Ground density measurement device and measurement method

Abstract

This ground density measurement device is provided with a first measurement unit, a second measurement unit, and a control unit. The first measurement unit is installed underground, in ground to be measured, and measures the muon flux. The second measurement unit is installed at a predetermined location for reference, and measures the muon flux. The control unit acquires measured values of the muon flux that were measured simultaneously, and estimates the areal density h of the ground to be measured on the basis of the value IA / IB of the ratio of the measured value IA of the muon flux measured by the first measurement unit to the measured value IB of the muon flux measured by the second measurement unit, where λ is an attenuation constant of the ground to be measured and h is the areal density of the ground to be measured.

Description

Measurement device and method for measuring ground density

[0001] This disclosure relates to a device and method for measuring soil density.

[0002] In recent years, construction work on underground tunnels or piping, and / or long-term soil erosion, can create voids in underground spaces, leading to road collapses and other problems. Therefore, attempts are being made to prevent road collapses and other problems by conducting ground density surveys. In particular, it is desirable to be able to measure ground density within tens of meters of the surface, where there are many buried objects beneath the road and where voids may be created due to construction.

[0003] One known method for investigating soil density involves irradiating electromagnetic waves from the surface into the ground and measuring the subsurface conditions by the reflection of the electromagnetic waves (see, for example, Non-Patent Document 1).

[0004] Furthermore, it is known that ground density can be estimated by placing muon detectors in underground cavities such as underground tunnels and measuring the intensity of the detected cosmic ray muons (see, for example, Non-Patent Literature 2). Muons always reach the surface in a certain amount and have very high energies ranging from 1 GeV to tens of GeV, so they have high penetrating power. For this reason, muons are also used to measure the interiors of volcanoes and pyramids. By measuring the muon intensity underground and estimating the attenuation by the ground, the surface density and density of the ground can be calculated.

[0005] IREC Engineering, "i-ESP-R", [online], [Retrieved September 13, 2024], https: / / www.airec.co.jp / products / pdf / iesparR.pdf Keiichi Suzuki, Jun Kanazawa, "Application of Exploration Technology Using Cosmic Ray Muons to the Field of Applied Geology", Applied Geology, Vol. 57, No. 6, pp. 266-276, 2017

[0006] However, in the method of using electromagnetic waves to explore the ground density, the measurable depth is limited because electromagnetic waves are strongly attenuated in the ground. For example, when using electromagnetic waves in the 400 MHz band, the detectable depth is about 2.5 m from the ground surface. It is difficult to measure the ground density using electromagnetic waves for the ground at a depth of about 10 m from the ground surface because electromagnetic waves hardly penetrate it.

[0007] On the other hand, in the method of using mu particles, when λ is the attenuation constant and h is the surface density, the measured value I of the mu particle flux can be expressed by the following formula (1) which is multiplied by the attenuation rate associated with the surface density h expressed by exp(−λh) with respect to the initial value I ００ of the mu particle flux.

[0008]

[0009] Here, the attenuation constant λ can be calculated or determined by various known methods. According to this formula, the surface density h can be calculated from the measured value I of the mu particle flux. However, when measuring the measured value I of the mu particle flux for a shallow ground and applying it to formula (1), the surface density h may become approximately 0 and the surface density h cannot be estimated. Also, if the initial value of the mu particle flux I ００ is smaller than the mu particle flux value I measured by actual measurement, the surface density h may not be calculable.

[0010] Furthermore, in the method of measuring mu particles, there is a problem that the number of mu particles reaching the ground surface increases and decreases with time due to solar activity. Cosmic rays with high energy originating from the galaxy are stable and reach deep into the ground, and the number of mu particles reaching there also has a small temporal variation. On the other hand, cosmic rays originating from the sun have low energy and are also observed in the atmosphere and shallow ground surface. These solar-originated cosmic rays are also affected by solar activity, the earth's geomagnetism, and atmospheric pressure, and have large temporal variations. Therefore, when evaluating the density of shallow ground from 3 m to several tens of m, it is necessary to measure a small attenuation of mu particles, but it is difficult to accurately measure the ground density due to the variation in the number of mu particles depending on the measurement timing.

