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

Abstract

The application discloses a kind of measurement methods of soil water characteristic curve of undisturbed soil under different humidity paths.The method includes taking undisturbed soil sample in cohesive soil body, and the undisturbed soil sample is divided into wetting soil sample group and humidifying soil sample group, vacuum saturation, drying treatment is carried out to wetting soil sample group and humidifying soil sample group, and the undisturbed soil sample after treatment is obtained;Then tension meter is stretched into the undisturbed soil sample to obtain the matric suction of undisturbed soil sample;Saturation of the excavated soil is measured;The matric suction of undisturbed soil sample under different humidity paths is drawn by using the saturation of soil in wetting soil sample group and humidifying soil sample group and the matric suction of undisturbed soil sample.The application uses micro tension meter to measure the change of matric suction in the process of humidifying and wetting fine-grained soil, can measure the change trend of matric suction of undisturbed soil body with water content without destroying the structure of fine-grained soil, and more truly reflects the property difference of undisturbed soil sample when it is subjected to different change processes.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of geotechnical test methods, and particularly relates to a method for measuring soil water characteristic curves of undisturbed soil under different humidity paths. BACKGROUND

[0002] Compared with saturated soil, unsaturated soil has a more extensive existence in nature. Saturation degree has a significant influence on the physical and mechanical parameters and engineering properties of soil, and it affects the strength, permeability and deformation characteristics of soil. The research on unsaturated soil plays a key role in the engineering field, and the matric suction is one of the key parameters of the mechanical properties of unsaturated soil, which is related to the stability analysis of foundation pits and slopes, the change of strength characteristics of foundation soil and the like. The mechanics of unsaturated soil 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 practice.

[0003] In the soil, the fine pores promote the water in the soil to rise like capillary tubes. Under different saturations, the interaction forms of soil, water and internal gas will change: under high saturation, it is "water-in-air" state, and under low saturation, it is "air-in-water" state, which causes the matric suction to change under different saturations. The matric suction acts on the soil in the form of ideal spherical stress, and the size of negative pressure is mainly affected by the size of the pore and the distribution of the channel. The specific surface area of sandy soil is small, the internal pore channel is large, and the matric suction is small; while the specific surface area of clay soil is large, the internal pore channel is very small, and therefore the matric suction is small. The matric suction also has a certain contribution to the strength of the soil, and to some extent, it affects the size of the internal friction angle and the cohesion. There are many models of soil water characteristic curves, such as the VG model proposed by the famous scholar Van Genuchten. At present, the test methods of matric suction of unsaturated soil include tensiometer method, pressure plate method, filter paper method and the like. Among them, the tensiometer method is based on the tension balance principle of water in the fine capillary and between soil particles, and has the characteristics of real-time, low cost, accurate results and simple application, and therefore becomes a commonly used method for measuring the matric suction of unsaturated soil. At present, the equipment of the tensiometer itself is also 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 method and operation details. At present, the relevant test specifications of unsaturated soil mechanics are still in the development stage, and basically focus on the measurement of remolded soil. The measurement of soil water characteristics of undisturbed clay soil is not simple and accurate. SUMMARY

[0004] In order to solve the problems in the background art, the purpose of the present application is to provide a method for measuring soil water characteristic curves of undisturbed soil under different humidity paths.

[0005] The technical scheme adopted by the present application comprises the following steps:

[0006] Step S1, a plurality of undisturbed soil samples are taken from the clayey soil body, the saturated water content of each undisturbed soil sample is measured, and the undisturbed soil samples are divided into two groups, namely a drying soil sample group and a wetting soil sample group, and the drying soil sample group and the wetting soil sample group are subjected to vacuum saturation and drying treatment respectively to obtain treated undisturbed soil samples;

[0007] Step S2, then the treated undisturbed soil samples in step S1 are subjected to hole digging treatment, and a saturated tensiometer is inserted into the undisturbed soil samples to obtain the matric suction of the undisturbed soil samples;

[0008] Step S3, the water content of the soil material dug out by the hole digging treatment is measured to obtain the saturation of the soil material;

[0009] Step S4, finally, the saturation of the soil samples in the drying soil sample group and the wetting soil sample group and the corresponding matric suction of the undisturbed soil samples are used to draw the soil water characteristic curve of the undisturbed soil samples under different humidity paths.

