High embankment modified reinforced surface soil slope flexible protection structure and stability estimation method

Abstract

This invention discloses a flexible protection structure for modified and reinforced surface soil slopes of high-fill embankments and a method for stability prediction. The protection structure includes a multi-level platform slope and a drainage structure. The top of each platform is a flexible retaining structure, which is constructed in layers of low-dosage modified soil. Each layer of low-dosage modified soil is wrapped by a layer of geogrid. Vertical steel beams for support are installed inside the flexible retaining structure at the toe of the slope. The slope of the multi-level platforms is filled with high-dosage modified soil. The drainage structure includes a mesh-like water collection and interception structure, T-shaped drainage pipes, and drainage boards. This invention fully utilizes the skeletal function of the slope protection structure, the erosion and softening prevention function of the drainage structure, and the flexible retaining structure to protect high-fill embankment slopes in hot and humid southern regions under the premise of low construction cost, fast construction speed, and guaranteed construction quality.

Description

Technical Field

[0001] This invention belongs to the field of slope treatment technology, and relates to a flexible protection structure for modified and reinforced surface soil slopes of high embankments and a method for stability prediction. Background Technology

[0002] With the continuous development of my country's economy, the construction of transportation infrastructure is also progressing steadily, with the newly added parts mainly located in the hot and humid regions of southern my country. These regions are primarily characterized by tropical and subtropical monsoon climates, abundant rainfall, and complex soil, geological, and hydrological conditions. Consequently, the slopes of high-fill embankments constructed in these areas frequently experience shallow landslides due to rainwater infiltration, surface runoff erosion, and localized waterlogging.

[0003] Currently, traditional slope protection methods mainly involve setting various structures and materials on the slope surface to slow down or prevent erosion and collapse, including masonry, lattice frames, turf cover, shotcrete, anchor bolt support, and retaining walls. Among these, masonry, retaining walls, and lattice frames have high construction costs, while shotcrete and anchor bolt support do not meet the requirements of ecological slope protection. Traditional slope protection methods have certain limitations in engineering applications. Based on this, some scholars have proposed improved slope protection methods. For example, patent application number CN202110064672.9 discloses a slope protection structure to prevent soil erosion, which helps improve soil and water conservation efficiency. However, the slope protection structure composed of protective layers, reinforcing layers, and planting layers is complex to construct, and whether its drainage holes can achieve the expected drainage effect in the humid and rainy southern regions is questionable. Patent application number CN201711132644.6 discloses a slope protection structure that divides the slope into several sections using lattice beams. Planting vegetation and installing water filters can reduce the erosion effect of water flow on the slope. However, in the hot and humid environment of the south, rigid structures such as lattice beams are prone to deformation and cracks, which will affect their service performance. Patent application number CN201610963648.8 discloses a cement-modified soil reinforced geogrid structure and its construction method, which can realize the panelless construction of the reinforced soil structure on steep slopes and has many advantages. However, the slope constructed with cement-modified soil is generally alkaline, and green plants cannot grow on the slope. Greening of the slope can only be achieved through planting bags.

[0004] In summary, the existing slope protection structures generally have the following problems in addressing the shallow instability caused by water damage to the slopes of high-fill embankments in the hot and humid regions of southern China: (1) They can alleviate the shallow instability caused by water damage to the slopes to a certain extent, but they are not very effective in addressing the scouring damage to the slopes of high-fill embankments in the hot and humid regions of southern China; (2) Most existing strong retaining structures have poor environmental compatibility and are prone to shrinkage cracks in hot and humid environments, leading to continuous deterioration of the structural performance; moreover, the construction of strong retaining structures is complex and costly, and there are certain requirements for construction conditions such as terrain and slope; (3) The construction process of traditional protective structures is mainly manual, the construction progress is slow, and the construction quality is difficult to guarantee; (4) Traditional cement-modified slopes are alkaline in their modified soil and can only be greened by planting bags. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a flexible protection structure for modified and reinforced surface soil slopes of high-fill embankments. It fully utilizes the skeletal function of long-distance slope protection structures, the erosion and softening prevention functions of drainage structures, and the flexible retaining structure. This structure can protect the slopes of high-fill embankments in humid and hot southern regions while ensuring low construction costs, fast construction speed, and guaranteed construction quality.

[0006] Another objective of this invention is to provide a method for predicting the stability of a flexible protective structure for modified and reinforced surface soil slopes of high-fill embankments.

[0007] The technical solution adopted in this invention is a flexible protection structure for modified and reinforced surface soil slopes of high-fill embankments, comprising a multi-level platform slope and drainage structure. The top of each platform is a flexible retaining structure, which is constructed by layering low-dosage modified soil layers. Each low-dosage modified soil layer is wrapped by a layer of geogrid. The side of the flexible retaining structure near the slope is provided with impermeable geotextile. Vertical steel beams for support are provided inside the slope of the flexible retaining structure at the toe of the slope. The slope of the multi-level platform is filled with high-dosage modified soil layers.

[0008] The drainage structure includes a mesh-like water collection and interception structure, a T-shaped drainage pipe, and a drainage board; the mesh-like water collection and interception structure is located on the surface of the high-dosage modified soil layer; the T-shaped drainage pipe is located inside the flexible retaining structure; and the drainage board is located at the bottom layer of the flexible retaining structure at the toe of the slope.

[0009] Furthermore, the mesh-like water collection and interception structure includes a longitudinal water collection ditch, a transverse water collection ditch, and a lateral interception ditch. The transverse water collection ditch and the lateral interception ditch are connected through a reinforcement point. The longitudinal water collection ditch is a catenary arch shape, and the concave part of the longitudinal water collection ditch has a high-modification soil layer with a depth of 30cm to 60cm to resist the expansion and contraction forces of the soil under the interaction of temperature and humidity.

