Granite residual soil slope section structure optimization method

Abstract

The invention discloses a granite residual soil slope section structure optimization method which is applied to the technical field of slope prevention and control. Comprising the steps that S1, geological drilling is conducted on a slope to be excavated, hydrogeological conditions are investigated to obtain relevant data of the slope, and the relevant data comprise stratum lithology, a slope body structure, an underground water level and a rainfall condition; s2, measuring physical and mechanical properties of stratum lithology according to the obtained side slope geological drilling core sample; s3, according to the height of the side slope, the stratum lithology, the land use red line and the surrounding environment, design parameters of the side slope stages, the slope ratio of each stage of the side slope, the height of each stage of the side slope and the platform width of the side slope to be excavated under different working conditions are designed; s4, obtaining slope stability coefficients corresponding to different working conditions based on S2 and S3, and obtaining an optimal section structure design working condition; s5, performing protection and retaining design on the slope to be excavated according to the principles of technology feasibility, economy, reasonability and ecological environmental protection on the basis of the step S4, obtaining a slope stability coefficient, and obtaining a protected slope section structure; and S6, on the basis of the S5, in combination with hydrogeology and meteorology, drainage design of the slope to be excavated is carried out, and finally an optimized slope section structure is obtained. According to the method, the long-term stability of the slope can be improved, better environmental adaptability and ecological friendliness are provided, engineering protection measures are reduced, and the construction and maintenance cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of slope prevention and control, and more specifically to a method for optimizing the cross-sectional structure of a granite residual soil slope. Background Art

[0002] Granite residual soil is widely distributed in my country. The overall stability of newly excavated granite residual soil slopes is good. Slope erosion and local collapse caused by untimely protection are the most common, while overall damage is relatively rare, and often occurs in granite residual soil slopes with deep road cuttings or potential unfavorable structural surfaces. Therefore, the focus of granite residual soil slope management is to prevent erosion and local collapse of shallow soil; for granite residual soil with deep road cuttings or potential unfavorable structural surfaces, the overall stability must be verified during the design process, taking into account both economic efficiency and environmental friendliness.

[0003] Slope failure is directly correlated with soil properties, slope gradient, and protection type. Granite residual soil is a special structural rock soil. The shear strength index of remolded soil is used, ignoring the structural properties of granite residual soil, making the slope stability calculation seriously inconsistent with the actual situation. In general, the gentler the slope gradient and the higher the protection level, the lower the probability of erosion, collapse, and landslide. However, there is a critical slope of about 46° for erosion damage on the slope surface of granite residual soil. It is necessary to further study the granite residual soil slope prevention and control technology and optimize the slope section structure in combination with the engineering properties of granite residual soil and the characteristics of slope failure.

[0004] Therefore, based on the problems existing in the prior art, the present invention proposes a method for optimizing the cross-sectional structure of a granite residual soil slope. Summary of the invention

[0005] In view of this, the present invention provides a method for optimizing the cross-sectional structure of a granite residual soil slope, which can improve the long-term stability of the slope, provide better environmental adaptability and eco-friendliness, reduce engineering protection measures, and reduce construction and maintenance costs.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for optimizing the cross-sectional structure of a granite residual soil slope comprises the following steps:

[0008] S1. Conduct geological drilling on the slope to be excavated and investigate the hydrogeological conditions to obtain relevant data of the slope, including stratum lithology, slope structure, groundwater level, and precipitation conditions;

[0009] S2. Determine the physical and mechanical properties of the stratum lithology based on the obtained slope geological drilling core samples;

[0010] S3. According to the slope height, stratum lithology, land red line and surrounding environment, design the slope levels, slope rate of each level, height of each level and platform width design parameters under different working conditions of the slope to be excavated;

[0011] S4, based on S2 and S3, obtain the slope stability coefficient corresponding to different working conditions and obtain the optimal cross-section structure design working condition;

[0012] S5. Based on the optimal cross-sectional structural design conditions of S4, the protection and support design of the slope to be excavated is performed to obtain the slope stability coefficient and the cross-sectional structure of the slope after protection;

[0013] S6. Based on the cross-sectional structure of the slope after protection obtained in S5, combined with hydrogeology and meteorology, drainage design of the slope to be excavated is carried out, and finally the optimized cross-sectional structure of the slope is obtained.

