Semi-embracing type expandable inter-pile reinforcing and connecting structure and construction method thereof

Abstract

The invention relates to the technical field of underground engineering supporting construction, and discloses a semi-embracing type expandable inter-pile reinforcing and connecting structure and a construction method thereof.The structure comprises a pair of expandable C-shaped hoops installed on a cast-in-place pile, one end of each C-shaped hoop is a hinged end, the other end of each C-shaped hoop is a locking end, and the outer side of each C-shaped hoop is provided with a connecting rib plate and a guide groove; a plurality of through holes are formed in the connecting rib plate, the connecting rib plate and the guide groove are jointly used for being connected with a reinforcing mesh between the cast-in-place piles, the sprayed concrete layer between the C-shaped hoop and the cast-in-place piles is integrally poured and formed and jointly stressed, and a mechanical meshing structure is formed between the sprayed concrete layer and the C-shaped hoop. The technical problems that an existing inter-pile connecting structure is low in positioning precision, poor in supporting integrity and low in construction efficiency are solved, reliable connection between the pile body and the inter-pile supporting layer is achieved, and the stability and safety of an underground engineering supporting system are improved.

Description

Technical Field

[0001] This invention relates to the field of underground engineering support construction technology, and in particular to a semi-embracing, openable pile reinforcement connection structure and its construction method. Background Technology

[0002] In the construction of underground engineering projects such as subway stations, deep foundation pits, and urban tunnels, bored piles are widely used as the main form of foundation pit retaining structures due to their advantages such as high bearing capacity and good construction adaptability. To prevent soil loosening, water seepage, and local collapse between piles, the engineering community commonly adopts the technique of laying steel mesh between adjacent bored piles and spraying concrete to form a reinforced pile-pile structure. This aims to create a continuous support system between the bored piles and the sprayed concrete layer, thereby resisting soil and water pressure from the outside of the foundation pit and ensuring structural stability during underground engineering construction. However, existing pile reinforcement construction techniques still have many technical defects that urgently need to be addressed, making it difficult to meet the construction requirements and safety standards of large-span bored pile support systems. First, traditional connection methods often involve directly welding the reinforcing mesh to the pile surface or embedding it in a steel plate. Due to factors such as pile misalignment during construction (typically ±15mm), pile roundness error (≥5mm), and insufficient on-site welding precision, gaps of 5-10mm easily form between the reinforcing mesh and the pile. This directly leads to uneven thickness of the shotcrete layer between the piles, with local thickness deviations reaching up to 30%, significantly reducing the overall integrity of the support system and hindering effective load transfer and distribution. Second, the fixation height of traditional connection structures relies heavily on on-site welding operations, and... The narrow construction space between piles not only increases the difficulty of welding operations but also leads to low construction efficiency. Once the pile spacing changes or the pile body is tilted, the positioning error of the steel mesh is difficult to adjust, which can easily cause problems such as cracking and leakage of the sprayed layer. In severe cases, it can even cause the soil between piles to collapse, posing a major threat to the safety of the foundation pit construction. Furthermore, some construction schemes require additional water-stopping devices or sealing layers to achieve the water-stopping effect. This not only makes the construction process more complicated but also extends the construction period by 5 to 7 days. Moreover, the sealing effect is easily affected by the construction quality, making it difficult to guarantee the reliability of the support structure in the long term.

[0003] To address the aforementioned issues, the industry urgently needs a pile connection structure that can be quickly assembled, precisely positioned, and integrally integrated with the shotcrete layer. This would solve the pain points of traditional technologies, such as poor fit, weak integrity, and difficult construction, thereby improving the efficiency and support effect of pile reinforcement construction and ensuring the safety of underground engineering construction. Summary of the Invention

[0004] In view of this, the present invention provides a semi-embracing, openable pile reinforcement connection structure and its construction method to solve the technical problems of low positioning accuracy, poor overall support integrity, and low construction efficiency of existing pile connection structures, thereby achieving a reliable connection between the pile body and the pile support layer and improving the stability and safety of the underground engineering support system.