[0010] Furthermore, the T-shaped drainage pipe includes a vertically arranged transverse drainage pipe and an oblique drainage pipe. The transverse drainage pipe is arranged longitudinally along the road, and the oblique drainage pipe is arranged transversely along the road. The slope of the transverse drainage pipe is 1° to 3°, and the slope of the oblique drainage pipe is 3° to 8°. The oblique drainage pipe is coplanar with and connected to the longitudinal water collection ditch, and is used to discharge the water in the T-shaped drainage pipe through the longitudinal water collection ditch.

[0011] Both the horizontal and inclined drainage pipes are equipped with one-way permeable holes for draining water from the soil into the T-shaped drainage pipes in one direction.

[0012] The inclined drain pipe is equipped with a first filter section and a second filter section. The filling medium of the first filter section is CCT heavy metal stabilizer, and the filling medium of the second filter section is microbial or algal metabolites. The outlet of the inclined drain pipe is equipped with a mesh screen.

[0013] Furthermore, the low-dosage modified soil layer includes gold tailings, slope topsoil, and cement, with the mass ratio of gold tailings, slope topsoil, and cement being x:10-xy:y, where x∈[0.5, 1.0] and y∈[0, 1.5].

[0014] Furthermore, the high-content modified soil layer includes gold tailings, slope topsoil, and cement, with the mass ratio of gold tailings, slope topsoil, and cement being x:10-xy:y, where x∈[1.5, 2.0] and y∈[0, 1.5].

[0015] Furthermore, a leveling pad is provided at the bottom of the drainage board.

[0016] Furthermore, the height of the flexible retaining structure located at the toe of the slope is greater than that of the flexible retaining structures at other locations; the steel beam includes a main body, a concave block, and a convex block; adjacent main bodies of two steel beams are connected by mortise and tenon joints using the concave block and the convex block.

[0017] Furthermore, the geogrid with the reverse wrapping is fixed by U-shaped nails, and ecological vegetation bags are embedded in the high-dosage modified soil layer in the gaps of the mesh water collection and interception structure.

[0018] Furthermore, a roadside ditch is provided on the top shoulder of the slope, and a drainage ditch is provided at the toe of the slope. A high-modification soil layer with a thickness of 20cm to 40cm is provided on both sides of the drainage ditch.

[0019] A method for predicting the stability of a flexible protective structure for a modified and reinforced surface soil slope of a high-fill embankment, specifically including the following:

[0020] The expression for the stability safety factor FS of the modified and reinforced surface soil flexible protection structure of high embankment slope:

[0021]

[0022] In the formula: γ is the natural unit weight of the soil; c', These represent the effective cohesion and internal friction angle of the soil, respectively; σ s The absorbed stress expressed in terms of normalized volumetric water content or saturation; u a L1 represents pore air pressure; L2 represents soil strip length; β represents slope gradient; p1 represents the resistance of the soil at the lower edge; and z represents the thickness of the soil strip.

[0023] In the formula, the anti-slip force K1 of the protective structure is:

[0024]

[0025] In the formula: c”, These represent the effective cohesion and internal friction angle of the modified soil, respectively; γ s The weight of the modified soil; z s The thickness of the modified soil;

[0026] In the formula, the anchorage pull-out force T1 of the reinforcing bar is calculated by the following formula:

[0027]

[0028] The anchorage pull-out force T of the i-th layer of reinforcement pi Calculate using the following formula:

[0029] T pi =2σ vi aL ei f

[0030] In the formula: σ vi σ is the vertical stress at the location of the geogrid. vi The value is the sum of the self-weight of the backfill and the pressure generated by the uniformly distributed permanent load on the top surface of the reinforced body, without considering traffic loads and other variable loads; a is the width of the geogrid; L ei denoted as the effective anchorage length of the geogrid; f is the coefficient of friction between the geogrid and the fill.

[0031] The beneficial effects of this invention are:

[0032] (1) This invention protects the slope by arranging transverse and vertical drainage ditches and lateral interception ditches in layers from top to bottom in the direction of slope scour and erosion, and adopting a multi-platform folded linear modified and reinforced surface soil flexible protection structure. Without affecting the slope stability safety factor, it can intercept a large amount of slope rainfall and road surface water. The design of shortening the scour path through graded platforms and reducing the water flow velocity through curved drainage ditches reduces the scour energy. Compared with traditional protection structures, the impact of rainfall scour on the slope is reduced by more than 40%. It is very suitable for high fill embankment slopes in the humid and rainy southern regions.

[0033] (2) Preliminary studies have shown that the modified soil obtained by mixing a certain amount of gold tailings with the in-situ shallow soil of the slope can adapt to local climate change and avoid drying shrinkage cracks. The modified reinforced surface soil flexible protection structure (high-dosage modified flexible long-distance slope protection structure + low-dosage modified flexible retaining wall) formed by this invention does not require rigid frame protection, thus meeting the overall stability requirements of the slope. Compared with the existing technology, the modified reinforced surface soil flexible protection structure overcomes the defect that flexible support cannot provide strong support, and can achieve faster, more economical and environmentally friendly support and reinforcement of high embankment slopes than traditional strong slope support schemes (anchor cable + anti-slide pile, anchor cable grid + anti-slide pile, anchor rod grid + anti-slide pile, pile plate wall), reducing slope reinforcement costs by more than 30%.

[0034] (3) The modified reinforced surface soil long-distance slope flexible protection structure of this invention uses mechanical construction instead of manual construction, resulting in faster construction speed (increasing construction speed by more than 50%), better safety, and easier quality assurance. It employs a combination of ecological vegetation bags and the protection structure for three-dimensional vegetation protection. Specifically, the use of plants such as Bermuda grass and Cosmos bipinnatus to green the gold tailings modified slope can significantly reduce slope protection costs and improve slope ecological benefits. Simultaneously, this invention incorporates a CCT heavy metal stabilizer and a microbial / algal metabolite drainage filtration section for infiltrated water, effectively avoiding heavy metal pollution problems that may result from solidifying solid waste materials. This invention is a new technology suitable for "quality improvement and cost reduction" in highway construction and for creating century-old quality projects, and it deserves widespread promotion in highway construction.

