In-situ evaluation method and system of loess collapsibility based on non-destructive time domain reflectometry

Abstract

The present invention discloses an in-situ evaluation method and system for loess collapsibility based on non-destructive time domain reflection technology, which utilizes non-destructive time domain reflection technology to in-situ test the dielectric constant and conductivity of loess; calculates the dry density and mass water content of loess based on the tested dielectric constant and conductivity; and considers the dry density, mass water content and basic physical property indicators of loess to evaluate the collapsibility of loess in-situ through a mathematical model. The in-situ evaluation method for loess collapsibility based on non-destructive time domain reflection technology of the present invention can not only realize the determination of whether loess has collapsibility, but also has the potential to distinguish between strong, medium and slight degrees of collapsibility. The method of the present invention is advanced in technology, short in time consumption, low in cost, easy to operate, highly reliable and highly practical, and is a new means of engineering survey technology in loess areas.

Description

Technical Field

[0001] The present invention belongs to the technical field of in-situ survey in the field of geotechnical engineering, and specifically relates to an in-situ evaluation method and system for loess collapsibility based on non-destructive time domain reflection technology. Background Art

[0002] Loess, a special soil with water sensitivity, is widely distributed in Northwest my country, accounting for about 6% of the country's land area. When carrying out engineering construction in loess areas, accurate site survey and evaluation of the collapsibility is an important prerequisite for ensuring the service performance and safety of engineering structures.

[0003] At present, there are two main methods for evaluating the collapsibility of loess: indoor test and field test. For the indoor test method, firstly, the original samples of loess at different depths are obtained by in-situ drilling, and then the mechanical compression and water saturation under the constant water content state are carried out in the laboratory using a one-dimensional consolidation instrument, and the collapsibility coefficient is tested. Finally, the collapsibility of loess is evaluated by the measured collapsibility coefficient. Although this method is simple, it has the disadvantages of difficulty in obtaining original samples and time-consuming. First, the process from obtaining original samples on site to indoor testing will inevitably cause damage to the loess structure, which will affect the accuracy of the evaluation of collapsibility. Secondly, the one-dimensional compression test at constant water content indoors requires 24 hours of stabilization for each load level, which is extremely time-consuming for testing a large number of original samples in a large area of ​​loess sites.

[0004] For the field test methods, they are divided into static load test and test pit immersion test. The static load test is used to determine the initial pressure of collapse, and the test pit immersion test is used to determine the self-weight collapse and the lower limit depth of self-weight collapse. For the static load test, the test site is first excavated on site, and then the loading device is used to pressurize and inject water and observe the settlement. Finally, the initial pressure of collapse is determined according to the pressure-settlement curve. For the test pit immersion test, the test pit is first excavated on site and punctuation marks are set. Then, during the immersion process, the collapse, water consumption, immersion range and ground cracks are observed. Finally, the self-weight collapse and the lower limit depth of self-weight collapse are obtained according to the punctuation monitoring results. Although the above two field test methods are highly reliable, they have the disadvantage of high cost. This is mainly because the field test requires the establishment of a test site and the supporting complex equipment and professional technicians.

[0005] In summary, the shortcomings of the existing loess collapsibility evaluation methods urgently require the study of new methods for in-situ rapid evaluation of loess collapsibility. The realization of in-situ rapid evaluation of loess collapsibility can be divided into three steps: first, comprehensively consider the main indicators affecting loess collapsibility and establish a mathematical model for collapsibility evaluation; second, use in-situ testing technology to accurately test the main indicators in the mathematical model for collapsibility evaluation; finally, based on the tested indicators and the mathematical model for collapsibility evaluation, the loess collapsibility is evaluated in situ. Based on the existing large number of loess collapsibility tests and theoretical studies, dry density and mass water content are two important indicators affecting loess collapsibility. The soil body is composed of three phases: soil particles, air and water. The dry density indicates the mass of soil particles per unit volume. The larger the dry density of loess, the fewer pores in the soil body, and the smaller the collapsibility deformation after immersion. The mass water content indicates the mass of water contained in the unit mass of soil particles. The larger the mass water content of loess, the smaller the amount of moisture allowed for the soil body to reach a saturated state, and the smaller the collapsibility deformation after immersion.

[0006] Therefore, establishing a mathematical model of loess collapsibility based on dry density and mass water content, and conducting accurate in-situ tests on the dry density and water content of loess, is an effective way to achieve in-situ rapid evaluation of loess collapsibility. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide an in-situ evaluation method and system for loess collapsibility based on non-destructive time domain reflection technology in view of the deficiencies in the above-mentioned prior art, which can determine whether the loess is collapsible and has the potential to distinguish between strong, moderate and slight degrees of collapsibility.

