A rough processing pebble modified red sandstone roadbed filler and a bearing ratio prediction method thereof

Abstract

The application provides a rough processing pebble modified red sandstone roadbed filler, which is formed by mixing 40%-80% rough processing pebble with red sandstone fine material, the red sandstone is pre-disintegrated and dried, and the bearing ratio of the modified red sandstone roadbed filler is quickly predicted by the following formula: CBR = A*S^B, wherein CBR is the bearing ratio of the rough processing pebble modified red sandstone roadbed filler; S is the area of the region surrounded by the transverse coordinate axis in the range of d (particle size) = 0.075 mm to the maximum particle size of the rough processing pebble modified red sandstone roadbed filler, which is simply referred to as the grading curve area; and A and B are model parameters. The application also provides a bearing ratio prediction method of the rough processing pebble modified red sandstone roadbed filler. The rough processing pebble is broken as a modified material to physically modify the red sandstone, the rough processing pebble-red sandstone multi-level particle system is optimized, a synergistic effect is formed, and the overall bearing performance of the red sandstone filler is significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of road engineering, in particular to a rough processing pebble improved red sandstone subgrade filler and a bearing ratio prediction method thereof. BACKGROUND

[0002] Red sandstone stratum is widely distributed in the east and south of Anhui Province. Red sandstone is usually red and reddish brown due to the presence of iron oxide. The physical state of red sandstone is mainly granular clastic structure and muddy cemented structure, and the cementing material is mainly argillaceous and calcareous, which is easy to soften and dissolve after being exposed to water. In addition, red sandstone has high porosity, developed fissures and mineral composition easy to weather. These special physical properties cause red sandstone to soften and disintegrate after being exposed to water, and have low bearing capacity, which is not suitable for direct use as a subgrade filler. However, according to the Anhui Provincial Highway Network Planning (2020-2035), large-scale road engineering will pass through and be built on red sandstone stratum, and the demand for subgrade filler is huge. In order to implement the concept of green highway construction and intensive use of earth resources, subgrade filler should not be transported and replaced over a long distance, and should usually be locally sourced. Therefore, if the red sandstone in the region can be improved and used as a subgrade filler, it will have important economic, environmental and social benefits.

[0003] In the geological evolution of the east and south of Anhui Province, there are also widely distributed floodplain and red floodplain geology, and there are a large number of pebbles in this geology. The distribution of pebbles overlaps with the distribution of red sandstone in a large area, resulting in the coexistence of red sandstone and pebbles in the construction of highway subgrade. If the pebbles and red sandstone are treated as waste, it will inevitably increase the engineering cost, occupy a large amount of land and damage the ecological environment. Therefore, in road engineering construction, the rational use of pebbles and red sandstone to prepare subgrade filler not only can effectively reduce the construction cost and shorten the construction period, but also has important significance for practicing the concept of intensive use of earth resources and promoting green highway engineering construction.

[0004] Therefore, by rough processing and crushing the pebbles and mixing them into the red sandstone in a certain mass ratio to improve the physical properties of the red sandstone, by optimizing the rough processing pebble-red sandstone multi-level particle system, a synergistic effect is formed, so that the red sandstone filler mixed with rough processing pebbles can form a high-strength skeleton structure through the multi-dimensional interlocking effect between particles during compaction, and the red sandstone fines can fully fill the voids during compaction, finally forming a composite structure with rough processing pebbles as the skeleton and red sandstone densely wrapped, thereby significantly improving the overall bearing capacity of the red sandstone filler.