[0035] (4) Addressing the issue that traditional support schemes, such as anti-slide piles, require extensive excavation of the original slope before support can be implemented, this invention employs a simultaneous excavation and support method. The original high-fill embankment slope is divided into multiple zigzag steps, constructed sequentially from top to bottom and from left to right. Simultaneously, small steel beams are used for temporary support during the toe excavation. Upon completion, this structure becomes a permanent support structure. All of the above effectively prevents slope instability accidents due to untimely support during construction, thus ensuring construction safety.

[0036] (5) In view of the problem that the traditional method of reducing seepage force and reducing slope gradient is mainly used to improve the safety factor in the stability verification of shallow slope instability mode, this invention provides a method for predicting the stability of shallow slope instability that can further consider the amount of modified reinforced soil, the number of reinforcement layers and the thickness of soil layer. According to the specification, the modified soil parameters required for the protection structure are inverted, which plays an important role in guiding slope design and construction. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a top view of the slope surface according to an embodiment of the present invention.

[0039] Figure 2 This is a sectional view of the slope I-I stepped section according to an embodiment of the present invention.

[0040] Figure 3 This is a typical cross-sectional view of slope II-II according to an embodiment of the present invention.

[0041] Figure 4 This is a detailed diagram of the long-distance flexible slope protection structure of the modified and reinforced surface soil in the AA region of the slope section II-II in an embodiment of the present invention.

[0042] Figure 5 This is a detailed diagram of the long-distance flexible slope protection structure of the modified and reinforced surface soil in the BB region of the slope section I-I in an embodiment of the present invention.

[0043] Figure 6 This is a schematic diagram of the stress analysis of a curved longitudinal water collection ditch.

[0044] Figure 7 The curves show the variation of shear strength of the surface red clay of the slope under different gold tailings and cement content conditions.

[0045] Figure 8 This is a schematic diagram of a drainage pipe embedded in a flexible modified reinforced soil retaining wall.

[0046] Figure 9 This is a schematic diagram of the stress conditions in shallow instability of a traditional slope.

[0047] Figure 10 A schematic diagram of the stress conditions of a long-distance flexible protective structure for modified and reinforced surface soil.

[0048] Figure 11 A schematic diagram of temporary support for small steel beams after excavation of a modified and reinforced retaining wall at the slope toe.

[0049] Figure 12 This is a schematic diagram of a mortise and tenon connection for a small steel beam.

[0050] In the diagram: 1. Longitudinal drainage ditch; 2. Transverse drainage ditch; 3. Drainage ditch; 4. High-modification soil layer; 5. Geogrid; 6. Low-modification soil layer; 7. Roadside ditch; 8. Lateral intercepting ditch; 9. Reinforcement point; 10. Ecological vegetation bag; 11. U-shaped nail; 12. Impermeable geotextile; 13. High embankment slope; 14. Drainage board; 15. Leveling layer; 16. T-shaped drainage pipe; 16-1. Transverse drainage pipe; 16-2. Inclined drainage pipe; 16-3. One-way permeable hole; 16-4. First filter section; 16-5. Second filter section; 16-6. Mesh grid; 17. Steel beam; 17-1. Concave block; 17-2. Protruding block. Detailed Implementation

[0051] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0052] Example 1,

[0053] A modified and reinforced surface soil flexible protection structure for high embankment slopes is installed on the slope 13 of a high embankment in a humid and hot southern region. The high embankment slope 13 is constructed during road engineering, and its filling height is greater than 18.0m (soil) or more than 20.0m (rock). In this specific implementation case, a soil embankment slope is used as an example.

[0054] The modified and reinforced surface soil flexible protection structure for high embankments includes long-distance slope protection structures, drainage and waterproofing structures, and flexible retaining structures, such as... Figure 1-5 As shown.

[0055] Modified reinforced topsoil refers to a reinforced soil structure formed by modifying the topsoil of a slope. Within a certain dosage range, the higher the gold tailings content, the higher the shear strength of the modified soil. X-ray diffraction and Fourier transform infrared spectroscopy analysis of soil at different depths on a slope revealed that the farther away from the slope surface, the higher the intensity of the active crystal diffraction peaks in the soil, and the sharper the frequency of the active functional group peaks (thus defining the slope topsoil as 0–0.5 m). Therefore, flexible protective structures constructed using slope topsoil can effectively avoid drying shrinkage deformation caused by climate change and are less prone to cracking.

[0056] In this embodiment of the invention, the high-dosage modified soil layer 4 and the low-dosage modified soil layer 6 use slope topsoil, and the modified materials mainly use solid waste materials such as tailings. Their main functions are: 1. Under long-term physical and chemical weathering, the topsoil becomes more crystalline, and the retaining wall structure formed by its modification and reinforcement can better adapt to the local environment, preventing deformation and cracking; 2. Due to the continuous extraction and consumption of resources, a large amount of solid waste materials such as tailings are generated, requiring mines and factories to spend a lot of money and high-quality land resources to treat them; this embodiment effectively solves the problem of tailings and other solid waste materials treatment by adding them as a modified material to the slope support structure, and the feasibility of this method has been verified through experiments and engineering.

[0057] The high-content modified soil layer 4 consists of 20% gold tailings + slope topsoil + a certain amount of cement (optional, depending on the modified soil parameters required for the design of the protective structure; if the geological conditions are too complex and the modified soil parameters are too high, and the gold tailings cannot meet the requirements, then a certain amount of cement is added); the high-content modified soil layer 4 includes gold tailings, slope topsoil, and cement, and the mass ratio of gold tailings, slope topsoil, and cement is x:10-xy:y, where x∈[1.5, 2.0], y∈[0, 1.5]; exceeding this range results in excessive cement content and excessive overall modification cost.

[0058] Low-dosage modified soil layer 6 consists of 10% gold tailings + slope topsoil + a certain amount of cement (optional); Low-dosage modified soil layer 6 includes gold tailings, slope topsoil, and cement, with a mass ratio of x:10-xy:y, where x∈[0.5, 1.0], y∈[0, 1.5]; exceeding this range results in excessive cement dosage and excessive overall modification cost.

