Density measurement method

Abstract

To properly measure ground density using a transmission type RI measuring device even if a recess is formed on the ground surface by a tamping roller.SOLUTION: A density measurement method uses an RI measurement device (1) that emits radiation into the ground and measures ground density based on scattered radiation from the ground. The density measurement method includes the steps of forming a recess in the ground surface, covering surroundings of the RI measurement device with a radiation shielding cover (33), installing the RI measurement device in a recess (45) formed in the ground surface, and starting density measurement in the recess using the RI measurement device.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a density measurement method. [Background technology]

[0002] Generally, the sand replacement method is used to manage the density of water-blocking materials in rockfill dams, while the transmission radio isotope (RI) method is used to manage the compaction of embankments in river and road earthworks. The sand replacement method and the transmission radio isotope method require drilling test holes and holes for inserting the radiation source. The transmission radio isotope method also requires a large workload, as it requires manual leveling of the measurement surface and carrying the measuring device to the measurement point. For this reason, the scattering radio isotope method, which does not require drilling work, has been proposed (see, for example, Patent Document 1). In the scattering radio isotope method, a radiation source and a detector are installed on the ground surface, radiation is emitted from the source into the ground, and the scattered radiation from the ground is detected by the detector to measure density. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-053127 Summary of the Invention [Problem to be solved by the invention]

[0004] In civil engineering works, the ground is compacted using a tamping roller or the like, which creates numerous depressions on the ground surface. For this reason, it is difficult to measure the density of the ground on a surface with depressions using the scattering RI method described in Patent Document 1.

[0005] The present invention has been made in consideration of the above points, and aims to provide a density measurement method that can accurately measure the density of the ground using an RI measurement device even if depressions are formed on the ground surface. [Means for solving the problem]

[0006] A density measurement method according to one aspect of the present invention is a density measurement method using an RI measurement device that emits radiation into the ground and measures the density of the ground based on scattered radiation from the ground, and includes the steps of forming a depression on the ground surface, covering the periphery of the RI measurement device with a radiation shielding cover, installing the RI measurement device in the depression formed on the ground surface, and starting density measurement in the depression using the RI measurement device. [Effects of the Invention]

[0007] A density measurement method according to one embodiment of the present invention utilizes a depression formed on the ground surface, and an RI measurement device is installed in the depression to measure the density of the ground. Even if radiation is emitted from the RI measurement device in the depression, the RI measurement device is surrounded by a shielding cover, which reduces the effects of diffuse reflection of the radiation on the surrounding walls of the depression. Therefore, the RI measurement device can accurately measure the density of the ground even in the depression. [Brief explanation of the drawings]

[0008] [Figure 1] 1A and 1B are a top view and a side view of the RI measurement device of the present embodiment. [Figure 2] 1 is a cross-sectional view of an RI measurement device according to an embodiment of the present invention. [Figure 3] 1 is an explanatory diagram of a density measurement method according to an embodiment of the present invention; [Figure 4] 10 is a graph showing an example of a comparison result of dry density. DETAILED DESCRIPTION OF THE INVENTION

[0009] The RI measurement device of this embodiment will be described below. Fig. 1 is a top view and a side view of the RI measurement device of this embodiment. Fig. 2 is a cross-sectional schematic view of the RI measurement device of this embodiment. Fig. 2(A) is a cross-sectional view of the RI measurement device of Fig. 1 taken along line AA, and Fig. 2(B) is a cross-sectional view of the RI measurement device of Fig. 1 taken along line BB. Arrows FR, RE, L, R, U, and LO in each figure indicate the front, rear, left, right, upper, and lower directions of the RI measurement device, respectively.

[0010] As shown in Figures 1(A) and 1(B), the RI measurement device 1 is a scattering-type RI measurement device that is configured to emit radiation into the ground and measure the density of the ground based on the scattered radiation from the ground. The case 10 of the RI measurement device 1 is formed in a rectangular parallelepiped shape (cubic shape in this embodiment). A display 11 is provided in the center of the top surface of the case 10, and a pair of handles 12 are provided on the left and right sides of the top surface of the case 10. A key panel 13 is provided on the front side of the top surface of the case 10, and a button switch 14, a charging connector 15, and a signal connector 16 are provided on the rear side of the top surface of the case 10.

