Penetration tester, soil quality determination method, and soil quality determination system

Abstract

To provide a penetration testing machine which has high measurement sensitivity, is resistant to an influence of the surrounding environment, and has high durability, when determining soil quality by a sound signal, a soil quality determination method, and a soil quality determination system.SOLUTION: A penetration testing machine X used in a screw weight penetration test comprises: a penetration rod 5 including a screw point 5b that penetrates into the ground in an axial direction; a sound collection unit 4 which is connected to the penetration rod 5 on the ground and in which a microphone 41 is built; and a determination section 14 that determines soil quality based on a sound signal output by the microphone 41. In at least one of the penetration rod 5 and the sound collection unit 4, a resonance chamber in which a fricative sound of the screw point 5b air-vibrates is formed in the axial direction, and the microphone 41 is positioned inside the resonance chamber.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a penetration tester used in a screw weight penetration test, a soil quality determination method using the penetration tester, and a soil quality determination system used in the penetration tester.

Background Art

[0002] Conventionally, as one of the ground investigation methods, there is a screw weight penetration test (old Swedish sounding test, hereinafter referred to as "SWS test") defined in JIS A 1221. As an apparatus for performing this SWS test, a penetration tester equipped with a penetration rod including a screw point to be penetrated into the ground is known (see, for example, Patent Documents 1 and 2).

[0003] The penetration tester described in Patent Document 1 automatically measures the penetration speed and the number of half rotations of the penetration rod, measures the vibration of the penetration rod by a vibration sensor that contacts a chuck sleeve that supports the penetration rod, detects a sound signal from this vibration, and determines the soil quality.

[0004] The penetration tester described in Patent Document 2 provides a resonance chamber inside the screw point and a microphone above the resonance chamber, picks up the frictional sound of the screw point where air vibrates in the resonance chamber with the microphone, converts it into a sound signal, and determines the soil quality.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The penetration tester described in Patent Document 1 has to use an accelerometer as a sensor, so the measurable frequency range is narrow and the measurement sensitivity is very poor. In addition, since it directly measures the vibration of the penetration rod, it is easily affected by the surrounding environment. Further, the penetration tester described in Patent Document 2 has a microphone provided at the screw point, so it is necessary to incorporate a cable for extracting a sound signal from the microphone into the penetration rod. There is a risk that the cable may be twisted and disconnected during the rotation of the penetration rod, or the microphone may be damaged due to strong vibration at the screw point.

[0007] Therefore, when determining the soil quality based on the sound signal, there is a need for a penetration tester, a soil quality determination method, and a soil quality determination system that have high measurement sensitivity, are not easily affected by the surrounding environment, and have high durability.

Means for Solving the Problems

[0008] The characteristic configuration of the penetration tester according to the present invention is a penetration tester used in a screw weight penetration test, including a penetration rod including a screw point that penetrates into the ground along the axial direction, a sound collection unit connected to the penetration rod on the ground and having a built-in microphone, and a determination unit that determines the soil quality based on the sound signal output by the microphone. At least one of the penetration rod and the sound collection unit is formed with a resonance chamber in which the frictional sound of the screw point causes air vibration along the axial direction, and the microphone is located inside the resonance chamber.

[0009] In this configuration, since the sound collection unit with a built-in microphone is connected to the penetration rod on the ground, when the sound signal output by the microphone is connected to the determination unit by wire, the cable length can be shortened. In addition, since it is not necessary to incorporate the microphone and the cable into the screw point and the penetration rod, problems such as damage to the microphone due to strong vibration at the screw point and disconnection of the cable due to twisting during the rotation of the penetration rod can be prevented.

[0010] In at least one of the penetration rod and the sound collecting unit in this configuration, a resonance chamber in which the frictional sound of the screw point causes air vibration is formed along the axial direction, and a microphone is located inside the resonance chamber. That is, instead of directly measuring the vibration of the penetration rod, it detects the sound of the air vibration propagating through the resonance chamber, is less affected by the surrounding environment, and has high detection sensitivity. As a result, the determination accuracy of the soil quality based on the sound signal can be improved.

[0011] In this way, with a simple configuration such as providing a sound collecting unit with a built-in microphone on the ground, when determining the soil quality by a sound signal, it is a penetration tester that is less affected by the surrounding environment and has high durability.

