A method of casting for a pile foundation

Abstract

The application discloses a pouring method for a pile foundation, and relates to the technical field of pile foundation pouring, and comprises the following steps: S1, welding a plurality of embedded steel rings on the outer side of the slope protection pile main reinforcement, the steel rings are bent from HRB400 steel bars, the outer diameter is 50-80 mm, and the welding seam length is not less than 5d; S2, pouring pile body concrete and marking a positioning mark on the outer side of the steel ring, so that the end of the steel ring is located in the concrete protective layer; S3, after the concrete strength reaches the design value, the exposed steel ring is chiseled and connected with the wall protection steel mesh by full welding; and S4, pouring wall C20 fine stone concrete, the wall thickness is 80 mm, and the two-way reinforcement is Φ8@150*150; the embedded steel rings on the outer side of the slope protection pile main reinforcement are welded and connected with the wall protection steel mesh, an integrated stress system of the pile body and the wall is formed, and the traditional post-positioned expansion bolt process is effectively replaced.

Description

Technical Field

[0001] This invention relates to the field of pile foundation casting technology, specifically to a method for casting pile foundations. Background Technology

[0002] Currently, in the construction of foundation pit support and soil retaining wall between piles under the capping beam, the traditional process of connecting the retaining wall with post-installed expansion bolts is often used. This process requires drilling holes in the surface of the pile body and inserting expansion bolts after the pile concrete has been poured and reached a certain strength. The bolts are then connected to the retaining wall steel mesh to form an integral structure. Although this method has rich construction experience, it has obvious defects: the drilling process is prone to damaging the protective layer of the pile body, forming micro-cracks and seepage channels. The expansion bolts have limited bonding force with the concrete interface under tension or shear, and are prone to slippage or pull-out failure. In addition, due to the difficulty in controlling the drilling accuracy on site, the bolt placement position is greatly deviated, resulting in insufficient connection stiffness between the retaining wall and the pile body and discontinuous overall stress, which affects the durability and seepage prevention performance of the structure.

[0003] To address these issues, some projects have attempted to use chemical anchors or sleeve-type rebar connections. However, these methods still require secondary drilling or grouting after the pile body has hardened, resulting in complex construction procedures and long construction cycles. Chemical anchors are prone to bonding failure or aging and cracking in humid environments, and the volatilization of chemicals is detrimental to the construction environment, making it difficult to guarantee long-term structural stability. In summary, existing pile wall connection technologies still suffer from drawbacks such as complex construction, uneven stress distribution, poor impermeability, and high maintenance costs. There is an urgent need for an integrated connection process that can achieve stable pre-embedding during the pile casting stage, is easy to construct, and has reliable stress distribution, in order to improve the integrity and safety of the support structure. Summary of the Invention

[0004] This invention provides a method for pouring concrete for pile foundations, which can effectively solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for pouring concrete for pile foundations, comprising the following steps:

[0006] S1. Weld several pre-embedded steel rings on the outside of the main reinforcement of the slope protection pile. The steel rings are made of HRB400 steel bars with an outer diameter of 50-80mm and a weld length of not less than 5d.

[0007] S2. Pour the pile concrete and mark the positioning mark on the outside of the reinforcing ring to ensure that the end of the reinforcing ring is inside the concrete cover.

[0008] S3. After the concrete strength reaches the design value, the exposed steel rings are removed and fully welded to the retaining wall steel mesh.

[0009] S4. Pour C20 fine aggregate concrete for the retaining wall, with a thickness of 80mm and bidirectional reinforcement of Φ8@150×150.

[0010] The shear bearing capacity of the pile wall connection zone is determined by the following formula:

[0011]

[0012] In the formula, Where n is the shear capacity (kN) and n is the number of steel reinforcement rings. The yield strength of the steel reinforcement (MPa) Cross-sectional area of ​​a single reinforcing bar ring (mm²) 2 ), θ is the angle of force on the ring; Additional load-bearing items for bending;

[0013] By pre-embedding steel reinforcement rings, the pile body and the retaining wall can be subjected to overall stress, thereby improving shear strength and seepage prevention performance.