[0005] In the construction of road subgrade, the bearing ratio (CBR) is an important indicator for evaluating the bearing performance of subgrade fill. The determination of the bearing ratio is usually carried out according to the bearing ratio (CBR) test method in the Highway Geotechnical Test Specification (JTG3430-2020), the optimum moisture content and the maximum dry density are determined through the compaction test, and the final bearing ratio value is determined through the penetration test. However, the artificially prepared subgrade fill of the coarsely processed pebble modified red sandstone needs to be combined in multiple gradations according to the specific situation on site, and the bearing ratio under different combinations needs to be determined through multiple test processes. At this time, compared with the traditional bearing ratio test method, the process is cumbersome, time-consuming, and requires professional personnel to operate. Therefore, it is necessary to obtain the bearing ratio of the artificially prepared subgrade fill of the coarsely processed pebble modified red sandstone through a more accurate and rapid method. SUMMARY

[0006] To solve the above problems, the present application aims to provide a coarsely processed pebble modified red sandstone subgrade fill and a bearing ratio prediction method thereof. The red sandstone is physically modified by using coarsely processed pebbles as the modified material, and the synergistic effect is formed by optimizing the coarsely processed pebble-red sandstone multi-grade particle system, thereby significantly improving the overall bearing performance of the red sandstone fill.

[0007] To achieve the above purpose, the technical scheme of the present application is as follows: A coarsely processed pebble modified red sandstone subgrade fill is formed by mixing coarsely processed pebbles with a mass ratio of 40%-80% and red sandstone fine material, the red sandstone is pre-disintegrated and dried, and the bearing ratio of the modified red sandstone subgrade fill is quickly predicted by the following formula: (1) In the formula, CBR is the bearing ratio of the coarsely processed pebble modified red sandstone subgrade fill, S is the area of the fitting gradation curve of the coarsely processed pebble modified red sandstone subgrade fill in the range of d (particle size) = 0.075 mm to the maximum particle size with the transverse coordinate axis, which is simply referred to as the gradation curve area, and A and B are model parameters.

[0008] Further, the gradation curve of the coarsely processed pebble is continuously distributed, the red sandstone fine material fills the voids thereof, and a skeleton-dense composite structure is formed.

[0009] Further, the particle size of the coarsely processed pebble is 5-40 mm, which is obtained by coarsely processing and crushing natural pebbles and sieving, and is used as A material.

[0010] Further, the particle size of the red sandstone is less than 5 mm, which is obtained by mechanically crushing the red sandstone, pre-disintegrating with water spraying, drying, and passing through a 5 mm sieve, and is used as B material.

[0011] In order to achieve the above object, the application further provides a bearing ratio prediction method for rough processing pebble modified red sandstone subgrade filler, comprising the following steps: S1, crushing and screening natural pebbles to obtain rough processing pebble particles with a particle size of 5-40 mm as A material, and determining the grading curve thereof through a screening test; S2, mechanically crushing, spraying water to pre-disintegrate, drying and passing through a 5 mm sieve red sandstone as B material, and determining the grading curve thereof through a screening test; S3, mixing the rough processing pebble A material into the red sandstone B material according to a set mass ratio, and uniformly mixing to obtain a modified red sandstone subgrade filler with a rough processing pebble mixing rate of 40%-80% by mass ratio; S4, performing a compaction test according to the Highway Soil Test Specification (JTG3430-2020) to obtain the optimum water content and the maximum dry density of the rough processing pebble modified red sandstone subgrade filler; S5, under the optimum water content, performing a bearing ratio test according to the Highway Soil Test Specification (JTG3430-2020) to obtain the bearing ratio of the rough processing pebble modified red sandstone subgrade filler.

[0012] Further, the red sandstone is a first or second type of easily disintegrating red sandstone which is not suitable for being directly used as a subgrade filler.

[0013] Further, the bearing ratio of the modified red sandstone subgrade filler is quickly predicted by the following formula: (1) In the formula, CBR is the bearing ratio of the rough processing pebble modified red sandstone subgrade filler; S is the area of the region surrounded by the fitting grading curve of the rough processing pebble modified red sandstone subgrade filler and the transverse coordinate axis in the range of d (particle size) = 0.075 mm to the maximum particle size, which is simply referred to as the grading curve area; A and B are model parameters.

[0014] Further, the determination process of the grading curve area S comprises the following steps: A1, obtaining the test grading of the rough processing pebble modified red sandstone subgrade filler through a screening test, with the horizontal coordinate being the particle size and the vertical coordinate being the cumulative mass percentage; A2, performing curve fitting on the obtained test grading by using a grading equation to obtain the corresponding grading parameters, and the grading equation used is: (2) In the formula, is the percentage content (%) of particles less than a certain particle size; is the particle size (mm); D50 is the median particle size, here taken as 40 mm; b and m are gradation parameters determined by the shape of the gradation curve.

