Double-array resistivity pore pressure static sounding device

Abstract

The invention discloses a double-array resistivity pore pressure static sounding device which comprises a conical probe, a pore pressure filter ring, a side wall upper friction cylinder, a resistivity test module, a digital circuit board and an analog-to-digital converter. The conical probe is connected with the friction cylinder on the side wall through a pore pressure filter ring; a pore pressure sensor, a conical tip resistance sensor, a side friction resistance sensor, a temperature compensator and an inclinometer which are connected with the digital circuit board are arranged in the friction cylinder on the side wall, which is in butt joint with the resistivity test module; the digital circuit board is connected with the resistivity test module and is connected with the analog-to-digital converter through a coaxial cable, and the coaxial cable is connected with the analog-to-digital converter and a data acquisition instrument outside the device; the soil body horizontal resistivity measured by the method has the characteristics of in-situ property, rapidness, continuity, reliability and the like, and a powerful detection tool is provided for geotechnical engineering practice.

Description

Technical Field

[0001] The present invention relates to the field of geotechnical engineering, and in particular to a dual-array resistivity pore pressure static penetration device. Background Art

[0002] As a lightweight, fast and efficient in-situ testing technology, piezocone penetration has been widely used in soil engineering investigation and geotechnical engineering monitoring and testing. Adding a resistivity test module to a conventional piezocone penetration device can test the in-situ resistivity of the soil. Current resistivity penetration probes generally use a four-electrode method, which involves setting a resistivity test module at the tail of a conventional piezocone penetration probe, vertically setting four annular electrodes on an insulating sleeve, and setting a test circuit inside. The resistivity of the soil is mostly measured vertically. How to measure the horizontal resistivity of the soil in situ through penetration testing, and further obtain detailed information such as the horizontal migration of pollutants in the soil layer and the distribution range of shallow gas, has become an urgent problem to be solved in in-situ testing of geotechnical engineering. Summary of the Invention

[0003] The purpose of the present invention is to address the defects of the existing domestic resistivity static penetration technology and propose a static penetration device that can directly measure the in-situ horizontal resistivity of soil.

[0004] To achieve the above functions, the present invention designs a dual-array resistivity pore pressure static penetration device, which includes a conical probe 1, a pore pressure filter ring 2, a sidewall friction cylinder 3, a resistivity test module 9, a digital circuit board 10, and an analog-to-digital converter 11. The conical probe 1 is located in the front half of the device and is connected to the sidewall friction cylinder 3 through the pore pressure filter ring 2. The sidewall friction cylinder 3 is connected to the resistivity test module 9.

[0005] A pore pressure sensor 4, a cone tip resistance sensor 5, a side friction resistance sensor 6, a temperature compensator 7 and an inclinometer 8 are provided inside the friction cylinder 3 on the side wall; a resistivity test module 9 is provided at the rear half of the device; a digital circuit board 10 and an analog-to-digital converter 11 are provided at the tail of the device. The digital circuit board 10 is connected to the resistivity test module 9, and a coaxial cable 12 is used to connect the digital circuit board 10 and the analog-to-digital converter 11. The coaxial cable 12 connects the analog-to-digital converter 11 and a data acquisition instrument 13 outside the device; the digital circuit board 10 is connected to the pore pressure sensor 4, the cone tip resistance sensor 5, the side friction resistance sensor 6, the temperature compensator 7 and the inclinometer 8 inside the friction cylinder 3 on the side wall.

[0006] As a preferred technical solution of the present invention: the outer layer of the resistivity test module 9 is an insulating sleeve 9.1, the middle layer is a PVC inner tube 9.2, and a cable 9.3 is arranged inside the PVC inner tube 9.2 and connected to the digital circuit board 10; the remaining space is filled with insulating mineral oil 9.4, and the resistivity test module 9 is provided with two groups of circular electrode arrays horizontally distributed along the circumference of the resistivity test module 9.

[0007] As a preferred technical solution of the present invention: the two groups of circular electrode arrays of the resistivity test module 9 include a lower electrode array 9.5 and an upper electrode array 9.6, each electrode array consists of two opposite current electrodes C1 and C2 and two groups of potential electrodes, each group of potential electrodes includes potential electrodes P1 and P2; the electrodes are equidistantly distributed along the inner wall of the insulating sleeve 9.1, the straight line connecting the current electrodes C1 and C2 is along the diameter of the insulating sleeve 9.1, and the two groups of potential electrodes are respectively distributed on both sides of the straight line connecting the current electrodes C1 and C2; each electrode is connected to a cable 9.3 and connected to the digital circuit board 10 through the cable 9.3.

