Lightweight Backfill Method and Structure for Underground Structures Based on Additional Stress Control

Abstract

This invention discloses a lightweight backfill method and structure for underground structures based on additional stress control. This method uses lightweight foamed soil with controllable density as the backfill material, and precisely designs its density and replacement volume to ensure that the total additional stress generated by the backfill and the superstructure does not exceed the in-situ pre-consolidation pressure of the foundation soil, thereby fundamentally suppressing new settlement. This invention not only effectively controls settlement and ensures the safety of adjacent structures, but also leverages the vibration isolation effect of lightweight foamed soil and facilitates the resource utilization of engineering waste and industrial solid waste, demonstrating significant environmental and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering technology, and in particular to a lightweight backfilling method and structure for underground structures based on additional stress control. Background Technology

[0002] In engineering projects such as road construction, slope protection, underground space backfilling, and excavation of areas adjacent to existing buildings, a large amount of earthwork replacement work is often required. Traditional replacement materials (such as graded sand and gravel, lime-soil, etc.) are heavy and will significantly increase the additional stress on the foundation, resulting in significant post-construction settlement and easily causing adverse effects on adjacent structures.

[0003] To reduce the additional stress after backfilling, lightweight materials such as polystyrene foam blocks and foamed concrete are increasingly being used. For example, Chinese patent CN219033296U discloses a backfill structure for an underground utility tunnel roof based on foamed lightweight soil, which achieves weight reduction, seismic isolation, and cost reduction by partially replacing gravel concrete with foamed lightweight soil. However, this type of existing technology mainly focuses on the "direct replacement" application of foamed lightweight soil as a lightweight material, and its specific structural combination with concrete beams, waterproof layers, and surface layers to achieve comprehensive functions such as load-bearing and waterproofing. These solutions share the following methodological limitations:

[0004] Design is based on experience: The selection of density and the determination of replacement volume of foamed lightweight soil are often based on experience or to meet single requirements such as the bearing capacity of the superstructure, lacking quantitative design basis that is directly related to the inherent properties of the foundation soil (such as preconsolidation pressure).

[0005] Settlement control is passive: While its weight reduction effect helps reduce settlement, it does not establish an active and precise control mechanism for the stress state between the backfill and the foundation. Settlement control is a matter of "mitigation of results" rather than "prevention at the source." For sensitive projects with extremely high requirements for post-construction settlement control (such as deep soft soil foundations, bridge approach sections, and adjacent existing structures), its control effect is uncertain.

[0006] The problem-solving approach is one-sided: it fails to systematically link the fundamental goals of "lightweight materials", "stress control" and "eliminating post-construction settlement" in a closed loop through rigorous soil mechanics principles, and the design methods are unsystematic and not universally applicable.

[0007] At the same time, the replacement method often generates a large amount of engineering waste soil, which is costly to transport and store and occupies land resources; while large-scale industrial production generates huge amounts of industrial solid waste such as steel slag, ore slag, and fly ash, and their storage causes serious environmental damage.

[0008] Therefore, there is an urgent need in the current technological field for a quantitative design method based on the fundamental principles of soil mechanics that goes beyond simple material replacement. This method should fully utilize the characteristics of lightweight materials such as foamed lightweight soil, and prevent post-construction settlement from the source by actively and precisely controlling the additional stress generated on the foundation by the backfilling project, while also taking into account the resource utilization of industrial solid waste, construction convenience, and engineering economy. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention proposes a lightweight backfilling method and structure for underground structures based on additional stress control. By using lightweight foamed soil with controllable density as the backfill material and precisely designing its density and replacement volume, it ensures that the total additional stress generated by the backfill and the superstructure does not exceed the in-situ pre-consolidation pressure of the foundation soil, thereby fundamentally suppressing new settlement.

[0010] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0011] A lightweight backfilling method for underground structures based on additional stress control includes the following steps:

[0012] S1. Determine the replacement range of the target area of ​​the project, the density and volume parameters of the underground structures, and the density, volume and preconsolidation pressure parameters of the soil to be replaced; S2. Select or design the target density of the foamed lightweight soil according to the project's requirements for the strength and deformation control of the backfill.

