Methods for quality control of embankments

Abstract

This invention provides a quality control method for embankments that allows for easy confirmation that the construction moisture content of the embankment material before compaction is within an acceptable range by utilizing the measurement results of electrical resistivity, which can be measured in a short time. [Solution] This is a method for quality control of embankments constructed by spreading and compacting embankment material. Then, there is the step of collecting embankment material before compaction, and the wet density ρ of the collected embankment material. t Step S3 involves measuring the electrical resistivity R after filling a mold, estimating the volumetric water content θ from the measured electrical resistivity R, and determining the degree of saturation Sr from the porosity n and volumetric water content θ, and the degree of saturation Sr and soil particle density ρ s and wet density ρ t The system includes a step S31 to determine the construction moisture content w based on the above, and a step S3 to confirm whether the construction moisture content w falls within a predetermined range of moisture content that allows for appropriate compaction.

Description

[Technical Field]

[0001] This invention relates to a method for quality control of embankments constructed by spreading and compacting embankment material. [Background technology]

[0002] In embankment construction for roads, rivers, railways, and land development, the moisture content of the embankment material, which greatly affects the quality of the embankment, is measured as part of the daily management of the construction moisture content ratio. In typical embankment construction, the embankment material is transported from a storage location such as a stockyard to the embankment construction site, spread using construction machinery, and compacted.

[0003] The quality of compaction work on such embankments is greatly affected by the moisture content of the soil. Therefore, it is necessary to measure the moisture content of the embankment material at some point during the process from storage to transportation and spreading with construction machinery, and to confirm that it is within an acceptable range before proceeding with compaction work.

[0004] The water content is a mass ratio obtained as the percentage of the mass difference between a wet sample and a dry sample of soil relative to the mass of a dry sample. As disclosed in Non-Patent Document 1, etc., the embankment material is brought to a facility with drying equipment, the mass of the wet sample is measured, and then the soil sample is dried using a constant-temperature drying oven (JIS A 1203) or a microwave oven (JGS 0122), after which the mass of the dry sample is measured.

[0005] In addition, the mass of the dry sample may be measured on-site by direct heating (ASTM D4959-10). The construction moisture content ratio is calculated from the mass of the dry sample and the mass of the wet sample, which are measured by either of these methods. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2023-119320 [Patent Document 2] Japanese Patent Publication No. 2024-42567 [Non-patent literature]

[0007] [Non-Patent Document 1] Methods and Explanations of Geotechnical Material Testing [First Revised Edition], Japanese Geotechnical Society, Laboratory Testing Standards and Criteria Committee, Japanese Geotechnical Society, December 21, 2020. [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, both the constant-temperature drying oven method and the microwave method require the on-site technician to leave the construction site to transport the sample to a facility with drying equipment and power supply. This means that if the technician is absent, the construction work may be temporarily suspended or on-site management may not be adequately maintained.

[0009] Furthermore, the method using a constant-temperature drying oven takes 24 hours just for drying the sample, and the microwave method takes about 40 to 50 minutes, so it is not possible to determine the moisture content immediately.

[0010] On the other hand, direct heating methods carry the risk of sample rupture or combustion due to rapid high-temperature heating, as well as the risk of uncertainty in measurement values ​​due to uneven drying, and require skilled techniques to adjust the heating temperature.

[0011] Incidentally, as disclosed in Patent Documents 1 and 2, a method is known for controlling the quality of embankment after compaction by measuring the electrical resistivity of the surface of the compacted embankment and estimating the dry density of the completed embankment based on the measurement results, thereby confirming the effectiveness of compaction by compaction machinery. However, these documents do not describe the management of embankment material carried out before compaction.

[0012] Therefore, the present invention aims to provide a quality control method for embankments that makes it possible to easily confirm that the construction moisture content of the embankment material before compaction is within an acceptable range by utilizing the measurement results of electrical resistivity, which can be measured in a short time. [Means for solving the problem]

[0013] To achieve the above objective, the present invention provides a method for quality control of an embankment constructed by spreading and compacting embankment material, comprising the steps of: collecting embankment material before compaction; and determining the wet density ρ of the collected embankment material. t The steps include: measuring the electrical resistivity R after filling a mold; estimating the volumetric water content θ of the embankment material taken from the measured electrical resistivity R using a predetermined relationship between volumetric water content and electrical resistivity; determining the degree of saturation Sr from the porosity n set to a predetermined value and the estimated volumetric water content θ; and determining the degree of saturation Sr and the soil particle density ρ of the embankment material which was determined in advance. s and the wet density ρ t The method is characterized by comprising the steps of determining the construction moisture content w based on and confirming whether the construction moisture content w falls within a predetermined range of moisture content that enables appropriate compaction.