[0005] On the one hand, the semi-openable pile reinforcement connection structure provided by the present invention includes a pair of openable C-shaped clamps installed on the cast-in-place pile. The inner wall of the C-shaped clamp is an arc shape that matches the outer arc surface of the cast-in-place pile. One end of the C-shaped clamp is set as a hinge end, which is used to realize the opening and closing of the C-shaped clamp. The other end of the C-shaped clamp is set as a locking end, which realizes the closing and fixing of the C-shaped clamp on the outer arc surface of the cast-in-place pile through a bolt assembly. The C-shaped clamp is provided with a connecting rib plate and a guide groove on the outer side near the locking end. The connecting rib plate and the guide groove are used together to connect with the steel mesh between the cast-in-place pile. The shotcrete layer between the C-shaped clamp and the cast-in-place pile is integrally cast and shares the load. The shotcrete layer and the C-shaped clamp form a mechanical interlocking structure.

[0006] Preferably, the inner wall of the C-shaped clamp is provided with a limiting flange at intervals along the longitudinal direction. The limiting flange is integrally formed with the C-shaped clamp to prevent the C-shaped clamp from sliding axially on the outer surface of the cast-in-place pile.

[0007] Preferably, the connecting stiffener and the C-shaped clamp are integrally formed, and the connecting stiffener and the guide groove are respectively connected to the inter-pile steel mesh by welding.

[0008] Preferably, the bolt assembly includes a bolt, a nut, and an elastic washer, the elastic washer being used to compensate for gaps during the bolt tightening process.

[0009] Preferably, the connecting reinforcement plate has a plurality of through holes, which are evenly distributed along the length of the connecting reinforcement plate, and the connecting reinforcement plate is tied to the inter-pile steel mesh through the through holes.

[0010] On the other hand, the pile reinforcement construction method provided by the present invention adopts the semi-embracing, openable pile reinforcement connection structure as described above, and includes the following steps: S1. Pile pretreatment: First, determine the inter-pile support area between adjacent cast-in-place piles, then clean the exposed surface of the cast-in-place piles in this area until fresh concrete base surface is exposed, and finally grind the base surface to control the surface roughness to Ra≤25μm. S2. Clamping installation: Open the semi-clamping C-shaped clamp from the outside of the foundation pit and fit it on the preset position of the outer arc of the cast-in-place pile. Check the levelness of the C-shaped clamp to ensure that the horizontal deviation is ≤3mm. After adjusting it into place, tighten the bolt assembly at the locking end so that the inner wall of the C-shaped clamp is tightly fitted with the outer arc surface of the cast-in-place pile, and the limiting flange is clamped to the surface of the cast-in-place pile. S3. Welded connection: Align the transverse steel bars of the inter-pile steel mesh with the connecting reinforcement plates on the outside of the C-shaped clamp and weld them together. Insert the longitudinal steel bars of the inter-pile steel mesh into the guide groove on the outside of the C-shaped clamp and weld the longitudinal steel bars to the groove wall to ensure that the steel mesh and the C-shaped clamp form an integral load-bearing frame. S4. Shotcrete reinforcement: Shotcrete is applied to the outside of the installed C-shaped clamps and steel mesh. The application is carried out in layers during the spraying process. During spraying, it is ensured that the concrete covers the C-shaped clamps and connecting stiffeners to form a continuous support surface. S5. Curing and Inspection: After the shotcrete construction is completed, water spraying is used for curing to ensure that the concrete strength meets the standard. After curing, the thickness of the sprayed layer is tested. The thickness deviation must be ≤5mm. The bonding strength between the sprayed layer and the pile body and clamp is tested. The bonding strength must be ≥1.5MPa. For areas that do not meet the standard, additional shotcrete is sprayed or the area is re-welded for reinforcement.

[0011] Preferably, before welding in step S3, the welding area of ​​the connecting stiffener and the reinforcing mesh is derusted by sandblasting to remove the surface oxide scale, achieving a derusting grade of Sa2.5, thus preventing rust from affecting the welding quality.

[0012] Preferably, the mix ratio of the sprayed concrete in step S4 is cement:sand:gravel:water = 1:2.2:3.5:0.45.

[0013] Preferably, in step S4, the strength grade of the shotcrete is not lower than C25, the maximum aggregate size is ≤15mm, the spraying pressure is controlled at 0.2~0.4MPa, and the thickness of each sprayed layer is 30~50mm.

[0014] Preferably, step S5 also includes a visual inspection, which involves observing whether there are cracks, hollow areas, or exposed reinforcement defects on the surface of the shotcrete layer. If cracks are found with a width ≥ 0.2 mm, they should be repaired by injecting epoxy resin grout; if hollow areas are found with an area ≥ 0.1 m², they should be repaired accordingly. 2 In the affected area, the hollow parts were removed and then sprayed with concrete again.

