Method for measuring soil-water characteristic curve of undisturbed soil under different humidity paths

Abstract

The invention discloses a method for measuring a soil-water characteristic curve of undisturbed soil under different humidity paths. The method comprises the following steps: taking out undisturbed soil samples from a cohesive soil body, dividing the undisturbed soil samples into a dehumidified soil sample group and a humidified soil sample group, and carrying out vacuum saturation and drying treatment on the dehumidified soil sample group and the humidified soil sample group to obtain treated undisturbed soil samples; then stretching a tensiometer into the undisturbed soil sample to obtain the matrix suction of the undisturbed soil sample; measuring the saturation degree of the dug soil material; and drawing a soil-water characteristic curve of the undisturbed soil sample under different humidity paths by utilizing the soil material saturation in the dehumidified soil sample group and the humidified soil sample group and the matrix suction of the undisturbed soil sample. According to the invention, the micro tensiometer is used for respectively measuring the change of the matrix suction in the humidifying and dehumidifying processes of the fine-grained soil, so that the change trend of the matrix suction of the undisturbed soil body along with the water content can be measured on the basis of not damaging the undisturbed structure of the fine-grained soil, and the property difference of the undisturbed soil sample in different change processes can be more truly reflected.

Description

Technical Field

[0001] The invention belongs to the field of geotechnical test methods, and in particular relates to a method for measuring soil-water characteristic curves of original soil under different humidity paths. Background Art

[0002] Compared with saturated soil, unsaturated soil is more widely present in nature. The degree of saturation has a significant impact on the physical and mechanical parameters and engineering properties of the soil, which affects the strength, permeability and deformation characteristics of the soil. The study of unsaturated soil plays a key role in the engineering field. Matrix suction is one of the key parameters of the mechanical properties of unsaturated soil, involving the stability analysis of foundation pits and slopes, and the changes in the strength characteristics of foundation soil. Unsaturated soil mechanics not only promotes the development of traditional soil mechanics, but also provides an important theoretical reference for solving specific practical problems in engineering. However, due to the complexity and particularity of unsaturated soil itself, the current theoretical system is still difficult to be widely applied to specific engineering practices.

[0003] In the soil, tiny pores act like capillaries to promote the rise of water in the soil. Under different saturations, the interaction between soil, water and internal gas will change: under high saturation, it is a "water-in-gas" state, while under low saturation, it is a "gas-in-water" state, which causes the matrix suction under different saturations to change. Matrix suction acts on the soil in the form of ideal spherical stress, and the magnitude of negative pressure is mainly affected by the pore size and channel distribution. Sandy soil has a small specific surface area, large internal pore channels, and small matrix suction; while clay soil has a large specific surface area and small internal pore channels, so the matrix suction is small. The matrix suction also contributes to the strength of the soil, and to a certain extent affects the internal friction angle and cohesion. There are also many models for the soil-water characteristic curve, such as the VG model proposed by the famous scholar Van Genuchten. At present, the test methods for the matrix suction of unsaturated soil include: tensiometer method, pressure plate method, filter paper method, etc. Among them, the tensiometer method is based on the principle of tension balance between water in fine capillaries and soil particles. It has the characteristics of real-time, low cost, accurate results and easy application. Therefore, it has become a common method for measuring the matrix suction of unsaturated soil. At present, the equipment of the tensiometer itself is constantly developing and iterating: the volume is gradually reduced, the range is continuously increased, and the results are more accurate. However, the accuracy of the test results is not only limited by the test equipment, but also closely related to the test methods and operation details adopted. At present, the relevant test specifications for unsaturated soil mechanics are still in the development stage, and basically focus on the measurement of reshaped soil. The measurement of soil and water characteristics of original clay soil is not simple and accurate enough. Summary of the invention

[0004] In order to solve the problems existing in the background technology, the purpose of the present invention is to provide a method for measuring the soil-water characteristic curve under different humidity paths of undisturbed soil.

