Ultra-deep covering type strong karst roadbed structure and construction method thereof

Abstract

The invention relates to an ultra-deep covering type strong karst roadbed structure and a construction method thereof.The roadbed structure comprises a microorganism curing hard shell layer, a cast-in-situ bored pile and a filling roadbed, the microorganism curing hard shell layer is arranged on a shallow foundation layer, the thickness of the microorganism curing hard shell layer is not smaller than 5 m, and the microorganism curing hard shell layer is formed by injecting a microorganism curing agent from a grouting hole through a grouting pump; the differential settlement of the roadbed is reduced; the cast-in-situ bored piles are of a shallow-buried friction type, the distance between every two adjacent cast-in-situ bored piles is 5-9 m, the pile diameter is 1-1.25 m, and the pile bottom ends enter the position below a karst cave bottom plate by not smaller than 2.0 m and are used for enhancing the stability of a foundation. The filling roadbed is arranged on the upper portions of the microorganism solidification hard shell layer and the cast-in-situ bored piles, is filled in a layered mode and comprises reinforced concrete plate beams, the thickness of the reinforced concrete plate beams is not smaller than 0.8 m, and the reinforced concrete plate beams are used for supporting train loads and plate top soil body loads. According to the method, the construction cost of karst subgrade projects can be reduced, construction of super-long cast-in-situ bored piles is avoided, construction operation is convenient, the construction period is shortened, and the green, low-carbon, efficient and safe karst subgrade disposal effect is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of geotechnical engineering and transportation infrastructure construction, and in particular relates to an ultra-deep cover type strong karst roadbed structure and a construction method thereof. Background Art

[0002] Karst geology is a common and unique geological phenomenon. According to statistics, karst covers an area of 3.46 million square kilometers in my country, accounting for over one-third of the country's land area. Approximately 70% of this karst area is covered by Quaternary sedimentary layers. Covered karst refers to karst covered by loose sedimentary deposits. Its foundations often suffer from engineering problems such as insufficient bearing capacity, poor foundation stability, and proneness to collapse, which can easily lead to uneven subgrade settlement and even collapse accidents. This unfavorable geological phenomenon is particularly common in railway projects, posing significant risks and challenges to subgrade design and construction, and directly threatening the safety of railway construction and operation. Ultra-deep covered karst foundations are particularly challenging to address, as karst caves often reach depths exceeding 30 or even 100 meters. Currently, the reinforcement of ultra-deep covered karst foundations typically utilizes ultra-long end-bearing pile-slab structures. Deeply buried bored piles transfer the load below the karst floor, thereby improving foundation stability and bearing capacity.

[0003] However, the existing ultra-long end-supported pile-slab structure has many problems. On the one hand, the structural engineering cost is high, and the construction process requires deep-buried bored piles, which leads to a significant increase in material and construction costs; on the other hand, the construction of ultra-long bored piles is difficult, with high requirements for equipment and technology, and low construction efficiency. In addition, in areas of roadbed collapse and instability, it is difficult to detect the collapse of the soil under the slab and it is impossible to backfill in time, which aggravates the hidden dangers of the foundation. These defects make it difficult for existing technologies to meet the requirements of economy, efficiency and safety. Therefore, there is an urgent need to propose an ultra-deep cover karst foundation reinforcement structure and method with low engineering cost, convenient construction and high safety, so as to promote the high-quality development of railway projects in karst areas. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides an ultra-deep cover type strong karst roadbed structure and a construction method thereof, so as to reduce construction costs, simplify the construction process and improve foundation stability and safety.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A super-deep cover type strong karst roadbed structure, the roadbed structure includes a microbial solidification hard shell layer, bored cast-in-place piles, and a filled roadbed. The microbial solidification hard shell layer is arranged in the shallow layer of the foundation, with a thickness of not less than 5 meters, and is formed by injecting a microbial curing agent from a grouting hole by a grouting pump, and is used to reduce the uneven settlement of the roadbed; the bored cast-in-place piles are shallow buried friction type, with a spacing of 5 to 9 meters and a pile diameter of 1 to 1.25 meters. The bottom of the pile extends not less than 2.0 meters below the bottom plate of the cave, and is used to enhance the stability of the foundation; the filled roadbed is arranged on the upper part of the microbial solidification hard shell layer and the bored cast-in-place piles, is filled in layers and includes reinforced concrete slab beams, with a thickness of not less than 0.8 meters, and is used to support train loads and slab top soil loads.