[0015] As can be seen from the above technical solution, compared with the prior art, the semi-embracing, openable pile reinforcement connection structure and its construction method provided by the present invention have the following beneficial effects: 1. This invention adopts a semi-embracing, openable structure design. The C-shaped clamp only needs to be opened from the outside of the foundation pit to fit the pile body, which can make the required operating space width ≥300mm, without the need to over-excavate the soil between piles, avoiding the inconvenience of working in the narrow space between piles in traditional construction. At the same time, the clamp can be adapted to the construction deviation of ±10mm of the cast-in-place pile. With the cooperation of a level instrument for detection (horizontal deviation ≤3mm) and the bolt assembly for precise locking, it can achieve a tight fit between the clamp and the pile body (fit deviation ≤2mm), effectively solving the problem of inaccurate positioning caused by pile body deviation and roundness error due to direct welding of steel mesh in traditional construction, shortening the installation time of clamp between single piles and improving construction efficiency. 2. This invention utilizes a rigid connection structure of "C-shaped clamp - connecting stiffener plate - guide groove - steel mesh" to form a stable pre-connection frame between the steel mesh and the pile body. This frame is then integrally cast with the shotcrete layer. The clamp and concrete achieve a dual connection effect of "mechanical interlocking + material bonding." On one hand, the through-hole design of the connecting stiffener plate and the anti-slip texture of the guide groove restrict the lateral and longitudinal displacement of the steel mesh, ensuring no relative slippage between the steel mesh and the clamp. On the other hand, the shotcrete completely covers the clamp and connecting stiffener plate, avoiding the uneven thickness of the shotcrete layer caused by gaps between the steel mesh and the pile body in traditional connections. Actual measurements show that this structure increases the bond strength between the shotcrete layer and the clamp by 15%~20% and the overall shear strength by 25%~30%. It effectively transmits soil and water pressure outside the foundation pit, preventing soil loosening, seepage, or collapse between piles. The maximum displacement of the shotcrete layer during foundation pit excavation can be controlled within 3mm, meeting the safety requirements for deep foundation pit support. 3. The bolt assembly of this invention is equipped with an elastic washer, which can compensate for the bolt tightening gap, effectively prevent bolt loosening caused by vibration during foundation pit construction, and avoid the risk of support failure caused by bolt loosening in traditional connections; the limiting flange and the clamp are integrally formed, which can prevent the clamp from sliding along the pile axis, ensure the stability of the connection position during long-term use, and further improve the structural reliability. 4. This invention eliminates the need for additional water-stopping devices or sealing layers, saving the steps of laying sealing layers and installing water-stopping components in traditional construction. The overall process is simplified, shortening the construction period by 10% to 15%. At the same time, the clamp can be adapted to cast-in-place piles with different diameters of Φ600 to Φ1200mm by adjusting the curvature of the arc-shaped steel plate, eliminating the need to redesign and manufacture molds for different pile diameters, thus reducing mold costs. In addition, the improved construction efficiency and reduced material consumption result in a 8% to 12% reduction in the reinforcement cost between single piles compared to traditional technologies. Significant economic benefits can be achieved in large-span cast-in-place pile support projects such as subway stations and underground integrated pipe corridors. 5. This invention is not only compatible with mainstream cast-in-place pile diameters of Φ600~Φ1200mm, but also allows for flexible adjustment of construction parameters based on the depth of the foundation pit and geological conditions. Furthermore, this structure and construction method can be widely applied to various underground engineering scenarios such as subway stations, underground integrated pipe corridors, and deep foundation pits of high-rise buildings. Whether it is complex geology such as silty clay and pebble layers, or the support requirements of foundation pits at different depths, it can achieve reliable inter-pile reinforcement effects, solving the problem of narrow adaptability of traditional technologies. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the overall assembly of the semi-embracing, openable pile reinforcement connection structure of the present invention. Figure 2 This is a schematic diagram of the C-shaped clamp in its closed state according to the present invention; Figure 3 This is a cross-sectional schematic diagram of the connecting stiffener plate when the C-shaped clamp of the present invention is closed; Figure 4 This is a schematic diagram illustrating the workflow of the pile reinforcement construction method of the present invention.

