Method for testing moisture content of soil material

Abstract

The invention relates to the technical field of soil moisture content testing, and discloses a soil moisture content testing method which comprises the following steps: S1, acquiring no-load resonant frequency and half-power bandwidth when the interior of a rectangular metal cavity is no-load, and calculating to obtain a no-load quality factor value; s2, the soil sample is compacted in the rectangular metal cavity, the resonant frequency f and the bandwidth value of the loaded soil sample are obtained, and a loading quality factor value is obtained through calculation; s3, obtaining a dielectric constant value of the soil sample according to a frequency deviation formula; and S4, correcting the dielectric constant value of the soil sample through a dielectric constant temperature correction formula, and substituting the corrected dielectric constant value of the soil sample into a humidity formula to obtain the moisture content of the soil sample. The method has the effects that the dielectric constant is corrected by considering the influence of the temperature on the dielectric constant, and then the corrected dielectric constant is substituted into the humidity formula to obtain the moisture content of the soil sample, so that the accuracy of the obtained moisture content of the soil sample is improved.

Description

Technical Field

[0001] This invention relates to the technical field of soil moisture content testing, and specifically to a method for testing soil moisture content. Background Technology

[0002] Soil is widely used in infrastructure construction in fields such as water conservancy, transportation, and municipal engineering. It is used as fill material for earth-rock dams, core wall seepage prevention material, roadbed fill material, concrete aggregate, and backfill material for foundation pits or earthwork. Among these applications, soil moisture content plays a crucial role in analyzing soil shear strength, stability, and compaction effect, as well as determining the number of compaction passes and compaction machinery. In the process of using the pit-testing method to test the compaction degree of earth-rock dams, soil moisture content is an important reference for adjusting compaction parameters for cohesive soils. For non-cohesive soils, adding appropriate water before compaction can effectively increase interparticle slippage, reduce filler separation, and significantly improve compaction effect. In the concrete mixing process, the moisture content of coarse and fine aggregates is an important reference for the amount of water added artificially. Inaccurate moisture content can easily lead to concrete failing to meet workability requirements and even affecting its strength and durability.

[0003] Currently, commonly used methods for detecting soil moisture content include the neutron method and the TRD method. The neutron method is significantly affected by the bulk density of the soil, while the TRD method can only provide a rough assessment of soil moisture and cannot meet the accuracy requirements for moisture content detection in engineering soil. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that the existing soil moisture content detection methods have low detection accuracy. The purpose is to provide a soil moisture content testing method that improves the accuracy of the obtained soil moisture content by considering quality factors and the influence of temperature on the dielectric constant value.

[0005] The present invention is achieved through the following technical solutions: A method for testing the moisture content of soil includes the following steps: S1, Obtain the no-load resonant frequency when the rectangular metal cavity is unloaded. and half-power bandwidth And obtain the no-load quality factor through calculation. value; S2, the soil sample is compacted inside a rectangular metal cavity to obtain the resonant frequency f and half-power bandwidth ▲f after loading the soil sample, and the loading quality factor is obtained through calculation. value; S3, the dielectric constant of the soil sample is obtained according to the frequency shift formula; S4. The dielectric constant value of the soil sample is corrected by the dielectric constant temperature correction formula, and then the corrected dielectric constant value of the soil sample is substituted into the moisture formula to obtain the soil sample moisture content.

[0006] The beneficial effect of this invention is that by obtaining the frequency and half-power bandwidth when the rectangular metal cavity is unloaded, it is convenient to obtain the no-load quality factor. The value, obtained by measuring the frequency and bandwidth of a compacted soil sample within a rectangular metal cavity, facilitates the determination of the loading quality factor when a soil sample is loaded. The dielectric constant of the soil sample is obtained by taking into account the changes in resonant frequency and quality factors. This improves the accuracy of the dielectric constant value. The dielectric constant is then corrected by considering the effect of temperature on the dielectric constant. Finally, the corrected dielectric constant is substituted into the humidity formula to obtain the moisture content of the soil sample, thus improving the accuracy of the obtained moisture content and meeting the accuracy requirements for moisture content detection in engineering soil materials.

