Construction method for composite foundation layer compaction replacement

Abstract

The application relates to the technical field of foundation treatment of building engineering, and particularly discloses a composite foundation layered compaction replacement construction method, which ensures the stability of a foundation bottom through dynamic deepening and foundation bottom treatment, strengthens quality control in combination with a test groove, optimizes material distribution and constraint structures through partition constraint layered backfill, forms a stepped working face to improve the continuity of construction in multi-elevation areas, enhances the bearing capacity of key areas through high-strength backfill around the structure, guarantees the compactness of a large area through final backfill and compaction, and realizes overall quality confirmation through foundation bearing capacity verification. The application effectively solves the problems of poor construction process coordination, low material utilization efficiency, non-precise quality control, limited construction efficiency, high environmental cost and the like.

Description

Technical Field

[0001] This invention relates to the field of foundation treatment technology for building engineering, and more specifically, to a method for layered compaction and replacement construction of composite foundations. Background Technology

[0002] In the field of construction engineering, foundation treatment is a crucial step in ensuring the stability and safety of buildings, especially for high-load factory buildings (such as industrial plants and storage facilities), where the requirements for foundation bearing capacity, uniformity, and deformation control are even more stringent. These types of buildings typically face challenges such as complex geological conditions (e.g., weak soil layers, backfill soil), uneven load distribution, and the need to coordinate multiple construction processes (e.g., excavation, backfilling, compaction, pile foundation construction). Therefore, developing efficient, reliable, and economical foundation treatment methods is of great significance. Currently, common foundation treatment technologies include replacement methods, compaction methods, and pile-foundation composite foundations. Replacement methods improve the foundation bearing capacity by excavating weak soil layers and backfilling with high-strength materials (e.g., graded sand and gravel, lime-soil); compaction methods enhance soil density through mechanical rolling or tamping. In practical applications, these methods are often used in combination, but existing technologies still have significant shortcomings.

[0003] 1. In traditional replacement construction, excavation depth control often relies solely on fixed depth standards without dynamic adjustments based on actual geological conditions, leading to substandard foundation treatment. The backfilling sequence lacks systematic zoning and layering control, particularly between the building's perimeter and core areas, failing to create an effective constraint structure. When buildings have different foundation elevations (e.g., tower and podium areas), the backfilling and pile foundation construction processes are poorly coordinated, making it difficult to form a continuous working surface. This obstructs machinery access, extending the construction period and increasing safety risks.

[0004] 2. Excavated soil is usually treated as waste and transported off-site, which not only generates additional transportation and disposal costs, but may also have a negative impact on the environment.

[0005] 3. Existing technologies lack refined management of layer thickness and compaction parameters (such as equipment weight and number of passes) during the backfilling process. Large areas and special areas (such as foundations, ground beams, and the area around structural columns) often use the same backfilling and compaction process, but the latter has higher requirements for compaction uniformity and bearing capacity, and mechanical compaction can easily cause damage or incomplete backfilling around the structure.

[0006] 4. Existing methods do not optimize the connection between backfilling and subsequent procedures (such as pile foundation construction and reverse excavation). For example, the step-like working face is not formed in advance, resulting in the disconnect between construction in different elevation areas, requiring frequent adjustments of machinery and reducing efficiency. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a composite foundation layered compaction replacement construction method, which has the advantages of improving the quality of foundation treatment, optimizing the coordination of construction process, enhancing material utilization, improving construction efficiency, and reducing environmental impact.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for layered compaction and replacement construction of composite foundations includes the following steps: S1. Dynamic Excavation Depth and Foundation Treatment: Clean the construction area and remove the topsoil within 1 meter outside the building projection line; the excavation depth is controlled by reaching the stable clay layer, and the initial design excavation depth is not less than 1.5 meters. If the clay layer is not reached, continue excavating until it is touched; after excavation, use vibratory compaction equipment to compact the foundation. S2. Joint inspection of the foundation: After step S1 is completed, the construction, supervision, design, survey and construction units shall jointly inspect and confirm the treated foundation. S3. Zonal-constrained layered backfilling: S3.1 Peripheral Layered Backfilling: First, backfill lime-soil in multiple layers in multiple directions around the building perimeter to form a partially enclosed lime-soil confinement body; S3.2 Core Layered Backfill: Within the area enclosed by the lime-soil confinement body, graded sand and gravel are backfilled in layers to form a core backfill body; S3.3 Closed constraint zone: Finally, backfill the remaining direction of the building perimeter with lime-soil in layers to form a complete closed constraint zone around the building perimeter. The width of the closed constraint zone shall be not less than 4 meters. S3.4 Layered backfilling of the outer perimeter: On the outer perimeter of the closed constraint zone, layered backfilling of the soil forms a soil backfill body. The outer width of the soil backfill body is not less than 4 meters. This soil backfilling is carried out alternately with the backfilling in steps S3.1 to S3.3. S4. Formation of stepped working face: When there are different foundation elevations in a building, the different elevation areas are backfilled in layers to their respective pile foundation construction surface design elevations, and connected by slope and ramp connection to form a continuous working face; wherein, the different elevation areas include the tower area with lower foundation elevation and the podium area with higher foundation elevation; S5. Construction of pile foundation and underground structure: Pile foundation construction is carried out on the continuous working surface, followed by reverse excavation and structural construction of the pile cap, ground beam and structural column areas; S6. High-strength backfill around the structure: After the construction of the foundation, ground beam and structural column is completed, the backfill area around it is backfilled manually in layers by using graded sand and gravel mixed with cement. S7. Final backfilling and compaction: After completing step S6, continue to lay the fill material in layers in the large area to the design elevation and then mechanically compact it. S8. Foundation bearing capacity verification: After all backfilling is completed, field load tests are conducted in different areas.