[0018] Explanation of reference numerals in the attached drawings: 1-cast pile, 2-C-shaped clamp, 21-hinged end, 22-locking end, 23-limiting flange, 3-connecting stiffener, 4-guide groove, 5-steel mesh, 6-bolt assembly, 7-rubber end. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of an exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] Example 1: like Figures 1-3As shown, the semi-embracing, openable pile reinforcement connection structure disclosed in this invention uses an "openable C-shaped clamp 2" as the core carrier, and together with connecting stiffeners 3, guide grooves 4, and bolt assemblies 6, forms an integrated support system of "pile body - C-shaped clamp 2 - steel mesh 5 - shotcrete". The specific structural composition and functions are as follows: C-shaped clamp 2: As the core connection, it is made of Q355B or Q235 steel with a thickness of 8~12mm (selected according to pile diameter and support load; 10~12mm thickness is selected when the pile diameter is ≥Φ1000mm). The inner arc radius matches the pile diameter of cast-in-place pile 1 (suitable for pile diameters of Φ600~Φ1200mm). The surface is treated with hot-sprayed zinc (zinc layer thickness ≥80μm) or epoxy anti-corrosion (coating thickness ≥50μm) to resist groundwater corrosion in the foundation pit and extend its service life. One end of the C-shaped clamp 2 is equipped with a hinge end 21 (connected by a Φ16~Φ20 pin, the pin material is 45 steel, and the surface is chrome-plated for rust prevention), which realizes the flexible opening and closing of the C-shaped clamp 2; the other end is equipped with a locking end 22, which is equipped with an M16~M20 high-strength bolt assembly 6 (bolt material is 40Cr, tensile strength ≥800MPa). The C-shaped clamp 2 is tightly fixed to the pile body by tightening the bolts. In addition, the inner wall of the C-shaped clamp 2 is provided with a 10-15mm high limiting flange 23 (integrated with the C-shaped clamp 2) at longitudinal intervals of 150-200mm, which can prevent the C-shaped clamp 2 from sliding along the pile axis and ensure the stability of the installation position.

[0021] Connecting stiffener 3: Welded to the outside of the C-shaped clamp 2, with a thickness of 6~10mm (matching the thickness of the C-shaped clamp 2; a 6mm stiffener is used when the C-shaped clamp 2 is 8mm thick, and an 8~10mm stiffener is used when the C-shaped clamp 2 is 10~12mm thick), a width of 50~80mm, and a length consistent with the arc length of the C-shaped clamp 2. It is formed by submerged arc welding with the main body of the C-shaped clamp 2, with a weld height ≥5mm, to ensure the welding connection strength with the reinforcing mesh 5. Furthermore, through holes with a diameter of 10~12mm are evenly opened along the length direction of the connecting stiffener 3, with a hole spacing of 50~80mm, to facilitate the welding and / or binding of the transverse reinforcing bars of the inter-pile reinforcing mesh 5 after installation, thereby enhancing the connection reliability between the reinforcing mesh 5 and the C-shaped clamp 2.

[0022] Guide groove 4: Welded to the outside of C-shaped clamp 2 (located between connecting stiffeners 3), it is a circular groove structure with a groove diameter of 20~30mm and a groove depth of 15~20mm. The inner side of the groove wall is provided with anti-slip textures of 1~2mm depth. It is used to insert the longitudinal steel bars of the inter-pile steel mesh 5. After being fixed by welding, it can restrict the lateral displacement of the steel mesh 5 and further improve the overall stress performance.

[0023] Bolt assembly 6: includes bolts, nuts and elastic washers. The elastic washers are made of nitrile rubber (oil-resistant and aging-resistant) with a thickness of 3~5mm. They can compensate for gaps when the bolts are tightened, improve locking stability, prevent bolts from loosening due to vibration during foundation pit construction, and ensure that the C-shaped clamp 2 is in long-term contact with the pile body.

[0024] Based on the above structure, such as Figure 4 As shown, the construction method of this invention consists of five main steps, which are standardized and easy to operate, as detailed below: S1. Pile Pretreatment: First, according to the foundation pit support design drawings, determine the inter-pile support area of ​​adjacent cast-in-place piles 1 (usually within the range of 1.5~3m pile height, adjusted according to the foundation pit depth; 2~3m when the foundation pit depth is ≥20m); then clean the exposed surface of cast-in-place piles 1 in this area. First, use a wire brush (wire diameter 0.3~0.5mm) to manually or mechanically remove surface laitance, cement residue and debris, then use a high-pressure water gun (nozzle diameter 8~10mm) with a pressure of 0.3~0.5MPa to rinse the surface until a fresh concrete base surface is exposed (no laitance, uniform color); finally, use 120~180 grit sandpaper to polish the base surface to control the surface roughness to Ra≤25μm, ensuring that the inner wall of the C-shaped clamp 2 is tightly fitted to the pile surface without gaps.

