A method and system for green regeneration and performance improvement of abandoned pile foundation in urban renewal

Abstract

This invention discloses a method and system for the green regeneration and performance enhancement of abandoned pile foundations in urban renewal. The method includes: conducting a recyclability classification assessment of abandoned pile foundations, dividing them into three levels: Level I, Level II, and Level III; selecting appropriate green regeneration technology paths based on the assessment level: Level I pile foundations are directly utilized in situ, Level II pile foundations undergo low-disturbance in-situ regeneration, and Level III pile foundations are utilized ex-situ for resource recovery; implementing performance enhancement treatments for in-situ regenerated pile foundations through pile body repair and interface reinforcement, including low-pressure grouting repair, segmented post-grouting of the pile side, carbon fiber composite reinforcement, and durability protection; and conducting testing and acceptance of the regenerated pile foundations. This invention constructs a systematic abandoned pile foundation evaluation and regeneration technology system, which can reduce carbon emissions by more than 55% and save approximately 40% of engineering costs compared to traditional pile extraction and transportation processes, achieving the green and high-value utilization of abandoned pile foundations in urban renewal projects.

Description

Technical Field

[0001] This invention relates to the field of urban renewal geotechnical engineering, and more specifically, to a method and system for green regeneration and performance improvement of abandoned pile foundations in urban renewal. Background Technology

[0004] Domestic and international scholars have conducted a series of studies on the recycling technology of abandoned pile foundations. Internationally, Jardine et al., through long-term field tests, systematically analyzed the evolution of the bearing capacity of existing pile foundations in urban redevelopment projects, clarifying the core influencing factors of the remaining bearing capacity of pile foundations; Brandes et al. summarized engineering cases of the reuse of existing pile foundations in urban renewal projects in Europe and the United States, and proposed a basic process for pile foundation suitability assessment. Domestically, Liu Songyu et al. reviewed the core issues of existing geotechnical engineering disposal in urban underground space development, clarifying the technological development direction of the recycling of abandoned pile foundations; Wang Weidong et al., based on the practice of urban renewal projects in Shanghai, summarized a complete set of technologies for the detection, assessment, and utilization of existing pile foundations; Zhang Zhongmiao et al. systematically studied the methods for detecting damage to existing pile foundations and the assessment system for the remaining bearing capacity of pile foundations, providing theoretical support for the recycling of pile foundations.

[0005] Existing research and engineering applications still face three major technological bottlenecks: First, a graded evaluation standard for the recyclability of abandoned pile foundations adapted to the complex scenarios of urban renewal has not yet been formed, and the matching degree between technology selection and engineering needs is insufficient; second, it is difficult to balance low-disturbance control and repair effects of in-situ regeneration technology, and there is a lack of complete construction processes for complex geological conditions in soft soil areas; third, the technologies for improving the bearing capacity and ensuring the long-term durability of regenerated pile foundations are not systematic, and there are certain safety hazards in engineering applications.

[0006] Among existing patent technologies, CN108729445B discloses a drill bit for breaking up old solid piles and a method for breaking up old solid piles and grouting new piles, mainly focusing on the design of the breaking drill bit, which belongs to destructive demolition technology; CN202510755599.8 discloses a composite pile foundation construction technology and construction method for reusing old piles, which connects new and old piles through composite plates, belonging to structural connection technology; CN202510262843 discloses a green and low-carbon foundation reconstruction technology and construction method for old pile sites, mainly focusing on carbon sequestration technology for backfilling extraction holes. None of the above-mentioned existing technologies involve a graded evaluation system for the recyclability of abandoned pile foundations, a technical system combining in-situ regeneration and ex-situ utilization, or key technologies for performance improvement through pile body repair and interface enhancement synergy.

[0007] Therefore, there is an urgent need to develop a green recycling and performance improvement technology for abandoned pile foundations that is suitable for the complex scenarios of urban renewal, in order to solve the problems of lack of evaluation standards, imperfect technical system and insufficient performance guarantee of existing technologies. Summary of the Invention

[0008] The purpose of this invention is to address the problems mentioned in the background art by providing a method, materials, and system for reinforcing the foundation of buildings in deep soft soil strata with minimal disturbance, thereby controlling the additional settlement of existing buildings to within 2mm, and adapting to the special constraints of construction in old residential areas and confined spaces.

[0009] The present invention adopts the following technical solution:

[0010] A method for green regeneration and performance improvement of abandoned pile foundations in urban renewal includes the following steps:

[0011] a. Conduct a renewability classification assessment of abandoned pile foundations within urban renewal sites to determine the evaluation level of the abandoned pile foundations;

[0012] b. Select an appropriate green recycling technology path based on the evaluation level of the abandoned pile foundation;

[0013] c. For abandoned pile foundations that are selected for in-situ regeneration, implement a performance improvement treatment that combines pile body repair and interface enhancement;

[0014] d. Conduct bearing capacity and durability tests on the recycled pile foundations for acceptance.

[0015] Furthermore, the renewability classification evaluation of abandoned pile foundations within urban renewal sites specifically includes:

[0016] a. The core evaluation indicators are pile integrity, concrete strength retention rate, steel corrosion rate, and single pile bearing capacity retention rate.

[0017] b. Classify abandoned pile foundations into three evaluation levels: Level I, Level II, and Level III;

[0018] c. Among them, Class I pile foundations are characterized by pile integrity of Class I, residual concrete strength ≥90%, steel corrosion rate ≤1%, and residual single pile bearing capacity ≥85%, which are suitable for direct in-situ utilization.