[0012] Another characteristic configuration is that the sound collecting unit has a sound collecting rod that forms the resonance chamber inside, and a lid body that is connected to the sound collecting rod and has the microphone built therein.

[0013] If a sound collecting rod with a resonance chamber formed inside is provided as in this configuration, there is no need to provide a resonance chamber inside the penetration rod, and the soil quality can be determined simply by connecting a sound collecting unit to a conventional solid penetration rod. Moreover, since the resonance chamber is provided in the sound collecting rod of the sound collecting unit arranged on the ground, there is no inconvenience such as the sound generated by the friction between the penetration rod other than the screw point and the soil around it directly propagating through the resonance chamber and increasing the noise.

[0014] Another characteristic configuration is that a hollow region serving as the resonance chamber is formed in the penetration rod along the axial direction.

[0015] If a hollow region along the axial direction is provided in the penetration rod as in this configuration, a resonance chamber corresponding to the axial length of the penetration rod can be secured, so that the sensitivity of air vibration can be increased.

[0016] Another characteristic configuration is that the sound collecting unit and the penetration rod are detachably screwed together.

[0017] Since the sound collecting unit and the penetration rod are detachably screwed together as in this configuration, it is only necessary to attach the sound collecting unit only during soil quality determination, and the vibration damage to the microphone can be extremely reduced.

[0018] The characteristics of the soil quality determination method using any of the above penetration testers are a stop step of stopping the movement of the penetration rod when the screw point reaches a predetermined position, a connection step of connecting the sound collecting unit to the penetration rod after the stop step, and a determination step of rotating the penetration rod while maintaining the screw point at the predetermined position and determining the soil quality by the determination unit based on the sound signal output by the microphone.

[0019] The soil quality determination method using the penetration tester having the above-described effects stops the movement of the penetration rod, then connects the sound collecting unit to the penetration rod and then rotates the penetration rod to detect a sound signal, so that the rotation of the sound collecting unit can be minimized. Therefore, it is possible to prevent problems such as the cable being twisted and broken when the penetration rod rotates, or the microphone being damaged due to strong vibration of the screw point.

[0020] The characteristic configuration of the soil quality determination system used in any of the above penetration testers is that it includes the sound collecting unit and a soil quality determination device that is electrically connected to the sound collecting unit and has the determination unit.

[0021] The soil quality determination system using the penetration tester having the above-described effects can be retrofitted to a conventional penetration tester.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0023] Hereinafter, embodiments of the penetration tester, the soil quality determination method, and the soil quality determination system according to the present invention will be described with reference to the drawings. In this embodiment, a penetration tester used in a screw weight penetration test (SWS test) will be described. However, the present invention is not limited to the following embodiments, and various modifications are possible without departing from the gist thereof.

[0024] As shown in FIG. 1, the penetration tester X includes a soil quality determination device 1, a support column 2, a lifting table 3 that can move up and down along the support column 2, a penetration rod 5 having a screw point 5b at the tip, a chuck 5c that holds the penetration rod 5, a sound collection unit 4 connected to the penetration rod 5 on the ground, a rotation motor 6 that rotationally drives the penetration rod 5, a lifting motor 8 that rotationally drives a sprocket 7, and a control device 9. The penetration tester X in this embodiment is an automatic penetration tester driven and controlled by the control device 9. The soil quality determination system Y includes a soil quality determination device 1 and a sound collection unit 4, and the soil quality determination device 1 determines the soil quality based on the sound signal output by the sound collection unit 4. The penetration rod 5 can be added with a plurality of rods having the same shape. Hereinafter, the first rod having a screw point 5b at the tip is referred to as the first penetration rod 5a.

[0025] The lifting table 3 bears the loads of a weight 3a of a predetermined weight, a rotation motor 6, a chuck 5c, a penetration rod 5, and a lifting motor 8, and is configured to be capable of performing a penetration test with a load of 1 kN applied to the penetration rod 5. The sound collection unit 4 is detachably screwed to the penetration rod 5, and the load of the sound collection unit 4 is applied to the penetration rod 5 during soil quality determination. The lifting table 3 has a sprocket 7 that meshes with a guide chain 2a arranged in the vertical direction along the support column 2, and is configured to be able to ascend by rotating the guide chain 2a by this sprocket 7.

