Soil property determination method and penetration rod

Abstract

To provide a soil determination method and a penetration rod which are hardly affected by ambient noise generated in the vicinity of a site where a penetration testing machine is used and by the surrounding ground, and can accurately determine the soil of the tip ground.SOLUTION: A penetration test is performed by mounting a penetration rod 1 having a screw point 2 on the tip side on a penetration testing machine 5, a noise vibration is reduced from an output signal of a vibration sensor 30 mounted on the rear end side of the penetration rod 1 in parallel with the penetration test, and soil quality for each penetration depth of the penetration rod 1 is determined based on the magnitude of an amplitude and a peak frequency extracted by processing for the output signal with the noise vibration reduced.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a soil quality assessment method that can be performed using a screw-weight penetration test and a penetration rod used in the screw-weight penetration test. [Background technology]

[0002] Patent Document 1 discloses an excavator equipped with a soil quality determination mechanism in which a sound and vibration measurement sensor is attached to the tip of the earth auger, and a frequency analyzer and a soil quality indicator are connected to the measurement sensor.

[0003] Patent Document 2 discloses a method for detecting a supporting layer by drilling in the ground, in which an acoustic emission sensor is installed in a ground drilling machine, and the acoustic emission sensor detects the cutting sound of the ground caused by the tip cutter bit when drilling the ground. This detected signal is input into a discrimination processing circuit and converted into an emission level, and the depth position of the supporting layer is detected based on changes due to soil properties.

[0004] Patent Document 3 discloses a penetration testing machine used in a screw weight penetration test. This penetration testing machine is equipped with a microphone that picks up sound generated in a resonance chamber provided in a screw point that is penetrated into the ground. The soil quality determination device is equipped with an extraction unit that extracts a sound signal of the test object from the sound picked up by the microphone based on a resonance frequency corresponding to the size of the resonance chamber, and a determination unit that determines the soil quality based on the sound signal of the test object extracted by the extraction unit and reference data.

[0005] Patent Document 4 discloses a penetration testing machine used in screw weight penetration tests. This penetration testing machine includes a penetration rod with a screw point that penetrates the ground along its axial direction, a sound collection unit with a built-in microphone, and a judgment unit that judges the soil quality based on the sound signal output by the microphone. At least one of the penetration rod and the sound collection unit has a resonance chamber axially formed to generate the frictional sound of the screw point in air vibrations, and the microphone is located inside the resonance chamber. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 62-258016 [Patent Document 2] Japanese Patent Publication No. 62-291392 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-224489 [Patent Document 4] Japanese Patent Application Publication No. 2023-81664 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the technologies disclosed in Patent Documents 1 and 2 are used to manage the bottoming of support piles and are technologies for determining whether the ground is hard or gravelly. Furthermore, because the spiral blades of an earth auger extend over the entire length, the contact length between the spiral blades and the surrounding ground increases the further the excavation progresses. Therefore, the further the excavation progresses, the greater the influence (noise) from the surrounding ground becomes and the more the influence changes. Since it is not possible to separate the influence from the surrounding ground from the influence from the tip ground, it is difficult to determine the soil quality of the intermediate layer. Therefore, this technology is not suitable for use in anything other than a hard gravel layer (supporting layer) where large vibrations occur during excavation.

[0008] Furthermore, the techniques disclosed in Patent Documents 3 and 4 may be affected by ambient noise generated near the site where the penetration tester is used.

[0009] The object of this invention is to provide a soil quality determination method and a penetration rod that are less susceptible to the influence of ambient noise generated near the site where the penetration tester is used and the influence of the surrounding ground, and that can accurately determine the soil quality of the tip ground. [Means for solving the problem]

[0010] The soil quality determination method of this invention involves attaching a penetration rod having a screw point on the tip side to a penetration testing machine to perform a penetration test, detecting the output signal of a vibration sensor attached to the rear end of the penetration rod in parallel with this penetration test, and using the testing machine vibration signal from the testing machine vibration sensor attached to the penetration testing machine to reduce noise vibration from the output signal of the vibration sensor, and determining the soil quality for each penetration depth of the penetration rod based on the magnitude of the amplitude and peak frequency extracted by processing the output signal from which the noise vibration has been reduced.