[0011] An attachment hole for the radiation source 23 (see FIG. 2) is formed in the front side of the right wall of the case 10, and a thin plate-like radiation source cover 21 is screwed to the outer surface of the right wall of the case 10 to close the attachment hole. Only the thin plate-like radiation source cover 21 is provided on the peripheral wall of the case 10, and no components are provided on the front, left, or rear walls of the case 10. Therefore, there are no protrusions protruding outward from the peripheral walls of the case 10, and a shielding cover 33 (see FIG. 3), which will be described later, is formed around the periphery of the case 10 so that it can be attached. In addition, operation keys are provided on the top surface of the case 10, so that the RI measurement device 1 can be operated even when installed in a recess.

[0012] As shown in Figures 2(A) and 2(B), a gate-shaped fixing bracket 22 is installed along the inner surface of the front right wall of the case 10. The fixing bracket 22 is located inside the radiation source cover 21, and a plate-shaped radiation source 23 is installed within the case 10 via the fixing bracket 22. The radiation source 23 is a general-purpose Cs radiation source, and radiation is emitted radially from the radiation source 23. A fixing plate 25 is installed within the case 10, and the fixing plate 25 faces the left wall at the rear of the case 10. A box-shaped detector 26 is installed on the left side of the fixing plate 25, and the detector 26 detects scattered radiation scattered by soil particles in the ground.

[0013] In this way, the radiation source 23 is installed near the right front corner of the case 10, and the detector 26 is installed near the left rear corner of the case 10. Because the radiation source 23 and the detector 26 are installed at diagonal positions on the case 10, a longer separation distance is ensured between the radiation source 23 and the detector 26 inside the case 10 compared to when the radiation source 23 and the detector 26 are installed at the front, rear, left and right sides of the case 10. Furthermore, because the radiation source 23 and the detector 26 are rectangular parallelepiped, the radiation source 23 and the detector 26 are in contact with the opposing walls of the case 10, thereby ensuring a longer separation distance. Note that the term "diagonal" does not necessarily mean a perfect diagonal, but also includes a positional relationship that is approximately diagonal and can be considered as a diagonal.

[0014] A shielding body 31 that shields radiation between the radiation source 23 and the detector 26 is installed inside the case 10. The shielding body 31 is formed of a plurality of rectangular shielding bars 32. In a plan view, the plurality of shielding bars 32 are arranged diagonally between the radiation source 23 and the detector 26 with their longitudinal directions facing the front-to-rear direction. More specifically, from right to left, the first row of shielding bars 32 faces the radiation source 23, and the last row of shielding bars 32 faces the detector 26. The shielding bars 32 in the rear row are arranged one step further back than the front row of shielding bars 32. In a plan view, a minimum number of shielding bars 32 are required to block radiation that is directly irradiated from the radiation source 23 to the detector 26.

[0015] The height of the detector 26 is greater than the height of the radiation source 23, and the multiple shielding bars 32 are stacked so that they increase in height from the radiation source 23 to the detector 26 in a side view. More specifically, the first row of shielding bars 32 is stacked three levels high, with the shielding bars 32 stacked higher than the radiation source 23, and the last row of shielding bars 32 is stacked five levels high, with the shielding bars 32 stacked higher than the detector 26. In a side view, a minimum number of shielding bars 32 are used to shield the detector 26 from radiation that is directly emitted from the radiation source 23. In this way, by reducing the number of shielding bars 32, costs can be reduced and the weight of the RI measurement device 1 can be made lighter.

