Anti-corrosion cast-in-place pile and construction method thereof

Abstract

This invention discloses an anti-corrosion cast-in-place pile and its construction method, belonging to the field of building pile foundation engineering technology. It includes a retaining structure composed of several interconnected PVC ring units. The retaining structure is equipped with a grouting system, an anti-corrosion membrane, a reinforcing cage, and pile shoes. Each ring unit is welded into a cylindrical shape from at least three PVC plates. The grouting system includes grouting pipes, and the anti-corrosion membrane is adhered to the inner wall of the retaining structure. The reinforcing cage has pre-embedded grouting sleeves corresponding to the grouting pipes. The pile shoes are located at the ends of the retaining structure. Construction involves sequentially drilling, installing the retaining structure, applying the anti-corrosion membrane, hoisting the reinforcing cage, underwater concrete pouring, and subsequent grouting reinforcement. This invention effectively solves the problems of cast-in-place piles being susceptible to corrosion, poor construction quality, and irreparable damage in highly corrosive environments. It has advantages such as significant anti-corrosion effect, convenient construction, safety and environmental protection, wide applicability, and strong maintainability. It is suitable for highly corrosive geological environments such as coastal high-chloride salt, inland sulfate / saline-alkali, and weakly acidic environments.

Description

Technical Field

[0001] This invention belongs to the field of building pile foundation engineering technology, and in particular relates to a corrosion-resistant cast-in-place pile and its construction method, which is applicable to cast-in-place pile foundation engineering in highly corrosive geological environments such as coastal high chloride salt, inland sulfate / saline-alkali, and weak acid. Background Technology

[0002] In highly corrosive geological environments such as saline soil, coastal high-chloride salts, and industrial acid and alkali pollution, the durability of foundations has always been a challenge in the engineering field. Currently, the main approach to treating saline soil foundations in China is a comprehensive "internal enhancement and external protection" approach. This involves improving the corrosion resistance of the concrete itself (e.g., using high-performance corrosion-resistant concrete and increasing the thickness of the protective layer), applying anti-corrosion materials to the structural surface, and laying a barrier layer around the structure to prevent contact with soluble salts. According to relevant specifications, cast-in-place piles are not suitable for highly corrosive areas. Previous projects often used large-scale excavation foundations, applying anti-corrosion coatings only after the foundation was poured. However, large-scale excavation foundations require dewatering, involve large construction surfaces, and have significant impacts on the ecological environment and soil and water conservation.

[0003] Cast-in-place piles have advantages such as high bearing capacity, low settlement, and fast construction speed, but their adaptability in highly corrosive environments faces the following key challenges:

[0004] 1. Cast-in-place piles are poured on-site. After the steel cage is in place, concrete is poured directly into the pile hole. The concrete in the pile body comes into direct contact with underground corrosive media (such as Cl⁻, SO4²⁻, etc.) during the flowing and incomplete hydration and hardening stage. Furthermore, it is difficult to vibrate and the curing conditions are poor, resulting in poor concrete density and impermeability, which weakens its corrosion resistance.

[0005] 2. Cast-in-place piles are a type of concealed engineering project, and many factors affect the quality of pile formation. During construction, defects such as pile breakage, borehole wall collapse, mud inclusion in the pile body, and honeycomb pitting are prone to occur.

[0006] To address the aforementioned issues, a large-diameter bagged concrete cast-in-place pile technology has been proposed in the prior art. This technology employs conventional drilling techniques to form the borehole. After cleaning the borehole, a steel pipe is placed along the borehole wall at the bottom as a grout drain pipe. Then, a factory-made anti-corrosion bag, after being weighted, is submerged into the cement slurry within the borehole. Once the anti-corrosion bag is confirmed to be at the same depth as the borehole, fresh cement slurry or fresh water is injected into the bag. The cement slurry within the borehole is then drained through the grout drain pipe using a drainage grouting method. After the anti-corrosion bag is tightly fitted to the borehole wall, the reinforcing cage is submerged inside the anti-corrosion bag, and the pile is formed using conventional underwater concrete pouring techniques.

[0007] However, this technology still has the following shortcomings:

[0008] 1. The traditional mud slurry wall protection process is used for hole formation, which makes it difficult to guarantee that the hole quality is a standard cylindrical shape. Gaps are easily formed between the anti-corrosion bag and the hole wall, resulting in a reduction in the side friction of the pile and endangering the structural safety.

[0009] 2. When using the drainage method to pour concrete, the concrete grade needs to be increased according to the specifications, and the pouring quality is not as good as that of dry hole construction.

[0010] 3. Since the anti-corrosion bag is in direct contact with the soil, if sharp stones or foreign objects are encountered during the drilling process, the anti-corrosion bag is very easy to be damaged. Moreover, since the inside and outside of the bag are filled with liquid, the damage is difficult to be detected in time, posing a safety hazard.