[0011] According to this method, the penetration rod is attached to a penetration tester and a penetration test is performed, while the soil quality for each penetration depth of the penetration rod can be determined from the output signal of the vibration sensor. Since the screw point is located only at the tip, there is no ground contact along the entire length like the spiral blades of an earth auger, and there is no disadvantage of increased influence (noise) from the surrounding ground as the excavation progresses. Furthermore, since the output signal of the vibration sensor is used, the penetration tester is less susceptible to the influence of ambient noise generated near the site where it is used. Since the vibration sensor is attached to the rear end of the penetration rod, it is susceptible to noise vibrations from the penetration tester, but the noise vibrations can be reduced using the tester vibration signal from the tester vibration sensor attached to the penetration tester. Furthermore, this method can be used in cases where it is difficult to incorporate a vibration sensor on the screw point side of the penetration rod.

[0012] In addition, the soil quality determination method of the present invention is characterized in that a penetration rod having a screw point at the tip side and a built-in vibration sensor is attached to a penetration testing machine to perform a penetration test, and the output signal of the vibration sensor is detected in parallel with this penetration test, and the soil quality for each penetration depth of the penetration rod is determined based on the magnitude of the amplitude and peak vibration frequency extracted by processing the output signal.

[0013] According to this method, the penetration rod is attached to a penetration tester and a penetration test is performed, while the soil quality for each penetration depth of the penetration rod can be determined from the output signal of the vibration sensor. Since the screw point is only located at the tip, there is no ground contact along the entire length like the spiral blades of an earth auger, and there is no disadvantage of increasing influence (noise) from the surrounding ground as the excavation progresses. In addition, since the output signal of the vibration sensor on the screw point side is used, it is less susceptible to the influence of ambient noise generated near the site where the penetration tester is used.

[0014] Of course, noise vibrations may be reduced from the output signal of the vibration sensor by using a tester vibration signal from a tester vibration sensor attached to the penetration tester, thereby enabling accurate reduction of noise vibrations generated by the penetration tester.

[0015] The penetration rod of this invention has a screw point at its tip end and is used to penetrate into the ground from this screw point side to determine the bearing capacity of the ground, and is characterized by having a vibration sensor, a processing unit for processing the output signal of this vibration sensor, and a power supply unit within the penetration rod.

[0016] With the above configuration, the output signal of the vibration sensor is processed within the penetration rod, so noise contamination can be avoided as much as possible compared to supplying the weak output signal of the vibration sensor to a processing device on the ground via a signal line extended to the ground.

[0017] The device may have a connecting rod that can be connected to and disconnected from the screw point, and the vibration sensor, the processing unit, and the power supply unit may be provided within the connecting rod, which allows for easy replacement of the vibration sensor and the power supply unit.

[0018] The processing unit may convert the output signal of the vibration sensor into a digital signal and write the digital signal into the memory unit.

[0019] The processing unit may transmit the output signal of the vibration sensor wirelessly or via a wire. [Effects of the Invention]

[0020] The present invention has the advantage of being less susceptible to the influence of ambient noise generated near the site where the penetration testing machine is used and the influence of the surrounding ground, and making it possible to accurately determine the soil quality of the ground. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is an explanatory diagram showing a penetration tester used in a soil quality determination method according to an embodiment. [Figure 2] 1 is an explanatory diagram showing an example of signal processing in a soil type determination method according to an embodiment; [Figure 3] FIG. 1 is an explanatory diagram showing a penetration testing machine equipped with a penetration rod according to an embodiment. [Figure 4] 1A is an explanatory diagram of the penetration rod of the embodiment, and FIG. 1B is an explanatory diagram of the connecting rod portion. [Figure 5] 10A and 10B are explanatory diagrams showing an example of signal processing in a soil type determination method according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0022] (Embodiment 1) Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. As shown in Figure 1, vibration information collection in the soil quality determination method of the embodiment is carried out in parallel with a screw-weight penetration test performed by attaching a penetration rod 1 to a penetration tester 5. The penetration tester 5 can be equipped with functions such as automatic measurement of load, number of half rotations, and penetration depth, display of measurement values ​​on a monitor (e.g., graph display of converted N-values), and data transfer to compatible devices via wireless LAN, etc.