[0010] The step S1 is specifically:

[0011] Step S1.1, first, a plurality of undisturbed soil samples are taken from the clayey soil body using the cutting ring method, and the undisturbed soil samples are divided into two groups, namely a drying soil sample group and a wetting soil sample group, wherein the drying soil sample group includes a completely dried soil sample group and a partially dried soil sample group; the wetting soil sample group includes a completely wetted soil sample group and a partially wetted soil sample group;

[0012] Step S1.2, the completely dried soil sample group in the drying soil sample group is subjected to complete drying treatment: all undisturbed soil samples in the completely dried soil sample group are placed in deaerated water for vacuum saturation for more than 24 hours, after the undisturbed soil samples are completely saturated, they are taken out of the deaerated water and placed in an oven for drying at a constant temperature for different times, after drying is completed, the undisturbed soil samples are taken out, sealed with plastic film and left to stand for 24-30 hours to obtain a plurality of completely dried undisturbed soil samples with different drying times;

[0013] Step S1.3, the partially dried soil sample group in the drying soil sample group is subjected to partial drying treatment: all undisturbed soil samples in the partially dried soil sample group are respectively placed in each oven for drying at a constant temperature for different times, after drying is completed, the undisturbed soil samples are taken out, sealed with plastic film and left to stand for 24-30 hours to obtain a plurality of partially dried undisturbed soil samples with different drying times;

[0014] Step S1.4, fully wetting treatment on the fully wetted soil sample group in the wetting soil sample group: all undisturbed soil samples in the fully wetted soil sample group are placed in an oven until the undisturbed soil samples are completely dried, and then the dried undisturbed soil samples are placed in a vacuum saturation barrel to be vacuum saturated for different times, after saturation, the undisturbed soil samples are taken out, sealed with plastic film and left to stand for 24-30 hours, to obtain a plurality of fully wetted undisturbed soil samples with different saturation times;

[0015] Step S1.5, partial wetting treatment on the partially wetted soil sample group in the wetting soil sample group: all undisturbed soil samples in the partially wetted soil sample group are respectively placed in each vacuum saturation barrel to be vacuum saturated for different times, after saturation, the undisturbed soil samples are taken out, sealed with plastic film and left to stand for 24-30 hours, to obtain a plurality of partially wetted undisturbed soil samples with different saturation times.

[0016] The step S2 is specifically:

[0017] Step S2.1, first, the plastic film sealed on the surface of the undisturbed soil sample is removed, then the undisturbed soil sample and the wetted undisturbed soil sample are subjected to hole digging treatment, then the saturated tensiometer is vertically buried in the hole dug out by the hole digging treatment, and finally the soil material dug out by the hole digging treatment is used to backfill the hole, so that there is no gap between the hole and the soil body of the undisturbed soil sample / wetted undisturbed soil sample, and then the plastic film is sealed;

[0018] The undisturbed soil sample includes fully undisturbed soil sample and partially undisturbed soil sample; the wetted undisturbed soil sample includes fully wetted undisturbed soil sample and partially wetted undisturbed soil sample;

[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 matric suction value of the undisturbed soil sample; the undisturbed soil sample includes the undisturbed soil sample and the wetted undisturbed soil sample.

[0020] The step S3 is specifically: the moisture content of the soil material dug out from each undisturbed soil sample and wetted undisturbed soil sample is measured, and the saturation of different soil materials is obtained as the saturation of the corresponding undisturbed soil sample.