[0008] The present invention adopts the following technical solutions:

[0009] An in-situ evaluation method for loess collapsibility based on non-destructive time domain reflectometry technology comprises the following steps:

[0010] S1. Test the time domain reflection waveform of the original loess at the on-site arrangement point by non-destructive time domain reflection technology, and obtain the dielectric constant and conductivity of the original loess at the arrangement point according to the time domain reflection waveform;

[0011] S2, combining the dielectric constant and conductivity of the original loess at the arrangement point obtained in step S1 and the indoor calibration parameters, calculating the dry density and mass water content of the original loess at the on-site arrangement point;

[0012] S3. Considering the original loess dry density, mass water content and basic physical property indicators calculated in step S2, the collapsibility of the loess is evaluated in situ through a mathematical model.

[0013] Specifically, step S1 is as follows:

[0014] The location and number of test points are selected according to the on-site test area environment; the proposed test points are leveled, and a non-invasive probe is used to fit the leveled test points tightly for 5 to 10 seconds. A computer-driven time domain reflection signal transmitting device is used to obtain the time domain reflection waveform of the test points through the non-invasive probe, and the dielectric constant and conductivity of the original loess are calculated based on the time domain reflection waveform.

[0015] Specifically, step S2 is as follows:

[0016] S201. Dry and sieve the loess debris retrieved from the site, and then prepare n groups of compacted soil samples with the same dry density and different mass water content for indoor calibration test, n ≥ 4, and then use the least squares method to obtain the indoor calibration parameter a 1 、b 1 、c 1 ,d 1 value;

[0017] S202, using the original loess dielectric constant and conductivity of the on-site layout point and the indoor calibration parameters a 1 、b 1 、c 1 ,d 1 , and obtain the dry density and mass moisture content of the original loess at the on-site layout point.

[0018] Furthermore, in step S201, the indoor calibration test is calculated as follows:

[0019]

[0020]

[0021] Among them, K a To calibrate the dielectric constant of the sample, EC b is the conductivity of the calibration sample, p w is the water density, p d is the calibrated dry density of loess, and w is the mass water content.

[0022] Furthermore, in step S202, the original loess mass water content w f and dry density p d,f The calculation is as follows:

[0023]

[0024]

[0025] Among them, K a,f and EC b,f are the dielectric constant and conductivity of the undisturbed loess tested in situ at the site, EC b,jf is the conductivity adjusted for the dielectric constant, pw is the water density, β and λ are b 1 and d 1 The correction factor of .

[0026] Furthermore, the conductivity EC after dielectric constant adjustment b,jf for:

[0027]

[0028] Among them, p d To calibrate the dry density of loess.

[0029] Specifically, step S3 is as follows:

[0030] Combined with the dry density, mass water content and basic physical property indicators of the original loess at the on-site layout point, the collapsibility evaluation index K of the original loess at the layout point is calculated. L Based on the indoor compression results, the collapsibility evaluation index K of the original loess at the layout point is L The calculated values ​​are divided into intervals to determine severe subsidence, moderate subsidence, slight subsidence and no subsidence.

[0031] Furthermore, the collapsibility evaluation index K L for:

[0032]

[0033] Among them, G s is the specific gravity of loess, I p is the loess plasticity index.

[0034] Furthermore, when K L <0.85, no sinkage; when 0.85≤K L <1.26, slight collapse; when 1.26≤K L <1.90, moderate collapse; when K L When ≥1.90, there is severe wetting.

[0035] Another technical solution of the present invention is an in-situ evaluation system for loess collapsibility based on non-destructive time domain reflectometry technology, comprising:

[0036] The acquisition module tests the time domain reflection waveform of the original loess at the on-site arrangement point through non-destructive time domain reflection technology, and obtains the dielectric constant and conductivity of the original loess at the arrangement point according to the time domain reflection waveform;

[0037] The calculation module calculates the dry density and mass water content of the original loess at the layout point on site by combining the dielectric constant and conductivity of the original loess at the layout point obtained by the acquisition module and the indoor calibration parameters;

[0038] The evaluation module considers the original loess dry density, mass water content and basic physical property indicators calculated by the calculation module, and conducts an in-situ evaluation of the loess collapsibility through a mathematical model.