[0011] Therefore, developing a cast-in-place pile and its construction method that can be applied to highly corrosive environments, has reliable anti-corrosion effect, controllable construction quality, and is maintainable in the later stage has important engineering application value. Summary of the Invention

[0012] The technical problem this invention aims to solve is to overcome the shortcomings of existing cast-in-place piles, such as susceptibility to corrosive media in highly corrosive environments, difficulty in controlling construction quality, and inability to be repaired later. The invention designs a corrosion-resistant cast-in-place pile. The device has a simple and practical structure, specifically including a retaining structure, a grouting system, an anti-corrosion membrane, a reinforcing cage, and pile shoes. The retaining structure is composed of several PVC ring units joined together. Each ring unit consists of at least three PVC plates welded together to form a cylindrical outline, serving as an outer physical isolation layer. The grouting system includes several grouting pipes arranged longitudinally along the pile body. Sealing tape is affixed to the top of each grouting pipe for air venting during construction and subsequent grouting reinforcement. The anti-corrosion membrane is adhered to the inner wall of the retaining structure via an air pump, forming a second physical anti-corrosion layer. Grouting sleeves corresponding to the positions of the grouting pipes are pre-embedded within the reinforcing cage. The pile shoes are located at the ends of the retaining structure and include a cross-shaped sheet pile tip and a steel casing slot, used for settlement in soft strata and maintaining airtightness. The construction process employs drilling, retaining structure installation, membrane bonding, rebar cage hoisting, underwater concrete pouring, and subsequent grouting reinforcement, forming a multi-layered anti-corrosion system consisting of an outer PVC isolation layer, a middle membrane protection layer, an inner concrete self-corrosion layer, and grouting maintenance. This invention effectively solves the problems of easy corrosion of cast-in-place piles in highly corrosive environments, poor pile quality, and inability to repair them later. It significantly reduces construction risks, extends the service life of the piles, and improves operational efficiency and safety. It is particularly suitable for pile foundation projects in highly corrosive geological environments such as coastal high-chloride salt, inland sulfate / saline-alkali, and weakly acidic environments, including power transmission lines, industrial and civil buildings, municipal transportation, and water conservancy ports.

[0013] The solution adopted by this invention to solve its technical problem is as follows:

[0014] A corrosion-resistant cast-in-place pile, comprising:

[0015] The enclosure structure is formed by sequentially connecting several ring-shaped units of equal length.

[0016] The ring segment unit is formed by joining and welding at least three PVC plates to form a cylindrical outline. The joints between adjacent PVC plates are filled with PVC welding rods and heated and welded. The weld width is ≥10mm. After welding, the outer ring of the enclosure structure forms a smooth cylindrical surface, and its outer diameter is the design diameter of the cast-in-place pile body.

[0017] The adjacent ring segments are welded together by socket welding, and the joints of the adjacent PVC panels are welded together by lap welding. All welds are treated with waterproofing and anti-corrosion measures.

[0018] The retaining structure is equipped with a grouting system, which includes a number of grouting pipes arranged longitudinally along the pile body. The grouting pipes are placed between adjacent PVC panels, and the top of the grouting pipes is covered with sealing tape.

[0019] The inner wall of the enclosure structure is covered with an anti-corrosion film by means of an air pump, and the anti-corrosion film serves as a second physical anti-corrosion layer.

[0020] The enclosure structure is equipped with a steel cage, which includes main bars, stirrups and grouting sleeves, and the position of the grouting sleeves corresponds to the position of the grouting pipes.

[0021] The outer end of the retaining structure is provided with a pile shoe, which includes a pile tip welded from a cross plate and a steel casing groove. An annular rubber pad is provided inside the steel casing groove. The steel casing groove of the pile shoe is located at one end close to the retaining structure. When the retaining structure sinks, its end is inserted into the groove and can automatically detach when pulled out.

[0022] As a preferred embodiment of the present invention

[0023] The cast-in-place piles are constructed using high-performance anti-corrosion concrete with a water-cement ratio of ≤0.45, and are mixed with fly ash, mineral powder, and steel reinforcement corrosion inhibitor.

[0024] The high-performance anti-corrosion concrete has a strength grade ≥ C40 and a slump of 180~220mm.

[0025] As a preferred embodiment of the present invention

[0026] The grouting sleeve of the reinforcing cage is made of φ20mm seamless steel pipe, one end of which is welded to the reinforcing cage at the position corresponding to the grouting pipe, and the other end is ground into a pointed shape.

[0027] As a preferred embodiment of the present invention

[0028] A reinforcing cage pad is provided on the side of the pile shoe, and the position of the reinforcing cage pad corresponds to the position of the reinforcing cage.

[0029] As a preferred embodiment of the present invention

[0030] The inner wall of one end of the ring segment unit is provided with a groove, and the outer side of the other end is provided with a rubber ring. When multiple ring segment units are connected, the rubber ring of one ring segment unit is inserted into the groove of another ring segment unit.

