Design method of railway subgrade structure based on comprehensive modified expanded rock soil

Abstract

The application provides a design method of a railway subgrade structure based on comprehensive modified swelling rock soil, and relates to the technical field of railway subgrade engineering. In view of the poor design precision in the prior art, the application obtains related parameters of a foundation, and determines the thickness of a chemical modification layer according to the related parameters of the foundation; designs a subgrade cross section based on line horizontal and vertical data and a topographic map; divides the foundation soil into layers according to a preset thickness according to the subgrade geometric parameters of the subgrade cross section, and determines the vertical stress parameters of each layer and the corresponding load compression swelling rates of the vertical stress parameters; calculates the subgrade swelling amount according to the load compression swelling rates, the layer thickness and the thickness of the chemical modification layer; determines the initial physical modification layer thickness based on the layer thickness; and adjusts the initial physical modification layer thickness to determine the final physical modification layer thickness corresponding to the case that the subgrade swelling amount meets a preset threshold. The application has high design precision.

Description

Technical Field

[0001] This invention relates to the field of railway subgrade engineering technology, and in particular to a design method for railway subgrade structures based on comprehensively modified expansive soil. Background Technology

[0002] As the foundational load-bearing structure of the railway track, the deformation control accuracy of the railway subgrade directly determines the operational safety, stability, and comfort of the railway line. Expansive soil is a common unfavorable foundation soil in railway subgrade engineering, exhibiting significant shrinkage and swelling characteristics. Among these, the camber deformation caused by water absorption and expansion has the most prominent impact on railway operation. Ballastless track railways have extremely low adaptability to vertical deformation; once expansive camber deformation occurs during operation, not only is remediation difficult, but maintenance costs also increase significantly. Therefore, the treatment of expansive soil foundations is a key challenge in railway subgrade structural design.

[0003] In existing technologies, the design of railway subgrade structures for expansive rock foundations mainly employs single or combined treatment methods such as replacement with non-expansive soil, drainage and waterproofing, composite foundations, pile networks, and pile-slab structures. Among these, the design method combining replacement and drainage and waterproofing is widely used. This method improves subgrade stability by increasing the thickness of the physical replacement layer. However, relying on experience to determine the thickness of the replacement layer leads to low design accuracy and makes it difficult to meet the stringent deformation control standards of high-speed railway ballastless tracks.

[0004] Therefore, developing a design method for railway subgrade structures based on comprehensively modified expansive soil is of great significance for improving the design accuracy of railway subgrade structures. Summary of the Invention

[0005] To address the issue of low design accuracy in existing technologies, this invention proposes a design method for railway subgrade structures based on comprehensively modified expansive soil and rock, specifically including the following steps:

[0006] S1. Obtain relevant foundation parameters and determine the thickness of the chemical modification layer based on the relevant foundation parameters;

[0007] S2. Based on the horizontal and vertical alignment data and topographic maps, design the roadbed cross section;

[0008] S3. Based on the roadbed geometric parameters of the roadbed cross section, the foundation soil is divided into layers according to the preset thickness, and the vertical stress parameters of each layer and the loaded compressibility expansion rate corresponding to the vertical stress parameters are determined.

[0009] S4. Calculate the subgrade expansion based on the loaded compressive expansion rate, layer thickness, and chemically modified layer thickness;

[0010] S5. Determine the initial physical modification layer thickness based on the layer thickness;

[0011] S6. Adjust the initial physical modification layer thickness to determine the final physical modification layer thickness when the roadbed expansion meets the preset threshold.

[0012] Furthermore, in S1, the foundation-related parameters include the expansibility grade, the loaded expansion rate, the loaded compressive expansion rate, and the atmospheric influence depth; the expansibility grade is determined by measuring the free expansion rate, montmorillonite content, and cation exchange capacity of the foundation soil; the loaded expansion rate and the loaded compressive expansion rate are determined by the sample compression under the original test height and preset pressure and the expansion of the sample after immersion in water in the loaded expansion rate test.