[0039] Compared with the prior art, the present invention has at least the following beneficial effects:

[0040] The invention discloses an in-situ evaluation method for loess collapsibility based on non-destructive time domain reflection technology. The non-destructive time domain reflection technology is used to in-situ test the dielectric constant and conductivity of loess; the dry density and mass water content of loess are calculated based on the tested dielectric constant and conductivity; the dry density, mass water content and basic physical property indicators of the loess are considered, and the collapsibility of the loess is evaluated in-situ through a mathematical model. The invention utilizes the dielectric properties of the soil body to not only realize the rapid, non-destructive and economical testing of the dry density and mass water content of the loess, but also has the potential to distinguish between strong, medium and slight collapsibility degrees.

[0041] Furthermore, the reasonable selection of the location and number of test points can control the distribution density of the test points, thereby improving the accuracy and reliability of the survey results. The leveling of the proposed test points and the close fit of the non-invasive probe can make the soil and the probe in good contact and reduce the structural damage of the original loess during the test, thereby obtaining a stable and accurate electromagnetic wave reflection signal. The use of time domain reflection technology to test the dielectric constant and conductivity of the original loess has a clear principle, mature technology, and simple operation.

[0042] Furthermore, the indoor calibration test uses n groups (n≥4) of compacted loess to cover a larger range of moisture content and ensures the same soil material composition as the in-situ test, providing representative parameters for the calculation of the dry density and mass moisture content of the original loess. 1 、b 1 、c 1 ,d 1 Calibration value. The dry density and mass water content of the original loess are calculated by combining the dielectric constant and conductivity of the original loess with the indoor calibration parameters. This calculation process not only utilizes the electrical properties of the original loess, but also includes representative calibration parameters, ensuring the accuracy of the calculation of the dry density and mass water content of the original loess.

[0043] Furthermore, through the calibration of dielectric constant and conductivity, the relationship between dielectric constant, conductivity and soil dry density and mass water content was established, providing a theoretical basis for indoor calibration experiments.

[0044] Furthermore, the empirical relationship between the dielectric constant, conductivity, indoor calibration parameters and the mass moisture content and dry density of the original loess is established by calculating the mass moisture content and dry density of the original loess, providing a theoretical basis for calculating the dry density and mass moisture content of the original loess. In addition, the above calculation formula introduces parameters β and λ to consider the changes in loess characteristics during the calibration process (such as drying, compaction, etc.) and the difference in pore water conductivity between the original loess and the calibrated compacted loess on the test results, thereby improving the accuracy of the test results.

[0045] Furthermore, the conductivity EC adjusted by the dielectric constant b,jf The relationship between dielectric constant and electrical conductivity is established. The dielectric constant is insensitive to changes in the electrical conductivity of the pore fluid in the soil. The electrical conductivity adjusted by the dielectric constant is used to improve the accuracy of calculating the mass moisture content of the original loess.

[0046] Furthermore, the collapsibility evaluation index K is calculated using the original loess dry density, mass water content and basic physical properties. L This index not only includes the main parameters that affect the collapsibility of loess, but is also relatively concise and easy to calculate. The collapsibility evaluation index K is evaluated by indoor compression test results (according to GB 50025-2018). L The calculated value is divided into intervals, and the index K after the interval division L Maintaining the consistency of the evaluation of the degree of collapse in the same specification, the index K is added L Operability in engineering applications.

[0047] Furthermore, the collapsibility evaluation index K L The relationship between the degree of loess collapse and dry density, mass water content and basic physical properties (such as specific gravity and plasticity index) was established to obtain the collapse evaluation index K. L It provides a theoretical basis. In addition, the calculation formula is simple and the parameters are easy to obtain, which makes it very practical.

[0048] Furthermore, according to the indoor compression test results (according to GB 50025-2018), the collapsibility evaluation index K is divided into L The interval is: when K L <0.85, no sinkage; when 0.85≤K L <1.26, slight collapse; when 1.26≤K L <1.90, moderate collapse; when K L When ≥1.90, it is severely collapsible. The evaluation index of collapsibility K L The divided intervals correspond clearly to the indoor compression results and have strong engineering applicability.

[0049] In summary, the in-situ rapid evaluation method of loess collapsibility based on non-destructive time domain reflectometry technology has the advantages of clear theory, little disturbance to soil sample structure, short test time, low cost, advanced technology, high reliability, and strong engineering applicability. It can become a new means of engineering survey technology in loess areas.

