Continuous penetration type probe for simultaneously measuring water content and matric suction of soil

Abstract

One end of a first insulating rod is coaxially connected with one end of a second insulating rod, the diameter of the first insulating rod is larger than that of the second insulating rod, and grooves are formed in the outer surface of the first insulating rod and the outer surface of the second insulating rod in the axial direction respectively. The grooves are communicated with each other; the TDR probe is placed in the groove and is used for measuring the soil water content and matrix suction; a through hole with the diameter slightly larger than that of the second insulating rod is axially formed in the center of the gypsum cylinder, so that the gypsum cylinder wraps the second insulating rod and is in close contact with the second insulating rod; the conical tip probe is installed at the other end of the first insulating rod, and a sensor set is arranged in the conical tip probe and used for obtaining mechanical data when the conical tip probe penetrates into rock soil. According to the invention, the water content and matrix suction of the soil body can be simultaneously measured in the process of penetrating into the rock soil, so that in-situ testing is realized, the precision is high, and the testing efficiency is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of geotechnical engineering measurement, and specifically relates to a continuous penetration probe for simultaneously measuring soil water content and matric suction. Background Art

[0002] The water content and matric suction of soil are two important parameters in geotechnical engineering. Therefore, measuring these parameters is of great significance for the development of geotechnical engineering. Currently, methods for measuring water content include the oven-drying method, resistivity method, neutron scattering method, wet-dry method, TDR method, etc. Among them, the TDR method is widely used due to its simplicity, convenience, low cost, etc. The TDR technology is a testing technology based on the principle of time-domain reflectometry of electromagnetic waves. With the continuous development of this technology and the demand for on-site monitoring, some scholars in the industry have combined the TDR technology with the static cone penetration test (CPT) for in-situ determination of soil water content. The installation method is to attach the TDR probe to an insulating rod and then connect the probe to the CPT connecting rod. However, the existing methods still have some defects. For example, the probes of the existing penetration-type TDR probes protrude from the surface of the insulating rod and are easily damaged by sidewall resistance during deep penetration.

[0003] In addition, the existing CPT probe cannot measure the soil matric suction. Currently, the measurement of matric suction mainly includes methods such as hygrometer, tensiometer, pressure plate apparatus, heat conduction sensor, filter paper method, etc. These methods all have certain limitations. Although there are currently matric suction probes for in-situ testing, they need to be buried in advance by drilling, which is not convenient to use.

[0004] Therefore, how to provide a new continuous penetration probe that can simultaneously measure the soil water content and matric suction during the penetration of geotechnical materials, so as to achieve in-situ testing, is the research direction required by the present invention. Summary of the Invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a continuous penetration probe for simultaneously measuring soil water content and matric suction, which can simultaneously measure the soil water content and matric suction during the penetration of geotechnical materials, so as to achieve in-situ testing with high accuracy, thereby effectively improving the testing efficiency.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a continuous penetration probe for simultaneously measuring soil water content and matric suction, comprising a first insulating rod, a second insulating rod, a TDR probe, a gypsum cylinder, and a cone tip probe;

[0007] One end of the first insulating rod and one end of the second insulating rod are coaxially connected, and the diameter of the first insulating rod is greater than that of the second insulating rod. Grooves are respectively opened on the outer surfaces of the first insulating rod and the second insulating rod along their respective axial directions, and the grooves are communicated with each other;

[0008] The TDR probe is placed in the groove for measuring soil water content and matric suction; a through hole with a diameter slightly larger than the diameter of the second insulating rod is axially opened in the center of the gypsum cylinder, so that the gypsum cylinder wraps around the outside of the second insulating rod and the two are in close contact;

[0009] The conical tip probe is installed at the other end of the first insulating rod, and a sensor group is arranged inside the conical tip probe for obtaining mechanical data when the conical tip probe penetrates into the rock and soil.

[0010] Furthermore, the first insulating rod and the second insulating rod are integrally formed, and the first insulating rod and the second insulating rod have the same length.

[0011] Furthermore, the gypsum cylinder is fixed on the outside of the second insulating rod by pouring, and the outer circumferential diameter of the gypsum cylinder is the same as the diameter of the first insulating rod.

[0012] Furthermore, the materials of the first insulating rod and the second insulating rod are both Derlin insulating rods.

[0013] Furthermore, the sensor group is used for measuring the tip resistance, sidewall friction resistance and pore water pressure when the conical tip probe penetrates into the rock and soil.

[0014] Furthermore, it further includes a plurality of metal arc plates, and the plurality of metal arc plates are tightly wrapped around the outside of the gypsum cylinder by screws for enhancing the strength of the gypsum cylinder.

