Method for measuring lateral expansive force of expansive soil

Abstract

The invention discloses a method for measuring lateral expansive force of expansive soil. The method comprises the following steps: manufacturing a plurality of groups of expansive soil test pieces with the same dry density and initial water content; the atmospheric influence depth is determined, and the overburden pressure of the soil body is determined according to the point positions where the lateral expansive force needs to be calculated in the atmospheric influence depth after the retaining structure is supported; a plurality of overburden pressure lateral confinement loaded expansion rate tests are conducted according to a standard method, and a relational expression among the water content increment, the overburden pressure and the loaded expansion rate is established; by improving a K0 consolidation test, the loaded expansion rate and the lateral expansion force of the soil body in the humidifying process under the action of overburden pressure are measured; substituting the result of the improved K0 consolidation test into the relational expression obtained by the lateral confinement load expansion rate test, and calculating to obtain the water content increment corresponding to the load expansion rate in the soil body humidifying process of the improved K0 consolidation test; and fitting to obtain a relational expression among the lateral expansive force, the overburden pressure and the water content increment. According to the method, the lateral expansion force at different depths behind the rigid retaining structure can be calculated.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering testing, and in particular to a method for measuring the lateral expansion force of expansive soil. Background Art

[0002] Retaining walls and anti-slide piles are commonly used retaining structures in highway and railway projects in expansive soil areas. In addition to bearing soil pressure, these structures also bear lateral expansion forces caused by water absorption and humidification of soil in the atmospheric influence depth under rainfall conditions. However, the current design specifications do not consider the lateral expansion forces of soil, nor do they provide a method for determining lateral expansion forces. As a result, the design of these retaining structures in expansive soil areas only considers soil pressure, while ignoring the lateral expansion forces caused by rainfall infiltration, especially the lateral expansion forces caused by rainwater infiltration within the atmospheric influence depth range. This makes the design of these retaining structures, especially those with limited sites and the horizontal direction of the retaining structures not allowed to deform (or displace), risky. In the rainy season, the anti-slide stability and anti-overturning stability are often insufficient, resulting in the failure of these retaining structures. Therefore, how to determine the lateral expansion forces of expansive soils within the atmospheric influence depth under different water absorption rates and different overburden pressures under rainfall conditions, and use them in the calculation of the lateral pressure of retaining structures has become a problem that geotechnical workers must consider.

[0003] At present, although some literature has reported on the measurement technology of the lateral expansion force of expansive soil, there are few studies on the measurement method of the lateral expansion force of retaining structures that are not allowed to deform in the horizontal direction. For example, 1. Chinese Patent: Calculation method of maximum lateral pressure on rigid retaining walls in expansive soil, application number: 202110960021.8, application date: 2021.08.20, Abstract: The present invention provides a calculation method for the maximum lateral pressure on rigid retaining walls in expansive soil, which provides a basis for the design of relevant retaining structures in expansive soil areas, meets actual engineering needs, and ensures the safety of retaining structures. The method comprises the following steps: ① Determine the natural moisture content w of the expansive soil at different depths behind the wall through field or indoor tests n (Z), unit %; shrinkage limit of expansive soil behind the wall w s , unit %; expansion limit of expansive soil behind the wall w e , unit %; ② Determine the vertical expansion force p generated by the expansion soil behind the wall when it is moistened from shrinkage limit to saturation under constant volume conditions through indoor tests sp, unit kPa; ③ through on-site investigation and measurement or relevant technical standards, determine the depth L of the atmospheric influence sharp layer of the expansive soil in the project area, unit m; ④ through the specific formula to determine the maximum lateral pressure at different depths of the retaining wall back in the expansive soil. 2. Chinese Patent: A strain-type lateral expansion force test device and measurement method, application number: 201810410658.8, application date: 2018.05.02, abstract: A strain-type lateral expansion force test device and measurement method; the device includes a measuring device, a data acquisition device and a loading device. The measurement method is to carry out a water immersion expansion test under no-load and no lateral strain conditions on the specimens in the same initial wet density state, and obtain the expansion limit moisture content and corresponding dry density of the specimens in the initial wet density state when the expansion is stable; by carrying out a consolidation test with step-by-step loading on the specimens with the initial wet density state of the expansion limit moisture content and its corresponding dry density, the lateral pressure coefficient K0 under different dry densities is measured, so as to separate the lateral expansion force from the lateral resultant force. The test method and device of the present invention are simple, easy to operate, reasonable in structure, and economical in cost. They solve the long-standing problem in the field of accurately evaluating the stability of expansive soil slopes after humidification and expansion, provide important design parameters for the design of engineering structures and wall back buffer layers in expansive soil areas, and are suitable for promotion and application in engineering.