[0059] The long-distance slope protection structure includes a high-content modified soil layer 4 and a mesh-like water collection and interception structure. The mesh-like water collection and interception structure includes a longitudinal water collection ditch 1, a transverse water collection ditch 2 and a lateral water interception ditch 8. The transverse water collection ditch 2 and the lateral water interception ditch 8 are connected by a reinforcement point 9. In this embodiment, the reinforcement point 9 is made of reinforced concrete, forming an integral slope protection structure composed of the transverse water collection ditch 2, the longitudinal water collection ditch 1 and the lateral water interception ditch 8.

[0060] The longitudinal water collection ditch 1 and the transverse water collection ditch 2 are naturally intersected. The longitudinal water collection ditch 1 is 2cm lower than the transverse water collection ditch 2 to prevent water from flowing back into the transverse water collection ditch 2 when it is flushed by the longitudinal water collection ditch 1.

[0061] Lateral intercepting ditch 8 serves as the edge boundary of the slope, connecting the side ditches on both sides of the road surface at the top and the drainage ditch at the bottom of the embankment slope at the bottom. It has no special shape characteristics and is designed and constructed according to the actual slope orientation. The cross-section of the longitudinal collection ditch 1 is smaller than that of the lateral intercepting ditch 8, and the expected flow rate is: longitudinal collection ditch 1 < lateral intercepting ditch 8.

[0062] The high-dosage modified soil is a modified soil formed by mixing gold tailings with the in-situ shallow soil of the slope. The mass fraction of gold tailings is 20%. The high-dosage modified soil is constructed by excavator and adhered to the slope 13 of the high embankment and the slope surface of the flexible retaining structure to form a high-dosage modified soil layer 4. During the construction process, ecological vegetation bags 10 are embedded into the high-dosage modified soil layer 4 through the gaps in the mesh water collection and interception structure. Figure 1 (Only a portion of the ecological vegetation bags 10 is shown.) The ecological vegetation bags 10 are arranged in a row at certain intervals along the slope.

[0063] The drainage structure includes a drainage structure and a waterproof structure. The drainage structure includes, from top to bottom, a transverse water collection ditch 2, a longitudinal water collection ditch 1, a lateral intercepting ditch 8, a roadside ditch 7, a drainage channel 3, a drainage board 14, and a T-shaped drainage pipe 16.

[0064] like Figure 1 As shown, the longitudinal water collection ditch 1 is a catenary arch, and its force analysis diagram is as follows. Figure 6 As shown, to resist the expansion and contraction forces of the soil under the interaction of temperature and humidity and to prevent the drainage structure from developing shrinkage cracks, there are two options: First, the catenary arch shape of the longitudinal drainage ditch 1 has good compressive strength; second, the longitudinal drainage ditch 1 is located within a high-modification soil layer 4, so that the concave part of the longitudinal drainage ditch 1 has a high-modification soil layer 4 with a depth of 30cm to 60cm, further improving the compressive strength to resist the expansion and contraction forces of the soil under the interaction of temperature and humidity. Simultaneously, the longitudinal drainage ditch 1 also has the following functions: the curved design can reduce the impact velocity of water flow, making it more suitable for steep slopes; compared to the straight design, the curved design is similar to interlocking two adjacent slope surfaces on the overall slope, playing a role in preventing slope instability; furthermore, compared to the straight design, the curved design is more aesthetically pleasing. Since on-site formwork and casting of the curved longitudinal drainage ditch 1 is relatively complex, it can be prefabricated in the factory and installed on-site during construction.

[0065] like Figure 5 As shown, the T-shaped drainage pipe 16 is installed inside the low-dosage modified soil layer 6, with a vertical spacing of 1 to 2 meters. Setting it smaller than this range is considered excessive and wasteful of resources. Because the capillary effect of the soil has a certain range, setting it larger than this range will not be able to cover the area inside the slope that needs drainage.

[0066] like Figure 8As shown, the T-shaped drainage pipe 16 includes a transverse drainage pipe 16-1 installed along the road's driving direction (longitudinal direction) and an oblique drainage pipe 16-2 installed transversely along the road. The oblique drainage pipe 16-2 is coplanar with and connected to the longitudinal collection ditch 1, and is used to discharge water from the T-shaped drainage pipe 16 through the longitudinal collection ditch 1. The transverse drainage pipe 16-1 is installed from both sides towards the middle, and its slope ranges from 1° to 3°. If the slope is too small, the water cannot be discharged; if the slope is too large, the construction process is complicated. The oblique drainage pipe 16-2 has a slope of 3° to 8°. If the slope is too small, the water cannot be discharged, and it may cause water in the longitudinal collection ditch 1 to flow back into the oblique drainage pipe 16-2.

[0067] Both the horizontal drain pipe 16-1 and the inclined drain pipe 16-2 are equipped with one-way permeable holes 16-3; the inclined drain pipe 16-2 is also equipped with a first filter section 16-4 and a second filter section 16-5. The filling medium of the first filter section 16-4 is CCT heavy metal stabilizer to reduce heavy metal pollution. The filling medium of the second filter section 16-5 is microbial or algal metabolites. The outlet of the inclined drain pipe 16-2 is equipped with a mesh screen 16-6 to prevent debris from entering the pipe and clogging it.

[0068] The purpose of the one-way permeable hole 16-3 is to drain water from the soil into the T-shaped drainage pipe 16 in one direction. The hole 16-3 has an absorbent layer inside, surrounded by a protective layer. The absorbent layer is made of superabsorbent fiber, and the pore diameter of the one-way permeable hole 16-3 ranges from 2mm to 10mm. The principle of one-way drainage is that superabsorbent fiber (SAF) has strong water absorption, absorbing 30 to 50 times its own weight in water through capillary action. As the absorbed water accumulates, it enters the T-shaped drainage pipe 16.