[0031] A construction method for corrosion-resistant cast-in-place piles includes the following steps:

[0032] Step S1: Drill holes using the mud-wall drilling method and perform secondary hole cleaning;

[0033] Step S2: Connect the ring segment units one by one and hoist them into the hole, and set a counterweight device on the top of the enclosure structure to prevent buoyancy;

[0034] Step S3: After the enclosure structure is lowered into place, an anti-corrosion film is attached to its inner wall using an air pump, and then the steel cage is hoisted and fixed.

[0035] Step S4: Concrete is continuously poured using the duct method. During the pouring process, the sealing tape on the grouting pipe is opened intermittently to release air and grout. Curing is carried out after pouring.

[0036] Step S5: Based on the test results of the integrity of the cast-in-place pile, grouting is performed using the grouting pipe.

[0037] As a preferred embodiment of the present invention

[0038] In step S1, the thickness of sediment at the bottom of the hole after the first cleaning is ≤100mm, the thickness of sediment after the second cleaning is ≤50mm, the sand content of the mud is ≤2%, and the mud specific gravity is controlled at 1.1~1.2.

[0039] As a preferred embodiment of the present invention

[0040] In step S2, the load of the counterweight device is greater than or equal to 1.1 times the buoyancy of the enclosure structure.

[0041] As a preferred embodiment of the present invention

[0042] In step S5, when grouting is performed using the grouting pipe, the grouting pressure is controlled at 0.5~1.0MPa, and the grout is selected as epoxy resin grout or cement-based penetrating crystallizing grout. Grouting is performed in a single pipe until the grout overflows from the adjacent grouting pipe, and the pressure is maintained for 10 minutes.

[0043] As a preferred embodiment of the present invention

[0044] The construction method described herein is applicable to coastal high-chloride salt corrosion environments, inland sulfate / salt-alkali corrosion environments, and weakly acidic corrosion environments. When the pH of the corrosion environment is less than 4, the PVC board should be replaced with a UPVC board.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1. This invention forms a double physical isolation layer through the enclosure structure (PVC material ring unit) and the internal anti-corrosion film, which effectively isolates groundwater and corrosive ions such as Cl⁻ and SO4²⁻ in the soil during the concrete pouring and curing process, avoiding direct contact between the freshly poured flowing concrete and the corrosive medium. This fundamentally solves the problem of reduced durability of traditional cast-in-place piles caused by erosion before the concrete has fully hardened. At the same time, the pre-embedded grouting pipe can inject anti-corrosion grout when defects are detected later, forming a secondary anti-corrosion layer, which increases the service life of the pile by more than 30% compared with traditional cast-in-place piles.

[0047] 2. The enclosure structure of the present invention adopts prefabricated ring segment units in the factory. On-site, only section-by-section docking, welding and hoisting are required, which greatly shortens the on-site construction cycle. Existing commonly used equipment such as drilling rigs, cranes, and concrete pumps can meet the construction conditions. There is no need to develop new construction equipment. The equipment has good adaptability and low promotion cost.

[0048] 3. The entire construction process of this invention does not require personnel to go down into the hole (such as manual bottom cleaning, vibration, etc.), avoiding safety risks such as hole collapse, poisoning, and suffocation; the bottom sealing of the retaining structure and the top ballast to prevent buoyancy, combined with the secondary hole cleaning process, effectively control the thickness of sediment and the sand content of the mud, reducing the pollution of the environment caused by mud discharge.

[0049] 4. This invention constrains the borehole wall through the retaining structure, avoiding problems such as borehole wall collapse and diameter reduction that are prone to occur in traditional mud wall forming; during the concrete pouring process, the sealing tape of the grouting pipe can be opened to release air and grout, eliminating defects such as honeycomb and voids caused by gas retention; the subsequent grouting reinforcement can repair micro-cracks and insufficient protective layer, making the quality of the pile body controllable throughout the process.

[0050] 5. This invention is applicable to coastal high-chloride salt corrosion environments (coastal wharves, cross-sea bridges, etc.), inland sulfate / salt-alkali corrosion environments (transmission lines, industrial plants, etc. in saline soil areas of Xinjiang and Gansu), and weakly acidic corrosion environments (acid rain mountainous areas, coal mine goaf areas, etc.). When pH < 4, the PVC board can be replaced with UPVC board for compatibility, and the cost is far lower than the stainless steel casing solution. For industrial and civil building pile foundations (pile diameter 500~1200mm, pile length ≤ 30m, bearing capacity ≤ 3000kN), the prefabricated retaining structure is easy to install and can shorten the on-site construction period. For municipal and transportation infrastructure (bridge abutment piles, ramp piles, underground pipe gallery support piles), maintenance can be carried out through grouting pipes in the later stage, with good durability and the ability to adapt to long-term loads and environmental erosion. For water conservancy and port projects (inland river wharves, docks, irrigation pumping stations), PVC pipes have good waterproof performance, can isolate long-term immersion corrosion by groundwater or river water, and are lightweight, making underwater installation easy.