[0015] A3, the area of the region surrounded by the transverse coordinate axis in the range of d=0.075 mm to d=40 mm of the fitting gradation curve, is taken as the gradation curve area; the formula (3) used for calculating the gradation curve area is derived by integral of the formula (2), and the specific calculation formula is as follows: (3) Beneficial effects: (1) The present application proposes to use rough processing pebbles to physically improve red sandstone and prepare roadbed fillers; when pebbles and red sandstone are simultaneously encountered along the highway engineering, the pebbles can be rough processed and broken as the improvement material to physically improve the red sandstone, the synergistic effect is formed by optimizing the rough processing pebble-red sandstone multi-level particle system, so as to significantly improve the overall bearing capacity of the red sandstone filler, realize the waste utilization, not only can effectively reduce the construction cost, shorten the construction period, but also has important significance to practice the concept of soil resource conservation and intensive use, and promote the construction of green highway engineering; (2) Based on the action mechanism of rough processing pebbles for physically improving red sandstone, the influence of particle gradation characteristic parameters on the bearing capacity of the artificially prepared rough processing pebble-red sandstone roadbed filler is considered, and a bearing ratio rapid prediction model suitable for rough processing pebble improved red sandstone roadbed filler is established; meanwhile, the model has clear physical meaning and simple structure, greatly reduces the test time and difficulty, provides obvious engineering convenience for the artificial preparation of rough processing pebble improved red sandstone roadbed filler with various gradation combinations and the units lacking test conditions, and has high market promotion value. BRIEF DESCRIPTION OF DRAWINGS

[0016] The accompanying drawings, which form a part of this application, are used to provide further understanding of the application, and the illustrative embodiments of the application and their description serve to explain the application. The accompanying drawings do not constitute an inappropriate limitation on the application. In the drawings: Figure 1 The flowchart of the bearing ratio prediction method of the rough processing pebble improved red sandstone roadbed filler described in the embodiments of the present application; Figure 2 The gradation curve diagram of the screening test result of the rough processing pebble used in the embodiments of the present application; Figure 3 The gradation curve diagram of the screening test result of the red sandstone used in the embodiments of the present application; Figure 4 The columnar chart of the bearing ratio test results of the rough processing pebble improved red sandstone roadbed filler under different rough processing pebble incorporation rates (40%, 50%, 60%, 70%, 80%) in the embodiments of the present application; Figure 5A particle size distribution curve fitting graph of the particle size distribution of the rough processing pebble modified red sandstone subgrade filler in different particle size distribution combinations in the embodiment of the present application is shown in the figure. Figure 6 A fitting particle size distribution curve area calculation schematic diagram in the embodiment of the present application is shown in the figure. Figure 7 A relationship graph between the predicted value and the measured value of the bearing ratio of the rough processing pebble modified red sandstone subgrade filler in the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0017] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0018] The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0019] Embodiment 1 A rough processing pebble modified red sandstone subgrade filler is formed by mixing 40%-80% of rough processing pebbles and red sandstone fine materials by mass ratio, the red sandstone is pre-disintegrated and dried, and the bearing ratio of the modified red sandstone subgrade filler is quickly predicted by the following formula: (1) In the formula, CBR is the bearing ratio of the rough processing pebble modified red sandstone subgrade filler, S is the area of the rough processing pebble modified red sandstone subgrade filler fitting particle size distribution curve in the range of d (particle size) = 0.075 mm to the maximum particle size from the transverse coordinate axis, which is simply referred to as the particle size distribution curve area, and A and B are model parameters.

[0020] The present embodiment realizes efficient use of resources: the proportion of pebbles is clearly limited (40%-80%), which not only forms a skeleton structure by using pebbles, but also avoids excessive mixing to cause the void ratio to rise, balancing the cost and performance; the pre-disintegration treatment is targeted: the stability of the red sandstone is improved after pre-disintegration, solving the problem that it is easy to disintegrate when encountering water, and ensuring that the fine material effectively fills the void; and the advantage of local material is that the pebbles and red sandstone in the region are directly used, reducing transportation costs and meeting the green construction concept.

