CN116815570A - Grouting construction method for expansive soil roadbed chemical agent - Google Patents

Abstract

The embodiment of the present application provides a chemical grouting construction method for an expansive soil roadbed, and relates to the field of expansive soil road modification. It includes step A, measuring the free expansion rate of the soil stabilizer and polypropylene fiber in a dry environment; step B, mixing the soil stabilizer and polypropylene fiber with the expansive soil respectively and then conducting a water stability test and unconfined compressive strength. Test; step C, determine the optimal dilution ratio of soil stabilizer alone and the optimal fiber content of polypropylene fiber alone based on the measured free expansion rate and analysis of the test results. This method can effectively improve the strength of the composite-improved expansive soil. Unconfined compressive strength, and the strength attenuation rate is suppressed, and the expansion rate of fine and microscopic cracks in the expansive soil is effectively controlled. The improved expansive soil can ensure the stability of the roadbed and the smoothness of the road surface for a long time. In order to achieve the purpose of safe and comfortable driving, a series of engineering problems caused by the expanded soil roadbed must be solved.

Description

Chemical grouting construction method for expansive soil roadbed

Technical field

This application relates to the technical field of expansive soil road modification, specifically to a chemical agent grouting construction method for expansive soil roadbed.

Background technique

Expansive soil is also called "expansive soil". It is a clay soil that expands violently after being immersed in water and shrinks significantly after losing water. Because the soil contains more clay minerals such as montmorillonite and illite, it is very hydrophilic. powerful. When the natural moisture content is high, the expansion amount and expansion force after water immersion are small, but the shrinkage amount and shrinkage force after water loss are large; when the natural void ratio is larger, the expansion amount and expansion force are smaller, and the shrinkage The volume and contraction force are larger. This type of soil can cause serious harm to buildings, but in its natural state it generally has high strength and low compressibility, and can easily be mistaken for a better foundation.

When using expansive soil to make a roadbed, anti-seepage and drainage measures should be taken on the surface. The foundation load and foundation depth can also be appropriately increased, the rigidity of the building can be increased, and settlement joints can be installed; or the expansive soil within the bearing layer can be excavated. , backfill with sand or other non-expansive soil;

The clay component of expansive soil is mainly composed of strongly hydrophilic minerals and has significant expansion and contraction properties. The soil has the properties of swelling when absorbing water, shrinking when losing water, and deforming back and forth. Its destructive effect on the roadbed cannot be underestimated, and the damage caused is difficult to repair.

Contents of the invention

This application aims to solve at least one of the technical problems existing in the prior art. To this end, this application proposes a construction method of chemical agent grouting for expansive soil roadbed, including the construction method of chemical agent grouting for expansive soil roadbed including:

Step A, measure the free expansion rate of the soil stabilizer and polypropylene fiber in a dry environment;

Step B: Mix the soil stabilizer and polypropylene fiber with the expansive soil respectively and then conduct a water stability test and an unconfined compressive strength test;

Step C, determine the optimal dilution ratio of soil stabilizer alone and the optimal fiber content of polypropylene fiber alone based on the measured free expansion rate and test result analysis;

Step D: Mix the determined dosage of soil stabilizer and polypropylene fiber with the expansive soil according to the predetermined dosage. Change the test environment to a humid environment and test again to determine the impact of dry-wet cycle conditions on the test results;

Step F: Analyze the effect of soil stabilizer-polypropylene fiber composite improvement on expansive soil based on macroscopic mechanical strength tests and observation of mesoscopic cracks and micropores;

In step G, after obtaining the analytical values, mix a large batch of soil stabilizer and polypropylene fiber according to the analytical values, and then inject them into the expanded soil used to make the roadbed in proportion.

According to the chemical agent grouting construction method of expansive soil roadbed according to the embodiment of the present application, in step C, the optimal dilution ratio (volume ratio) of soil stabilizer-modified expansive soil is 1:150, and the optimal fiber mixing ratio of polypropylene fiber is The quantity (mass ratio) is 1:500.

According to the chemical grouting construction method of expansive soil subgrade according to the embodiment of the present application, in step G, when using the improved expansive soil to lay the slope subgrade, it is necessary to first determine the cohesion of the expansive soil, which is the main factor in high slope stability ( C value) and internal friction angle (Φ value) on the stability of the slope subgrade. According to the relationship between the cohesion of the expansive soil (C value) and the internal friction angle (Φ value) on the stability of the slope subgrade, the grouting method is selected. When installing, unloading trough, short foot wall or high foot wall should be installed.