[0025] S2. Installation of C-shaped clamp 2: Two construction workers cooperate to open the semi-enclosed C-shaped clamp 2 from the outside of the foundation pit (opening angle ≥60°, to facilitate the installation of the pile body), and install it in the preset position on the outer arc of the cast-in-place pile 1 (central area between piles, deviation ≤10mm); use a level with an accuracy of 0.02mm / m to check the levelness of the C-shaped clamp 2, ensuring that the horizontal deviation is ≤3mm, to avoid uneven force due to tilting of the C-shaped clamp 2; after adjustment, use a torque wrench to tighten the bolt assembly 6 of the locking end 22, and control the bolt tightening torque to 30~40N・m (adjust according to the bolt specification, 30N・m for M16 bolts and 40N・m for M20 bolts), so that the inner wall of the C-shaped clamp 2 is tightly fitted with the outer arc surface of the pile body, and the limiting flange 23 is clamped to the surface of the pile body. At this time, the fit deviation between the C-shaped clamp 2 and the pile body is ≤2mm.

[0026] S3. Welding Connection: Before welding, the welding area of ​​the connecting stiffener 3 and the reinforcing mesh 5 is treated with sandblasting (sandblasting pressure 0.5~0.6MPa, sand particle size 0.5~1mm) to remove surface oxide scale, achieving a rust removal grade of Sa2.5 (no visible oxide scale, rust, or dirt on the surface, only slight traces are allowed); then, the transverse reinforcing bars (diameter 12~16mm) of the inter-pile reinforcing mesh 5 are aligned with the through holes of the connecting stiffener 3 on the outside of the C-shaped clamp 2, and CO2 gas shielded welding is used (welding wire diameter 1.2~1.6mm, welding... Full welding is performed for connections with a current of 180~220A and a voltage of 22~26V. The weld thickness is ≥6mm and the weld length is ≥60% of the circumference of the C-shaped clamp 2 (to ensure connection strength). The longitudinal steel bars (diameter 14~18mm) between the piles are inserted into the guide groove 4 on the outside of the C-shaped clamp 2. The longitudinal steel bars are fixed to the groove wall of the guide groove 4 by spot welding. The number of welding points for each section of steel bar is not less than 2 (spacing 150~200mm). After welding, the flatness of the steel mesh 5 is checked. The deviation is ≤5mm to ensure that the steel mesh 5 and the C-shaped clamp 2 form an integral load-bearing frame.

[0027] S4. Shotcrete Reinforcement: Wet spraying process (concrete delivery pressure 0.8~1.2MPa, spraying machine working air pressure 0.5~0.7MPa) is used for shotcrete application. The shotcrete strength grade is not lower than C25, and the mix ratio is cement:sand:aggregate:water = 1:2.2:3.5:0.45 (cement selection...). Ordinary silicate cement, medium sand with a mud content ≤3%, and 5~15mm continuously graded crushed stone with a mud content ≤1% are used. Before spraying, thickness markings (80mm, 100mm, and 120mm grades) are affixed to the outside of the C-shaped clamps 2. During spraying, the work is carried out in layers, with each layer being 30~50mm thick. After each layer is sprayed, the surface is smoothed with a wooden trowel to avoid hollow areas. The total thickness of the sprayed concrete is maintained until the design value (80~120mm, selected according to the depth of the foundation pit; 100~120mm is used when the depth is ≥20m) is reached. During spraying, ensure that the concrete completely covers the C-shaped clamps 2 and the connecting stiffeners 3 to form a continuous and gapless support surface.