[0013] Furthermore, the thickness of the chemically modified layer is determined based on relevant foundation parameters, including: classifying the foundation soil into categories according to its expansibility level; matching the recommended thickness of the chemically modified layer for the corresponding foundation soil category with engineering experience and field test results; and, in the absence of engineering experience and field test results, setting the initial chemically modified layer thickness according to the preset thickness range corresponding to the expansibility level, and then correcting and determining the final chemically modified layer thickness after verification by field tests.

[0014] Furthermore, in step S3, based on the roadbed geometric parameters of the roadbed cross-section, the foundation soil is layered according to a preset thickness, and the vertical stress parameters of each layer and the corresponding loaded compressive expansion rate of the vertical stress parameters are determined. This includes: layering the foundation soil into equal thicknesses according to the roadbed center height and filler unit weight of the roadbed cross-section; calculating the vertical stress parameters at the center of each layer based on the roadbed surface load, filler unit weight, roadbed center height, and self-weight stress of each layer; and determining the loaded compressive expansion rate corresponding to the vertical stress parameters of each layer by using linear interpolation based on the relationship between load and loaded compressive expansion rate obtained from the loaded expansion test.

[0015] Furthermore, the formula for calculating the vertical stress parameter is as follows:

[0016] ;

[0017] in, Let be the vertical stress parameter at the center of the i-th soil layer. For roadbed surface load, For the packing density, The height of the roadbed center. Let be the unit weight of the i-th layer of foundation soil. The preset thickness for the soil layers in the foundation.

[0018] Furthermore, in step S4, the subgrade expansion is calculated based on the loaded compressive expansion rate, layer thickness, and chemically modified layer thickness, including: delineating the modification treatment range of the foundation soil based on the chemically modified layer thickness, determining the modification coefficient and deformation transfer coefficient corresponding to each layer; calculating the loaded compressive expansion of each layer by combining the loaded compressive expansion rate, layer thickness, modification coefficient, and deformation transfer coefficient of each layer; and summing the loaded compressive expansion of all layers to obtain the subgrade expansion.

[0019] Furthermore, the formula for calculating the loaded compressive expansion of each layer is as follows:

[0020] ;

[0021] in, The compressed expansion under load is the amount of expansion of each layer. The modification coefficient is... The deformation transfer coefficient, Let be the compressive expansion rate of the i-th soil layer under load.

[0022] Furthermore, in step S6, adjusting the initial physical modification layer thickness to determine the final physical modification layer thickness corresponding to the subgrade expansion amount meeting a preset threshold includes: comparing the subgrade expansion amount with a preset threshold; when the subgrade expansion amount is less than or equal to the preset threshold, using the initial physical modification layer thickness as a candidate physical modification layer thickness; when the subgrade expansion amount is greater than the preset threshold, adjusting the initial physical modification layer thickness, recalculating the subgrade expansion amount based on the adjusted initial physical modification layer thickness, and comparing the subgrade expansion amount with the preset threshold until the subgrade expansion amount is less than or equal to the preset threshold; determining the candidate physical modification layer thickness corresponding to the subgrade expansion amount meeting the preset threshold; determining the structural physical modification layer thickness according to railway grade standards; and taking the maximum value between the candidate physical modification layer thickness and the structural physical modification layer thickness as the final physical modification layer thickness.

[0023] Furthermore, the preset threshold is a roadbed arch deformation control value determined according to railway grade standards and track type.