[0004] Through construction design research, it was found that although the lateral pressure obtained by the technology of the above-mentioned document 1 is suitable for the situation where deformation (or displacement) is not allowed in the horizontal direction, the lateral pressure is the expansion force when the soil is fully hydrated (the water content increment is the largest) under different overburden pressure conditions. It is suitable for the design of retaining structures under conditions of abundant rainfall and no protection or insufficient protection, and is often too conservative; because in the K0 consolidation test, the specimen is covered with a rubber sleeve and fixed in a box, and the measurement of water absorption during the soil wetting process requires frequent disassembly of the instrument. There is a possibility that the specimen cannot be installed after disassembly. Therefore, it is also difficult to accurately obtain the lateral pressure under different water absorption conditions (i.e., the water absorption process). The measurement method of the above-mentioned document 2 is to conduct a immersion expansion test under no-load and no lateral strain conditions on the specimens in the same initial wet density state, and obtain the expansion limit moisture content and corresponding dry density of the specimens in the initial wet density state when the expansion is stable; by conducting a consolidation test with step-by-step loading on the specimens with the expansion limit moisture content and its corresponding dry density in the initial wet density state, the lateral pressure coefficient K0 under different dry densities is measured, and the lateral expansion force is separated from the lateral resultant force. This method is suitable for determining the lateral expansion force with allowable deformation and non-allowable deformation in the horizontal direction. The result is the lateral expansion force when the soil absorbs water fully (the moisture content increment is the largest) under the condition of no overburden pressure and allowable (or non-allowable) lateral deformation. If the expansion force under different water absorption rates is to be obtained, the specimens need to be taken out continuously during the test process for mass measurement and calculation of the water absorption rate. Since the strength of the expansive soil specimens decreases after absorbing water, frequent removal and installation can easily lead to specimen damage, and the lateral expansion force under different water absorption rates cannot be accurately obtained.

[0005] In summary, the current lateral expansion force measurement methods all have the disadvantage of not being able to accurately determine the lateral expansion force under different water absorption conditions. Therefore, a method for measuring the lateral expansion force under different water absorption rates and different overburden pressures is urgently needed through a simple test. Summary of the invention

[0006] The purpose of the present invention is to address the problems existing in the prior art and to provide a method for determining the lateral expansion force of expansive soil under different water absorption conditions within the atmospheric influence depth range behind a rigid retaining structure that does not allow deformation (or displacement) in the horizontal direction. The method can calculate the lateral expansion force at different depths behind the rigid retaining structure.

[0007] The present invention is achieved by adopting the following technical solutions: A method for measuring the lateral expansion force of expansive soil comprises the following steps: S1. Take soil on site for wet heavy compaction test to measure the maximum dry density and optimum moisture content of fill, so as to determine the dry density and initial moisture content w0 of the specimen, and make multiple parallel specimens.

[0008] S2. Determine the atmospheric influence depth of expansive soil in the project area through on-site investigation and measurement or relevant technical standards, so as to determine the overburden pressure P of soil at different depths within the atmospheric influence depth behind the retaining structure.

[0009] S3. For the test piece made by S1, use the overburden pressure P determined by S2, and carry out multiple overburden pressure limit load expansion rate tests according to the standard method: apply the required overburden pressure P once, and after the compression is stable, fill the instrument with water, and always keep the water level 5mm above the top surface of the soil sample. After immersion in water, record the dial indicator reading once every 2 hours until the difference between the two readings does not exceed 0.01mm, and calculate the load expansion rate ε, then drain the water, remove the load, take out the soil sample, wipe off the annular wall and other floating water, weigh and dry, and calculate the water content increase ΔW after expansion.