According to the chemical agent grouting construction method of expansive soil roadbed according to the embodiment of the present application, when determining the optimal dilution ratio of soil stabilizer alone and the optimal fiber content of polypropylene fiber alone in step D, humidification is simulated based on thermal expansion comparison Principle of expansion, test the differential expansion between horizontal and vertical directions, derive the stress-strain equation of soil humidification expansion, and use the unloaded expansion rate test finite element model to verify the parameters; establish the ABAQUS finite element strength reduction model, using the normal Cross-test range analysis method was used to study the effect and sensitivity of factors affecting slope stability under conditions of changing moisture content.

According to the chemical grouting construction method of expansive soil subgrade according to the embodiment of the present application, in step G, when using the improved expansive soil to lay the slope subgrade, it is necessary to additionally measure the impact of rainfall, temperature, air humidity, wind and solar radiation on the slope. stability, and analyze the correlation effects between soil cracks, surface vegetation and soil-atmosphere interaction.

According to the chemical grouting construction method of the expansive soil roadbed in the embodiment of the present application, in step G, when using the improved expansive soil to lay the slope roadbed, anti-slide piles and anchors are installed in the expansive soil roadbed.

According to the chemical agent grouting construction method of expansive soil roadbed according to the embodiment of the present application, in step C, according to the calculation principle of the strip method, the expansion force is considered in the limit equilibrium condition, and in the numerical model, the expansion force in the humidity field is equivalent For the water pressure, the safety of the expansive soil foundation pit is calculated, and after the simulation experiment, a quantitative function curve diagram of the rainfall time-the safety factor of the subgrade foundation pit is made.

According to the chemical agent grouting construction method of expansive soil roadbed according to the embodiment of the present application, in step C, the expansive soil is compacted based on the water and soil characteristic curve and compaction curve constructed based on suction, saturation, average effective stress, modified suction, and void ratio. Conduct experiments on the changes in suction and volume, and create function charts based on the experimental results.

According to the chemical agent grouting construction method of expansive soil roadbed according to the embodiment of the present application, in step C, the effects of different dry-wet cycle times and different confining pressures on the stress-strain and shear strength of the expansive soil are analyzed and tested to determine and explore rainfall -The influence of evaporation on the strength properties of expansive soil subgrade.

According to the chemical grouting construction method of expansive soil roadbed according to the embodiment of the present application, on the basis of step C, the deformation and failure mechanism of the expansive soil slope caused by rainfall infiltration was added to study the length and spacing of different vertical planting reinforcement belts. Deformation and failure characteristics of expansive soil when making slopes under other influencing factors.

Beneficial effects of this application:

1. This method uses polypropylene fiber and soil stabilizer to work together, which can effectively improve the unconfined compressive strength of composite-improved expansive soil, and the strength attenuation rate is suppressed, and the expansion rate of fine and microscopic cracks in the expansive soil is effectively controlled. , which can provide certain help for the application of soil stabilizer and polypropylene fiber composite improved expansive soil in slope engineering.

2. This method adds expanded anchors + supporting piles when filling the roadbed after making modified expansive soil, which has good applicability to foundation pit projects in expansive soil areas and can provide certain foundation pit support design for similar projects. s help.

3. This method provides sufficient experiments and tests on the expanded soil before and after modification in three environments (dry environment, humid environment, and dry-wet cycle environment). Finally, the chemical properties of high-quality polypropylene fiber and soil stabilizer can be obtained. The filling ratio of the agent can be adjusted to form a better quality modified expansive soil.

4. This device breaks through the multi-field information monitoring and landslide disaster early warning technology of expansive soil slopes, develops a "surface-shallow-deep" integrated expansive soil slope toughness ecological protection technology, and forms an expansive soil slope protection project. Health diagnosis methods and rapid repair technologies have significant social, economic and environmental benefits and broad application prospects.