[0069] The purpose of setting up the first filter section 16-4 and the second filter section 16-5 is as follows: Since solid waste materials are used for filling and protecting the slope structure, heavy metals in the solid waste materials will dissolve in the water under the action of water infiltration; in order to completely solidify the heavy metals in the tailings and prevent them from flowing into the drainage system through the drainage pipe (because the anti-scouring effect is good, there are fewer heavy metal ions in the slope runoff), two filter sections are specially set up; CCT is a stabilizer that is applicable to most non-variable valence heavy metal pollution, and the metabolites of algae and microbial cells have a good adsorption effect on heavy metals, and have the advantages of low cost, good selectivity, large adsorption capacity and wide range of applicable concentrations.

[0070] The drainage ditch 3 is lined with compacted, high-modification soil of 20cm to 40cm thickness on both sides to accommodate drying shrinkage deformation in a hot and humid environment. A thickness exceeding this range constitutes excessive support and wastes resources. A thickness less than this range will fail to achieve the intended purpose.

[0071] Drainage board 14 is located at the bottom layer. The middle of drainage board 14 is an extruded plastic core board, which is the skeleton and channel of drainage board 14. Its cross section is in the shape of a parallel cross. It is wrapped with non-woven geotextile as a filter layer. The core board plays a supporting role and drains the water that seeps into the filter layer. Through the transverse water collection ditch 2, longitudinal water collection ditch 1, lateral intercepting ditch 8, and T-shaped drainage pipe 16, it can collect the water from the slope, the road surface water collected in the roadside ditch 7, and the water seeping into the soil, and finally collect it into the drainage ditch 3 at the toe of the high fill embankment slope.

[0072] The waterproof structure includes an impermeable geotextile 12. Runoff scouring and erosion are the main causes of shallow water damage to slopes. The impermeable geotextile 12 can further prevent water from stagnant on the slope from entering the interior of the slope, preventing slope instability caused by the softening of the soil due to increased water content. The high-modification soil layer 4 has a certain strength. According to the principle that the slope stability safety factor remains unchanged when the total slope ratio of a zigzag slope is equal to that of a straight slope, the multi-platform zigzag design can reduce the scouring energy of rainfall on the slope.

[0073] Flexible retaining structures include partially flexible modified reinforced retaining walls in the slope and flexible modified reinforced retaining walls at the toe of high embankment slopes. The difference between the two types of flexible modified reinforced retaining walls is that the flexible modified reinforced retaining walls at the toe of high embankment slopes have inconsistent heights compared to partially flexible modified reinforced retaining walls, and often include the following structures: steel beams 17, drainage boards 14, and leveling bedding layers 15. The flexible modified reinforced retaining walls consist of transverse drainage ditches 2, geogrids 5, U-shaped nails 11, and low-dosage modified compacted soil.

[0074] Flexible modified reinforced retaining walls are installed at the top of each level of the zigzag multi-platform to reinforce the toe of the upper-level slope platform. Low-dosage modified compacted soil refers to modified soil formed by mixing 10% gold tailings with the in-situ shallow soil of the slope.

[0075] All geogrids 5 are fixed with U-shaped nails 11 and compacted in stages with low-dosage modified compacted soil. One layer of geogrid 5 wraps around one layer of compacted soil.

[0076] Steel beam 17 serves as temporary support before the final stage of flexible modified reinforced retaining wall construction. Once the construction is completed, this structure will become a permanent support structure. Figure 11-12 As shown, the steel crossbeam 17 includes a steel crossbeam body, a concave block 17-1, and a convex block 17-2; adjacent steel crossbeam bodies are connected by mortise and tenon joints through the concave block 17-1 and the convex block 17-2.

[0077] Example 2,

[0078] A method for predicting the stability of a flexible protective structure for a modified and reinforced surface soil slope of a high-fill embankment, specifically including the following:

[0079] The traditional shallow slope instability model consists of a three-stage combined sliding body: a lower compression zone, an upper tension zone, and a central main sliding zone. The central main sliding body is subjected to a thrust p2 from the upper soil edge and a resistance p1 from the lower soil edge. Figure 9 For the analysis of the stress conditions of shallow slope instability in traditional methods (J1 is seepage force, N1 is landslide thrust, F1 is soil strip anti-sliding force, W1 is soil strip weight), the expression for the stability safety factor FS can be obtained as follows:

[0080]

[0081] In the formula, z represents the thickness of the soil strip.

[0082] When the rainfall intensity exceeds the infiltration rate, the shallow soil of the slope is saturated. The expression for the stability safety factor FS of the main sliding body is:

[0083]

[0084] In this embodiment of the invention, due to the use of a multi-stage slope design with a broken line shape, it can be assumed to be an infinitely long slope, with no thrust from the upper edge soil. However, the flexible modified and reinforced retaining wall can provide the lower edge soil with resistance to the upper slope. At the same time, research has found that the protective structure has significant anti-scouring and drainage effects, and there is no stress form under saturation. In addition, the protective structure can be regarded as a single-layer structure in the design analysis, and its shear strength is much greater than that of the shallow soil, providing a sliding resistance force to the main sliding body. Finally, the geogrid wraps around the shallow soil, connecting the protective structure with the shallow soil and providing a sliding resistance force. Figure 10 For the stress analysis of the modified reinforced surface soil long-distance slope flexible protection structure in the embodiments of the present invention, the expression for the stability safety factor FS of the modified reinforced surface soil long-distance slope flexible protection structure of high embankment can be obtained as follows:

[0085]

[0086] Where: γ, γ', γ sat These are the natural unit weight, saturated unit weight, and effective unit weight of the soil, respectively; c', These represent the effective cohesion and internal friction angle of the soil, respectively; σ s The absorbed stress expressed in terms of normalized volumetric water content or saturation; u a L1 represents pore air pressure; L2 represents soil strip length; β represents slope gradient.

[0087] In formula (3), the anti-slip force K1 of the protective structure is:

[0088]

[0089] In the formula: c”, These represent the effective cohesion and internal friction angle of the modified soil, respectively; γ s The weight of the modified soil; z s The thickness of the modified soil.