[0010] S4. According to S3, the relationship between the water content increment ΔW, the overburden pressure P and the load expansion rate ε is established:

[0011] Where A1 to A4 are fitting parameters, ΔW is the moisture content increment, P is the vertical pressure, and ε is the load expansion rate.

[0012] S5. For the specimens made in S1, the overburden pressure P determined in S2 is used to determine the loaded expansion rate ε and the lateral expansion force σ of the soil after wetting through the improved K0 consolidation test.

[0013] S6. Substitute the overburden pressure P of the S5 test and the randomly measured load expansion rate ε into the relationship established in S4 to obtain the moisture content increment ΔW of the specimen at that moment in the improved K0 consolidation test; at the same time, record the lateral expansion force σ when measuring the load expansion rate.

[0014] S7. Repeat steps S5 and S6 and fit the measurement results to obtain the relationship between the overburden pressure P, the water content increment ΔW and the lateral expansion force σ:

[0015] Where B1 to B4 are fitting parameters, P is the overburden pressure, ΔW is the water content increment, and σ is the lateral expansion force.

[0016] According to the "Highway Geotechnical Test Code" (JTG 3430-2020), multiple expansive soil specimens with the same dry density and initial moisture content are made; the atmospheric influence depth of the expansive soil in the project area is determined according to on-site investigation and measurement or relevant technical standards, so as to determine multiple overburden pressures (the deadweight of the upper soil at different depths); the overburden pressure of the determined soil is used to carry out confined load expansion rate tests with different overburden pressures according to the standard method, and the load expansion rate and moisture content increment are measured; according to the results of the confined load expansion rate test, the relationship between the moisture content increment, the load expansion rate and the overburden pressure is fitted; The improved K0 consolidation test was carried out with the same load expansion rate and overburden pressure respectively, and multiple groups of loaded expansion rates and corresponding lateral expansion forces were measured during the water absorption and expansion process of the specimens; the loaded expansion rate at a certain moment obtained by the improved K0 consolidation test and the overburden pressure during the test process were substituted into the fitting relationship of the lateral limit loaded expansion rate, and the water content increment corresponding to the loaded expansion rate and lateral expansion force at a certain moment could be obtained; the lateral expansion forces corresponding to different overburden pressures and water content increments of the improved K0 consolidation test were fitted, and the relationship between the lateral expansion force and the overburden pressure and water content increment could be obtained.

[0017] Specifically, the original soil ring knife specimens are made according to the sampling method in the "Highway Geotechnical Test Code" (JTG 3430-2020), or the remolded soil specimens with the same initial moisture content are prepared by back-calculating the dry density based on the compaction degree.

[0018] Further preferably, the steps of the side limit load expansion rate test described in S3 are as follows: Step 1: Apply a thin layer of Vaseline evenly on the inner wall of the ring cutter, wipe the outer wall of the ring cutter clean, and weigh the total mass of the ring cutter and soil to an accuracy of 0.01g.

[0019] Step 2: After the sample is placed in the container, put the permeable stone and cover plate on it, install the dial indicator, apply a pressure of 1kPa to make the various parts of the instrument contact; after the deformation of the sample is stable, that is, the deformation is less than 0.01mm per hour, record the vertical dial indicator reading.

[0020] Step 3: Apply the planned overburden pressure load once; when the deformation does not exceed 0.01mm per hour, the deformation is considered stable, and then pure water is injected into the container, and the water level is always kept about 5mm above the top surface of the soil, so that the sample is immersed in water from bottom to top.

[0021] Step 4: After immersion in water, record the dial indicator reading every 2 hours and calculate the load expansion rate.

[0022] Step 5: Drain the water, release the load, take out the sample, wipe off the ring wall and other floating water, weigh it, and calculate the moisture content increase after expansion.