[0050] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 1 is a diagram of the non-destructive time domain reflection device of the present invention, wherein (a) is a test diagram of the non-destructive time domain reflection device; (b) is a contour diagram of the non-invasive probe; (c) is a plane layout diagram of the probes in the non-invasive probe;

[0052] Figure 2 The result diagram of the test site 1 based on the non-destructive time domain reflection technology and the drying method of the present invention, wherein (a) is the dry density; (b) is the mass water content;

[0053] Figure 3 This is a comparison chart of the results of the wet collapse determined by the method of the present invention and the indoor compression test for site 1;

[0054] Figure 4 The result diagram of the test site 2 based on the non-destructive time domain reflection technology and the drying method of the present invention, wherein (a) is the dry density; (b) is the mass water content;

[0055] Figure 5 This is a comparison chart of the results of wetting collapse determined based on the method of the present invention and the indoor compression test for Site 2.

[0056] Among them, 1. time domain reflection signal transmitting device; 2. non-invasive probe; 3. computer; 4. coaxial cable; 5. epoxy resin; 6. probe. DETAILED DESCRIPTION

[0057] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] In the description of the present invention, it should be understood that the terms “include” and “comprises” indicate the presence of described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0059] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0060] It should be further understood that the term "and / or" used in the present specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes these combinations. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects are in an "or" relationship.

[0061] It should be understood that, although the terms first, second, third, etc. may be used to describe preset ranges, etc. in the embodiments of the present invention, these preset ranges should not be limited to these terms. These terms are only used to distinguish preset ranges from each other. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0062] The word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrases "if it is determined" or "if (stated condition or event) is detected" may be interpreted as "when it is determined" or "in response to determining" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)", depending on the context.

[0063] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0064] The present invention provides a method and system for evaluating the collapsibility of loess in situ based on non-destructive time-domain reflection technology. The non-destructive time-domain reflection technology is used to test the dielectric constant and conductivity of loess in situ; the dry density and mass water content of loess are calculated based on the tested dielectric constant and conductivity; the dry density, mass water content and basic physical property indicators of loess are considered to evaluate the collapsibility of loess in situ through a mathematical model. The in-situ evaluation method for the collapsibility of loess based on the non-destructive time-domain reflection technology of the present invention can not only determine whether the loess has collapsibility, but also has the potential to distinguish between strong, medium and slight degrees of collapsibility. The method of the present invention is advanced in technology, short in time, low in cost, easy to operate, highly reliable and practical, and is a new means of engineering survey technology in loess areas.

[0065] The present invention discloses an in-situ evaluation method for loess collapsibility based on non-destructive time domain reflectometry, comprising the following steps:

[0066] S1. Test the time domain reflection waveform of the original loess at the on-site arrangement point by non-destructive time domain reflection technology, and then obtain the dielectric constant and conductivity of the original loess at the arrangement point;

[0067] See also Figure 1 The non-invasive probe 2 is connected to the computer 3 via the time domain reflection signal transmitting device 1, and the time domain reflection signal transmitting device 1 is electrically connected to the probe 6 of the non-invasive probe 2 via the coaxial cable 4. The end of the coaxial cable 4 is provided with epoxy resin 5. The probe 6 is a two-needle non-destructive probe. The probe adopts a copper conductor with a width of 1 mm and a thickness of 0.02 mm. The center distance between the two copper conductors is 3 mm.

[0068] The time domain reflection signal transmitting device 1 and the non-invasive probe 2 are used to test the time domain reflection waveform of the original loess at the on-site arrangement point, and the dielectric constant and conductivity of the original loess are calculated by the computer 3, specifically:

[0069] S101. According to the complexity of the engineering geological conditions in the on-site test area, refer to the field drilling point test collapsibility investigation method (according to GB 50025-2018) to reasonably select the location and number of test points under the corresponding engineering geological conditions;

[0070] S102, leveling the intended test point, and then making the non-invasive probe fit closely with the leveled test point;

[0071] S103, 5 to 10 seconds after lamination, using a microcomputer to drive a time domain reflection signal transmitting device, obtaining a time domain reflection waveform diagram of the test point through a non-invasive probe, and then calculating the dielectric constant and conductivity of the original loess;

[0072] After each test, use dry cotton cloth to clean the residual loess on the non-invasive probe.

[0073] After each test, the same mass of loess is taken from the non-invasive probe test site, and finally loess with a total weight of about 10 to 15 kg is obtained for indoor calibration.