[0009] As a preferred embodiment of the present invention, in step S1, the preset depth is not less than 1.5 meters downward from the existing ground surface, and should be dug to a stable clay layer; the vibratory compaction equipment is a vibratory compactor with a weight of not less than 10 tons, and the number of compaction passes is not less than 6.

[0010] As a preferred embodiment of the present invention, in steps S3.1 and S3.3, the lime-soil is made by mixing lime and clay in a volume ratio of 3:7, and all or part of the clay comes from the excavated soil in step S1.

[0011] As a preferred embodiment of the present invention, in step S3.2, the graded sand and gravel is made by mixing sand and crushed stone in a mass ratio of 3:7.

[0012] As a preferred embodiment of the present invention, in step S3.4, the plain soil backfill needs to be sloped, with the inner slope ratio near the lime-soil constraint zone being 1:0.33 and the outer slope ratio being 1:1.

[0013] As a preferred embodiment of the present invention, in step S6, the cement is 425 grade silicate cement, and the dosage is 250 kg per cubic meter of graded sand and gravel filler; the specific range is: within 1 meter around the structural column, within 0.5 meters on both sides of the ground beam, and within 0.5 meters around the foundation; the thickness of the manually compacted layer is not greater than 200 mm.

[0014] As a preferred embodiment of the present invention, the excavated soil in step S1, provided that the engineering requirements are met, is preferentially used for the plain soil backfilling in step S3.4.

[0015] As a preferred embodiment of the present invention, when the excavated soil to be backfilled is temporarily stockpiled in step S1, the stockpiling location shall be no less than 2 meters away from the excavation slope, the height of the stockpile shall be no more than 2 meters, and covering and dust suppression measures shall be taken.

[0016] As a preferred embodiment of the present invention, in the entire layered backfilling process, for large areas, a vibratory compaction device with a weight of not less than 10 tons is used for compaction, the layer thickness is not greater than 500 mm, and the number of compaction passes is not less than 6; for the areas around the foundation, foundation, ground beam and structural column, manual compaction is used, and the layer thickness is not greater than 200 mm.

[0017] As a preferred embodiment of the present invention, in step S8, the on-site load test is a pressure plate load test, with no less than 6 test points, which are respectively located in the key areas of the tower and podium of the building.

[0018] As can be seen from the above, the composite foundation layered compaction replacement construction method of the present invention has the following advantages compared with the prior art: it ensures the stability of the foundation through dynamic excavation and foundation treatment, strengthens quality control through joint inspection, optimizes material distribution and constraint structure through zoned constrained layered backfilling, improves the construction continuity of multi-elevation areas through stepped working face formation, enhances the bearing capacity of key areas through high-strength backfilling around the structure, ensures the overall compaction through final backfilling and compaction, and achieves comprehensive quality confirmation through foundation bearing capacity verification. It effectively solves the problems of poor coordination of construction process, low material utilization efficiency, imprecise quality control, limited construction efficiency, and high environmental costs. It has the advantages of improving the quality of foundation treatment, optimizing the coordination of construction process, enhancing material utilization, improving construction efficiency, and reducing environmental impact. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a construction flowchart of the composite foundation layered compaction and replacement construction method proposed in an embodiment of the present invention; Figure 2 This is a schematic diagram of the layout of the layered backfill and replacement areas in an embodiment of the present invention; Figure 3 This is a schematic diagram showing the temporary stockpile of excavated soil to be backfilled in an embodiment of the present invention. Figure 4 This is a schematic cross-sectional view of the foundation structure after construction according to an embodiment of the present invention; Figure 5 This is a cross-sectional schematic diagram of the high-strength backfill around the foundation, foundation beams, and structural columns after construction according to an embodiment of the present invention. Figure 6 This is a top view of the high-strength backfill around the foundation cap in the foundation structure after construction according to an embodiment of the present invention; Figure 7 This is a top view of the high-strength backfill around the ground beam in the foundation structure after construction according to an embodiment of the present invention; Figure 8 This is a top view of the high-strength backfill around the structural columns in the foundation structure after construction according to an embodiment of the present invention; Figure 9 This is an overall construction zoning diagram of a building with different foundation elevations in the tower area and podium area, as shown in this embodiment of the invention.

[0021] 1. Foundation; 2. Closed constraint zone; 3. Core backfill; 31. Tower area; 32. Podium area; 33. Transition section; 4. Plain soil backfill; 41. Inner slope; 42. Outer slope; 5. High-strength backfill; 6. Building foundation; 7. Building ground beam; 8. Building structural column; 9. Soil to be backfilled; 10. Pile foundation. Detailed Implementation

[0022] 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.