[0014] Here, it is preferable that the mold has four electrodes for measuring electrical resistivity. Also, the relationship between the volumetric water content and electrical resistivity, the porosity n and the soil particle density ρ s Alternatively, the range of the water content is preferably set based on the results of a laboratory soil test or a test construction conducted in advance using the embankment material. [Effects of the Invention]

[0015] The embankment quality control method of the present invention, configured in this way, involves measuring the wet density ρ of the embankment material collected before compaction. tMeasure the electrical resistivity R, and determine the construction water content ratio w based on these measured values and the relationship between the volume water content ratio and the electrical resistivity that was previously known.

[0016] By using the measurement results of the electrical resistivity R that can be measured in a short time in this way, it is possible to implement quality control to confirm that the construction water content ratio of the embankment material before compaction is within the allowable range.

Brief Description of the Drawings

[0017] [Figure 1] This is a flowchart for explaining the steps of the embankment quality control method of this embodiment. [Figure 2] This is an explanatory diagram showing an overview of the appropriate range of the construction water content ratio of the embankment material. [Figure 3] This is an explanatory diagram showing an overview of the mold for measuring the electrical resistivity. [Figure 4] This is an explanatory diagram showing an overview of the method of filling the soil sample into the mold. [Figure 5] This is an explanatory diagram for explaining the method of obtaining the porosity n from the relationship between the saturation Sr and the volume water content ratio θ in the laboratory soil test. [Figure 6] This is an explanatory diagram for explaining the method of obtaining the relationship (calibration curve) between the volume water content ratio θ and the electrical resistivity R in the electrical resistivity measurement test. [Figure 7] This is an explanatory diagram exemplifying the method of obtaining the volume water content ratio θ from the electrical resistivity R measured to manage the construction water content ratio of the embankment material.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart for explaining the steps of the embankment quality control method of this embodiment.

[0019] The embankment quality control method of this embodiment can be broadly divided into preparatory steps performed before the start of embankment construction and steps for quality control of the embankment material during embankment construction. The embankment quality control method of this embodiment is applied to efficiently construct embankments.

[0020] Embankments are constructed by transporting embankment materials, which are stored in a stockyard or similar location, from the storage site to the embankment construction site, spreading the transported embankment materials onto the construction site using construction machinery, and compacting them with compaction machinery such as compaction rollers.

[0021] When constructing such embankments, preliminary work includes laboratory soil testing (Step S1) to understand the physical properties of the embankment material, and test construction using the embankment material and compaction equipment to be used in construction. Construction specifications such as the physical properties of the embankment material, the spreading thickness, the number of compaction cycles required by the compaction equipment, and the optimal range of construction moisture content are determined.

[0022] Figure 2 is an explanatory diagram illustrating the general range of appropriate moisture content for embankment materials during construction, with the horizontal axis representing moisture content and the vertical axis representing dry density. The degree of compaction (dry density), which is used to evaluate the final quality of the embankment, is influenced not only by the material of the embankment but also by the moisture content before compaction.

[0023] Therefore, before carrying out embankment construction, it is necessary to conduct laboratory soil tests (Step S1, Step S2) to determine the range of moisture content (construction moisture content range) that allows for proper compaction, as shown in Figure 2. This optimal construction moisture content range can be determined through test construction, or it may be known in advance depending on the embankment material.

[0024] During the construction of the embankment, quality control is performed to ensure that the construction moisture content falls within the range shown in Figure 2 before compaction (Step S3). Specifically, the construction moisture content is checked by taking a sample of the embankment material from storage, during transport, or during spreading. The shorter the time required to check the construction moisture content of the embankment material, the sooner compaction work can be started (Step S4), leading to increased construction efficiency.

[0025] Therefore, in the embankment quality control method of this embodiment, the construction water content of the embankment material is determined from the measurement results of electrical resistivity. Measuring the electrical resistivity of the embankment material filled in the mold can be done in a short time.

[0026] Figure 3 is an explanatory diagram illustrating the outline of a mold for measuring electrical resistivity. This mold is a container for measuring electrical resistivity using the four-electrode method. A soil sample is filled into the mold, which is made of insulating material, and the electrical resistivity R is measured using the electrode terminals attached to the side of the mold.

[0027] Specifically, a test specimen consisting of a soil sample housed in an insulating mold has a pair of current electrodes connected to the top and bottom, and a pair of potential difference electrodes connected in the middle. Then, using the two current electrodes, an AC power supply I(A) is passed through the test specimen from a constant voltage ammeter, and the potential difference V(V) generated between the two potential difference electrodes is measured with a voltmeter, and the electrical resistivity R(Ω)(=πd) is calculated using Ohm's law. 2 Calculate ( / 4L·V / I). Here, L represents the electrode spacing, which is 50 mm in Figure 3.