[0005] The technical solution adopted by the present invention comprises the following steps:

[0006] Step S1, taking out a number of original soil samples from the clay soil, measuring the saturated moisture content of each original soil sample at the same time, and dividing the original soil samples into two groups, namely a dehumidified soil sample group and a humidified soil sample group, performing vacuum saturation and drying treatment on the dehumidified soil sample group and the humidified soil sample group respectively, to obtain the treated original soil samples;

[0007] Step S2, then digging a hole in the original soil sample processed in step S1, and inserting a saturated tensiometer into the original soil sample to obtain the matrix suction of the original soil sample;

[0008] Step S3, measuring the moisture content of the soil material excavated by the hole digging process to obtain the saturation of the soil material;

[0009] Step S4: Finally, the saturation of the soil samples in the dehumidified soil sample group and the humidified soil sample group, as well as the corresponding matrix suction of the original soil sample, are used to draw the soil-water characteristic curve of the original soil sample under different humidity paths.

[0010] The step S1 is specifically as follows:

[0011] Step S1.1, first, using the ring knife method to take out a number of original soil samples from the clay soil, and divide the taken original soil samples into two groups, namely a dehumidified soil sample group and a humidified soil sample group, wherein the dehumidified soil sample group includes a completely dehumidified soil sample group and a partially dehumidified soil sample group; the humidified soil sample group includes a completely humidified soil sample group and a partially humidified soil sample group;

[0012] Step S1.2, perform complete dehumidification treatment on the completely dehumidified soil sample group in the dehumidified soil sample group: put all the original soil samples in the completely dehumidified soil sample group into air-free water and saturate them by vacuum for more than 24 hours. After the original soil samples are completely saturated, take them out from the air-free water and put them into an oven to dry them at a constant temperature for different periods of time. After the drying is completed, take out the original soil samples, seal them with plastic film and let them stand for 24-30 hours to obtain several completely dehumidified original soil samples with different drying times;

[0013] Step S1.3, partially dehumidify the partially dehumidified soil sample group in the dehumidified soil sample group: put all the original soil samples in the partially dehumidified soil sample group into respective ovens, dry them at a constant temperature for different time periods, take out the original soil samples after drying, seal them with plastic film and let them stand for 24-30 hours, and obtain several partially dehumidified original soil samples with different drying time periods;

[0014] Step S1.4, perform complete humidification treatment on the completely humidified soil sample group in the humidified soil sample group: put all the original soil samples in the completely humidified soil sample group into an oven until the original soil samples are completely dried, then put the dried original soil samples into a vacuum saturation barrel and perform vacuum saturation for different periods of time, after the saturation is completed, take out the original soil samples, seal them with plastic film and let them stand for 24-30 hours, to obtain a number of completely humidified original soil samples with different saturation times;

[0015] Step S1.5, perform partial humidification treatment on some of the humidified soil sample groups: put all the original soil samples in the partially humidified soil sample group into respective vacuum saturation barrels and perform vacuum saturation for different periods of time. After saturation, take out the original soil samples, seal them with plastic film and let them stand for 24-30 hours to obtain several partially humidified original soil samples with different saturation times.

[0016] The step S2 is specifically as follows:

[0017] Step S2.1, first remove the plastic film sealed on the surface of the original soil sample, then dig holes in the dehumidified original soil sample and the humidified original soil sample, then vertically bury the saturated tensiometer in the hole dug by the digging process, and finally backfill the hole with the soil material dug by the digging process so that there is no gap between the hole and the soil body of the dehumidified original soil sample / humidified original soil sample, and then seal it with a plastic film;

[0018] The dehumidified original soil samples include completely dehumidified original soil samples and partially dehumidified original soil samples; the humidified original soil samples include completely humidified original soil samples and partially humidified original soil samples;

[0019] Step S2.2: After the tensiometer reading in the undisturbed soil sample is stable and no longer changes, the tensiometer reading is obtained as the matrix suction value of the undisturbed soil sample; the undisturbed soil sample includes a dehumidified undisturbed soil sample and a humidified undisturbed soil sample.

[0020] The step S3 specifically includes: measuring the moisture content of the soil materials excavated from each dehumidified original soil sample and the humidified original soil sample, and obtaining the saturation of different soil materials as the saturation of the corresponding original soil sample.