Summary: The soil stabilizer in this method can effectively reduce the free expansion of expansive soil and enhance the water stability of expansive soil. The optimal dilution ratio (volume ratio) of modified expansive soil is 1:150; polypropylene fiber reinforcement It can effectively improve the unconfined compressive strength of expansive soil, and the optimal fiber content is 0.2% (mass ratio); polypropylene fiber and soil stabilizer work together to effectively improve the unconfined compressive strength of expanded soil after composite improvement. The compressive strength is limited, and the strength attenuation rate is suppressed, and the expansion rate of fine and microscopic cracks in the expansive soil is effectively controlled. The improved expansive soil can ensure the stability of the roadbed and the smoothness of the road surface for a long time, while also ensuring the stability of the roadbed and the smoothness of the road surface. To achieve safe and comfortable driving, a series of engineering problems caused by expansive soil roadbed must be solved.

Description of the drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, therefore This should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without exerting creative efforts.

Figure 1 is a schematic diagram of the work flow of the present invention;

Figure 2 is a schematic flow chart for determining the depth of a foundation pit according to the present invention;

Figure 3 is a schematic cross-sectional structural diagram of adding anchor piles and pile support to the modified expansive soil slope roadbed in the present invention;

Figure 4 is a schematic diagram of the quantitative function curve relationship between rainfall time and the safety factor of the expansive soil roadbed pit in the present invention;

Figure 5 is a schematic diagram of the quantitative function curve relationship between the soil compaction coefficient and the water content of the modified expansive soil in the present invention;

Figure 6 is a schematic diagram of the quantitative function curve relationship between soil resilience coefficient and saturation degree of modified expansive soil in the present invention.

Detailed ways

The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application.

In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments It is a part of the implementation of this application, but not all the implementation. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this application.

Example 1,

The chemical grouting construction method and production method of the expansive soil roadbed according to the embodiment of the present application will be described below with reference to the accompanying drawings.

As shown in Figures 1 to 6, according to the construction method of chemical agent grouting for expansive soil roadbed according to the embodiment of the present application, the construction method of chemical agent grouting for expansive soil roadbed includes:

Step A, measure the free expansion rate of the soil stabilizer and polypropylene fiber in a dry environment;

Step B: Mix the soil stabilizer and polypropylene fiber with the expansive soil respectively and then conduct a water stability test and an unconfined compressive strength test;

Step C, determine the optimal dilution ratio of soil stabilizer alone and the optimal fiber content of polypropylene fiber alone based on the measured free expansion rate and test result analysis;

Step D: Mix the determined dosage of soil stabilizer and polypropylene fiber with the expansive soil according to the predetermined dosage. Change the test environment to a humid environment and test again to determine the impact of dry-wet cycle conditions on the test results;

Step F: Analyze the effect of soil stabilizer-polypropylene fiber composite improvement on expansive soil based on macroscopic mechanical strength tests and observation of mesoscopic cracks and micropores;

In step G, after obtaining the analytical values, mix a large batch of soil stabilizer and polypropylene fiber according to the analytical values, and then inject them into the expanded soil used to make the roadbed in proportion.

According to some embodiments of the present application, in step C, the optimal dilution ratio (volume ratio) of soil stabilizer modified expansive soil is 1:150, and the optimal fiber content (mass ratio) of polypropylene fiber is 1: 500.

According to some embodiments of the present application, in step G, when using improved expansive soil to lay the slope subgrade, it is necessary to first determine the cohesion (C value) and internal friction angle ( Φ value) on the stability of the slope subgrade. According to the influence of the cohesion of the expansive soil (C value) and the internal friction angle (Φ value) on the stability of the slope subgrade, it is selected to add unloading grooves and short feet during grouting. Wall or stilt wall.

According to some embodiments of the present application, when determining the optimal dilution ratio of soil stabilizer alone and the optimal fiber content of polypropylene fiber alone in step D, based on the principle of thermal expansion analogous humidification expansion, test horizontal and vertical Differential expansion between soils, deducing the stress-strain equation of soil humidification and expansion, using the unloaded expansion rate test finite element model for parameter verification; establishing an ABAQUS finite element strength reduction model, using the orthogonal test range analysis method to study Effect and sensitivity of factors affecting slope stability under changing moisture content.

According to some embodiments of the present application, in step G, when using improved expansive soil to lay the slope subgrade, it is necessary to additionally measure the effects of rainfall, temperature, air humidity, wind and solar radiation on the stability of the slope, and analyze the soil The correlation effect between body cracks, surface vegetation and soil-atmosphere interaction.

