Foam light soil roadbed multi-element load shedding deformation regulation and control method based on structural stress control and roadbed structure

Abstract

The invention relates to the technical field of road engineering, and provides a foam light soil roadbed multi-element load shedding deformation regulation and control method based on structural stress control and a roadbed structure.The method comprises the steps that soil bodies of different sections and different depths of a construction road section are selected for drilling and sampling; carrying out a one-dimensional consolidation compression test on the undisturbed soil to determine the yield stress of the soil body structure; foam light soil light filler deformation regulation and control are preferentially considered, and if the process cannot meet the requirement that the upper load is smaller than the soil body structure yield stress, vacuum preloading and foam light soil deformation regulation and control can be combined. Under the extreme condition (the foundation structure is extremely weak or the upper design load is large), vacuum preloading and foam light soil embedded large-diameter pipes are combined for deformation regulation and control. According to the multi-element deloading deformation regulation and control thought based on structural stress control, it can be ensured that the load borne by the foundation in the roadbed construction process is always lower than the structural yield stress, the soil body structural integrity is kept to the maximum extent, foundation deformation is effectively controlled, and the engineering stability is improved.

Description

Technical Field

[0001] This invention relates to the field of road engineering technology, specifically to a method for constructing a roadbed on a soft soil foundation, and particularly to a multi-element load reduction deformation control method for foamed lightweight soil roadbed based on structural stress control, and a roadbed structure. Background Technology

[0002] When constructing roads in coastal areas and river networks, deep soft soil foundations are often encountered. These foundations are characterized by high water content, high compressibility, low bearing capacity, and poor permeability. Under embankment loads, they experience significant and uneven settlement, severely impacting construction safety and long-term operational performance. Therefore, soft soil foundation treatment is a crucial aspect of such projects.

[0003] Traditional soft soil treatment methods, such as surcharge preloading, accelerate soil consolidation and settlement by applying temporary loads exceeding the design load, allowing road construction to proceed only after settlement has stabilized. While widely used, this method relies on "trading settlement for stability" without considering the inherent structural properties of soft soil. Soft soil develops a certain structural strength, known as "structural yield stress," during deposition. When external loads exceed this critical value, irreversible damage to the soil structure occurs, leading to a sharp drop in strength and a dramatic increase in compressibility, potentially triggering sudden, uncontrollable large deformations or instability.

[0004] Furthermore, traditional methods often employ conventional fillers (such as earth and rock) for high-fill operations, resulting in significant self-weight loads. In structurally soft soil areas, such large loads can easily exceed the soil's yield stress, inducing excessive post-construction settlement and differential settlement. While existing technologies have begun to utilize lightweight materials such as foamed lightweight soil to reduce loads, or employ vacuum preloading to reinforce foundations, these techniques are often used in isolation or simply superimposed, lacking a unified theoretical framework for quantitative design and systematic control. Accurately identifying the structural yield point of the foundation and using this as the core to coordinate various load reduction and reinforcement technologies, thereby shifting from "passively treating settlement" to "actively controlling stress and deformation," is a pressing technical problem that needs to be solved. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a multi-faceted load reduction and deformation control method for foamed lightweight soil subgrade based on structural stress control, as well as a subgrade structure. This method uses the yield stress of the soil structure as the core control threshold. Through scientific testing and evaluation, it progressively selects multiple technologies such as lightweight filler replacement, combined vacuum preloading, and composite hollow structures to achieve active and precise control of the stress path in soft soil foundations, ensuring the stability and controllable deformation of the subgrade during construction and operation.

[0006] The present invention adopts the following technical solution: On the one hand, this invention provides a multi-element load reduction deformation control method for foamed lightweight soil subgrade based on structural stress control, including the following steps: S1: Select soil samples with different cross sections and depths in the construction section for drilling and sampling, and determine the basic mechanical parameters of the soil through tests; S2: Conduct a one-dimensional consolidation compression test on the obtained undisturbed soil, plot the compression curve based on the test data and the basic mechanical parameters, and determine the yield stress of the soil structure according to the inflection point of the compression curve. S3: Based on the structural yield stress determined in step S2 and the additional stress generated by the design load, select and implement a load reduction deformation control scheme; the control scheme includes: Scheme (1): Deformation control of foamed lightweight soil: Foamed lightweight soil is used as lightweight filler in embankment construction to reduce the overlying load and control the additional stress below the yield stress of the structure. Scheme (2): Vacuum preloading combined with foam lightweight soil deformation control: When scheme (1) cannot meet the requirement that the additional stress is less than the yield stress of the structure, vacuum preloading is carried out on the foundation before the embankment is filled, and then foam lightweight soil is filled. Scheme (3): Vacuum preloading combined with foam lightweight soil embedded with large diameter pipe deformation control: When scheme (2) still cannot meet the requirement that the additional stress is less than the yield stress of the structure, while performing vacuum preloading and foam lightweight soil filling, a large diameter hollow pipe is embedded in the foam lightweight soil.