[0014] In the above method, optionally, the physical properties of the soil layer structure measured in S2 include: particle composition, moisture content, and density of the test soil; the mechanical properties of the soil layer structure measured include: soil cohesion and internal friction angle determined by indoor shear test, in-situ direct shear test or parameter inverse algorithm.

[0015] The above method is optional. In S2, the test device for the in-situ direct shear test uses an HTYZ-20 computer-controlled fully automatic large-scale direct shear instrument, applies a vertical load to the sample, and applies a horizontal shear force after the consolidation is stable, so that the sample is destroyed on the shear plane, the failure shear stress of the sample is recorded, and a relationship curve between the failure shear stress and the vertical load is drawn, thereby calculating the cohesion and internal friction angle of the soil.

[0016] In the above method, optionally, the test device includes a shear box, a loading system and a data recording system connected in sequence; the shear box is made of a steel plate.

[0017] In the above method, optionally, in S3, when the slope height h ≤ 8m, the different working conditions are respectively slope ratios of 1:0.75, 1:1, 1:1.25, and 1:1.5 for the slope; when the slope height 8m < h ≤ 15m, a stepped section is adopted, the number of slope levels is 2, the platform width is 2m, and when the slope classification height is 8m, the different working conditions are respectively one or two of the slope ratios of 1:1, 1:1.25, and 1:1.5; when the slope height 15m < h ≤ 30m, a stepped section is adopted, there are two cases of slope classification heights of 8m and 10m, the platform width is 2m, and for each slope classification height, the different working conditions are respectively one or more of the slope ratios of 1:1, 1:1.25, 1:1.5, 1:1.75, and 1:2; when the slope height h > 30m, a stepped section is adopted, there are two cases of slope classification heights of 8m and 10m, the middle platform is set as a wide platform, the platform widths are 5m, 10m, and 15m, the widths of the remaining platforms are 2m, and for each slope classification height and each platform width, the different working conditions are respectively one or more of the slope ratios of 1:1, 1:1.25, 1:1.5, 1:1.75, and 1:2;

[0018] In S3, the number of slope levels is set based on the slope height and the slope classification height, including a first-level slope, a second-level slope,..., a multi-level slope, and then a first-level platform, a second-level platform,..., a multi-level platform are set.

[0019] In the above method, optionally, in S4, the FLAC numerical simulation software is used to analyze the slope stability coefficient under different working conditions.

[0020] In the above method, optionally, the specific content of S5 is as follows:

[0021] Based on the optimal working condition obtained in S4, combined with the slope height and the slope ratio, the subgrade protection design is carried out, and the protection types include: plant protection, frame plant protection, bamboo lattice plant protection, geosynthetic material plant protection, retaining wall protection, anchor rod / cable frame protection.

[0022] In the above method, optionally, in S5, the FLAC numerical simulation software is used to analyze the stability of the protected slope, and the obtained stability coefficient should comply with the relevant regulations of the "Code for Design of Highway Subgrade" (JTG D30).

[0023] In the above method, optionally,

[0024] In S6, the drainage facilities for the granite residual soil slope include intercepting ditches, rapids chutes, drainage ditches, inclined drainage holes, and drainage holes in the protective structure.

[0025] It can be seen from the above technical solutions that compared with the prior art, the present invention discloses and provides a method for optimizing the cross-section structure of a granite residual soil slope, which has the following beneficial effects:

[0026] (1) The beneficial effects of the cross-sectional structure optimization method of granite residual soil slope are mainly reflected in improving the stability and safety of the slope. By optimizing the slope gradient and grade, rainfall infiltration and erosion can be effectively reduced, while making full use of the strength of the granite residual soil itself, thereby reducing the risk of instability.