[0013] S3. According to the formula:

[0014] (Formula 1),

[0015] With the target density ρ of the foamed lightweight soil F Let V be a variable, and calculate and determine its replacement volume V within the replacement area. F To ensure that the additional stress generated by the foamed lightweight soil and underground structures after replacement does not exceed the pre-consolidation pressure of the replaced soil layer; wherein,

[0016] ρ F The target density of foamed lightweight soil is kg / m³. 3 ;

[0017] V F The volume of foamed lightweight soil in the replacement area is m. 3 ;

[0018] ρ j The density of various underground structures in the replacement area, kg / m³ 3 ;

[0019] V jThe volume of various underground structures within the replacement area is given in m. 3 ;

[0020] ρ i The density of each soil layer being replaced is given in kg / m³. 3 ;

[0021] V i The volume of each soil layer being replaced is expressed in m. 3 ;

[0022] S4. Based on the target density of the foamed lightweight soil determined in step S2 and the replacement volume V within the replacement area determined in step S3. F The foamed lightweight soil is then backfilled into the target area.

[0023] Preferably, the foamed lightweight soil is prepared using at least one of cement, engineering waste soil and / or industrial solid waste as raw materials.

[0024] Preferably, in step S4, the foamed lightweight soil is transported in slurry form and filled into the target area by pumping or pouring, and then allowed to solidify.

[0025] Preferably, reinforcing materials are laid during the backfilling process of the foamed lightweight soil or between layers of it during layered backfilling.

[0026] Preferably, the reinforcing material is at least one of geogrid, wire mesh, or fiber mesh.

[0027] The present invention further discloses a lightweight backfill structure for underground structures based on additional stress control. The structure is constructed by the aforementioned lightweight backfill structure for underground structures based on additional stress control. The structure includes a foamed lightweight soil backfill body located within the target replacement area. The density and volume of the foamed lightweight soil backfill body satisfy the following condition: the additional stress generated by its interaction with the underground structures in the area does not exceed the pre-consolidation pressure of the undisturbed soil layer.

[0028] Preferably, the foamed lightweight soil backfill contains reinforcing materials.

[0029] Preferably, the lightweight backfill structure for underground structures is used in soft soil foundation treatment, bridge abutment embankment filling, or backfilling projects adjacent to existing underground structures.

[0030] The beneficial effects of this invention are as follows:

[0031] First, by fully utilizing the advantages of low and controllable density of foamed lightweight soil, and based on the basic theory of soil mechanics, the density of foamed lightweight soil and the amount of replacement can be controlled to ensure that the additional stress after backfilling does not exceed the pre-consolidation pressure, thereby eliminating the settlement problem caused by the increase in load due to the replacement from the root. It is especially suitable for sensitive projects that are adjacent to existing structures or soft foundations.

[0032] Second, it is safe and reliable: it avoids the risk of instability in high embankments, reduces defects such as "bridge approach slab settlement", and ensures the safety of adjacent structures.

[0033] Third, it is green and environmentally friendly: it realizes the on-site utilization of engineering waste soil and the resource-based consumption of industrial solid waste, reduces external transportation and storage, and has significant environmental benefits.

[0034] Fourth, life-cycle economics: Although the unit price of materials may be high, it significantly saves on expensive maintenance and repair costs in the later stages, as well as social costs caused by settlement problems.

[0035] Fifth, it is convenient to construct and has wide applicability: the fluid construction method is highly adaptable and can be widely applied to various engineering scenarios that require backfilling and replacement. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of the present invention;

[0037] Figure 2 This is an explanatory diagram for Example 2;

[0038] Among them, 1. Roadbed constructed after backfilling; 2. Foamed lightweight soil for backfilling; 3. Underground structures (integrated utility tunnels); 4. Additional loads; 5. Reinforcing materials; 6. Bridge abutments. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] In this application, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0041] A lightweight backfilling method for underground structures based on additional stress control includes the following steps:

[0042] S1. Determine the replacement range of the target area of ​​the project, the density and volume parameters of the underground structures, and the density, volume and preconsolidation pressure parameters of the soil to be replaced. S2. Select or design the target density of foamed lightweight soil according to the project's requirements for strength and deformation control of the backfill.