[0051] 6. This invention is equipped with grouting holes, which can be used for inspection and repair at any time during the operation of the cast-in-place pile. Grouting reinforcement is low-cost and simple to operate, avoiding the major losses that traditional cast-in-place piles cannot be repaired once corrosion or cracks occur and need to be replaced as a whole, thus significantly reducing the maintenance cost throughout the entire life cycle. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the structure of an anti-corrosion cast-in-place pile proposed in this invention;

[0053] Figure 2 This is a perspective view of a corrosion-resistant cast-in-place pile ring segment unit proposed in this invention;

[0054] Figure 3 This is a schematic diagram of the structure of a corrosion-resistant cast-in-place pile ring segment unit proposed in this invention;

[0055] Figure 4 This is a cross-sectional view of a corrosion-resistant cast-in-place pile retaining structure proposed in this invention;

[0056] Figure 5 This is a partial perspective view of a corrosion-resistant cast-in-place pile retaining structure proposed in this invention;

[0057] Figure 6 This is a top view of an anti-corrosion grouting pile shoe proposed in this invention;

[0058] Figure 7 This is a schematic diagram of the structure of an anti-corrosion grouting pile shoe proposed in this invention;

[0059] Figure 8 This is a bottom view of a corrosion-resistant cast-in-place pile shoe proposed in this invention.

[0060] Explanation of reference numerals in the attached figures:

[0061] 1. Enclosure structure,

[0062] 2. Ring segment unit,

[0063] 3. PVC board,

[0064] 4. Grouting pipe,

[0065] 5. Anti-corrosion film,

[0066] 6. Main reinforcement bars,

[0067] 7. Stirrups,

[0068] 8. Pile boots,

[0069] 9. Pile tip,

[0070] 10. Steel casing slot,

[0071] 11. Circular rubber pad,

[0072] 12. Concrete

[0073] 13. Rebar rust inhibitor,

[0074] 14. Reinforcing cage spacers. Detailed Implementation

[0075] The specific embodiments of the present invention are described below with reference to the accompanying drawings and examples:

[0076] It should be noted that the structures, colors, proportions, sizes, etc. shown in the accompanying drawings are only used to complement the content disclosed in the specification, so that those skilled in the art can understand and read them, and are not intended to limit the conditions under which the present invention can be implemented. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0077] At the same time, in the description of the present invention, it should be understood that the terms "one end", "the other end", "middle", "upper", "side", "top", "inner", "front", "center", "both ends", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0078] Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," "third," or "fourth" may explicitly or implicitly include at least one of those features.

[0079] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," "connection," "fixing," "screw connection," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0080] This embodiment provides a corrosion-resistant cast-in-place pile for use in highly corrosive environments (such as saline soil areas in Xinjiang and Gansu), suitable for overhead power transmission line foundations, industrial and civil building pile foundations, municipal transportation infrastructure, water conservancy and port projects, etc. The pile diameter is 500~1200mm, the pile length is ≤30m, and the vertical bearing capacity of a single pile is ≤3000kN.

[0081] Specifically, it includes a retaining structure 1, which uses prefabricated PVC pipes as the outer protective layer of the cast-in-place piles. Utilizing the excellent acid, alkali, and salt corrosion resistance of PVC material, it physically isolates groundwater and soil from corrosive ions such as Cl⁻ and SO₄²⁻, preventing them from contacting the reinforced concrete 12. The retaining structure 1 is fabricated in segments, divided into n equal-length PVC ring segment units 2. The length of each ring segment unit 2 is adjusted according to project requirements.

[0082] Each ring segment 2 consists of at least three identical PVC panels 3. During fabrication, the PVC panels 3 are first joined together to form the cylindrical foundation outline of the cast-in-place pile. Then, using a plastic welding gun, PVC welding rods are used to fill the joints between adjacent PVC panels 3 and heat-weld them. The weld width is ≥10mm to ensure the sealing and integrity of the ring segment. After welding, the outer ring forms a smooth cylindrical surface, and its outer diameter is the designed diameter of the pile body. This structure has advantages such as simple processing, good integrity, and strong corrosion resistance.

[0083] The joints of adjacent ring units 2 are welded using socket welding. One end of the inner wall of ring unit 2 has a groove, and the other end has a rubber ring. When two ring units 2 are joined, the rubber ring of one ring unit 2 is inserted into the groove of the other ring unit 2. The joints of adjacent PVC panels 3 are welded using lap welding. All welds must be waterproofed and corrosion-resistant to prevent corrosive media from penetrating.