[0016] Furthermore, the multiple shielding bars 32 are made of tungsten. By using tungsten, which has high shielding performance, for the shielding bars 32, the radiation source 23 and the detector 26 are brought closer together, thereby achieving a compact RI measurement device 1. For example, lead has a smaller specific gravity than tungsten, and if lead were used for the shielding bars, more identical bars would be required. In this way, in the RI measurement device 1 of this embodiment, the diagonal corners of the case 10 are used to ensure the distance between the radiation source 23 and the detector 26, and the tungsten, which has high shielding performance, blocks direct radiation from the radiation source 23 to the detector 26, thereby achieving a compact size.

[0017] Specifically, the case 10 of the RI measurement device 1 of this embodiment is compact, measuring 100 mm × 100 mm × 100 mm. Twenty-two shielding bars 32 measuring 50 mm × 10 mm × 10 mm and a detector 26 measuring 38 mm × 38 mm × 25 mm are installed inside the case 10. By minimizing the number of shielding bars 32, the weight of the RI measurement device 1 is kept to 2.5 kg. This makes the RI measurement device 1 easy to carry and enables measurement of ground density within a depression measuring 110 mm × 130 mm × 85 mm formed by a tamping roller.

[0018] A density measurement method using an RI measurement device will be described with reference to Fig. 3. Fig. 3 is an explanatory diagram of the density measurement method of this embodiment.

[0019] As shown in Figure 3(A), when compacting the ground, the ground surface is compacted by a tamping roller 41. Countless protrusions 43 are provided on the outer peripheral surface of roller 42 of tamping roller 41, and the weight of roller 42 presses protrusions 43 into the ground surface, compressing the highly viscous soil and compacting the ground. After tamping roller 41 passes, countless depressions 45 are formed on the ground surface. Because the tips of protrusions 43 of tamping roller 41 are formed flat, the bottoms of depressions 45 created by compacting the ground surface are also formed flat. The depressions 45 on the ground surface are used to form the measurement surface of RI measurement device 1.

[0020] 3(B), a shielding cover 33 that shields against radiation is attached to the peripheral wall of the case 10 of the RI measurement device 1. The shielding cover 33 is formed from a lead plate and is formed in a rectangular shape in a plan view so as to cover all four sides of the case 10 of the RI measurement device 1. Since there are no protrusions on the peripheral wall of the case 10, the shielding cover 33 can be easily attached to the case 10. Note that, since it is only necessary for the radiation shielding cover 33 to cover the periphery of the RI measurement device 1, instead of attaching the shielding cover 33 to the case 10 of the RI measurement device 1, the shielding cover 33 may be installed in the recess 45 so as to cover the inner periphery of the recess 45.

[0021] As shown in Figure 3(C), the RI measurement device 1 is installed in a depression 45 formed on the ground surface. The front-to-back and left-to-right dimensions of the RI measurement device 1 with the shielding cover 33 attached are smaller than the front-to-back and left-to-right dimensions of the depression 45, and the height of the RI measurement device 1 with the shielding cover 33 attached is greater than the height of the depression 45. Because the top of the RI measurement device 1 protrudes from the depression 45, it is easy to install the RI measurement device 1 in the depression 45. Furthermore, because the bottom of the depression 45 is formed flat and the effect of unevenness is reduced by the miniaturization of the RI measurement device 1, unevenness correction is not required, reducing the workload.

[0022] As shown in Figure 3(D), density measurement is started in the cavity 45 by the RI measurement device 1. When the operation key is pressed to start measurement, the wet density and average RI count are displayed on the display 11 (see Figure 1) after the measurement time has elapsed. At this time, since the RI measurement device 1 is surrounded by a shielding cover 33, radiation directed from the radiation source 23 toward the inner periphery of the cavity 45 is blocked by the shielding cover 33, and the influence of diffuse reflection of radiation on the peripheral wall of the cavity 45 is suppressed. In addition, direct radiation from the radiation source 23 to the detector 26 is blocked by multiple shielding bars 32. Therefore, accurate measurements are made based on scattered radiation from the ground.