[0021] The step S4 is specifically as follows: different humidity paths refer to a dehumidification path and a humidification path, and the original soil samples under the humidification path and the dehumidification path correspond to the humidification soil sample group and the dehumidification soil sample group, respectively. For the dehumidified soil sample group, the matrix suction value of the dehumidified original soil sample is used as the horizontal coordinate, and the saturation of the dehumidified original soil sample is used as the vertical coordinate to draw the dehumidification soil water characteristic curve of the clay soil under the dehumidification process, wherein, according to the different dehumidification processes, the dehumidification soil water characteristic curve is divided into a completely dehumidified soil water characteristic curve and a partially dehumidified soil water characteristic curve, the horizontal coordinate and vertical coordinate of the completely dehumidified soil water characteristic curve are the matrix suction value and saturation of the completely dehumidified original soil sample, respectively, and the horizontal coordinate and vertical coordinate of the partially dehumidified soil water characteristic curve are the matrix suction value and saturation of the partially dehumidified original soil sample, respectively; for the dehumidified soil sample group, the matrix suction value and saturation of the partially dehumidified original soil sample are used as the vertical coordinate; For the humidified soil sample group, the matrix suction value of the humidified original soil sample was used as the horizontal coordinate, and the saturation of the humidified original soil sample was used as the vertical coordinate to draw the humidified soil-water characteristic curve of the clay soil under the humidification process. Among them, according to the different treatments of the humidification process, the humidified soil-water characteristic curve is divided into a complete humidification soil-water characteristic curve and a partial humidification soil-water characteristic curve. The horizontal coordinate and vertical coordinate of the complete humidification soil-water characteristic curve are the matrix suction value and saturation of the complete humidification original soil sample, respectively, and the horizontal coordinate and vertical coordinate of the partial humidification soil-water characteristic curve are the matrix suction value and saturation of the partial humidification original soil sample, respectively.

[0022] In step S2, a saturated tensiometer is used to measure the matrix suction of the original soil sample. The saturation process of the tensiometer is as follows: first, the porous ceramic head in the tensiometer is removed, and then the removed porous ceramic head is placed in air-free water for vacuum saturation for more than 24 hours. After the saturation is completed, the tensiometer is assembled in air-free water to obtain a saturated tensiometer. The better the saturation effect of the micro tensiometer, the higher the accuracy of the tested matrix suction.

[0023] The height of the original soil sample is greater than twice the length of the tensiometer to ensure that the tensiometer can be placed in the ring cutter without contacting the outside air and to reduce the influence of the boundary effect.

[0024] In step S2, when the original soil sample is dug, the hole is opened in the middle of the original soil, and the hole size is slightly larger than the maximum diameter of the tensiometer. The depth of the hole must be less than the height of the original soil to ensure that some distance is retained from the bottom of the soil to prevent penetration of the soil or contact with the air.

[0025] The present invention performs dehumidification operation and humidification operation on the original soil sample, wherein the dehumidification operation includes complete dehumidification and partial dehumidification; the humidification operation includes complete humidification and partial humidification.

[0026] Clayey soil particles are small in size and have strong natural structure. The pore distribution of reshaped samples and original samples is very different, which will lead to certain differences in the soil-water characteristic curves of the two. The original samples were taken for testing using the ring knife method. For the soil-water characteristic curve of the dehumidification process, the completely dehumidified soil-water characteristic curve requires the original sample to be placed in airless water for vacuum saturation for 24 hours. After it is completely saturated, it is taken out and placed in an oven; the partially dehumidified soil-water characteristic curve is to directly put the taken original sample into the oven; then the dehumidified original soil samples (completely dehumidified original soil samples and partially dehumidified original soil samples) are dried at a constant temperature for different times. Immediately seal with plastic film after taking out and let it stand for 24 hours. For the soil-water characteristic curve of the humidification process, the complete humidification soil-water characteristic curve requires the original sample to be placed in an oven for drying until it is completely dried, and then placed in a vacuum saturation barrel after being taken out; for the partial humidification soil-water characteristic curve, the original soil sample taken out is directly placed in a vacuum saturation barrel; then the humidified original soil samples (completely humidified original soil samples and partially humidified original soil samples) are vacuumed and saturated for different times, and immediately sealed with plastic film after being taken out and left to stand for 24 hours. Before the test, a smaller drilling device is used to make a hole on the surface of the original soil sample, and the last excavated soil is used as a sample for the moisture content test. Then place the micro tensiometer, backfill the remaining soil, and compact it appropriately to ensure that the porous ceramic head of the tensiometer is completely wrapped by the soil and does not come into contact with the air. Record the reading after the indication is stable.