According to some embodiments of the present application, in step G, when the improved expansive soil is used to lay the slope subgrade, anti-slide piles and anchor rods are installed in the expanded soil subgrade.

According to some embodiments of the present application, in step C, according to the calculation principle of the strip method, the expansion force is considered in the limit equilibrium condition. In the numerical model, the expansion force in the humidity field is equivalent to water pressure, and the expansion soil foundation is calculated. The safety of the pit, and after simulation experiments, a quantitative function curve diagram of rainfall time-subgrade pit safety factor was made.

According to some embodiments of the present application, in step C, experiments are conducted on changes in suction and volume in compacted expansive soil based on water and soil characteristic curves and compaction curves constructed by suction, saturation, mean effective stress, modified suction, and void ratio. , and create a function diagram based on the experimental results.

According to some embodiments of the present application, in step C, the effects of different dry-wet cycles and different confining pressures on the stress-strain and shear strength of the expansive soil are analyzed and tested to determine the impact of rainfall-evaporation on the strength of the expansive soil roadbed. influence of characteristics.

According to some embodiments of the present application, on the basis of step C, the deformation and failure mechanism of the expansive soil slope caused by rainfall infiltration is added to study the edge construction of the expansive soil under different influencing factors such as the length of the vertical reinforcement belt and the setting spacing. Deformation and failure characteristics of slope.

This invention conducts numerical analysis on the slope of the expansive soil foundation pit using the limit equilibrium method, and studies its parameter sensitivity, crack influence law and support design effect based on the slope safety factor and concludes:

(1) Through a series of sensitivity analyzes of various parameters of the expansive soil layer and foundation pit slopes, it is shown that the cohesion (C value) of the expansive soil, the main factor in the stability of high slopes, has a greater impact on stability. The internal friction angle (Φ value) should be large.

(2) Analysis of the impact of tensile cracks shows that when cracks are generated at different positions on the top of the slope and develop downward, the impact on the overall stability of the slope will change from no impact to increased impact to a stable impact stage, in which the initial impact depth can be used as the crack The basic value for early warning, and the stabilizing influence depth can be used as a reference value for the most unfavorable depth for crack development;

(3) Comparative analysis of support effects shows that, when other conditions are met, the design of foot-locking support at the bottom of the slope is the most economical way. The most effective area of the support reaction force is the area 1/3 of the slope height from the toe of the slope. The 1/3 slope height area at the top of the slope is not recommended as the design scope of the support resultant force;

(4) The analysis of shallow foundation pits (<5m) shows that it should be supported by anchoring and spraying combined with stress relief grooves and short footing walls (the height of the footing walls is not more than 0.5m). The anchor rods in the clay layer ( Soil nails) are only considered for processing and are not suitable for grouting;

(5) Application analysis of medium-deep foundation pits (5-10m) shows that when the thickness of the clay is no more than 5.0mm and the clay layer is at the lower part of the pit wall, the support method should be to use anchor spraying combined with unloading grooves and elevated foot walls (foot walls). The wall height is within the range of 0.5m to 1.0m) for support. The anchor rods (soil nails) in the clay layer are only considered to be processed with barbs, and grouting is not suitable. If the clay layer is in the upper part of the pit wall, the support method Row piles and soil support between piles should be used;

(6) Application analysis of deep foundation pits (>10m) shows that it is more suitable to use anchor piles and soil support between piles for support.

By analyzing the correlation effects between soil cracks, surface vegetation and soil-atmosphere interaction, it can be concluded that:

(1) Rainfall causes slope instability and damage in various ways, including rainwater infiltration directly causing slope instability and sliding, rainfall erosion destroying the slope surface, and rainfall-drought cycles causing expansion and contraction deformation of soil slopes;

(2) Under rainfall conditions, the degree of damage to soil slopes is controlled by both the rainfall threshold and soil penetration characteristics;

(3) Rising temperature accelerates the process of soil evaporation, shrinkage and cracking. High temperature environment has adverse effects on the stability of frozen soil slopes;

(4) The three factors of high wind speed, low air humidity and strong solar radiation increase the evaporation rate of the soil and indirectly enhance the stability of the soil slope;

(5) The cracks formed by cracks in the soil become new channels for moisture exchange between the soil and the atmosphere. Cracks increase the evaporation area of the soil and increase the evaporation rate of the soil. At the same time, cracks provide priority paths for rainfall infiltration, allowing rainfall to penetrate faster and deeper into the slope, reducing the stability of the slope;

(6) Plants release the water absorbed by their roots into the atmosphere through the transpiration of their leaves, reducing the soil moisture content. Plant roots increase the water-holding capacity of the soil and reduce the permeability of the soil. At the same time, the root system reinforces the soil in the form of reinforcement, improving the stability of the slope.