[0023] See Figures 1 to 9 This invention proposes a method for layered compaction and replacement construction of composite foundations, comprising the following steps: S1. Dynamic Excavation Depth and Base 1 Treatment: Clear the construction area and remove topsoil within a 1-meter radius beyond the building projection line. The excavation depth should be controlled by reaching a stable clay layer; the initial design depth should be no less than 1.5 meters. If the clay layer is not reached, continue excavating until it is. After excavation, compact the base 1 using vibratory compaction equipment. In practice, the construction area can be cleared manually or mechanically, removing surface debris, vegetation, etc. Topsoil removal can be done using earthmoving machinery such as excavators. Excavation depth control can be based on the preliminary judgment in the geological survey report, and during actual excavation, the color, moisture, and density of the soil layer can be observed, combined with on-site drilling or test pit verification, to determine whether a stable clay layer has been reached. Compaction of base 1 can be performed using various compaction machines, such as vibratory rollers and impact rollers, to compact the excavated base 1 multiple times to achieve a certain density requirement.

[0024] S2. Joint Inspection: After step S1 is completed, the construction, supervision, design, surveying, and construction units jointly inspect and confirm the treated foundation 1. In practice, the inspection process typically includes checking the foundation 1's planar position, elevation, soil conditions, compaction, and the presence of weak interlayers or adverse geological phenomena. Each participating unit can verify the various indicators of foundation 1 according to their respective responsibilities and form a written confirmation opinion.

[0025] S3. Zoned constrained layered backfilling. For example... Figure 2 and Figure 4 As shown, this step is broken down into the following sub-steps: S3.1 Peripheral Layered Backfilling: First, backfill with lime-soil in multiple layers around the building's perimeter to form a partially enclosed lime-soil confinement structure. In specific implementation, lime-soil can be used as the backfill material in designated areas around the building. Lime-soil is prepared by mixing lime and soil in a certain proportion. During backfilling, the lime-soil is laid in layers, and each layer is compacted after reaching a certain thickness, gradually forming a partially enclosed lime-soil structure.

[0026] S3.2 Core Layered Backfill: Within the area enclosed by the lime-soil confinement body, graded sand and gravel are backfilled in layers to form the core backfill body 3. Specifically, in the internal area enclosed by the lime-soil structure, graded sand and gravel can be selected as the backfill material. The graded sand and gravel can be a mixture of sand and crushed stone of different particle sizes. During backfilling, the same layered laying and compaction method is adopted to ensure the density and bearing capacity of the core area.

[0027] S3.3 Closed Constraint Zone 2: Finally, backfill with lime-soil in layers in the remaining direction around the building perimeter, forming a complete closed constraint zone 2 around the building perimeter. The width of this closed constraint zone 2 is not less than 4 meters. In practice, continue backfilling with lime-soil in the remaining area around the building perimeter, connecting with the previously formed partial lime-soil structure to ultimately form a complete annular lime-soil strip. The width of this lime-soil strip can be controlled according to design requirements to provide sufficient lateral restraint.

[0028] S3.4 Layered Backfilling of Outer Subsoil: Around the perimeter of the closed constraint zone 2, subsoil is backfilled in layers to form a subsoil backfill body 4. The outward expansion width of this subsoil backfill body 4 is not less than 4 meters. This subsoil backfilling is carried out alternately with the backfilling in steps S3.1 to S3.3. Specifically, subsoil can be backfilled on the outer side of the closed constraint zone 2 (i.e., the ground surface outside the building foundation pit). The subsoil can be sourced from excavated soil or other suitable materials. Subsoil backfilling also needs to be carried out in layers, alternating with the internal lime-soil and graded sand and gravel backfilling to maintain the overall balance and continuity of the construction. The outward expansion width of the backfill area can be determined according to project requirements.

[0029] S4. Formation of stepped working face: such as Figure 9 As shown, when a building has different foundation elevations, the different elevation areas are backfilled in layers to their respective pile foundation 10 construction surface design elevations, and connected by sloping and ramping to form a continuous working surface. These different elevation areas include the tower area 31 with a lower foundation elevation and the podium area 32 with a higher foundation elevation. In practice, when the building has different foundation elevations such as the tower area 31 and the podium area 32, the backfilling construction must be carried out according to their respective design elevations. Between different elevation areas, a transition section 33 (sloping) with a certain slope and connecting ramps (ramping) can be set to create a smooth connection between the high and low areas, facilitating the passage of construction machinery and personnel, thereby forming one or more continuous working surfaces.

[0030] S5. Construction of Pile Foundation 10 and Underground Structure: Pile foundation 10 will be constructed on this continuous working face, followed by reverse excavation and structural construction of the areas including the pile cap 6, ground beam 7, and structural column 8. Specifically, after forming the continuous working face, drilling, reinforcement cage installation, and concrete pouring for pile foundation 10 can be carried out. After the pile foundation 10 construction is completed, according to the underground structure design, partial excavation (reverse excavation) will be performed on the pile cap 6, ground beam 7, and structural column 8, followed by reinforcement binding, formwork erection, and concrete pouring.