[0026] The penetration rod 5 is formed in a long shape including a screw point 5b that penetrates into the ground along the axial direction. At the end of the penetration rod 5 opposite to the screw point 5b, a male screw portion 51 is formed to which a sound collection unit 4 incorporating a microphone 41 is screwed. The screw point 5b has a drill shape with one twist applied to a total length of 200 mm as defined in JIS A1221.

[0027] The chuck 5c is configured such that the chuck shaft can rotate together with the penetration rod 5 by the driving force of the rotation motor 6 while holding the penetration rod 5 with a chuck shaft (not shown). At the upper part of the chuck 5c, the male screw portion 51 formed at the end of the penetration rod 5 is exposed, and since the sound collection unit 4 is screwed to this male screw portion 51, the sound collection unit 4 is configured to be detachable from the penetration rod 5. The penetration rod 5 is attached to the chuck 5c in a state where the lifting table 3 is waiting at the upper limit position (1 m from the ground surface) and is configured to be extendable. Further, the chuck 5c is provided with a load cell 39 as a load sensor, and the load applied to the penetration rod 5 can be measured by this load cell 39.

[0028] The rotary motor 6 is composed of an induction motor or the like, and a rotary encoder (not shown) is attached to the end of a drive shaft (not shown). It is rotationally controlled by the control device 9 based on the output value of the rotary encoder. A one-way clutch (not shown) is provided in the rotary motor 6. When the rotary motor 6 is driven forward in the direction of screwing the penetration rod 5 into the ground in accordance with the twist of the screw point 5b, the penetration rod 5 rotates. Conversely, when the rotary motor 6 is driven in reverse, it idles and the penetration rod 5 does not rotate.

[0029] The lifting motor 8 is composed of an induction motor or the like, and a drive shaft (not shown) and a sprocket 7 rotate integrally via a speed reduction mechanism (not shown) such as a planetary gear. A rotary encoder 21 is attached to the end of the drive shaft of the lifting motor 8, and it is rotationally controlled by the control device 9 based on the output value of the rotary encoder 21. A one-way clutch (not shown) is provided in the lifting motor 8. When the lifting motor 8 is driven forward in the direction in which the lifting platform 3 ascends, the sprocket 7 rotates. Conversely, when the lifting motor 8 is driven in reverse, it idles and the sprocket 7 does not rotate. When the sprocket 7 rotates, the penetration rod 5 can be loaded with a load obtained by subtracting the upward force based on the output torque of the lifting motor 8 from 1 kN (maximum test load) based on the total weight of the lifting platform 3. On the other hand, when the sprocket 7 does not rotate, the penetration rod 5 can be loaded with 1 kN (maximum test load) based on the total weight of the lifting platform 3.

[0030] In addition, the lifting motor 8 is provided with a rotary encoder 17 that outputs a pulse signal associated with the rotation of the sprocket 7. The control device 9 calculates the penetration amount and penetration speed of the penetration rod 5 based on the lifting amount and lifting speed of the lifting platform 3 by processing the pulse signal.

[0031] The control device 9 includes a program stored in hardware such as an HDD or a memory as software for controlling at least the operations of the rotation motor 6 and the lifting motor 8, and is executed by a processor including an ASIC, an FPGA, a CPU, or other hardware of a computer. The control device 9 has an inverter control unit 92 that controls the drive of the lifting motor 8, an inverter control unit 93 that controls the drive of the rotation motor 6, and a main control unit 91 that sends commands to these inverter control units 92 and 93.

[0032] The inverter control unit 92 that controls the drive of the lifting motor 8 receives a torque command from the main control unit 91, feedback-controls the value of the load cell 39, and sets the actual load applied to the penetration rod 5 to a target test load. At this time, the control device 9 calculates the penetration amount of the penetration rod 5 from the rotation speed of the sprocket 7 and stores the actual load for each depth. When the actual load applied to the penetration rod 5 exceeds the maximum test load and the penetration speed of the penetration rod 5 becomes equal to or less than a predetermined value, the inverter control unit 93 that controls the drive of the rotation motor 6 receives a torque command from the main control unit 91 and drives the rotation motor 6 in the forward rotation direction to screw the penetration rod 5 into the ground. At this time, the control device 9 calculates the number of half rotations of the penetration rod 5 every time the penetration rod 5 penetrates a predetermined amount from the rotation speed of the sprocket 7 and the rotation speed of the rotation motor 6, and stores the number of half rotations for each depth. Then, the control device 9 calculates an evaluation index value (Nsw value) of the ground strength from the actual load and the number of half rotations for each depth.