[0043] S3. According to the formula:

[0044] (Formula 1),

[0045] With the target density ρ of the foamed lightweight soil F Let V be a variable, and calculate and determine its replacement volume V within the replacement area. F To ensure that the additional stress generated by the foamed lightweight soil and underground structures after replacement does not exceed the pre-consolidation pressure of the replaced soil layer; wherein,

[0046] ρ F The target density of foamed lightweight soil is kg / m³. 3 ;

[0047] V F The volume of foamed lightweight soil in the replacement area is m. 3 ;

[0048] ρ j The density of various underground structures in the replacement area, kg / m³ 3 ;

[0049] V j The volume of various underground structures within the replacement area is given in m. 3 ;

[0050] ρ i The density of each soil layer being replaced is given in kg / m³. 3 ;

[0051] V i The volume of each soil layer being replaced is expressed in m. 3 ;

[0052] S4. Based on the target density of the foamed lightweight soil determined in step S2 and the replacement volume V within the replacement area determined in step S3. F The foamed lightweight soil is then backfilled into the target area.

[0053] As a preferred embodiment of the above technical solution of the present invention, the foamed lightweight soil is prepared using at least one of cement, engineering waste soil and / or industrial solid waste as raw materials.

[0054] Furthermore, in step S4, the foamed lightweight soil is transported in slurry form and filled into the target area by pumping or pouring, and then allowed to solidify.

[0055] Example 1:

[0056] Highway construction after backfilling of underground utility tunnels on soft soil foundation

[0057] (1) Project Background

[0058] A new integrated utility tunnel is being constructed beneath a newly built highway. The highway subgrade is 76 cm high, the tunnel's top is buried 1.4 m deep, its cross-section has an outer width of 3.6 m and an outer height of 2.6 m. The route passes through a section of deep, soft soil, with a surface layer of 2-3 meters of plastic clay, beneath which lies over 8 meters of fluid-plastic silty soil with a density of ρ = 1500 kg / m³, high natural moisture content, extremely low bearing capacity, and extremely high compressibility.

[0059] (2) Foamed lightweight soil replacement scheme

[0060] Foamed lightweight soil 2 was used for replacement to control post-construction settlement. The replacement depth was 5.5m and the base width was 5m.

[0061] The foamed lightweight soil 2 used for filling has a density of ρ. F = 800 kg / m³, 7-day unconfined compressive strength ≥ 0.8MPa. Reinforcing material 5 uses steel wire mesh. The self-weight of the integrated utility tunnel is 10 tons / m, and the roadbed density is taken as 2000 kg / m³.

[0062] Verify the additional stress on the base:

[0063]

[0064] The additional load 4 is less than the pre-consolidation pressure, which meets the requirements.

[0065] (3) Implementation effect

[0066] After preparing foamed lightweight soil on site, it was injected into the excavation area. Post-construction monitoring showed that the post-construction settlement of this section was only about one-third of that of the adjacent section using conventional sand and gravel replacement, and the settlement was uniform, effectively avoiding the instability risk commonly seen in high fills on deep soft soil.

[0067] Example 2: Embankment Construction at the Approach of a High-Fill Bridge

[0068] (1) Engineering problem:

[0069] A highway bridge abutment in a mountainous area requires the construction of an embankment with a height of 9 meters. The abutment sits on bedrock, while the foundation behind it consists of colluvial gravelly soil, 3.0 meters thick, with a density of 2000 kg / m³ and relatively high compressibility. The total height of the roadbed and pavement is 0.8 meters, with a density of 1800 kg / m³. To prevent "bridge approach slab settlement" caused by roadbed settlement far exceeding abutment settlement, it is necessary to reduce the settlement caused by the embankment's own weight.

[0070] (2) Foamed lightweight soil filling scheme

[0071] In the area adjacent to the abutment (usually within 30-50 meters behind the abutment), foamed lightweight soil 2 is used for load reduction filling to form a rigid transition section, smoothing out the difference in stiffness and settlement between the abutment and the general roadbed. The foamed lightweight soil 2 is backfilled in layers, with soil arch grids used as reinforcement materials.

[0072] Using a high-strength mix design, primarily composed of cement, slag, and fine aggregates, foamed lightweight soil was prepared. The density ρ of the foamed lightweight soil was... F = 1000 kg / m³ foamed lightweight soil, 28-day unconfined compressive strength ≥ 2.0 MPa.

[0073]

[0074] The additional load 4 is less than the pre-consolidation pressure, which meets the requirements.