[0008] As a preferred technical solution of the present invention: the lower electrode array 9.5 and the upper electrode array 9.6 work independently, reverse at a preset frequency, and provide alternating rectangular waveform current.

[0009] As a preferred technical solution of the present invention: the digital circuit board 10 includes a MOS-EFT switch, a constant current source, a high-pass filter, an instrumentation amplifier, an anti-aliasing filter, and a multiplexing processor;

[0010] The output ends of the current electrodes C1 and C2 of the lower electrode array 9.5 and the upper electrode array 9.6 are respectively connected to the input end of the MOS-EFT switch, and the constant current source is connected to the MOS-EFT switch; the output signals of the lower electrode array 9.5 and the upper electrode array 9.6 are divided into two paths, and the potential electrode P1 and the potential electrode P2 of each electrode array are respectively connected to the two input ends of the high-pass filter, the two output ends of the high-pass filter are connected to the two input ends of the instrument amplifier, the output end of the instrument amplifier is connected to the input end of the anti-aliasing filter, and the output end of the anti-aliasing filter is connected to the input end of the multiplexing processor; the pore pressure sensor 4, the cone tip resistance sensor 5, the side friction resistance sensor 6, the temperature compensator 7 and the inclinometer 8 inside the friction cylinder 3 on the side wall are connected to the input end of the multiplexing processor.

[0011] Beneficial effects: Compared with the prior art, the advantages of the present invention include:

[0012] Determining soil resistivity is crucial in geotechnical engineering practice. Resistivity is an indirect indicator of soil properties, including porosity, density, and the distribution of contaminants and gas-bearing zones. Current field resistivity tests using static cone penetration (CEP) methods mostly measure soil resistivity vertically. High-density electrical resistivity measurements, on the other hand, are typically used for large-scale soil profiles on project sites, resulting in lower accuracy.

[0013] This invention overcomes the drawback of existing domestic pore pressure static testing technology, which cannot directly measure the horizontal resistivity of soil. It can conveniently and quickly measure the in-situ horizontal resistivity of soil layers, effectively detecting the horizontal migration of pollutants and the horizontal distribution of gas-bearing soil layers. This makes static penetration testing technology more accurate and comprehensive in geotechnical engineering. This technology is characterized by high stability, reliability, and good repeatability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 2 is a schematic structural diagram of a dual-array resistivity pore pressure static penetration device provided according to an embodiment of the present invention;

[0015] Figure 2 2 is a schematic structural diagram of a resistivity testing module provided in an embodiment of the present invention;

[0016] Figure 3 is a structural schematic diagram of a digital circuit board provided according to an embodiment of the present invention;

[0017] Figure 4 is a horizontal arrangement diagram of an electrode array in a resistivity testing module provided according to an embodiment of the present invention;

[0018] In the figure: 1. Cone probe; 2. Pore pressure filter ring; 3. Friction cylinder on the side wall; 4. Pore pressure sensor; 5. Cone tip resistance sensor; 6. Side friction resistance sensor; 7. Temperature compensator; 8. Inclinometer; 9. Resistivity test module; 9.1. Insulating sleeve; 9.2. PVC inner cylinder; 9.3. Cable; 9.4. Insulating mineral oil; 9.5. Upper electrode array; 9.6. Lower electrode array; 10. Digital circuit board; 11. Analog-to-digital converter; 12. Coaxial cable; 13. Data acquisition instrument. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0020] The embodiment of the present invention provides a dual array resistivity pore pressure static penetration device, referring to Figure 1, including a conical probe 1, a pore pressure filter ring 2, a friction cylinder on the side wall 3, a resistivity test module 9, a digital circuit board 10, and an analog-to-digital converter 11; wherein the conical probe 1 is located in the front half of the device, and the conical probe 1 is connected to the friction cylinder on the side wall 3 through the pore pressure filter ring 2, and the friction cylinder on the side wall 3 is connected to the resistivity test module 9;

[0021] A pore pressure sensor 4, a cone tip resistance sensor 5, a side friction resistance sensor 6, a temperature compensator 7 and an inclinometer 8 are provided inside the friction cylinder 3 on the side wall; a resistivity test module 9 is provided at the rear half of the device; a digital circuit board 10 and an analog-to-digital converter 11 are provided at the tail of the device. The digital circuit board 10 is connected to the resistivity test module 9, and a coaxial cable 12 is used to connect the digital circuit board 10 and the analog-to-digital converter 11 to transmit signals and data; the coaxial cable 12 connects the analog-to-digital converter 11 and a data acquisition device 13 outside the device; the digital circuit board 10 is connected to the pore pressure sensor 4, the cone tip resistance sensor 5, the side friction resistance sensor 6, the temperature compensator 7 and the inclinometer 8 inside the friction cylinder 3 on the side wall, thereby measuring various parameters of the in-situ soil.