[0007] Preferably, the microbial solidifying agent comprises concentrated bacterial liquid, microbial nutrient solution and bentonite slurry, wherein the bentonite slurry is prepared by mixing nano-bentonite and guar gum in a mass ratio of 100:1.

[0008] Preferably, the grouting holes are arranged in a square or equilateral triangle form, the grouting range extends to no less than 5 meters outside the slope foot, and the grouting depth is no less than 5 meters to ensure uniform distribution of the microbial solidified crust layer.

[0009] Preferably, during the grouting process, the pressure of the grouting pump is 0.5-2.5 MPa and the flow rate is 10-50 L / min, which are used to achieve uniform distribution of the slurry and induce calcium carbonate precipitation.

[0010] Preferably, after grouting is completed, the soil is left to stand for 24 to 48 hours to ensure that the microorganisms complete the MICP reaction to form a hard crust layer.

[0011] Preferably, a plain concrete cushion layer of not less than C15 with a thickness of 0.1 meters is laid on the top of the bored pile to improve the stability of the pile top.

[0012] Preferably, the reinforced concrete slab beam is made of C35 concrete and is located at an elevation of not less than 1.0 meter below the top of the roadbed.

[0013] On the other hand, the present invention also discloses a construction method of an ultra-deep cover type strong karst roadbed structure, which is characterized by comprising the following steps:

[0014] S1, inoculating Bacillus pasteurianus strains onto a solid culture medium to form a single colony, culturing by shaking, collecting by centrifugation, and resuspending in sterile physiological saline to obtain a concentrated bacterial solution; dissolving urea and calcium chloride in water at a mass ratio of 1:1 to prepare a microbial nutrient solution, and mixing and stirring the solution with the concentrated bacterial solution to obtain a bacterial culture solution; uniformly mixing nano-bentonite and guar gum in water to obtain a bentonite slurry; and mixing the bacterial culture solution and the bentonite slurry at a volume ratio of 2:1 to prepare a microbial curing agent;

[0015] S2: Use full-surface grouting, extending the grouting range to at least 5 meters beyond the slope toe. Grouting holes are arranged in a square or equilateral triangle pattern, and microbial curing agent is injected at a pressure of 0.5-2.5 MPa and a flow rate of 10-50 L / min to ensure uniform distribution of the slurry and induce calcium carbonate precipitation. After grouting, the soil is left to stand for 24-48 hours to ensure that the microorganisms complete the MICP reaction and form a microbial curing crust layer with a thickness of at least 5 meters.

[0016] S3: Determine the pile length, pile spacing, and pile diameter based on the slab elevation, train load, and soil load on the slab top. The pile spacing is 5 to 9 meters, the pile diameter is 1.0 to 1.25 meters, and the bottom of the pile must be no less than 2.0 meters below the cave floor.

[0017] S4, fill the roadbed in layers to the design elevation of the pile-slab structure, construct bored cast-in-place piles, lay a 0.1-meter-thick plain concrete cushion layer of not less than C15 on the top of the piles, construct a reinforced concrete slab beam of not less than 0.8 meters thick and not less than C35, and finally fill the remaining upper roadbed in layers.

[0018] Preferably, in step S1, the mass ratio of nano-bentonite to guar gum in the bentonite slurry is 100:1, so as to improve the dispersibility of the microbial curing agent and the grouting effect.

[0019] Preferably, in step S2, the full grouting method ensures that the slurry is evenly distributed within the reinforcement range by arranging dense grouting holes within the roadbed range, thereby forming an overall continuous microbial solidified hard crust layer.