[0027] (2) Optimized design reduces engineering costs and may provide better environmental adaptability and eco-friendliness; in actual engineering applications, this optimization method helps ensure the long-term stability of the slope while reducing maintenance costs and potential safety hazards. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0029] Figure 1 A flow chart of a granite residual soil slope cross-section structure optimization method provided by the present invention;

[0030] Figure 2 It is a line graph of the calculation results of the slope stability coefficient of the granite residual soil slope disclosed in the present invention;

[0031] Figure 3 It is a line graph of the calculation results of the stability coefficient of the platform span of the granite residual soil slope disclosed in the present invention;

[0032] Figure 4 The image of the intercepting ditch on the slope platform disclosed in the present invention;

[0033] Figure 5 The image of the deep drainage hole in the slope disclosed by the present invention;

[0034] Figure 6 A stability comparison diagram of the three-level slope disclosed in the present invention;

[0035] Figure 7 The present invention discloses a secondary slope stability calculation model for a bare slope without protection;

[0036] Figure 8 The secondary slope stability calculation model for the frame beam (without anchor rod) protection disclosed in the present invention;

[0037] Fig. 9 The present invention discloses Figure 7 and Figure 8 Comparison chart of slope stability coefficients corresponding to two situations;

[0038] Fig.10 A secondary slope stability calculation model for protection of a facing wall disclosed in the present invention;

[0039] Fig.11 For the present invention Figure 7 and Fig.10 Comparison chart of slope stability coefficients corresponding to two situations. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] Reference Figure 1 As shown, the present invention discloses a method for optimizing the cross-section structure of a granite residual soil slope, comprising the following steps:

[0042] S1. Conduct geological drilling on the slope to be excavated and investigate the hydrogeological conditions to obtain relevant data of the slope, including stratum lithology, slope structure, groundwater level, and precipitation conditions;

[0043] S2. Determine the physical and mechanical properties of the stratum lithology based on the obtained slope geological drilling core samples;

[0044] S3. According to the slope height, stratum lithology, land red line and surrounding environment, design the slope levels, slope rate of each level, height of each level and platform width design parameters under different working conditions of the slope to be excavated;

[0045] S4, based on S2 and S3, obtain the slope stability coefficient corresponding to different working conditions and obtain the optimal cross-section structure design working condition;

[0046] S5. Based on the optimal cross-sectional structural design conditions of S4, the protection and support design of the slope to be excavated is carried out in accordance with the principles of technical feasibility, economic rationality, and ecological environmental protection, the slope stability coefficient is obtained, and the cross-sectional structure of the slope after protection is obtained;

[0047] S6. Based on the cross-sectional structure of the slope after protection obtained in S5, combined with hydrogeology and meteorology, drainage design of the slope to be excavated is carried out, and finally the optimized cross-sectional structure of the slope is obtained.

[0048] Furthermore, the physical properties of the soil structure measured in S2 include: particle composition, moisture content, and density of the test soil; the mechanical properties of the soil structure measured include: soil cohesion and internal friction angle determined comprehensively through indoor shear tests, in-situ direct shear tests, or parameter inverse calculations.

[0049] In S2, the in-situ direct shear test was carried out using a HTYZ-20 computer-controlled fully automatic large direct shear apparatus. A vertical load was applied to the sample, and a horizontal shear force was applied after the consolidation was stable, so that the sample was destroyed on the shear plane. The failure shear stress of the sample was recorded, and a curve of the relationship between the failure shear stress and the vertical load was drawn, thereby calculating the cohesion and internal friction angle of the soil.

[0050] The test device includes a shear box, a loading system and a data recording system which are connected in sequence; the shear box is made of a steel plate.