[0024] Furthermore, after determining the final thickness of the physical modification layer, the following steps are also included: designing a drainage system based on relevant foundation parameters, relevant roadbed cross-sectional parameters, the thickness of the physical modification layer, and the thickness of the chemical modification layer; the drainage system includes a waterproof sealing layer on the roadbed surface, a waterproof layer on the bottom surface of the physical modification layer, surface drainage ditches, side ditches, and underground seepage blind ditches.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] This invention acquires relevant foundation parameters and determines the thickness of the chemically modified layer based on these parameters. It designs the roadbed cross-section based on longitudinal and horizontal alignment data and topographic maps. According to the roadbed geometric parameters of the cross-section, the foundation soil is layered according to a preset thickness, and the vertical stress parameters and corresponding compressive expansion rates of each layer are determined. The roadbed expansion is calculated based on the compressive expansion rate, layer thickness, and chemically modified layer thickness. The initial physical modified layer thickness is determined based on the layer thickness. The initial physical modified layer thickness is adjusted to determine the final physical modified layer thickness when the roadbed expansion meets a preset threshold. By integrating the chemically modified layer thickness as a key parameter into the entire roadbed expansion calculation process, the invention avoids relying on empirical values ​​for the physical modified layer thickness. Instead, it uses the inhibitory effect of chemical modification on foundation expansion as a quantitative basis, combined with the expansion results calculated from the actual stress on the roadbed, for precise adjustments, thus improving design accuracy. By combining chemical and physical modification, the thickness of the physical modification layer is optimized while effectively suppressing the expansibility of the foundation through the chemical modification layer. This allows for a reasonable design of the physical modification layer thickness, ensuring the stability of the roadbed structure and meeting deformation control standards, thus better adapting to the stringent deformation control standards of high-speed railway ballastless track. Attached Figure Description

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 This is a flowchart of a design method for railway subgrade structure based on comprehensively modified expansive soil, provided by an embodiment of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0030] The specific embodiments of the present invention will be described below.

[0031] To address the issue of poor design accuracy in existing technologies, this invention acquires relevant foundation parameters and determines the thickness of the chemically modified layer based on these parameters. It designs the roadbed cross-section based on the alignment and topographic data. According to the roadbed geometric parameters of the cross-section, the foundation soil is layered according to a preset thickness, and the vertical stress parameters and corresponding compressive expansion rates for each layer are determined. The roadbed expansion is calculated based on the compressive expansion rate, layer thickness, and chemically modified layer thickness. The initial physical modified layer thickness is determined based on the layer thickness. The initial physical modified layer thickness is adjusted to determine the final physical modified layer thickness when the roadbed expansion meets a preset threshold. This invention achieves high design accuracy.

[0032] This invention provides a design method for railway subgrade structures based on comprehensively modified expansive soil and rock. Figure 1 This is a flowchart illustrating a design method for railway subgrade structures based on comprehensively modified expansive soil, as provided in an embodiment of the present invention. Figure 1 As shown, the specific steps include the following:

[0033] S1. Obtain relevant foundation parameters and determine the thickness of the chemical modification layer based on the relevant foundation parameters.

[0034] Foundation-related parameters refer to key parameters related to the engineering characteristics and expansion deformation of expansive rock and soil foundations. These parameters include expansibility grade, loaded expansion rate, loaded compressive expansion rate, and atmospheric influence depth. The thickness of the chemically modified layer refers to the vertical depth of the soil layer treated with chemical modifiers in the expansive rock and soil foundation beneath the railway subgrade.

[0035] The expansibility grade of expansive soil is determined by measuring the free swelling rate, montmorillonite content, and cation exchange capacity. Table 1 shows the expansibility classification of expansive soil. The expansibility grade is a grading index characterizing the strength of the expansibility of expansive soil. It is determined by three indicators: the free swelling rate, montmorillonite content, and cation exchange capacity of the foundation soil, and is divided into three grades: weak, medium, and strong expansibility. This is the core basis for classifying foundation soil types.

[0036] Table 1

[0037]

[0038] The loaded expansion rate and the loaded compression expansion rate are determined by the sample compression at the original height and preset pressure and the expansion of the sample after immersion in water in the loaded expansion rate test.

[0039] The loaded swelling rate test is a geotechnical test used to determine the swelling deformation index of expansive soil under loaded conditions. The initial test height refers to the initial standard height of the specimen before the test begins. The preset pressure refers to the specified vertical pressure value applied to the specimen during the test; the specimen compression refers to the decrease in height after the specimen is compressed under the preset pressure. The swelling after water immersion refers to the increase in height after the specimen has stabilized from compression and is immersed in water. The loaded compression swelling rate characterizes the ability of expansive soil to swell under loaded conditions when immersed in water; it also characterizes the comprehensive deformation index of expansive soil after compression and subsequent swelling under loaded conditions.