[0020] Compared with the prior art, the advantages of the present invention are:

[0021] The present invention achieves efficient reinforcement of the foundation and environmentally friendly construction by combining the innovative design of a shallow microbial solidified hard shell layer with bored cast-in-place friction piles. The hard shell layer formed by the superficial microbial solidification method effectively reduces the uneven settlement of the roadbed, and this reinforcement method is green and low-carbon, with little pollution to the environment; shallow buried friction bored cast-in-place piles are used for foundation reinforcement, and there is no need for the pile body to pass through the karst area, which reduces the disturbance to the karst area, significantly reduces the construction difficulty, and improves the construction efficiency. The roadbed structure and construction method of the present invention not only avoid the complexity of the construction of ultra-long bored cast-in-place piles, are easy to operate and significantly shorten the construction period, but also achieve the effect of reducing engineering costs and improving foundation stability and safety, thereby providing a reliable solution for the efficient and safe disposal of karst foundations. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the ultra-deep covered strong karst roadbed structure of the present invention;

[0023] Figure 2This is a flow chart of the construction method of the ultra-deep cover type strong karst roadbed structure of the present invention. DETAILED DESCRIPTION

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the present invention.

[0025] In addition, described feature, structure or characteristic can be combined in one or more embodiments in any suitable manner.In the following description, many specific details are provided so as to provide a full understanding of the embodiments of the present application. However, it will be appreciated by those skilled in the art that the technical scheme of the present application can be put into practice without one or more of the specific details, or other methods, components, devices, steps etc. can be adopted. In other cases, known methods, devices, implementations or operations are not shown or described in detail to avoid blurring the various aspects of the application.

[0026] like Figure 1 As shown, this embodiment discloses an ultra-deep cover type strong karst roadbed structure, which includes a microbial solidified hard crust layer, bored cast-in-place piles and a filled roadbed. The microbial solidified hard crust layer is arranged in the shallow layer of the foundation, with a thickness of not less than 5 meters, and is formed by injecting a microbial solidifying agent from the grouting hole by a grouting pump. This microbial solidified hard crust layer solidifies the loose soil into a hard crust layer with a certain strength and stability by microbial induced calcium carbonate precipitation, effectively reducing the risk of uneven settlement of the roadbed, and is particularly suitable for areas prone to settlement in karst geology. The bored cast-in-place piles are shallow buried friction type, with a spacing of 5 to 9 meters, a pile diameter of 1 to 1.25 meters, and the bottom of the pile is not less than 2 meters below the bottom plate of the cave. Through the friction between the pile foundation and the soil, this type of pile can provide sufficient support to the foundation without penetrating the cave area, thereby enhancing the overall stability of the foundation, while reducing the disturbance to the cave, and significantly reducing the construction difficulty and cost. The subgrade is constructed atop a microbially solidified crust and bored piles, using a layered approach. It comprises reinforced concrete slab beams with a thickness of at least 0.8 meters. These slab beams not only distribute train loads and the load of the soil atop the slabs, but also provide additional structural support, thereby ensuring the subgrade's bearing capacity and long-term stability. This design and construction of the entire subgrade structure not only optimizes the foundation treatment effect, but also balances economical and convenient construction, making it suitable for railway infrastructure construction in ultra-deep, overburdened, and strongly karst geological conditions.

[0027] Furthermore, the microbial curing agent includes concentrated bacterial liquid, microbial nutrient solution and bentonite slurry, wherein the bentonite slurry is made by mixing nano bentonite and guar gum in a mass ratio of 100:1. This proportion formula of the bentonite slurry can ensure the fluidity and dispersibility of the slurry during the grouting process, while enhancing the stability and adhesion properties of the microbial curing agent. The grouting holes are arranged in a square or equilateral triangle form, and the grouting range extends to no less than 5 meters outside the slope foot, and the grouting depth is no less than 5 meters. This arrangement ensures that the microbial solidified crust layer forms a continuous and uniform reinforcement effect in key areas by increasing the grouting coverage, and is particularly suitable for treating potential settlement areas in karst geology. During the grouting process, the pressure of the grouting pump is maintained between 0.5 and 2.5 MPa, and the flow rate is controlled within the range of 10-50 L / min. This parameter setting ensures that the slurry is injected into the soil at an appropriate rate while avoiding soil disturbance or slurry leakage caused by excessive pressure. This ensures uniform distribution of the slurry within the soil and induces calcium carbonate precipitation, thereby enhancing the strength and stability of the hard crust. After grouting, the soil is allowed to rest for 24 to 48 hours. This rest period provides sufficient conditions for the microorganisms to complete the MICP reaction, ensuring that the generated calcium carbonate crystals effectively bond the soil particles, ultimately forming a hard crust layer of uniform thickness, high strength, and stability.