[0021] The step S4 is specifically: the different humidity paths are a dehumidification path and a humidification path, and the undisturbed soil samples in the dehumidification path and the humidification path correspond to a humidification soil sample group and a dehumidification soil sample group respectively. For the dehumidification soil sample group, the matric suction value of the dehumidification undisturbed soil sample is taken as the abscissa, and the saturation of the dehumidification undisturbed soil sample is taken as the ordinate, to draw the dehumidification soil water characteristic curve of the clay in the dehumidification process, wherein, according to the different dehumidification processes, the dehumidification soil water characteristic curve is divided into a complete dehumidification soil water characteristic curve and a partial dehumidification soil water characteristic curve, the abscissa and the ordinate of the complete dehumidification soil water characteristic curve are respectively the matric suction value and the saturation of the complete dehumidification undisturbed soil sample, and the abscissa and the ordinate of the partial dehumidification soil water characteristic curve are respectively the matric suction value and the saturation of the partial dehumidification undisturbed soil sample; for the humidification soil sample group, the matric suction value of the humidification undisturbed soil sample is taken as the abscissa, and the saturation of the humidification undisturbed soil sample is taken as the ordinate, to draw the humidification soil water characteristic curve of the clay in the humidification process, wherein, according to the different humidification processes, the humidification soil water characteristic curve is divided into a complete humidification soil water characteristic curve and a partial humidification soil water characteristic curve, the abscissa and the ordinate of the complete humidification soil water characteristic curve are respectively the matric suction value and the saturation of the complete humidification undisturbed soil sample, and the abscissa and the ordinate of the partial humidification soil water characteristic curve are respectively the matric suction value and the saturation of the partial humidification undisturbed soil sample.

[0022] In the step S2, the matric suction of the undisturbed soil sample is measured by using a saturated tension meter, and the saturation process of the tension meter is as follows: firstly, the porous ceramic head in the tension meter is disassembled, then the disassembled porous ceramic head is placed in air-free water for vacuum saturation for more than 24 hours, and after saturation, the tension meter is assembled in the air-free water to obtain a saturated tension meter; the better the saturation effect of the micro tension meter is, the higher the accuracy of the measured matric suction is.

[0023] The height of the undisturbed soil sample is greater than twice the length of the tension meter, so as to ensure that the tension meter can be placed in the cutting ring and not contact with the external air, and reduce the influence of the boundary effect.

[0024] In the step S2, when the undisturbed soil sample is subjected to hole digging treatment, the hole is arranged in the middle of the undisturbed soil body, and the size of the hole is slightly larger than the maximum diameter of the tension meter; the depth of the hole should be less than the height of the undisturbed soil body, so as to ensure a certain distance from the bottom of the soil body and prevent the hole from penetrating the soil body or contacting with the air.

[0025] The undisturbed soil sample is subjected to dehumidification operation and humidification operation, wherein the dehumidification operation includes complete dehumidification and partial dehumidification; and the humidification operation includes complete humidification and partial humidification.

[0026] The clay soil has small particle size and strong natural structure, and the pore distribution of the remolded sample and the undisturbed sample is quite different, which will cause the soil water characteristic curve of the two to have certain difference. The undisturbed sample is taken by the ring knife method for testing, and for the soil water characteristic curve of the dewetting process, the undisturbed sample is placed in the vacuum saturated water for 24 hours after being completely saturated, and then taken out and placed in the oven; the undisturbed soil sample (the completely dewetted undisturbed soil sample and the partially dewetted undisturbed soil sample) is dried for different time at a constant temperature. After being taken out, it is immediately sealed with plastic film and left for 24 hours. For the soil water characteristic curve of the wetting process, the undisturbed sample is first dried in the oven until it is completely dried, and then placed in the vacuum saturation barrel; the partially wetted undisturbed soil sample is directly placed in the vacuum saturation barrel; then the wetted undisturbed soil sample (the completely wetted undisturbed soil sample and the partially wetted undisturbed soil sample) is vacuum saturated for different time, and immediately sealed with plastic film after being taken out and left for 24 hours. Before testing, a smaller drilling equipment is used to drill holes on the surface of the undisturbed soil sample, and the last excavated soil is used as the sample for water content testing. Then the microtensiometer is placed, and the remaining soil is backfilled and compacted appropriately to ensure that the porous ceramic head part of the tensiometer is completely wrapped by the soil and does not contact with air, and the reading is recorded after the reading is stable.

[0027] In the general soil water characteristic curve measurement process, most of them use remolded soil for testing, and lack of the soil water characteristic curve of the undisturbed soil sample, and most of them only measure one soil water characteristic curve, i.e. the wetting curve or the dewetting curve. Since the undisturbed soil sample has structure, after being treated in different ways (wetting or dewetting), the matric suction of the undisturbed soil sample is measured, and it is found that the matric suction of the undisturbed soil sample will have a large difference when passing through different humidity paths. Therefore, by treating the undisturbed soil sample in different ways and increasing different humidity paths, the properties of the undisturbed soil sample can be better reflected.

