Quality control method for backfilled areas

Abstract

To provide a quality control method of a backfilled part which can avoid instability of strength.SOLUTION: A method for managing construction quality of a backfilled part which is constructed by using cement milk containing a cement-based solidification material and water includes: a step of, while recovering mud water from a hole that is backfilled to the ground, injecting cement milk into this hole and replacing the inside of the hole with the cement milk; and a step of estimating a cement-based solidification material amount contained in a material in an un-consolidated state at the time of replacement or a mixing ratio of the cement-based solidification material with respect to water, and determining whether or not the estimated cement-based solidification material amount or the mixing ratio is within a predetermined range set based on design reference strength.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for quality control of a backfilled portion. [Background technology]

[0002] In conventional redevelopment projects, when the framework or piles of an existing structure are not reused in a new structure, it is common to remove portions of the existing structure that interfere with the new structure and then backfill the area. Lean-mix cement milk is sometimes used as backfill material in existing pile removal and backfilling work. Lean-mix cement milk is composed of cement, water, and bentonite, with a water-cement ratio of approximately 200% to 400%. When lean-mix cement milk is injected into a removal hole, the lean-mix cement milk and the drilling mud water separate within the hole. Therefore, after injection of the lean-mix cement milk, attempts have been made to agitate the backfill area with a dedicated agitator to homogenize the physical properties of the backfill area along its depth. However, even in backfilling work that involves agitation, the strength of the backfill area may not meet the design strength standard (see, for example, Non-Patent Document 1). This is because the necessity of agitation and the agitation method are not clearly specified. Furthermore, mixing the backfilled area requires a separate, dedicated mixing device, which shortens the construction period and increases construction costs.

[0003] Backfilling work using lean-mix cement milk has traditionally been managed by the amount of lean-mix cement milk injected during the mix planning stage. The quality of the backfilled area is managed by the strength of mold specimens taken in an unconsolidated state or core specimens taken in an undisturbed state, depending on the contractor's judgment.

[0004] On the other hand, methods for determining the strength of soil cement using chemical techniques are known, for example, as described in Patent Documents 1 and 2 (hereinafter referred to as CW-QUIC). Also, a method for controlling the quality of soil cement using shear wave velocity is known, for example, as described in Patent Document 3 (hereinafter referred to as Vs-QUIC). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] "Properties of solidified mud backfilled into excavated holes after removal of existing piles," [online], [Retrieved February 22, 2022], Internet<URL:https: / / www.smcon.co.jp / service / assets / uploads / RandD / report-2019 / r-04.pdf> [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-119337 [Patent Document 2] Japanese Patent Publication No. 2020-094872 [Patent Document 3] Patent No. 4120809 Summary of the Invention [Problem to be solved by the invention]

[0007] As an example of insufficient strength in the backfilled area, a case where mixing work was carried out is shown in Figure 4. As shown in this figure, the strength (average value) of the core specimens taken from the original location was 55.7 kPa (at an age of 28 days) and 68.4 kPa (at an age of 56 days), compared to the design strength of 175 kPa, which did not satisfy the design strength.

[0008] If the in-situ strength of the backfilled area does not meet the design standard strength, there is a high possibility of problems such as hole bending, collapse of the hole walls, and misalignment of the piles when the new piles are installed, which will require a review of the soil properties used in the design of the new piles. To avoid this situation, the backfilled area must be re-excavated and re-constructed, which shortens the construction period and increases construction and material costs. Furthermore, the quality inspection of the backfilled area after construction is completed takes into account the age of the solidified material (compression tests are usually conducted after 28 days), which could affect the next process. For this reason, a quality control method that can avoid instability in the strength of the backfilled area was needed.

[0009] The present invention has been made in view of the above, and has an object to provide a quality control method for a backfilled portion that can avoid instability in strength. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems and achieve the object, the quality control method for backfilled areas according to the present invention is a method for controlling the construction quality of backfilled areas constructed using cement milk containing cement-based solidification material and water, and is characterized by comprising the steps of recovering mud water from the backfilled hole to the ground while injecting cement milk into the hole to replace the contents of the hole with cement milk, and estimating the amount of cement-based solidification material contained in the unconsolidated material at the time of replacement or the mixing ratio of the cement-based solidification material to water, and determining whether the estimated amount of cement-based solidification material or the mixing ratio is within a predetermined range set based on the design standard strength.