[0028] In this embodiment, a plain concrete cushion layer of not less than C15 with a thickness of 0.1 meters is laid on the top of the bored pile to improve the stability of the pile top. This plain concrete cushion layer serves as a transition layer between the pile top and the superstructure, which can evenly disperse the load transferred by the superstructure, reduce local stress concentration, thereby effectively protecting the pile top from damage, and enhancing the bearing capacity and long-term stability of the entire pile foundation system. The reinforced concrete slab beam is made of C35 concrete and is located at an elevation of not less than 1.0 meters below the top of the roadbed. C35 concrete has a high strength grade and can withstand train loads and upper soil loads. At the same time, its location at an elevation of not less than 1.0 meters below the top of the roadbed helps to further protect the slab beam from the influence of the external environment, such as temperature changes and surface water erosion, thereby improving the overall durability and structural stability of the roadbed. This design ensures the long-term use of the slab beam under complex load conditions and provides reliable support for the roadbed structure.

[0029] Another embodiment of the present invention further discloses a construction method for an ultra-deep covered strong karst roadbed structure, comprising the following steps:

[0030] S1. Bacillus pasteurianus is inoculated onto a solid culture medium and cultured to form a single colony. The culture is then shaken, collected by centrifugation, and resuspended in sterile physiological saline to obtain a concentrated bacterial solution. Urea and calcium chloride are dissolved in water at a mass ratio of 1:1 to prepare a microbial nutrient solution, and the solution is mixed and stirred with the concentrated bacterial solution to obtain a bacterial culture solution. Na-bentonite and guar gum are uniformly mixed in water to obtain a bentonite slurry. The bacterial culture solution and the bentonite slurry are mixed at a volume ratio of 2:1 to prepare a microbial curing agent.

[0031] The microbial curing agent prepared by the above steps not only has good stability and fluidity, but can also induce calcium carbonate precipitation during the grouting process, effectively improving the physical properties and bearing capacity of the foundation soil. The mixing ratio of nano-bentonite and guar gum ensures the adhesion and dispersion effect of the slurry, which helps to evenly distribute the slurry in the foundation soil. Specifically, the bentonite slurry is made by mixing nano-bentonite and guar gum in a mass ratio of 100:1. This ratio design can significantly improve the dispersibility of the microbial curing agent, allowing it to better penetrate into the tiny gaps in the soil during the grouting process.

[0032] S2 adopts the full-volume grouting method, and the grouting range extends to no less than 5 meters outside the slope foot; the grouting holes are arranged in a square or equilateral triangle, and the microbial curing agent is injected at a pressure of 0.5-2.5 MPa and a flow rate of 10-50 L / min to ensure that the slurry is evenly distributed and induce calcium carbonate precipitation. After the grouting is completed, the soil is left to stand for 24-48 hours to ensure that the microorganisms complete the MICP reaction to form a microbial curing hard crust layer with a thickness of no less than 5 meters.

[0033] In this step, this full-surface grouting method can form a continuous and stable hard crust layer within the reinforcement area, minimizing the risk of uneven roadbed settlement. Control of grouting pressure and flow rate ensures the injection efficiency of the slurry while avoiding soil disturbance or slurry leakage that may be caused by high pressure. The static time provides sufficient conditions for microbial reaction, thereby ensuring the quality and thickness of the hard crust layer. The full-surface grouting method ensures that the slurry is evenly distributed within the reinforcement area by arranging dense grouting holes within the roadbed.

[0034] S3: Determine the pile length, pile spacing, and pile diameter based on the plate elevation, train load, and soil load on the top of the plate. The pile spacing is 5 to 9 meters, the pile diameter is 1 to 1.25 meters, and the bottom of the pile must be no less than 2.0 meters below the bottom of the cave.

[0035] In this step, this pile foundation design provides sufficient support through friction with the soil. It also prevents the pile bottom from directly penetrating the karst cave area, minimizing disturbance to the karst foundation and reducing construction difficulty and costs. The design parameters for pile length and spacing are based on actual load conditions, ensuring the stability and bearing capacity of the roadbed structure.