[0007] In addition to any of the possible implementations described above, another implementation is provided in which the basic mechanical parameters in step S1 include the initial void ratio, the compressibility consolidation coefficient, the cohesion, and the internal friction angle.

[0008] In addition to any of the possible implementations described above, another implementation is provided in which the one-dimensional consolidation compression test process in step S2 is loading-unloading-reloading, and the loading path is: 12.5→25→50→75→100→150→200→150→100→75→50→25→50→75→100→150→200→300→400 kPa.

[0009] In addition to any of the possible implementations described above, another implementation is provided in which the compression curve in step S2 is a porosity-pressure (lg e - lg p) curve in a double logarithmic coordinate system.

[0010] In addition to any of the possible implementations described above, another implementation is provided, which includes a scheme pre-selection step before step S3: based on the basic mechanical parameters of the soil (internal friction angle, cohesion) determined in step S1 and the structural yield stress determined in step S2, and combined with the design load of the upper embankment, the structural strength of the foundation is pre-evaluated. If the pre-assessment indicates that the yield stress of the structure is lower than the design load, scheme (1) shall be preferred. If the yield stress of the structure is still lower than the design load after the review and evaluation of scheme (1), then scheme (2) or scheme (3) should be adopted. For extremely soft and weak foundations with large thickness and high water content, or for major projects with design loads far exceeding the structural yield stress, scheme (3) can be directly adopted.

[0011] In addition to any of the possible implementations described above, a further implementation is provided in which, in step S3, the foamed lightweight soil is filled on top of the sand cushion layer, and the sand cushion layer is laid on top of the original roadbed; the vacuum preloading treatment uses a drainage board for drainage, and a cross-section pipe is used to monitor the vertical settlement of the soil on the entire continuous profile; the large-diameter hollow pipe is a low-density hollow pipe.

[0012] In addition to any of the possible implementations described above, another implementation is provided in which, during and after the implementation of any control scheme in step S3, the earth pressure and settlement of the roadbed are monitored in real time, and the deformation control effect is evaluated based on the monitoring data. If necessary, construction parameters or reinforcement measures are dynamically adjusted.

[0013] In addition to any of the possible implementations described above, another implementation is provided in which the wet bulk density of the foamed lightweight soil is 5-12 kN / m³. 3 The unconfined compressive strength after 28 days is not less than 0.5 MPa; the vacuum degree of the vacuum pre-compression treatment is not less than 80 kPa, and the pre-compression period is determined according to the degree of consolidation requirements.

[0014] In addition to any of the possible implementations described above, another implementation is provided in which the initial void ratio of the soil measured in step S1 is used to plot the compression curve in step S2.

[0015] In addition to any of the possible implementations described above, another implementation is provided in which the determination of the pre-selected scheme should also take into account the impact of factors such as construction progress and cost.

[0016] In addition to any of the possible implementations described above, another implementation is provided in which the thickness of the sand pad layer can be 40cm to 60cm, and the vacuum degree under the membrane should reach 80kPa and remain stable during vacuum pre-compression treatment.

[0017] In addition to any of the possible implementations described above, another implementation is provided in which the drainage boards are arranged in an equilateral triangle with a spacing of 1.5m; and the cross-section pipes are laid across the entire roadbed.

[0018] In addition to any of the possible implementations described above, another implementation is provided in which the large-diameter hollow pipe is a corrugated steel pipe. Its preferred diameter is 4.0m, and it should be arranged perpendicular to the road centerline, with a pipe spacing of 2.0m to 3.0m.

[0019] On the other hand, the present invention also provides a roadbed structure, which is constructed using the above-mentioned multi-element load reduction and deformation control method for foamed lightweight soil roadbed based on structural stress control.

[0020] The beneficial effects of this invention are as follows: 1. Advanced theory and precise control: For the first time, the core mechanical property of structural soft soil, "structural yield stress", is used as the direct control threshold for subgrade design, realizing the transformation from experience-based design to theoretical quantitative design, and making the control target more scientific and precise.