[0033] When calculating this Nsw value, by discriminating the soil type for each depth, more necessary ground design constants can be known. Therefore, the penetration tester X in this embodiment is provided with a soil discrimination system Y including a sound collection unit 4 and a soil discrimination device 1. This soil discrimination device 1 is connected by wire between a control device 9 and the sound collection unit 4. The soil discrimination device 1 includes a program stored in hardware such as an HDD or a memory as software that detects at least the frictional sound of the screw point 5b and determines the soil type, and is executed by a processor including an ASIC, an FPGA, a CPU, or other hardware of a computer. Note that the soil discrimination device 1 and the sound collection unit 4 may be wirelessly connected, or the soil discrimination device 1 may be built into the control device 9.

[0034] The soil discrimination device 1 includes an input unit 11, a storage unit 12, an extraction unit 13, and a determination unit 14. The input unit 11 is a communication interface that receives a digital signal (hereinafter referred to as a "sound signal") of the sound detected by the microphone 41 of the sound collection unit 4. The storage unit 12 is hardware that stores various programs, resonance frequency data, and soil standard data. Details of the extraction unit 13 and the determination unit 14 will be described later.

[0035] [First Embodiment] The sound collection unit 4 according to the first embodiment will be described with reference to FIGS. 2 to 3. As shown in FIG. 3, a solid long rod-shaped penetration rod 5 and a sound collection unit 4 in which a resonance chamber 42 is formed as a closed space are detachably screwed together. As shown in FIGS. 2 to 3, the sound collection unit 4 has a sound collection rod 4a having a resonance chamber 42 formed therein, and a lid 43 that is screwed to the sound collection rod 4a to close the resonance chamber 42. The resonance chamber 42 is a closed space where the frictional sound of the screw point 5b causes air vibration.

[0036] The sound collecting rod 4a is formed in a cylindrical shape with a resonance chamber 42 having a predetermined length (e.g., 200 mm) formed hollow inside along the axial direction. The sound collecting rod 4a has a male screw portion 4a1 formed at one end on the lid body 43 side, and a female screw portion 4a2 formed at the other end on the penetration rod 5 side that is screwed into the male screw portion 51 of the penetration rod 5. A housing space for accommodating the microphone 41 is formed in the resonance chamber 42 formed at one end of the sound collecting rod 4a, and the resonance chamber 42 formed at the other end of the sound collecting rod 4a is closed by a closing member 44, and the resonance chamber 42 is a closed space between the lid body 43 and the closing member 44. The resonance chamber 42 in the present embodiment is formed by drilling with a cutting drill having a predetermined diameter (e.g., 5 mm) from the female screw portion 4a2 side and then closing the female screw portion 4a2 side with a closing member 44 made of the same material as the penetration rod 5.

[0037] As shown in FIG. 2, the lid body 43 has an elastic member 43a that holds the microphone 41, a split member 43b that holds the elastic member 43a, and a fixing member 43c that fixes the split member 43b. The elastic member 43a has a step portion 43a1 that is locked to the split member 43b, and is clamped and fixed to the split member 43b in a state where downward movement is restricted by this step portion 43a1.

[0038] The split member 43b is composed of a pair of opposed semi-cylindrical members positioned by pins 43b1, and is fixed to the fixing member 43c by a plurality (four in this embodiment) of bolts B. The fixing member 43c is composed of a cylindrical member, and a female screw portion 43c1 into which the male screw portion 4a1 of the sound collecting rod 4a is screwed is formed on the inner peripheral surface. A cable C that electrically connects the microphone 41 and the soil determination device 1 is exposed on the upper surface of the lid body 43 of the sound collecting unit 4 formed in this way.

[0039] Thus, by providing the sound collecting rod 4a with the resonance chamber 42 formed therein, there is no need to provide the resonance chamber 42 inside the penetration rod 5, and soil quality determination can be performed simply by connecting the sound collecting unit 4 to the conventional solid penetration rod. Moreover, since the resonance chamber 42 is provided in the sound collecting rod 4a of the sound collecting unit 4 arranged on the ground, there is no inconvenience such that the sound generated by the friction between the penetration rod 5 other than the screw point 5b and the soil around it directly propagates through the resonance chamber 42 and the noise increases.