[0031] S6. High-strength backfill around the structure: such as Figure 5 As shown, after the construction of the foundation 6, ground beam 7, and structural column 8 is completed, the backfill area within a specific range around them is manually backfilled in layers using graded sand and gravel mixed with cement, forming a high-strength backfill body 5. Specifically, after the underground structures such as the foundation 6, ground beam 7, and structural column 8 are completed, the adjacent surrounding area is backfilled. Graded sand and gravel can be used as backfill material, and a certain proportion of curing agent or cementitious material (such as cement) can be added as needed to improve the strength of the backfill soil. During backfilling, manual layering and compaction are used to ensure that the backfill is dense and uniform, avoiding damage to the constructed structure. The backfill range and layer thickness can be controlled according to design requirements.

[0032] S7. Final Backfilling and Compaction: After completing step S6, continue to lay the fill material in layers over the large area to the design elevation and then mechanically compact it. Specifically, after completing the high-strength backfill around the structure, continue backfilling the entire large area in layers until the design elevation is reached. After each layer is laid, use mechanical equipment to compact it, ensuring that the density and bearing capacity of the entire foundation meet the design requirements.

[0033] S8. Foundation Bearing Capacity Verification: After all backfilling is completed, field load tests will be conducted in different areas. Specifically, after all backfilling work is completed, to verify whether the actual bearing capacity of the foundation meets the design standards, test points can be selected in different representative areas to conduct field load tests. The test results will be used to evaluate the overall performance of the foundation.

[0034] The composite foundation layered compaction replacement construction method in this embodiment effectively solves the problems of uneven foundation treatment and large settlement differences in traditional foundation treatment through refined measures such as dynamic excavation depth, zoned constrained layered backfilling, and high-strength backfilling around the structure. Simultaneously, by optimizing earthwork utilization and forming a stepped working face, it improves material utilization efficiency and construction efficiency, while reducing environmental impact and construction costs. This method ensures that the foundation bearing capacity, uniformity, and deformation control meet the stringent requirements of large-load factory buildings.

[0035] In some implementations, the lack of clear and strict limitations on the excavation depth standard and the compaction parameters of the foundation 1 may lead to insufficient treatment depth of the foundation 1 or uneven compaction effect, thereby affecting the overall stability of the foundation and the safety of subsequent structures. To address this, this embodiment of the invention further proposes that in step S1 above, the preset depth is no less than 1.5 meters downwards from the existing ground surface, and should be excavated to a stable clay layer; the vibratory compaction equipment is a vibratory compactor with a weight of no less than 10 tons, and the number of compaction passes is no less than 6.

[0036] Understandably, in step S1, the preset depth is explicitly defined as no less than 1.5 meters downwards from the existing ground level, with the excavation to a stable clay layer serving as the final control standard. The quantitative indicator of "no less than 1.5 meters downwards from the existing ground level" aims to ensure that any weak soil layers, organic matter, or backfill soil that may exist on the surface of the construction area are thoroughly removed, providing a solid foundation for subsequent replacement construction. Even if seemingly stable soil layers are encountered at shallower depths in some areas, the minimum excavation depth requirement of no less than 1.5 meters must be met to avoid potential risks caused by insufficient local soil layer thickness or poor stability. Simultaneously, "excavation to a stable clay layer" provides a final geological control standard, ensuring that the foundation ultimately rests on a natural clay layer with sufficient bearing capacity, low compressibility, and good stability. Stable clay layers are typically confirmed through on-site investigation, drilling sampling analysis, or empirical judgment. Their characteristics include uniform soil texture, density, absence of obvious weak interlayers or pores, and the ability to effectively resist the load of the superstructure, reducing long-term settlement.

[0037] Meanwhile, the vibratory compaction equipment is specifically defined as a vibratory compactor weighing no less than 10 tons, with a minimum of 6 compaction passes. This heavy-duty vibratory compactor, through its own static weight and the dynamic load generated by vibration, can effectively perform deep compaction of the base soil layer, improving the soil density and shear strength, thereby significantly enhancing the bearing capacity of the foundation. Compared to light-duty compaction equipment, its compaction effect is more uniform and deeper, better eliminating porosity in the soil and reducing compressibility. Furthermore, the requirement of at least 6 compaction passes ensures the sufficiency and uniformity of the compaction process. Typically, the first few compaction passes are mainly used to eliminate large pores in the soil, while subsequent passes are used to further improve density, making the soil structure more stable.

[0038] Through the above technical solutions, this embodiment effectively solves the problems of insufficient foundation treatment depth and uneven compaction. Specifically, the clearly defined excavation depth standard ensures that all weak surface soil is reliably removed, and the foundation always rests on a stable clay layer, fundamentally improving the long-term stability and safety of the foundation. Simultaneously, by specifying a heavy vibratory compactor and sufficient compaction passes, it ensures that the foundation soil receives sufficient and uniform compaction energy, improving the density and bearing capacity of the foundation and effectively controlling the compressive deformation and uneven settlement of the foundation. The introduction of these specific parameters standardizes and controls the foundation treatment process, greatly improving the overall quality and engineering reliability of the composite foundation, and providing solid and reliable support for the superstructure.