[0021] 2. Diverse System, Hierarchical Adaptation: Three hierarchical control schemes, ranging from simple to complex and from single to combined, are proposed, and decision-making rules based on pre-assessment are established. The optimal technology combination can be selected economically and rationally according to the quality of the foundation conditions and the level of engineering requirements, avoiding the misuse or inadequate treatment of technologies.

[0022] 3. Synergistic effect, significant results: The organic integration of lightweight load reduction (foamed lightweight soil, hollow pipe) and foundation reinforcement (vacuum preloading) technologies exerts a synergistic effect. It reduces the load at the source and fundamentally improves the bearing capacity of the foundation. With this dual protection, it can more effectively suppress structural failure and control total settlement and uneven settlement.

[0023] 4. Safe, economical, and widely applicable: This method maximizes the preservation of the structural integrity of the foundation soil, reduces the risk of secondary deformation caused by structural damage, and improves engineering safety. At the same time, the tiered approach helps control engineering costs while ensuring safety, and can be widely applied to subgrade engineering in soft soil areas such as highways, railways, and municipal roads. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall process of the method of the present invention.

[0025] Figure 2 A schematic diagram (lg e - lg p curve) for determining the yield stress p_c2 of soil structure through one-dimensional consolidation test.

[0026] Figure 3aThis is a schematic diagram of the cross-sectional structure of the roadbed using scheme (1) (deformation control of foamed lightweight soil).

[0027] Figure 3b The diagram shows the stress path and deformation control corresponding to scheme (1).

[0028] Figure 4a This is a schematic diagram of the cross-sectional structure of the roadbed using scheme (2) (vacuum preloading combined with deformation control of lightweight foam soil).

[0029] Figure 4b The diagram shows the stress path and deformation control corresponding to scheme (2) (showing the increase in structural yield stress).

[0030] Figure 5a This is a schematic diagram of the cross-sectional structure of the roadbed using scheme (3) (deformation control of large-diameter pipes embedded in vacuum preloading combined with foamed lightweight soil).

[0031] Figure 5b The diagram shows the stress path and deformation control corresponding to scheme (3) (showing the reduction of the load limit).

[0032] Figure 6 This is a schematic diagram of the construction of a certain project using scheme (3).

[0033] Figure 7a This is a monitoring curve showing the change of earth pressure over time at a certain engineering section.

[0034] Figure 7b This is a monitoring curve showing the change of the stratified settlement of a certain engineering section over time.

[0035] Figure 3b , Figure 4b , Figure 5b The red curves in the figure represent the compression curves obtained from the one-dimensional consolidation compression test of the undisturbed soil. Figure 4b , Figure 5b The purple curves in the figure represent the compression curves obtained after the soil has undergone vacuum preloading.

[0036] In the diagram: ①- Road surface structure; ②- Foamed lightweight soil lightweight filler; ③- Sand cushion layer; ④- Original roadbed (soft soil foundation); ⑤- Cross-section pipe; ⑥- Drainage board; ⑦- Large diameter hollow pipe. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0038] The accompanying drawings illustrate a layer structure according to an embodiment of the present invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0039] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0040] In the description of this invention, it should be noted that the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0041] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0042] like Figure 1 As shown in the figure, an embodiment of the present invention provides a multi-element load reduction deformation control method for foamed lightweight soil subgrade based on structural stress control, comprising the following steps: Step 1: Geological Investigation and Parameter Acquisition: Representative cross-sections and samples at different depths are selected along the construction section to obtain undisturbed soil samples. Basic mechanical parameters of the soil samples, such as initial void ratio, compressibility coefficient, cohesion, and internal friction angle, are determined through indoor physical and mechanical tests.

[0043] Step Two: Determine the yield stress of the soil structure: Conduct a one-dimensional consolidation compression test on the obtained undisturbed soil sample. The test process adopts a loading-unloading-reloading path (e.g.: (12.5→25→50→75→100→150→200→150→100→75→50→25→50→75→100→150→200→300→400 kPa). Based on the initial void ratio of the soil measured in step one, the data of the compression stage are plotted on a double logarithmic coordinate system (lg e - lg p) to form a compression curve. By identifying significant inflection points on this curve, the yield stress p_c2 of the soil structure is determined. This stress value is considered as the critical threshold for yield failure of the soil structure.