[0022] Reference Figure 2 The outer layer of the resistivity test module 9 is an insulating sleeve 9.1, the middle layer is a PVC inner tube 9.2, and a cable 9.3 is arranged inside the PVC inner tube 9.2, which is connected to the digital circuit board 10; the remaining space is filled with insulating mineral oil 9.4. The resistivity test module 9 is provided with two groups of circular electrode arrays horizontally distributed along the circumference of the resistivity test module 9.

[0023] The two circular electrode arrays of the resistivity test module 9 include a lower electrode array 9.5 and an upper electrode array 9.6. Each electrode array consists of two opposing current electrodes C1 and C2 and two groups of potential electrodes, each group of potential electrodes including potential electrodes P1 and P2. The electrodes are evenly spaced along the inner wall of the insulating sleeve 9.1. The straight line connecting the current electrodes C1 and C2 is along the diameter of the insulating sleeve 9.1, and the two groups of potential electrodes are distributed on either side of the straight line connecting the current electrodes C1 and C2. Each electrode is connected to a cable 9.3, which connects to the digital circuit board 10 via cable 9.3.

[0024] The lower electrode array 9.5 and the upper electrode array 9.6 work independently, inverting at a preset frequency to provide alternating rectangular waveform current.

[0025] Reference Figure 3 , the digital circuit board 10 includes a MOS-EFT switch, a constant current source, a high-pass filter, an instrumentation amplifier, an anti-aliasing filter, and a multiplexing processor;

[0026] Connect the output terminals of the current electrodes C1 and C2 of the lower electrode array 9.5 and the upper electrode array 9.6 to the input terminals of the MOS-EFT switch, and connect the constant current source to the MOS-EFT switch; divide the output signals of the lower electrode array 9.5 and the upper electrode array 9.6 into two paths, and connect the potential electrodes P1 and P2 of each electrode array to the two input terminals of the high-pass filter respectively. Connect the two output terminals of the high-pass filter to the two input terminals of the instrumentation amplifier, connect the output terminal of the instrumentation amplifier to the input terminal of the anti-aliasing filter, and connect the output terminal of the anti-aliasing filter to the input terminal of the multiplexing processor; connect the pore pressure sensor 4, the cone tip resistance sensor 5, the side friction resistance sensor 6, the temperature compensator 7 and the inclinometer 8 inside the friction cylinder 3 on the side wall to the input terminal of the multiplexing processor.

[0027] The horizontal resistivity of the soil measured by a double-array resistivity piezocone penetration testing device designed by the present invention has the characteristics of in-situ, fast, continuous, reliable, etc., providing a powerful detection tool for geotechnical engineering practice.

[0028] The principle of measuring the horizontal resistivity based on the device of the present invention is as follows:

[0029] Existing research shows that according to the relationship between resistivity and resistance in the tested soil, the resistivity ρ is obtained:

[0030]

[0031] In the formula, V W is the voltage, I is the current, and k is the calibration coefficient related to the electrode geometric characteristics.

[0032] The upper and lower electrode arrays work independently. Refer to Figure 3 , the DC constant current source provides 10 mA (maximum potential difference of 30 V), reverses at a frequency of 1200 Hz to provide an alternating rectangular waveform current of 600 Hz. A complete cycle is fed to the current electrode of the first electrode array, and 10 result potential data samples are synchronously collected from the corresponding potential electrodes arranged in parallel within each electrode array. Then the first array is disconnected, and the next cycle is fed to the second array, and the sampling process is repeated. Finally, the 10 samples from a single electrode array are combined into a single RMS value. Therefore, both electrode arrays are measured in a time-division multiplexing manner, and the final sampling frequency is 300 Hz. Whenever the array switches, these samples are collected to sample the pore water pressure, cone tip resistance, side friction resistance, and depth at a frequency of 300 Hz.

[0033] The horizontal layout diagram of the upper and lower electrode arrays is as shown in Figure 4 Based on existing theoretical research, where the voltage V W is obtained from the voltage between 4 circular electrodes:

[0034] V W =V(r A ∣r M )-V(r A ∣r N )-V(r B ∣r M )+V(r B ∣r N )

[0035] Where, V(r A ∣r M ) is the voltage between electrodes AM, V(r A ∣r N ) is the voltage between electrodes AN, V(r B ∣r M ) is the voltage between electrodes BM, V(r B ∣r N ) is the voltage between electrodes BN.