[0036] S4, fill the roadbed in layers to the design elevation of the pile-slab structure, construct bored cast-in-place piles, lay a 0.1-meter-thick plain concrete cushion layer of not less than C15 on the top of the piles, construct a reinforced concrete slab beam of not less than 0.8 meters thick and not less than C35, and finally fill the remaining upper roadbed in layers.

[0037] In this step, the layered filling method can effectively reduce the risk of settlement during roadbed construction, while ensuring the density of each layer of filling soil and enhancing the stability of the entire roadbed. The construction of bored cast-in-place piles provides an important support structure for the foundation. The 0.1-meter-thick plain concrete cushion layer of no less than C15 is laid on the pile top, which can serve as a transition layer between the pile top and the superstructure, playing a role in uniformly transferring loads and protecting the pile top. A reinforced concrete slab beam of no less than 0.8 meters thick and no less than C35 is constructed on the pile top plain concrete cushion layer. The high-strength material of the slab beam can effectively withstand train loads and the load of the soil on the slab top. At the same time, its thickness design further improves the bending and shear resistance of the roadbed. This slab beam design not only enhances the overall rigidity of the roadbed, but also provides additional load dispersing capacity, thereby ensuring the stability and reliability of the entire roadbed structure in long-term use. Finally, by filling the remaining upper roadbed in layers, not only the roadbed structure is further consolidated, but also the uniformity and construction efficiency of the roadbed construction are guaranteed, providing an important guarantee for the realization of the overall performance of the roadbed.

[0038] In summary, the present invention discloses an ultra-deep covering strong karst roadbed structure and a construction method thereof, wherein the roadbed structure comprises a microbial solidified hard crust layer, shallow buried friction type bored piles and a layered filled roadbed, and the overall roadbed reinforcement is achieved through the steps of preparing a microbial solidifying agent, full-volume grouting, constructing bored piles and roadbed filling. The present invention adopts microbial induced calcium carbonate precipitation technology to form a hard crust layer with a thickness of not less than 5 meters in the shallow layer of the foundation, thereby reducing the uneven settlement of the roadbed, and at the same time, combined with the friction type pile foundation design to avoid penetrating the cave area, thereby reducing the disturbance to the karst foundation. The reinforced concrete slab beam design in the roadbed structure provides a strong supporting capacity, further improving the overall stability and durability of the roadbed. While ensuring the stability of the ultra-deep covering strong karst roadbed, the present invention significantly reduces the construction difficulty and project cost. Through the combination of innovative microbial solidification technology and friction type pile foundation, not only the green and low-carbon effect of roadbed reinforcement is achieved, but also the construction period is effectively shortened and the construction efficiency is improved. The uniform distribution and overall continuity of the hard shell layer enhance the bearing capacity of the foundation, while the optimized grouting and pile foundation design ensure the convenience and safety of construction.

[0039] The implementation of this invention provides an efficient, economical, and environmentally friendly solution for engineering construction under karst geological conditions, particularly for the complex geological conditions of ultra-deep, overburdened, and strongly karst areas. It possesses significant technical value and application prospects. The promotion and application of this invention will not only provide technical support for the construction of infrastructure such as railways and highways, but will also further promote the realization of green and sustainable development in the field of geotechnical engineering, with far-reaching significance for the development of the industry.

[0040] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the present invention as described above. For the sake of simplicity, they are not provided in detail. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in this field should understand that it is still possible to modify the technical solutions described in the above embodiments, or to make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An ultra-deep covered strong karst roadbed structure, characterized in that: The roadbed structure includes a microbial solidified hard crust layer, bored cast-in-place piles, and a filled roadbed. The microbial solidified hard crust layer is arranged in the shallow layer of the foundation, with a thickness of not less than 5 meters. It is formed by injecting a microbial solidifier from the grouting hole through a grouting pump, and is used to reduce the uneven settlement of the roadbed; the bored cast-in-place piles are shallow buried friction type, with a spacing of 5 to 9 meters, a pile diameter of 1 to 1.25 meters, and the bottom of the pile is not less than 2.0 meters below the bottom plate of the cave, which is used to enhance the stability of the foundation; the filled roadbed is arranged on the upper part of the microbial solidified hard crust layer and the bored cast-in-place piles, and is formed by layered filling and includes reinforced concrete slab beams, with a thickness of not less than 0.8 meters, which is used to support train loads and slab top soil loads.