[0044] Step 3: Scheme Pre-assessment and Decision: Based on the soil strength mechanical parameters (internal friction angle, cohesion) obtained in Step 1, the structural yield stress p_c2 determined in Step 2, and combined with the design load of the upper embankment, a pre-assessment of the structural strength and bearing risk of the foundation is conducted; according to the pre-assessment results, one of the following three progressive control schemes is pre-selected: (1) If the pre-assessment shows that the structural yield stress p_c2 is slightly lower than the design load, and the foundation structure is in a relatively stable state, then the decision is to adopt scheme (1): foamed lightweight soil deformation control. (2) If the pre-assessment shows that the structural yield stress p_c2 is significantly higher than the design load, and scheme (1) still cannot meet the requirements, then the decision is to adopt scheme (2): vacuum preloading combined with foamed lightweight soil deformation control. (3) If the pre-assessment shows that the foundation is a thick, highly water-containing, extremely soft soil layer, or the design load is much greater than the structural yield stress p_c2, then the decision is to adopt scheme (3): vacuum preloading combined with foamed lightweight soil embedded with large-diameter pipe deformation control. In addition, the impact of factors such as construction progress and cost must be comprehensively considered when conducting the preliminary assessment.

[0045] Step 4: Implementation and Deformation Control: Based on the decision made in Step 3, implement the corresponding control scheme. Scheme (1): Lay a sand cushion layer (thickness can be 40cm~60cm) directly on the original roadbed, and then use foamed lightweight soil as the embankment filling material to replace the traditional filling material. By significantly reducing the self-weight of the embankment, the additional stress generated is controlled below the structural yield stress p_c2. The schematic diagram of the roadbed cross section structure of Scheme (1) (deformation control of foamed lightweight soil) is shown below. Figure 3a As shown, the corresponding stress path and deformation control are as follows: Figure 3b As shown in the diagram (blue path in the red curve), the self-weight of the overlying embankment is significantly reduced after the foamed lightweight soil replacement treatment, and the additional stress is controlled below the yield stress of the soil structure. Scheme (2): First, drainage boards and cross-section pipes are arranged on the original subgrade, and then a sealing film is covered for vacuum preloading, so that the vacuum degree under the film reaches 80kPa and remains stable. The negative pressure accelerates the discharge of pore water, improves the effective stress and strength of the foundation soil, and raises the structural yield stress point on its compression curve. Then, foamed lightweight soil is filled. This method forms a two-way regulation of "improving the foundation resistance (structural yield stress) + reducing external load". The schematic diagram of the subgrade cross section structure using Scheme (2) (vacuum preloading combined with foamed lightweight soil deformation regulation) is shown in the diagram. Figure 4a As shown, stress path and deformation control are as follows: Figure 4bAs shown (blue path in purple curve), the illustration shows that: introducing vacuum preloading technology before embankment filling promotes the reduction of pore water pressure and the increase of effective stress in the soil through preloading consolidation, thereby delaying structural failure and improving the structural level. That is, the original compression curve (red curve) becomes purple curve. On this basis, foamed lightweight soil is used for replacement, realizing two-way regulation, so that the additional stress is controlled below the yield stress of the soil structure. Scheme (3): On the basis of vacuum preloading reinforcement in Scheme (2), large-diameter, low-density hollow pipes (such as corrugated steel pipes) are embedded in the foamed lightweight soil filling body at the design spacing to form a "lightweight material-hollow structure" composite. This composite can further and extremely reduce the unit area load transmitted to the top surface of the foundation, ensuring that it is still lower than the yield stress of the soil structure after preloading reinforcement under extremely harsh conditions. The cross-sectional structure of the subgrade in Scheme (3) (vacuum preloading combined with deformation control of large-diameter pipes embedded in foamed lightweight soil) is as follows Figure 5a As shown, stress path and deformation control are as follows: Figure 5b As shown in the diagram (blue path within the purple curve), embedding large-diameter, low-density hollow pipes into lightweight fillers (such as foamed lightweight soil) on the basis of vacuum preloading to construct a "lightweight material-hollow structure" composite can greatly reduce the additional stress per unit area up to the stress point of the structure, thus achieving ultimate load reduction design.

[0046] Preferably, the wet bulk density of the foamed lightweight soil is controlled at 5-12 kN / m³. 3 The unconfined compressive strength after 28 days is not less than 0.5 MPa.