[0019] d. Class II pile foundations are characterized by pile integrity of Class II, concrete strength remaining rate of 70% to 90%, steel corrosion rate of 1% to 5%, and single pile bearing capacity remaining rate of 60% to 85%. They are adapted for repair and then regenerated in situ.

[0020] e. Class III pile foundations are characterized by pile integrity of Class III or IV, residual concrete strength of <70%, steel corrosion rate of >5%, and residual single pile bearing capacity of <60%, which are suitable for off-site resource utilization.

[0021] The formula for calculating the residual strength rate of concrete is as follows:

[0022] 00%

[0023] in, Residual strength of concrete The measured cubic compressive strength of the pile concrete. The original design cubic compressive strength of the pile concrete;

[0024] The formula for calculating the corrosion rate of the reinforcing steel is:

[0025] 00%

[0026] in, For steel reinforcement corrosion rate, To ensure the initial quality of the reinforcing steel is free of rust, The measured quality of the reinforcing steel after rust removal;

[0027] The formula for calculating the residual bearing capacity ratio of a single pile is as follows:

[0028] 100%

[0029] in, This refers to the residual bearing capacity of a single pile. This represents the characteristic value of the measured vertical bearing capacity of a single pile in a pile foundation. The characteristic value of the vertical bearing capacity of a single pile in the original design of the pile foundation.

[0030] Furthermore, the selection of an appropriate green recycling technology path based on the evaluation level of the abandoned pile foundation specifically includes:

[0031] a. For Class I pile foundations, the direct in-situ utilization technology is adopted, and after the pile top elevation is adjusted, the pile foundations are directly used as pile foundations for new construction projects;

[0032] b. For Class II pile foundations, low-disturbance in-situ green recycling technology is adopted, and after pile defect repair and interface enhancement, it is used as a pile foundation for new construction projects;

[0033] c. For Class III pile foundations, off-site resource utilization technology is adopted, and the piles are recycled as recycled aggregates after crushing, purification and modification.

[0034] The low-disturbance in-situ green regeneration technology includes:

[0035] a. Static diamond wire saws are used to adjust the pile top elevation, and the construction vibration speed is controlled within 0.3 cm / s;

[0036] b. Use fully enclosed drilling equipment for grouting hole construction, and provide a mud circulation and treatment system;

[0037] c. Use portable non-destructive testing equipment for real-time quality monitoring of the repair process;

[0038] The off-site resource utilization technology includes: using a combination of a closed jaw crusher and an impact crusher to grade and crush waste pile concrete; removing impurities and mud powder from the crushed aggregate through screening and washing; using a silane coupling agent to perform surface modification treatment on the recycled aggregate; and using the modified recycled aggregate for foundation pit backfilling, roadbed subbase, or preparation of recycled concrete.

[0039] Furthermore, the performance enhancement treatment of abandoned pile foundations selected for in-situ regeneration, which combines pile body repair and interface enhancement, specifically includes:

[0040] a. Low-pressure grouting repair and polymer-modified cementitious material reinforcement are used to repair defects such as pile body cracks and local concrete defects;

[0041] b. Perform grouting interface reinforcement treatment on the pile side segment after segmenting the void area at the pile-soil interface;

[0042] c. For pile foundations with insufficient structural strength, reinforce them with carbon fiber cloth wrapping;

[0043] d. Perform long-term durability protection treatment on the recycled pile foundation.

[0044] Furthermore, the low-pressure grouting repair specifically includes:

[0045] a. For transverse and longitudinal cracks in the pile body, a low-pressure permeation grouting process is adopted, and the grouting pressure is controlled at 0.3~0.5MPa;

[0046] b. The grouting material is epoxy-modified cement-based grout, which has both high adhesion and micro-expansion properties;

[0047] c. For areas where the concrete cover has detached or is partially damaged, polymer-modified concrete should be used for local reinforcement.

[0048] Furthermore, the post-segmentation grouting interface enhancement treatment on the pile side specifically includes:

[0049] a. Install 3 to 4 grouting pipes along the longitudinal direction of the pile, each section being 6 to 8 meters long;

[0050] b. The grouting hole adopts a one-way valve design to avoid grout leakage or overflow during the grouting process;

[0051] c. The grouting material is cement-water glass double-liquid grout, and the water-cement ratio is controlled at 0.6 to 0.8;

[0052] d. The grouting pressure is adjusted according to the soil properties. For soft soil layers, the pressure is controlled at 0.5–0.8 MPa, and for silty clay layers, the pressure is controlled at 0.8–1.2 MPa.

[0053] Furthermore, the carbon fiber cloth outer layer composite reinforcement and long-term durability protection treatment specifically includes:

[0054] a. Carbon fiber cloth is bonded to the surface of the pile body using epoxy resin adhesive;

[0055] b. The carbon fiber cloth is bonded in two layers, with an overlap length of not less than 200mm;

[0056] c. Forming a "concrete-carbon fiber cloth" composite stress system to improve the bending and shear bearing capacity and ductility of the pile body;

[0057] d. A penetrating steel reinforcement corrosion inhibitor is used, which is injected under low pressure through the pile concrete borehole, allowing the corrosion inhibitor to penetrate to the steel reinforcement surface and reform a passivation film;

[0058] e. Use penetrating crystalline waterproof coating, apply it to the surface of the pile body, penetrate into the concrete to form a crystalline layer, and block the pores of the concrete.