[0084] The ring unit 2 is equipped with a grouting system, which includes grouting pipes 4 arranged longitudinally along the pile body. The grouting pipes 4 are made of rigid PVC pipes and are installed between adjacent PVC panels 3. During fabrication, a PVC panel 3 is heat-fused and welded between two grouting pipes 4, which serves both as a fixation tool and enhances the circumferential stiffness of the retaining structure 1. The holes are positioned to avoid the location of the main reinforcing bars 6 of the steel cage.

[0085] The top of the grouting pipe 4 (i.e., the outside of the grouting hole) is covered with sealing tape to prevent grout from entering and clogging the grouting channel when concrete 12 is poured. After concrete 12 is poured and cured, and when subsequent grouting reinforcement is required, the sealing tape is removed or punctured, and the grouting equipment is connected for grouting operations. This achieves the dual function of "preventing blockage during construction and maintainingability during operation," significantly improving the later repairability of the pile foundation.

[0086] An anti-corrosion film 5 is adhered to the inner wall of the pipe in the retaining structure 1 using an air pump, serving as a second physical anti-corrosion layer. During construction, the retaining structure 1 is first lowered to the designated design position. Then, the anti-corrosion film 5 is adhered to the inner wall of the pipe using an air pump. After the anti-corrosion film 5 is applied, the reinforcing cage is hoisted to the designated position inside the pile hole, followed by underwater concrete 12 pouring. This anti-corrosion film 5 is suitable for projects with extremely high corrosion levels or special durability requirements, and can further extend the service life of the pile.

[0087] The reinforcing cage includes main bars 6, stirrups 7, and grouting sleeves. Main bars 6 are made of HRB400 grade steel (or epoxy resin coated steel), and stirrups 7 are made of HPB300 grade steel. The grouting sleeve is a φ20mm seamless steel pipe, its length adjusted according to the length of the grouting pipe 4. One end of the grouting sleeve is welded to the reinforcing cage at the position corresponding to the grouting hole, and the other end is ground into a pointed shape to quickly pierce the sealing tape during subsequent grouting. The grouting sleeve corresponds to the grouting pipe 4, ensuring unobstructed grouting channels.

[0088] The pile body concrete 12 uses C40 or higher grade anti-corrosion high-performance concrete 12, with a water-cement ratio ≤0.45, and incorporates fly ash, mineral powder, and steel reinforcement corrosion inhibitor 13. The slump is controlled at 180~220mm (to meet underwater casting requirements). Depending on the type of corrosion (such as chloride corrosion, sulfate corrosion, etc.), the concrete 12 mix proportion and corrosion inhibitor addition amount can be dynamically adjusted to meet the durability requirements under different highly corrosive environments. This concrete 12 has high density, low permeability, and excellent corrosion resistance.

[0089] During the sinking of the cast-in-place piles, pile shoes 8 are installed at the outer end of the retaining structure 1 to adapt to soft geological conditions. Specifically, the pile shoe 8 is a pile tip 9 welded from a cross-shaped plate, used for breaking and compacting the soil to facilitate the later installation of the anti-corrosion membrane 5. A steel casing groove 10 is provided at one end near the retaining structure 1. The end of the retaining structure 1 is inserted into the groove during pile sinking and automatically detaches upon removal. A grooved annular rubber pad 11 is installed inside the groove to reduce vibration between the retaining structure 1 and the pile shoe 8 during sinking and to ensure airtightness between the retaining structure 1 and the anti-corrosion membrane 5 during negative pressure operation.

[0090] A construction method for corrosion-resistant cast-in-place piles is applicable to coastal high-chloride salt corrosion environments, inland sulfate / salt-alkali corrosion environments, and weakly acidic corrosion environments. The core process is as follows: hole formation → installation of retaining structure 1 → installation of anti-corrosion membrane 5 and reinforcing cage → underwater concrete pouring 12 → subsequent grouting reinforcement. Specifically, it includes the following steps:

[0091] Step S1: Drilling and cleaning the hole.

[0092] Material and site preparation: Level the construction site and compact it to a bearing capacity of ≥150kPa to ensure stable operation of the drilling rig; set up mud pits and sedimentation tanks, and control the mud specific gravity at 1.1~1.2 (clay wall protection). Select the type of drilling rig according to geological conditions: impact drills are suitable for gravelly soil and weathered rock layers; rotary drills are suitable for soft soil layers such as silty clay and silt.

[0093] Drilling: The drilling method with mud wall protection is used for drilling. After the drilling rig is in place, the verticality is adjusted and the deviation is ≤1%. The allowable deviation of the pile diameter is ±50mm. The hole depth must exceed the designed pile length by 500mm to reserve space for sediment.