[0021] The action mechanism of the rough processing pebble modified red sandstone subgrade filler in the present embodiment is as follows: The particle size distribution of the red sandstone filler can be changed by mixing the rough processing pebbles, the rough processing pebble-red sandstone multi-level particle system is optimized, a synergistic effect is formed, the red sandstone filler mixed with the rough processing pebbles can form a high-strength skeleton structure through the multi-dimensional embedding and extrusion effect between particles in the compaction process, at the same time, the red sandstone fine material fully fills the void in the compaction process, and finally a composite structure body with the rough processing pebble as the skeleton and the red sandstone densely wrapped is formed, thereby significantly improving the overall bearing performance of the red sandstone filler.

[0022] In a specific example, the gradation curve of the roughly processed pebbles is continuously distributed, and the red sandstone fine material fills the voids thereof to form a skeleton-dense composite structure.

[0023] This embodiment realizes the optimization of mechanical properties: the continuous gradation particles form a high-strength skeleton through multi-dimensional embedding and extrusion, and the red sandstone fine material filling reduces the void ratio, thereby improving the overall bearing capacity; the anti-deformation capacity is enhanced: the continuous gradation avoids local looseness and reduces the risk of construction segregation, thereby ensuring the uniformity and stability of the roadbed; and the engineering adaptability is realized: the method is suitable for roadbed engineering with high requirements for compactness, and is more universal than the intermittent gradation.

[0024] In a specific example, the particle size of the roughly processed pebbles is 5-40 mm, which is obtained by roughly processing and crushing natural pebbles and sieving, as A material.

[0025] This embodiment realizes the controllability of the process: the particle size range after crushing is limited to ensure that the aggregate can form an effective skeleton and avoid the construction difficulty caused by too large particles; and the cost is saved: the rough processing process is simple, and fine crushing is not required, thereby reducing the processing cost.

[0026] In a specific example, the particle size of the red sandstone is less than 5 mm, which is obtained by mechanically crushing the red sandstone, pre-disintegrating by spraying water, drying, and passing through a 5 mm sieve, as B material.

[0027] This embodiment realizes the functionality of the fine material: the fine material with a particle size of less than 5 mm fills the voids of the skeleton, improves the compactness, and solves the problem of looseness of the red sandstone itself; the necessity of the pre-disintegration process: the water-softening characteristics of the red sandstone are simulated by pre-disintegration by spraying water, the disintegration risk is released in advance, and the long-term stability of the filling material is ensured; and the drying standardization: the water content of the fine material is controlled to avoid the influence of water content fluctuation on the compaction effect during construction.

[0028] Embodiment 2 In order to achieve the above-mentioned purpose, see Figures 1-7 The embodiment also provides a bearing ratio prediction method for a roughly processed pebble improved red sandstone roadbed filling material, comprising the following steps: S1, roughly processing and crushing natural pebbles to obtain roughly processed pebble particles with a particle size of 5-40 mm as A material, and determining the gradation curve thereof through a sieving test; S2, mechanically crushing the red sandstone, pre-disintegrating by spraying water, drying, and passing through a 5 mm sieve as B material, and determining the gradation curve thereof through a sieving test; S3, mixing the roughly processed pebbles A material into the red sandstone B material at a set mass ratio, and uniformly mixing to obtain an improved red sandstone roadbed filling material with a roughly processed pebble mixing rate of 40%-80% by mass ratio; S4, perform compaction test according to "Highway Geotechnical Test Procedures" (JTG3430-2020) to obtain the optimum moisture content and maximum dry density of the rough processing pebble improved red sandstone subgrade filler; S5, under the condition of optimum moisture content, perform bearing ratio test according to "Highway Geotechnical Test Procedures" (JTG3430-2020) to obtain the bearing ratio of the rough processing pebble improved red sandstone subgrade filler.