[0051] Specifically, the test device includes a shear box, a loading system and a data recording system connected in sequence; the shear box is a 50cm×50cm×41cm (length, width, height) shear box made of thick steel plate, and a rolling slide is set on the top of the shear box to reduce the friction between the specimen and the vertical jack base. The loading system includes a stacking platform or other reverse load for providing vertical load and a bidirectional hydraulic cylinder jack and a pressurized oil pump for providing horizontal shear. The data acquisition system includes a stress strain sensor, a computer fully automatic collector and a computer. The computer fully automatic collector can realize automatic data collection, and the computer can monitor the test process in real time. The displacement accuracy measured by the device is 0.01mm, the load accuracy is 0.02kN, and the maximum shear displacement is 50mm. The computer fully automatic data collector is powered by a 220v outdoor power supply. The vertical stacking load in this test uses a 25-ton excavator on site to provide reverse load.

[0052] Furthermore, the critical slope for scour of the granite residual soil slope is 46°, that is, the slope ratio is about 1:1.

[0053] The slope rate is an important factor affecting the stability and scouring of granite residual soil. The critical slope of slope erosion refers to the slope when the slope scouring intensity is the largest, which is the slope limit value that designers should avoid. For engineering protection, the factors affecting slope scouring are not only the slope, but also the slope length, protection technology, and timeliness of protection. According to the analysis of engineering research results, no matter what the slope is, there will be different degrees of scouring damage on the slope, indicating that the slope rate of granite residual soil should be based on ensuring the stability of the roadbed.

[0054] For granite residual soil slopes with a height of less than 8m, when the slope ratio is 1:0.75 and 1:0.5, the slope without protection can ensure its stability. However, the slope ratio of soil slopes should not be too steep. It is recommended that the safety slope ratio of granite residual soil slopes with biological protection should be gentler than 1:1.25, the safety slope ratio of granite residual soil slopes with skeleton biological protection should be gentler than 1:1.0, and the safety slope ratio of granite residual soil slopes with facing wall protection should be gentler than 1:0.75.

[0055] Furthermore, for granite residual soil slopes with a height less than 8m, when the slope ratios are 1:0.75 and 1:0.5, the unprotected slopes can ensure their stability.

[0056] Furthermore, in S2, the number of slope levels is set based on different slope heights, including a single-level platform and multi-level platforms;

[0057] Then, the widths and heights of the single-level platform and the second-level platform are set.

[0058] Furthermore, in S3, when the slope height h ≤ 8m, the different working conditions are slope ratios of 1:0.75, 1:1, 1:1.25, and 1:1.5; when the slope height 8m < h ≤ 15m, a stepped cross-section is adopted, the number of slope levels is 2, the platform width is 2m, and when the slope grading height is 8m, the different working conditions are one or two of the slope ratios of 1:1, 1:1.25, and 1:1.5; when the slope height 15m < h ≤ 30m, a stepped cross-section is adopted, the slope grading heights are 8m and 10m, the platform width is 2m, and for each slope grading height, the different working conditions are one or more of the slope ratios of 1:1, 1:1.25, 1:1.5, 1:1.75, and 1:2; when the slope height h > 30m, a stepped cross-section is adopted, the slope grading heights are 8m and 10m, the middle single-level platform is set as a wide platform with widths of 5m, 10m, and 15m, the widths of the remaining platforms are 2m, and for each slope grading height and each platform width, the different working conditions are one or more of the slope ratios of 1:1, 1:1.25, 1:1.5, 1:1.75, and 1:2;

[0059] In S3, the number of slope levels is set based on the slope height and the slope grading height, including a single-level slope, a two-level slope,..., a multi-level slope, and then the single-level platform, the second-level platform,..., the multi-level platforms are set.

[0060] See Figure 3 As shown, when the slope platform width is less than 3m, the platform width has little influence on the slope stability coefficient.

[0061] Furthermore, in S4, the FLAC numerical simulation software is used to analyze the slope stability coefficients under different working conditions.