[0023] Step 6. Place the sample into a container and repeat steps 2, 3 and 4 several times until the difference between two readings every 2 hours does not exceed 0.01 mm.

[0024] Step 7: Drain the water, release the load, take out the sample, wipe off the ring wall and other floating water, weigh, dry, and calculate the moisture content after expansion.

[0025] Further preferably, the humidification K0 consolidation test in S5 is carried out using an improved consolidation instrument provided in the literature (Wan Lianglong. Research on reducing the lateral pressure of expansive soil retaining wall by polystyrene foam (EPS) [D]. Wuhan University, 2019), comprising the following steps: Step 1: Place the pad with embedded permeable stone, permeable stone and filter paper at the bottom of the K0 consolidation instrument at one time, take out the test piece from the ring cutter and put it into the rubber sealing ring, place the filter paper, permeable stone and the pad with embedded permeable stone on the top in sequence, install the pressure cover, pressure rod and dial indicator.

[0026] Step 2: Connect the middle ring burette valve. The water pressure will form a confining pressure on the rubber sealing ring, so that the test piece is in close contact with the sealing rubber ring.

[0027] Step 3: Apply an initial pressure of 1 kPa through the lever to ensure that there is complete contact without gaps between the test piece and the instrument, and between the various parts of the instrument, and read the original readings of the vertical dial indicator and the lateral expansion force.

[0028] Step 4: Use the loading system to apply the proposed vertical load to the pressurized upper cover, and wait until the vertical deformation of the specimen is no more than 0.01 mm per hour, that is, the vertical dial indicator reading changes no more than 0.01 mm per hour.

[0029] Step 5. Turn on the burette switch, and water will seep from top to bottom through the upper embedded permeable stone gasket, permeable stone, and filter paper, and penetrate into the ring knife specimen for humidification. Record the dial indicator reading and lateral expansion force reading every 2 to 3 hours until the dial indicator reading changes by no more than 0.01 mm within 2 hours. Step 6. After determining that the deformation is stable, unload, carefully take out the sample, weigh it, and record the data. After drying, weigh it again and record the data, and calculate the final moisture content.

[0030] Compared with the prior art, the present method for determining the lateral expansion force of expansive soil is to calibrate the incremental moisture content of K0 consolidation under the same working conditions through a confined load expansion test, and the influence of different moisture content increments on the expansibility of expansive soil can be considered, thus overcoming the drawback that the traditional K0 consolidator cannot determine the lateral expansion force of expansive soil under different moisture content increments during the test. The relationship between the lateral expansion force and the moisture content increment and the overburden pressure is obtained through the confined load expansion rate test and the unsaturated soil K0 consolidation test, and the lateral expansion force at different depths is obtained according to the backfill depth and moisture content increment of the retaining structure, providing a simple new idea for calculating the lateral expansion force of retaining structures in expansive soil areas; it is suitable for calculating the lateral expansion force of retaining structures such as retaining walls and anti-sliding piles within the atmospheric influence depth, and has the advantages of economy, practicality, simplicity, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of retaining wall, atmospheric influence depth, and moisture content distribution gradient. DETAILED DESCRIPTION

[0032] The technical solutions in the invention are clearly and completely described below in conjunction with the embodiments. The described embodiments are only a part of the present invention, rather than all the embodiments.

[0033] Example 1 A method for measuring the lateral expansion force of expansive soil comprises the following steps: S1. Take soil on site for wet heavy compaction test to measure the maximum dry density and optimum moisture content of fill, so as to determine the dry density and initial moisture content w0 of the specimen, and make multiple parallel specimens.

[0034] S2. Determine the atmospheric influence depth of expansive soil in the project area through on-site investigation and measurement or relevant technical standards, so as to determine the overburden pressure P of soil at different depths within the atmospheric influence depth behind the retaining structure.