[0059] Furthermore, the specific acceptance testing of the bearing capacity and durability of the recycled pile foundation includes:

[0060] a. Low-strain testing method was used to inspect the integrity of the pile body;

[0061] b. The vertical bearing capacity of a single pile is tested using a static load test.

[0062] c. Inspect the maximum settlement of the regenerated pile foundation to ensure that the deformation is controlled within the allowable range specified in the code.

[0063] On the other hand, the present invention also discloses a green regeneration and performance improvement system for abandoned pile foundations in urban renewal, comprising:

[0064] a. Renewability assessment module, used to conduct renewable rating assessment of abandoned pile foundations and determine the assessment level of abandoned pile foundations;

[0065] b. Technology path selection module, used to select the appropriate green recycling technology path based on the evaluation level of the abandoned pile foundation;

[0066] c. Performance enhancement processing module, used to perform performance enhancement processing of pile body repair and interface enhancement in combination for abandoned pile foundations selected for in-situ regeneration;

[0067] d. Testing and Acceptance Module, used for testing and accepting the bearing capacity and durability of regenerated pile foundations.

[0068] Furthermore, the renewability evaluation module includes an index acquisition unit, a grade determination unit, and a technology adaptation unit. The index acquisition unit is used to acquire four core evaluation indicators: pile integrity, concrete strength retention rate, steel corrosion rate, and single pile bearing capacity retention rate. The grade determination unit is used to classify abandoned pile foundations into three evaluation grades: Grade I, Grade II, and Grade III, based on the four core evaluation indicators. The technology adaptation unit is used to determine the corresponding technology adaptation direction based on the evaluation grade.

[0069] The technology path selection module includes an in-situ utilization unit, an in-situ regeneration unit, and an off-situ utilization unit; the in-situ utilization unit is used to select a direct in-situ utilization technology path for Class I pile foundations; the in-situ regeneration unit is used to select a low-disturbance in-situ green regeneration technology path for Class II pile foundations; and the off-situ utilization unit is used to select an off-situ resource utilization technology path for Class III pile foundations.

[0070] The performance enhancement module includes a pile defect repair unit, an interface reinforcement unit, a composite reinforcement unit, and a durability protection unit. The pile defect repair unit is used for low-pressure grouting repair and polymer-modified cement-based material reinforcement of pile cracks and local concrete defects. The interface reinforcement unit is used for segmented grouting interface reinforcement treatment of the pile-soil interface void area. The composite reinforcement unit is used for carbon fiber cloth wrapping composite reinforcement of pile foundations with insufficient pile structural strength. The durability protection unit is used for long-term durability treatment of recycled pile foundations, including steel reinforcement corrosion prevention and concrete protection.

[0071] The testing and acceptance module includes a pile integrity testing unit, a bearing capacity testing unit, and a deformation testing unit. The pile integrity testing unit is used to test the pile integrity using a low-strain testing method. The bearing capacity testing unit is used to test the vertical bearing capacity of a single pile using a single pile static load test. The deformation testing unit is used to test the maximum pile top settlement of the regenerated pile foundation.

[0072] Beneficial effects

[0073] 1. A three-level evaluation system for abandoned pile foundations was constructed, with pile integrity, concrete strength residual rate, steel corrosion rate, and single pile bearing capacity residual rate as the core indicators. This system clarifies the technical compatibility boundaries of different grades of pile foundations and solves the problems of lack of existing technical evaluation standards and blind selection of technologies.

[0074] 2. A complete set of green recycling technology systems was proposed, which mainly focuses on low-disturbance in-situ regeneration and supplements it with off-site resource utilization, realizing low-carbon disposal of abandoned pile foundations in all scenarios. Compared with the traditional pile extraction and transportation process, carbon emissions can be reduced by more than 55%, and engineering costs can be saved by about 40%, which has significant low-carbon and economic advantages.

[0075] 3. A performance enhancement technology combining pile defect repair and pile-soil interface reinforcement was developed. Through the synergistic effect of low-pressure grouting repair, segmented post-grouting on the pile side, carbon fiber cloth composite reinforcement, and durability protection, the bearing capacity and long-term durability of recycled pile foundations can be effectively restored, solving the industry problem of insufficient performance guarantee of recycled pile foundations.

[0076] 4. A low-disturbance construction process was developed to support the entire process. It adopts technologies such as static diamond wire saw cutting, fully enclosed drilling, and mud circulation treatment. The construction vibration speed is controlled within 0.3cm / s, which meets the construction requirements of sensitive environments in built-up areas and solves the problems of large disturbance and serious pollution caused by traditional processes. Attached Figure Description

[0077] Figure 1 This is a flowchart illustrating the method for green regeneration and performance improvement of abandoned pile foundations in urban renewal, as provided in an embodiment of the present invention.

[0078] Figure 2 This is a schematic diagram of the structure of the graded evaluation system for the renewability of abandoned pile foundations provided in an embodiment of the present invention;

[0079] Figure 3 This is a structural block diagram of a green regeneration and performance improvement system for abandoned pile foundations in urban renewal, provided in an embodiment of the present invention. Detailed Implementation

[0080] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0081] Example 1

[0082] This embodiment provides a method for the green regeneration and performance improvement of abandoned pile foundations in urban renewal, such as... Figure 1 As shown, it includes the following steps:

[0083] Step S101: Conduct a renewability classification evaluation of abandoned pile foundations within the urban renewal site to determine the evaluation level of the abandoned pile foundations.