[0039] In some implementations, if the composition and source of the lime-soil mixture are unclear, it may lead to unstable backfill material quality, increased construction costs, and improper handling of the excavated soil in step S1 may result in resource waste and environmental burden. To address this, this embodiment of the invention further proposes that in steps S3.1 and S3.3, the lime-soil mixture is composed of lime and cohesive soil mixed in a volume ratio of 3:7, and all or part of the cohesive soil originates from the excavated soil in step S1.

[0040] It is understandable that the mixing of lime and clay can effectively improve the engineering properties of clay through a series of physicochemical reactions, such as hydration, carbonation, and ion exchange, significantly enhancing its strength, stability, and water resistance. Specifically, the addition of lime can reduce the plasticity index of clay, increase its bearing capacity, and form cementing substances, strengthening the overall integrity of the soil. The 3:7 volume ratio is an optimized proportion verified through engineering practice, aiming to balance material costs and performance requirements, ensuring that the lime-soil backfill has sufficient strength and stability to effectively exert its restraining effect. Furthermore, all or part of the clay originates from the excavated soil in step S1, meaning that the clay generated in step S1 through dynamic excavation and foundation treatment during the initial construction phase can be recycled, provided it meets engineering requirements. This recycling not only reduces the need for new material procurement and lowers engineering costs but also avoids the environmental problems of transporting and disposing of large amounts of excavated soil, aligning with the principles of sustainable development. By screening and treating the excavated soil, its quality as a component of the lime-soil mixture can be ensured to meet requirements.

[0041] In some implementations, improper composition ratios of graded sand and gravel may prevent the backfill from achieving optimal compaction, bearing capacity, and deformation resistance, thereby affecting the overall stability and long-term performance of the composite foundation, especially in core areas that need to withstand large loads. To address this, this embodiment of the invention further proposes that in step S3.2, the graded sand and gravel is composed of sand and crushed stone mixed at a mass ratio of 3:7.

[0042] Understandably, in engineering practice, good gradation can significantly improve the mechanical properties and stability of backfill materials. The 3:7 mass ratio of sand to crushed stone means that in preparing the graded sand and gravel filler, sand accounts for 30% of the total mass, and crushed stone accounts for 70%. This ratio aims to optimize the gradation between particles, allowing smaller sand particles to fill the voids between larger crushed stone particles, thus forming a denser skeleton structure with lower porosity and a larger internal friction angle. Besides the 3:7 mass ratio, other ratios can be used depending on specific engineering geological conditions and material properties, such as a 2:8 or 4:6 mass ratio of sand to crushed stone. However, the 3:7 ratio has been proven in many engineering practices to provide good overall performance. This precise ratio allows sand particles to effectively fill the voids between crushed stone particles, thereby significantly reducing the porosity of the backfill material and increasing its density. Increased density directly enhances the overall strength and load-bearing capacity of the core backfill body 3, making it less prone to compressive deformation when subjected to superstructure loads. Furthermore, optimized gradation can improve the shear strength and stability of the backfill, effectively reduce uneven settlement of the foundation, and ensure the long-term stability and safety of the composite foundation. Compared with using only general-graded sand and gravel, this specific gradation of backfill can better cooperate with the surrounding lime-soil confinement to jointly resist external loads, forming a more robust and reliable composite foundation structure.

[0043] In some implementations, improper slope treatment between the plain soil backfill 4 and the lime-soil constraint zone, as well as on the outer side of the plain soil backfill 4, may lead to slope instability, collapse, or erosion of the plain soil backfill 4 during construction or later use, affecting the backfill quality and the overall foundation stability. This is especially true when there are significant differences in the properties of the plain soil and lime-soil materials, placing higher demands on the boundary stability of the plain soil backfill 4. Therefore, as... Figure 4 As shown in the embodiment of the present invention, in step S3.4, the plain soil backfill needs to be sloped, with the inner slope ratio 41 close to the lime-soil constraint zone being 1:0.33 and the outer slope ratio 42 being 1:1.

[0044] Understandably, slope protection is typically achieved during backfilling by layering and compacting according to a pre-defined slope line. Specifically, "the inner slope 41 near the lime-soil constraint zone has a ratio of 1:0.33" indicates that the slope of the plain soil backfill 4 adjacent to the lime-soil constraint zone has a vertical height to horizontal width ratio of 1:0.33. This is a relatively steep slope designed to ensure the plain soil backfill 4 fits tightly against the lime-soil constraint zone, maximizing the use of limited site space while maintaining stability, and providing effective lateral support or enclosure for the lime-soil constraint zone. Conversely, "the outer slope 42 has a ratio of 1:1" indicates that the slope of the plain soil backfill 4 facing outwards or connecting with the natural strata has a vertical height to horizontal width ratio of 1:1. This is a relatively gentle slope designed to provide better slope stability, effectively resisting rainwater erosion, weathering, and external disturbances, thereby significantly reducing the risk of slope instability. This design with differentiated inner and outer slopes fully considers the stress characteristics and functional requirements of the backfill material 4 in different directions, making the entire composite foundation structure more reasonable, stable and reliable, thereby ensuring the smooth progress of subsequent pile foundation 10 and underground structure construction, and improving the overall engineering quality of the foundation.

