CN106066350A - Soil body quality moisture content correction method of testing based on bushing type probe TDR method - Google Patents

Abstract

A soil quality moisture content correction test method based on the casing probe TDR method, comprising the following steps: A. Calibration: Through the calibration tests of four different soil samples in the previous period, each soil mass measured by the TDR moisture sensor was obtained. The volume moisture content of the soil sample θ _i , the real mass moisture content w _i of each soil sample measured by the drying method, and then through the function The value of the unknown parameter a is obtained by fitting the above test values, thus clarifying the functional relationship. B. Test: Test that the dry density of the soil to be tested is _ρd and the minimum distance from the TDR moisture sensor to the boundary of the soil to be tested is L/2; use the casing probe TDR moisture sensor to measure the volumetric moisture content of the soil to be tested value θ, that is, the mass water content of the soil to be tested w, This method eliminates the influence of other media within the effective test range of the sensor in the casing probe TDR method on the dielectric properties of the soil to be tested, improves the accuracy of the water content of the test soil, and thus provides more information for the design and construction of geotechnical engineering. Reliable and accurate test data.

Description

Correction test method for moisture content of soil mass based on casing probe TDR method

technical field

The invention relates to a method for testing the water content of soil by using the casing probe TDR method.

Background technique

Accurate measurement of soil moisture content in geotechnical engineering plays an important role in engineering property evaluation, stability analysis and compaction quality control. The drying method is a standard method for measuring the moisture content of soil mass in the current norms, and its test results are accurate, but there are problems such as sampling difficulties, damage to the structure, and inability to monitor automatically for a long time in field applications.

Since the apparent dielectric constant of the soil is the comprehensive value of the dielectric constant of water (K _water = 81), air (K _air = 1) and soil particles (K _soil = 3~5) in the soil, the soil dielectric constant The electrical constant is mainly determined by the volumetric moisture content of the soil. By testing the propagation velocity of the electromagnetic wave on the probe inserted into the soil, the apparent permittivity of the soil to be tested can be measured, and then the relationship between the established apparent permittivity K _a of the soil and the volume moisture content θ of the soil can be used The relational model (K _a — θ equation) among them determines the soil volume moisture content, and can be converted to obtain the soil mass moisture content. This method is called electromagnetic wave time domain reflectometry (Time Domain Reflectometry, TDR). Compared with the drying method, since no sampling is required and there is no damage to the soil structure, the TDR method significantly improves the efficiency of soil moisture content testing, and can realize long-term automatic dynamic monitoring of soil moisture content.

The moisture sensor used in the TDR method generally uses a needle probe. When testing the moisture content of the soil, it is still a point measurement method. When measuring the moisture content distribution of the soil space, it is necessary to bury sensors in different positions in the soil layer, resulting in low sensor utilization efficiency. , The workload is large and it will affect the results of moisture content determination. The improved method is the casing probe TDR method, that is, through a special casing pre-buried or driven into the soil, the probe is inserted into the casing, and the probe can move up and down in the casing during the test, so as to realize a probe in different spatial positions. Continuous testing of soil moisture content; at the same time, the introduction of the casing can avoid direct contact between the probe and the soil, protect the probe from damage, and realize the long-term repeated use of the TDR moisture sensor. However, since the volumetric moisture content test result of the casing probe TDR method is a reflection of the comprehensive dielectric properties of the medium to be measured within the effective measurement range around the sensor, when the casing probe TDR moisture sensor is actually used, if the sensor is within the effective measurement range There is interference from other media other than the tested medium, that is, changes in the boundary of the tested soil will cause changes in the dielectric properties of the medium around the sensor, which in turn will have a significant impact on the TDR moisture content test results of the tested soil, reducing the test performance. Result accuracy and reliability.

Contents of the invention

The object of the present invention is to provide a soil quality moisture content correction test method based on the casing probe TDR method, which eliminates the dielectric properties of other media in the effective test range of the casing probe TDR moisture sensor. The resulting impact can improve the accuracy of TDR testing soil moisture content, thereby providing more reliable and accurate test data for geotechnical engineering design and construction.

The technical solution adopted by the present invention to realize its object of the invention is: a kind of soil quality water content correction test method based on casing type probe TDR method, comprises the following steps:

A kind of soil mass water content correction test method based on casing type probe TDR method, comprises the following steps:

A. Calibration

A1. Prepare four rectangular parallelepiped test chambers or cylindrical test chambers with the same height as the measurement section of the TDR moisture sensor probe, wherein the bottom surface of the rectangular parallelepiped test chamber is a square; the side lengths or diameters of the four test chambers are different, and the ith one The side length or diameter of the test box is L _i , i is the serial number of the test box, i=1, 2, 3, 4;

A2. Vertically place a special casing for the TDR moisture sensor probe test in the center of the test chamber. The bottom of the casing is closed and the top is open. The height of the casing is 50mm higher than the height of the test chamber;

A3. Prepare soil samples with a dry density of _ρd0 in each test chamber, then place the TDR moisture sensor probe in the casing, and make the probe height equal to half the height of the test chamber; turn on the TDR moisture sensor and test out The volumetric water content θ _i at the middle section of the soil sample in each test box;