When using improved expansive soil to lay slope roadbed and establish slope protection, according to the instability characteristics of expansive soil slopes, the instability and sliding of expansive soil slopes are divided into shallow fissure controlled landslides and deep structural plane controlled landslides. For two types of expansive soil landslides, a safety evaluation method for expansive soil slopes was proposed; the prevention and control technologies for expansive soil slopes were divided into three categories: "isolation" technology, "support" technology and "reinforcement" technology (referred to as "reinforcement" technology). "Separate", "block", "solid"). The "separation" technology includes non-expandable clay cover, geowoven bag, reinforced turn-up and anti-drainage structural layer, and the "retaining" technology mainly includes various types of retaining walls, such as pile board walls and geowoven bag retaining walls. etc., the reinforcement "reinforcement" technology mainly includes anti-slide piles, anchor rods, etc.; standardized design methods for geowoven bags, reinforced turn-backs, and pile sheet wall prevention and control technologies were proposed, and geowoven bags, reinforced turn-ups, and anti-slip wall prevention technologies were completed. The application demonstration project of drainage structure layer and pile board wall uses on-site fully automatic real-time monitoring technology to verify the protective effect of expansive soil slopes.

And when the initial moisture content is low, the decrease in soil strength has the most significant impact on slope stability, followed by the expansion effect, and the impact of soil weight gain is relatively small. As the initial moisture content of the soil increases, the expansion effect, soil The influence of body weight gain is weakened; when the initial moisture content of the soil is low, the stability safety factor calculated by considering the differential expansion of the soil horizontally and vertically is 0.11 to 0.13 lower than the traditional isotropic expansion assumption. As , the influence of differential expansion decreases.

Based on the dynamic triaxial test results of the modified expansive soil reshaped under dry-wet cycles, the dynamic characteristics of the expansive soil were analyzed from the changing relationship between dynamic stress, dynamic elastic modulus, damping ratio and elastic-plastic deformation. The results show that: under different numbers of dry-wet cycles, the dynamic elastic modulus decreases with the increase of dynamic strain; the exponential decay model is used to determine the maximum dynamic elastic modulus under different numbers of dry-wet cycles, and the first time The wet and dry cycle has a significant impact on the maximum dynamic elastic modulus; the damping ratio increases with the increase of dry and wet cycles, and gradually becomes gentle with the increase of dynamic strain; the elastic deformation increases linearly with the dynamic stress amplitude. And the dry-wet cycle has an enhanced effect on elastic deformation. There are two types of changes in elastic deformation with the increase in the number of vibrations: when the vibration is stable, the elastic deformation tends to be stable with the increase in the number of vibrations; when the vibration is damaged, the elastic deformation is rapidly destroyed in the early stage of vibration.

As a flexible reinforcement and water-holding material, vertical reinforcement strips on the expansive soil slope roadbed can effectively reduce the water fluctuations and expansion and contraction deformation of the expansive soil slope, and improve the stability of the expansive soil slope; planting reinforcement The smaller the spacing, the better the vertical reinforcement strips inhibit the expansion deformation of the expansive soil slope. The water-holding effect of the vertical reinforcement strips can also provide an important guarantee for the harmonious coexistence between expansive soil, vegetation and rainfall.

The above are only examples of the present application and are not intended to limit the scope of protection of the present application. For those skilled in the art, the present application may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this application shall be included in the protection scope of this application. It should be noted that similar reference numerals and letters represent similar items in the following figures, therefore, once an item is defined in one figure, it does not need further definition and explanation in subsequent figures.

The above are only specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application. should be covered by the protection scope of this application. Therefore, the protection scope of this application should be determined by the protection scope of the claims.