[0094] Hole cleaning: A two-stage hole cleaning process is adopted. The first cleaning is carried out after drilling to the designed depth, and before lifting the drill, mud is circulated to replace the sediment at the bottom of the hole, with the sediment thickness ≤100mm. The second cleaning is carried out after the steel cage and retaining structure 1 are installed, the guide pipe is lowered, and mud is sprayed through the guide pipe under high pressure, with the final sediment thickness ≤50mm, the mud sand content ≤2%, and the mud specific gravity controlled at 1.1~1.2.

[0095] Step S2: Installation and fixing of prefabricated enclosure structure 1.

[0096] Pipe segment splicing: Connect the ring unit 2 sections one by one on site, ensuring that the rubber ring of one ring unit 2 is embedded in the groove of another ring unit 2 with an insertion depth of ≥50mm. After splicing, check the joint sealing to ensure that it is sealed and leak-proof and prevents mud from seeping in.

[0097] Lifting into the hole: Use a crane to vertically lift the connected ring segment unit 2 and slowly lower it into the hole. The bottom of the unit is sealed with a 5mm thick steel plate to prevent mud from entering the pipe.

[0098] Anti-buoyancy measures: A counterweight device (sandbag or steel beam) is installed on the top of the retaining structure 1. The counterweight load is ≥ 1.1 times the buoyancy of the retaining structure 1 to prevent the pipe from floating when the concrete 12 is poured.

[0099] Step S3: Installation of anti-corrosion membrane 5 and reinforcing cage.

[0100] After the enclosure structure 1 is lowered to the designated position, an anti-corrosion membrane 5 is adhered to the inner wall of its pipes using an air pump. Specifically, a bag-shaped anti-corrosion membrane 5 is used, with adhesive applied to its surface, sealed at the bottom, and open at the top. Air is injected into the membrane using a compressed air pump, causing it to expand and adhere tightly to the inner wall of the enclosure structure 1. After the adhesive has cured, the top of the membrane is fixed to the top of the enclosure structure 1 using clamps. This membrane installation process is simple to operate, provides a tight fit, and effectively forms a continuous anti-corrosion layer.

[0101] After the anti-corrosion film 5 is applied, the reinforcing cage is hoisted to the designated position inside the pile hole, kept vertical, and lowered to the design elevation before being fixed. The grouting sleeves on the reinforcing cage correspond one-to-one with the grouting pipes 4 on the retaining structure 1 to ensure unobstructed grouting channels for subsequent grouting.

[0102] Step S4: Underwater concrete pouring 12.

[0103] Conduit installation: The conduit is made of φ250mm seamless steel pipe, and the joint is connected by thread and sealed; the bottom of the conduit is 300~500mm from the bottom of the hole, and the top is 2m above the concrete pouring surface.

[0104] Pouring operation: Continuous pouring is adopted using the tremie pipe method. The initial pour of concrete must meet the requirement that the tremie pipe is buried at a depth of ≥1.0m. During the pouring process, the tremie pipe burial depth is controlled between 2 and 6m. It is strictly forbidden to pull out the tremie pipe. The concrete pouring surface must be 500 to 1000mm higher than the designed pile top elevation (for later removal of laitance).

[0105] Venting and grouting: During pouring, the sealing tape on the grouting pipe 4 can be opened intermittently to release air and excess grout from the grouting pipe 4, ensuring the compactness of the concrete 12. This operation uses the grouting pipe 4 as a venting channel, avoiding quality defects such as honeycomb and voids caused by gas retention in traditional construction.

[0106] Curing: After concrete 12 is poured, cover it and keep it moist for curing. The curing time is ≥14 days (the curing period for anti-corrosion concrete 12 needs to be extended).

[0107] Step S5: Post-treatment grouting reinforcement (optional, depending on test results)

[0108] 28 days after pile completion, the integrity of the pile body is tested using the low-strain reflected wave method; if defects such as insufficient protective layer or microcracks are found, grouting reinforcement is required.

[0109] Grouting is performed using pre-embedded grouting pipes 4: connect the high-pressure grouting pump to grouting pipe 4, control the grouting pressure at 0.5~1.0MPa, and use either epoxy resin grout (for crack repair) or cement-based penetrating crystalline grout (for corrosion protection and reinforcement). Grouting is carried out in a single pipe until the grout overflows from the adjacent grouting pipe 4, then the grouting valve is closed, and the pressure is maintained for 10 minutes. The purpose of grouting is to fill the gap between the pile and the PVC pipe, increase the pile side friction, form a secondary anti-corrosion layer, repair micro-cracks in the concrete, and further extend the service life of the pile.

[0110] The typical application scenarios of this invention are:

[0111] 1. Coastal high-chlorine salt corrosion scenario.