[0011] In addition, another quality control method for backfilled areas according to the present invention is characterized in that, in the above-mentioned invention, it further includes a step of mixing construction by-products that serve as cement raw materials with the cement milk to be replaced.

[0012] Furthermore, another quality control method for backfilled areas according to the present invention is characterized in that, in the above-mentioned invention, it further includes a step of measuring the shear wave velocity of the backfilled area in a solidified state after replacement is completed, and determining whether the measured shear wave velocity is within a predetermined range set based on the design standard strength. [Effects of the Invention]

[0013] According to the quality control method for backfilled areas of the present invention, there is provided a method for controlling the construction quality of backfilled areas constructed using cement milk containing cement-based solidification material and water, and the method includes the steps of recovering mud water from the hole to be backfilled and bringing it to the surface, while injecting cement milk into the hole to replace the contents of the hole with cement milk, and estimating the amount of cement-based solidification material contained in the unconsolidated material at the time of replacement 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. Therefore, by replacing the hole with cement milk while estimating whether the design standard strength is met, it is possible to avoid instability in the strength of the backfilled area after construction.

[0014] In addition, another quality control method for backfilled areas according to the present invention further includes a step of mixing construction by-products that serve as cement raw materials with the cement milk to be replaced, thereby achieving the effect of reducing the amount of cement used in the backfill material.

[0015] Furthermore, another quality control method for backfilled areas according to the present invention further includes a step of measuring the shear wave velocity of the backfilled area in a solidified state after replacement is completed, and determining whether the measured shear wave velocity is within a predetermined range set based on the design standard strength, thereby achieving the effect of directly evaluating the strength exhibited in situ. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a flow chart showing an embodiment of a quality control method for a backfilled portion according to the present invention. [Figure 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 material in the backfilled area is determined to have sufficient strength. [Figure 3] FIG. 3 is a side cross-sectional view showing a replacement method using lean cement milk. [Figure 4]FIG. 4 shows examples of the unconfined compressive strength of conventional lean blend cement milk (cited from FIGS. 7 and 8 of Non-Patent Document 1). DETAILED DESCRIPTION OF THE INVENTION

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes in detail an embodiment of a quality control method for a backfilled portion according to the present invention with reference to the accompanying drawings. However, the present invention is not limited to the embodiment.

[0018] As described above, to construct a backfill area of ​​stable quality using lean cement milk, it is necessary to thoroughly mix the lean cement milk and drilling mud water that have accumulated in a separated state in the removal hole, or to completely replace them with lean cement milk, and to quickly test the amount of cement added required to develop strength. Therefore, in this embodiment, quality control is carried out by the steps of completely replacing the drilling mud water with lean cement milk on site, mixing construction by-products that serve as cement raw materials with the lean cement milk during replacement, testing the cement amount of the lean cement milk at the time of replacement using the above-mentioned CW-QUIC, and testing the surface strength of the backfill area after solidification using the above-mentioned Vs-QUIC. 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 backfilling section, an indoor mix test is carried out according to the following steps S1 to S3.

[0020] First, in step S1, the amount of cement-based solidification material added is set to about 3 to 4 levels, and lean cement milk is prepared. It is desirable to prepare about 30 specimens of lean cement milk for each blend.

[0021] In the next step S2, shear wave velocity Vs is measured and compression tests are performed using specimens of lean cement milk at various ages. For example, it is preferable to perform the tests at ages of 8 hours, 12 hours, 24 hours, 2 days, 3 days, 7 days, 14 days, and 28 days, but other ages are also acceptable. It is preferable to use two to three specimens for Vs measurement and compression tests per age.

[0022] In the next step S3, 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 solidification material added (amount of cementitious solidification material) Cspe corresponding to the design strength Fc (the target value of strength for quality assurance), or the cement-water ratio (mix ratio) C / Wspe and Vs value (hereinafter referred to as Vs, spe) are determined. The amount of solidification material added Cspe is the amount required to achieve the design strength Fc.

[0023] (On-site construction of lean cement milk) Next, the lean blend cement milk is applied to the site in the following steps S4 to S8. First, in step S4, lean cement milk is produced at the on-site plant based on the amount of solidifying agent added determined in step S3 above.