[0007] In some embodiments, the no-load quality factor in step S1 The value is obtained through a first calculation formula, which is: ; in, This is the no-load resonant frequency. This represents the half-power bandwidth. When the resonant cavity is unloaded, the controller transmits a frequency sweep signal, receives and records the signal amplitude at each frequency point from the sensors, and plots the unloaded resonance curve. It identifies the f0 corresponding to the peak value of the curve, finds two frequency points where the amplitude drops by 3dB (half-power point), and calculates the bandwidth. ,get .

[0008] In some embodiments, the loading quality factor in step S2 The value is obtained through a second calculation formula, which is: ; in, The resonant frequency after loading the soil sample. This represents the half-power bandwidth after loading a soil sample. When the cavity is loaded with a soil sample, the controller transmits a frequency sweep signal, and the receiver records the signal amplitude at each frequency point, plotting the no-load resonance curve; the value f corresponding to the peak value of the curve is identified, and the half-power bandwidth after loading the soil sample is calculated. ,get .

[0009] In some embodiments, the frequency offset formula in step S3 is: ; in, The resonant frequency after loading the soil sample. f represents the frequency change. For soil sample volume, Let V be the volume of the resonant cavity. Let be the dielectric constant of the soil sample. Since increased humidity leads to increased dielectric loss, The value decreases, satisfying the requirement. ( (For quality factors related to dielectric loss), therefore, through The relationship between the value and the resonant frequency f is obtained, thus yielding The relationship between the dielectric constant of the soil sample and its dielectric constant, and how to improve the dielectric constant of the soil sample. The accuracy.

[0010] In some embodiments, the frequency change f= ,in, This is the no-load resonant frequency. The resonant frequency after loading the soil sample is denoted as .

[0011] In some embodiments, the dielectric constant temperature correction formula in step S4 is: ;in, This is the actual temperature. For reference temperature, For temperature coefficient, Let be the dielectric constant of the soil sample. By considering the effect of temperature on the dielectric constant of the soil sample, the value of the dielectric constant is corrected to further improve the accuracy of the dielectric constant of the soil sample.

[0012] In some embodiments, the humidity formula in step S4 is: ; in, Let be the dielectric constant of the soil sample. The dielectric constant of dry soil, k Humidity sensitivity coefficient H This refers to the moisture content (volume fraction).

[0013] In some embodiments, the frequency offset formula and the dielectric constant temperature correction formula from step S3 are substituted into the humidity formula to obtain the moisture content. ;in, Let be the dielectric constant of the soil sample. The dielectric constant of dry soil, Where is the dielectric constant of water. k Humidity sensitivity coefficient H The moisture content (volume fraction) is calculated. By considering the effect of temperature on the dielectric constant, the dielectric constant is corrected. Then, the corrected dielectric constant is substituted into the humidity formula. This method uses a humidity inversion model to obtain the moisture content of the soil sample, improving the accuracy of the obtained moisture content and meeting the accuracy requirements for moisture content detection in engineering soil materials.

[0014] In some embodiments, during soil sample compaction, pressure is stopped when the pressure value that the soil sample can withstand reaches a preset optimal pressure value. By considering stopping pressure only when the preset optimal pressure value is detected, the soil sample is ensured to be compacted, thus improving the accuracy of the obtained soil sample data.

[0015] In some embodiments, the optimal pressure value is 200 N.

[0016] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. By obtaining the frequency and half-power bandwidth of the rectangular metal cavity under no-load conditions, it is easier to obtain the no-load quality factor. The value, obtained by measuring the frequency and bandwidth of a compacted soil sample within a rectangular metal cavity, facilitates the determination of the loading quality factor when a soil sample is loaded. The dielectric constant of the soil sample is obtained by taking into account the changes in frequency and quality factors, and then using the frequency offset formula. This improves the accuracy of the dielectric constant value.

[0017] 2. By considering the effect of temperature on the dielectric constant, the dielectric constant is corrected, and then the corrected dielectric constant is substituted into the humidity formula to obtain the moisture content of the soil sample. This improves the accuracy of the obtained soil moisture content and meets the accuracy requirements for moisture content detection of soil materials used in engineering. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a structural diagram of a test device that may be implemented based on the present invention; Figure 2 In this invention Figure 1 A partial sectional view of the structure; Figure 3 This is a partial schematic diagram of the present invention; Figure 4 This is a schematic diagram of the present invention.