[0035] S3. For the test piece made by S1, use the overburden pressure P determined by S2, and carry out multiple overburden pressure limit load expansion rate tests according to the standard method: apply the required overburden pressure P once, and after the compression is stable, fill the instrument with water, and always keep the water level 5mm above the top surface of the soil sample. After immersion in water, record the dial indicator reading once every 2 hours until the difference between the two readings does not exceed 0.01mm, and calculate the load expansion rate ε, then drain the water, remove the load, take out the soil sample, wipe off the annular wall and other floating water, weigh and dry, and calculate the water content increase ΔW after expansion.

[0036] S4. According to S3, the relationship between the water content increment ΔW, the overburden pressure P and the load expansion rate ε is established:

[0037] Where A1 to A4 are fitting parameters, ΔW is the moisture content increment, P is the vertical pressure, and ε is the load expansion rate.

[0038] S5. For the specimens made in S1, the overburden pressure P determined in S2 is used to determine the loaded expansion rate ε and the lateral expansion force σ of the soil after wetting through the improved K0 consolidation test.

[0039] S6. Substitute the overburden pressure P of the S5 test and the randomly measured load expansion rate ε into the relationship established in S4 to obtain the moisture content increment ΔW of the specimen at that moment in the improved K0 consolidation test; at the same time, record the lateral expansion force σ when measuring the load expansion rate.

[0040] S7. Repeat steps S5 and S6 and fit the measurement results to obtain the relationship between the overburden pressure P, the water content increment ΔW and the lateral expansion force σ:

[0041] Where B1 to B4 are fitting parameters, P is the overburden pressure, ΔW is the water content increment, and σ is the lateral expansion force.

[0042] According to the "Highway Geotechnical Test Code" (JTG 3430-2020), multiple expansive soil specimens with the same dry density and initial moisture content are made; the atmospheric influence depth of the expansive soil in the project area is determined according to on-site investigation and measurement or relevant technical standards, so as to determine multiple overburden pressures (the deadweight of the upper soil at different depths); the overburden pressure of the determined soil is used to carry out confined load expansion rate tests with different overburden pressures according to the standard method, and the load expansion rate and moisture content increment are measured; according to the results of the confined load expansion rate test, the relationship between the moisture content increment, the load expansion rate and the overburden pressure is fitted; The improved K0 consolidation test was carried out with the same load expansion rate and overburden pressure respectively, and multiple groups of loaded expansion rates and corresponding lateral expansion forces were measured during the water absorption and expansion process of the specimens; the loaded expansion rate at a certain moment obtained by the improved K0 consolidation test and the overburden pressure during the test process were substituted into the fitting relationship of the lateral limit loaded expansion rate, and the water content increment corresponding to the loaded expansion rate and lateral expansion force at a certain moment could be obtained; the lateral expansion forces corresponding to different overburden pressures and water content increments of the improved K0 consolidation test were fitted, and the relationship between the lateral expansion force and the overburden pressure and water content increment could be obtained.

[0043] Specifically, the original soil ring knife specimens are made according to the sampling method in the "Highway Geotechnical Test Code" (JTG 3430-2020), or the remolded soil specimens with the same initial moisture content are prepared by back-calculating the dry density based on the compaction degree.

[0044] Further preferably, the steps of the side limit load expansion rate test described in S3 are as follows: Step 1: Apply a thin layer of Vaseline evenly on the inner wall of the ring cutter, wipe the outer wall of the ring cutter clean, and weigh the total mass of the ring cutter and soil to an accuracy of 0.01g.

[0045] Step 2: After the sample is placed in the container, put the permeable stone and cover plate on it, install the dial indicator, apply a pressure of 1kPa to make the various parts of the instrument contact; after the deformation of the sample is stable, that is, the deformation is less than 0.01mm per hour, record the vertical dial indicator reading.

[0046] Step 3: Apply the planned overburden pressure load once; when the deformation does not exceed 0.01mm per hour, the deformation is considered stable, and then pure water is injected into the container, and the water level is always kept about 5mm above the top surface of the soil, so that the sample is immersed in water from bottom to top.

[0047] Step 4: After immersion in water, record the dial indicator reading every 2 hours and calculate the load expansion rate.