[0074] S2. Combined with the original loess dielectric constant, conductivity and indoor calibration parameters a at the layout point 1 、b 1 、c 1 ,d 1 , calculate the dry density and mass water content of the original loess at the on-site layout point;

[0075] Combined with the dielectric constant and conductivity of the original loess at the on-site layout point and the indoor calibration parameter a 1 、b 1 、c 1 ,d 1 , the dry density and mass water content of the original loess are calculated using the empirical model, as follows:

[0076] S201. Dry and sieve the loess debris retrieved from the site, and then prepare n groups (n≥4) of compacted soil samples with the same dry density and different mass water content. Perform indoor calibration tests according to formulas (1) and (2), and then use the least squares method to obtain the indoor calibration parameter a. 1 、b 1 、c 1 ,d 1 value:

[0077]

[0078]

[0079] Among them, K a To calibrate the dielectric constant of the sample, EC b is the conductivity of the calibration sample, p w is the water density, p d is the dry density of loess, w is the mass water content, a 1 、b 1 、c 1 ,d 1 is the calibration parameter;

[0080] S202, taking into account the difference in conductivity between the pore water of the original loess at the field test point and the pore water of the indoor calibrated compacted loess and the change in loess characteristics before and after the calibration test, the dielectric constant and conductivity of the original loess at the field layout point and the indoor calibration parameters a 1 、b 1 、c 1 ,d 1 Combining equations (1) and (2), we can obtain the empirical calculation equations (3) and (4) for the dry density and mass water content of the original loess at the site layout point:

[0081]

[0082]

[0083] Among them, w f and p d,f are the moisture content and dry density of the original loess calculated after in-situ testing at the site layout point, K a,f and EC b,f are the dielectric constant and conductivity of the undisturbed loess tested in situ at the site, EC b,jf To measure the conductivity after the dielectric constant is adjusted by in-situ testing, β and λ are b 1 and d 1 The correction coefficient β (0.5-1.3) is used to eliminate the influence of changes in loess properties caused by the calibration process (such as drying). The correction coefficient λ (0-1) is used to eliminate the influence of the difference in pore water conductivity between the original loess and the calibrated compacted loess.

[0084] In addition, the calibration parameter a 1 The range is 0.7~1.8, b 1 The range is 7.5 to 11; due to a 1 The value is usually around 1, so no correction is performed. Calibration parameter c 1 It is a conductivity parameter related to dry loess. It does not change much in situ and during calibration, so it is not adjusted.

[0085] EC b,jf The empirical calculation is as follows:

[0086]

[0087] S3. Considering the original loess dry density, mass water content and basic physical properties, the collapsibility of loess is evaluated in situ through a statistical mathematical model.

[0088] Considering the dry density, mass water content and basic physical property indicators of the original loess, the collapsibility of the original loess at the site layout point is quickly evaluated through a mathematical model, specifically:

[0089] S301. Combined with the dry density, mass water content and basic physical property indexes of the original loess at the site layout point, the collapsibility evaluation index K of the original loess at the layout point is calculated using formula (6): L :

[0090]

[0091] Among them, G s is the specific gravity of loess, I p is the loess plasticity index;

[0092] S302. Based on the indoor compression results, the collapsibility evaluation index K of the original loess at the layout point is determined according to the strong collapsibility, moderate collapsibility, slight collapsibility and no collapsibility determined in the standard (GB 50025-2018). L The calculated values ​​are divided into intervals.

[0093] When K L When <0.85, there is no sinkage;

[0094] When 0.85≤K L <1.26, slight collapse;

[0095] When 1.26≤K L <1.90, moderate collapse;

[0096] When K L When ≥1.90, there is severe wetting.

[0097] In another embodiment of the present invention, a loess collapsible in-situ evaluation system based on non-destructive time domain reflection technology is provided. The system can be used to implement the above-mentioned loess collapsible in-situ evaluation method based on non-destructive time domain reflection technology. Specifically, the loess collapsible in-situ evaluation system based on non-destructive time domain reflection technology includes an acquisition module, a calculation module and an evaluation module.

[0098] Among them, the acquisition module tests the time domain reflection waveform of the original loess at the on-site arrangement point through non-destructive time domain reflection technology, and obtains the dielectric constant and conductivity of the original loess at the arrangement point according to the time domain reflection waveform;

[0099] The calculation module calculates the dry density and mass water content of the original loess at the layout point on site by combining the dielectric constant and conductivity of the original loess at the layout point obtained by the acquisition module and the indoor calibration parameters;

[0100] The evaluation module considers the original loess dry density, mass water content and basic physical property indicators calculated by the calculation module, and conducts in-situ rapid evaluation of loess collapsibility through a mathematical model.

[0101] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0102] In order to further illustrate the in-situ rapid evaluation method of loess collapsibility based on non-destructive time domain reflectometry technology of the present invention, the present invention specifically selects two sites for verification as example analysis and illustration.