[0023] The penetration rod 1 has a screw point 2 at its tip end. A vibration sensor 30 (accelerometer) is attached to the rear end of the penetration rod 1. In a penetration test using the penetration rod 1, the ground is penetrated from the screw point 2 side to determine the bearing capacity of the ground. When extending the rod portion of the penetration rod 1, the vibration sensor 30 can be removed and replaced with the vibration sensor 30 on the newly extended rod portion. A testing machine vibration sensor 51 (accelerometer) is also attached to the penetration testing machine 5.

[0024] The testing machine vibration signal from the testing machine vibration sensor 51 is used to reduce the noise vibration generated by the penetration tester 5 from the output signal of the vibration sensor 30. In this example, the testing machine vibration sensor 51 is attached as close as possible to the penetration rod 1 attached to the penetration tester 5, and the testing machine vibration sensor 51 is of the same type (same principle) as the vibration sensor 31. The vibration detection direction of the vibration sensor 31 and the testing machine vibration sensor 51 can be limited to the vertical direction (Z direction).

[0025] The output signal (a) of the vibration sensor 30 is a signal that changes on the time axis, and in processing after the penetration test, this output signal (a) can be Fourier transformed to calculate a Fourier spectrum (b), and the amplitude and peak frequency can be extracted from this Fourier spectrum (b). Then, based on this amplitude and peak frequency, the soil quality for each penetration depth of the penetration rod 1 can be determined. The process of Fourier transforming the output signal (a) and the process of extracting the amplitude and peak frequency from the Fourier spectrum (b) are existing processes.

[0026] Furthermore, a Fourier spectrum (d) is calculated by Fourier transforming the output signal (c) of the testing machine vibration sensor 51. Then, a bandpass filter (e) is created from this Fourier spectrum (d) based on vibration characteristics such as the dominant frequency. Furthermore, by passing the Fourier spectrum (b) based on the output signal (a) of the vibration sensor 31 through the bandpass filter (e), the noise vibration generated by the penetration test machine 5 is reduced and the vibration characteristics of the ground at the tip of the penetration rod 1 are extracted. In other words, based on the amplitude and peak frequency of the Fourier spectrum (f), which is the signal that has been corrected in this way, the soil quality of the ground at the tip of the penetration rod 1 for each penetration depth can be accurately determined by the land discrimination method (g).

[0027] Although the relationship between the amplitude, peak frequency, and soil quality is not specifically shown, for example, by repeatedly conducting trial runs of the soil quality determination method on known soil strata (natural strata and artificial strata), the relationship between the amplitude, peak frequency, and soil quality can be learned. Furthermore, for example, when the vibration sensor 30 is turned on, ON information is sent to the penetration tester 5, and the output signal of the vibration sensor 30 is written to memory in association with the time information of its built-in clock in the penetration tester 5. Then, if the penetration depth is recorded in association with the time information in the penetration tester 5, it can be determined at what penetration depth the output signal of the vibration sensor 30 read from the memory corresponds to after the penetration test.

[0028] According to the above method, the penetration rod 1 is attached to the penetration tester 5, and a penetration test is performed while the soil quality for each penetration depth of the penetration rod 1 can be determined from the output signal of the vibration sensor 30. Because the screw point 2 is located only at the tip, there is no ground contact along the entire length like the spiral blades of an earth auger, and there is no disadvantage of increased influence (noise) from the surrounding ground as the excavation progresses. Furthermore, because the output signal of the vibration sensor 30 is used, it is less susceptible to the influence of ambient noise generated near the site where the penetration tester 5 is used. Because the vibration sensor 30 is attached to the rear end of the penetration rod 1, it is easily affected by the vibrations of the penetration tester 5, but noise vibrations can be reduced using the tester vibration signal from the tester vibration sensor 51 attached to the penetration tester 5. Furthermore, this method can be used in cases where it is difficult to incorporate a vibration sensor on the screw point 2 side of the penetration rod 1.

[0029] (Embodiment 2) Another embodiment of the present invention will now be described with reference to the accompanying drawings. As shown in Figure 3, the penetration rod 1 has a screw point 2 at the tip end and a built-in vibration sensor 31 (accelerometer).