[0029] The bearing ratio prediction method of the embodiment includes the whole process of material preparation, compaction test and CBR test; advantages: the whole process covers: from material processing to performance test, forming a standardized process to guide actual construction; Specification compliance: according to "Highway Geotechnical Test Procedures", ensure data authority and reduce engineering risk; repeatability: clear steps, easy for construction personnel to operate, suitable for large-scale engineering application.

[0030] In a specific example, the red sandstone is a first or second class easily disintegrating red sandstone which is not suitable for direct use as a subgrade filler.

[0031] The embodiment is suitable for easily disintegrating red sandstone, realizes waste utilization, and solves the engineering problem of direct filling.

[0032] In a specific example, the bearing ratio of the improved red sandstone subgrade filler is quickly predicted by the following formula: (1) In the formula, CBR is the bearing ratio of the rough processing pebble improved red sandstone subgrade filler; S is the area of the region surrounded by the fitting gradation curve of the rough processing pebble improved red sandstone subgrade filler and the transverse coordinate axis in the range of d (particle size) = 0.075 mm to the maximum particle size, which is simply referred to as the gradation curve area; A and B are model parameters.

[0033] The embodiment realizes quick prediction: replaces traditional time-consuming tests, shortens the construction period (prediction time is reduced by more than 70%); clear physical meaning: the gradation area S comprehensively reflects the tightness of particle distribution, and the model parameters A and B can be calibrated through local tests and adapted to different regional materials; cost saving: reduces the need for repeated tests and reduces testing costs.

[0034] In a specific example, the determination process of the gradation curve area S includes the following steps: A1, obtain the test gradation of the rough processing pebble improved red sandstone subgrade filler through a screening test, with the horizontal coordinate being the particle size and the vertical coordinate being the cumulative mass percentage; A2, curve fitting is performed on the obtained test gradation by using a gradation equation to obtain corresponding gradation parameters, and the gradation equation used is: (2) In the formula, is the percentage (%) of particles less than a certain particle size; is the particle size (mm); is the maximum particle size, which is taken as 40 mm; b and m are gradation parameters determined by the shape of the gradation curve.

[0035] A3, calculate the area of the region enclosed by the fitting gradation curve in the range of d=0.075mm to d=40mm and the transverse coordinate axis as the gradation curve area; the formula (3) used to calculate the gradation curve area is derived by integrating formula (2), and the specific calculation formula is as follows: (3) In this embodiment, the test data is fitted by the gradation equation, and the gradation curve area S is calculated by integration; the advantages are: scientific rigor: using a nonlinear equation (formula 2) to fit the gradation curve improves the prediction accuracy; calculation standardization: the integral formula (formula 3) quantifies the gradation area, avoiding manual judgment bias; dynamic adaptability: parameters b and m are dynamically adjusted according to the gradation shape, adapting to the particle distribution under different crushing processes.

[0036] The gradation curve of the rough processing pebble modified red sandstone subgrade filler in this embodiment can quickly predict the bearing ratio (CBR) of the rough processing pebble modified red sandstone subgrade filler through the model constructed above.

[0037] In a specific implementation, taking typical pebbles and red sandstone in the mountainous area of southern Anhui as an example, a rough processing pebble modified red sandstone subgrade filler and a rapid prediction method for its bearing ratio are proposed based on the above embodiment. Different gradation combinations of rough processing pebble modified red sandstone subgrade fillers are prepared, and a rapid prediction model of bearing ratio is constructed to predict different gradation combinations of rough processing pebble modified red sandstone subgrade fillers. The specific steps are as follows: (1) The pebbles used in this example are taken from a highway construction project section in the mountainous area of southern Anhui, which are coarsely processed and crushed and sieved to obtain coarse processing pebble particles with a particle size of 5-40mm as A material; then, a sieving test is performed, and the results are shown in Table 1. Figure 2

[0038] (2) The red sandstone used in this example is also taken from a highway construction project section in the mountainous area of southern Anhui; the red sandstone used is a type II red sandstone that is easy to disintegrate and not easy to be directly used as a subgrade filler. It is mechanically crushed, pre-disintegrated by spraying water, dried, and passed through a 5mm sieve as B material; then, a sieving test is performed, and the results are shown in Table 2. Figure 3

[0039] ​​(3) The rough processing pebbles (A material) are mixed into the red sandstone (B material) according to a certain mass ratio, and are uniformly mixed to obtain modified red sandstone subgrade fillers with different rough processing pebble mixing rates. The rough processing pebble mixing rate combination is set to 40%, 50%, 60%, 70%, and 80%.