[0103] Site 1: A typical exploration well in a survey project in Jingyang County, Shaanxi Province. The depth of the exploration well is 20.0m, and the testers conducted tests at intervals of 1.0m along the depth of the well. Among them, 10.0m to 14.0m is an ancient soil layer and contains many calcareous nodules. The leveling effect is poor and no test was conducted. During the implementation process, the testers conducted the test application according to the specific implementation method of the present invention.

[0104] S1. Enter the exploration well at a depth of 1.0m by crane, and level the test points on the left and right sides of the well wall; then, make the non-invasive probe fit closely with the leveled test point for 5 to 10 seconds, and use a microcomputer to drive the time domain reflection signal transmitter to test through the non-invasive probe, and then obtain the time domain reflection waveform of the test point. It should be noted that after each test, the residual loess at the test end of the non-invasive probe should be removed with a dry cotton cloth. Further, after completing the test at the same depth, the staff descended with the crane and conducted the same test at intervals of 1.0m until the exploration well depth was 20.0m. Among them, the exploration well depth of 10.0m-14.0m is the ancient soil layer and contains more calcareous nodules. Due to the poor leveling effect of the test surface, no test was performed. Therefore, a total of 32 non-destructive time domain reflection waveform tests were conducted along the exploration well depth of 0m-20.0m, and finally the dielectric constant and conductivity of 32 groups of original loess were calculated. In addition, after each test, original loess blocks and debris loess with a size of about 150mm×150mm×150mm were taken from the non-invasive probe test site. The original loess blocks were used for indoor drying method to verify the accuracy of the non-destructive time domain reflection technology test of loess dry density and mass water content, and for indoor compression test to verify the applicability of the mathematical model for evaluating loess collapsibility, and the debris loess was used for indoor calibration test and basic physical parameter test.

[0105] S2, the debris loess retrieved on site was dried and sieved to prepare 5 groups of compacted soil samples with the same dry density and different mass moisture content, and then the indoor calibration test was carried out. Then the least squares method was used to obtain the parameter a. 1 、b 1 、c 1 and d 1 The values ​​are 1.3644, 10.789, 0.0784 and 0.6237 respectively; further, the dielectric constant and conductivity of the original loess at the field layout point are compared with the indoor calibration parameter a 1 、b 1 、c 1 ,d 1 , calculate the mass moisture content and dry density of the original loess at the on-site arrangement point. Among them, the mass moisture content of the original loess at the on-site arrangement point is calculated using formulas (3) and (5), and the β and λ values ​​are 0.990 and 0.481, respectively. Subsequently, the dry density of the original loess at the on-site arrangement point is calculated using the calculated mass moisture content of the original loess and formula (4). It is worth noting that in order to more clearly illustrate the feasibility of the present invention, this case uses the indoor drying method and the non-destructive time domain reflection technology to compare the obtained loess dry density and mass moisture content results, as shown in the figure. Figure 2 shown.

[0106] S3, combined with loess dry density, mass water content and basic physical properties (such as plasticity index I p And specific gravity G s ) Evaluation index K of the collapsibility of original loess at different layout points L Calculate according to formula (6). Then, according to K L The values ​​correspond to severe collapsibility (K L ≥1.90), medium collapse (1.26≤K L <1.90), slight collapse (0.85≤K L <1.26) and no collapse (K L <0.85), and the collapsibility of the original loess at different arrangement points was evaluated. It is worth noting that in order to more clearly illustrate the feasibility of the present invention, this case uses the indoor compression results to compare with the prediction results of the loess collapsibility evaluation mathematical model, such as Figure 3 shown.

[0107] Site 2: A foundation pit site in Xixian New District, Xi'an City, Shaanxi Province. The foundation pit site is 25.0m long and 15.0m wide. In this test, two measuring lines with a spacing of 4.0m were selected along the excavation surface of the foundation pit. Each measuring line is 16.0m long, and the test point spacing is 1.0m. A total of 32 tests were conducted. The test personnel conducted the test application according to the specific implementation method of the present invention.