[0084] Specifically, this step uses pile integrity, concrete strength retention rate, steel corrosion rate, and single pile bearing capacity retention rate as core evaluation indicators to classify abandoned pile foundations into three evaluation levels: Level I, Level II, and Level III.

[0085] like Figure 2 As shown, the evaluation criteria for the renewability of abandoned pile foundations are as follows:

[0086] 1. Class I pile foundation: The pile body integrity is Class I pile, the remaining concrete strength is ≥90%, the steel corrosion rate is ≤1%, the remaining single pile bearing capacity is ≥85%, and the technical adaptation direction is direct in-situ utilization;

[0087] 2. Class II pile foundation: The pile body integrity is Class II pile, the remaining concrete strength is 70% to 90%, the steel corrosion rate is 1% to 5%, the remaining single pile bearing capacity is 60% to 85%, and the technical adaptation direction is in-situ regeneration after repair;

[0088] 3. Class III pile foundation: The pile body integrity is Class III or IV pile, the remaining concrete strength is <70%, the steel corrosion rate is >5%, the remaining single pile bearing capacity is <60%, and the technical adaptation direction is off-site resource utilization.

[0089] The calculation formulas for each evaluation indicator are as follows:

[0090] The formula for calculating the residual strength rate of concrete is as follows:

[0091] 00%

[0092] in, Residual strength of concrete The measured cubic compressive strength of the pile concrete. The original design cubic compressive strength of the pile concrete;

[0093] The formula for calculating the corrosion rate of the reinforcing steel is:

[0094] 00%

[0095] in, For steel reinforcement corrosion rate, To ensure the initial quality of the reinforcing steel is free of rust, The measured quality of the reinforcing steel after rust removal;

[0096] The formula for calculating the residual bearing capacity ratio of a single pile is as follows:

[0097] 100%

[0098] in, This refers to the residual bearing capacity of a single pile. This represents the characteristic value of the measured vertical bearing capacity of a single pile in a pile foundation. The characteristic value of the vertical bearing capacity of a single pile in the original design of the pile foundation.

[0099] Step S102: Select a suitable green recycling technology path based on the evaluation level of the abandoned pile foundation.

[0100] Specifically, based on the evaluation level determined in S101, the following technical paths are selected respectively:

[0101] 1. For Class I pile foundations, the direct in-situ utilization technology is adopted. This technical approach is suitable for abandoned pile foundations with good pile integrity and bearing capacity that meet the requirements of new construction projects. After adjusting the pile top elevation, they can be directly used as pile foundations for new construction projects.

[0102] 2. For Class II pile foundations, a low-disturbance in-situ green recycling technology is adopted. This technology is suitable for abandoned pile foundations with minor defects but repair value. After repair of pile defects and interface reinforcement, they can be used as pile foundations for new construction projects. This approach can achieve the repair and utilization of abandoned pile foundations without removing them, avoiding the high carbon emissions and construction disturbance caused by pile removal and transportation.

[0103] 3. For Class III pile foundations, an off-site resource utilization technology is adopted, in which the piles are crushed, purified, and modified before being recycled as aggregate. This technology is suitable for abandoned pile foundations that cannot be utilized in situ, replacing traditional waste disposal methods and achieving high-value utilization of abandoned pile materials.

[0104] The specific construction techniques supporting the low-disturbance in-situ green recycling technology include:

[0105] 1. Static diamond wire saws are used to adjust the pile top elevation, replacing the traditional crushing process. The construction vibration speed is controlled within 0.3cm / s, which meets the safety protection requirements of surrounding existing buildings.

[0106] 2. Fully enclosed drilling equipment is used for grouting hole construction, and a mud circulation and treatment system is provided to achieve zero mud discharge;

[0107] 3. Portable non-destructive testing equipment is used to achieve real-time quality monitoring of the repair process and ensure the construction effect.

[0108] Step S103: For abandoned pile foundations selected for in-situ regeneration, implement a performance improvement treatment that combines pile body repair and interface enhancement.

[0109] This step implements a performance improvement process that combines pile repair and interface enhancement, specifically including four core components:

[0110] (1) Low-pressure grouting repair of pile defects

[0111] For defects such as pile body cracks and local concrete defects in Class II pile foundations, a complete process of low-pressure grouting repair + polymer-modified cement-based material reinforcement is adopted.

[0112] For transverse and longitudinal cracks in the pile body, a low-pressure penetration grouting process is adopted, with the grouting pressure controlled at 0.3–0.5 MPa to avoid further expansion of the cracks caused by high-pressure grouting. Epoxy-modified cement-based grout is selected as the grouting material, possessing both high adhesion and micro-expansion properties, enabling effective crack filling and overall pile repair. The mixing ratio of the epoxy-modified cement-based grout is: cement: water: epoxy resin: curing agent = 100:35:15:3. Under this mixing ratio, the grout's bonding strength can reach over 2.5 MPa, and the micro-expansion rate is 0.02%–0.05%.

[0113] For areas where the concrete protective layer has detached or is partially damaged, polymer-modified concrete is used for local reinforcement. The mix proportion of polymer-modified concrete is: cement: sand: aggregate: polymer emulsion: water = 100:150:200:15:30. After repair, the concrete strength of the pile body can be restored to more than 90% of the original design strength.

[0114] (2) Grouting reinforcement after segmentation of pile-soil interface

[0115] To address the issues of voids at the pile-soil interface and decreased pile-side friction, a segmented post-grouting technique is employed to enhance the interface.