[0027] In the general soil-water characteristic curve measurement process, most of them are tested using remolded soil, lacking the soil-water characteristic curve of the original soil sample, and most of them only measure one soil-water characteristic curve, namely the humidification curve or the dehumidification curve. Since the original soil sample has structure, after different treatments (humidification or dehumidification) of the original soil sample, its matrix suction is measured. It is found that when passing through different humidity paths, the matrix suction of the original soil sample will be greatly different. Therefore, different treatments of the original soil sample and adding different humidity paths can better reflect the properties of the original soil sample.

[0028] The beneficial effects of the present invention are:

[0029] 1. The present invention uses a micro tensiometer to measure the change of matrix suction of original fine-grained soil in different humidity paths. The present invention can measure the change trend of matrix suction of original soil with humidity (saturation) without destroying the original structure of fine-grained soil, that is, the soil-water characteristic curve.

[0030] 2. The present invention adds different humidity paths to the original sample of fine-grained soil, and can obtain four soil-water characteristic curves of the original sample passing through different humidity change paths, namely: a completely dehumidified soil-water characteristic curve, a partially dehumidified soil-water characteristic curve, a completely humidified soil-water characteristic curve and a partially humidified soil-water characteristic curve. This can reflect in more detail the changes in matrix suction when the original soil sample undergoes different humidity paths, especially for the original soil sample that is sensitive to humidity changes, and can better reflect its characteristics.

[0031] 3. The humidity change path of the original soil sample carried out in the present invention is divided into a dehumidification path and a humidification path, specifically including a complete dehumidification path and a partial dehumidification path, a complete humidification path and a partial humidification path, which can more truly and accurately reflect the change of the matrix suction of the original soil sample with humidity when it undergoes a dry-wet cycle (partial dehumidification-complete humidification-complete dehumidification or partial humidification-complete dehumidification-complete humidification) at a certain humidity.

[0032] 4. Compared with a conventional soil-water characteristic curve, the four soil-water characteristic curves obtained by the present invention can more accurately predict the size of the matrix suction and water migration of the original samples with different humidity when they pass through different humidity paths, and can more accurately calculate the deformation and strength of the soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the clay layer testing process of the present invention;

[0034] Figure 2 This is the soil-water characteristic curve of clay soil under different humidity paths. DETAILED DESCRIPTION

[0035] The present invention is described in detail below in conjunction with specific implementation cases. The following implementation cases will help those skilled in the art to further understand the present invention, but will not limit the present invention in any form.

[0036] The embodiment of the present invention includes the following steps: Figure 1 Shown

[0037] Step S1, taking out 28 original soil samples from the same box of clay soil samples, and dividing the original soil samples into two groups, a dehumidification group and a humidification group, wherein the dehumidification group includes a complete dehumidification group and a partial dehumidification group; the humidification group includes a complete humidification group and a partial humidification group; then vacuum saturation and drying treatments are performed on the dehumidified soil sample group and the humidified soil sample group respectively to obtain the treated original soil samples:

[0038] Step S1 is specifically as follows:

[0039] Step S1.1: First, use 200cm 3A large ring knife was used to take out 28 undisturbed soil samples from the clay soil, and the taken undisturbed soil samples were divided into two groups, namely, a dehumidified soil sample group (14 samples) and a humidified soil sample group (14 samples). The dehumidified soil sample group (14 samples) included a completely dehumidified soil sample group (7 samples) and a partially dehumidified soil sample group (7 samples), and the humidified soil sample group (14 samples) included a completely humidified soil sample group (7 samples) and a partially humidified soil sample group (7 samples).

[0040] Step S1.2, perform complete dehumidification treatment on the completely dehumidified soil sample group in the dehumidified soil sample group: put all the original soil samples in the completely dehumidified soil sample group into air-free water and saturate them by vacuum for more than 24 hours. After the original soil samples are completely saturated, take them out from the air-free water and put them into an oven. Dry them at a constant temperature of 105°C for different time periods. The drying time of the 7 original soil samples in the completely dehumidified soil sample group is 15min, 30min, 60min, 180min, 360min, 600min, and 1440min, respectively. After the drying is completed, take out the original soil samples, seal them with plastic film, and let them stand for 24 hours to obtain 7 completely dehumidified original soil samples with different drying times.