[0108] S1. Level the test points in the selected area. Then, after the non-invasive probe is closely attached to the leveled test point for 5 to 10 seconds, the time domain reflection signal transmitting device driven by a microcomputer is used to test through the non-invasive probe, and then the time domain reflection waveform of the test point is obtained. It should be noted that after each test, the residual loess on the non-invasive probe is removed with a dry cotton cloth. Furthermore, 16 tests are performed on each measuring line, and finally 32 sets of time domain reflection waveforms are obtained in the selected area, and then the dielectric constant and conductivity of 32 sets of original loess are calculated. In addition, after each test, the original loess block and the debris loess with a size of about 150mm×150mm×150mm are taken at the non-invasive probe test site, and finally 32 original loess blocks and debris loess with a total weight of about 10 to 15kg are obtained. Among them, the original loess blocks are used for indoor drying method to verify the accuracy of non-destructive time domain reflection technology to test the dry density and mass moisture content of loess, and for indoor compression test to verify the applicability of the mathematical model for evaluating loess collapsibility. The debris loess is used for indoor calibration test and testing of basic physical parameters.

[0109] S2, the debris loess retrieved on site was dried and sieved to prepare 5 groups of compacted soil samples with the same dry density and different mass water content, and then indoor calibration was performed according to formulas (1) and (2). Then the least squares method was used to obtain the parameter a 1 、b 1 、c 1 ,d 1 The values ​​are 1.1611, 10.465, 0.0873, and 0.6562, respectively. Furthermore, the dielectric constant and conductivity of the original loess at the site layout point are compared with the indoor calibration parameter a 1 、b 1 、c 1 ,d 1 , calculate the mass moisture content and dry density of the original loess at the on-site arrangement point. Among them, the mass moisture content of the original loess at the on-site arrangement point is calculated using formulas (3) and (5), and the β and λ values ​​are 0.841 and 0.046, respectively. Subsequently, the dry density of the original loess at the on-site arrangement point is calculated using the mass moisture content of the original loess and formula (4). It is worth noting that in order to more clearly illustrate the feasibility of the present invention, this case uses the indoor drying method and the non-destructive time domain reflection technology to compare the obtained loess dry density and mass moisture content results, as shown in the figure. Figure 4 shown.

[0110] S3, combined with loess dry density, mass water content and basic physical properties (such as plasticity index I p And specific gravity G s ) Evaluation index K of the collapsibility of original loess at different layout points L Calculate according to formula (6). Then, according to K LThe values ​​correspond to severe collapsibility (K L ≥1.90), medium collapse (1.26≤K L <1.90), slight collapse (0.85≤K L <1.26) and no collapse (K L <0.85), and the collapsibility of the original loess at different arrangement points was evaluated. It is worth noting that in order to more clearly illustrate the feasibility of the present invention, this case uses the indoor compression results to compare with the prediction results of the loess collapsibility evaluation mathematical model, such as Figure 5 shown.

[0111] In summary, the in-situ evaluation method and system for loess collapsibility based on non-destructive time domain reflectometry technology of the present invention have the following characteristics:

[0112] (1) Compared with the traditional loess collapsibility survey technology, the in-situ rapid evaluation method of loess collapsibility based on non-destructive time domain reflectometry has the advantages of small disturbance to the soil sample structure, short time, low cost, advanced technology and high reliability;

[0113] (2) The present invention uses non-destructive time domain reflection technology to test the dry density and mass water content of loess in situ. The technology is mature and advanced, the test takes a short time, and the reliability is high. Furthermore, the equipment is easy to operate, easy to carry, and has strong adaptability to the site;

[0114] (3) The loess collapsibility evaluation mathematical model used in the present invention has good prediction effect, requires fewer parameters, and is highly practical;

[0115] (4) The in-situ rapid evaluation method of loess collapsibility based on non-destructive time domain reflectometry technology of the present invention can not only determine whether loess is collapsible, but also has the potential to distinguish between strong, moderate and slight collapsibility (standard GB50025-2018);

[0116] (5) The evaluation method of the present invention enriches the means of engineering survey technology in the Loess Plateau region, has strong engineering promotion and applicability, and can become a new means of engineering survey technology in the Loess Plateau region.