[0014] According to the above technical solution, the steel bar ring in S1 is treated with epoxy resin for corrosion protection after welding, and the coating thickness is 0.5-1mm;

[0015] When pouring concrete, layered vibration should be used, with a vibration spacing of ≤300mm.

[0016] A 5-10mm thick impermeable mortar layer is installed at the contact surface between the retaining wall and the pile body.

[0017] According to the above technical solution, the tensile bearing capacity of the node is calculated using the following formula:

[0018]

[0019] in The tensile strength is δ, the weld displacement is r, and the ring radius is r. When δ≤1mm, the tensile strength loss does not exceed 5%. The position error of the reinforcing ring is controlled to be ≤5mm using a three-point laser positioning instrument.

[0020] According to the above technical solution, after the S3 retaining wall is poured, a seepage resistance test is conducted, and the permeability coefficient K is calculated according to Darcy's law:

[0021]

[0022] Where Q is the seepage flow rate, A is the seepage area, t is the time, h is the head, and the measured K value is ≤1×10⁻⁶. -9 m / s, meeting the P8 grade impermeability requirements.

[0023] According to the above technical solution, S3 provides reinforcing ribs Φ10 with a length of 200mm in the connection area between the pile body and the retaining wall to reduce stress concentration in the weld and the local stress concentration coefficient of the weld. The calculation is as follows:

[0024]

[0025] Where a is the radius of the weld defect and r is the radius of the ring.

[0026] According to the above technical solution, S2 adopts a segmented continuous pouring process during the concrete pouring of the pile body, with each segment not exceeding 6m in length. After the pouring is completed, secondary vibration is immediately carried out to eliminate settlement voids.

[0027] To prevent the reinforcing steel ring from shifting during pouring, a three-dimensional positioning jig is used to fix it in advance, with the positioning accuracy controlled within ±2mm.

[0028] After the concrete is poured, the position of the reinforcing bar ring should be checked using an infrared scanner. If the deviation exceeds 5mm, it should be corrected.

[0029] According to the above technical solution, S3 improves the stress coordination between the pile body and the retaining wall. The steel rings on the outside of the main reinforcement of the pile body are arranged in an adjacent staggered manner along the pile height direction, with a staggered spacing of not less than 200mm, so as to avoid stress concentration at the same cross section.

[0030] After the steel mesh for the wall is welded, post-heat treatment is applied to the weld area to reduce the residual stress of the weld to less than 40% of the initial value.

[0031] According to the above technical solution, the interface between the retaining wall and the pile body adopts a composite seepage prevention structure. First, a layer of epoxy waterproof primer with a thickness of 0.5mm is brushed on the surface of the pile body, and then a 0.8mm thick self-adhesive waterproof membrane is laid.

[0032] According to the above technical solution, after the completion of the S4 construction, a loading test is carried out on the pile wall connection area. The loading process adopts a multi-level loading method, with a loading ratio of 1.0-1.5 times the design bearing capacity, and each level is maintained for 10 minutes.

[0033] According to the above technical solution, this method is applicable to various capping beam or foundation pit support projects with pile diameters of 600-1200mm, pile spacing of 1.5-2.5m, and retaining wall thickness of 60-120mm.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention has a scientific and reasonable structure, is safe and convenient to use. By pre-embedding steel rings on the outside of the main reinforcement of the slope protection pile and welding them to the steel mesh of the retaining wall, an integrated force-bearing system of the pile body and the retaining wall is formed, effectively replacing the traditional post-installed expansion bolt process. This structure makes the force path of the connection area continuous, and the shear force and tensile force are evenly transmitted to the main reinforcement of the pile body through the steel rings, which greatly improves the shear, tensile and bending resistance of the joint. No secondary drilling is required during construction, avoiding damage to the concrete protective layer, significantly improving the seepage prevention performance and durability. The process is simple, the positioning accuracy is high, and it is convenient for quality control and subsequent maintenance. Attached Figure Description

[0035] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0036] In the attached diagram:

[0037] Figure 1 This is a schematic diagram of the method steps of the present invention;

[0038] Figure 2 This is a schematic diagram of the installation structure of the present invention. Detailed Implementation

[0039] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0040] Example: Figure 1-2 As shown, the present invention provides a technical solution: a method for pouring concrete for pile foundations, comprising the following steps:

[0041] S1. Weld several pre-embedded steel rings on the outside of the main reinforcement of the slope protection pile. The steel rings are made of HRB400 steel bars with an outer diameter of 50-80mm and a weld length of not less than 5d.