[0030] 4, in this embodiment, the penetration rod 1 has a metal connecting rod portion 3 that can be connected to and disconnected from the screw point 2. One end of the connecting rod portion 3 has a first screw portion 3a (female screw) that screws into the male screw 2a of the screw point 2, and the other end of the connecting rod portion 3 has a second screw portion 3b (male screw) that screws into the female screw 11a of the rod portion 11 of the penetration rod 1. Rubber waterproof rings 4 are attached to the connection point between one end of the connecting rod portion 3 and the screw point 2, and to the connection point between the other end of the connecting rod portion 3 and the rod portion 11.

[0031] The vibration sensor 31 is built into the connecting rod 3. The vibration detection direction of the vibration sensor 31 can be limited to the vertical direction (Z direction). The connecting rod 3 also includes a processing unit 32 for processing the output signal of the vibration sensor 31, a memory unit 33, and a power supply unit 34. The processing unit 32 converts the output signal of the vibration sensor 31 into a digital signal (A-D conversion) and writes it to the memory unit 33. The connecting rod 3 also includes a USB terminal (read terminal, charging terminal) 35 for reading data from the memory unit 33 and charging the power supply unit 34. If the power supply unit 34 is a primary battery, the charging terminal is not necessary, and the power supply unit 34 is a replaceable battery type. Alternatively, for example, the vibration sensor 31, processing unit 32, memory unit 33, power supply unit 34, and USB terminal 35 may be disposed in a plastic tube (not shown), which can be inserted into the connecting rod 3. The plastic tube can be removed for battery replacement or other operations.

[0032] Furthermore, an ON / OFF switch (not shown) is disposed on the connecting rod portion 3 so that it can be operated, for example, from the first screw portion 3a (female screw), and an operator turns the switch ON when connecting the connecting rod portion 3 to the screw point 2 and the rod portion 11. For example, when this ON operation is performed, the processing unit 32 writes the output signal of the vibration sensor 31 to the memory unit 33 in association with the time information of its built-in clock. Meanwhile, if the penetration depth is also recorded in association with the time information of the penetration tester 5, it will be possible to determine at what penetration depth the output signal of the vibration sensor 31 read from the memory unit 33 corresponds when the connecting rod portion 3 is removed and processing is performed after the penetration test.

[0033] In collecting vibration information in this soil quality determination method, it is not limited to the above-mentioned time setting, but for example, a timer in the processing unit 32 may be started when the processing unit 32 receives an external start signal via an antenna provided in the penetration rod 1, and the output signal of the vibration sensor 31 may be written to the memory unit 33 in association with the time information from the timer in the processing unit 32. The start signal may be sent by the operator pressing a button on the start command transmitter at the start timing of the penetration test.

[0034] On the other hand, if the processing unit 32 modulates (AM modulation, FM modulation, etc.) the output signal of the vibration sensor 31 and transmits it wirelessly to the ground using an antenna, the memory unit 33 is not necessary. A receiver (dedicated receiver, smartphone, etc.) located on the penetration tester 5 side may demodulate the received radio waves, perform A-D conversion on the output signal of the vibration sensor 31, and store it in memory. This makes it possible for the penetration tester 5 side to determine the value at which penetration depth the output signal of the vibration sensor 31 corresponds, without the need for the time information or time information. Since the penetration rod 1 is made of metal and extends to the ground surface by extending the rod portion, the penetration rod 1 itself can be used as an antenna. The processing unit 32 can also A-D convert the output signal of the vibration sensor 31, modulate this digital signal, and transmit it wirelessly. Furthermore, in addition to wireless transmission, the processing unit 32 can also amplify the output signal of the vibration sensor 31 or its digitally converted signal and transmit it via a wired connection to the penetration tester 5 side using a cord passed through the penetration rod 1.

[0035] 5, the output signal (a) of the vibration sensor 31 is a signal that changes on the time axis, and in processing after the penetration test, this output signal (a) is Fourier transformed to calculate a Fourier spectrum (b), and the amplitude and peak frequency can be extracted from this Fourier spectrum (b). Then, based on the amplitude and peak frequency, the soil quality for each penetration depth of the penetration rod 1 can be determined.