[0040] (4) According to the Highway Geotechnical Test Specification (JTG3430-2020), the modified red sandstone samples with rough processing pebble mixing rates of 40%, 50%, 60%, 70%, and 80% are subjected to compaction tests to determine the optimum water content and maximum dry density of the rough processing pebble modified red sandstone subgrade fillers with different gradation combinations, as shown in Table 1.

[0041] Table 1 Compaction test results

[0042] (5) According to the Highway Geotechnical Test Specification (JTG3430-2020), under the optimum water content, the samples for bearing ratio test are prepared by static pressure method, with a sample size of 152 mm in diameter and 120 mm in height, and a compaction degree of 96%. Through penetration test, the bearing ratio of the rough processing pebble modified red sandstone subgrade fillers with different gradation combinations is determined, as shown in Table 2. Figure 4

[0043] (6) Through the sieve test, the test gradation of the rough processing pebble modified red sandstone subgrade fillers with different gradation combinations is obtained (the horizontal coordinate is the particle size, and the vertical coordinate is the cumulative mass percentage).

[0044] (7) The test gradation of the rough processing pebble modified red sandstone subgrade fillers with different gradation combinations is curve-fitted by using the following gradation equation (Equation 1), and the corresponding gradation parameters are obtained (Table 2), and the gradation equation used is: Figure 5

[0045] In the formula, w is the percentage content (%) of particles less than a certain particle size; d is the particle size (mm); D is the maximum particle size; and b and m are gradation parameters determined by the shape of the gradation curve.

[0046] Table 2 Gradation parameters

[0047] (8) The area of the region surrounded by the fitting gradation curve of the rough processing pebble modified red sandstone subgrade fillers with different gradation combinations and the horizontal coordinate axis in the range of d = 0.075 mm to d = 40 mm is calculated (A). Figure 6 ​​​), as the grading curve area S (Table 3), the specific calculation formula is as follows:

[0048] Table 3 Grading curve area

[0049] (9) Based on the above test results, a bearing ratio rapid prediction model of the rough processing pebble improved red sandstone subgrade filler considering the influence of particle grading area is established, and the model is as follows:

[0050] In the formula, CBR is the bearing ratio (%) of the rough processing pebble improved red sandstone subgrade filler; A and B are model parameters, and based on the above test data, the model parameters A=160.919 and B=2.495 are obtained by nonlinear fitting analysis using origin software.

[0051] (10) In order to determine the applicability of the model constructed in embodiment 2, the measured value of the bearing ratio of the rough processing pebble improved red sandstone subgrade filler is compared with the predicted value of the established model for verification. Among them, the measured value of the bearing ratio is taken as the abscissa, and the model predicted value is taken as the ordinate to draw a scatter plot, and the result is as shown in Figure 7 It can be seen from Figure 7 that each data point is floating up and down on the Y=X straight line, which shows that the prediction model can better predict the bearing ratio of the rough processing pebble improved red sandstone subgrade filler, and the predicted value has strong representativeness and meets the engineering needs.

[0052] The above only describes the preferred embodiments of the present application and does not limit the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A coarsely processed pebble-modified red sandstone roadbed filler, characterized in that, The improved red sandstone roadbed fill is composed of 40%-80% coarsely processed pebbles and fine red sandstone by mass ratio. The red sandstone is pre-disintegrated and dried. The bearing capacity ratio of the improved red sandstone roadbed fill is quickly predicted using the following formula: （1） In the formula, CBR is the bearing ratio of the coarsely processed gravel-modified red sandstone roadbed fill; S is the area enclosed by the fitted gradation curve of the coarsely processed gravel-modified red sandstone roadbed fill and the transverse coordinate axis in the range of d (particle size) = 0.075 mm to the maximum particle size, which is simply referred to as the gradation curve area; A and B are model parameters.