[0019] The attached diagram shows the markings and corresponding component names: 1. Test chamber; 110. Top frame; 12. Electric push rod; 13. Pressure plate; 14. Pressure sensor; 15. Feeder; 16. Receiving box; 17. Guide rail; 2. Roller; 21. Box body; 22. Microwave humidity sensor; 24. Spring; 25. Support leg. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0021] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "an embodiment," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the illustrations provided herein are for illustrative purposes and are not necessarily drawn to scale. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] In the description of this invention, the terms "front", "rear", "left", "right", "up", "down", "vertical", "horizontal", "high", "low", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this invention.

[0023] The terms "first," "second," etc., used in this invention are merely for clarity of description and are not intended to limit any order or emphasize importance. Furthermore, the term "connection" as used herein, unless otherwise specified, can refer to a direct connection or an indirect connection via other components.

[0024] Example The soil moisture content testing method in this invention can be implemented using testing equipment. For details of the testing equipment's structure, please refer to [link / reference needed]. Figure 1-Figure 2The test chamber includes a test box 1, a top frame 11 fixedly connected to the surface of the test box 1, an electric push rod 12 fixedly connected to the surface of the top frame 11, a pressure plate 13 fixedly connected to the piston end of the electric push rod 12, a pressure sensor 14 provided at the bottom of the pressure plate 13, a feeder 15 fixedly connected to the bottom of the test box 1, a receiving box 16 inserted into the bottom of the test box 1, a guide rail 17 fixedly connected to the surface of the test box 1, a box body 21 inserted into the surface of the test box 1, a roller 2 provided on the surface of the box body 21, the roller 2 slidably connected to the guide rail 17, a microwave humidity sensor 22 slidably connected to the surface of the box body 21, a sensing part provided on the surface of the microwave humidity sensor 22, a spring 24 fixedly connected to the end of the microwave humidity sensor 22 away from the sensing part, the end of the spring 24 away from the microwave humidity sensor 22 fixedly connected to the surface of the box body 21, and a support leg 25 rotatably connected to the bottom of the box body 21. During operation, the spring force of spring 24 causes microwave humidity sensor 22 to enter the detection area of ​​test chamber 1, and the sensing part 23 is positioned at the bottom of the compaction zone of test chamber 1. The sensing part 23 supports the soil at the bottom of the compaction zone and can detect the soil moisture content. The microwave humidity sensor 22 detects the soil moisture content primarily using the microwave resonant cavity method. The soil is then fed into test chamber 1 from feeder 15 and compacted in the compaction zone of the test chamber by pressure plate 13. The compaction is controlled by pressure sensor 14. After testing, the soil sample can be output to the receiving box, and then compacted again to load more soil samples for testing, thus improving testing efficiency.

[0025] See Figure 3 and Figure 4 This embodiment provides a method for testing the moisture content of soil, including the following steps: S1, Obtain the no-load resonant frequency when the rectangular metal cavity (i.e., test chamber 1) is unloaded. and half-power bandwidth And obtain the no-load quality factor through calculation. value; S2, the soil sample is compacted inside a rectangular metal cavity (i.e., test chamber 1) to obtain the resonant frequency f and half-power bandwidth ▲f after loading the soil sample, and the loading quality factor is obtained by calculation. value; S3, the dielectric constant of the soil sample is obtained according to the frequency shift formula; S4. The dielectric constant value of the soil sample is corrected using a temperature correction formula. The corrected dielectric constant value is then substituted into the moisture content formula to obtain the soil moisture content. By considering variations in frequency and quality factors, the accuracy of the dielectric constant value is improved. Furthermore, the dielectric constant is corrected by considering the effect of temperature on the dielectric constant. This corrected dielectric constant is then substituted into the moisture content formula to obtain the soil moisture content, further improving the accuracy of the obtained moisture content and meeting the precision requirements for moisture content testing in engineering soil materials.