[0062] The FLAC numerical simulation software is used to analyze the slope stability of six working conditions with slope ratios of 1:0.5, 1:0.75, 1:1, 1:1.25, 1:1.5, and 1:1.75. The stability of a single-level slope and a two-level slope is analyzed for each working condition, and the platform width of the two-level slope is set to 2m. When analyzing the stability, the calculation parameters of the granite residual soil are density 1.78g / cm 3, modulus 4.5MPa, Poisson's ratio 0.25, cohesion 24.5kPa, internal friction angle 13.5°. The model soil layers are all granite residual soil. During the calculation, the bottom of the model is a fixed boundary, the surroundings are roller boundary constraints, and the top is a free boundary. Under each working condition, the simulated excavation process is set to 4 steps: the first step is excavation 0~4m, the second step is excavation 5~8m, the third step is excavation 9~12m, and the fourth step is excavation 13~16m. The safety factor is calculated when excavating to the first and fourth steps.

[0063] See also Figure 2 As shown in the figure, when the granite residual soil slope is a first-level slope, even when the slope rate is 1:0.5, its stability coefficient (1.29) meets the requirements of the Highway Roadbed Design Code (JTG D30-2015). However, when the granite residual soil slope is a second-level slope, the stability coefficients of the slope rates of 1:0.5 and 1:0.75 are both less than 1.0, and the slope is in an unstable state; the slopes of 1:1.0 and 1:1.25 are in a basically stable state, and the slopes of 1:1.5 and 1:1.75 are in a stable state.

[0064] The specific contents of S5 are as follows:

[0065] Based on the optimal working conditions obtained by S4, the roadbed protection design is carried out in combination with the slope height and slope gradient, as shown in Table 1. The protection types include: plant protection, skeleton plant protection, bamboo lattice plant protection, geosynthetics plant protection, face wall protection and anchor (anchor cable) frame protection.

[0066] Table 1 Protection design types

[0067]

[0068]

[0069] The drainage facilities for granite residual soil slopes include intercepting ditches, drainage ditches, platforms and drainage holes of protective structures.

[0070] Rainfall and slope runoff are the main causes of shallow damage such as slope scour and collapse, and are also an important mechanism for shallow disturbance of granite residual soil slopes. Therefore, necessary engineering measures such as prevention, drainage and drainage should be taken to drain the slope surface and slope body, which is of great significance to improving the stability of granite residual soil slopes. The drainage facilities of granite residual soil slopes include intercepting ditches, drainage ditches, platforms and drainage holes of protective structures. Figure 4 The figure shows the intercepting ditch on the granite residual soil slope platform, see Figure 5 Shown are deep drainage holes in the slope.

[0071] In a specific embodiment, the relationship between the protection type and the applicable slope is obtained through actual work investigation:

[0072] 1) Relationship between unprotected slope failure and slope rate

[0073] A total of 32 unprotected granite residual soil slopes were investigated, of which 22 were damaged by scouring, and only 4 slopes had partial collapse or were in a state of collapse and damage, with no overall instability. Among them, the slopes with collapse damage were all steep slopes, and the slopes were all steeper than 1:0.5; the slopes with scouring damage had slopes of steep, 1:1.0, 1:1.25 and 1:1.5, that is, granite residual soil slopes with different slope ratios had scouring. Therefore, for granite residual soil slopes, pure soil slopes of granite residual soil with a slope ratio of less than 1:1.5 have good stability, but are prone to scouring damage, followed by partial collapse. In actual projects, the anti-scouring management of granite residual soil slopes should be strengthened.

[0074] 2) Relationship between bioprotection slope damage and slope rate

[0075] A total of 12 bioprotected high liquid limit soil slopes were investigated, of which 5 were eroded, 2 collapsed, and 2 were overall unstable. Among them, the slope ratios were basically 1:1 and 1:1.25, the collapsed slopes were in a steep state, and the overall unstable slope ratio was slower than 1:1.75, but the slope height was large, exceeding 20m, and was a Class III slope. The survey showed that bioprotection has a very limited effect on improving slope stability. However, it has a significant effect on preventing and controlling erosion damage to granite residual soil slopes.