[0040] Specifically, the formula for calculating the load expansion rate is:

[0041] ;

[0042] The formula for calculating the compressive expansion rate under load is:

[0043] ;

[0044] Wherein, s0 is the original height of the test in the loaded expansion rate test (mm), s1 is the compression amount of the sample under the preset pressure p (mm), and s2 is the expansion amount of the sample after immersion in water (mm).

[0045] For example, in a high-speed railway project using tropical volcanic ash expansive soil, the foundation is medium expansive soil. The test results of the loaded swelling rate and the loaded compressive swelling rate are shown in Table 2.

[0046] Table 2

[0047]

[0048] The atmospheric influence depth is determined through on-site measurements or by selecting preset values. The atmospheric influence depth generally ranges from 4 to 8 meters and should be determined based on on-site measurement data. If no measurement data is available, it can be calculated as 6 meters. For example, in a high-speed railway project using tropical volcanic ash expansive soil, the atmospheric influence depth is calculated as 6 meters.

[0049] Specifically, the thickness of the chemically modified layer is determined based on relevant foundation parameters, including: classifying the foundation soil according to its expansibility level; matching the recommended thickness of the chemically modified layer for the corresponding foundation soil category with engineering experience and field test results; and, in the absence of engineering experience and field test results, setting the initial chemically modified layer thickness according to the preset thickness range corresponding to the expansibility level, and then correcting and determining the final chemically modified layer thickness after verification by field tests.

[0050] The foundation soil category is a classification of expansive soil and rock based on their expansibility level, while also including the integrity classification of expansive rock. This category serves as the direct basis for matching the thickness of the chemically modified layer. Engineering experience refers to the practical experience accumulated in the design and construction of chemically modified layer thicknesses during past treatments of similar foundation soil categories in railway expansive soil subgrade engineering. Field test results are the compatibility data obtained after conducting on-site chemical modification tests on the expansive soil and rock at the target project site, serving as the on-site measurement basis for thickness design.

[0051] Based on the expansibility grade of the foundation soil, the expansive soil and rock at the engineering site are classified, and corresponding foundation soil categories are defined. Taking into account past engineering experience in railway expansive soil and rock subgrade projects and the results of on-site chemical modification tests for the target project, recommended values ​​for the thickness of the chemical modification layer are selected to match the classified foundation soil categories. The matching status of the recommended chemical modification layer thickness values ​​is shown in Table 3. If there is no relevant engineering experience for the project and no prior on-site tests have been conducted, an initial chemical modification layer thickness is set according to the pre-defined range. On-site tests are then conducted on the initial chemical modification layer thickness to verify its engineering suitability. Based on the verified test results, the initial chemical modification layer thickness is adjusted and corrected accordingly, ultimately determining the chemical modification layer thickness that can be directly applied to the engineering design.

[0052] Table 3

[0053]

[0054] The foundation soil is classified according to its expansibility level, and then the corresponding chemical modification layer thickness is matched to ensure that the design thickness of the chemical modification layer is highly adapted to the actual expansibility characteristics of the foundation soil. The thickness is determined by combining engineering experience and field test results, taking into account the mature experience of similar projects and the actual conditions of the site, so that the design value is more in line with the project site and improves the actual effect of chemical modification treatment.

[0055] S2. Based on the horizontal and vertical alignment data and topographic maps, design the roadbed cross section.

[0056] Railway alignment and longitudinal profile data refer to the basic design data of a railway line, such as its horizontal alignment and vertical profile. Topographic maps are drawings that reflect the topography, landforms, and ground elevation of the engineering site. Roadbed cross-sections are the sections of the roadbed perpendicular to the railway line's direction.

[0057] Based on the horizontal and vertical alignment data of the railway line and the on-site topographic map, the form planning and geometric parameters of the roadbed cross section are determined, resulting in a roadbed cross section design that meets the requirements of the line and the terrain. By designing the roadbed cross section to fit the on-site terrain and line conditions, the accuracy and rationality of the roadbed geometric parameters are ensured. This provides a reliable geometric basis for subsequent subgrade layering, stress calculation, expansion calculation, and modification layer thickness design, thereby improving the accuracy and applicability of the overall design.