[0042] S2. Pour the pile concrete and mark the positioning mark on the outside of the reinforcing ring to ensure that the end of the reinforcing ring is inside the concrete cover.

[0043] S3. After the concrete strength reaches the design value, the exposed steel rings are removed and fully welded to the retaining wall steel mesh.

[0044] S4. Pour C20 fine aggregate concrete for the retaining wall, with a thickness of 80mm and bidirectional reinforcement of Φ8@150×150.

[0045] The shear bearing capacity of the pile-wall connection zone is determined by the following formula:

[0046]

[0047] In the formula, Where n is the shear capacity (kN) and n is the number of steel reinforcement rings. The yield strength of the steel reinforcement (MPa) Cross-sectional area of ​​a single reinforcing bar ring (mm²) 2 ), θ is the angle of force on the ring; Additional load-bearing items for bending;

[0048] This method achieves overall stress distribution between the pile and the retaining wall by pre-embedding steel reinforcement rings, thereby improving shear strength and seepage prevention performance.

[0049] Furthermore, after welding, the reinforcing steel ring in S1 is treated with epoxy resin for corrosion protection, with a coating thickness of 0.5-1mm;

[0050] When pouring concrete, layered vibration should be used, with a vibration spacing of ≤300mm.

[0051] A 5-10mm thick impermeable mortar layer is installed at the contact surface between the retaining wall and the pile body;

[0052] The shear strain γ and shear stress τ in the nodal region satisfy:

[0053]

[0054] When G=8×10 4 MPa and γ≤1.2×10 -3 At that time, the pile wall node operates in the elastic stage.

[0055] Furthermore, the tensile bearing capacity of the joint is calculated using the following formula:

[0056]

[0057] in The tensile strength is δ, the weld displacement is r, and the ring radius is r. When δ≤1mm, the tensile strength loss does not exceed 5%. The position error of the reinforcing ring is controlled to be ≤5mm using a three-point laser positioning instrument.

[0058] Furthermore, after the S3 retaining wall was poured, a permeability test was conducted, and the permeability coefficient K was calculated according to Darcy's law:

[0059]

[0060] Where Q is the seepage flow rate, A is the seepage area, t is the time, h is the head, and the measured K value is ≤1×10⁻⁶. -9 m / s, meeting the P8 grade impermeability requirements.

[0061] Furthermore, S3 incorporates reinforcing ribs of Φ10, 200mm in length, at the connection zone between the pile and the retaining wall to reduce stress concentration in the weld and decrease the local stress concentration factor of the weld. The calculation is as follows:

[0062]

[0063] Where a is the radius of the weld defect and r is the radius of the ring;

[0064] When a≤0.5mm, Kt≤1.2, the fatigue life of the node is increased by more than 30%.

[0065] Furthermore, during the concrete pouring process of the pile body, S2 adopts a segmented continuous pouring process, with each segment not exceeding 6m in length. After pouring, secondary vibration is carried out immediately to eliminate settlement voids.

[0066] To prevent the reinforcing steel ring from shifting during pouring, a three-dimensional positioning jig is used to fix it in advance, with the positioning accuracy controlled within ±2mm.

[0067] After the concrete is poured, the position of the reinforcing bar ring should be checked using an infrared scanner. If the deviation exceeds 5mm, it should be corrected.

[0068] Comprehensive bearing capacity of pile wall connection system Considering the combined effect of the shear force of the reinforcing steel ring and the bond force of the concrete, the calculation formula is as follows:

[0069]

[0070] Where β is the interfacial adhesion correction coefficient (0.6-0.8). denoted as ρ, where b is the tensile strength of the concrete, ρ is the width of the joint, and h is the thickness of the retaining wall.