[0011] Therefore, the object of the present disclosure made by paying attention to these points is to provide a ground density measurement device and a measurement method capable of measuring the ground density without being affected by the time variation of mu particles.

[0012] A ground density measurement device according to an embodiment includes a first measurement unit installed underground of the ground to be measured for measuring a mu particle flux, a second measurement unit installed at a predetermined position for reference for measuring a mu particle flux, and obtaining measurement values of the mu particle fluxes simultaneously measured by the first measurement unit and the second measurement unit. Taking λ as the attenuation constant of the ground to be measured and h as the areal density of the ground to be measured, the measurement value I of the mu particle flux measured by the second measurement unit Ｂ to the measurement value I of the mu particle flux measured by the first measurement unit Ａ of the ratio value I Ａ / I Ｂ and a control unit for estimating the areal density h of the ground to be measured based on the above.

[0013] A ground density measurement method according to an embodiment includes obtaining measurement values of the mu particle fluxes simultaneously measured by a first measurement unit installed underground of the ground to be measured for measuring a mu particle flux and a second measurement unit installed at a predetermined position for reference for measuring a mu particle flux. Taking λ as the attenuation constant of the ground to be measured and h as the areal density of the ground to be measured, the measurement value I of the mu particle flux measured by the second measurement unit Ｂ to the measurement value I of the mu particle flux measured by the first measurement unit Ａ of the ratio value I Ａ / I Ｂ and estimating the areal density h of the ground to be measured based on the above.

[0014] According to the present disclosure, the ground density can be measured without being affected by the time variation of mu particles.

[0015] This is a block diagram showing the schematic configuration of a ground density measuring device according to one embodiment. This shows an example of the arrangement of the ground density measuring device in Figure 1. This shows an example of the arrangement of the ground density measuring device in Figure 1. This shows an example of the arrangement of the ground density measuring device in Figure 1. This is a flowchart showing the procedure for measuring ground density.

[0016] Embodiments of this disclosure will be described below with reference to the drawings. The figures used in the following description are schematic.

[0017] (Measurement device) The measurement device 1 of this disclosure is a ground density measurement device using muons. This measurement device 1 utilizes the fact that the number of muons reaching the ground surface changes in the same way due to solar activity, even if geographically distant. Therefore, as shown in Figure 1, the measurement device 1 of this disclosure comprises a first measurement unit 10 for measurement, a second measurement unit 20 for reference, and a measurement value I output from the first measurement unit 10 and the second measurement unit. Ａ and I Ｂ The system includes a main unit 30 that acquires and processes the data.

[0018] (Configuration of the first and second measurement units) The first measurement unit 10 is installed underground in the ground 40 (see Figures 2A-2C) to be measured and measures the muon flux. The first measurement unit 10 includes at least one first detector 11 and at least one second detector 12, which are spaced apart from each other and detect cosmic ray muons.

[0019] The first detector 11 and the second detector 12 are, for example, scintillation detectors. A scintillation detector includes a scintillator, which is a material that emits light when charged particles pass through it, and a photodetector capable of detecting the light emitted by the scintillator. The scintillation detector can detect when muons have passed through.

[0020] The first detection unit 10 can detect the direction of arrival and the number of muons by detecting muons passing through the first detector 11 and the second detector 12 almost simultaneously. The flow of multiple muons is called the muon flux. Measured value I of the muon flux ＡThis is expressed by the number of muons passing through a unit area per unit time. The first measuring unit 10 can, for example, measure the muon flux arriving from above in a substantially vertical direction. In Figure 1, the arrows indicate the direction from which the muons are arriving. In another embodiment, the first measuring unit 10 may individually detect muons passing through the first detector 11 and the second detector 12 and transmit them to the main unit 30. In this case, the main unit 30 counts muons that pass through the first detector 11 and the second detector 12 simultaneously.

[0021] In Figure 1, the first detector 11 and the second detector 12 are shown as one each. However, both or either of the first detector 11 and the second detector may be arranged in multiples, and the first measurement unit may be configured to simultaneously measure muons arriving from multiple directions, according to their direction of arrival.