[0116] Three to four grouting pipes, each 6 to 8 meters long, are installed along the longitudinal direction of the pile. The grouting pipes are made of Φ25mm galvanized steel pipes and are arranged symmetrically around the pile. The grouting holes are designed with one-way valves, with an opening pressure of 0.2MPa, to prevent cross-contamination and leakage of grout during the grouting process.

[0117] The grouting material used is a cement-water glass two-component grout, with a water-cement ratio controlled between 0.6 and 0.8, and the water glass content being 3% to 5% of the cement mass. The grouting pressure is adjusted according to the soil properties: 0.5–0.8 MPa for soft soil layers and 0.8–1.2 MPa for silty clay layers. The grouting volume control standard is: no less than 50 L of grout per meter of pile length, or the grouting pressure reaching the design upper limit and stabilizing for more than 5 minutes.

[0118] Grouting can form a 50-100mm thick cement-soil reinforcement around the pile, filling the voids at the pile-soil interface and significantly improving the pile's side friction. Field tests show that this technology can increase the bearing capacity of a single pile by more than 30%.

[0119] The characteristic value of the vertical bearing capacity of a single pile in a recycled pile foundation can be calculated using the following formula:

[0120] Ra=up∑qsiali+qpaAp

[0121] In the formula, Ra is the characteristic value of the vertical bearing capacity of a single pile in the regenerated pile foundation (kN); up is the pile perimeter (m); qsia is the characteristic value of the side resistance after grouting of the i-th soil layer on the pile side (kPa); li is the pile length in the i-th soil layer (m); qpa is the characteristic value of the pile end resistance (kPa); and Ap is the cross-sectional area of ​​the pile end (m²).

[0122] (3) Carbon fiber cloth outer wrapping composite reinforcement

[0123] For pile foundations with insufficient pile strength, carbon fiber reinforced polymer (CFRP) external reinforcement technology is adopted. The carbon fiber reinforced polymer is bonded to the surface of the pile body with epoxy resin adhesive to form a "concrete-carbon fiber reinforced polymer" composite stress system, which greatly improves the bending and shear bearing capacity and ductility of the pile body.

[0124] The carbon fiber cloth is selected from Grade I 300g / m² carbon fiber cloth, with a tensile strength standard value ≥3400MPa and an elastic modulus ≥2.35×10^5MPa. The epoxy resin adhesive has a bond strength ≥2.5MPa and an elongation ≥1.5%.

[0125] Parameter optimization was achieved through orthogonal experiments. The results showed that when the number of carbon fiber cloth layers was two and the overlap length was not less than 200mm, the ultimate bearing capacity of the pile could be increased by more than 40%, and the reinforcement effect was stable over a long period. The carbon fiber cloth was bonded in a circumferential direction with a spacing of 150mm, and the bonding range was within 5m below the pile top.

[0126] (4) Long-term durability protection treatment

[0127] To address the corrosive environment of high groundwater levels and high chloride ion content in the soft soil region of the Yangtze River Delta, a long-term durability protection technology system for regenerated pile foundations was developed.

[0128] To address the issue of steel reinforcement corrosion in piles, a penetrating steel reinforcement corrosion inhibitor is used. This is injected under low pressure through drilled holes in the pile concrete. The holes are 10mm in diameter, reaching the steel reinforcement level, and spaced 500mm apart in a staggered pattern. The corrosion inhibitor penetrates to the surface of the steel reinforcement, reforming a passivation film and blocking the electrochemical reactions that cause corrosion. The penetration depth of the penetrating steel reinforcement corrosion inhibitor can reach over 50mm, and the passivation film thickness on the steel reinforcement surface can reach over 100nm.

[0129] For the problem of concrete corrosion in piles, a penetrating crystalline waterproof coating is used. Applied to the pile surface, it penetrates the concrete to form a crystalline layer, blocking the concrete pores and preventing the intrusion of corrosive media such as chloride ions and carbon dioxide. The application rate of the penetrating crystalline waterproof coating is 0.8–1.2 kg / m², applied in two coats with an interval of 6–8 hours between each coat.

[0130] Through the above-mentioned protective technologies, the design service life of regenerated pile foundations can reach more than 50 years, meeting the durability requirements of new construction projects.

[0131] Step S104: Conduct bearing capacity and durability tests on the recycled pile foundation for acceptance.

[0132] Specifically, a three-tiered quality control system is established throughout the construction process, consisting of self-inspection by the work team, re-inspection by the project department, and final inspection by a third-party testing agency. Each process is completed and passes inspection before proceeding to the next process, ensuring that the construction quality is controllable throughout the entire process.

[0133] After the project is completed, the recycled pile foundation will be inspected and accepted using the following testing methods:

[0134] 1. Low-strain testing method is used to test the integrity of the pile body to ensure that the integrity of all recycled pile foundations meets the Class I pile standard;

[0135] 2. A static load test on a single pile is used to detect the vertical bearing capacity of the single pile to ensure that the ultimate bearing capacity of the single pile meets the design requirements;

[0136] 3. Detect the maximum settlement of the pile top of the recycled pile foundation to ensure that the deformation is controlled within the allowable range specified in the code.

[0137] Example 2

[0138] This embodiment uses an urban renewal project in Shanghai as the engineering background to provide a detailed description of the technical solution of the present invention.