[0048] Step 5: Drain the water, release the load, take out the sample, wipe off the ring wall and other floating water, weigh it, and calculate the moisture content increase after expansion.

[0049] Step 6. Place the sample into a container and repeat steps 2, 3 and 4 several times until the difference between two readings every 2 hours does not exceed 0.01 mm.

[0050] Step 7: Drain the water, release the load, take out the sample, wipe off the ring wall and other floating water, weigh, dry, and calculate the moisture content after expansion.

[0051] Further preferably, the humidification K0 consolidation test in S5 is carried out using an improved consolidation instrument provided in the literature (Wan Lianglong. Research on reducing the lateral pressure of expansive soil retaining wall by polystyrene foam (EPS) [D]. Wuhan University, 2019), comprising the following steps: Step 1: Place the pad with embedded permeable stone, permeable stone and filter paper at the bottom of the K0 consolidation instrument at one time, take out the test piece from the ring cutter and put it into the rubber sealing ring, place the filter paper, permeable stone and the pad with embedded permeable stone on the top in sequence, install the pressure cover, pressure rod and dial indicator.

[0052] Step 2: Connect the middle ring burette valve. The water pressure will form a confining pressure on the rubber sealing ring, so that the test piece is in close contact with the sealing rubber ring.

[0053] Step 3: Apply an initial pressure of 1 kPa through the lever to ensure that there is complete contact without gaps between the test piece and the instrument, and between the various parts of the instrument, and read the original readings of the vertical dial indicator and the lateral expansion force.

[0054] Step 4: Use the loading system to apply the proposed vertical load to the pressurized upper cover, and wait until the vertical deformation of the specimen is no more than 0.01 mm per hour, that is, the vertical dial indicator reading changes no more than 0.01 mm per hour.

[0055] Step 5. Turn on the burette switch, and water will seep from top to bottom through the upper embedded permeable stone gasket, permeable stone, and filter paper, and penetrate into the ring knife specimen for humidification. Record the dial indicator reading and lateral expansion force reading every 2 to 3 hours until the dial indicator reading changes by no more than 0.01 mm within 2 hours. Step 6. After determining that the deformation is stable, unload, carefully take out the sample, weigh it, and record the data. After drying, weigh it again and record the data, and calculate the final moisture content.

[0056] Take the expansive soil embankment of a highway in Guangxi as an example. The embankment retaining wall is gravity type, and the backfill behind the wall is expansive soil. Take the representative sample on site, dry it, crush it through a 2mm soil sieve, and configure it to the best moisture content. Stew the material for 24 hours. Select 93% compaction degree to make a dry density of 1.52×10 3 kg / m 3 The moisture content is controlled at 17.6%, and the size of the ring knife specimen is Φ61.8mm×20mm.

[0057] The atmospheric influence depth is 2.5m, and the overburden pressure is proposed to be 12.5kPa, 25kPa, 37.5kPa, and 50kPa. Through the side-confined load expansion rate test, the humidification expansion test of the above four vertical loads is carried out. The results are shown in Table 1:

[0058] From Table 1, we can get the relationship between the water content increment ΔW, the overburden pressure P and the load expansion rate ε:

[0059] Through the humidification K0 consolidation test, the load expansion rate ε, overburden pressure P and lateral expansion force σ are obtained. The results are shown in Table 2:

[0060] Substituting the relevant data in Table 2 into the formula, we can obtain the moisture content increment ΔW of ε under the vertical load P and the load expansion rate in the K0 consolidation test, and the moisture content increment ΔW, the overburden pressure P, and the lateral expansion force σ. The results are shown in Table 3:

[0061] By fitting the data in Table 3, we can obtain the relationship between the lateral expansion force, the overburden pressure and the water content increment:

[0062] Assume that the moisture content of retaining wall fill is 17.6% and the dry density is 1.52×10 3 kg / m 3 , the atmospheric influence depth is 2.5m. Under rainfall conditions, the moisture content of the fill behind the wall decreases linearly from 31.2% at the surface saturation state to 17.6% at 2.5m. The schematic diagram of the retaining wall, atmospheric influence depth, and moisture content distribution gradient is shown in Figure 1 .