A4. Take 50g of soil in each test box close to the position of the probe, and test according to the drying method to obtain the real mass moisture content w _i of the sampled soil; find the proportional coefficient _ki of the soil sample in each test box, Wherein, ρ _w is the density of water;

A5. Take the side length or diameter of the test box, that is, twice the minimum distance from the casing type TDR moisture sensor to the boundary of the soil to be tested, as the abscissa L, and take the scale factor of the soil to be tested is the vertical coordinate, forming a rectangular coordinate system; in this coordinate system, the side length or diameter L _i of the four test boxes and the corresponding proportional coefficient The four points of are plotted, and then the function Fit the four points in the coordinate system to obtain the value of parameter a;

B. to test

First test the dry density of the soil to be tested as _ρd , and measure the minimum distance L/2 from the TDR moisture sensor to the boundary of the soil to be tested; use the casing probe TDR moisture sensor to measure the volume moisture content of the soil to be tested, substitute function The mass moisture content w of the soil to be measured can be obtained,

Compared with prior art, the beneficial effect of the present invention is:

The applicant found that there is a functional relationship between the soil boundary L/2 and the moisture content w of the soil mass, the dry density ρ _d of the soil, and the volumetric moisture content θ of the soil sample measured by the casing probe TDR moisture sensor: The present invention further obtains the unknown parameter a in the above-mentioned functional relationship through calibration tests of different soil samples in the previous stage, and obtains the mass water content w of the soil to be tested and the volume water content of the soil measured by the casing probe TDR method The explicit relationship between the test value θ and the soil sample boundary L/2 is

Therefore, after the present invention has measured the boundary of the soil body to be tested, and then utilizes the above-mentioned relational expression, the impact of other media in the effective test range of the moisture sensor in the casing probe TDR method can be eliminated. The accuracy of the soil moisture content test is improved, thereby providing more reliable and accurate test data for the design and construction of geotechnical engineering.

The test results show that the absolute error between the mass moisture content measured by the present invention and the mass moisture content obtained by the drying method is 0.07%, while the conversion mass moisture content obtained by the existing sleeve type probe TDR moisture sensor test is 0.07%. The absolute error of the mass moisture content obtained by the drying method is 0.81%. Compared with the test of the casing probe TDR moisture sensor, the test absolute error of the present invention is lower than 1/10 of the test absolute error.

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Description of drawings

Figure 1 The relationship curve between the side length or diameter L _i and the proportional coefficient _ki of the test box.

detailed description

Example

A specific embodiment of the present invention is: a method for correcting the water content of soil mass based on the casing probe TDR method, comprising the following steps:

A kind of soil mass water content correction test method based on casing type probe TDR method, comprises the following steps:

A. Calibration

A1. Prepare four rectangular parallelepiped test chambers or cylindrical test chambers with the same height as the measurement section of the TDR moisture sensor probe, wherein the bottom surface of the rectangular parallelepiped test chamber is a square; the side lengths or diameters of the four test chambers are different, and the ith one The side length or diameter of the test box is L _i , i is the serial number of the test box, i=1, 2, 3, 4;

A2. Vertically place a special casing for the TDR moisture sensor probe test in the center of the test chamber. The bottom of the casing is closed and the top is open. The height of the casing is 50mm higher than the height of the test chamber;

A3. Prepare soil samples with a dry density of _ρd0 in each test chamber, then place the TDR moisture sensor probe in the casing, and make the probe height equal to half the height of the test chamber; turn on the TDR moisture sensor and test out The volumetric water content θ _i at the middle section of the soil sample in each test box;

A4. Take 50g of soil in each test box close to the position of the probe, and test according to the drying method to obtain the real mass moisture content w _i of the sampled soil; find the proportional coefficient _ki of the soil sample in each test box, Wherein, ρ _w is the density of water;

A5. Take the side length or diameter of the test box, that is, twice the minimum distance from the casing type TDR moisture sensor to the boundary of the soil to be tested, as the abscissa L, and take the scale factor of the soil to be tested is the vertical coordinate, forming a rectangular coordinate system; in this coordinate system, the side length or diameter L _i of the four test boxes and the corresponding proportional coefficient The four points of are plotted, and then the function Fit the four points in the coordinate system to obtain the value of parameter a;

B. to test

First test the dry density of the soil to be tested as _ρd , and measure the minimum distance L/2 from the TDR moisture sensor to the boundary of the soil to be tested; use the casing probe TDR moisture sensor to measure the volume moisture content of the soil to be tested, substitute function The mass moisture content w of the soil to be measured can be obtained,

Test verification

The TRIME-PICO-IPH series TDR intelligent moisture sensor is used for calibration test. The sensor is composed of TRIME-HD handheld reading meter, TRIME-T3 cylindrical casing probe and high-frequency cable transmission line, of which TRIME-HD handheld reading meter can Directly display the test value of soil volume moisture content, TRIME-T3 cylindrical casing probe has a diameter of 37mm, and the length of the probe measurement section is 220mm. The probe test casing is made of special TECANAT (polycarbonate) material, with an outer diameter of 44mm and an inner diameter of 42mm , length 270mm. According to the "Railway Engineering Geotechnical Test Regulations" (TB10102-2010) sieving test, the maximum particle size of the standard sand does not exceed 1.0mm, the particle content of less than 0.5mm is 99.94%, the particle content of less than 0.25mm is 99.82%, and the particle content of less than 0.075 The particle content of mm is 0.80%, the coefficient of unevenness is 2.00, and the coefficient of curvature is 1.04; the maximum dry density ρ _dmax = 1.663g/cm ³ and the minimum dry density ρ _dmin = 1.337g/cm ³ of the standard sand measured by the relative density test .