[0139] Project Overview: This project is an urban renewal project in Shanghai, located in Wusong Street, Baoshan District, Shanghai. The total construction area is 127,000 square meters, and the construction content includes the construction of new high-standard industrial R&D facilities, supporting commercial facilities and underground parking garages.

[0140] The project site was originally the old industrial plant of Baosteel Special Steel Co., Ltd., built in 1982 and demolished in 2022 after production ceased. The pile foundation had a service life of 40 years. The site is located in a typical soft soil area of ​​Shanghai, with the following strata from top to bottom: ①1 plain fill (1.2-2.5m thick), ②1 silty clay (8.5-12.3m thick), ③1 silty clay (6.2-9.7m thick), ④1 sandy silt (10.5-14.2m thick); the stable groundwater level is 0.7-1.5m deep, and the chloride ion content of the groundwater is 128-156mg / L, which is weakly corrosive to concrete structures.

[0141] A total of 528 abandoned piles remain on the site, including 332 PHC-AB500(125) prestressed concrete pipe piles with a designed pile length of 25m and an original design characteristic value of 1800kN for the vertical compressive bearing capacity of a single pile; and 196 Φ600 bored cast-in-place piles with a designed pile length of 30m and an original design characteristic value of 2200kN for the vertical compressive bearing capacity of a single pile. The project is adjacent to Songbao Road, a major municipal road, on the east side, and is at least 11.8m away from an existing residential area on the south side. The requirements for controlling construction vibration, noise, and dust are extremely high, and the traditional pile extraction and transportation process cannot meet the requirements for construction safety and environmental protection.

[0142] Renewability evaluation results: Through on-site low-strain testing, core sampling, and single-pile static load testing, the renewability evaluation of abandoned pile foundations was completed. The results show that: 87 Class I pile foundations in the site can be directly reused in situ; 381 Class II pile foundations need to be repaired and regenerated in situ; and 60 Class III pile foundations need to be utilized off-site.

[0143] Specialized technical solution: Based on the evaluation results and in accordance with the design requirements for pile foundations in new construction projects, a specialized technical solution was developed:

[0144] 1. Class I pile foundation: After adjusting the pile top elevation with a diamond wire saw, it can be directly used as an anti-tension pile for new buildings;

[0145] 2. Class II pile foundation: Low-pressure grouting is used to repair pile defects, and the performance is improved by using segmented post-grouting technology on the pile side. After repair, it can be used as a compression pile for new construction projects.

[0146] 3. Class III pile foundation: After static cutting and demolition, the piles are transported to a closed crushing and disposal area on site for resource recycling. The modified recycled aggregates are used entirely for backfilling of the project's foundation pit and construction of the roadbed subbase.

[0147] Key construction procedures and quality control:

[0148] 1. Pile top cutting: Diamond wire saws were used for pile top cutting, and the vibration speed was controlled within 0.2cm / s throughout the construction process, without causing any impact on surrounding residential buildings and municipal pipelines;

[0149] 2. Repair of pile defects: A dual control standard for grouting pressure and grouting volume is adopted to ensure that cracks are filled tightly;

[0150] 3. Post-grouting of pile side: A segmented grouting process from bottom to top is adopted, and the grouting pressure and grouting volume are strictly controlled to avoid problems such as cross-grouting and grout overflow.

[0151] Implementation Results: After the project was completed, the recycled pile foundation was inspected and accepted through low-strain testing and single-pile static load testing. The results showed that the integrity of all recycled pile foundations met the Class I pile standard, the ultimate bearing capacity of single piles met the design requirements, the maximum pile top settlement was only 7.8 mm, and the deformation was controlled within the allowable range of the specifications.

[0152] Comprehensive benefit analysis: By using green recycling technology for waste pile foundations, this project reduces the amount of concrete waste transported by approximately 2,950 m³ compared to the traditional pile extraction and transportation process, and reduces carbon emissions by approximately 642 tons, achieving a carbon emission reduction rate of 59.2%; it also saves approximately RMB 1.92 million in project costs, a cost reduction rate of 42.7%; and it shortens the construction period by 22 days, a period reduction rate of 34.4%, achieving significant economic, environmental, and social benefits.

[0153] Example 3

[0154] This embodiment provides a green regeneration and performance improvement system for abandoned pile foundations in urban renewal, including: a renewability evaluation module, a technology path selection module, a performance improvement processing module, and a testing and acceptance module.

[0155] 1. Renewability Assessment Module: Used to conduct a renewable rating assessment of abandoned pile foundations and determine their assessment level. Specifically, it includes:

[0156] The indicator acquisition unit is used to acquire four core evaluation indicators: pile integrity, concrete strength remaining rate, steel corrosion rate, and single pile bearing capacity remaining rate.

[0157] The grading unit is used to classify abandoned pile foundations into three evaluation levels: Level I, Level II, and Level III, based on four core evaluation indicators.

[0158] The technology adaptation unit is used to determine the corresponding technology adaptation direction based on the evaluation level.

[0159] 2. Technology path selection module, used to select appropriate green recycling technology paths based on the evaluation level of abandoned pile foundations. Specifically, it includes:

[0160] In-situ utilization unit, used to select direct in-situ utilization technology path for Class I pile foundations;

[0161] In-situ regeneration unit is used to select a low-disturbance in-situ green regeneration technology path for Class II pile foundations;

[0162] The off-site utilization unit is used to select off-site resource utilization technology paths for Class III pile foundations.