[0090] In formula (3), the anchorage pull-out force T1 of the reinforcing bar is calculated by the following formula:

[0091]

[0092] In formula (5), the anchorage pull-out force T of the i-th layer of reinforcement is... pi The effective length L of the reinforcing material outside the cracked surface of the retaining wall should be used as the basis. ei The frictional force generated with the surrounding soil is calculated using the following formula:

[0093] T pi =2σ vi aL ei f (6)

[0094] In the formula: σ vi is the vertical stress at the location of the reinforcement, which is the sum of the pressure generated by the self-weight of the backfill and the uniformly distributed permanent load on the top surface of the reinforcement (ignoring traffic loads and other variable loads); 'a' is the width of the reinforcement, and a = 1m when the sheet reinforcement is fully laid. L ei is the effective anchorage length of the reinforcement, i.e. the length of the reinforcement outside the potential fracture surface (m), and its value shall not be less than 1.0m; f is the friction coefficient between the reinforcement and the backfill, which should be determined according to the pull-out test, and the value of f is taken as 0.8 in this calculation.

[0095] Formulas (3)-(6) can be used to invert the modified soil parameters required for the protective structure according to the safety factor specified in the standard, and further obtain the amount of admixture (such as gold tailings) and thickness required for the slope protection structure.

[0096] Experimental Example 1,

[0097] like Figure 1-3 As shown, on a section of the Baicang-Xinning Expressway in Hunan Province, the red clay high-fill embankment slope, after road engineering treatment, has a height of 19.5 meters and a length of 182.5 meters. The first layer (from top to bottom) of the multi-platform zigzag slope has a slope height of 4.5 meters, the second layer and subsequent layers have a slope height of 3 meters, until the last transversely modified and reinforced surface soil long-distance slope protection structure; the above heights are the intervals for the transverse drainage ditches, and the intervals for the curved longitudinal drainage ditches are 40 meters.

[0098] In this specific implementation case, the gold tailings were taken from a gold mine in the Daxin mining area of ​​Xinshao County, Hunan Province. The main chemical composition of the gold tailings is shown in Table 1. Figure 7The shear strength variation curves of the surface red clay of the slope under different gold tailings and cement admixture conditions are shown (the red clay moisture content is 28%, which is greater than the optimum moisture content, and the dry density is 1.83 g / cm³). 3 (The compaction degree of the sample was 90% during the test, and the curing period was 14 days), as shown in Table 1. Figure 7 It can be seen that the Al2O3 content is relatively high, and within a certain dosage range, gold tailings can significantly increase the shear strength of the soil compared to unmodified soil, but the modification effect is slightly inferior to that of cement (e.g., Figure 7 (As shown), at the same time, major gold mines generate a large amount of gold tailings every day, which is a solid waste material that urgently needs to be treated. The five construction planes described in step 1 are processed in sequence.

[0099] Table 1. Main chemical components (mass fraction) of gold tailings

[0100] Gold tailings 57.10 17.67 4.851 4.672 1.87 1.96 0.819

[0101] The specific construction steps are as follows:

[0102] Step 1: Conduct surveying and sampling of the red clay high embankment slope to obtain the basic physical and mechanical parameters of the slope soil. Based on the stability analysis method of long-distance flexible slope protection structure of modified and reinforced surface soil for high embankment, design and analyze the slope, take the value of the safety factor required by the specification, and inversely calculate the parameters required for high-dosage modified soil and low-dosage modified soil for slope protection structure. Further obtain the different admixture dosages and the thickness of the high-dosage protection structure required for the slope protection structure.

[0103] Step 2: Divide the entire high embankment slope into five construction planes according to the reserved longitudinal drainage ditch 1 position (the subsequent construction sequence is not based on the distribution of the five planes, but on the multi-level broken platform in the order from bottom to top); first use a small excavator to clear the slope debris, and then place the cleared slope debris on the broken platform of the next level on the same construction plane.

[0104] Step 3: Construct the earthen trench for drainage ditch 3 at the toe of the slope, and pour concrete after setting up the formwork.

[0105] Step 4: The construction method for the modified and reinforced retaining wall of the lowest level of the zigzag platform at the toe of the slope is slightly different from that of the other zigzag platforms.

[0106] (1) First, the original soil at the location of the modified and reinforced retaining wall is excavated according to the design. The small steel beam 17 is driven into the excavated inner slope in sequence with the cooperation of a crane and an excavator, so that 1 / 2 of the small steel beam 17 penetrates into the soil. The concave block 17-1 and the convex block 17-2 on the small steel beam 17 are connected by tenon and mortise to form a whole to form temporary support at the excavation location at the slope foot (after the construction of the flexible modified and reinforced retaining wall is completed, this structure will become a permanent support structure).

[0107] (2) After temporary support is provided, leveling layer 15 and drainage board 14 are laid. Then, layered compaction of low-dosage modified soil (using multiple excavators to mix the reserved slope crushed soil with gold tailings at 10% of the soil mass to form low-dosage modified soil, which will be used for flexible modified reinforced retaining wall) and installation of bidirectional geogrid 5 and impermeable geotextile 12 are carried out. T-shaped drainage pipes 16 should be embedded in the middle of this part of the construction. The compaction of the modified reinforced retaining wall is carried out by excavator rolling back and forth. However, during the rolling operation after laying drainage board 14 and drainage pipe, care should be taken to prevent damage to drainage board 14 and drainage pipe. Backfilling should be carried out from the perimeter to the inside. When laying geogrid 5, the bottom surface of the geogrid 5 should be flat and compacted. Adjacent geogrid sheets should overlap by 0.2m. Along the transverse direction of the roadbed, the overlapping portions of the geogrid 5 should be connected every 1 meter with No. 8 iron wire. U-shaped nails (No. 11) should be used to fix the laid geogrid 5 to the ground every 1.5-2m. The laying direction should be perpendicular to the slope, wrapping upwards to form an overlap. For small inverted wraps, two layers of compacted soil are used before slope trimming, followed by one layer of inverted wrap, with a thickness of 50cm and a length of ≥100cm from the upper structural surface. For large inverted wraps, one layer of bidirectional geogrid is laid every two layers of compacted soil (50cm thick) until the slope is filled to the top, at which point the slope is completely trimmed. Simultaneously, there should be no debris in the upper and lower layers of fill material that could damage the geogrid 5. When laying the geogrid 5, the direction with higher strength should be perpendicular to the embankment axis. The geogrid 5 is laid transversely, and longitudinal splicing uses an overlapping method with an overlap width of not less than 20cm.