[0028] S5. Curing and Inspection: After the shotcrete construction is completed, cover the surface with geotextile (weight ≥200g / m). 2The concrete will be cured using a water spraying method, with a spraying frequency of once every 2 hours (keeping the geotextile moist). The curing time will be no less than 7 days (if the ambient temperature is below 5℃, insulation measures should be taken, and the curing time will be extended to 10 days) to ensure that the concrete strength meets the standards. After curing, three tests will be conducted: ① The thickness of the sprayed layer will be tested using an ultrasonic testing instrument (accuracy ±1mm), and the thickness deviation must be ≤5mm; ② The bond strength between the sprayed layer and the pile body and C-shaped clamp 2 will be tested using a pull-out tester (range 0~100kN), and the bond strength must be ≥1.5MPa; ③ Visual inspection will be conducted to observe whether there are defects such as cracks, hollow areas, and exposed reinforcement on the surface of the sprayed layer. If the crack width is ≥0.2mm, it will be repaired by grouting with epoxy resin grout (ratio of epoxy resin: hardener = 5:1), and the hollow area must be ≥0.1m². 2 After removing the hollow areas (expanding the removal area to 50mm beyond the edge of the hollow area), spray concrete again.

[0029] Example 2: The deep foundation pit project of a station on Metro Line 3 in a certain city has an excavation depth of 22m. Φ800mm bored cast-in-place piles are used as the retaining structure, with a pile length of 35m and a pile spacing of 1.2m. A shotcrete reinforcement support layer (design thickness 100mm, concrete strength grade C25) needs to be installed between the piles. The geological conditions are silty clay (layer thickness 5~8m) + gravel layer (layer thickness 10~12m), with a groundwater level depth of 3m. It is necessary to ensure that the seepage resistance and shear strength of the support layer between the piles meet the standards and to prevent the loss of soil from the gravel layer.

[0030] Based on the engineering conditions, the structural component parameters selected in this embodiment are shown in Table 1 below: Table 1 Key Parameters of Structural Components

[0031] The construction process follows the construction method of this invention, and the specific implementation steps are as follows: S1. Pile pretreatment: The support area between piles is determined to be within the range of 2-3m in pile height (corresponding to an excavation depth of 19-20m, which is a critical stress area); the laitance on the surface of pile 1 is removed by using a wire brush, and after rinsing with a high-pressure water gun (pressure 0.4MPa), the base surface is polished with 150-grit sandpaper, and the surface roughness Ra=20μm is tested, which meets the requirements; S2. C-shaped clamp installation: Two construction workers open the C-shaped clamp 2 from the outside of the foundation pit and place it in the center of the outer arc of the cast-in-place pile 1. The horizontal deviation is checked with a level and found to be 2mm. The M18 bolts are tightened using a torque wrench, with the torque controlled at [value missing]. Check the fit between clamp 2 and pile 1. The deviation is 1.5mm. The limiting flange is tightly clamped to the pile body, and there is no risk of slippage. S3. Welding connection: Sandblasting (Sa2.5 grade) is used to remove rust from the welding area of ​​the connecting stiffener plate 3 and the reinforcing mesh 5. The transverse Φ14mm reinforcing bars are inserted into the through holes of the connecting stiffener plate and fully welded with CO2 gas shielded welding (welding wire diameter 1.4mm, current 200A, voltage 24V). The weld thickness is 6mm and the welding length is 300mm (the hoop circumference is 502.4mm, and the welding length accounts for 59.7%, which is close to 60%). The longitudinal Φ16mm reinforcing bars are inserted into the O-shaped guide groove 4, and two spots are welded on each section of reinforcing bars at a spacing of 180mm. After welding, the flatness deviation of the reinforcing mesh 5 is 3mm. S4. Shotcrete reinforcement: Wet spraying process is adopted, with concrete mix ratio of 1:2.2:3.5:0.45, delivery pressure of 1.0MPa, and spraying air pressure of 0.6MPa; spraying is carried out in layers, each layer is 40mm thick, for a total of 3 layers (total thickness of 120mm, 20mm thicker than the design thickness to consider the risk of seepage from the pebble layer). After spraying, the surface is smoothed with a wooden trowel, and the concrete covers the hoop 2 and connecting stiffener 3, with no exposed areas. S5. Curing and Inspection: Cover with geotextile and spray with water for 8 days (ambient temperature 15~20℃). After curing, the following tests are conducted: ① Ultrasonic testing of the sprayed layer thickness, average value 118mm, deviation 2mm; ② Pull-out test of bond strength, average value 1.8MPa; ③ Visual inspection shows no cracks or hollow areas, meeting the requirements.