[0047] Preferably, the vacuum degree of the vacuum preloading is maintained at not less than 80 kPa, and the preloading time is determined based on the calculated average degree of consolidation of the foundation reaching the design requirements (e.g., more than 90%).

[0048] Preferably, the soil pressure, stratified settlement, and horizontal displacement of the foundation are monitored throughout the construction process and for a period of time after construction to verify the control effect, and information feedback and dynamic adjustments can be made based on the monitoring data.

[0049] Example A section of a highway is located in the soft soil region of the Pearl River Delta, with a layer of fluid-plastic silt about 11-15 meters thick beneath the surface. This silt has high water content and extremely poor structure, making it a typical section with unfavorable geological conditions. The design requires strict control of post-construction settlement of the roadbed to a low standard.

[0050] Steps One & Two: Geological Investigation and Determination of Structural Yield Stress The project began with a detailed geological survey and borehole sampling. One-dimensional consolidated compression tests were conducted on representative undisturbed silt samples. The test loading paths were 12.5, 25, 50, 75, 100, 150, and 200 kPa, followed by unloading and reloading. The lg e - lg p curve was plotted (e.g., ...). Figure 2 As shown in the figure, a clear inflection point is determined on the curve, and the corresponding pressure value p_c2 is about 45 kPa, which is the structural yield stress of the silt layer.

[0051] Step 3: Preliminary Assessment and Decision-Making of the Solution The calculated design load of the embankment (including pavement structure) for this section is approximately 110 kPa. Obviously, the design load (110 kPa) is much greater than the structural yield stress of the foundation (45 kPa). The preliminary assessment conclusion is that the foundation is extremely weak and the design load far exceeds the structural yield point, which is a high-risk condition. Therefore, the decision is to adopt the most reliable scheme (3): vacuum preloading combined with deformation control of large-diameter pipes embedded in lightweight foam soil.

[0052] Step Four: The implementation of the plan is divided into two parts: foundation treatment and embankment filling (e.g., Figure 6 (as shown) Foundation treatment (vacuum preloading): A sand cushion layer ③ is laid on the soft soil surface after clearing, plastic drainage boards ⑥ are installed to the bottom of the silt layer, cross-section pipes ⑤ are installed, and then a sealing membrane is covered. Vacuum pumping equipment is installed. Vacuum preloading begins, and the vacuum degree under the membrane is maintained above 85 kPa for a long period. Preloading continues for about 250 days, which effectively drains and consolidates the deep silt layer, significantly improving its strength.

[0053] Embankment construction (composite lightweight structure): After vacuum preloading, large-diameter double-wall corrugated steel pipes (as ⑦) are installed on the sand cushion layer at the designed positions. Then, foamed lightweight soil ② is poured in layers around and on top of the pipes to form a lightweight composite embankment. The wet density of the foamed lightweight soil is approximately 6.5 kN / m³. 3 .

[0054] Effect monitoring and verification: Comprehensive monitoring of key sections was carried out during the construction process.

[0055] Earth pressure monitoring ( Figure 7a The earth pressure gauge embedded in the bottom of the corrugated steel pipe shows that after the completion of the 5m high lightweight composite embankment, the pressure of the bottom of the pipe on the foundation stabilized at about 40 kPa. This value is not only much lower than that of ordinary fill embankments (which may exceed 100 kPa), but also lower than the bearing capacity of the foundation after preloading reinforcement, proving the excellent load reduction effect.

[0056] Stratified settlement monitoring ( Figure 7bMonitoring showed that settlement mainly occurred during the vacuum preloading period (linear growth in the first 100 days), with a gradual increase in settlement during embankment construction. Total settlement primarily originated from the deep silt layer, with almost zero settlement in the underlying silty clay layer. After vacuum unloading, the foundation experienced slight rebound, stabilizing again as the embankment was constructed. The final total surface settlement was 170.4 cm. The settlement development pattern, rate, and total amount were effectively predicted and controlled, with no sudden deformation.

[0057] Conclusion: This embodiment demonstrates that the method of the present invention, through quantitative identification of structural yield stress and pre-assessment decision based on this, successfully applied the most suitable composite control scheme (scheme (3)) on extremely soft foundations. Monitoring data confirms that the method achieved the core objective of "load lower than structural strength", controlling the foundation stress within a safe range, thereby effectively managing the large-scale settlement process, making it stable and controllable, and ultimately ensuring the stability and safety of the high-standard highway subgrade. For foundations with better conditions, more economical schemes (1) or (2) can be adopted accordingly.

