, the amount of solidifier added Cspe, or the cement-water ratio C / Wspe and Vs value (hereinafter referred to as Vs,spe) corresponding to the design criteria strength Fc (target value of strength for quality confirmation) is determined. The amount of solidifier added Cspe is the amount required to realize the design criteria strength Fc.

[0023] In the next step S5, liquefied treated soil that satisfies the requirements of step S4 above is produced at a manufacturing plant and delivered to the construction site.

[0024] (Viscosity measurement) Next, the viscosity of the liquefied treated soil is measured in the following steps S6 to S8. First, in step S6, the liquefied treated soil is sampled from the delivery vehicle as an acceptance inspection of the delivered liquefied treated soil.

[0025] In the next step S7, the viscosity of the collected unconsolidated liquefied treated soil is measured. For example, the viscosity may be measured using a B-type viscometer.

[0026] In the next step S8, it is determined whether the measured viscosity is within the range of μspe determined in step S2 above. In other words, it is determined whether the requirement that the viscosity be within the range of μspe required for material separation resistance is met. If the result of the determination is pass (within range) (Yes in step S8), the process proceeds to the next step S9. If the result is fail (outside range) (No in step S8), the soil is returned to the manufacturing plant (the liquefied treated soil is discarded) (step S14), and the manufacturing method and composition are reviewed (step S18), and the process returns to step S5.

[0027] (Estimation of amount of solidification material) In the next step S9, the amount of solidification material contained in the unconsolidated liquefied soil that satisfies step S8 above is estimated. For example, the above-mentioned CW-QUIC can be used for the estimation. That is, the amount of solidification material is estimated by utilizing the initial pH change rate (time change characteristic) when the liquefied soil is neutralized with acid. The acid can be an acid of a constant concentration adjusted to, for example, about pH = 2.0, and can be an acid such as hydrochloric acid or an organic acid. According to this method, estimation is possible within about 30 minutes after the liquefied soil is collected. In addition, since no expensive equipment is required, it can be performed inexpensively. Therefore, the amount of solidification material can be estimated quickly and inexpensively. For reference, FIG. 2 (3) shows an image of a case where it is determined that the liquefied soil has sufficient strength.

[0028] In the next step S10, it is judged whether the amount of solidification material contained in the estimated liquefied treated soil satisfies the amount of solidification material added Cspe determined in the above step S4, or whether it satisfies the cement-water ratio C / Wspe. If it satisfies (Yes in step S10), it is judged that the specified construction quality is satisfied (passed) and the process proceeds to the next step S11. If it does not satisfy (No in step S10), it is judged that the specified construction quality is not satisfied (failed), and the soil is returned to the manufacturing plant (the liquefied treated soil is discarded) (step S15), and after reviewing the manufacturing method and the mix (step S18), the process returns to step S5. The construction quality is the quality of the construction, such as whether mixing is sufficient, whether sufficient solidification material is added, and whether it can be judged that the strength is ensured by the result.

[0029] In the next step S11, the unconsolidated liquefied treated soil that satisfies the above step S10 is poured into a predetermined location at the construction site. This completes the construction of the liquefied treated soil.

[0030] (Estimation of strength from shear wave velocity) Next, the strength of the hardened liquefied treated soil is estimated in the following steps S12 to S13 and S16. For the estimation, for example, the above-mentioned Vs-QUIC can be used.

[0031] First, in step S12, after the in-situ liquefied treated soil has hardened, the shear wave velocity is measured on the surface of the liquefied treated soil, and Vs-QUIC is performed.

[0032] In the next step S13, it is judged whether the measured shear wave velocity Vs value is equal to or greater than the Vs,spe determined in the above step S4. If it is equal to or greater than Vs,spe, it is expected that the strength of the in-situ liquefied treated soil will be equal to or greater than the design strength Fc. Therefore, if the measured Vs value is equal to or greater than Vs,spe, it is judged as passing, and the process is terminated (Yes in step S13). On the other hand, if the measured Vs value is less than Vs,spe (No in step S13) and the material age at the time of measurement is less than 28 days (Yes in step S16), the process returns to step S12, and the shear wave velocity Vs is measured again at a later date. On the other hand, if the measured Vs value is less than Vs,spe (No in step S13) and the material age at the time of measurement is 28 days or more (No in step S16), the poured area with insufficient strength is excavated (step S17), the manufacturing method and mix are reviewed (step S18), and then the process returns to step S5. In addition, a boring core may be used to measure the shear wave velocity Vs value. In this case, a boring core is collected and Vs-QUIC is performed on the collected core. The quality inspection is completed by the above procedure.

[0033] Figure 3 shows an example of the depth distribution of the unconfined compressive strength of liquefied treated soil applied using this embodiment. As shown in this figure, it can be determined that the applied liquefied treated soil has strength exceeding the design standard strength over the entire depth.

[0034] Therefore, according to this embodiment, by adjusting the viscosity to increase the resistance to material separation during the mix planning of the liquefied treated soil, it is possible to avoid instability in strength. Also, by applying CW-QUIC to the unconsolidated liquefied treated soil at the time of acceptance inspection, it is possible to judge the construction quality, such as whether or not sufficient solidification material has been added, in a short time (for example, one hour).