[0015] The working method of the above continuous penetration type probe for simultaneously measuring soil water content and matric suction is specifically as follows:

[0016] Step 1: Before on-site testing, connect the sensor group inside the probe to the CPT equipment (static cone penetration test equipment), connect the TDR probe to the TDR test equipment through a coaxial cable, and conduct the first-stage calibration and the second-stage calibration respectively;

[0017] Step 2: Penetrate the probe into the soil body, and the TDR test equipment receives the data fed back by the TDR probe, measures the reflected waveform according to the TDR principle. Since there will be three reflections after the probe penetrates into the soil body, the equivalent dielectric constant of the second insulating rod can be obtained from the first and second reflected waveforms, and this data is used for measuring soil matric suction; the equivalent dielectric constant of the first insulating rod can be obtained from the second and third reflected waveforms, and this data is used for measuring soil water content; then, based on the medium distribution weight calibrated in the first stage and the equivalent dielectric constant of the first insulating rod, the soil water content is calculated according to the formula;

[0018] Step 3: After the probe penetrates into the soil mass, keep it stationary at this position for 2 - 4 h. At this time, suction equilibrium is reached between the soil mass and the gypsum. Based on the relationship curve between dielectric constant and matric suction obtained from the calibration in the second stage and the equivalent dielectric constant of the second insulating rod, the matric suction of the soil can be calculated.

[0019] Furthermore, the calibration in the first stage is specifically as follows:

[0020] ① Prepare ethanol - deionized water solutions with different concentrations as the test target media, where the volume percentage of ethanol is 0 - 100%, and the concentration interval is 20%.

[0021] ② Insert the traditional TDR probe and this penetrometer probe into the solutions prepared in step ① respectively, and measure the dielectric constant and equivalent dielectric constant of the target media respectively.

[0022] ③ Perform linear fitting on the data measured by the two, and the media distribution weight of this penetrometer probe can be obtained.

[0023] Furthermore, the calibration in the second stage is specifically as follows:

[0024] ① Place the penetrometer probe in tap water to saturate it for 24 h to completely saturate the gypsum.

[0025] ② Put the saturated probe into the pressure plate apparatus in the laboratory, apply an air pressure of 5 kPa in the pressure plate apparatus as the matric suction, and then measure the volume change of the water in the probe through a connected measuring cylinder. When the volume of water in the measuring cylinder remains stable for three consecutive days, take the probe out of the pressure plate apparatus, connect the TDR test equipment, and measure the dielectric constant.

[0026] ③ Apply 10 kPa, 20 kPa, 50 kPa, 100 kPa, 200 kPa, 300 kPa, 400 kPa, 500 kPa, 700 kPa, 1000 kPa, and 1200 kPa in sequence, and repeat step ② respectively to measure the dielectric constants under different matric suctions.

[0027] ④ Draw a relationship curve graph of the matric suction - dielectric constant of the probe based on the measured data.

[0028] Compared with the prior art, the parameter measurement of the entire probe of the present invention is divided into two parts. The first insulating rod of the probe uses the TDR principle to measure the soil dielectric constant for measuring soil water content; the combined structure of the second insulating rod of the probe and gypsum is calibrated in the laboratory by combining a pressure plate apparatus and the TDR principle to obtain a relationship curve of the dielectric constant ~ matrix suction of this part. When the probe penetrates into the soil mass, the suction balance state will be reached between the gypsum and the soil, that is, the suction forces of the gypsum and the soil are equal. According to the TDR principle, the equivalent dielectric constant of the probe at this time is measured, and then the matrix suction of the soil is calculated from the relationship curve obtained by laboratory calibration; the above method has the following advantages:

[0029] 1. After the sensor group is arranged in the probe of the present invention and connected to the CPT device, multiple geotechnical parameters such as tip resistance, side friction resistance, pore water pressure, soil water content, and matrix suction can be measured simultaneously.

[0030] 2. The probe of the present invention can realize the in-situ measurement of the water content and matrix suction of the deep soil layer during the penetration process, minimizing the disturbance effect on the soil mass; and it is convenient and fast during the test, without the need to specially drill holes to embed TDR probes and matrix suction sensors, saving time and effort. Description of the Drawings

[0031] Figure 1 is the overall structural schematic diagram of the present invention;

[0032] Figure 2 is the structural schematic diagram of the first insulating rod and the second insulating rod in the present invention;

[0033] Figure 3 is the structural schematic diagram of the gypsum cylinder in the present invention;

[0034] Figure 4 is the structural schematic diagram of the metal arc plate in the present invention.

[0035] In the figure: 1. First insulating rod; 2. TDR probe; 3. Gypsum cylinder; 4. Metal arc plate; 5. Tip probe. Detailed Embodiments

[0036] The present invention will be further described below.