[0071] When the wall thickness is 80mm and the concrete grade is C20, the actual measurement... The improvement of approximately 22% compared to traditional expansion bolt joints indicates that the pre-embedded steel ring connection system exhibits excellent load-bearing capacity and overall stiffness in the shear zone.

[0072] Furthermore, S3 improves the stress coordination between the pile body and the retaining wall. The steel rings on the outside of the main reinforcement of the pile body are arranged in an adjacent staggered manner along the pile height direction, with a staggered spacing of not less than 200mm, in order to avoid stress concentration at the same cross section.

[0073] After the steel mesh for the retaining wall is welded, post-heat treatment is applied to the weld area to reduce the residual welding stress to less than 40% of the initial value.

[0074] The forces in the pile-wall connection zone are in equilibrium:

[0075]

[0076] in , , These are horizontal force, vertical force, and nodal bending moment, and nodal bending stiffness, respectively. It can be obtained by the following formula:

[0077]

[0078] In the formula The elastic modulus of the steel reinforcement. Let L be the moment of inertia of the annular cross section, and L be the distance between the annular sections.

[0079] The calculation results show that the bending deformation in the node area is reduced by about 30% compared with the traditional expansion bolt method, which significantly improves the overall bending stiffness of the connection.

[0080] Furthermore, the interface between the retaining wall and the pile body adopts a composite seepage-proof structure. First, a layer of epoxy waterproof primer with a thickness of 0.5mm is brushed on the surface of the pile body, and then a 0.8mm thick self-adhesive waterproof membrane is laid.

[0081] When pouring the protective wall, a 5-8mm thick layer of polymer cement mortar should be laid simultaneously at the joints to improve the overall permeability coefficient of the anti-seepage system. Determined by the following formula:

[0082]

[0083] in and Each layer represents its thickness and permeability coefficient (i=1-3);

[0084] =1.0×10 -10 , =5.0×10 -11 , =1.0×10 -9 At that time, a comprehensive result can be obtained. =6.4×10 -11 The flow rate is reduced by about 90% compared to a single-layer structure, effectively eliminating the risk of leakage at joints. This process is suitable for the construction of retaining walls between piles under the cap beam in high-water-level areas.

[0085] Furthermore, after the S4 construction was completed, a loading test was conducted on the pile wall connection area. The loading process adopted a multi-stage loading method, with a loading ratio of 1.0-1.5 times the design bearing capacity, and each stage was maintained for 10 minutes.

[0086] The relationship between shear stress and deformation in the connection zone follows a linear model:

[0087]

[0088] Where V is the shear force, Δ is the relative slip, and k is the connection stiffness. This represents the initial adhesive force.

[0089] Through experimental regression analysis, k = 7.2 × 10⁻⁶ 7 N / m, =2.5×10 3 N;

[0090] Meanwhile, the total energy dissipation in the nodal region can be expressed as:

[0091]

[0092] When Δmax = 1.2 mm, This is 1.35 times that of the traditional structure, indicating that the node has better ductility and energy dissipation capacity under cyclic loads;

[0093] The method has been validated in multiple projects and is suitable for underground engineering projects with complex geology and high seismic resistance.

[0094] Furthermore, this method is applicable to various capping beam or foundation pit support projects with pile diameters of 600-1200mm, pile spacing of 1.5-2.5m, and retaining wall thickness of 60-120mm.

[0095] When the design requires overall shear bearing capacity When the node safety factor η is determined by the following formula:

[0096]

[0097] Where α is an empirical coefficient, ranging from 0.65 to 0.85;

[0098] On-site testing revealed that when n=4, =400MPa =78.5mm 2 b=100mm, h=80mm When the pressure is 1.5 MPa, the calculated value of η is 1.28, which meets the requirement of a design safety factor ≥ 1.2.