Claims (10)

1. The construction method for grouting the expansive soil roadbed chemical agent is characterized by comprising the following steps of:

step A, measuring the free expansion rate of a soil stabilizer and polypropylene fibers in a dry environment;

step B, respectively mixing the soil stabilizer and the polypropylene fibers with expansive soil, and then carrying out a water stability test and an unconfined compressive strength test;

step C, analyzing and determining the optimal dilution ratio of the single-doped soil stabilizer and the optimal fiber doping amount of the single-doped polypropylene fiber according to the measured free expansion rate and the test result;

step D, mixing the soil stabilizer and the polypropylene fiber with the determined mixing amount with expansive soil according to the predetermined mixing amount, changing the testing environment into a wet environment, testing again, and determining the influence on the testing result under the dry-wet circulation condition;

step F, analyzing the effect of improving the expansive soil by compounding the soil stabilizer and the polypropylene fiber based on macroscopic mechanical strength test and microscopic crack and microscopic pore observation;

and G, after the analysis value is obtained, mixing a large amount of soil stabilizer and polypropylene fibers according to the analysis value, and then injecting the mixture into the expansive soil for preparing the roadbed according to the proportion.

2. The method of grouting construction for expansive soil subgrade chemical agent according to claim 1, characterized in that in step C, the optimal dilution ratio (volume ratio) of the soil stabilizer modified expansive soil is 1:150, and the optimal fiber blending amount (mass ratio) of the polypropylene fiber is 1:500.

3. The method according to claim 1, wherein in the step G, when the slope subgrade is laid with the improved expansive soil, the influence of the cohesion (C value) and the internal friction angle (Φ value) of the expansive soil on the stability of the slope subgrade is measured, and the loading/unloading groove, the low-foot wall or the high-foot wall is selected according to the influence relationship of the cohesion (C value) and the internal friction angle (Φ value) of the expansive soil on the stability of the slope subgrade.

4. The construction method of grouting of expansive soil subgrade chemical agent according to claim 1, characterized in that when the optimal dilution ratio of single-doped soil stabilizer and the optimal fiber doping amount of single-doped polypropylene fiber are measured in the step D, the differential expansibility between horizontal and vertical is tested based on the thermal expansion comparison humidifying expansion principle, the stress-strain equation of soil humidifying expansion is deduced, and the parameter verification is carried out by using a non-load expansion rate test finite element model; and (3) establishing an ABAQUS finite element strength reduction model, and researching the effect and sensitivity of the slope stability influence factors under the condition of water content change by adopting an orthogonal test range analysis method.

5. A method of grouting construction using expansive soil subgrade chemical agent according to claim 3, wherein in step G, when the improved expansive soil is used to lay the slope subgrade, the influence of rainfall, air temperature, air humidity, wind and solar radiation on slope stability is additionally measured, and the correlation effect among soil cracks, surface vegetation and soil-atmosphere interaction is analyzed.

6. The method for grouting construction of expansive soil subgrade chemical agent according to claim 3, wherein in the step G, when the improved expansive soil is used for paving the slope subgrade, the anti-slip piles and the anchor rods are additionally arranged in the expansive soil subgrade.

7. The construction method of chemical grouting for expansive soil subgrade according to claim 1, wherein in the step C, the expansive force is considered in the limit balance condition according to the principle of calculation by the strip division method, the expansive force in the humidity field is equivalent to the water pressure in the numerical model, the safety of the expansive soil foundation pit is calculated, and a quantitative function curve relation graph plate of rainfall time and the safety coefficient of the subgrade foundation pit is made according to the simulation experiment before and after the expansive soil subgrade is modified.

8. The method according to claim 1, wherein in the step C, the suction force and volume change in the compacted expansive soil is tested based on the suction force, saturation, average effective stress, corrected suction force, and pore ratio, and the soil-water characteristic curve and the compaction curve constructed, and a function chart is prepared according to the test result.

9. The construction method of the expansive soil roadbed chemical agent grouting according to claim 8, wherein in the step C, the influence of different dry and wet cycle times and different confining pressures on the stress-strain and the shear strength of the expansive soil is analyzed and tested, and the influence relation of rainfall-evaporation effect on the strength characteristics of the expansive soil roadbed is determined.

10. The construction method of grouting chemical agent for expansive soil roadbed according to claim 7, wherein on the basis of the step C, the deformation and damage characteristics of expansive soil when preparing the slope under the influence factors of different vertical reinforcement belt lengths, set intervals and the like are researched by adding the expansive soil slope deformation and damage mechanism caused by rainfall infiltration.