[0163] 3. Performance Enhancement Module: This module performs performance enhancement on abandoned pile foundations selected for in-situ regeneration by combining pile body repair and interface enhancement. Specifically, it includes:

[0164] The pile defect repair unit is used for low-pressure grouting repair of pile cracks and local concrete defects, and for reinforcement with polymer-modified cement-based materials.

[0165] The interface enhancement processing unit is used to perform grouting interface enhancement processing on the pile-soil interface void area after pile side segmentation.

[0166] Composite reinforcement unit, used for composite reinforcement of pile foundations with insufficient pile structure strength by wrapping with carbon fiber cloth;

[0167] Durability protection unit, used for long-term durability treatment of recycled pile foundations, including steel reinforcement corrosion prevention and concrete protection.

[0168] 4. Testing and Acceptance Module: Used for testing and accepting the bearing capacity and durability of recycled pile foundations. Specifically includes:

[0169] The pile integrity testing unit is used to test the pile integrity using the low-strain testing method.

[0170] The bearing capacity testing unit is used to test the vertical bearing capacity of a single pile using a static load test.

[0171] The deformation detection unit is used to detect the maximum settlement at the top of the regenerated pile foundation.

[0172] The system in this embodiment can realize full-process digital management of green recycling and performance improvement of abandoned pile foundations, and improve the standardization of technology implementation and quality control level.

[0173] The above description is merely a preferred embodiment of the present invention; however, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concepts, should be covered within the scope of protection of the present invention.

Claims

1. A method for green regeneration and performance improvement of abandoned pile foundation in urban renewal, characterized in that, Includes the following steps: a. Conduct a renewability classification assessment of abandoned pile foundations within urban renewal sites to determine the evaluation level of the abandoned pile foundations; b. Select an appropriate green recycling technology path based on the evaluation level of the abandoned pile foundation; c. For abandoned pile foundations that are selected for in-situ regeneration, implement a performance improvement treatment that combines pile body repair and interface enhancement; d. Conduct bearing capacity and durability tests on the recycled pile foundations for acceptance.

2. The green recycling and performance improving method of abandoned pile foundation according to claim 1, characterized in that, The renewability classification assessment of abandoned pile foundations within urban renewal sites specifically includes: a. The core evaluation indicators are pile integrity, concrete strength retention rate, steel corrosion rate, and single pile bearing capacity retention rate. b. Classify abandoned pile foundations into three evaluation levels: Level I, Level II, and Level III; c. Among them, Class I pile foundations are characterized by pile integrity of Class I, residual concrete strength ≥90%, steel corrosion rate ≤1%, and residual single pile bearing capacity ≥85%, which are suitable for direct in-situ utilization. d. Class II pile foundations are characterized by pile integrity of Class II, concrete strength remaining rate of 70% to 90%, steel corrosion rate of 1% to 5%, and single pile bearing capacity remaining rate of 60% to 85%. They are adapted for repair and then regenerated in situ. e. Class III pile foundations are characterized by pile integrity of Class III or IV, residual concrete strength of <70%, steel corrosion rate of >5%, and residual single pile bearing capacity of <60%, which are suitable for off-site resource utilization. The formula for calculating the residual strength rate of concrete is as follows: 00% wherein, is the concrete strength remaining rate, is the pile concrete measured cubic compressive strength, is the pile concrete original design cubic compressive strength; The formula for calculating the corrosion rate of the reinforcing steel is: 00% wherein, is the steel reinforcement corrosion rate, is the initial non-corroded mass of the steel reinforcement, is the measured mass of the steel reinforcement after rust removal; The formula for calculating the residual bearing capacity ratio of a single pile is as follows: 100% wherein, is the single pile bearing capacity residual rate, is the measured single pile vertical bearing capacity characteristic value of the pile foundation, is the original design single pile vertical bearing capacity characteristic value of the pile foundation.

3. The green recycling and performance improving method of abandoned pile foundation according to claim 1 or 2, characterized in that, The selection of appropriate green recycling technology pathways based on the evaluation level of abandoned pile foundations specifically includes: a. For Class I pile foundations, the direct in-situ utilization technology is adopted, and after the pile top elevation is adjusted, the pile foundations are directly used as pile foundations for new construction projects; b. For Class II pile foundations, low-disturbance in-situ green recycling technology is adopted, and after pile defect repair and interface enhancement, it is used as a pile foundation for new construction projects; c. For Class III pile foundations, off-site resource utilization technology is adopted, and the piles are recycled as recycled aggregates after crushing, purification and modification. The low-disturbance in-situ green regeneration technology includes: a. Static diamond wire saws are used to adjust the pile top elevation, and the construction vibration speed is controlled within 0.3 cm / s; b. Use fully enclosed drilling equipment for grouting hole construction, and provide a mud circulation and treatment system; c. Use portable non-destructive testing equipment for real-time quality monitoring of the repair process; The off-site resource utilization technology includes: using a combination of a closed jaw crusher and an impact crusher to grade and crush waste pile concrete; removing impurities and mud powder from the crushed aggregate through screening and washing; using a silane coupling agent to perform surface modification treatment on the recycled aggregate; and using the modified recycled aggregate for foundation pit backfilling, roadbed subbase, or preparation of recycled concrete.

4. The green recycling and performance improving method of abandoned pile foundation according to claim 1, characterized in that, The performance enhancement treatment for abandoned pile foundations selected for in-situ regeneration, which combines pile body repair and interface enhancement, specifically includes: a. Low-pressure grouting repair and polymer-modified cementitious material reinforcement are used to repair defects such as pile body cracks and local concrete defects; b. Perform grouting interface reinforcement treatment on the pile side segment after segmenting the void area at the pile-soil interface; c. For pile foundations with insufficient structural strength, reinforce them with carbon fiber cloth wrapping; d. Perform long-term durability protection treatment on the recycled pile foundation.