[0058] S3. Based on the roadbed geometric parameters of the roadbed cross section, the foundation soil is divided into layers according to the preset thickness, and the vertical stress parameters of each layer and the corresponding loaded compressive expansion rate of the vertical stress parameters are determined.

[0059] Subgrade geometric parameters refer to geometric and fill-related parameters obtained from the subgrade cross-section and used for stress calculations, such as subgrade center height and fill unit weight. Preset thickness refers to a fixed thickness value set in advance for uniformly layering the foundation soil.

[0060] Specifically, based on the roadbed geometric parameters of the roadbed cross-section, the foundation soil is layered according to a preset thickness, and the vertical stress parameters of each layer and the corresponding loaded compressive expansion rate are determined. This includes: layering the foundation soil into equal thicknesses according to the roadbed center height and fill unit weight of the roadbed cross-section; calculating the vertical stress parameters at the center of each layer based on the roadbed surface load, fill unit weight, roadbed center height, and self-weight stress of each layer; and determining the loaded compressive expansion rate corresponding to the vertical stress parameters of each layer by using linear interpolation based on the relationship between load and loaded compressive expansion rate obtained from the loaded expansion test.

[0061] First, based on the center height of the subgrade and the unit weight of the fill material in the subgrade cross-section, the foundation soil is divided into layers of equal thickness according to a predetermined thickness. Then, based on the subgrade surface load, fill material unit weight, subgrade center height, and the self-weight stress of each layer, the vertical stress parameters at the center of each layer are calculated. Finally, using the relationship between load and compressive expansion rate obtained from the loaded expansion test, a linear interpolation method is used to match the corresponding compressive expansion rate for the vertical stress parameters of each layer.

[0062] When stratifying the foundation soil, the preset thickness range is 0.2-0.5m, and the calculation formula for the vertical stress parameter is:

[0063] ;

[0064] in, Let be the vertical stress parameter at the center of the i-th soil layer. For roadbed surface load, For the packing density, The height of the roadbed center. Let be the unit weight of the i-th layer of foundation soil. The preset thickness for the soil layers in the foundation.

[0065] By uniformly layering the foundation soil, the subsequent stress and deformation calculations are more closely aligned with the actual stress state. Quantitative calculations are used to determine the vertical stress, and tests and linear interpolation are used to determine the loaded compressive expansion rate. This improves the accuracy and rationality of parameter values ​​and provides accurate and reliable basic data for subsequent calculations of subgrade expansion.

[0066] S4. Calculate the subgrade expansion based on the loaded compressive expansion rate, layer thickness, and chemically modified layer thickness.

[0067] Layer thickness refers to the vertical thickness of a single layer after the foundation soil is divided into layers of predetermined thickness, i.e., the predetermined thickness of the foundation soil layers. Subgrade expansion refers to the total vertical expansion deformation that may occur in the subgrade under stress and water immersion conditions.

[0068] Specifically, the subgrade expansion is calculated based on the loaded compressive expansion rate, layer thickness, and chemical modification layer thickness. This includes: delineating the modification treatment range of the foundation soil based on the chemical modification layer thickness, and determining the modification coefficient and deformation transfer coefficient corresponding to each layer; calculating the loaded compressive expansion amount of each layer by combining the loaded compressive expansion rate, layer thickness, modification coefficient, and deformation transfer coefficient; and summing the loaded compressive expansion amounts of all layers to obtain the subgrade expansion amount.

[0069] The modification range of foundation soil refers to the vertical depth range within the foundation soil that has undergone chemical modification and whose expansion characteristics have been suppressed, directly defined by the thickness of the chemically modified layer. The modification coefficient is a coefficient reflecting the effect of chemical modification on the suppression of expansion of expansive soil and rock, while the deformation transfer coefficient reflects the degree to which the layered deformation of the foundation is transmitted upward to the subgrade.

[0070] The modification treatment range of the foundation soil is divided according to the thickness of the chemical modification layer. The corresponding modification coefficient and deformation transfer coefficient are determined for each layer. Then, the loaded compressive expansion rate, layer thickness, modification coefficient and deformation transfer coefficient of each layer are combined to calculate the loaded compressive expansion amount of each layer. Finally, the expansion amounts of all layers are added together to obtain the subgrade expansion amount.