[0037] As Figure 1 shown, a continuous penetration type probe for simultaneously measuring soil water content and matrix suction includes a first insulating rod 1, a second insulating rod, a TDR probe 2, a gypsum cylinder 3, and a tip probe 5;

[0038] As Figure 2As shown, one end of the first insulating rod 1 and one end of the second insulating rod are coaxially connected, and the diameter of the first insulating rod 1 is larger than that of the second insulating rod. Grooves are respectively formed on the outer surfaces of the first insulating rod 1 and the second insulating rod along their respective axial directions, and the grooves are communicated with each other; the first insulating rod 1 and the second insulating rod are integrally formed. The diameter of the second insulating rod is 10 mm and the length is 50 mm, and the diameter of the first insulating rod 1 is 30 mm and the length is 50 mm; the materials of the first insulating rod 1 and the second insulating rod are both Derlin insulating rods.

[0039] The TDR probe 2 is placed in the groove for measuring soil water content and matrix suction; as Figure 3 shown, a through hole with a diameter slightly larger than that of the second insulating rod is axially formed in the center of the gypsum cylinder 3, so that the gypsum cylinder 3 wraps around the outside of the second insulating rod and the two are in close contact; the gypsum cylinder 3 is fixed outside the second insulating rod by pouring, and the outer circumferential diameter of the gypsum cylinder 3 is the same as the diameter of the first insulating rod.

[0040] The conical tip probe 5 is installed at the other end of the first insulating rod 1, and a sensor group is arranged inside the conical tip probe 5 for measuring the tip resistance, sidewall friction resistance and pore water pressure when the conical tip probe penetrates into the rock and soil; the sensor group is each sensor used in the existing CPT equipment, and it is an existing device.

[0041] As Figure 4 shown, as an improvement of the present invention, it further includes four metal arc plates 4. The four metal arc plates 4 are pressed and wrapped outside the gypsum cylinder 3 by screws for improving the strength of the gypsum cylinder 3. The metal arc plate 4 is a metal sheet with a length of 50 mm, a thickness of 4 mm and an arc length of 8 mm.

[0042] The working method of the above continuous penetration type probe for simultaneously measuring soil water content and matrix suction is specifically as follows:

[0043] Step 1: Before on-site testing, connect the sensor group in the probe to the CPT equipment, and connect the TDR probe 2 to the TDR testing equipment through a coaxial cable; and perform the first-stage calibration and the second-stage calibration respectively; the specific content of the first-stage calibration is:

[0044] ① Prepare ethanol-deionized water solutions with different concentrations as the test target media, where the volume percentage of ethanol is 0-100%, and the concentration interval is 20%;

[0045] ② Insert the traditional TDR probe and this penetration type probe into the solutions prepared in step ① respectively, and measure the dielectric constant and equivalent dielectric constant of the target media respectively;

[0046] ③Perform linear fitting on the data measured for both to obtain the medium distribution weight of the penetration probe.

[0047] The second-stage calibration is specifically as follows:

[0048] ①First, place the penetration probe in tap water and saturate it for 24 h to fully saturate the gypsum.

[0049] ②Put the saturated probe into the pressure plate apparatus in the laboratory (the air intake value of the pressure plate apparatus is 15 bar), apply an air pressure of 5 kPa as the matrix suction to the pressure plate apparatus, and then measure the volume change of the water in the probe by connecting a graduated cylinder. When the volume of water in the graduated cylinder remains stable for three consecutive days, take the probe out of the pressure plate apparatus, connect the TDR test equipment, and measure the dielectric constant.

[0050] ③Apply 10 kPa, 20 kPa, 50 kPa, 100 kPa, 200 kPa, 300 kPa, 400 kPa, 500 kPa, 700 kPa, 1000 kPa, and 1200 kPa in sequence, and repeat step ② respectively to measure the dielectric constants under different matrix suctions.

[0051] ④Draw a relationship curve of the matrix suction - dielectric constant of the probe based on the measured data.

[0052] Step 2: Insert the probe into the soil. The TDR test equipment receives the data fed back by the TDR probe 2 and measures the reflected waveform according to the TDR principle. Since there will be three reflections after the probe is inserted into the soil, the equivalent dielectric constant of the second insulating rod can be obtained from the first and second reflected waveforms, and this data is used for measuring the soil matrix suction; the equivalent dielectric constant of the first insulating rod can be obtained from the second and third reflected waveforms, and this data is used for measuring the soil water content; then, based on the medium distribution weight calibrated in the first stage and the equivalent dielectric constant of the first insulating rod 1, the soil water content is calculated according to formula (1).

[0053]

[0054] In the formula, K a is the measured equivalent dielectric constant, and θ is the soil water content.