[0045] In some implementations, failure to clearly define the type and dosage of cement, the specific range of backfill, and the layer thickness of manual compaction may lead to uneven backfill strength, material waste, or insufficient structural support, thereby affecting the overall bearing capacity and stability of the composite foundation. To address this, this embodiment of the invention further proposes that when performing high-strength backfill around the structure, the cement is preferably 425-grade silicate cement, with a dosage of 250 kg per cubic meter of graded sand and gravel filler.

[0046] Understandably, 425-grade silicate cement is a general-purpose silicate cement with a strength grade of 42.5 MPa, characterized by high early strength, rapid setting and hardening, and moderate heat of hydration. The selection of this grade of cement aims to ensure that the backfill material can quickly reach its design strength, providing reliable support for the superstructure and helping to shorten the construction cycle. The dosage of 250 kg of cement per cubic meter of graded aggregate filler is an optimized ratio verified through engineering practice, designed to ensure that the graded aggregate filler can form a high-strength backfill body with sufficient strength and stability after curing. This dosage ensures the load-bearing capacity of the backfill body while avoiding problems such as increased costs or shrinkage cracking caused by excessive cement usage.

[0047] In addition, such as Figures 6 to 8As shown, the specific areas are precisely defined as follows: within 1 meter of the structural column 8, within 0.5 meters on each side of the ground beam 7, and within 0.5 meters of the foundation 6. These areas are key regions determined based on the structural stress characteristics and engineering experience. The structural column 8, ground beam 7, and foundation 6 are the main components in the underground structure that bear and transmit loads, and the soil in their surrounding areas needs to have higher bearing capacity and deformation resistance. By precisely defining the backfill area, it is possible to ensure that these key stress areas are adequately reinforced, effectively improving their bearing capacity and deformation resistance, while avoiding unnecessary expansion of the backfill area, thereby optimizing construction efficiency and cost.

[0048] Meanwhile, the thickness of each layer of manually compacted material is strictly controlled to no more than 200 mm. Limiting the layer thickness ensures that each layer of fill material is fully and evenly compacted during manual compaction. Thinner layer thickness allows the energy of the compaction tools to be effectively transferred to the deeper layers of the fill material, thereby significantly improving the density and overall strength of the fill material, avoiding localized loosening or uneven compaction, and guaranteeing the construction quality of the high-strength backfill material 5.

[0049] In some implementations, a lack of overall planning regarding the sources of excavated earth and backfill materials may lead to waste of earth resources, increased transportation costs, and unnecessary environmental burden. To address this, this embodiment of the invention further proposes that the earth excavated in step S1, provided it meets engineering requirements, be preferentially used for backfilling in step S3.4.

[0050] Understandably, the excavated soil in step S1 needs to undergo rigorous quality testing before being reused to ensure that its physical and mechanical properties (such as particle size distribution, moisture content, and compaction degree) and environmental indicators meet the requirements of engineering design and relevant specifications for backfill materials. If the soil does not meet the requirements, necessary treatments, such as screening, blending, or improvement, are required until it meets the usage standards. Under the premise of meeting the above engineering requirements, "prioritizing use" means that when performing the outer layered backfilling in step S3.4, the use of on-site excavated and inspected soil should be considered first, rather than directly purchasing new soil from external sources. This method effectively realizes the recycling of soil resources, significantly reduces the amount of waste soil transported during construction, lowers soil disposal costs and the demand for purchased soil, thereby saving on engineering material costs and transportation costs. At the same time, this method also reduces the exploitation of natural resources, reduces the environmental impact of construction, embodies the concept of green construction, and improves the economic and social benefits of construction.

[0051] In some implementations, improper temporary stockpiling and management of the excavated soil in step S1 may lead to slope instability, limited construction site space, and dust pollution, affecting construction safety, efficiency, and the environment. Therefore, if... Figure 3 As shown in the embodiment of the present invention, when the excavated soil to be backfilled is temporarily stockpiled in step S1, the stockpiling location shall be no less than 2 meters away from the excavation slope, the height of the stockpile shall be no more than 2 meters, and covering and dust suppression measures shall be taken.

[0052] Understandably, maintaining sufficient safety distances facilitates the passage of construction personnel and equipment, ensuring working space and safety within the construction area. Limiting the height of temporary soil stockpiles helps prevent instability caused by excessively high piles, reducing the risk of landslides. Furthermore, lower stockpile heights facilitate subsequent soil removal and management, and minimize visual impact on the surrounding environment. Covering measures typically include using materials such as dust nets, tarpaulins, or plastic films to cover the surface of the soil piles to prevent windblown dust and rain erosion, protecting the quality of the soil. Dust suppression measures may include regular watering and mist cannons to effectively suppress dust at the construction site, improve air quality, and reduce the impact on the surrounding environment and residents. These measures work together to not only enhance the safety and environmental friendliness of the construction site but also provide favorable conditions for the subsequent reuse of excavated soil, ensuring the smooth progress of the entire construction process.