[0117] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0118] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0119] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0120] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0121] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. In-situ evaluation method of loess collapsibility based on non-destructive time domain reflectometry technology, It is characterized in that The following steps are involved: S1. Testing the time domain reflection waveform of the original loess at the on-site arrangement point by non-destructive time domain reflection technology, and obtaining the dielectric constant and conductivity of the original loess at the arrangement point according to the time domain reflection waveform; S2. Calculate the dry density and mass water content of the original loess at the site layout point by combining the dielectric constant, conductivity and indoor calibration parameters of the original loess at the site layout point obtained in step S1, specifically: S201. Dry and sieve the loess debris retrieved from the site, and then prepare n groups of compacted soil samples with the same dry density and different mass water content for indoor calibration test, n ≥ 4, and then use the least squares method to obtain the indoor calibration parameter a 1 、b 1 、c 1 d 1 value; S202, using the original loess dielectric constant and conductivity of the on-site layout point and the indoor calibration parameters a 1 、b 1 、c 1 d 1 , and the original loess dry density at the site layout point is obtained and mass water content ; S3. Considering the original loess dry density, mass water content and basic physical property indicators calculated in step S2, the collapsibility of loess is evaluated in situ through a mathematical model, specifically: Combined with the dry density, mass water content and basic physical property indicators of the original loess at the on-site layout point, the collapsibility evaluation index K of the original loess at the layout point is calculated. L Based on the indoor compression results, the collapsibility evaluation index K of the original loess at the layout point is L The calculated values ​​are divided into intervals to determine strong collapse, moderate collapse, slight collapse and no collapse. L <0.85, no sinkage; when 0.85≤K L <1.26, slight collapse; when 1.26≤K L <1.90, moderate collapse; when K L When ≥1.90, it is severely collapsible, and the evaluation index of collapsibility is K L for: Among them, G s is the specific gravity of loess, I p is the loess plasticity index.

2. According to claim 1, the in-situ evaluation method for loess collapsibility based on non-destructive time domain reflectometry technology, It is characterized in that Step S1 is specifically as follows: The location and number of test points were selected according to the on-site test area environment. The proposed test points were leveled, and a non-invasive probe was used to fit the leveled test points tightly for 5 to 10 seconds. A computer-driven time domain reflection signal transmitting device was used to obtain the time domain reflection waveform of the test points through the non-invasive probe, and the dielectric constant and conductivity of the original loess were calculated based on the time domain reflection waveform.

3. The in-situ evaluation method for loess collapsibility based on non-destructive time domain reflectometry according to claim 1, It is characterized in that In step S201, the indoor calibration test is calculated as follows: Among them, K a To calibrate the dielectric constant of the sample, EC b is the conductivity of the calibration sample, p w is the water density, p d is the calibrated dry density of loess, and w is the mass water content.

4. The in-situ evaluation method for loess collapsibility based on non-destructive time domain reflectometry according to claim 1, It is characterized in that In step S202, the original loess mass water content and dry density The calculation is as follows: in, and They are the dielectric constant and conductivity of the undisturbed loess tested in situ at the site arrangement point, is the conductivity adjusted for the dielectric constant, p w is the water density, β and λ are b 1 and d 1 The correction factor of .

5. The in-situ evaluation method for loess collapsibility based on non-destructive time domain reflectometry according to claim 4, It is characterized in that Conductivity after dielectric constant adjustment for: Among them, p d To calibrate the dry density of loess.

6. An in-situ evaluation system for loess collapsibility based on non-destructive time domain reflectometry technology. It is characterized in that include: The acquisition module tests the time domain reflection waveform of the original loess at the on-site arrangement point through non-destructive time domain reflection technology, and obtains the dielectric constant and conductivity of the original loess at the arrangement point according to the time domain reflection waveform; The calculation module calculates the dry density and mass water content of the original loess at the on-site layout point by combining the dielectric constant and conductivity of the original loess at the layout point obtained by the acquisition module and the indoor calibration parameters. Specifically: After drying and sieving the debris loess retrieved from the site, n groups of compacted soil samples with the same dry density and different mass water content were prepared for indoor calibration tests, n ≥ 4, and then the indoor calibration parameter a was obtained using the least squares method. 1 、b 1 、c 1 d 1 Value; using the original loess dielectric constant and conductivity of the on-site layout point and the indoor calibration parameter a 1 、b 1 、c 1 d 1 , and the original loess dry density at the site layout point is obtained and mass water content ; The evaluation module considers the original loess dry density, mass water content and basic physical property indicators calculated by the calculation module, and uses a mathematical model to evaluate the loess collapsibility in situ, specifically: Combined with the dry density, mass water content and basic physical property indicators of the original loess at the on-site layout point, the collapsibility evaluation index K of the original loess at the layout point is calculated. L Based on the indoor compression results, the collapsibility evaluation index K of the original loess at the layout point is L The calculated values ​​are divided into intervals to determine strong collapse, moderate collapse, slight collapse and no collapse. L <0.85, no sinkage; when 0.85≤K L <1.26, slight collapse; when 1.26≤K L <1.90, moderate collapse; when K L When ≥1.90, it is severely collapsible, and the evaluation index of collapsibility is K L for: Among them, G s is the specific gravity of loess, I p is the loess plasticity index.

Images