Moisture content measuring system based on parallel spiral telescopic time domain reflection probe

Abstract

The invention discloses a moisture content measuring system based on a parallel spiral telescopic time domain reflection probe. The system comprises a time domain reflection probe, an insulation converter, a flexible cylinder and a time domain reflection signal generation collector. The time domain reflection probe comprises a positive electrode probe and at least one negative electrode probe. Thepositive electrode probe and the negative electrode probe are spirally arranged on the inner side wall of the flexible cylinder in parallel. The arranged time domain reflection probe at least accounts for 90% of the height of the flexible cylinder, and the positive electrode probe and the negative electrode probe penetrate through the insulation converter and are connected with the time domain reflection signal generator through coaxial cables. The scheme can be used for nondestructive real-time measurement of the moisture content of frozen soil, natural gas hydrate-containing soil, sandy soil, silt, clay, loess, special soil, rock and other samples in a triaxial shear test. The system not only guarantees the measurement effect of the moisture content of the sample, but also avoids the influence on the triaxial shear test data of the sample, and has a wide application prospect in the triaxial shear test of unsaturated soil and natural gas hydrate-containing soil samples.

Description

technical field [0001] The invention belongs to the field of water content testing of rock and soil samples in the geotechnical engineering industry, agriculture and unconventional oil and gas industries, and in particular relates to a water content measurement system based on a parallel spiral stretchable time domain reflection probe. Background technique [0002] The water content of rock and soil samples is a key parameter that affects its mechanical properties and seepage properties, and is also an important indicator for evaluating the water demand of soil plants. It is of great significance to measure it accurately and quickly. Time domain reflectometry is a method to measure the internal moisture content of various soils by using the difference in propagation speed of electromagnetic waves in different media. It has been widely used in geotechnical engineering, agriculture and unconventional oil and gas industries in the past forty years. At present, rigid time-domain...

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Problems solved by technology

However, the above-mentioned flexible parallel two-needle time-domain reflectometry probe puts forward high requirements on sample preparation, and it is necessary to ensure the spatial distribution position of the probe used in the triaxial shear test and the correlation empirical calibration test of dielectric constant-moisture content. The spatial distribution positions of the probes used are consistent, for example, to ensure that the two probes are consistently parallel up and down and that the two probes are located on the same plane, but in the actual application process in recent years, it has been found that this is usually difficult to achieve

Because the flexible probe (soft copper wire) is arranged vertically inside the sample, the flexible probe is straightened while loading the sand, which makes it difficult to ensure that the distance between the internal probes is equal after the sand is installed. This has a great impact on the measurement effect of time domain reflectometry, because it is necessary to pre-calibrate an empirical relation when measuring with a time domain reflectometry probe. This empirical relation is related to the probe. If the spatial distribution of the probe used in the experiment If it is not consistent with the calibration, the effect of this empirical relationship will be greatly affected, which will lead to obvious uncertainty deviations in the water cut measurement results.

In addition, the above-mentioned flexible parallel two-needle TDR probe will continuously curl during the shearing process, which also affects the measurement effect of the water content of the sample

[0005] To sum up, the existing TDR probes suitable for water content measurement in triaxial shear tests have the following deficiencies: (1) Rigid parallel short probes cannot measure the overall water content of samples; (2) The spatial expansion of flexible parallel probes It is difficult to precisely control the cloth during sample preparation; and because the flexible probe is inside the sample, after the sample is compressed, the flexible probe will also be compressed, and the flexible parallel probe will continuously curl due to triaxial shearing

The existence of the above deficiencies makes it difficult for the probe pre-calibrated empirical relation to be applied to the triaxial shear test, it is difficult to accurately measure the water content of the sample during the shearing process, and the measurement results of the water content are not representative, which seriously affects the time-domain reflectometry. Application effect of technology in triaxial shear test

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