[0053] In some implementations, due to significant differences in the geometry and spatial constraints of the foundation backfill area—for example, large areas versus narrow areas around structures—using a single compaction device and parameters may result in uneven compaction or make effective construction difficult in confined spaces, thus affecting the overall bearing capacity and stability of the foundation. To address this, this embodiment of the invention further proposes that during the entire layered backfilling process, for large areas, a vibratory compaction device weighing no less than 10 tons should be used for compaction, with a layer thickness no greater than 500 mm and at least 6 compaction passes; for the areas surrounding the foundation 6, ground beam 7, and structural columns 8, manual compaction should be used, with a layer thickness no greater than 200 mm.

[0054] Understandably, "large areas" typically refer to open, unobstructed, and large backfill areas, such as the core backfill (3), the plain soil backfill (4), and the final large-area fill material paving area. In these areas, using a vibratory compactor with a weight of at least 10 tons facilitates deep compaction of the fill material, improving its density. Simultaneously, controlling the layer thickness to no more than 500 mm ensures that the compaction energy of the vibratory compactor is effectively transferred throughout the entire layer thickness, preventing a denser top and looser bottom, and guaranteeing uniform compaction of the fill material. If the layer is too thick, the compaction effect may not meet design requirements; if the layer is too thin, construction efficiency will be reduced. Furthermore, the number of compaction passes should not be less than 6, based on engineering experience and test data, to ensure that the fill material achieves the minimum compaction effort required to reach the designed density. Sufficient compaction passes can effectively eliminate porosity in the fill material, improving its density and bearing capacity. For the areas surrounding the foundation 6, ground beam 7, and structural columns 8, these areas are typically narrow, irregularly shaped, and close to important structural components, requiring high compaction quality and construction precision. In these areas, manual compaction is employed. Manual compaction refers to compacting localized areas using small manual compaction tools, such as vibratory rammers, impact rammers, or electric rammers. This method is highly flexible and allows for precise operation, adapting to narrow and irregular construction spaces, ensuring the density of the fill material around the structure, and avoiding insufficient compaction caused by the inability or inconvenience of large machinery. Furthermore, the layer thickness for manual compaction is no more than 200 mm, considering the relatively low energy and efficiency of manual compaction equipment; thinner layers are needed to ensure each layer of fill material is fully compacted. Thinner layers help improve the uniformity of compaction and prevent under-compaction in localized areas. Therefore, this embodiment of the invention employs differentiated compaction strategies tailored to the characteristics of different areas during the layered backfilling process of composite foundations. This zoned, layered, and differentiated compaction method greatly improves construction quality and efficiency, ensuring the overall stability and durability of the composite foundation.

[0055] In some implementations, a lack of clear guidance regarding the type of on-site load test, the number of test points, and the specific locations may lead to insufficient representativeness and reliability of the foundation bearing capacity verification results. This is especially true for buildings with complex structures and uneven load distribution, making it difficult to comprehensively and accurately assess the actual bearing capacity of the foundation, thereby affecting project quality and safety. To address this, this embodiment of the invention further proposes that in step S8, the on-site load test is a plate load test, with no fewer than six test points, located in key areas of the building's tower and podium.

[0056] Understandably, the plate load test is a method for directly determining the bearing capacity and deformation modulus of foundation soil. Its specific implementation typically includes: placing a rigid bearing plate (e.g., a circular or square steel plate) of a certain size on a leveled test surface at selected test locations; applying progressively increasing loads to the bearing plate using a loading system (e.g., jacks with reaction frames or anchor piles); and simultaneously measuring the settlement of the bearing plate under different loads using displacement sensors (e.g., dial gauges or displacement meters). By plotting load-settlement curves, the bearing characteristics and deformation patterns of the foundation soil can be intuitively analyzed, and the characteristic values ​​of the foundation bearing capacity and deformation modulus can be calculated. Compared to other indirect testing methods, the plate load test can more realistically reflect the stress and deformation of the foundation under actual loads, providing a reliable basis for the final verification of the foundation bearing capacity. Furthermore, the number of test locations is designed to ensure the statistical representativeness and comprehensiveness of the foundation bearing capacity verification results. In practical engineering, the properties of foundation soil may exhibit a certain degree of heterogeneity, making it difficult to comprehensively reflect the bearing capacity of the entire foundation from a single or few test sites. Therefore, setting up no fewer than six test sites can effectively increase the sampling range, reduce evaluation biases caused by differences in local geological conditions, and thus improve the reliability and accuracy of the foundation bearing capacity verification results. These test sites can be rationally arranged based on geological survey reports, structural load distribution characteristics, and anomalies discovered during construction. Furthermore, the tower area 31 of a building typically bears a large vertical load and is more sensitive to settlement and differential settlement; while the podium area 32, although bearing a relatively smaller load, may have a complex foundation stress state due to its foundation type, depth, and connection method with the tower area 31. Therefore, arranging test sites in key areas of the tower and podium allows for targeted evaluation of the foundation bearing capacity of these crucial components for overall structural safety and functionality. The selection of key areas can be based on structural analysis results, such as selecting load concentration areas, stress concentration areas, areas with varying foundation types, or areas with expected large settlement. This targeted arrangement of points ensures that the bearing capacity of the weakest or most critical parts of the foundation is verified, thereby providing sufficient protection for the foundation safety of the entire building.