[0028] In conventional resistivity surveys of natural ground and rock masses, it is known that resistivity varies depending on porosity, saturation, pore water, mineral properties, and temperature, resulting in a wide range of parameters.

[0029] In contrast, the materials used at embankment construction sites are handled after prior investigation, so their physical properties are known. We hypothesized that, given the same embankment material and limited density conditions (porosity), the water content conditions could be determined by electrical resistivity, and confirmed this through experiments. In short, we experimentally determined the relationship that holds true within the range of water content ratios that allows for appropriate compaction, as shown in Figure 2.

[0030] The water content parameter obtained from electrical resistivity is the volume ratio of water to the total soil volume. For construction sites to use a mass ratio-based construction water content, density information is required to convert it to a water content ratio.

[0031] Therefore, in order to calculate the construction water content from the electrical resistivity in embankment construction, the items that are set in advance in the preparatory work will be explained with reference to Figure 1. The preparatory work includes an indoor soil test (Step S1) to confirm the physical properties of the embankment material, which is generally performed, and an indoor soil test (Step S2) to measure the electrical resistivity R of the test specimen, which is performed in the quality control method of the embankment in this embodiment.

[0032] In detail, step S2 is the calibration curve for electrical resistivity R (R = A × [θ] B The coefficients (A,B) of ) will be tested. That is, a test specimen will be prepared and an electrical resistivity R will be measured. In this electrical resistivity R measurement test, a mold with known volume and mass will be prepared, as shown in Figure 3.

[0033] The mold container is filled with embankment material until it is evenly full. Figure 4 is an explanatory diagram illustrating the general method of filling the mold with soil samples. The soil samples in the mold are compacted manually in five layers using a tamper, referring to the JGS 0520 standard.

[0034] The test specimen prepared in this manner is measured by its total weight including the mold. Furthermore, a constant voltage power supply ammeter and voltmeter are connected to the four electrodes of the mold in this state, as shown in Figure 3, and the electrical resistivity R is measured.

[0035] After measuring the electrical resistivity R, the specimen is taken out of the mold, and the water content is measured by an indoor soil test. The measurement test (step S2) of the electrical resistivity R is repeatedly performed a plurality of times using specimens under different conditions with different water contents w (saturation degrees Sr) of the specimens.

[0036] For example, specimens with five to six different conditions are prepared and data is collected. FIG. 5 is a graph summarizing the data collected in the measurement test of the electrical resistivity R in terms of the relationship between the saturation degree Sr and the volumetric water content θ.

[0037] Here, the volumetric water content θ is the ratio of the volume of water to the volume of the specimen (volume ratio), and can be calculated if the water content w (mass ratio) of the specimen, the density ρ of water w and the density ρ of soil particles s are known. On the other hand, the saturation degree Sr is the ratio of the volume of water to the volume of voids in the specimen (volume ratio), and can be calculated if the water content w (mass ratio) of the specimen and the density ρ of water w are known.

[0038] Therefore, as shown in FIG. 5, the results of the indoor soil tests of a plurality of specimens are plotted in terms of the relationship between the saturation degree Sr and the volumetric water content θ, and a regression equation of a straight line is obtained by the least squares method. [[ID=ID=19]]

[0039] Here, the relationship between the porosity n, which is the ratio of the volume of voids to the volume of the specimen (volume ratio), the saturation degree Sr, and the volumetric water content θ is expressed by the following equation. θ = n·Sr

[0040] That is, the slope of this regression line indicates the porosity n. Thus, it can be seen that within a limited range of water content for the same fill material, the porosity n can be set to a predetermined value.

[0041] On the other hand, FIG. 6 is a graph summarizing the results of the above-described measurement test of the electrical resistivity R in terms of the relationship between the volumetric water content θ and the electrical resistivity R. That is, the results of measuring the electrical resistivity R using a plurality of specimens are plotted in terms of the relationship with the volumetric water content θ, and a regression equation (calibration curve) is obtained by the least squares method.

[0042] The calibration curve obtained in this way is expressed by the following equation. R = A·θ B In other words, the coefficients A and B of the calibration curve can be determined from the results of the measurement test of electrical resistivity R.

[0043] Thus, using the calibration curve determined in advance during the preparatory work, the construction moisture content w is calculated during embankment construction (Step S31). Specifically, during embankment construction, the embankment material is sampled from the storage location before compaction.

[0044] Then, similar to the preparatory work described above, the collected embankment material is filled into the mold to prepare the test specimen. The wet density ρ of the collected embankment material t This can be determined by measuring the total weight of the mold and the test specimen at the construction site.