[0071] The formula for calculating the loaded compressive expansion of each layer is as follows:

[0072] ;

[0073] in, The compressed expansion under load is the amount of expansion of each layer. The modification coefficient is... The deformation transfer coefficient, Let be the compressive expansion rate of the i-th soil layer under load.

[0074] By directly incorporating the thickness of the chemically modified layer into the expansion calculation, the collaborative design of chemical and physical modifications is achieved, making the expansion calculation more closely reflect the actual modification effect, significantly improving the calculation accuracy, providing a reliable basis for the subsequent quantitative adjustment of the thickness of the physically modified layer, and making the subgrade structure design more precise.

[0075] S5. Determine the initial physical modification layer thickness based on the layer thickness.

[0076] Using the layer thickness of the foundation soil as the basic unit, and following the principles of matching the layer thickness and facilitating engineering implementation, the initial physical modification layer thickness is determined. The initial physical modification layer thickness is then set. ;m=0,1,2,3....... By using the foundation layer thickness as a benchmark and determining the initial physical modification layer thickness as an integer multiple of the layer thickness, the initial thickness value can be standardized and uniform, and highly coordinated with the foundation layer system, avoiding calculation deviations and construction inconveniences caused by arbitrary and irregular initial values.

[0077] S6. Adjust the initial physical modification layer thickness to determine the final physical modification layer thickness when the roadbed expansion meets the preset threshold.

[0078] Specifically, this includes: comparing the subgrade expansion amount with a preset threshold; when the subgrade expansion amount is less than or equal to the preset threshold, using the initial physical modification layer thickness as a candidate physical modification layer thickness; when the subgrade expansion amount is greater than the preset threshold, adjusting the initial physical modification layer thickness, recalculating the subgrade expansion amount based on the adjusted initial physical modification layer thickness, and comparing the subgrade expansion amount with the preset threshold until the subgrade expansion amount is less than or equal to the preset threshold; determining the candidate physical modification layer thickness corresponding to when the subgrade expansion amount meets the preset threshold; determining the structural physical modification layer thickness according to railway grade standards; and taking the maximum value between the candidate physical modification layer thickness and the structural physical modification layer thickness as the final physical modification layer thickness. The preset threshold is the subgrade camber deformation control value determined according to railway grade standards and track type, and the subgrade camber deformation control value is determined according to Table 4.

[0079] Table 4

[0080]

[0081] The thickness of the physical modification layer is determined according to Table 5.

[0082] Table 5

[0083]

[0084] The thickness of the structural physical modification layer refers to the minimum replacement thickness required to meet the basic structural requirements of the roadbed. The initial physical modification layer thickness is repeatedly checked and adjusted using the roadbed arch deformation control values ​​to ensure it meets the roadbed deformation control requirements and avoids excessive expansion. The thickness of the structural physical modification layer is determined in conjunction with the railway grade, balancing deformation control and basic roadbed structural requirements to ensure design compliance. Furthermore, the maximum value between the candidate physical modification layer thickness and the structural physical modification layer thickness is taken as the final physical modification layer thickness, satisfying both safety deformation requirements and engineering structural specifications, thus improving the accuracy and practicality of the design.

[0085] After determining the final thickness of the physical modification layer, the following steps are also included: designing a drainage system based on relevant foundation parameters, relevant roadbed cross-sectional parameters, the thickness of the physical modification layer, and the thickness of the chemical modification layer; the drainage system includes a waterproof sealing layer for the roadbed surface, a waterproof layer for the replacement bottom surface, surface drainage ditches, side ditches, and underground seepage blind ditches.