[0108] (3) After the main construction of the flexible modified reinforced retaining wall is completed, high-dosage modified soil (made by mixing the reserved slope crushed soil with gold tailings at 20% of the soil mass using multiple excavators to form high-dosage modified soil, which will be used for the modified soil flexible long-distance slope protection structure) is loosely laid on the slope using an excavator. The loose-lay thickness is set according to the total thickness and the number of layers compacted. In this specific construction case, a 20cm thick layer of high-dosage modified soil 4 is formed on the surface of the high fill embankment slope using multiple excavators. A row of ecological vegetation bags 10 is placed every 40cm along the longitudinal direction of the slope for subsequent ecological protection.

[0109] (4) After completing the above construction steps, excavate the soil trenches of longitudinal water collection ditch 1, transverse water collection ditch 2 and lateral intercepting ditch 8 on this level of broken line platform, thus completing the construction of this level of flexible modified reinforced retaining wall.

[0110] Step 5: Steps (1) and (2) above refer to the construction of the last level of flexible modified and reinforced retaining wall at the toe of the slope. Except for the construction of the last level of flexible modified and reinforced retaining wall at the toe of the slope, the flexible modified and reinforced retaining walls on the other zigzag platforms do not need to be operated in (1). The operation in (2) is also simplified, including the elimination of the need to construct the leveling layer 15 and drainage board 14. At the same time, the height of the flexible modified and reinforced retaining walls is also different (some flexible modified and reinforced retaining walls only need to be set at about half of the zigzag slope, which is calculated in advance during the design. This embodiment mainly targets the shallow instability of the slope. The main cause of shallow instability is the softening of the rock and soil by water or the scouring by water flow. Therefore, it is only necessary to construct the flexible modified and reinforced retaining wall on the upper part of the zigzag slope). This means that the number of layers of geogrid 5 laid is different.

[0111] Step 6: Clean up any debris that fell into the longitudinal collection ditch 1, transverse collection ditch 2, and lateral intercepting ditch 8 during the aforementioned construction process. After setting up the formwork, pour concrete. Place the connecting steel bars between the transverse collection ditch 2 and the lateral intercepting ditch 8 at reinforcement point 9. During pouring, add protrusions to increase roughness in the longitudinal collection ditch 1, and symmetrically set a certain slope along the centerline in the transverse collection ditch 2. In this embodiment, the slope is 5%. At the same time, an expansion joint is set at 10m intervals in the transverse collection ditch 2, but no expansion joint is set at the connection with the longitudinal collection ditch 1 and the lateral intercepting ditch 8. After pouring, a curved mesh structure of longitudinal collection ditch 1, transverse collection ditch 2, and lateral intercepting ditch 8 is formed.

[0112] Step 7: Repeat steps 4 and 5 to complete the construction of each slope step on the entire slope.

[0113] Step 8: Fill all joints with waterproof material to further enhance waterproof performance; plant greenery on the slope after construction, selecting Bermuda grass and Cosmos bipinnatus as vegetation.

[0114] In the hot and humid regions of southern my country, excavated slopes made of red soil, red mudstone, granite residual soil, and carbonaceous shale are frequently damaged by floods and landslides during the rainy season, creating an objective market demand for the promotion of modified and reinforced surface soil technology.

[0115] Traditional modified soil technology, when used for slope support, often fails to define the original slope soil as surface, middle, or deep layers, instead employing large-scale excavation. This results in poor homogeneity of the modified soil, which, while not causing immediate damage, leads to a significant decline in the structural performance under long-term climatic effects. The flexible protective structure constructed using surface soil from the slope in this invention effectively reduces drying shrinkage deformation caused by climate change.

[0116] In this embodiment of the invention, longitudinal drainage ditches 1, transverse drainage ditches 2, and lateral intercepting ditches 8 are arranged in layers from top to bottom along the direction of slope scouring and erosion. The longitudinal drainage ditches 1, transverse drainage ditches 2, lateral intercepting ditches 8, and drainage channels 3 are all cast-in-place concrete structures. Furthermore, the transverse drainage ditches 2 and lateral intercepting ditches 8 are connected with reinforcing steel bars at their joints, forming a mesh-like water collection and interception structure. All are located on a high-modification soil layer 4, reducing shrinkage deformation. Simultaneously, the entire slope is treated in stages, preventing the soil from generating significant stress on the mesh-like water collection and interception structure. The curved longitudinal drainage ditches 1 employ a curved design, with interlocking and overlapping sections that embed adjacent slope surfaces together, thus... The mesh-like water collection and interception structure works synergistically to bear the load. A high-modification soil layer 4 on the slope encases the flexible retaining structure. This high-modification soil layer 4 works in conjunction with the low-modification soil layer 6 within the flexible retaining structure to form an integrated protective structure, further improving the stability of the shallow slope. Without affecting the slope's stability safety factor, it can intercept a large amount of slope rainfall and road surface water. Furthermore, the graded platform shortens the scour path, and the catenary arched longitudinal water collection ditch 1 reduces water flow velocity, thereby lowering scour energy. Compared to traditional protective structures, the impact of rainfall scour on the slope is reduced by more than 40%, making it highly suitable for high-fill embankment slopes in humid and rainy southern regions. Simultaneously, the slope protection structure can promptly drain rainwater after infiltration; and although its shear strength decreases when the moisture content increases, it still maintains stability, preventing shallow instability.

[0117] The main reason why traditional structures cannot achieve long-distance slope construction is that concrete structures that have been in service for a long time are prone to shrinkage cracks on the surface under humid and hot environments, leading to water infiltration, continuous erosion, and eventually a decrease in the strength of the internal soil and rock, resulting in slope collapse. Because the flexible slope protection structure of this invention is more stable, with a protection depth of over 0.8m (compared to only about 0.4m in traditional technology), it can effectively prevent rainwater infiltration and damage to the slope. In some embodiments, this flexible slope protection structure can reach 300 meters (i.e., the longitudinal length of a single construction unit along the road), realizing long-distance flexible slope protection structures, ensuring protection effectiveness while shortening the construction period.