5. The method for green recycling and performance improvement of abandoned pile foundations according to claim 4, characterized in that, The low-pressure grouting repair specifically includes: a. For transverse and longitudinal cracks in the pile body, a low-pressure permeation grouting process is adopted, and the grouting pressure is controlled at 0.3 to 0.5 MPa; b. The grouting material is epoxy-modified cement-based grout, which has both high adhesion and micro-expansion properties; c. For areas where the concrete cover has detached or is partially damaged, polymer-modified concrete should be used for local reinforcement.

6. The method for green recycling and performance improvement of abandoned pile foundations according to claim 4, characterized in that, The post-grouting interface enhancement treatment for segmented pile sides specifically includes: a. Install 3 to 4 grouting pipes along the longitudinal direction of the pile, each section being 6 to 8 meters long; b. The grouting hole adopts a one-way valve design to avoid grout leakage or overflow during the grouting process; c. The grouting material is cement-water glass double-liquid grout, and the water-cement ratio is controlled at 0.6 to 0.8; d. The grouting pressure is adjusted according to the soil properties. For soft soil layers, the pressure is controlled at 0.5–0.8 MPa, and for silty clay layers, the pressure is controlled at 0.8–1.2 MPa.

7. The method for green recycling and performance improvement of abandoned pile foundations according to claim 4, characterized in that, The carbon fiber cloth outer wrapping composite reinforcement and long-term durability protection treatment specifically includes: a. Carbon fiber cloth is bonded to the surface of the pile body using epoxy resin adhesive; b. The carbon fiber cloth is bonded in two layers, with an overlap length of not less than 200mm; c. Forming a "concrete-carbon fiber cloth" composite stress system to improve the bending and shear bearing capacity and ductility of the pile body; d. A penetrating steel reinforcement corrosion inhibitor is used, which is injected under low pressure through the pile concrete borehole, allowing the corrosion inhibitor to penetrate to the steel reinforcement surface and reform a passivation film; e. Use penetrating crystalline waterproof coating, apply it to the surface of the pile body, penetrate into the concrete to form a crystalline layer, and block the pores of the concrete.

8. The method for green recycling and performance improvement of abandoned pile foundations according to claim 1, characterized in that, The specific procedures for testing and accepting the bearing capacity and durability of the recycled pile foundations include: a. Low-strain testing method was used to inspect the integrity of the pile body; b. The vertical bearing capacity of a single pile is tested using a static load test. c. Inspect the maximum settlement of the regenerated pile foundation to ensure that the deformation is controlled within the allowable range specified in the code.

9. A green regeneration and performance improvement system for abandoned pile foundations in urban renewal, characterized in that, include: a. Renewability assessment module, used to conduct renewable rating assessment of abandoned pile foundations and determine the assessment level of abandoned pile foundations; b. Technology path selection module, used to select the appropriate green recycling technology path based on the evaluation level of the abandoned pile foundation; c. Performance enhancement processing module, used to perform performance enhancement processing of pile body repair and interface enhancement in combination for abandoned pile foundations selected for in-situ regeneration; d. Testing and Acceptance Module, used for testing and accepting the bearing capacity and durability of regenerated pile foundations.

10. A green regeneration and performance improvement system for abandoned pile foundations in urban renewal according to claim 9, characterized in that, The renewability evaluation module includes an index acquisition unit, a grade determination unit, and a technology adaptation unit. The index acquisition unit is used to acquire four core evaluation indicators: pile integrity, concrete strength retention rate, steel corrosion rate, and single pile bearing capacity retention rate. The grade determination unit is used to classify abandoned pile foundations into three evaluation grades: Grade I, Grade II, and Grade III, based on the four core evaluation indicators. The technology adaptation unit is used to determine the corresponding technology adaptation direction based on the evaluation grade. The technology path selection module includes an in-situ utilization unit, an in-situ regeneration unit, and an off-situ utilization unit; the in-situ utilization unit is used to select a direct in-situ utilization technology path for Class I pile foundations; the in-situ regeneration unit is used to select a low-disturbance in-situ green regeneration technology path for Class II pile foundations; and the off-situ utilization unit is used to select an off-situ resource utilization technology path for Class III pile foundations. The performance enhancement module includes a pile defect repair unit, an interface reinforcement unit, a composite reinforcement unit, and a durability protection unit. The pile defect repair unit is used for low-pressure grouting repair and polymer-modified cement-based material reinforcement of pile cracks and local concrete defects. The interface reinforcement unit is used for segmented grouting interface reinforcement treatment of the pile-soil interface void area. The composite reinforcement unit is used for carbon fiber cloth wrapping composite reinforcement of pile foundations with insufficient pile structural strength. The durability protection unit is used for long-term durability treatment of recycled pile foundations, including steel reinforcement corrosion prevention and concrete protection. The testing and acceptance module includes a pile integrity testing unit, a bearing capacity testing unit, and a deformation testing unit. The pile integrity testing unit is used to test the pile integrity using a low-strain testing method. The bearing capacity testing unit is used to test the vertical bearing capacity of a single pile using a single pile static load test. The deformation testing unit is used to test the maximum pile top settlement of the regenerated pile foundation.

Images