According to the method of the above embodiment, select a rectangular cuboid test box with a square bottom surface, numbered No. 1, 2, 3, and 4, and its plane side length L _i (i=1, 2, 3, 4) is successively 200mm, 300mm, and 400mm , 500mm, and a height of 220mm, vertically place a special casing for the TDR moisture sensor probe test at the center of the test chamber plane, prepare a standard sand sample with a dry density of _ρd0 = 1.45g/cm ³ and fill it in layers build. After the filling is completed, the TDR moisture sensor probe is inserted into the casing to test the volumetric moisture content θ _i of the soil in the middle of the test chamber; after the TDR measurement is completed, the soil is taken from the middle of each test chamber, and the real mass moisture content is obtained through the drying method test w _i . After the measurement, take L as the abscissa, For the ordinate, use the function Curve fitting is performed on the four point curves of L _i and _ki in the coordinate system, as shown in FIG. 1 , and the parameter a=26 can be obtained.

Test that the dry density of the soil to be tested is ρ _d = 1.51g/cm ³ , and the minimum distance from the TDR moisture sensor of the casing probe to the boundary of the soil to be tested is L/2 = 50mm, and the TDR moisture sensor of the casing probe is used Measure the test value of the volumetric moisture content of the soil to be tested θ = 5.56%, and substitute it into the function The mass moisture content of the soil to be tested can be obtained as w=4.42%. In order to verify the accuracy of the function, samples were taken at the middle section of the test chamber, and the real mass moisture content of the soil sample was obtained by the drying method test w ₀ =4.49%. Since the volume moisture content of the TDR test is converted into the mass moisture content Therefore, it is believed that when the minimum distance from the TDR moisture sensor of the casing probe to the boundary of the soil to be tested is L/2=50mm, that is, L=100mm, the TDR test results are significantly affected, and the TDR conversion mass moisture content w ₀ ′ and drying The absolute value of the true mass water content w ₀ absolute error obtained by the method is |w ₀ ′-w ₀ |=0.81%, and the present invention passes the function The obtained mass moisture content of the soil to be tested is w=4.42%, and the absolute value of the absolute error with the mass moisture content of the drying method is only |ww ₀ |=0.07%.

It can be seen that, adopting the function of the present invention Considering the large error of the test results caused by the influence of other media on the soil to be tested within the effective test range of the casing probe TDR moisture sensor, the accuracy of the test results of the moisture content of the soil is improved.

Claims (1)

1. A soil mass water content correction test method based on casing probe TDR method, comprising the following steps: A. Calibration A1. Prepare four rectangular parallelepiped test chambers or cylindrical test chambers with the same height as the measurement section of the TDR moisture sensor probe, wherein the bottom surface of the rectangular parallelepiped test chamber is a square; the side lengths or diameters of the four test chambers are different, and the ith one The side length or diameter of the test box is L _i , i is the serial number of the test box, i=1, 2, 3, 4; A2. Vertically place a special casing for the TDR moisture sensor probe test in the center of the test chamber. The bottom of the casing is closed and the top is open. The height of the casing is 50mm higher than the height of the test chamber; A3. Prepare soil samples with a dry density of _ρd0 in each test chamber, then place the TDR moisture sensor probe in the casing, and make the probe height equal to half the height of the test chamber; turn on the TDR moisture sensor and test out The volumetric water content θ _i at the middle section of the soil sample in each test box; A4. Take 50g of soil in each test box close to the position of the probe, and test according to the drying method to obtain the real mass moisture content w _i of the sampled soil; find the proportional coefficient _ki of the soil sample in each test box, Wherein, ρ _w is the density of water; A5. Take the side length or diameter of the test box, that is, twice the minimum distance from the casing type TDR moisture sensor to the boundary of the soil to be tested, as the abscissa L, and take the scale factor of the soil to be tested is the vertical coordinate, forming a rectangular coordinate system; in this coordinate system, the side length or diameter L _i of the four test boxes and the corresponding proportional coefficient The four points of are plotted, and then the function Fit the four points in the coordinate system to obtain the value of parameter a; B. to test First test the dry density of the soil to be tested as _ρd , and measure the minimum distance L/2 from the TDR moisture sensor to the boundary of the soil to be tested; use the casing probe TDR moisture sensor to measure the volume moisture content of the soil to be tested, substitute function The mass moisture content w of the soil to be measured can be obtained,