[0057] In summary, through the above series of closely linked construction steps, this method systematically solves the problems existing in the foundation treatment of large-load factory buildings, such as poor coordination of construction process, low material utilization efficiency, imprecise quality control, limited construction efficiency, and environmental and cost issues.

[0058] The above description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for constructing a composite foundation using layered compaction and replacement, characterized in that, Includes the following steps: S1. Dynamic Excavation Depth and Foundation Treatment: Clean the construction area and remove the topsoil within 1 meter outside the building projection line; the excavation depth is controlled by reaching the stable clay layer, and the initial design excavation depth is not less than 1.5 meters. If the clay layer is not reached, continue excavating until it is touched; after excavation, use vibratory compaction equipment to compact the foundation. S2. Joint inspection of the foundation: After step S1 is completed, the construction, supervision, design, survey and construction units shall jointly inspect and confirm the treated foundation. S3. Zonal-constrained layered backfilling: S3.1 Peripheral Layered Backfilling: First, backfill lime-soil in multiple layers in multiple directions around the building perimeter to form a partially enclosed lime-soil confinement body; S3.2 Core Layered Backfill: Within the area enclosed by the lime-soil confinement body, graded sand and gravel are backfilled in layers to form a core backfill body; S3.3 Closed constraint zone: Finally, backfill the remaining direction of the building perimeter with lime-soil in layers to form a complete closed constraint zone around the building perimeter. The width of the closed constraint zone shall be not less than 4 meters. S3.4 Layered backfilling of the outer perimeter: On the outer perimeter of the closed constraint zone, layered backfilling of the soil forms a soil backfill body. The outer width of the soil backfill body is not less than 4 meters. This soil backfilling is carried out alternately with the backfilling in steps S3.1 to S3.

3. S4. Formation of stepped working face: When there are different foundation elevations in a building, the different elevation areas are backfilled in layers to their respective pile foundation construction surface design elevations, and connected by slope and ramp connection to form a continuous working face; wherein, the different elevation areas include the tower area with lower foundation elevation and the podium area with higher foundation elevation; S5. Construction of pile foundation and underground structure: Pile foundation construction is carried out on the continuous working surface, followed by reverse excavation and structural construction of the pile cap, ground beam and structural column areas; S6. High-strength backfill around the structure: After the construction of the foundation, ground beam and structural column is completed, the backfill area around it is backfilled manually in layers by using graded sand and gravel mixed with cement. S7. Final backfilling and compaction: After completing step S6, continue to lay the fill material in layers in the large area to the design elevation and then mechanically compact it. S8. Foundation bearing capacity verification: After all backfilling is completed, field load tests are conducted in different areas.

2. The composite foundation layered compaction and replacement construction method according to claim 1, characterized in that, In step S1, the preset depth is no less than 1.5 meters downward from the existing ground level, and should be dug to a stable clay layer; the vibratory compaction equipment is a vibratory compactor with a weight of no less than 10 tons, and the number of compaction passes is no less than 6.

3. The composite foundation layered compaction and replacement construction method according to claim 1, characterized in that, In steps S3.1 and S3.3, the lime-soil is made by mixing lime and clay in a volume ratio of 3:7, and all or part of the clay comes from the excavated soil in step S1.

4. The composite foundation layered compaction and replacement construction method according to claim 1, characterized in that, In step S3.2, the graded sand and gravel is made by mixing sand and crushed stone in a mass ratio of 3:

7.

5. The composite foundation layered compaction and replacement construction method according to claim 6, characterized in that, In step S3.4, the plain soil backfill needs to be sloped, with the inner slope ratio near the lime-soil constraint zone being 1:0.33 and the outer slope ratio being 1:

1.

6. The composite foundation layered compaction and replacement construction method according to claim 1, characterized in that, In step S6, the cement is 425 grade silicate cement, and the dosage is 250 kg per cubic meter of graded sand and gravel filler; the specific range is: within 1 meter around the structural column, within 0.5 meters on both sides of the ground beam, and within 0.5 meters around the foundation; the thickness of the manually compacted layer is no more than 200 mm.

7. The composite foundation layered compaction and replacement construction method according to claim 1, characterized in that, The excavated soil in step S1, provided that the engineering requirements are met, shall be used first for the plain soil backfilling in step S3.

4.

8. The composite foundation layered compaction and replacement construction method according to claim 7, characterized in that, When the excavated soil to be backfilled in step S1 is temporarily stockpiled, the stockpiling location shall be no less than 2 meters away from the excavation slope, the height of the stockpile shall not exceed 2 meters, and covering and dust suppression measures shall be taken.

9. The composite foundation layered compaction and replacement construction method according to claim 1, characterized in that, During the entire layered backfilling process, for large areas, a vibratory compaction device with a weight of not less than 10 tons is used for compaction, with a layer thickness of not more than 500 mm and a compaction pass of not less than 6 passes; for the areas around the foundation, foundation, beams and structural columns, manual compaction is used, with a layer thickness of not more than 200 mm.

10. The composite foundation layered compaction and replacement construction method according to claim 1, characterized in that, In step S8, the on-site load test is a pressure plate load test, with no fewer than 6 test points, located in key areas of the tower and podium of the building.

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