[0022] A second measurement unit 20 is installed in a predetermined position for reference and measures the muon flux. The second measurement unit 20 includes at least one third detector 21 and at least one fourth detector 22, which are spaced apart from each other and detect cosmic ray muons. The third detector 21 and the fourth detector 22 may be the same type of detector as the first detector 11 and the second detector 12, for example, a scintillation detector. The third detector 21 and the fourth detector 22 are oriented in the same direction as the first detector 11 and the second detector 12 so as to detect muons arriving from the same direction as the muons detected by the first detector 11 and the second detector 12.

[0023] For example, as shown in Figures 2A to 2C, the first measurement unit 10 is located in an underground space 41 below the ground 40 to be measured. The underground space 41 is, for example, an underground tunnel. In this case, the second measurement unit 20 may be located on the ground surface 42 above the ground 40, as shown in Figure 2A. Alternatively, the second measurement unit 20 may be located on the ground surface 43 at the same altitude as the underground space 41, as shown in Figure 2B. Furthermore, the second measurement unit 20 may be located in the same underground space 41 as the first measurement unit 10, as shown in Figure 2C. In the case of the arrangement in Figure 2C, it is a condition that the ground density of the ground 40 above the second measurement unit 20 is known. In this application, "altitude" means the height from the Earth's reference plane, for example, the height from sea level.

[0024] Muons are known to be affected by the Earth's magnetic field. The number of muons that reach the Earth's surface is higher closer to the Earth's poles and lower closer to the equator. Therefore, it is preferable that the second measurement unit 20 be installed at the same latitude as the first measurement unit 10.

[0025] (Configuration of the main unit) The main unit 30 can use a dedicated device or a dedicated computer for the measuring device 1. Alternatively, the main unit 30 can be implemented using a general-purpose computer and program, and the program can be recorded on a recording medium or provided via a network. General-purpose computers include PCs (Personal Computers) and workstations. As shown in Figure 1, the main unit 30 includes an acquisition unit 31, a control unit 32, an input / output unit 33, and a storage unit 34. In Figure 1, the main unit 30 is shown as a single device, but the main unit 30 is not limited to a single device. Multiple devices may share the functions of the main unit 30. For example, the main unit 30 may include a part located inside the underground space 41 near the first measuring unit 10 and a part located above ground. When the functions of the main unit 30 are distributed among multiple devices, each device may be able to communicate with each other by any means of communication.

[0026] The acquisition unit 31 includes an interface for transmitting and receiving signals with the first measurement unit 10 and the second measurement unit 20. The acquisition unit 31 includes a communication module that supports wired and wireless communication. The acquisition unit 31 receives the measured value I of the muon flux measured by the first measurement unit 10. Ａ , and the measured value I of the muon particle flux measured by the second measurement unit 20. Ｂ The acquisition unit 31 can obtain the measured value I of the muon particle flux that was measured at the same time. Ａ and measured value I Ｂ You can obtain and .

[0027] The control unit 32 includes one or more processors. In one embodiment, the "processor" is a general-purpose processor or a dedicated processor specialized for a specific process, but is not limited to these. The processor may be, for example, a CPU (Central Processing Unit), a DSP (Digital Signal Processor), or an ASIC (Application Specific Integrated Circuit). The control unit 32 may manage the overall operation of the measuring device 1. The control unit 32 may execute processing according to a program stored in the storage unit 34.

[0028] The input / output unit 33 may include an input device for the user of the ground exploration device 1 to input instructions and information, and a display for the ground exploration device 1 to display the exploration results. The input device may include a keyboard and a mouse, etc. The display may be, for example, a liquid crystal display (LCD), an organic electro-luminescence (EL) display, or an inorganic EL display. The input / output unit 33 may include a touch panel that detects input by contacting the surface of the display.