[0035] In addition, if viscosity measurements during on-site pouring and CW-QUIC reveal an excess or deficiency in viscosity or amount of solidifying material, the manufacturing method and mix plan can be immediately reviewed, and the liquefied treated soil can be reapplied before it hardens.

[0036] By carrying out Vs-QUIC in situ after the liquefied soil has solidified, the strength exhibited in situ can be directly evaluated. Compared to conventional compression tests of molded specimens taken from the discharge port during production or pouring at 28 days of age, the time required for quality inspection can be significantly reduced, allowing for an early assessment of construction quality.

[0037] As described above, the quality control method for liquefied treated soil according to the present invention is a method for controlling the construction quality of liquefied treated soil which contains soil material, cement-based solidification material, and water and is poured into the ground for construction, and includes the steps of: adjusting the fine particle content of the soil material or the amount of cement-based solidification material added when planning the mix proportion of the liquefied treated soil to adjust the viscosity of the liquefied treated soil in advance to within a predetermined range that enhances resistance to material separation; sampling the liquefied treated soil in an unconsolidated state immediately before construction; and measuring the viscosity of the sampled liquefied treated soil and determining whether the measured viscosity is within the predetermined range. The method includes the steps of: estimating the amount of cement-based solidification material contained in the collected liquefied treated soil or the mixing ratio of the cement-based solidification material to water and determining whether the estimated amount of cement-based solidification material or mixing ratio is within a predetermined range set based on the design standard strength; and measuring the shear wave velocity of the liquefied treated soil in a solidified state after construction and determining whether the measured shear wave velocity is within a predetermined range set based on the design standard strength.Therefore, by adjusting the viscosity to increase the resistance to material separation when mixing the liquefied treated soil, strength instability can be avoided.

[0038] In addition, according to another quality control method for liquefied treated soil of the present invention, the amount or mixing ratio of cement-based solidification material is estimated by utilizing the time change characteristics of the initial pH when the liquefied treated soil is neutralized with acid, so that the amount or mixing ratio of cement-based solidification material can be estimated quickly and inexpensively.

[0039] Furthermore, according to another quality control method for liquefied treated soil of the present invention, there is further provided a step of conducting a mixing test by mixing soil material, cement-based solidification material, and water prior to construction of the liquefied treated soil, and this mixing test includes a step of measuring shear wave velocity and testing compressive strength while changing the amount of cement-based solidification material added and the material age of specimens of liquefied treated soil, obtaining the relationship between the amount of cement-based solidification material added and the compressive strength, and the relationship between shear wave velocity and compressive strength, and a step of setting the amount of cement-based solidification material added and the shear wave velocity corresponding to a specified design standard strength based on the obtained relationship, so that the amount of cement-based solidification material added and the shear wave velocity required to realize the specified design standard strength can be accurately grasped. [Industrial Applicability]

[0040] As described above, the quality control method for liquefied treated soil according to the present invention is useful for construction management of liquefied treated soil used as backfill material, etc., and is particularly suitable for avoiding strength instability in liquefied treated soil.

Claims

1. A method for managing the quality of liquefied treated soil which contains a soil material, a cement-based solidification material, and water and is poured into the ground, comprising: A quality control method for liquefied treated soil, comprising the steps of: adjusting the fine particle content of the soil material or the amount of cement-based solidification material added when planning the mixture composition of liquefied treated soil, to adjust in advance the viscosity of the liquefied treated soil within a predetermined range that increases resistance to material separation; sampling the unconsolidated liquefied treated soil immediately before construction; measuring the viscosity of the sampled liquefied treated soil and determining whether the measured viscosity is within the predetermined range; estimating the amount of cement-based solidification material contained in the sampled liquefied treated soil or the mixture ratio of the cement-based solidification material to water, and determining whether the estimated amount of cement-based solidification material or mixture ratio is within a predetermined range set based on the design standard strength; and measuring the shear wave velocity of the liquefied treated soil in a solidified state after construction, and determining whether the measured shear wave velocity is within a predetermined range set based on the design standard strength.

2. A quality control method for liquefied treated soil as described in claim 1, characterized in that the amount or mixing ratio of cement-based solidification material is estimated by utilizing the time change characteristics of the initial pH when the liquefied treated soil is neutralized with acid.

3. A quality control method for liquefied treated soil as described in claim 1 or 2, characterized in that it further comprises a step of conducting a mixing test by mixing soil material, cement-based solidification material, and water prior to the construction of the liquefied treated soil, and this mixing test includes a step of measuring shear wave velocity and testing compressive strength while changing the amount of cement-based solidification material added and the material age of the liquefied treated soil test specimens, obtaining the relationship between the amount of cement-based solidification material added and the compressive strength, and the relationship between shear wave velocity and compressive strength, and a step of setting the amount of cement-based solidification material added and the shear wave velocity corresponding to a specified design standard strength based on the obtained relationship.

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