[0041] Step S1.3, partially dehumidify the partially dehumidified soil sample group in the dehumidified soil sample group: put all the original soil samples in the partially dehumidified soil sample group into respective ovens, and dry them at a constant temperature of 105°C for different time periods, the drying time of the 7 original soil samples in the partially dehumidified soil sample group is 15 min, 30 min, 60 min, 180 min, 360 min, 600 min, and 1440 min, respectively. After the drying is completed, take out the original soil samples, seal them with plastic film, and let them stand for 24 hours, to obtain 7 partially dehumidified original soil samples with different drying times;

[0042] Step S1.4, perform complete humidification treatment on the completely humidified soil sample group in the humidified soil sample group: put all the original soil samples in the completely humidified soil sample group into an oven until the original soil samples are completely dried, and then put the dried original soil samples into a vacuum saturation barrel for vacuum saturation for different times. The saturation time of the 7 original soil samples in the completely humidified soil sample group is 30min, 60min, 120min, 240min, 480min, 720min, and 1440min respectively. After the saturation is completed, take out the original soil sample, seal it with a plastic film and let it stand for 24 hours to obtain 7 completely humidified original soil samples with different saturation times;

[0043] Step S1.5, perform partial humidification treatment on the partially humidified soil sample group in the humidified soil sample group: put all the original soil samples in the partially humidified soil sample group into respective vacuum saturation barrels for vacuum saturation for different periods of time. The saturation time of the 7 original soil samples in the partially humidified soil sample group is 30min, 60min, 120min, 240min, 480min, 720min and 1440min respectively. After the saturation is completed, take out the original soil samples, seal them with plastic film and let them stand for 24 hours to obtain 7 partially humidified original soil samples with different saturation times.

[0044] Step S2: Then, the original soil sample processed in step S1 is subjected to a hole digging process, and a saturated tensiometer is inserted into the original soil sample to obtain the matrix suction of the original soil sample:

[0045] Step S2.1, first remove the plastic film sealed on the surface of the original soil sample, then dig holes for the dehumidified original soil sample and the humidified original soil sample, the diameter of the hole is controlled to be about 20 mm, and the depth is controlled to be about 30 mm to ensure that the tensiometer sensor part can be completely covered and wrapped by the soil body, and then vertically bury the saturated tensiometer into the hole dug by the hole digging process, and finally backfill the hole with the soil material dug by the hole digging process, so that there is no gap between the hole and the soil body of the dehumidified original soil sample / humidified original soil sample, and then seal it with a plastic film;

[0046] Since clay has a large specific surface area and small internal pore channels, it takes a long time for the soil water potential to balance, so the reading may take a long time to stabilize. Therefore, after the filling is completed, it is necessary to wrap a circle of plastic film around the test soil to prevent changes in moisture.

[0047] Step S2.2, after the tensiometer reading in the original soil sample stabilizes and no longer changes, obtain the tensiometer reading as the matrix suction value of the original soil sample; the original soil sample includes a dehumidified original soil sample and a humidified original soil sample, wherein the dehumidified original soil sample includes a completely dehumidified original soil sample and a partially dehumidified original soil sample, and the humidified original soil sample includes a completely humidified original soil sample and a partially humidified original soil sample.

[0048] The matrix suction of the dehumidified soil sample group and the humidified soil sample group after drying and vacuum saturation at different times is shown in Table 1.

[0049] Step S3: measuring the moisture content of the soil excavated by the hole digging process to obtain the saturation of the soil:

[0050] In the specific implementation, the saturation of the soil material (20g) excavated from each dehumidified original soil sample and humidified original soil sample was measured, and the saturation of different soil materials was obtained as the saturation of the corresponding original soil sample. After drying and vacuum saturation for different periods of time, the saturation of the excavated soil material of the dehumidified soil sample group and the humidified soil sample group was tested, and the data obtained are shown in Table 1.

[0051] Table 1 Relationship between matrix suction and saturation of original soil samples after different treatments

[0052]

[0053] Step S4: Finally, using the saturation of the soil materials in the dehumidified soil sample group and the humidified soil sample group, and the corresponding matrix suction of the original soil sample, the soil-water characteristic curve of the original soil sample under different humidity paths is drawn:

[0054] For the dehumidified soil sample group, the matrix suction value of the dehumidified original soil sample is used as the horizontal coordinate, and the saturation of the dehumidified original soil sample is used as the vertical coordinate to draw the dehumidified soil-water characteristic curve of the clay soil in the dehumidification process; for the humidified soil sample group, the matrix suction value of the humidified original soil sample is used as the horizontal coordinate, and the saturation of the humidified original soil sample is used as the vertical coordinate to draw the humidified soil-water characteristic curve of the clay soil in the humidification process, such as Figure 2 shown.