[0076] Combined with the case of bioprotection granite residual soil slope instability engineering, the stability of the third-level slope under different slope rates was analyzed using FLAC numerical simulation software. The calculation results are as follows: Figure 6 As shown in the table, when the slope ratio is 1:1.75, the stability coefficient of the newly exposed third-level slope is only 1.10, which is in an unstable and basically stable state. As the excavation exposure height increases, the slope stability coefficient decreases. The excavation exposure height of the granite residual soil slope should not exceed 16m (two-level slope), otherwise continued excavation without protection will easily cause slope instability. Numerical simulation results also show that when the slope height exceeds 20m, after a long period of dry-wet cycle, biological protection cannot guarantee the stability of the slope.

[0077] 3) Relationship between slope collapse damage and slope rate of skeleton grass planting

[0078] A total of 21 granite residual soil slopes protected by grass planting frameworks were investigated (including anchor frames and cable frames, of which 3 were scours). The slopes of granite residual soil slopes investigated in this study were mainly 1:1 and 1:1.25. The stability of the slopes protected by the herringbone framework, anchor frame beam framework and cable frame beam framework was good, and no overall instability or damage occurred.

[0079] In order to study the effect of skeleton protection on the stability of granite residual soil slope, the FLAC numerical simulation software was used to construct a bare slope without protection (see Figure 7 The calculation model of the secondary slope stability with frame beam (without anchor rod) as shown in Figure 8 As shown in Figure 2), the slope stability coefficients for the two cases are obtained. Fig. 9 As shown in the figure, the stability coefficient of the slope protected by pure frame beams is slightly higher than that of the bare slope. The stability coefficient of the excavated first-level slope (8m) is only 0.1 higher than that of the unprotected condition, and the stability coefficient of the excavated second-level slope (16m) is 0.3 higher than that of the unprotected condition. It can be seen that the higher the slope height, the more obvious the effect of skeleton protection on slope stability. However, further comprehensive comparative analysis of bare slope and pure frame beam protection shows that pure skeleton protection has very limited effect on improving slope stability.

[0080] 4) Relationship between the damage of the slope protected by the facing wall and the slope rate

[0081] A total of 1 granite residual soil slope was investigated with a retaining wall, which was a treatment measure for the overall unstable slope. The slope ratio was about 1:1, and the granite residual soil slope after protection was stable. Therefore, the retaining wall protection is very effective in improving the stability and safety of the granite residual soil slope. When the granite residual soil slope does not meet the conditions for slope reduction, it is recommended to use a retaining wall for protection, and the slope ratio should be gentler than 1:0.75.

[0082] In order to study the effect of facing wall protection on the stability of granite residual soil slope, the FLAC numerical simulation software was used to construct a bare slope without protection (see Figure 7 The calculation model of the secondary slope stability with protection of the primary slope protection wall and the secondary slope protection wall (see Fig.10 The slope stability coefficients of the two cases are obtained, see Fig.11 As shown, it can be seen that the stability coefficient of the slope protected by the retaining wall is significantly improved compared with the bare slope. When the slope is excavated 16m, the stability coefficient is increased by 0.14 compared with the unprotected condition.

[0083] Furthermore, in S5, the stability of the protective slope is analyzed using FLAC numerical simulation software, and the stability coefficient obtained should comply with the relevant provisions of the Highway Subgrade Design Code (JTG D30).

[0084] Furthermore, in S6, the drainage and prevention facilities of the granite residual soil slope include intercepting ditches, rapids troughs, drainage ditches, inclined drainage holes and drainage holes of the protective structure.

[0085] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0086] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for optimizing the cross-sectional structure of a granite residual soil slope, characterized in that: The following steps are involved: S1. Conduct geological drilling on the slope to be excavated and investigate the hydrogeological conditions to obtain relevant data of the slope, including stratum lithology, slope structure, groundwater level, and precipitation conditions; S2. Determine the physical and mechanical properties of the stratum lithology based on the obtained slope geological drilling core samples; S3. According to the slope height, stratum lithology, land red line and surrounding environment, design the slope levels, slope rate of each level, height of each level and platform width design parameters under different working conditions of the slope to be excavated; S4, based on S2 and S3, obtain the slope stability coefficient corresponding to different working conditions and obtain the optimal cross-section structure design working condition; S5. Based on the optimal cross-sectional structural design conditions of S4, the protection and support design of the slope to be excavated is performed to obtain the slope stability coefficient and the cross-sectional structure of the slope after protection; S6. Based on the cross-sectional structure of the slope after protection obtained in S5, combined with hydrogeology and meteorology, drainage design of the slope to be excavated is carried out, and finally the optimized cross-sectional structure of the slope is obtained.