2. The ultra-deep cover type strong karst roadbed structure according to claim 1, characterized in that: The microbial curing agent comprises concentrated bacterial liquid, microbial nutrient solution and bentonite slurry, wherein the bentonite slurry is prepared by mixing nano bentonite and guar gum in a mass ratio of 100:

1.

3. The ultra-deep cover type strong karst roadbed structure according to claim 1, characterized in that: The grouting holes are arranged in a square or equilateral triangle form, the grouting range extends to no less than 5 meters outside the slope foot, and the grouting depth is no less than 5 meters to ensure uniform distribution of the microbial solidified hard crust layer.

4. The ultra-deep cover type strong karst roadbed structure according to claim 3, characterized in that: During the grouting process, the pressure of the grouting pump is 0.5-2.5 MPa and the flow rate is 10-50 L / min, which is used to achieve uniform distribution of the slurry and induce calcium carbonate precipitation.

5. The ultra-deep cover type strong karst roadbed structure according to claim 4, characterized in that: After grouting is completed, the soil is left to stand for 24 to 48 hours to ensure that the microorganisms complete the MICP reaction to form a hard crust layer.

6. The ultra-deep cover type strong karst roadbed structure according to claim 1, characterized in that: A plain concrete cushion layer of not less than C15 with a thickness of 0.1 meters is laid on the top of the bored pile to improve the stability of the pile top.

7. The ultra-deep cover type strong karst roadbed structure according to claim 1, characterized in that: The reinforced concrete slab beam is made of C35 concrete and is located at an elevation of not less than 1.0 meter below the top of the roadbed.

8. A construction method for an ultra-deep covered strong karst roadbed structure, characterized in that: The following steps are involved: S1, inoculating Bacillus pasteurianus strains onto a solid culture medium to form a single colony, culturing by shaking, collecting by centrifugation, and resuspending in sterile physiological saline to obtain a concentrated bacterial solution; dissolving urea and calcium chloride in water at a mass ratio of 1:1 to prepare a microbial nutrient solution, and mixing and stirring the solution with the concentrated bacterial solution to obtain a bacterial culture solution; uniformly mixing nano-bentonite and guar gum in water to obtain a bentonite slurry; and mixing the bacterial culture solution and the bentonite slurry at a volume ratio of 2:1 to prepare a microbial curing agent; S2: Use full-surface grouting, extending the grouting range to at least 5 meters beyond the slope toe. Grouting holes are arranged in a square or equilateral triangle pattern, and microbial curing agent is injected at a pressure of 0.5-2.5 MPa and a flow rate of 10-50 L / min to ensure uniform distribution of the slurry and induce calcium carbonate precipitation. After grouting, the soil is left to stand for 24-48 hours to ensure that the microorganisms complete the MICP reaction and form a microbial curing crust layer with a thickness of at least 5 meters. S3: Determine the pile length, pile spacing, and pile diameter based on the slab elevation, train load, and soil load on the slab top. The pile spacing is 5 to 9 meters, the pile diameter is 1.0 to 1.25 meters, and the bottom of the pile must be no less than 2.0 meters below the cave floor. S4, fill the roadbed in layers to the design elevation of the pile-slab structure, construct bored cast-in-place piles, lay a 0.1-meter-thick plain concrete cushion layer of not less than C15 on the top of the piles, construct a reinforced concrete slab beam of not less than 0.8 meters thick and not less than C35, and finally fill the remaining upper roadbed in layers.

9. The construction method according to claim 8, characterized in that: In step S1, the mass ratio of nano-bentonite to guar gum in the bentonite slurry is 100:1, so as to improve the dispersibility of the microbial curing agent and the grouting effect.

10. The construction method according to claim 8, characterized in that: In step S2, the full grouting method ensures that the slurry is evenly distributed within the reinforcement range by arranging dense grouting holes within the roadbed range, thereby forming an overall continuous microbial solidified hard crust layer.

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