[0036] Assume that the resistivity test module is an infinitely long cylinder with a radius of a, and the following relationship is satisfied between a and k:

[0037]

[0038] Where x is the integral variable associated with the Bessel function, f(x) is the Bessel function, and m is an integer in the series, representing the number of terms in the series.

[0039] As a function of x, the integrand decreases monotonically, so that the upper limit of the integral reaches six digits of precision at x = 12. Numerical calculation of the right side of the above equation yields 0.099968, and the relationship between k and a is obtained as follows:

[0040] k=10.00319·a

[0041] Combining the above formula, the horizontal resistivity ρ of the soil can be determined.

[0042] In engineering practice, the in-situ horizontal resistivity profile of the soil layer can be obtained by computer programming, which is more intuitive and quick. The method of the present invention has the characteristics of stability, reliability and repeatability.

[0043] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A double-array resistivity piezocone penetration testing device, characterized in that It includes a cone penetrometer (1), a pore pressure filter ring (2), a sidewall friction sleeve (3), a resistivity test module (9), as well as a digital circuit board (10) and an analog-to-digital converter (11); among them, the cone penetrometer (1) is located in the front half of the device, and the cone penetrometer (1) is connected to the sidewall friction sleeve (3) through the pore pressure filter ring (2), and the sidewall friction sleeve (3) is docked with the resistivity test module (9); Inside the sidewall friction sleeve (3), there are a pore pressure sensor (4), a tip resistance sensor (5), a side friction resistance sensor (6), a temperature compensator (7) and an inclinometer (8); the resistivity test module (9) is provided in the rear half of the device; at the tail of the device, there are a digital circuit board (10) and an analog-to-digital converter (11). The digital circuit board (10) is connected to the resistivity test module (9), and a coaxial cable (12) is used to connect the digital circuit board (10) and the analog-to-digital converter (11). The coaxial cable (12) connects the analog-to-digital converter (11) and a data collector (13) outside the device; the digital circuit board (10) is connected to the pore pressure sensor (4), the tip resistance sensor (5), the side friction resistance sensor (6), the temperature compensator (7) and the inclinometer (8) inside the sidewall friction sleeve (3).

2. The double-array resistivity piezocone penetration testing device according to claim 1, characterized in that, The outer layer of the resistivity test module (9) is an insulating sleeve (9.1), the middle layer is a PVC inner cylinder (9.2), and inside the PVC inner cylinder (9.2), there is a cable (9.3) connected to the digital circuit board (10); the remaining space is filled with insulating mineral oil (9.4). The resistivity test module (9) is provided with two sets of circular electrode arrays horizontally distributed along the circumference of the resistivity test module (9).

3. The double-array resistivity piezocone penetration testing device according to claim 2, wherein, The two sets of circular electrode arrays of the resistivity test module (9) include a lower electrode array (9.5) and an upper electrode array (9.6). Each electrode array consists of two opposite current electrodes C1, C2 and two sets of potential electrodes. Each set of potential electrodes includes potential electrodes P1, P2; each electrode is equally spaced along the inner wall of the insulating sleeve (9.1). The straight line connected by the current electrodes C1, C2 is the diameter of the insulating sleeve (9.1), and the two sets of potential electrodes are respectively distributed on both sides of the straight line connected by the current electrodes C1, C2; each electrode is connected to the cable (9.3) and is connected to the digital circuit board (10) through the cable (9.3).

4. A double-array resistivity piezocone penetration testing device according to claim 3, wherein, The lower electrode array (9.5) and the upper electrode array (9.6) work independently and reverse at a preset frequency to provide an alternating rectangular waveform current.

5. A double-array resistivity piezocone penetration testing device according to claim 1, characterized in that, The digital circuit board (10) includes a MOS-EFT switch, a constant current source, a high-pass filter, an instrumentation amplifier, an anti-aliasing filter, and a multiplexing processor; Connect the output terminals of the current electrodes C1 and C2 of the lower electrode array (9.5) and the upper electrode array (9.6) to the input terminals of the MOS-EFT switch respectively, and connect the constant current source to the MOS-EFT switch; divide the output signals of the lower electrode array (9.5) and the upper electrode array (9.6) into two paths, and connect the potential electrodes P1 and P2 of each electrode array to the two input terminals of the high-pass filter respectively. Connect the two output terminals of the high-pass filter to the two input terminals of the instrumentation amplifier. Connect the output terminal of the instrumentation amplifier to the input terminal of the anti-aliasing filter. Connect the output terminal of the anti-aliasing filter to the input terminal of the multiplexing processor; connect the pore pressure sensor (4), the tip resistance sensor (5), the side friction resistance sensor (6), the temperature compensator (7) and the inclinometer (8) inside the friction cylinder (3) on the side wall to the input terminal of the multiplexing processor.

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