[0026] See Figure 4 The no-load quality factor in step S1 The value is obtained through a first calculation formula, which is: ; in, This is the no-load resonant frequency. The bandwidth is half-power. When the resonant cavity is unloaded, a frequency sweep signal is transmitted, and the signal amplitude at each frequency point is recorded by the microwave humidity sensor 22. The unloaded resonance curve is plotted. The f0 corresponding to the peak value of the curve is identified, and two frequency points where the amplitude drops by 3dB (half-power point) are found. The bandwidth is then calculated. ,get .

[0027] See Figure 4 The loading quality factor in step S2 The value is obtained through a second calculation formula, which is: ; in, The resonant frequency after loading the soil sample. The half-power bandwidth after loading the soil sample is calculated. When the cavity is loaded with soil, a sweep frequency signal is transmitted, and the signal amplitude at each frequency point is recorded by the microwave humidity sensor 22. An unloaded resonance curve is plotted; the value f corresponding to the peak value of the curve is identified, and the half-power bandwidth after loading the soil sample is calculated. ,get .

[0028] See Figure 4 The frequency offset formula in step S3 is: ; in, The resonant frequency after loading the soil sample. f represents the frequency change. For soil sample volume, Let V be the volume of the resonant cavity. Let be the dielectric constant of the soil sample. Since increased humidity leads to increased dielectric loss, The value decreases, satisfying the requirement. ( (For quality factors related to dielectric loss), therefore, through The relationship between the value and the resonant frequency f is obtained, thus yielding The relationship between the dielectric constant of the soil sample and its dielectric constant, and how to improve the dielectric constant of the soil sample. The accuracy.

[0029] See Figure 4 The frequency change f= ,in, This is the no-load resonant frequency. The resonant frequency after loading the soil sample is denoted as .

[0030] See Figure 4 The dielectric constant temperature correction formula in step S4 is as follows: ;in, This is the actual temperature. For reference temperature, For temperature coefficient, Let be the dielectric constant of the soil sample. By considering the effect of temperature on the dielectric constant of the soil sample, the value of the dielectric constant is corrected to further improve the accuracy of the dielectric constant of the soil sample.

[0031] See Figure 4 The moisture content in step S4 With dielectric constant The relationship (i.e., the humidity formula) is: ; in, Let be the dielectric constant of the soil sample. The dielectric constant of dry soil, k Humidity sensitivity coefficient H This refers to the moisture content (volume fraction).

[0032] See Figure 4 Substituting the frequency offset formula and the dielectric constant temperature correction formula from step S3 into the humidity formula, that is, combining the humidity inversion model, and using the formula to invert the moisture content through frequency, Q value, and temperature correction: ;in, Let be the dielectric constant of the soil sample. The dielectric constant of dry soil, Where is the dielectric constant of water. k Humidity sensitivity coefficient H The moisture content (volume fraction) is calculated by correcting the dielectric constant by considering the effect of temperature on the dielectric constant, and then substituting the corrected dielectric constant into the humidity formula to obtain the moisture content of the soil sample. This improves the accuracy of the obtained soil sample moisture content and meets the accuracy requirements for moisture content detection in engineering soil materials.

[0033] See Figure 4 During soil sample compaction, pressure sensor 14 detects that the soil sample's pressure resistance has reached the preset optimal pressure value and then stops applying pressure. By considering stopping pressure only when the soil sample's pressure resistance reaches the preset optimal pressure value, the soil sample is ensured to be compacted, thus improving the accuracy of the obtained soil sample data.

[0034] See Figure 4 The optimal pressure value is 200N.

[0035] Specific process: (a) Initial placement and compaction control of soil samples 1. Placement and Removal: After the soil sample is placed on the testing platform, microcontroller (model) The series sends PWM drive signals to the push rod motor via the L298N motor driver (pins IN1 / IN2 control the direction, ENA controls the duty cycle), driving the push rod to move towards the detection area at a speed of 0.5mm / s. The L298N driver uses a 12V DC power supply, and a 100nF decoupling capacitor is connected in parallel with the motor wiring to prevent interference.