[0075] (3) Implementation effect

[0076] Two years of monitoring after the road opened to traffic showed that the post-construction settlement of the foamed lightweight soil section was only 1 cm, with a smooth transition to the bridge abutment and no "bridge approach bumping" phenomenon. In contrast, the comparison section using conventional soil and rock filling showed obvious settlement differences and a bumping sensation, requiring repeated repairs. Although the unit price of materials in this solution is slightly higher, it saves on expensive maintenance costs and hidden costs associated with unsafe driving, resulting in significant economic benefits throughout the entire life cycle.

[0077] The purpose of this invention is to overcome the shortcomings of existing lightweight replacement materials, such as limited performance, poor environmental benefits, and a lack of systematic design methods. It aims to achieve high-value, large-scale resource utilization of bulk industrial solid waste and engineering spoil, and to establish a replacement method centered on additional stress control. By controlling the additional stress after replacement to not exceed the pre-consolidation pressure, it eliminates the post-construction settlement problems caused by traditional replacement methods. This provides a green, economical, and reliable technical solution for the protection of adjacent existing structures, the treatment of weak foundations, and high-fill engineering projects. Simultaneously, it fully utilizes the seismic isolation function of foamed lightweight soil to improve the seismic performance of underground structures.

[0078] The significance of this invention lies in effectively preventing post-construction settlement caused by replacement and additional loading, ensuring the safety of adjacent structures, and improving the stability and seismic performance of underground structures.

[0079] Although the present invention has been illustrated and described with reference to preferred embodiments, those skilled in the art should understand that various changes and modifications can be made to the present invention without departing from the scope defined by the claims.

Claims

1. A lightweight backfilling method for underground structures based on additional stress control, characterized in that, Includes the following steps: S1. Determine the replacement range of the target area of ​​the project, the density and volume parameters of the underground structures, and the density, volume and preconsolidation pressure parameters of the soil to be replaced; S2. Select or design the target density of the foamed lightweight soil according to the project's requirements for the strength and deformation control of the backfill. S3. According to the formula: (Official 1), With the target density ρ of the foamed lightweight soil F Let V be a variable, and calculate and determine its replacement volume V within the replacement area. F To ensure that the additional stress generated by the foamed lightweight soil and underground structures after replacement does not exceed the pre-consolidation pressure of the replaced soil layer; wherein, ρ F The target density of foamed lightweight soil is kg / m³. 3 ; V F The volume of foamed lightweight soil in the replacement area is m. 3 ; ρ j The density of various underground structures in the replacement area, kg / m³ 3 ; V j The volume of various underground structures within the replacement area is given in m. 3 ; ρ i The density of each soil layer being replaced is given in kg / m³. 3 ; V i The volume of each soil layer being replaced is expressed in m. 3 ; S4. Based on the target density of the foamed lightweight soil determined in step S2 and the replacement volume V within the replacement area determined in step S3. F The foamed lightweight soil is then backfilled into the target area.

2. The lightweight backfilling method for underground structures based on additional stress regulation according to claim 1, characterized in that, The foamed lightweight soil is prepared using at least one of cement, engineering waste soil and / or industrial solid waste as raw materials.

3. The lightweight backfilling method for underground structures based on additional stress control according to claim 1, characterized in that, In step S4, the foamed lightweight soil is transported in slurry form and filled into the target area by pumping or pouring, and then allowed to solidify.

4. The lightweight backfilling method for underground structures based on additional stress regulation according to any one of claims 1 to 3, characterized in that, Reinforcing materials are laid during the construction of the foamed lightweight soil backfill or between its layered filling layers.

5. The lightweight backfilling method for underground structures based on additional stress regulation according to claim 4, characterized in that, The reinforcing material is at least one of geogrid, wire mesh, or fiber mesh.

6. A lightweight backfill structure for underground structures based on additional stress regulation, characterized in that, The structure is constructed by lightweight backfilling of underground structures based on additional stress control as described in any one of claims 1 to 5; the structure includes a foamed lightweight soil backfill located within the target replacement area, wherein the density and volume of the foamed lightweight soil backfill satisfy the following: the additional stress generated by its interaction with the underground structures in the area does not exceed the pre-consolidation pressure of the original soil layer.

7. The lightweight backfill structure for underground structures based on additional stress regulation according to claim 6, characterized in that, The foamed lightweight soil backfill is mixed with reinforcing materials.

8. The lightweight backfill structure for underground structures based on additional stress regulation according to claim 6 or 7, characterized in that, The lightweight backfill structure for underground structures is used in soft soil foundation treatment, bridgehead embankment filling, or backfilling projects adjacent to existing underground structures.

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