[0086] A drainage system is a comprehensive protective system designed to intercept and drain surface water and groundwater from the roadbed, preventing moisture intrusion into the foundation and modified layers. A roadbed surface waterproof sealing layer is a waterproof layer laid on the roadbed surface, capable of preventing surface water from seeping into the roadbed interior. A replacement bottom waterproof layer is a waterproof structure located at the bottom of the physical modified layer, preventing groundwater from seeping upwards into the physical modified layer, chemical modified layer, and the upper part of the roadbed. Surface drainage ditches are drainage structures on both sides of the roadbed, draining surrounding surface water to prevent soaking the foundation. Side ditches are drainage ditches at the bottom of the roadbed slope and outside the shoulder, draining accumulated water from the roadbed surface and slopes. Underground seepage blind ditches are buried underground, filled with permeable materials, draining groundwater from the foundation and roadbed interior, lowering the groundwater level.

[0087] Based on the determined foundation parameters and relevant parameters of the roadbed cross-section, and in conjunction with the final thickness of the physical and chemical modified layers, a drainage system is designed to integrate with the aforementioned roadbed layering, stress calculation, expansion verification, and modified layer design. This ensures that the drainage system is highly compatible with the overall roadbed structure and modification treatment scheme, enhancing the targeted effectiveness of drainage. Furthermore, through the synergistic action of multiple components, including the waterproof sealing layer on the roadbed surface and the waterproof layer at the bottom of the physical modified layer, it comprehensively intercepts and drains surface water and groundwater, preventing moisture intrusion into the foundation and modified layer. This effectively inhibits the expansion of expansive soil and rock upon contact with water, ensuring the effectiveness of both chemical and physical modification treatments.

[0088] This embodiment acquires relevant foundation parameters and determines the thickness of the chemically modified layer based on these parameters. It designs the roadbed cross-section based on the alignment and topographic data. According to the roadbed geometric parameters of the cross-section, the foundation soil is layered according to a preset thickness, and the vertical stress parameters and corresponding compressive expansion rates for each layer are determined. The roadbed expansion is calculated based on the compressive expansion rate, layer thickness, and chemically modified layer thickness. The initial physical modified layer thickness is determined based on the layer thickness. The initial physical modified layer thickness is adjusted to determine the final physical modified layer thickness when the roadbed expansion meets a preset threshold. By integrating the chemically modified layer thickness as a key parameter into the entire roadbed expansion calculation process, the physical modified layer thickness is avoided by relying on empirical values. Instead, it uses the inhibitory effect of chemical modification on foundation expansion as a quantitative basis, combined with the expansion results calculated from the actual stress on the roadbed, for precise adjustments, thus improving design accuracy. By combining chemical and physical modification, the thickness of the physical modification layer is optimized while effectively suppressing the expansibility of the foundation through the chemical modification layer. This allows for a reasonable design of the physical modification layer thickness, ensuring the stability of the roadbed structure and meeting deformation control standards, thus better adapting to the stringent deformation control standards of high-speed railway ballastless track.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A design method for railway subgrade structures based on comprehensively modified expansive soil and rock, characterized in that, include: S1. Obtain relevant foundation parameters and determine the thickness of the chemical modification layer based on the relevant foundation parameters; S2. Based on the horizontal and vertical alignment data and topographic maps, design the roadbed cross section; S3. Based on the roadbed geometric parameters of the roadbed cross section, the foundation soil is divided into layers according to the preset thickness, and the vertical stress parameters of each layer and the loaded compressibility expansion rate corresponding to the vertical stress parameters are determined. S4. Calculate the subgrade expansion based on the loaded compressive expansion rate, layer thickness, and chemically modified layer thickness; S5. Determine the initial physical modification layer thickness based on the layer thickness; S6. Adjust the initial physical modification layer thickness to determine the final physical modification layer thickness when the roadbed expansion meets the preset threshold; specifically including: Compare the roadbed expansion amount with a preset threshold; When the roadbed expansion is less than or equal to a preset threshold, the initial physical modification layer thickness is used as the candidate physical modification layer thickness. When the roadbed expansion exceeds the preset threshold, the initial physical modification layer thickness is adjusted, the roadbed expansion is recalculated based on the adjusted initial physical modification layer thickness, and the roadbed expansion is compared with the preset threshold until the roadbed expansion is less than or equal to the preset threshold; the candidate physical modification layer thickness corresponding to the roadbed expansion meeting the preset threshold is determined. The thickness of the structural physical modification layer is determined according to railway grade standards; The maximum value between the candidate physical modification layer thickness and the constructed physical modification layer thickness is taken as the final physical modification layer thickness.