2. The method for optimizing the cross-sectional structure of a granite residual soil slope according to claim 1, characterized in that: The physical properties of the soil structure measured in S2 include: particle composition, moisture content, and density of the test soil; the mechanical properties of the soil structure measured include: soil cohesion and internal friction angle determined by indoor shear test, in-situ direct shear test or parameter inverse algorithm.

3. The method for optimizing the cross-sectional structure of a granite residual soil slope according to claim 1, characterized in that: In S2, the in-situ direct shear test was carried out using a HTYZ-20 computer-controlled fully automatic large direct shear apparatus. A vertical load was applied to the sample, and a horizontal shear force was applied after the consolidation was stable, so that the sample was destroyed on the shear plane. The failure shear stress of the sample was recorded, and a curve of the relationship between the failure shear stress and the vertical load was drawn, thereby calculating the cohesion and internal friction angle of the soil.

4. The method for optimizing the cross-sectional structure of a granite residual soil slope according to claim 3, characterized in that: The test device includes a shear box, a loading system and a data recording system which are connected in sequence; the shear box is made of a steel plate.

5. The method for optimizing the cross-sectional structure of a granite residual soil slope according to claim 1, characterized in that: In S3, when the slope height h ≤ 8m, the different working conditions are slope ratios of 1:0.75, 1:1, 1:1.25, and 1:1.5 respectively; when the slope height 8m < h ≤ 15m, a stepped section is adopted, the number of slope levels is 2, the platform width is 2m, and when the slope classification height is 8m, the different working conditions are one or two of the slope ratios of 1:1, 1:1.25, and 1:1.5; when the slope height 15m < h ≤ 30m, a stepped section is adopted, the slope classification heights are 8m and 10m, the platform width is 2m, and for each slope classification height, the different working conditions are one or more of the slope ratios of 1:1, 1:1.25, 1:1.5, 1:1.75, and 1:2; when the slope height h > 30m, a stepped section is adopted, the slope classification heights are 8m and 10m, the middle platform is set as a wide platform, the platform widths are 5m, 10m, and 15m, the widths of the remaining platforms are 2m, and for each slope classification height and each platform width, the different working conditions are one or more of the slope ratios of 1:1, 1:1.25, 1:1.5, 1:1.75, and 1:2; In S3, the number of slope levels is set based on the slope height and the slope classification height, including the first-level slope, the second-level slope,..., the multi-level slope, and then the first-level platform, the second-level platform,..., the multi-level platform are set.

6. The optimization method for the granite residual soil slope section structure according to claim 1, characterized in that, In S4, the FLAC numerical simulation software is used to analyze the slope stability coefficient under different working conditions.

7. The optimization method for the granite residual soil slope section structure according to claim 6, characterized in that, The specific content of S5 is: Based on the optimal working condition obtained in S4, combined with the slope height and the slope ratio, the subgrade protection design is carried out, and the protection types include: vegetation protection, skeleton vegetation protection, bamboo lattice vegetation protection, geosynthetic material vegetation protection, retaining wall protection, anchor rod / cable frame protection.

8. The optimization method for the granite residual soil slope section structure according to claim 6, characterized in that, In S5, the FLAC numerical simulation software is used to analyze the stability of the protected slope, and the obtained stability coefficient shall comply with the relevant provisions of the "Code for Design of Highway Subgrade" (JTG D30).

9. The optimization method for the granite residual soil slope section structure according to claim 1, characterized in that, In S6, the drainage facilities for the granite residual soil slope include intercepting ditches, chute spillways, drainage ditches, inclined drainage holes, and drain holes in the protection structure.

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