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

[0029] 1. The present application uses a microtensiometer to measure the change of the matric suction of the undisturbed fine-grained soil in different humidity paths, and the present application can measure the change trend of the matric suction of the undisturbed soil with humidity (saturation) without destroying the undisturbed structure of the fine-grained soil, i.e. the soil water characteristic curve.

[0030] 2、The present application can obtain four soil water characteristic curves of the undisturbed soil sample through different humidity change paths, including a complete drying soil water characteristic curve, a partial drying soil water characteristic curve, a complete wetting soil water characteristic curve and a partial wetting soil water characteristic curve, which can more accurately reflect the change of the matric suction of the undisturbed soil sample when the undisturbed soil sample experiences different humidity paths, especially for the undisturbed soil sample sensitive to humidity change.

[0031] 3、The humidity change path of the undisturbed soil sample in the present application includes a drying path and a wetting path, specifically including a complete drying path and a partial drying path, and a complete wetting path and a partial wetting path, which can more accurately reflect the change of the matric suction of the undisturbed soil sample when the undisturbed soil sample experiences a drying-wetting cycle (partial drying-complete wetting-complete drying or partial wetting-complete drying-complete wetting) process.

[0032] 4、Compared with the conventional soil water characteristic curve, the four soil water characteristic curves obtained by the present application can more accurately predict the matric suction and water migration of the undisturbed soil sample when the undisturbed soil sample experiences different humidity paths, and can more accurately calculate the deformation and strength of the soil body. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 It is a schematic diagram of the test process of the clay layer of the present application.

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

[0035] The present application will be described in detail below in combination with specific implementation examples, and the following implementation examples will help the person skilled in the art to further understand the present application, but do not limit the present application in any form.

[0036] The embodiments of the present application include the following steps, as shown in Figure 1

[0037] Step S1, 28 undisturbed soil samples are taken from the same box of clay soil samples, and the undisturbed soil samples are divided into two groups, a drying group and a wetting group, wherein the drying group includes a complete drying group and a partial drying group; the wetting group includes a complete wetting group and a partial wetting group; then the undisturbed soil sample group is treated by vacuum saturation and drying to obtain the treated undisturbed soil sample:

[0038] Step S1 specifically includes:

[0039] Step S1.1, first, use a 200cm 3 ​The large ring cutter utilizes the ring cutter method to take out 28 undisturbed soil samples in the clayey soil, and divides the taken undisturbed soil samples into two groups, namely a dehumidified soil sample group (14) and a humidified soil sample group (14), wherein the dehumidified soil sample group (14) includes a completely dehumidified soil sample group (7) and a partially dehumidified soil sample group (7), and the humidified soil sample group (14) includes a completely humidified soil sample group (7) and a partially humidified soil sample group (7).

[0040] Step S1.2, completely dehumidifying the completely dehumidified soil sample group in the dehumidified soil sample group: placing all the undisturbed soil samples in the completely dehumidified soil sample group into the water-free water for vacuum saturation for more than 24 hours, after the undisturbed soil samples are completely saturated, taking them out of the water-free water and placing them into an oven for drying at a constant temperature of 105 DEG C for different time, the drying time of the 7 undisturbed soil samples in the completely dehumidified soil sample group is respectively 15 min, 30 min, 60 min, 180 min, 360 min, 600 min and 1440 min, after drying, the undisturbed soil samples are taken out and sealed with plastic film for 24 hours to obtain 7 completely dehumidified undisturbed soil samples with different drying time;

[0041] Step S1.3, partially dehumidifying the partially dehumidified soil sample group in the dehumidified soil sample group: placing all the undisturbed soil samples in the partially dehumidified soil sample group into respective ovens for drying at a constant temperature of 105 DEG C for different time, the drying time of the 7 undisturbed soil samples in the partially dehumidified soil sample group is respectively 15 min, 30 min, 60 min, 180 min, 360 min, 600 min and 1440 min, after drying, the undisturbed soil samples are taken out and sealed with plastic film for 24 hours to obtain 7 partially dehumidified undisturbed soil samples with different drying time;