[0058] The above description of the embodiments is only for the purpose of helping to understand the method and core idea of ​​this application; at the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​this application. Therefore, the content of this specification should not be construed as a limitation of this application.

[0059] Certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The terms "comprising" and "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising / including but not limited to". "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error. The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0060] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.

[0061] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0062] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A multi-element load reduction deformation control method for foamed lightweight soil subgrade based on structural stress control, characterized in that, Includes the following steps: S1: Select soil samples with different cross sections and depths in the construction section for drilling and sampling, and determine the basic mechanical parameters of the soil through tests; S2: Conduct a one-dimensional consolidation compression test on the obtained undisturbed soil, plot the compression curve based on the test data and the basic mechanical parameters, and determine the yield stress of the soil structure according to the inflection point of the compression curve. S3: Based on the structural yield stress determined in step S2 and the additional stress generated by the design load, select and implement a load reduction deformation control scheme. The control scheme includes: Scheme (1): Deformation control of foamed lightweight soil: Foamed lightweight soil is used as lightweight filler in embankment construction to reduce the overlying load and control the additional stress below the yield stress of the structure. Scheme (2): Vacuum preloading combined with foam lightweight soil deformation control: When scheme (1) cannot meet the requirement that the additional stress is less than the yield stress of the structure, vacuum preloading is carried out on the foundation before the embankment is filled, and then foam lightweight soil is filled. Scheme (3): Vacuum preloading combined with foam lightweight soil embedded with large diameter pipe deformation control: When scheme (2) still cannot meet the requirement that the additional stress is less than the yield stress of the structure, while performing vacuum preloading and foam lightweight soil filling, a large diameter hollow pipe is embedded in the foam lightweight soil.

2. The method according to claim 1, characterized in that, The basic mechanical parameters in step S1 include the initial void ratio, the compressibility consolidation coefficient, the cohesion, and the internal friction angle.

3. The method according to claim 1, characterized in that, The one-dimensional consolidation compression test process in step S2 is loading-unloading-reloading, and the loading path is: 12.5→25→50→75→100→150→200→150→100→75→50→25→50→75→100→150→200→300→400 kPa.

4. The method according to claim 1, characterized in that, The compression curve in step S2 is a porosity-pressure curve on a double logarithmic coordinate system.

5. The method according to claim 2, characterized in that, Before step S3, there is also a scheme pre-selection step: based on the basic mechanical parameters of the soil determined in step S1 and the structural yield stress determined in step S2, combined with the design load of the upper embankment, the structural strength of the foundation is pre-evaluated. If the pre-assessment indicates that the yield stress of the structure is lower than the design load, scheme (1) shall be preferred. If the yield stress of the structure is still lower than the design load after the review and evaluation of scheme (1), then scheme (2) or scheme (3) shall be adopted. For extremely soft and weak foundations with large thickness and high water content, or for major projects with design loads far exceeding the structural yield stress, scheme (3) is directly adopted.

6. The method according to claim 1, characterized in that, In step S3, the foamed lightweight soil is filled on top of the sand cushion layer, and the sand cushion layer is laid on top of the original roadbed; the vacuum preloading treatment uses drainage boards for drainage, and a cross-section pipe is used to monitor the vertical settlement of the soil on the entire continuous profile; the large-diameter hollow pipe is a low-density hollow pipe.

7. The method according to claim 1, characterized in that, During and after the implementation of any control scheme in step S3, the soil pressure and settlement of the roadbed are monitored in real time, and the deformation control effect is evaluated based on the monitoring data. If necessary, construction parameters or reinforcement measures are dynamically adjusted.

8. The method according to claim 1, characterized in that, The wet bulk density of the foamed lightweight soil is 5-12 kN / m³. 3 The unconfined compressive strength after 28 days is not less than 0.5 MPa; the vacuum degree of the vacuum pre-compression treatment is not less than 80 kPa, and the pre-compression period is determined according to the degree of consolidation requirements.

9. The method according to claim 6, characterized in that, The drainage boards are arranged in an equilateral triangle pattern with a spacing of 1.5m; the cross-section pipes are laid across the entire roadbed; the large-diameter hollow pipes are corrugated steel pipes, arranged perpendicular to the road centerline, with a pipe spacing of 2.0m to 3.0m.

10. A roadbed structure, characterized in that, The roadbed was constructed using the multi-element load reduction and deformation control method for foamed lightweight soil subgrade based on structural stress control, as described in any one of claims 1 to 9.

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