[0112] This invention is applicable to coastal wharves, cross-sea bridges, coastal industrial plants, and island buildings. High concentrations of Cl⁻ in seawater and saline soil easily cause steel reinforcement corrosion. The PVC enclosure structure 1 of this invention can physically isolate corrosive media; subsequent injection of anti-corrosion grout through grouting holes can repair micro-cracks and extend the life of the pile foundation (by more than 30% compared to traditional cast-in-place piles). If located in the intertidal zone (with periodic wet-dry alternation), the joint sealing needs to be strengthened.

[0113] 2. Inland sulfate / salt corrosion scenarios in Xinjiang, Gansu, Qinghai and other inland areas.

[0114] This invention is applicable to overhead power transmission lines, industrial and civil buildings, municipal transportation, water conservancy and port projects in saline soil regions such as Xinjiang, Gansu, and Qinghai. Traditional open-cut foundations require dewatering, involve large construction surfaces, and present significant environmental and soil conservation issues; this invention overcomes the limitations of soil and water corrosion, improving foundation durability. This solution also offers advantages such as convenient installation, shorter on-site construction time, and strong maintainability.

[0115] 3. Scenarios with weak acid corrosion.

[0116] Suitable for acid rain mountainous areas, acidic water areas in coal mine goaf, and acidic clay layers rich in organic matter. Ordinary rigid PVC pipes can withstand weakly acidic environments with pH 4~6; if pH < 4, simply replace PVC board 3 with UPVC board 3 for compatibility, which is much cheaper than the stainless steel casing solution.

[0117] To ensure the safety and reliability of the retaining structure 1 during the construction and operation phases, it is necessary to verify the circumferential compressive strength and the spacing of the grouting holes.

[0118] During the construction phase (concrete 12 pouring), the outer side of the retaining structure 1 is subjected to the pressure of the borehole wall mud, and the inner side is subjected to the lateral pressure of the newly poured concrete 12, which is the most unfavorable working condition of bidirectional pressure.

[0119] The formula for verifying circumferential compressive strength is as follows: ;

[0120] In the formula:

[0121] The circumferential stress is (MPa).

[0122] The allowable short-term compressive stress for rigid PVC pipes is 30~40MPa in this embodiment (refer to GB / T 2040-2008).

[0123] The maximum radial pressure (MPa) is taken as the larger value between the concrete 12 lateral pressure and the mud pressure. The formula for calculating the concrete 12 lateral pressure is as follows: ;

[0124] The outer diameter (mm) of the enclosure structure 1 pipe;

[0125] The wall thickness (mm) of the enclosure structure 1 pipe body must be ≥8mm;

[0126] Taking a pile diameter of 800mm, a retaining structure 1 pipe body outer diameter of 750mm, and a retaining structure 1 pipe body wall thickness of 10mm as an example, the calculation is as follows:

[0127] =24kN / m3, =5h, =1.0, =1.0, so the side pressure of concrete 12 is: P=0.22×24×5×1×1=26.4kPa.

[0128] Then circumferential stress =990kPa=0.99MPa<30MPa, which meets the requirements.

[0129] In addition, the sealing performance of the pipe joints needs to be checked separately, and the pull-out resistance of the socket-type rubber rings should be no less than 1.2 times the buoyancy of the enclosure structure to prevent the joints from coming apart.

[0130] The spacing between grouting holes must simultaneously meet the dual requirements of air venting and grout drainage during construction and subsequent grouting reinforcement. A reasonable spacing is determined by verifying the grout diffusion radius.

[0131] The longitudinal spacing L must satisfy L≤2R, where L is the longitudinal spacing and R is the effective diffusion radius of the grout, to ensure that the pile body forms a continuous anti-corrosion grouting layer.

[0132] Based on the grouting pressure (0.5~1.0MPa) and formation conditions, the following empirical formulas are used for calculation:

[0133] ;

[0134] In the formula:

[0135] The grouting pressure is preferably 0.5~1.0 MPa in this embodiment;

[0136] The radius of the grouting sleeve,

[0137] The permeability coefficient is taken as 10⁻⁶ to 10⁻⁷ cm / s for silty clay and 10⁻³ to 10⁻⁴ cm / s for sand.

[0138] The specific gravity of water is taken as 10 kN / m³.

[0139] i represents the hydraulic gradient, which is preferably 1.0 to 1.5 in this embodiment.

[0140] The grouting hole spacing determined by the above calculations can ensure that a continuous anti-corrosion grouting layer is formed in the pile body, achieving the expected reinforcement effect.

[0141] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

[0142] Many other changes and modifications can be made without departing from the concept and scope of this invention. It should be understood that this invention is not limited to the specific embodiments, and the scope of this invention is defined by the appended claims.