2. The coarsely processed pebble-improved red sandstone roadbed filler according to claim 1, characterized in that, The coarsely processed pebbles have a continuously distributed gradation curve, with fine red sandstone filling their gaps, forming a skeleton-dense composite structure.

3. The coarsely processed pebble-improved red sandstone roadbed filler according to claim 1, characterized in that, The coarsely processed pebbles have a particle size of 5-40 mm and are obtained by coarsely processing, crushing, and screening natural pebbles, and are used as material A.

4. The coarsely processed pebble-improved red sandstone roadbed filler according to claim 1, characterized in that, The red sandstone has a particle size of less than 5mm. It is obtained by mechanically crushing the red sandstone, pre-disintegrating it with water, drying it, and passing it through a 5mm sieve, and is used as material B.

5. A method for predicting the bearing ratio of coarsely processed gravel-improved red sandstone roadbed fill, characterized in that, Includes the following steps: S1. The natural pebbles are coarsely processed, crushed, and screened to obtain coarsely processed pebble particles with a particle size of 5-40mm, which are used as material A. The gradation curve is determined by screening test. S2. The red sandstone is mechanically crushed, pre-disintegrated by water spraying, dried, and passed through a 5 mm sieve as material B. Its gradation curve is determined by sieve analysis. S3. Add the coarsely processed pebble A material to the red sandstone B material according to the set mass ratio, mix evenly, and obtain the improved red sandstone subgrade filler with a mass ratio of 40%-80% coarsely processed pebble incorporation. S4. Conduct compaction tests according to the "Specifications for Geotechnical Testing of Highways" (JTG3430-2020) to obtain the optimal moisture content and maximum dry density of coarsely processed gravel-improved red sandstone subgrade fill. S5. Under optimal moisture content conditions, conduct a bearing ratio test according to the "Specifications for Geotechnical Testing of Highways" (JTG3430-2020) to obtain the bearing ratio of the coarsely processed gravel-modified red sandstone subgrade fill.

6. The method for predicting the bearing ratio of coarsely processed gravel-improved red sandstone roadbed fill according to claim 5, characterized in that, The red sandstone in question is classified as Class I or II easily disintegrating red sandstone, which is unsuitable for direct use as roadbed fill material.

7. The method for predicting the bearing ratio of coarsely processed gravel-improved red sandstone roadbed fill according to claim 5, characterized in that, The bearing capacity ratio of the improved red sandstone roadbed filler can be quickly predicted using the following formula: （1） In the formula, CBR is the bearing ratio of the coarsely processed gravel-modified red sandstone roadbed fill; S is the area enclosed by the fitted gradation curve of the coarsely processed gravel-modified red sandstone roadbed fill and the transverse coordinate axis in the range of d (particle size) = 0.075 mm to the maximum particle size, which is simply referred to as the gradation curve area; A and B are model parameters.

8. The method for predicting the bearing ratio of coarsely processed gravel-improved red sandstone roadbed fill according to claim 7, characterized in that, The process of determining the area S of the gradation curve includes the following steps: A1. The test gradation of coarsely processed gravel-modified red sandstone roadbed filler was obtained through sieve analysis. The horizontal axis represents particle size and the vertical axis represents cumulative mass percentage. A2. The obtained experimental gradation is curve-fitted using the gradation equation to obtain the corresponding gradation parameters. The gradation equation used is as follows: （2） In the formula, The percentage (%) of particles smaller than a certain particle size; Particle size (mm); The maximum particle size is 40 mm; b and m are gradation parameters, determined by the morphology of the gradation curve itself. 9.A3. Calculate the area of ​​the region enclosed by the fitted gradation curve and the horizontal coordinate axis within the range of d=0.075mm to d=40mm, and take it as the area of ​​the gradation curve; the formula (3) used to calculate the area of ​​the gradation curve is derived by integral of formula (2), and the specific calculation formula is as follows: （3）。

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