[0024] In the next step S5, a replacement device for replacing the lean cement milk with drilling mud water is installed at a predetermined location on-site. For example, a device used in the reverse circulation method (cast-in-place pile) can be used as this replacement device.

[0025] In the next step S6, as shown in FIG. 3, an air lift pipe 3 with lifting capabilities is installed at the bottom 2 of the removal hole 1 installed on the ground surface G, and the drilling mud water in the removal hole 1 is collected through this air lift pipe 3 into a surplus soil tank (not shown) on the ground. At the same time, lean-mix cement milk produced at the on-site plant is injected into the removal hole 1 from the ground surface G using an injection device 4. Initially, the drilling mud water is collected, and over time, it changes into drilling mud water mixed with lean-mix cement milk. Note that the collection of the drilling mud water can be achieved using a general-purpose lifting device, and is not limited to an air lift pipe. Depending on the mechanism of the lifting device, lean-mix cement milk may be poured from the bottom of the removal hole and the drilling mud water may be collected from the shallow part of the removal hole.

[0026] In the next step S7, samples are taken from the mixture of drilling mud water and lean cement milk recovered on the ground, and CW-QUIC is performed on the samples, completing the replacement of the lean cement milk produced on site. The amount of solidification agent added (Cobs) or the cement-water ratio (C / Wobs) measured by CW-QUIC is recorded.

[0027] In the next step S8, dry powdered construction by-products, which serve as cement raw materials, are added to the mixture of drilling mud water and lean-mix cement milk collected on the ground. This mixture is poured into the removal hole 1 using an injection device 4 and collected from the removal hole 1 using an air lift pipe 3, thereby commencing circulating pouring into the removal hole 1. Examples of cement raw materials include fresh concrete sludge and recycled concrete powder. This reduces the water content of the unconsolidated lean-mix cement milk, making it easier to develop strength. Furthermore, reducing the water content of the lean-mix cement milk increases its viscosity, improving material separation resistance. Note that the addition of construction by-products is not required in the present invention. Furthermore, the materials added to the mixture are not limited to cement raw materials such as construction by-products; other materials may be used as long as they reduce the water content of the unconsolidated lean-mix cement milk and make it easier to develop strength.

[0028] (Estimation of amount of solidification material) In the next step S9, a sample is collected from the circulating lean cement milk on the ground. CW-QUIC is then performed on the collected sample to estimate the solidification agent amount Cobs (or the cement-water ratio C / Wobs) contained in the sample. Specifically, the solidification agent amount Cobs (or the cement-water ratio C / Wobs) is estimated based on the initial pH change rate (time-dependent change characteristics) when the collected sample is neutralized with acid. The acid can be a constant concentration acid adjusted to approximately pH 2.0, such as hydrochloric acid or an organic acid. This method allows for estimation within approximately 30 minutes of sample collection. Furthermore, it is inexpensive because it does not require expensive equipment. Therefore, the solidification agent amount or cement-water ratio can be estimated quickly and inexpensively. For reference, Figure 2(3) shows an example of a sample of lean cement milk (backfilled area) that is determined to have sufficient strength.

[0029] In the next step S10, it is determined whether the estimated amount of solidifying agent added, Cobs, is equal to or greater than Cspe, or whether the cement-water ratio, C / Wobs, is equal to or greater than C / Wspe. If the result of the determination is that the required conditions are met (Yes in step S10), it is determined that the required construction quality is met (passed), the input and circulation of construction by-products that will become cement raw materials is completed, and the process proceeds to the next step, S11. If the required conditions are not met (No in step S10), it is determined that the required construction quality is not met (failed), and the process returns to step S8.

[0030] (Estimation of strength) In the next step S11, after the lean-mix cement milk in situ (in the removal hole) has hardened, the shear wave velocity Vs is measured on the poured surface of the lean-mix cement milk to perform Vs-QUIC. Note that a borehole core may also be used to measure the shear wave velocity Vs value. In this case, a borehole core is collected and Vs-QUIC is performed on the collected core.