[0040] [Second Embodiment] The sound collecting unit 4 and the penetration rod 5 according to the second embodiment will be described with reference to FIG. 4. The sound collecting unit 4 according to the present embodiment is configured by omitting the sound collecting rod 4a according to the first embodiment and connecting the lid body 43 to the penetration rod 5. That is, the female screw portion 43c1 of the lid body 43 is screwed into the male screw portion 51 of the penetration rod 5. Since the structure of the lid body 43 is the same as that of the first embodiment, the description thereof will be omitted.

[0041] The penetration rod 5 is formed in a cylindrical shape with a resonance chamber 42 formed therein in a hollow manner. The penetration rod 5 has a joining structure in which a plurality of rods having the same shape can be joined, and has a first penetration rod 5a having a screw point 5b at the tip.

[0042] One penetration rod 5 has a male screw portion 51 formed at one end on the side of the lid body 43, and a female screw portion 52 that is screwed into the male screw portion 51 of the other penetration rod 5 is formed at the other end on the side of the other penetration rod 5. The resonance chamber 42 is formed by communicating a first hollow region 42a1 having an opening area equivalent to the tip surface of the male screw portion 51 of the penetration rod 5, a second hollow region 42a2 that is reduced in diameter from the first hollow region 42a1 and extends in the axial direction, and a third hollow region 42a3 that is slightly enlarged in diameter from the second hollow region 42a2 and can accommodate the microphone 41. In this way, the hollow regions 42a1, 42a2, and 42a3 as the resonance chamber 42 are formed along the axial direction in the penetration rod 5.

[0043] A hollow space communicating with the resonance chamber 42 (first hollow region 42a1) may be formed inside the screw point 5b, or the screw point 5b may be formed with a solid drill. When a hollow space is formed inside the screw point 5b, the frictional noise of the screw point 5b is directly propagated to this hollow space, and the microphone 41 detects the frictional noise through the resonance chamber 42. That is, the hollow regions 42a1, 42a2, and 42a3 according to the present embodiment may be continuously formed up to the inside of the screw point 5b of the penetration rod 5.

[0044] In this way, if the hollow regions 42a1, 42a2, and 42a3 along the axial direction are provided in the penetration rod 5, a resonance chamber 42 corresponding to the axial length of the penetration rod 5 can be secured, so that the sensitivity of air vibration can be enhanced. Note that the penetration tester X in the second embodiment can be used for soil determination in the screw weight penetration test. That is, for the screw weight penetration test defined in JIS A 1221, a penetration tester equipped with a solid penetration rod as in the prior art may be used, and the penetration tester X in the second embodiment may be used for the purpose of obtaining reference data for the screw weight penetration test.

[0045] In the penetration tester X according to the first and second embodiments, since the sound collection unit 4 incorporating the microphone 41 is connected to the penetration rod 5 on the ground, the cable length of the cable C connecting the sound signal output from the microphone 41 to the soil determination device 1 can be shortened. In addition, since there is no need to incorporate the microphone 41 and the cable C into the penetration rod 5, problems such as the cable C being twisted and disconnected when the penetration rod 5 rotates or the microphone 41 being damaged due to strong vibration of the screw point 5b can be prevented. Furthermore, since there is no need to search for a disconnection point inside the penetration rod 5, even when a plurality of penetration rods 5 are added, there is no need to disassemble and repair the penetration rod 5, and maintenance is easy. In addition, since the sound collection unit 4 and the penetration rod 5 are detachably screwed together, the sound collection unit 4 may be attached only during soil determination, and the vibration damage to the microphone 41 can be extremely reduced.

[0046] In at least one of the penetration rod 5 and the sound collection unit 4 in the first embodiment and the second embodiment, a resonance chamber 42 in which the frictional sound of the screw point 5b causes air vibration is formed along the axial direction, and a microphone 41 is positioned inside the resonance chamber 42. That is, instead of directly measuring the vibration of the penetration rod 5, it detects the sound of the air vibration propagating through the resonance chamber 42, is less affected by the surrounding environment, and has high detection sensitivity. As a result, the determination accuracy of the soil quality based on the sound signal can be improved.