[0045] Next, a constant voltage power supply ammeter and voltmeter are connected to the four electrodes of the mold to measure the electrical resistivity R (see Figure 3). Figure 7 is an explanatory diagram illustrating a method for determining the volumetric water content θ from the measured electrical resistivity R in order to control the construction water content w of the embankment material.

[0046] In short, the volumetric water content θ can be determined by applying the value of electrical resistivity R measured at the embankment construction site to the calibration curve obtained in the preparatory work. As mentioned above, the volumetric water content θ, porosity n, and saturation degree Sr are related by the equation θ = n·Sr.

[0047] The porosity n is set to a predetermined value during the preparatory work, as described above with reference to Figure 5. Therefore, the degree of saturation Sr can be determined from the known volumetric water content θ and porosity n. Sr=θ / n

[0048] The construction water content w of the embankment material used in embankment construction can be estimated using the following formula (see Figure 1). w / 100=[ρ w·(Sr / 100) / ρ t -(Sr / 100) / (ρ s / ρ w )]·ρ t / (ρ t -ρ w (Sr / 100))

[0049] The estimated construction moisture content w is then checked to see if it falls within the acceptable range of construction moisture content (see Figure 2) (Step S3). If it falls outside the acceptable moisture content range, compaction work cannot proceed, so the embankment material is readjusted, and the calculation of the construction moisture content w is repeated until it falls within the acceptable range.

[0050] If the construction moisture content w of the embankment material falls within the range of moisture content that allows for proper compaction, the next construction steps, such as spreading and compacting the embankment material, can be started (Step S4).

[0051] Next, the operation of the embankment quality control method of this embodiment will be explained. The quality control method for the embankment constructed in this manner involves measuring the wet density ρ of the embankment material collected before compaction. t The electrical resistivity R is measured, and the construction moisture content w is determined based on these measurements and the relationship between volumetric moisture content and electrical resistivity (see Figure 7) which was determined in advance.

[0052] By utilizing the measurement results of electrical resistivity R, which can be measured in a short time, it becomes possible to easily confirm, as part of quality control for the embankment material, that the construction moisture content w of the embankment material before compaction is within the acceptable range as illustrated in Figure 2.

[0053] In other words, with the embankment quality control method of this embodiment, there is no need to move to another location with drying equipment to measure the construction moisture content w, and the electrical resistivity R and the soil weight (wet density ρ) of the embankment material can be measured at the embankment construction site. t The construction moisture content w can be determined simply by measuring ( ).

[0054] This allows on-site technicians to avoid being absent from the site for moisture content measurement, and enables a smooth transition to the next construction step, compaction, thus contributing to increased efficiency and labor savings in embankment construction.

[0055] As mentioned above, conventional electrical resistivity surveying techniques targeting natural ground and bedrock involve many parameters. However, under conditions where the target is limited to embankment material, the range of variation of each parameter affecting electrical resistivity R becomes limited. Therefore, by utilizing this relationship and conducting the necessary physical property tests for construction management in advance, it is possible to estimate the construction moisture content w at the construction site quickly and with high accuracy.

[0056] While embodiments of the present invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments, and any design modifications that do not depart from the spirit of the present invention are included in the present invention.

[0057] For example, the above embodiment described an example in which a measuring mold having four electrodes for measuring electrical resistivity is used, but it is not limited to this, and the electrical resistivity of the embankment material may be measured by any method.

Claims

1. This is a method for quality control of embankments constructed by spreading and compacting embankment material. The steps include collecting embankment material before compaction, The wet density ρ of the collected embankment material t The steps include measuring the electrical resistivity R after filling the mold, The steps include: estimating the volumetric water content θ of the embankment material taken from the measured electrical resistivity R using a predetermined relationship between volumetric water content and electrical resistivity; The steps include determining the degree of saturation Sr from the porosity n set to a predetermined value and the estimated volumetric water content θ, The saturation level Sr and the soil particle density ρ of the embankment material, which were determined in advance, are mentioned above. s and the wet density ρ t The steps include determining the construction moisture content w based on the above, A method for managing the quality of an embankment, characterized by comprising the step of confirming whether the construction moisture content w falls within a predetermined range of moisture content that allows for appropriate compaction.

2. The method for quality control of an embankment according to claim 1, characterized in that the mold has four electrodes for measuring electrical resistivity.

3. The relationship between the volumetric water content and electrical resistivity, the porosity n and the soil particle density ρ s The method for controlling the quality of an embankment according to claim 1 or 2, characterized in that the value is set based on the results of an indoor soil test conducted in advance using the embankment material.

4. The method for controlling the quality of an embankment according to claim 3, characterized in that the range of water content is set based on the results of a test construction carried out in advance using the embankment material.

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