[0029] The storage unit 34 may be configured to include, for example, one or more of semiconductor memory, magnetic memory, and optical memory. Semiconductor memory may include volatile memory and non-volatile memory. Magnetic memory may include, for example, a hard disk. Optical memory may include, for example, a CD (Compact Disc), DVD (Digital Versatile Disc), and BD (Blu-ray® Disc). The storage unit 34 may function as, for example, a main memory, an auxiliary memory, or a cache memory. The storage unit 34 may store information acquired by the main unit 30, information processed by the main unit 30, and information for operating the main unit 30. The storage unit 34 may store a program for operating the control unit 32.

[0030] (Measurement Method) Next, a measurement method using the measurement device 1 will be described. As an example, the first measurement unit 10 and the second measurement unit 20 are arranged as shown in Figure 2B. The main device 30 measures the measured value I of the muon particle flux measured simultaneously from the first measurement unit 10 and the second measurement unit 20. Ａ , I Ｂ The measured value I of the muon particle flux detected by the first measurement unit 10 is obtained. For example, if the second measurement unit 20 is located at the position of the second measurement device 20 shown in Figure 2B, the measured value I of the muon particle flux detected by the first measurement unit 10 is obtained. Ａ This is the measured value I of the muon particle flux detected by the second measurement unit 20, which is the amount of attenuation due to the ground 40. Ｂ It becomes smaller than the measured value I. Ａ and I Ｂ The following equation (2) holds between them.

[0031]

[0032] Here, λ is the damping constant of the ground 40 as described above. Also, h is the surface density of the ground 40. The damping constant λ can be calculated or determined by various known methods. λ may also be expressed as a function of the surface density h. The surface density h of the ground 40 represents the amount of substance contained per unit area of ​​the ground. The control unit 32 of the main device 30 can calculate the surface density h of the ground 40 using formula (2). In other words, the control unit 32 calculates the measured value IＡ and I Ｂ The ratio value I Ａ / I Ｂ The surface density h can be determined based on this. Furthermore, the control unit 32 can determine the ground density ρ of the ground 40 by ρ = h / D (3), where D is the thickness of the ground 40 to be measured.

[0033] Since muons attenuate even in the atmosphere, the altitude at which the first measurement unit 10 and the second measurement unit 20 are positioned affects the number of muons measured. Therefore, the highest measurement accuracy is achieved when the second measurement unit 20 is positioned at the same altitude as the first measurement unit 10, as shown in Figure 2B. However, considering the use of the measurement device 1 in urban areas, it is not often possible to position the first measurement unit 10, which is located in the underground space 41 as shown in Figure 2B, and the second measurement unit 20 for reference at the same altitude. In most cases, the second detection unit 20 is positioned on the ground surface 42 above the ground 40 above the underground space 41 where the first detection unit 10 is located. When the second measurement unit 20 is positioned on the ground surface 42 as shown in Figure 2A, a correction calculation can be performed based on the case where the second measurement unit 20 is installed at the position shown in Figure 2B, as shown in the following formula (4).

[0034]

[0035] In equation (4), λ' represents the atmospheric damping constant, and ρ ａ This represents the density of air. λ' is the atmospheric damping constant, and ρ is the density of air. ａ And the thickness D of the ground is known or measurable. Equation (4) may also be expressed as equation (5) below, without separating the atmospheric damping constant λ' and the ground damping constant λ.

[0036]

[0037] The control unit 32 of the main unit 30 applies the measured value I measured by the first measuring unit 10 to these formulas (4) or (5). Ａ and the measured value I measured by the second measurement unit 20 Ｂ By applying this, the surface density h of the ground 40 can be calculated. That is, in the former case, the control unit 32 calculates the measured value I Ａ and measured value I ＢThe ratio value I Ａ / I Ｂ ga exp(-λh) to exp(-λ'ρ) ａ Based on the value obtained by multiplying by D), the surface density h of the ground 40 being measured can be estimated. In the latter case, the control unit 32 calculates the measured value I Ａ and measured value I Ｂ The ratio value I Ａ / I Ｂ is exp{−λ(h+ρ ａ Based on the condition D), the surface density h of the ground 40 being measured can be estimated. Furthermore, the control unit 32 can calculate the density ρ of the ground 40 from the surface density h using formula (3).