[0042] Step S1.4, completely humidifying the completely humidified soil sample group in the humidified soil sample group: placing all the undisturbed soil samples in the completely humidified soil sample group into an oven until the undisturbed soil samples are completely dried, then placing the dried undisturbed soil samples into a vacuum saturation barrel for vacuum saturation for different time, the saturation time of the 7 undisturbed soil samples in the completely humidified soil sample group is respectively 30 min, 60 min, 120 min, 240 min, 480 min, 720 min and 1440 min, after saturation, the undisturbed soil samples are taken out and sealed with plastic film for 24 hours to obtain 7 completely humidified undisturbed soil samples with different saturation time;

[0043] Step S1.5, partial wetting treatment is performed on part of the wetted soil sample groups: all undisturbed soil samples in the partial wetting soil sample groups are respectively placed in each vacuum saturation barrel for different time of vacuum saturation, and the saturation time of the seven undisturbed soil samples in the partial wetting soil sample groups is respectively 30 min, 60 min, 120 min, 240 min, 480 min, 720 min and 1440 min. After saturation, the undisturbed soil samples are taken out and sealed with plastic film for 24 hours to obtain seven partial wetting undisturbed soil samples with different saturation time.

[0044] Step S2, then the undisturbed soil samples treated in step S1 are subjected to hole digging treatment, and the saturated tensiometer is inserted into the undisturbed soil sample to obtain the matric suction of the undisturbed soil sample:

[0045] Step S2.1, first, the plastic film sealed on the surface of the undisturbed soil sample is removed, then the dehumidified undisturbed soil sample and the wetted undisturbed soil sample are subjected to hole digging treatment, the diameter of the hole is controlled at about 20 mm, and the depth is controlled at about 30 mm to ensure that the tensiometer sensor part can be completely covered by the soil body, then the saturated tensiometer is vertically buried in the hole dug by the hole digging treatment, finally, the soil material dug by the hole digging treatment is used to backfill the hole to make there be no gap between the hole and the dehumidified undisturbed soil sample / wetted undisturbed soil sample, and then the plastic film is sealed.

[0046] Because the specific surface area of clay soil is large, the internal pore channel is small, and the soil water potential balance time is long, the reading stable time may be long, so after filling, a circle of plastic film is wrapped around the test soil body to prevent water from changing.

[0047] 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 matric suction value of the undisturbed soil sample; the undisturbed soil sample includes dehumidified undisturbed soil sample and wetted undisturbed soil sample, wherein the dehumidified undisturbed soil sample includes completely dehumidified undisturbed soil sample and partially dehumidified undisturbed soil sample, and the wetted undisturbed soil sample includes completely wetted undisturbed soil sample and partially wetted undisturbed soil sample.

[0048] After the dehumidified soil sample group and the wetted soil sample group are subjected to different time of drying and vacuum saturation, the obtained matric suction is shown in Table 1.

[0049] Step S3, the moisture content of the soil material dug by the hole digging treatment is measured to obtain the saturation degree of the soil material:

[0050] In the implementation, the saturation of the soil material (20g) taken from each of the undisturbed soil sample and the undisturbed soil sample is measured, and the saturation of the different soil materials is obtained as the saturation of the corresponding undisturbed soil sample. After the soil samples in the undisturbed soil sample group and the undisturbed soil sample group are dried and vacuum saturated for different times, the saturation of the taken soil material is tested, and the obtained data is shown in Table 1.

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

[0052]

[0053] In step S4, the saturation of the soil material in the undisturbed soil sample group and the undisturbed soil sample group and the matric suction of the corresponding undisturbed soil sample are used to draw the soil-water characteristic curve of the undisturbed soil sample under different humidity paths.