Claims

1. A corrosion-resistant cast-in-place pile, Its features are, Include: Enclosure structure (1), wherein the enclosure structure (1) is formed by sequentially connecting several ring segments (2) of equal length; The ring unit (2) is formed by connecting and welding at least three PVC plates (3) to form a cylindrical outline. The joint between adjacent PVC plates (3) is filled with PVC welding rods and heated and welded. The weld width is ≥10mm. After welding, the outer ring of the enclosure structure (1) forms a smooth cylindrical surface, and its outer diameter is the design diameter of the grouting pile body. The adjacent ring segments (2) are welded together by socket welding, and the joints of the adjacent PVC panels (3) are welded together by lap welding. All welds are treated with waterproof and anti-corrosion measures. The retaining structure (1) is equipped with a grouting system, which includes a number of grouting pipes (4) arranged longitudinally along the pile body. The grouting pipes (4) are arranged between adjacent PVC panels (3), and the top of the grouting pipes (4) is covered with sealing tape. The inner wall of the enclosure structure (1) is covered with an anti-corrosion film (5) by means of an air pump, and the anti-corrosion film (5) serves as a second physical anti-corrosion layer. The enclosure structure (1) is equipped with a steel cage, which includes main bars (6), stirrups (7) and grouting sleeves. The position of the grouting sleeves corresponds to the position of the grouting pipes (4). The outer end of the retaining structure (1) is provided with a pile shoe (8). The pile shoe (8) includes a pile tip (9) welded from a cross plate and a steel casing groove (10). An annular rubber pad (11) is provided inside the steel casing groove (10). The steel casing groove (10) of the pile shoe (8) is located at one end close to the retaining structure (1). When the retaining structure (1) sinks, its end is inserted into the groove and can automatically detach when pulled out.

2. The corrosion-resistant cast-in-place pile as described in claim 1, Its features are, The cast-in-place piles are cast with high-performance anti-corrosion concrete (12), the water-cement ratio of the concrete (12) is ≤0.45, and fly ash, mineral powder and steel reinforcement rust inhibitor (13) are added. The high-performance anti-corrosion concrete (12) has a strength grade ≥ C40 and a slump of 180~220mm.

3. A corrosion-resistant cast-in-place pile as described in claim 1, Its features are, The grouting sleeve of the steel cage is made of φ20mm seamless steel pipe. One end is welded to the steel cage at the position corresponding to the grouting pipe (4), and the other end is ground into a pointed shape.

4. A corrosion-resistant cast-in-place pile as described in claim 1, Its features are, The pile shoe (8) is provided with a steel cage pad (14) on its side, and the position of the steel cage pad (14) corresponds to the position of the steel cage.

5. A corrosion-resistant cast-in-place pile as described in claim 1, Its features are, The inner wall of one end of the ring segment unit (2) is provided with a groove, and the outer side of the other end is provided with a rubber ring. When multiple ring segment units (2) are connected, the rubber ring of one ring segment unit (2) is inserted into the groove of another ring segment unit (2).

6. A construction method for corrosion-resistant cast-in-place piles, employing a corrosion-resistant cast-in-place pile as described in any one of claims 1 to 5. Its features are, Includes the following steps: Step S1: Drill holes using the mud-wall drilling method and perform secondary hole cleaning; Step S2: Connect the ring segment units (2) section by section and hoist them into the holes, and set a counterweight device on the top of the enclosure structure (1) to prevent buoyancy; Step S3: After the enclosure structure (1) is lowered into place, an anti-corrosion film (5) is pasted on its inner wall by an air pump, and then the steel cage is hoisted and fixed. Step S4: Concrete is continuously poured using the duct method (12). During the pouring process, the sealing tape on the grouting pipe (4) is opened intermittently to release air and grout. Curing is carried out after pouring. Step S5: Based on the test results of the integrity of the cast-in-place pile, grouting is performed using the grouting pipe (4).

7. The construction method for corrosion-resistant cast-in-place piles as described in claim 6, Its features are, In step S1, the thickness of sediment at the bottom of the hole after the first cleaning is ≤100mm, the thickness of sediment after the second cleaning is ≤50mm, the sand content of the mud is ≤2%, and the mud specific gravity is controlled at 1.1~1.

2.

8. The construction method for corrosion-resistant cast-in-place piles as described in claim 6, Its features are, In step S2, the load of the counterweight device is greater than or equal to 1.1 times the buoyancy of the enclosure structure (1).

9. The construction method for a corrosion-resistant cast-in-place pile as described in claim 6, Its features are, In step S5, when grouting is performed using the grouting pipe (4), the grouting pressure is controlled at 0.5~1.0MPa. The grout is selected as epoxy resin grout or cement-based penetrating crystallizing grout. Grouting is performed in a single pipe until the grout overflows from the adjacent grouting pipe (4), and the pressure is maintained for 10 minutes.

10. The construction method for corrosion-resistant cast-in-place piles as described in claim 6, Its features are, The construction method is applicable to coastal high chloride salt corrosion environment, inland sulfate / salt-alkali corrosion environment and weak acid corrosion environment; when the pH of the corrosion environment is less than 4, the PVC board (3) is replaced with UPVC board.

Images