[0038] When precisely determining the surface density h and density ρ, it is preferable to use formula (4) rather than formula (5), which calculates the atmospheric damping constant λ' and the ground damping constant λ together. The atmospheric and ground damping constants λ can differ by a factor of 10 to 100. However, the ground damping constant λ changes depending on the soil and rocks that make up the ground 40. Therefore, unless the condition of the ground 40 is clear from prior boring surveys, it is also effective to express the damping constants together as λ, as in formula (5), and calculate the surface density h and density ρ.

[0039] When the first measurement unit 10 and the second measurement unit 20 are arranged as shown in Figure 2C, and the surface density of the ground 40 above the second measurement unit 20 is known, the measured value I Ａ and measured value I Ｂ Using this method, the surface density h and density ρ of the ground 40 can be calculated.

[0040] (Measurement Procedure) Figure 3 is a flowchart of the process performed by the control unit 32 of the main unit 30.

[0041] First, as a prerequisite, the first measurement unit 10 and the second measurement unit 20 are installed as illustrated in Figures 2A to 2C. The control unit 32 receives the measured value I of the muon particle flux simultaneously measured from the first measurement unit 10 and the second measurement unit 20 via the acquisition unit 31. Ａ and I Ｂ Obtain (step S301).

[0042] The control unit 32 calculates the surface density h of the ground 40 to be measured based on one of the formulas (2), (4), and (5) stored in the storage unit 34, according to the installation method of the first detection unit 10 and the second detection unit 20 and the required measurement accuracy (step S302).

[0043] The control unit 32 calculates the density ρ of the ground 40 from the surface density h of the ground 40 based on formula (3) (step S303).

[0044] The control unit 32 stores the calculated surface density h and / or density ρ of the ground 40 in the storage unit 34 and outputs it to the input / output unit 33.

[0045] As explained above, according to the ground density measuring device 1 of this embodiment, the measured value I of the first measuring unit 10 for measurement, which is measured simultaneously, Ａ , and the measured value I of the second measurement unit 20 for reference Ｂ The ratio value I Ａ / I Ｂ This method utilizes the following technique: This allows for the measurement of ground surface density h and ground density ρ without being affected by the time variation of muons originating from solar activity.

[0046] Furthermore, according to this embodiment, the initial value I ００ Unlike conventional measurement methods that set the measurement value I of the first measurement unit 10, Ａ and the measured value I of the second measurement unit 20 Ｂ The ratio value I Ａ / I Ｂ It never becomes greater than 1. Furthermore, even with a minute decrease in muon flux, the ratio value I Ａ / I Ｂ This is reflected in the measurement device 1 of this embodiment, which makes it possible to detect differences in the measured values ​​of minute muon particle flux, and to estimate the surface density h and density ρ even in relatively shallow ground.

[0047] Furthermore, according to this embodiment, the first measurement unit 10 for measurement is placed in the underground space 41, and the second measurement unit 20 for reference is installed at various locations to perform measurements. These various locations include the ground surface 42 separated by the ground 40 above the underground space 41, the ground surface 43 at the same height as the underground space 41, and the interior of the underground space 41 where the first measurement unit 10 is located.

[0048] Although the embodiments described above are representative examples, it will be apparent to those skilled in the art that many modifications and substitutions are possible within the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited by the embodiments and examples described above, and various modifications and / or changes are possible without departing from the scope of the claims. For example, it is possible to combine multiple component blocks described in the embodiments and examples into one, or to divide one component block.

[0049] For example, in the above embodiment, the first detection unit 10 and the second detection unit 20 each have two detectors. However, it is also possible to configure the first detection unit 10 and the second detection unit 20 to each have one detector. In this case, the number of muons that have passed through each detector is counted, but the direction from which the muons arrive is not limited.

[0050] The following additional information is disclosed regarding the embodiments described above.