[0047] [Soil Quality Determination Device and Soil Quality Determination Method] As shown in FIG. 1, the extraction unit 13 of the soil quality determination device 1 acquires the sound signal detected by the microphone 41 from the cable C via the input unit 11, and extracts the sound signal of the screw point 5b based on the resonance frequency corresponding to the size of the resonance chamber 42. In the first embodiment, since the resonance chamber 42 is formed inside the sound collection rod 4a, the axial length L is constant. However, in the second embodiment, the axial length L of the resonance chamber 42 varies depending on the number of added penetration rods 5. When the axial length L is used as the size of the resonance chamber 42, the resonance frequency f can be calculated by f = V (speed of sound) × L. The extraction unit 13 may use a low-pass filter that extracts frequency components less than this resonance frequency f, or a high-pass filter that removes a predetermined low-frequency component obtained according to the resonance frequency f as noise. Note that the extraction unit 13 may be omitted and all the sound signals detected by the microphone 41 may be used.

[0048] The determination unit 14 of the soil quality determination device 1 determines the soil quality based on the sound signal of the screw point 5b extracted by the extraction unit 13 and the soil quality reference data stored in the storage unit 12. The soil quality reference data has a reference value of sound for determining that it is the corresponding soil quality for each soil quality to be determined. The determination result of this determination unit 14 is displayed on the display screen of the soil quality determination device 1, printed, or transmitted to the control device 9.

[0049] Next, a soil quality determination method will be described with reference to FIG. 5. The soil quality determination method according to the present embodiment includes a stop step (♯53 in FIG. 5) of stopping the movement of the penetration rod 5 when the screw point 5b reaches a predetermined position (a multiple of 0.25 m), a connection step (♯54 in FIG. 5) of connecting the sound collection unit 4 to the penetration rod 5 after the stop step, and a determination step (♯55 in FIG. 5) of rotating the penetration rod 5 while maintaining the screw point 5b at the predetermined position and determining the soil quality by the determination unit 14 based on the sound signal output by the microphone 41.

[0050] Using the penetration tester X without the sound collection unit 4 attached, an SWS test (penetration test) is performed (#51). As described above, in the penetration test, the control device 9 controls the rotation motor 6 and the lifting motor 8 and repeats the test until a predetermined position (a multiple of 0.25 m) is reached. When the screw point 5b reaches the predetermined position (#52 Yes), the penetration test is temporarily stopped (#53, stop step). At this time, the control device 9 controls the lifting motor 8 to set the load applied to the penetration rod 5 to a no-load state where the load is zero.

[0051] A soil quality determination system Y including the sound collection unit 4 and the soil quality determination device 1 is connected between the penetration tester X and the control device 9 (#54, connection step). At this time, since the load of the sound collection unit 4 is applied to the penetration rod 5, the control device 9 controls the lifting motor 8 so that the load applied to the penetration rod 5 becomes zero. Next, the control device 9 controls the rotation motor 6 to rotate the penetration rod 5 in a no-load state, and the soil quality determination device 1 determines the soil quality (♯55, determination step).

[0052] By rotating the penetration rod 5, the frictional sound of the screw point 5b causes air vibration in the closed space of the resonance chamber 42, and the digital signal of the sound detected by the microphone 41 is transmitted to the soil quality determination device 1 via the cable C. At this time, the control device 9 controls the rotation speed and rotation time of the rotation motor 6 to preset values, so that the soil quality determination device 1 receives the digital signal over a predetermined time.

[0053] The extraction unit 13 of the soil quality determination device 1 acquires the sound signal detected by the microphone 41, and extracts the sound signal at the screw point 5b based on the resonance frequency corresponding to the size of the resonance chamber 42. The determination unit 14 of the soil quality determination device 1 determines the soil quality based on the sound signal at the screw point 5b extracted by the extraction unit 13 and the soil quality reference data stored in the storage unit 12. As a specific method for soil quality determination, for example, the method described in Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2015-224489) can be used. That is, the sound signal extracted by the extraction unit 13 is compared with the soil quality reference data (reference value of the sound signal of the soil quality) stored in the storage unit 12, and based on the result of the comparison, the soil quality at each predetermined position is determined. Examples of the reference value of the sound signal of the soil quality include those obtained by mapping the fine particle content rate for each sound pressure level of the sound signal.