[0118] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A flexible protection structure for modified and reinforced surface soil slopes of high embankments, comprising a multi-level platform slope and drainage structure, characterized in that, The top of each platform is a flexible retaining structure, which is constructed by layering low-dosage modified soil layers (6). Each low-dosage modified soil layer (6) is wrapped by a geogrid (5). The flexible retaining structure is provided with impermeable geotextile (12) on the side near the slope. Vertical steel beams (17) for support are provided inside the slope of the flexible retaining structure at the toe of the slope. The slope surface of the multi-level platform is filled with high-dosage modified soil layers (4). The drainage structure includes a mesh water collection and interception structure, a T-shaped drainage pipe (16), and a drainage board (14); the mesh water collection and interception structure is located on the surface of the high-dosage modified soil layer (4); the T-shaped drainage pipe (16) is located inside the flexible retaining structure; and the drainage board (14) is located at the bottom layer of the flexible retaining structure at the toe of the slope. The mesh-like water collection and interception structure includes a longitudinal water collection ditch (1), a transverse water collection ditch (2), and a lateral interception ditch (8). The transverse water collection ditch (2) and the lateral interception ditch (8) are connected by reinforcement points (9). The longitudinal water collection ditch (1) is a catenary arch shape. The concave part of the longitudinal water collection ditch (1) has a high-modification soil layer (4) with a depth of 30cm~60cm, which is used to resist the expansion and contraction forces of the soil under the interaction of temperature and humidity. The low-dosage modified soil layer (6) includes gold tailings, slope topsoil and cement, and the mass ratio of gold tailings, slope topsoil and cement is x:10-xy:y, where x∈[0.5,1.0] and y∈[0,1.5]. The high-dosage modified soil layer (4) includes gold tailings, slope topsoil and cement, and the mass ratio of gold tailings, slope topsoil and cement is x:10-xy:y, where x∈[1.5,2.0] and y∈[0,1.5].

2. The flexible protection structure for modified and reinforced surface soil slope of a high embankment according to claim 1, characterized in that, The T-shaped drainage pipe (16) includes a horizontal drainage pipe (16-1) and an inclined drainage pipe (16-2) set vertically. The horizontal drainage pipe (16-1) is set longitudinally along the road, and the inclined drainage pipe (16-2) is set transversely along the road. The slope of the horizontal drainage pipe (16-1) is 1°~3°, and the slope of the inclined drainage pipe (16-2) is 3°~8°. The inclined drainage pipe (16-2) is coplanar with and connected to the longitudinal water collection ditch (1), and is used to discharge the water in the T-shaped drainage pipe (16) through the longitudinal water collection ditch (1). The horizontal drainage pipe (16-1) and the inclined drainage pipe (16-2) are each provided with a one-way permeable hole (16-3) for draining water in the soil into the T-shaped drainage pipe (16) in one direction. The inclined drain pipe (16-2) is provided with a first filter section (16-4) and a second filter section (16-5). The filling medium of the first filter section (16-4) is CCT heavy metal stabilizer, and the filling medium of the second filter section (16-5) is microbial or algal metabolites. The outlet of the inclined drain pipe (16-2) is provided with a mesh screen (16-6).

3. The flexible protection structure for modified and reinforced surface soil slope of a high embankment according to claim 1, characterized in that, The bottom of the drainage board (14) is provided with a leveling pad (15).

4. The flexible protection structure for modified and reinforced surface soil slope of a high embankment according to claim 1, characterized in that, The height of the flexible support structure located at the toe of the slope is greater than the height of the flexible support structures at other locations; the steel beam (17) includes a steel beam body, a concave block (17-1), and a convex block (17-2); adjacent steel beam bodies are connected by mortise and tenon joints through the concave block (17-1) and the convex block (17-2).

5. The flexible protection structure for modified and reinforced surface soil slope of a high embankment according to claim 1, characterized in that, The geogrid (5) with the reverse wrapping is fixed by U-shaped nails (11), and ecological planting bags (10) are embedded in the high-dosage modified soil layer (4) in the gap of the mesh water collection and interception structure.

6. The flexible protection structure for modified and reinforced surface soil slope of a high embankment according to claim 1, characterized in that, The top shoulder of the slope is provided with a roadside ditch (7), and the bottom of the slope is provided with a drainage ditch (3). On both sides of the drainage ditch (3), there is a high-mixture modified soil layer (4) with a thickness of 20cm~40cm.

7. The stability prediction method for a modified and reinforced surface soil flexible protection structure for high embankment slopes as described in claim 1, characterized in that, Specifically, it includes the following: The expression for the stability safety factor FS of the modified and reinforced surface soil flexible protection structure of high embankment slope: ； In the formula: The natural unit weight of the soil; , These are the effective cohesion and internal friction angle of the soil, respectively. The absorbed stress is expressed as normalized volumetric water content or saturation. Pore ​​gas pressure; The length of the soil strip; The slope is the gradient of the slope. For the resistance of the lower edge soil, Indicates the thickness of the soil strip; In the formula, the anti-slip force of the protective structure for: ； In the formula: , These are the effective cohesion and internal friction angle of the modified soil, respectively. The weight of the modified soil; The thickness of the modified soil; In the formula, the anchorage pull-out force of the reinforcing bar is... Calculated by the following formula: ； No. Anchorage pull-out force of layered reinforcement Calculate using the following formula: ； In the formula: The vertical stress at the location of the geogrid (5) is the stress. The value is the sum of the self-weight of the backfill and the pressure generated by the uniformly distributed permanent load on the top surface of the reinforced body, without considering traffic loads and other variable loads. The width of the geogrid (5); The effective anchorage length of the geogrid (5); is the coefficient of friction between the geogrid (5) and the fill.

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