[0063] The moisture content increment is calculated, and the vertical load at the sampling point is calculated based on the dry density. The lateral expansion force at different depths can be calculated according to formula (4), see Table 4.

[0064]

[0065] This method is clearly explained by the above examples, and is not limited to the scope of use described in the above examples. It can also be used for rigid support structures such as anti-slide piles and road cutting retaining walls.

[0066] The above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Any changes, modifications, additions or substitutions made by ordinary technicians in this technical field within the essential scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for measuring the lateral expansion force of expansive soil, characterized in that: The following steps are involved: S1. Take soil on site for wet heavy compaction test, measure the maximum dry density and optimum moisture content of fill, so as to determine the dry density and initial moisture content w0 of the specimen, and make multiple parallel specimens; S2. Determine the atmospheric influence depth of the expansive soil in the project area through on-site investigation and measurement or relevant technical standards, so as to determine the overburden pressure P of the soil at different depths within the atmospheric influence depth behind the retaining structure; S3. For the test piece made in S1, use the overburden pressure P determined in S2, and carry out multiple overburden pressure limit load expansion rate tests according to the standard method: apply the required overburden pressure P once, wait for the compression to stabilize, fill the instrument with water, and always keep the water surface 5mm above the top surface of the soil sample, record the reading of the dial gauge once every 2 hours after immersion, until the difference between the two readings does not exceed 0.01mm, and calculate the load expansion rate ε, then drain the water, release the load, take out the soil sample, wipe off the ring wall and other floating water, weigh, dry, and calculate the water content increment ΔW after expansion; S4. According to S3, the relationship between the water content increment ΔW, the overburden pressure P and the load expansion rate ε is established: ； Among them, A1 to A4 are fitting parameters, ΔW is the moisture content increment, P is the vertical pressure, and ε is the load expansion rate; S5. For the specimens made in S1, the overburden pressure P determined in S2 is used to determine the load expansion rate ε and lateral expansion force σ of the soil after wetting through the improved K0 consolidation test; S6. Substitute the overburden pressure P of the S5 test and the randomly measured load expansion rate ε into the relationship established in S4 to obtain the water content increment ΔW of the specimen at this moment in the improved K0 consolidation test; at the same time, record the lateral expansion force σ when measuring the load expansion rate; S7. Repeat steps S5 and S6 and fit the measurement results to obtain the relationship between the overburden pressure P, the water content increment ΔW and the lateral expansion force σ: ； Where B1 to B4 are fitting parameters, P is the overburden pressure, ΔW is the water content increment, and σ is the lateral expansion force.

2. The method for measuring the lateral expansion force of expansive soil according to claim 1, characterized in that: The procedure for the confined load expansion test described in S3 is as follows: Step 1: Apply a thin layer of vaseline evenly on the inner wall of the ring cutter, wipe the outer wall of the ring cutter clean, and weigh the total mass of the ring cutter and soil to an accuracy of 0.01g; Step 2: After the sample is placed in the container, put the permeable stone and cover plate, install the dial gauge, apply a pressure of 1kPa, and make all parts of the instrument contact; after the deformation of the sample is stable, that is, the deformation is less than 0.01mm per hour, record the vertical dial gauge reading; Step 3: Apply the proposed overburden pressure load once; when the deformation does not exceed 0.01mm per hour, the deformation is considered stable, and then pure water is injected into the container, and the water surface is always kept about 5mm above the top surface of the soil, so that the sample is immersed in water from bottom to top; Step 4: After immersion in water, record the reading of the dial gauge every 2 hours and calculate the load expansion rate; Step 5: Drain the water, release the load, take out the sample, wipe off the ring wall and other floating water, weigh it, and calculate the moisture content increment after expansion; Step 6: Place the sample in a container and repeat steps 2, 3 and 4 several times until the difference between the two readings every 2 hours does not exceed 0.01 mm; Step 7: Drain the water, release the load, take out the sample, wipe off the ring wall and other floating water, weigh, dry, and calculate the moisture content after expansion.

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