[0054] For the undisturbed soil sample group, the matric suction value of the undisturbed soil sample is taken as the abscissa, and the saturation of the undisturbed soil sample is taken as the ordinate, to draw the undisturbed soil-water characteristic curve of the clay soil in the undisturbed process; for the undisturbed soil sample group, the matric suction value of the undisturbed soil sample is taken as the abscissa, and the saturation of the undisturbed soil sample is taken as the ordinate, to draw the undisturbed soil-water characteristic curve of the clay soil in the undisturbed process, as shown in Figure 2

[0055] Before the test, the microtensiometer needs to be completely saturated. The structure of the clay soil is strong, and the undisturbed sample can be taken out by the cutting ring method. The soil-water characteristic curve measurement operation in the drying process is as follows: for the complete drying soil-water characteristic curve, the sample needs to be placed in the vacuum saturated water for 24 hours after being taken out; for the partial drying soil-water characteristic curve, vacuum saturation is not required. Then, the dried soil samples (complete drying soil sample and partial drying soil sample) are taken out and placed in an oven for different drying times at a constant temperature. After being taken out, the plastic film is immediately sealed and left for 24 hours. The soil-water characteristic curve measurement operation in the wetting process is as follows: for the complete wetting soil-water characteristic curve, the undisturbed soil sample needs to be placed in the oven after being taken out until it is completely dried; for the partial wetting soil-water characteristic curve, drying is not required. Then, the wetting soil samples (complete wetting soil sample and partial wetting soil sample) are vacuum saturated for different times, and the plastic film is immediately sealed after being taken out and left for 24 hours. Before the test, the undisturbed soil after drying / wetting is drilled on the surface of the clay cutting ring undisturbed sample by using a smaller drilling device, and the water content of the last taken-out soil body is taken as the standard value for the test. Then, the microtensiometer is placed, the remaining soil body is backfilled, and appropriate compaction is performed to ensure that the tensiometer sensor is completely wrapped by the soil body, and the plastic film is sealed again to prevent air contact and water evaporation. The entire process of burying the tensiometer needs to be continuously operated, and the time interval should not be too long to prevent the water content from changing too much, especially in the case of low water content.​

[0056] The undisturbed soil sample of the cohesive soil ring knife is placed in the oven after being saturated, and needs to 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 arbitrarily. Different samples with different degrees of saturation can be obtained by taking them out at different times. After the undisturbed soil sample is taken out of the oven, the surface of the soil body is immediately wrapped and sealed with plastic film, and the internal moisture is allowed to migrate to a certain extent.

[0057] The soil material closest to the porous ceramic head part of the tension meter is used as the measurement sample of the water content to prevent measurement errors caused by uneven water content. After the tension meter is placed in the predetermined position, the excavated soil is used for backfilling and compaction to ensure that the tension meter sensor is completely covered by the soil body and does not come into contact with the air. After the tension meter is buried, the soil body is again sealed 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 application, and are not limited thereto; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for part or all of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solution deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for measuring soil water characteristic curve of undisturbed soil under different humidity paths, characterized in that, The method comprises the following steps: Step S1, a plurality of undisturbed soil samples are taken from the clayey soil body, and the undisturbed soil samples are divided into two groups, namely a dehumidified soil sample group and a humidified soil sample group, and the dehumidified soil sample group and the humidified soil sample group are subjected to vacuum saturation and drying treatment to obtain treated undisturbed soil samples; The step S1 is specifically: Step S1.1, first, a plurality of undisturbed soil samples are taken from the clayey soil body using a cutting ring method, and the taken undisturbed soil samples are divided 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, the completely dehumidified soil sample group in the dehumidified soil sample group is subjected to complete dehumidification treatment: all undisturbed soil samples in the completely dehumidified soil sample group are placed in deaerated water for vacuum saturation for more than 24 hours, after the undisturbed soil samples are completely saturated, the undisturbed soil samples are taken out of the deaerated water and placed in an oven for drying at a constant temperature for different times, after drying, the undisturbed soil samples are taken out, sealed with plastic film and left to stand for 24-30 hours to obtain a plurality of completely dehumidified undisturbed soil samples with different drying times; Step S1.3, the partially dehumidified soil sample group in the dehumidified soil sample group is subjected to partial dehumidification treatment: all undisturbed soil samples in the partially dehumidified soil sample group are respectively placed in each oven for drying at a constant temperature for different times, after drying, the undisturbed soil samples are taken out, sealed with plastic film and left to stand for 24-30 hours to obtain a plurality of partially dehumidified undisturbed soil samples with different drying times; Step S1.4, the completely humidified soil sample group in the humidified soil sample group is subjected to complete humidification treatment: all undisturbed soil samples in the completely humidified soil sample group are placed in an oven until the undisturbed soil samples are completely dried, then the dried undisturbed soil samples are placed in a vacuum saturation barrel for vacuum saturation for different times, after saturation, the undisturbed soil samples are taken out, sealed with plastic film and left to stand for 24-30 hours to obtain a plurality of completely humidified undisturbed soil samples with different saturation times; Step S1.5, the partially humidified soil sample group in the humidified soil sample group is subjected to partial humidification treatment: all undisturbed soil samples in the partially humidified soil sample group are respectively placed in each vacuum saturation barrel for vacuum saturation for different times, after saturation, the undisturbed soil samples are taken out, sealed with plastic film and left to stand for 24-30 hours to obtain a plurality of partially humidified undisturbed soil samples with different saturation times; Step S2, then the treated undisturbed soil samples in step S1 are subjected to hole digging treatment, and a saturated tensiometer is inserted into the undisturbed soil samples to obtain the matric suction of the undisturbed soil samples; Step S3, the moisture content of the soil material dug out by the hole digging treatment is measured to obtain the saturation degree of the soil material; Step S4, finally, the saturation degrees of the soil samples in the dehumidified soil sample group and the humidified soil sample group, and the corresponding matric suction of the undisturbed soil samples are used to draw the soil water characteristic curve of the undisturbed soil samples under different humidity paths.