[0054] When the soil quality determination by the soil quality determination device 1 is completed (#56Yes), when continuing the penetration test (#57Yes), the soil quality determination system Y connected between the penetration tester X and the control device 9 is removed, and the penetration test is restarted (#58).

[0055] FIG. 6 shows a comparison diagram of the sound pressure levels between a conventional example in which a resonance chamber and a microphone are provided inside a screw point 5b as described in Patent Document 2 (Japanese Patent Application Laid-Open No. 2015-224489), and this example in which the sound collection unit 4 in the first embodiment is connected to the penetration rod 5 on the ground. In the comparative example, the frictional sound of the screw point 5b directly becomes an air sound that causes air vibration in the resonance chamber. However, in this example, the frictional sound of the screw point 5b propagates as a solid sound through the penetration rod 5, and this solid sound propagates as an air sound that causes air vibration in the resonance chamber 42. As shown in FIG. 6, although the propagation paths of the frictional sounds are different, when the comparative example and this example are compared, the sound pressure levels are equivalent. Therefore, in this embodiment, it has been demonstrated that while maintaining the determination accuracy, the durability can be enhanced without incorporating a microphone or a cable into the penetration rod 5. In particular, in this embodiment, since the sound collection unit 4 is provided on the ground, there was a concern that ambient noise might be picked up. However, it can be seen that the solid sound in the frictional sound of the screw point 5b propagates as an air sound that causes air vibration in the resonance chamber 42, so that the soil quality can be determined without being affected by noise.

[0056] [Other Embodiments] (1) Although the penetration tester X has been described as an automatic penetration tester that is driven and controlled by the control device 9, it may be a manual penetration tester that penetrates the penetration rod 5 into the ground while manually attaching and detaching the weight 3a. (2) The penetration rod 5 connected to the sound collection unit 4 of the first embodiment may have a hollow region as the resonance chamber 42 formed along the axial direction as in the second embodiment. (3) In the above-described embodiment, the microphone 41 is provided at the end of the resonance chamber 42, but it may be provided in the middle of the resonance chamber 42, and the installation position is not limited as long as the microphone 41 is located on the ground. (4) In the above-described embodiment, the sound collection unit 4 and the penetration rod 5 are detachably screwed together, but they may be in a form in which the sound collection unit 4 and the penetration rod 5 are always connected. [Industrial Applicability]

[0057] The present invention can be used for a penetration tester used in a ground investigation of a screw weight penetration test, a soil quality determination method using the penetration tester, and a soil quality determination device used for the penetration tester.

Explanation of Signs

[0058] 1: Soil quality determination device 4: Sound collection unit 4a: Sound collection rod 5: Penetration rod 5b: Screw point 14: Determination unit 41: Microphone 42: Resonance chamber 42a1, 42a2, 42a3: Hollow region 43: Cover X: Penetration tester Y: Soil quality determination system

Claims

1. A penetration tester used in a screw weight penetration test, comprising: a penetration rod including a screw point that penetrates into the ground along the axial direction; a sound collecting unit connected to the penetration rod on the ground and having a built-in microphone; a determination unit that determines the soil quality based on the sound signal output by the microphone, wherein at least one of the penetration rod and the sound collecting unit has a resonance chamber in which the frictional sound of the screw point causes air vibration, formed along the axial direction, and the microphone is located inside the resonance chamber.

2. The penetration tester according to claim 1, wherein the sound collecting unit has a sound collecting rod having the resonance chamber formed therein, and a lid body connected to the sound collecting rod and having the microphone built therein.

3. The penetration tester according to claim 1, wherein the penetration rod has a hollow region serving as the resonance chamber formed along the axial direction.

4. The penetration tester according to any one of claims 1 to 3, wherein the sound collecting unit and the penetration rod are detachably screwed together.

5. A soil quality determination method using the penetration tester according to any one of claims 1 to 4, comprising: a stop step of stopping the movement of the penetration rod when the screw point reaches a predetermined position; a connection step of connecting the sound collecting unit to the penetration rod after the stop step; a determination step of rotating the penetration rod while maintaining the screw point at the predetermined position and determining the soil quality by the determination unit based on the sound signal output by the microphone.

6. A soil quality determination system used in the penetration tester according to any one of claims 1 to 4, comprising: the sound collecting unit, and a soil quality determination device electrically connected to the sound collecting unit and having the determination unit.

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