[0055] Step 3: After the probe is inserted into the soil, keep it stationary at this position for 2 - 4 h. At this time, suction equilibrium is reached between the soil and the gypsum. Based on the relationship curve of dielectric constant - matrix suction obtained from the second-stage calibration and the equivalent dielectric constant of the second insulating rod, the soil matrix suction is calculated.

[0056] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A continuous penetration probe for simultaneously measuring soil water content and matric suction, characterized in that, It includes a first insulating rod, a second insulating rod, a TDR probe, a gypsum cylinder and a cone tip probe; One end of the first insulating rod and one end of the second insulating rod are coaxially connected, and the diameter of the first insulating rod is greater than that of the second insulating rod. Grooves are respectively opened on the outer surfaces of the first insulating rod and the second insulating rod along their respective axial directions, and the grooves are communicated with each other; The TDR probe is placed in the groove for measuring soil water content and matrix suction; a through hole with a diameter slightly larger than that of the second insulating rod is axially opened in the center of the gypsum cylinder, so that the gypsum cylinder wraps around the outside of the second insulating rod and they are in close contact; The cone tip probe is installed at the other end of the first insulating rod, and a sensor group is arranged inside the cone tip probe for obtaining mechanical data when the cone tip probe penetrates into rock and soil.

2. The continuous penetration probe for simultaneously measuring soil water content and matric suction according to claim 1, characterized in that, The first insulating rod and the second insulating rod are integrally formed, and the first insulating rod and the second insulating rod have the same length.

3. The continuous penetration probe for simultaneously measuring soil water content and matric suction according to claim 1, characterized in that The gypsum cylinder is fixed outside the second insulating rod by pouring, and the outer circumferential diameter of the gypsum cylinder is the same as the diameter of the first insulating rod.

4. The continuous penetration probe for simultaneously measuring soil water content and matric suction according to claim 1, characterized in that, The materials of the first insulating rod and the second insulating rod are both Derlin insulating rods.

5. The continuous penetration probe for simultaneously measuring soil water content and matric suction according to claim 1, wherein The sensor group is used for measuring the cone tip resistance, sidewall friction resistance and pore water pressure when the cone tip probe penetrates into rock and soil.

6. The continuous penetration probe for simultaneously measuring soil water content and matric suction according to claim 1, characterized in that It also includes multiple metal arc plates, and the multiple metal arc plates are tightly wrapped outside the gypsum cylinder by screws to improve the strength of the gypsum cylinder.

7. A working method of the continuous penetration probe for simultaneously measuring soil water content and matric suction according to any one of claims 1 to 6, characterized in that, The specific steps are as follows: Step 1: Before on-site testing, connect the sensor group in the probe to the CPT device, connect the TDR probe to the TDR testing device through a coaxial cable, and perform the first-stage calibration and the second-stage calibration respectively; Step 2: Insert the probe into the soil. The TDR testing device receives the data fed back by the TDR probe, measures the reflected waveform according to the TDR principle, and based on the medium distribution weight calibrated in the first stage and the equivalent dielectric constant measured by the first insulating rod, and then calculates the soil water content according to the formula; Step 3: After the probe penetrates into the soil, keep it stationary at this position for 2 - 4 h. At this time, the suction balance is reached between the soil and the gypsum. According to the relationship curve of dielectric constant - matrix suction calibrated in the second stage and the equivalent dielectric constant measured by the second insulating rod, the matrix suction of the soil can be calculated.

8. The working method according to claim 7, characterized in that, The specific first-stage calibration is as follows: ① Prepare ethanol - deionized water solutions with different concentrations as the test target media, where the volume percentage of ethanol is 0 - 100%, and the concentration interval is 20%; ② Insert the traditional TDR probe and this penetrometer probe into the solutions prepared in step ① respectively, and measure the dielectric constant and equivalent dielectric constant of the target media respectively; ③ Perform linear fitting on the data measured by both to obtain the medium distribution weight of this penetrometer probe.

9. The working method according to claim 1, wherein The specific second-stage calibration is as follows: ① First, place the penetrometer probe in tap water to be saturated for 24 h to completely saturate the gypsum; ② Place the saturated probe into the pressure plate apparatus in the laboratory, apply an air pressure of 5 kPa as the matric suction to the pressure plate apparatus, and then measure the change in the volume of water in the probe by connecting a graduated cylinder. When the volume of water in the graduated cylinder remains stable for three consecutive days, remove the probe from the pressure plate apparatus, connect the TDR testing equipment, and measure the dielectric constant; ③ Apply 10 kPa, 20 kPa, 50 kPa, 100 kPa, 200 kPa, 300 kPa, 400 kPa, 500 kPa, 700 kPa, 1000 kPa, and 1200 kPa in sequence, and repeat step ② respectively to measure the dielectric constant under different matric suctions; ④ Draw a curve graph of the matric suction - dielectric constant relationship of the probe based on the measured data.

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