2. The design method for railway subgrade structure based on comprehensively modified expansive soil and rock according to claim 1, characterized in that, In S1, the foundation-related parameters include expansibility level, loaded expansion rate, loaded compressive expansion rate, and atmospheric influence depth. The expansibility grade is determined by measuring the free swelling rate, montmorillonite content, and cation exchange capacity of the foundation soil. The loaded expansion rate and the loaded compression expansion rate are determined by the sample compression at the original height and preset pressure and the expansion of the sample after immersion in water in the loaded expansion rate test.

3. The design method for railway subgrade structure based on comprehensively modified expansive soil and rock according to claim 2, characterized in that, The thickness of the chemically modified layer is determined based on relevant foundation parameters, including: Foundation soil is classified according to its expansibility level; Based on engineering experience and field test results, recommend the thickness of the chemical modification layer for the corresponding foundation soil type; When there is no engineering experience and field test results, the initial chemical modification layer thickness is set according to the preset thickness range corresponding to the expansion level, and the final chemical modification layer thickness is determined after verification by field tests.

4. The design method for railway subgrade structure based on comprehensively modified expansive soil and rock according to claim 1, characterized in that, In step S3, based on the roadbed geometric parameters of the roadbed cross-section, the foundation soil is layered according to a preset thickness, and the vertical stress parameters of each layer and the corresponding loaded compressive expansion rate of the vertical stress parameters are determined, including: Based on the center height of the roadbed cross section and the unit weight of the fill material, the foundation soil is divided into equal-thickness layers according to the preset thickness. Based on the subgrade surface load, fill unit weight, subgrade center height, and self-weight stress of each layer, the vertical stress parameters at the center of each soil layer are calculated. Based on the relationship between load and compressive expansion rate obtained from the loaded expansion test, the compressive expansion rate corresponding to the vertical stress parameters of each layer is determined by linear interpolation.

5. The design method for railway subgrade structure based on comprehensively modified expansive soil and rock according to claim 4, characterized in that, The formula for calculating the vertical stress parameter is: ； in, Let be the vertical stress parameter at the center of the i-th soil layer. For roadbed surface load, For the packing density, The height of the roadbed center. Let be the unit weight of the i-th layer of foundation soil. The preset thickness for the soil layers in the foundation.

6. The design method for railway subgrade structure based on comprehensively modified expansive soil and rock according to claim 1, characterized in that, In step S4, the subgrade expansion is calculated based on the loaded compressive expansion rate, layer thickness, and chemically modified layer thickness, including: The modification treatment range of the foundation soil is delineated based on the thickness of the chemical modification layer, and the modification coefficient and deformation transfer coefficient corresponding to each layer are determined. By combining the loaded compressive expansion rate, layer thickness, modification coefficient and deformation transfer coefficient of each layer, the loaded compressive expansion amount of each layer is calculated. The amount of roadbed expansion is obtained by summing the loaded compressive expansion of all layers.

7. The design method for railway subgrade structure based on comprehensively modified expansive soil and rock according to claim 6, characterized in that, The formula for calculating the compressive expansion of each layer under load is as follows: ； in, The compressed expansion under load is the amount of expansion of each layer. The modification coefficient is... The deformation transfer coefficient, Let be the compressive expansion rate of the i-th soil layer under load.

8. The design method for railway subgrade structure based on comprehensively modified expansive soil and rock according to claim 1, characterized in that, The preset threshold is a roadbed arching deformation control value determined according to railway grade standards and track type.

9. The design method for railway subgrade structure based on comprehensively modified expansive soil and rock according to claim 1, characterized in that, After determining the final thickness of the physical modification layer, the following steps are also included: Based on the relevant parameters of the foundation, the relevant parameters of the roadbed cross section, the thickness of the physical modification layer, and the thickness of the chemical modification layer, a drainage system is designed. The drainage system includes a waterproof sealing layer on the roadbed surface, a waterproof layer on the bottom of the physical modification layer, surface drainage ditches, side ditches, and underground seepage blind ditches.

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