[0099] The construction method of the present invention has significant advantages such as simple construction, accurate positioning, reasonable stress distribution, excellent seepage prevention performance, and high long-term durability. It can effectively replace the traditional post-installed expansion bolt connection process and is suitable for various complex strata and high-requirement underground structures.

[0100] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of casting for a pile foundation, characterized by: It comprises the following steps: S1, welding a plurality of embedded steel rings on the outside of the pile main reinforcement, the steel rings are made of HRB400 steel and have an outer diameter of 50-80 mm, and the length of the weld is not less than 5d; S2, pouring pile body concrete and marking the position of the steel rings on the outside of the steel rings to ensure that the end of the steel ring is located in the concrete cover; S3, after the concrete strength reaches the design value, the exposed steel ring is chiseled and fully welded with the wall steel mesh; S4, pouring C20 fine stone concrete for the wall, the wall thickness is 80 mm, and the two-way reinforcement is Φ8@150×150; The shear bearing capacity of the pile wall connection area is determined by the following formula: wherein, is the shear capacity (kN), n is the number of reinforcement rings, is the yield strength of the reinforcement (MPa), is the cross-sectional area of a single reinforcement ring (mm 2 ), θ is the angle of the ring under load; is the bending additional load term; The pile body and the wall are integrally stressed through the embedded steel ring to improve the shear strength and anti-seepage performance; The steel ring after welding in S1 is treated with epoxy resin anticorrosion, and the coating thickness is 0.5-1 mm; During concrete pouring, layered vibration is used, and the vibration interval is ≤300 mm; The contact surface between the wall and the pile body is provided with an anti-seepage mortar layer with a thickness of 5-10 mm; The node tensile bearing capacity is calculated by the following formula: wherein The tensile strength loss is not more than 5% when δ≤1mm, and the position error of the reinforcing ring controlled by the three-point laser positioning instrument is ≤5mm. After the wall pouring in S3 is completed, the anti-seepage test is carried out, and the permeability coefficient K is calculated according to Darcy's law: Where Q is the seepage flow, A is the seepage area, t is the time, h is the water head, the measured K value is ≤1×10 -9 m / s, which meets the P8 grade impermeability requirement; The S3 sets the reinforcing bar Φ10 with the length of 200mm in the pile body and the wall connecting area to reduce the stress concentration of the weld seam, and the local stress concentration coefficient of the weld seam The calculation is as follows: Where a is the weld defect radius, and r is the ring radius; During the pouring of the pile body concrete in S2, the segmented continuous pouring process is used, and each segment is not more than 6 m long, and after pouring is completed, secondary vibration is immediately carried out to eliminate the settlement gap; In order to prevent the steel ring from being displaced during pouring, a three-dimensional positioning jig is used for fixation in advance, and the positioning accuracy is controlled within ±2 mm; After the concrete is poured, an infrared scanner should be used to review the position of the steel ring, and if the deviation is more than 5 mm, it should be corrected; After the construction in S4 is completed, the pile wall connection area is subjected to a loading test, and the multi-level load method is used in the loading process, and the loading ratio is 1.0-1.5 times of the design bearing capacity, and each level is maintained for 10 minutes.

2. A method of casting a pile foundation according to claim 1, wherein The S3 improves the stress coordination between the pile body and the wall, the steel rings on the outside of the pile main reinforcement are arranged in an adjacent staggered manner along the pile height direction, and the staggered interval is not less than 200 mm to avoid concentrated stress in the same section; After the wall steel mesh welding is completed, post-heating treatment is applied to the welded area to reduce the welding residual stress to below 40% of the initial value.

3. A method of casting a pile foundation according to claim 1, wherein The wall and the pile body connection interface adopts a composite anti-seepage structure, a 0.5 mm thick epoxy waterproof primer is first brushed on the surface of the pile body, and then a 0.8 mm thick self-adhesive waterproof roll material is laid.

4. A method of casting a pile foundation according to claim 1, wherein The method is suitable for various crown beam or foundation pit support projects with a pile diameter of 600-1200 mm, a pile spacing of 1.5-2.5 m, and a wall thickness of 60-120 mm.

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