[0055] Before the test of the present invention, it is necessary to ensure that the micro-tensiometer is completely saturated. The structure of clay soil is relatively strong, and the original sample can be taken out by the ring knife method. The measurement operation of the soil-water characteristic curve in the dehumidification process is as follows: for the completely dehumidified soil-water characteristic curve, it is necessary to put it into airless water for vacuum saturation for 24 hours after sampling; for the partially dehumidified soil-water characteristic curve, there is no need for vacuum saturation. Then the dehumidified soil samples (completely dehumidified soil samples and partially dehumidified soil samples) are uniformly taken out and put into an oven, and dried at a constant temperature for different times. Immediately seal it with plastic film after taking it out and let it stand for 24 hours. The measurement operation of the soil-water characteristic curve in the humidification process is as follows: for the completely humidified soil-water characteristic curve, the original soil sample must be placed in an oven after sampling until it is completely dried; for the partially humidified soil-water characteristic curve, there is no need to dry it. Then the humidified soil samples (completely humidified soil samples and partially humidified soil samples) are uniformly vacuum saturated for different times, and immediately seal it with plastic film after taking it out and let it stand for 24 hours. Before testing the original soil after dehumidification / humidification, use a smaller drilling device to drill holes on the surface of the original sample of the clay soil ring knife, and use the moisture content of the last excavated soil as the standard value for the test. Then place the micro tensiometer, backfill the remaining soil, and compact it appropriately to ensure that the tensiometer sensor is completely wrapped by the soil, and seal it again with plastic film to prevent it from contacting the air and preventing water evaporation. The entire process of burying the tensiometer needs to be operated continuously, and the time interval should not be too long to prevent excessive changes in moisture content, especially in the case of low moisture content.

[0056] When the original soil sample of clay soil ring knife is saturated and put into the oven, it must be placed at the same height to ensure the consistency of the temperature field. The baking process must not be interrupted and the temperature must not be adjusted at will. Samples with different saturation can be obtained by taking them out at different intervals. After taking out the original soil sample from the oven, immediately use plastic film to seal the soil surface, let it cool, and allow the internal moisture to migrate to a certain extent.

[0057] Use the soil closest to the porous ceramic head of the tensiometer as the moisture content measurement sample to prevent measurement errors caused by uneven moisture content. After the tensiometer is placed in the predetermined position, backfill and compact it with the excavated soil to ensure that the tensiometer sensor is completely covered by the soil and does not come into contact with the air. After burying the tensiometer, seal the soil again with plastic film to prevent water evaporation.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for measuring soil-water characteristic curves under different humidity paths of undisturbed soil, characterized in that: The following steps are involved: Step S1, taking out a number of original soil samples from the clay soil, and dividing the original soil samples into two groups, namely a dehumidified soil sample group and a humidified soil sample group, and performing vacuum saturation and drying treatments on the dehumidified soil sample group and the humidified soil sample group respectively to obtain the treated original soil samples; Step S2, then digging a hole in the original soil sample processed in step S1, and inserting a saturated tensiometer into the original soil sample to obtain the matrix suction of the original soil sample; Step S3, measuring the moisture content of the soil material excavated by the hole digging process to obtain the saturation of the soil material; Step S4: Finally, the saturation of the soil samples in the dehumidified soil sample group and the humidified soil sample group, as well as the corresponding matrix suction of the original soil sample, are used to draw the soil-water characteristic curve of the original soil sample under different humidity paths.