[0036] 2. Pressure Monitoring and Compaction Judgment: Pressure sensor 14 uses an FSR402 thin-film pressure sensor (range 0-20kg, sensitivity 0.3mV / N) to monitor pressure in real time. The thin-film pressure sensor is connected to the STM32's ADC1 channel (PA0 pin) via the AO analog signal pin. After the signal is processed by a 2.2kΩ pull-up resistor and a 0.1μF filter capacitor, the STM32 acquires the voltage value at a sampling rate of 100Hz. When the pressure corresponding to the ADC conversion value reaches 200N (approximately 2.4V), the STM32 sends a reversing signal to the L298N to retract the push rod; if the threshold is not reached, compaction continues at a 50% PWM duty cycle.

[0037] 3. Hardware connection details: Sensor: Blue wire connected Connect the red wire to 3.3V and the black wire to... IN1 / IN2 Connect ENA to PB2, connect the motor interface M1 to the push rod motor, and connect VCC to the 12V power supply.

[0038] (II) Microwave Resonance Detection and Data Processing 1. Testing Environment and Parameter Acquisition: The testing structure is a rectangular metal cavity (test chamber 1), with both ends short-circuited to create a standing wave field. After the soil sample is compacted, the microwave humidity sensor is activated to simultaneously acquire the resonant frequency (no-load frequency). Frequency after loading ) and quality factors (unloaded) After soil sample loading ).

[0039] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for testing the moisture content of soil, characterized in that, Includes the following steps: S1, Obtain the no-load resonant frequency when the rectangular metal cavity is unloaded. and half-power bandwidth And obtain the no-load quality factor through calculation. value; S2, the soil sample is compacted inside a rectangular metal cavity to obtain the resonant frequency f and half-power bandwidth ▲f after loading the soil sample, and the loading quality factor is obtained through calculation. value; S3, the dielectric constant of the soil sample is obtained according to the frequency offset formula; S4. The dielectric constant value of the soil sample is corrected by the dielectric constant temperature correction formula, and then the corrected dielectric constant value of the soil sample is substituted into the moisture formula to obtain the soil sample moisture content.

2. The method for testing the moisture content of soil according to claim 1, characterized in that, The no-load quality factor in step S1 The value is obtained through a first calculation formula, which is: ； in, This is the no-load resonant frequency. It is half-power bandwidth.

3. The method for testing the moisture content of soil according to claim 1, characterized in that, Loading quality factor in step S2 The value is obtained through a second calculation formula, which is: ； in, The resonant frequency after loading the soil sample. This represents the half-power bandwidth after loading the soil sample.

4. The method for testing the moisture content of soil according to claim 1, characterized in that, The frequency offset formula in step S3 is: ； in, The resonant frequency after loading the soil sample. f represents the frequency change. For soil sample volume, Let V be the volume of the resonant cavity. Let be the dielectric constant of the soil sample.

5. The method for testing the moisture content of soil according to claim 4, characterized in that, The frequency change f= ,in, This is the no-load resonant frequency. The resonant frequency after loading the soil sample is denoted as .

6. The method for testing the moisture content of soil according to claim 1, characterized in that, The dielectric constant temperature correction formula in step S4 is as follows: ; in, This is the actual temperature. For reference temperature, For temperature coefficient, Let be the dielectric constant of the soil sample.

7. The method for testing the moisture content of soil according to claim 1, characterized in that, The humidity formula in step S4 is: ; in, Let be the dielectric constant of the soil sample. The dielectric constant of dry soil, k Humidity sensitivity coefficient H This refers to the moisture content (volume fraction).

8. The method for testing the moisture content of soil according to claim 7, characterized in that, Substituting the frequency offset formula and the dielectric constant temperature correction formula from step S3 into the humidity formula, the moisture content is obtained. ; in, Let be the dielectric constant of the soil sample. The dielectric constant of dry soil, Where is the dielectric constant of water. k Humidity sensitivity coefficient H This refers to the moisture content (volume fraction).

9. The method for testing the moisture content of soil according to any one of claims 1-8, characterized in that, When compacting soil samples, pressure is stopped when the pressure value that the soil sample can withstand reaches the preset optimal pressure value.

10. The method for testing the moisture content of soil according to claim 9, characterized in that, The optimal pressure value is 200N.

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