[0031] In the next step S12, it is determined whether the measured shear wave velocity Vs is equal to or greater than the Vs,spe determined in step S3. If Vs,spe is equal to or greater than Vs,spe, the strength of the backfilled area is expected to be equal to or greater than the design strength Fc. Therefore, if the measured Vs is equal to or greater than Vs,spe, the test is deemed to be acceptable, and the process ends (Yes in step S12). On the other hand, if the measured Vs is less than Vs,spe (No in step S12) and the material age at the time of measurement is less than 28 days (Yes in step S13), the process returns to step S11, and the shear wave velocity Vs is measured again at a later date. On the other hand, if the measured Vs is less than Vs,spe (No in step S12) and the material age at the time of measurement is 28 days or more (No in step S13), the poured area that is lacking in strength is excavated (step S14), and the manufacturing method and mix are reviewed (step S15), and the process returns to step S4. This completes the quality inspection.

[0032] According to this embodiment, the removal hole can be completely replaced with lean-mix cement milk without using any special dedicated equipment, thereby avoiding instability in strength. Also, by applying CW-QUIC to unconsolidated lean-mix cement milk, construction quality, such as whether or not sufficient solidification material has been added, can be determined in a short time (for example, one hour).

[0033] Since construction by-products, which are used as cement raw materials, are reused in the lean cement milk during circulation, the amount of cement used as backfill material can be reduced. In addition, by adding the construction by-products, which are used as cement raw materials, in a dry, powdered state, the water content of the lean cement milk is reduced, making it easier for strength to be developed. Furthermore, by reducing the water content of the lean cement milk, viscosity is increased, which improves resistance to material separation and stabilizes the quality of the backfill area.

[0034] By conducting Vs-QUIC in situ after the lean blend cement milk has solidified, it is possible to directly evaluate the strength developed in situ. Compared to conventional compression tests using molded specimens taken in an unconsolidated state or core specimens taken in an undisturbed state at 28 days of age, this method significantly reduces the time required for quality inspection, allowing for an early assessment of construction quality.

[0035] As described above, the quality control method for backfilled sections according to the present invention is a method for controlling the construction quality of backfilled sections constructed using cement milk containing cement-based solidification material and water, and includes the steps of recovering mud water from the hole to be backfilled and bringing it to the surface, while injecting cement milk into the hole to replace the contents of the hole with cement milk, and estimating the amount of cement-based solidification material contained in the unconsolidated material at the time of replacement 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.Therefore, by replacing the hole with cement milk while estimating whether the design standard strength is met, instability in the strength of the backfilled section after construction can be avoided.

[0036] In addition, another quality control method for backfilled areas according to the present invention further includes a step of mixing construction by-products that serve as cement raw materials into the cement milk to be replaced, thereby reducing the amount of cement used in the backfill material.

[0037] Furthermore, another quality control method for backfilled areas according to the present invention further includes a step of measuring the shear wave velocity of the backfilled area in a solidified state after replacement is completed, and determining whether the measured shear wave velocity is within a predetermined range set based on the design standard strength, thereby making it possible to directly evaluate the strength exhibited in situ. [Industrial Applicability]

[0038] As described above, the quality control method for backfilled areas according to the present invention is useful for managing the construction of backfilled areas constructed in existing pile removal and backfilling work, and is particularly suitable for avoiding instability in the strength of backfilled areas. [Explanation of symbols]

[0039] 1 Removal hole 2 bottom 3 Air lift pipe 4 Injection device G surface

Claims

1. A method for managing the construction quality of a backfilled section constructed using cement milk containing a cement-based solidification material and water, comprising: A step of recovering muddy water from the hole to be backfilled to the surface while injecting cement milk into the hole to replace the contents of the hole with cement milk; A quality control method for backfilled areas, comprising the steps of estimating the amount of cement-based solidification material contained in the unconsolidated material at the time of replacement or the mixing ratio of the cement-based solidification material to water, and determining whether the estimated amount of cement-based solidification material or the mixing ratio is within a predetermined range set based on the design standard strength.

2. 2. The method for quality control of backfilled areas according to claim 1, further comprising the step of mixing construction by-products that serve as cement raw materials with the cement milk to be replaced.

3. 3. The quality control method for backfilled areas according to claim 1, further comprising the step of measuring the shear wave velocity of the backfilled area in a solidified state after the replacement is completed, and determining whether the measured shear wave velocity is within a predetermined range set based on the design standard strength.

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