2. The method for measuring soil-water characteristic curves of undisturbed soil under different humidity paths according to claim 1, characterized in that: The step S1 is specifically as follows: Step S1.1, first, using the ring knife method to take out a number of original soil samples from the clay soil, and divide the taken original soil samples into two groups, namely a dehumidified soil sample group and a humidified soil sample group, wherein the dehumidified soil sample group includes a completely dehumidified soil sample group and a partially dehumidified soil sample group; the humidified soil sample group includes a completely humidified soil sample group and a partially humidified soil sample group; Step S1.2, perform complete dehumidification treatment on the completely dehumidified soil sample group in the dehumidified soil sample group: put all the original soil samples in the completely dehumidified soil sample group into air-free water and saturate them with vacuum for more than 24 hours. After the original soil samples are completely saturated, take them out from the air-free water and put them into an oven to dry them at a constant temperature for different periods of time. After the drying is completed, take out the original soil samples, seal them with plastic film and let them stand for 24-30 hours to obtain several completely dehumidified original soil samples with different drying times; Step S1.3, partially dehumidify the partially dehumidified soil sample group in the dehumidified soil sample group: put all the original soil samples in the partially dehumidified soil sample group into respective ovens, dry them at a constant temperature for different time periods, take out the original soil samples after drying, seal them with plastic film and let them stand for 24-30 hours, and obtain several partially dehumidified original soil samples with different drying time periods; Step S1.4, perform complete humidification treatment on the completely humidified soil sample group in the humidified soil sample group: put all the original soil samples in the completely humidified soil sample group into an oven until the original soil samples are completely dried, then put the dried original soil samples into a vacuum saturation barrel and perform vacuum saturation for different periods of time, after the saturation is completed, take out the original soil samples, seal them with plastic film and let them stand for 24-30 hours, to obtain a number of completely humidified original soil samples with different saturation times; Step S1.5, perform partial humidification treatment on some of the humidified soil samples in the humidified soil sample group: put all the original soil samples in the partially humidified soil sample group into respective vacuum saturation barrels and perform vacuum saturation for different periods of time. After saturation, take out the original soil samples, seal them with plastic film and let them stand for 24-30 hours to obtain several partially humidified original soil samples with different saturation times.

3. The method for measuring soil-water characteristic curves under different humidity paths of undisturbed soil according to claim 1, characterized in that: The step S2 is specifically as follows: Step S2.1, first remove the plastic film sealed on the surface of the original soil sample, then dig holes in the dehumidified original soil sample and the humidified original soil sample, then bury the saturated tensiometer in the holes dug by the digging process, and finally backfill the holes with the excavated soil material so that there is no gap between the holes and the soil body of the original soil sample, and then seal them with a plastic film; The dehumidified original soil samples include completely dehumidified original soil samples and partially dehumidified original soil samples; the humidified original soil samples include completely humidified original soil samples and partially humidified original soil samples; Step S2.2: After the tensiometer reading in the original soil sample is stable and no longer changes, the tensiometer reading is obtained as the matrix suction value of the original soil sample.

4. The method for measuring soil-water characteristic curves of undisturbed soil under different humidity paths according to claim 1, characterized in that: The step S3 specifically includes: measuring the moisture content of the soil materials excavated from each dehumidified original soil sample and the humidified original soil sample, and obtaining the saturation of different soil materials as the saturation of the corresponding original soil sample.

5. The method for measuring soil-water characteristic curves of undisturbed soil under different humidity paths according to claim 1, characterized in that: The step S4 is specifically as follows: for the dehumidified soil sample group, the matrix suction value of the dehumidified original soil sample is used as the horizontal coordinate, and the saturation of the dehumidified original soil sample is used as the vertical coordinate to draw the dehumidification soil-water characteristic curve of the clay soil in the dehumidification process; for the humidified soil sample group, the matrix suction value of the humidified original soil sample is used as the horizontal coordinate, and the saturation of the humidified original soil sample is used as the vertical coordinate to draw the humidification soil-water characteristic curve of the clay soil in the humidification process.

6. The method for measuring soil-water characteristic curves of undisturbed soil under different humidity paths according to claim 1, characterized in that: In step S2, a saturated tensiometer is used to measure the matrix suction of the original soil sample. The saturation process of the tensiometer is as follows: first, the porous ceramic head in the tensiometer is removed, and then the removed porous ceramic head is placed in air-free water for vacuum saturation for more than 24 hours. After the saturation is completed, the tensiometer is assembled in air-free water to obtain a saturated tensiometer.

7. The method for measuring soil-water characteristic curves of undisturbed soil under different humidity paths according to claim 1, characterized in that: The height of the original soil sample is greater than twice the length of the tensiometer.

8. The method for measuring soil-water characteristic curves of undisturbed soil under different humidity paths according to claim 1, characterized in that: In the step S2, when the original soil sample is subjected to a hole digging process, the hole is opened in the middle of the original soil body, and the hole size is larger than the maximum diameter of the tensiometer, and the depth of the hole is smaller than the height of the original soil body.

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