[0036] In this way, when the vibration sensor 31 is built into the screw point 2 side, it is less susceptible to the influence of noise from the penetration testing machine 5 installed on the ground, so the friction noise between the ground and the screw point 2 can be measured directly, making it possible to make a judgment without noise processing. Of course, in order to make a more accurate judgment, it is also possible to reduce noise using the testing machine vibration sensor 51, as described in embodiment 1.

[0037] In this case, the output signal of the testing machine vibration sensor 51 may be recorded in a separate memory (not shown), and the output signal of the testing machine vibration sensor 51 may be read from the memory during noise reduction processing. Also, if the output signal of the vibration sensor 31 is transmitted wirelessly or via a cable, it is possible to process the output signal of the vibration sensor 31 and the output signal of the testing machine vibration sensor 51 in real time. Furthermore, other known processes may be used instead of the noise vibration reduction process described above. For example, a noise cancellation process may be performed in which a signal having an opposite phase to the output signal of the testing machine vibration sensor 51 is generated and added to the output signals of the vibration sensors 31 and 30.

[0038] In a penetration test using a penetration testing machine 5, sampling may be performed by scraping off a portion of the ground around the investigation hole, but this sampling makes it difficult to determine the boundaries of the soil layers. On the other hand, the soil quality determination method of the embodiment makes it possible to determine the soil quality across all layers of the ground, making it easy to grasp the boundaries of the soil layers and the layer thickness. Furthermore, if the vibration characteristics of each region and each soil layer are accumulated as big data, the reliability of the soil quality determination will improve.

[0039] Although the embodiments of the present invention have been described above with reference to the drawings, the present invention is not limited to the illustrated embodiments. Various modifications and variations can be made to the illustrated embodiments within the same scope as the present invention or within an equivalent scope. [Explanation of symbols]

[0040] 1: Penetration rod 2:Screw point 2a: Male screw 3: Connecting rod part 3a: First screw part 3b: 2nd screw part 4: Waterproof ring 5: Penetration tester 11: Rod part 11a: Female screw 30: Vibration sensor 31: Vibration sensor 32: Processing section 33: Memory section 34: Power supply section 35: USB port 51: Testing machine vibration sensor

Claims

1. A penetration test is performed by attaching a penetration rod having a screw point on the tip side to a penetration testing machine, and in parallel with this penetration test, the output signal of a vibration sensor attached to the rear end of the penetration rod is detected, and the test machine vibration signal from the testing machine vibration sensor attached to the penetration testing machine is used to reduce noise vibration from the output signal of the vibration sensor, and the noise vibration is reduced. A soil quality determination method characterized by determining the soil quality for each penetration depth of the penetration rod based on the magnitude of the amplitude and peak frequency extracted by processing the output signal.

2. A penetration rod having a screw point at the tip side and a built-in vibration sensor is attached to a penetration testing machine to perform a penetration test, and the output signal of the vibration sensor is detected in parallel with this penetration test. A soil quality determination method characterized by determining the soil quality for each penetration depth of the penetration rod based on the magnitude of the amplitude and peak vibration frequency extracted by processing this output signal.

3. 3. The soil quality determination method according to claim 2, wherein a testing machine vibration signal from a testing machine vibration sensor attached to the penetration testing machine is used to reduce noise vibration from the output signal of the vibration sensor.

4. A penetration rod having a screw point at the tip end and used to penetrate into the ground from this screw point side to determine the bearing capacity of the ground, characterized in that the penetration rod is equipped with a vibration sensor, a processing unit for processing the output signal of the vibration sensor, and a power supply unit.

5. 5. The penetration rod according to claim 4, further comprising a connecting rod portion that can be connected to and disconnected from the screw point side, and the vibration sensor, the processing portion, and the power supply portion are provided within the connecting rod portion.

6. 6. The penetration rod according to claim 4 or claim 5, further comprising a memory unit, wherein the processing unit converts the output signal of the vibration sensor into a digital signal and writes the digital signal into the memory unit.

7. 6. The penetration rod according to claim 4 or 5, wherein the processing unit transmits the output signal of the vibration sensor wirelessly or via a wire.

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