[0051] (Note 1) A first measurement unit installed underground in the ground to be measured to measure the muon particle flux, a second measurement unit installed at a predetermined position for reference to measure the muon particle flux, and the measured values ​​of the muon particle flux measured simultaneously by the first measurement unit and the second measurement unit are obtained, and the measured value of the muon particle flux measured by the second measurement unit I is obtained with λ as the attenuation constant of the ground to be measured and h as the surface density of the ground to be measured. Ｂ The measured value I of the muon particle flux measured by the first measurement unit for the above Ａ The ratio value I Ａ / I ＢA ground density measuring device comprising a control unit that estimates the surface density h of the ground to be measured based on the fact that is proportional to exp(-λh). (Note 2) The second measuring unit is placed on the ground, and the control unit takes λ' as the atmospheric attenuation constant and ρ ａ Let I be the density of air, and let D be the thickness of the ground being measured, then the ratio I Ａ / I Ｂ ga exp(-λh) to exp(-λ'ρ) ａ A ground density measuring device as described in Appendix 1, which estimates the surface density h of the ground to be measured based on the value obtained by multiplying by D). (Appendix 3) The second measuring unit is placed on the ground, and the control unit sets λ' to the atmospheric attenuation constant, and ρ ａ Let I be the density of air, and let D be the thickness of the ground being measured, then the ratio I Ａ / I Ｂ is exp{−λ(h+ρ ａ A ground density measuring device as described in Appendix 1, which estimates the surface density h of the ground to be measured based on the condition D). (Appendix 4) A first measuring unit installed underground in the ground to be measured to measure the muon particle flux, and a second measuring unit installed at a predetermined position for reference to measure the muon particle flux, which simultaneously obtain the measured value of the muon particle flux, and the measured value of the muon particle flux measured by the second measuring unit, where λ is the attenuation constant of the ground to be measured and h is the surface density of the ground to be measured. Ｂ The measured value I of the muon particle flux measured by the first measurement unit for the above Ａ The ratio value I Ａ / I Ｂ A method for measuring ground density, which includes estimating the surface density h of the ground to be measured based on the fact that is proportional to exp(-λh).

[0052] 1 Measurement device 10 First measurement unit 11 First detector 12 Second detector 20 Second measurement unit 21 Third detector 22 Fourth detector 30 Measurement device 31 Acquisition unit 32 Control unit 33 Input / output unit 34 Storage unit 40 Ground 41 Underground space 42 Ground surface 43 Ground surface

Claims

1. A first measurement unit is installed underground in the ground to be measured and measures the muon particle flux. A second measurement unit is installed at a predetermined location for reference and measures the muon particle flux. The measured values ​​of the muon particle flux measured simultaneously by the first and second measurement units are acquired, and the measured value I of the muon particle flux measured by the second measurement unit is obtained with λ as the attenuation constant of the ground to be measured and h as the surface density of the ground to be measured. Ｂ The measured value I of the muon particle flux measured by the first measurement unit. Ａ The ratio value I Ａ / I Ｂ A ground density measuring device comprising a control unit that estimates the surface density h of the ground to be measured based on [a specific value].

2. The second measurement unit is placed on the ground, and the control unit sets λ' to the atmospheric attenuation constant, and ρ ａ Let I be the density of air, and let D be the thickness of the ground being measured, then the ratio I Ａ / I Ｂ ga exp(-λh) to exp(-λ'ρ) ａ The ground density measuring device according to claim 1, which estimates the surface density h of the ground to be measured based on the value obtained by multiplying by D).

3. The second measurement unit is disposed on the ground, and the control unit uses ρ ａ as the density of air, D as the thickness of the ground to be measured, and the value I of the ratio Ａ / I Ｂ becomes exp{−λ(h + ρ ａ D)} to estimate the surface density h of the ground to be measured. The ground density measuring device according to claim 1.

4. Obtain the measured value of the muon particle flux measured simultaneously by a first measurement unit installed underground in the ground to be measured and measuring the muon particle flux, and a second measurement unit installed at a predetermined position for reference and measuring the muon particle flux, and, with λ being the attenuation constant of the ground to be measured and h being the surface density of the ground to be measured, the measured value of the muon particle flux measured by the second measurement unit I Ｂ The measured value I of the muon particle flux measured by the first measurement unit for the above Ａ The ratio value I Ａ / I Ｂ A method for measuring ground density, which includes estimating the surface density h of the ground to be measured based on [a certain condition].

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