[0023] An example of the measurement results of density measurement using an RI measurement device will be described with reference to Fig. 4. Fig. 4 is a graph showing an example of the comparison results of dry density. The vertical axis of the graph in Fig. 4 is the dry density [g / cm 3 ] and the horizontal axis of the graph indicates the number of measurements.

[0024] The dry density of the ground was measured using three methods: the sand replacement method, the transmission RI method, and the scattering RI method. In the sand replacement method, a test hole was drilled on the ground surface, the weight of the soil was measured, and the volume of the test sand filled in the test hole was replaced with the volume of the soil to determine the dry density of the ground. In the transmission RI method, the dry density of the ground was measured using SRID (registered trademark), by inserting a radiation source rod into the ground. In the scattering RI method, a shielding cover was attached to the RI measurement device of this embodiment, and the RI measurement device was installed in a depression formed by the rolling pressure of a tamping roller. The wet density of the ground was then measured using the RI measurement device, and the dry density was calculated based on this wet density and the moisture content.

[0025] As shown in Figure 4, the sand replacement method, the transmission RI method, and the scattering RI method gave almost identical measurement results. Specifically, the dry density of the sand replacement method was approximately 1.77-1.85 g / cm 3 ], and the dry density for the transmission RI method is approximately 1.64-1.71 [g / cm 3 ], and the dry density for the scattering RI method is approximately 1.76-1.82 [g / cm 3 In this way, it was confirmed that sufficient measurement accuracy could be obtained even when the small RI measurement device of this embodiment was installed inside a depression. Furthermore, when the RI measurement device of this embodiment was used to measure on the ground surface outside the depression, the dry density was approximately 1.75 [g / cm 3 ] and sufficient measurement accuracy was obtained.

[0026] As described above, according to the density measurement method of this embodiment, a depression 45 on the ground surface formed by the rolling of the tamping roller 41 is utilized, and the RI measurement device 1 is installed in the depression 45 to measure the density of the ground. Even if radiation is emitted from the RI measurement device 1 in the depression 45, the RI measurement device 1 is surrounded by the shielding cover 33, so the influence of diffuse reflection of the radiation on the peripheral wall of the depression 45 is suppressed. Therefore, the density of the ground can be measured satisfactorily by the RI measurement device 1 even in the depression 45.

[0027] In this embodiment, the steps of rolling the ground surface with a tamping roller, covering the periphery of the RI measurement device with a shielding cover, and installing the RI measurement device in the depression are performed, but the order of these steps may be changed as appropriate. For example, after covering the periphery of the RI measurement device with a shielding cover, the ground surface may be rolled with a tamping roller to form a depression, and the RI measurement device may be installed in the depression.

[0028] In addition, in this embodiment, the depressions are formed by rolling the ground surface with a tamping roller having countless protrusions, but the depressions may be formed on the ground surface by a machine other than a tamping roller, or may be formed on the ground surface by hand.

[0029] In addition, in this embodiment, the shielding body is formed by a plurality of shielding bars, but the shielding body may extend between the radiation source and the detector in a diagonal direction from the radiation source to the detector. For example, the shielding body may be formed by a plurality of shielding plates interposed between the radiation source and the detector, or may be formed by a single member interposed between the radiation source and the detector.

[0030] Although the shielding body is made of tungsten in this embodiment, the shielding body may be made of any material that can block radiation. For example, the shielding body may be made of lead.

[0031] Furthermore, in this embodiment, a general-purpose Cs radiation source is used as the radiation source, but other radiation sources that can be used to measure the density of the ground may also be used.

[0032] Furthermore, in this embodiment, the case of the RI measurement device is formed in a cube shape, but the case of the RI measurement device may be formed in a rectangular parallelepiped shape.

[0033] In addition, although the radiation source and the detector are formed in a rectangular parallelepiped shape in this embodiment, the shapes of the radiation source and the detector are not particularly limited as long as they are formed so that they can be installed at diagonal corners of the case.

[0034] Furthermore, the above-mentioned RI measuring device is effective not only for measuring the density of impermeable materials in rockfill dams, but also for measuring the density of filter materials and semi-permeable materials.