2. The method according to claim 1, wherein: The step S2 is specifically: Step S2.1, firstly, plastic film sealed on the surface of the undisturbed soil sample is removed, then the undisturbed soil sample after dehydration and the undisturbed soil sample after wetting are subjected to hole digging treatment, then the saturated tension meter is buried into the hole dug by the hole digging treatment, finally the hole is backfilled with the dug soil material, so that there is no gap between the hole and the soil body of the undisturbed soil sample, and then the plastic film is sealed; The undisturbed soil sample after dehydration includes a completely undisturbed soil sample after dehydration and a partially undisturbed soil sample after dehydration; the undisturbed soil sample after wetting includes a completely undisturbed soil sample after wetting and a partially undisturbed soil sample after wetting; Step S2.2, after the tension meter reading in the undisturbed soil sample is stable and no longer changes, the tension meter reading is obtained as the matric suction value of the undisturbed soil sample.

3. The method according to claim 1, wherein the method is characterized by: The step S3 is specifically: the water content of the soil material dug from each undisturbed soil sample after dehydration and undisturbed soil sample after wetting is measured, and the saturation of different soil materials is obtained as the saturation of the corresponding undisturbed soil sample.

4. The method according to claim 1, wherein: The step S4 is specifically: for the undisturbed soil sample group, the matric suction value of the undisturbed soil sample after dehydration is taken as the horizontal coordinate, and the saturation of the undisturbed soil sample after dehydration is taken as the vertical coordinate, to draw the undisturbed soil water characteristic curve of clay in the dehydration process; for the undisturbed soil sample group, the matric suction value of the undisturbed soil sample after wetting is taken as the horizontal coordinate, and the saturation of the undisturbed soil sample after wetting is taken as the vertical coordinate, to draw the undisturbed soil water characteristic curve of clay in the wetting process.

5. The method according to claim 1, wherein: In the step S2, the matric suction of the undisturbed soil sample is measured by using the saturated tension meter, and the saturation process of the tension meter is as follows: firstly, the porous ceramic head in the tension meter is removed, then the removed porous ceramic head is placed in air-free water for vacuum saturation for more than 24 hours, and after saturation, the tension meter is assembled in the air-free water to obtain the saturated tension meter.

6. The method according to claim 1, wherein: The height of the undisturbed soil sample is greater than twice the length of the tension meter.

7. The method according to claim 1, wherein: In the step S2, when the undisturbed soil sample is subjected to hole digging treatment, the hole is opened in the middle of the undisturbed soil body, and the size of the hole is greater than the maximum diameter of the tension meter, and the depth of the hole is less than the height of the undisturbed soil body.

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