[0035] The RI measurement device may be transported by a drone, etc. In this case, the RI measurement device may be provided with a bracket for mounting the drone, etc.

[0036] As described above, the first aspect is a density measurement method using an RI measurement device (1) that emits radiation into the ground and measures the density of the ground based on scattered radiation from the ground. The method includes the steps of forming a depression on the ground surface, covering the periphery of the RI measurement device with a radiation shielding cover (33), installing the RI measurement device in the depression (45) formed on the ground surface, and starting density measurement in the depression using the RI measurement device. According to this configuration, a depression formed on the ground surface is utilized, and the RI measurement device is installed in the depression to measure the density of the ground. Even if radiation is emitted from the RI measurement device in the depression, the periphery of the RI measurement device is covered with the shielding cover, thereby suppressing the effects of diffuse reflection of the radiation on the surrounding walls of the depression. Therefore, the RI measurement device can accurately measure the density of the ground even in the depression.

[0037] In a second aspect, in the first aspect, the step of forming the depressions includes forming the depressions by rolling the ground surface with a tamping roller having numerous protrusions. According to this configuration, the density of the ground is measured by utilizing the depressions formed on the ground surface by the rolling of the tamping roller.

[0038] In the third aspect, the RI measurement device of the first or second aspect includes a rectangular parallelepiped case (10) installed in a depression, a radiation source (23) installed in the case and emitting radiation, a detector (26) installed in the case and detecting scattered radiation, and a shield (31) installed in the case and blocking radiation, with the radiation source and detector installed at diagonal positions on the case. With this configuration, the radiation source and detector are installed at diagonal positions on the case, ensuring sufficient spacing between the radiation source and detector within the case, thereby miniaturizing the RI measurement device. The compact case reduces the effect of unevenness on the ground surface, allowing density measurements to be performed even in depressions formed by a tamping roller.

[0039] In the fourth aspect, in the third aspect, a shield extends between the radiation source and the detector in a diagonal direction from the radiation source to the detector. With this configuration, the shield extends in the diagonal direction, so that radiation emitted from the radiation source toward the detector is effectively shielded, thereby reducing the weight of the RI measurement device. The reduced weight of the RI measurement device improves the workability of installation in a recess.

[0040] Although the present embodiment and modifications have been described, other embodiments may be obtained by combining the above-described embodiments and modifications in whole or in part.

[0041] Furthermore, the technology of the present invention is not limited to the above-described embodiments, and may be variously changed, substituted, or modified within the scope of the spirit of the technical idea. Furthermore, if the technical idea can be realized in a different way due to technological advances or other derived technologies, it may be implemented using that method. Therefore, the claims cover all embodiments that may fall within the scope of the technical idea. [Explanation of symbols]

[0042] 1: RI measurement device 10: Case 23 :Radiation source 26: Detector 31: Shield 32: Shielding bar 33: Shielding cover 41: Tamping roller 43: Protrusion 45: Depression

Claims

1. A density measurement method using an RI measurement device that emits radiation into the ground and measures the density of the ground based on scattered radiation from the ground, comprising: forming a depression in the surface of the earth; a step of covering the periphery of the RI measurement device with a radiation shielding cover; placing the RI measurement device in a depression formed on the ground surface; and starting density measurement in the cavity by the RI measurement device.

2. 2. The density measuring method according to claim 1, wherein the step of forming the depressions comprises forming the depressions by rolling the ground surface with a tamping roller having numerous protrusions.

3. The RI measurement device is a case formed in a rectangular parallelepiped shape and installed in a recess; a radiation source disposed within the case and emitting radiation; a detector disposed within the case to detect scattered radiation; a shielding body that is installed in the case and that blocks radiation, 3. The density measurement method according to claim 1, wherein the radiation source and the detector are disposed at diagonal positions of the case.

4. 4. The density measurement method according to claim 3, wherein the shielding body extends between the radiation source and the detector in a diagonal direction from the radiation source toward the detector.

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