[0032] After the application of this embodiment, the pile support layer and the cast-in-place pile 1 form an integral force-bearing system. During the excavation of the foundation pit, there is no water seepage or soil loosening between the piles. Through monitoring, the maximum displacement of the sprayed layer is 3mm, which is less than the design limit of 5mm. The shear test shows that the shear strength of the pile support layer reaches 1.2MPa, which meets the engineering requirements and verifies the practicality and reliability of the present invention.

[0033] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A semi-encircling openable inter-pile reinforcement connection structure, characterized by, The utility model provides a kind of pair of openable C-shaped hoop (2) including installation on cast-in-place pile (1), the inner wall of the C-shaped hoop (2) is arc-shaped and matches the outer arc surface of cast-in-place pile (1), one end of the C-shaped hoop (2) is hinged end (21), the hinged end (21) is used to realize the opening and closing of C-shaped hoop (2), the other end of the C-shaped hoop (2) is locking end (22), the locking end (22) is closed and fixed by bolt assembly (6) that C-shaped hoop (2) realizes on the outer arc surface of cast-in-place pile (1); The outer side of the C-shaped hoop (2) is provided with connecting rib plate (3) and guide slot (4) close to locking end (22), connecting rib plate (3) and guide slot (4) are used to connect between the reinforcing mesh (5) between the C-shaped hoop (2) and cast-in-place pile (1), the C-shaped hoop (2) and cast-in-place pile (1) are integrally formed and jointly stressed between the sprayed concrete layer, and the sprayed concrete layer and the C-shaped hoop (2) form a mechanical interlocking structure.

2. The semi-encircling openable intermediate pile reinforcing connection structure according to claim 1, characterized by, The inner wall of the C-shaped hoop (2) is provided with limiting flange (23) along longitudinal direction, limiting flange (23) is integrally formed with C-shaped hoop (2), for preventing C-shaped hoop (2) from sliding along axial direction on the outer surface of cast-in-place pile (1).

3. The semi-encircling openable intermediate pile reinforcing connection structure according to claim 1, characterized by, Connecting rib plate (3) is integrally formed with C-shaped hoop (2), connecting rib plate (3) and guide slot (4) are connected by welding between reinforcing mesh (5) between piles.

4. The semi-encircling openable intermediate pile reinforcing connection structure according to claim 1, characterized by, The bolt assembly (6) includes bolt, nut and elastic washer, the elastic washer is used to compensate the gap during bolt tightening process.

5. The semi-encircling openable intermediate pile reinforcing connection structure according to claim 1, characterized by, A plurality of through holes are formed in the connecting rib plate (3), the plurality of through holes are uniformly distributed along the length direction of the connecting rib plate (3), and the connecting rib plate (3) and the reinforcing mesh (5) between piles are connected by the through holes.

6. A method of pile-to-pile reinforcement construction using the semi-encircling expandable pile-to-pile reinforcement connection structure according to any one of claims 1 to 5, characterized by, The utility model provides a kind of pair of openable C-shaped hoop (2) including installation on cast-in-place pile (1), the inner wall of the C-shaped hoop (2) is arc-shaped and matches the outer arc surface of cast-in-place pile (1), one end of the C-shaped hoop (2) is hinged end (21), the hinged end (21) is used to realize the opening and closing of C-shaped hoop (2), the other end of the C-shaped hoop (2) is locking end (22), the locking end (22) is closed and fixed by bolt assembly (6) that C-shaped hoop (2) realizes on the outer arc surface of cast-in-place pile (1); The outer side of the C-shaped hoop (2) is provided with connecting rib plate (3) and guide slot (4) close to locking end (22), connecting rib plate (3) and guide slot (4) are used to connect between the reinforcing mesh (5) between the C-shaped hoop (2) and cast-in-place pile (1), the C-shaped hoop (2) and cast-in-place pile (1) are integrally formed and jointly stressed between the sprayed concrete layer, and the sprayed concrete layer and the C-shaped hoop (2) form a mechanical interlocking structure. The inner wall of the C-shaped hoop (2) is provided with limiting flange (23) along longitudinal direction, limiting flange (23) is integrally formed with C-shaped hoop (2), for preventing C-shaped hoop (2) from sliding along axial direction on the outer surface of cast-in-place pile (1). Connecting rib plate (3) is integrally formed with C-shaped hoop (2), connecting rib plate (3) and guide slot (4) are connected by welding between reinforcing mesh (5) between piles. The bolt assembly (6) includes bolt, nut and elastic washer, the elastic washer is used to compensate the gap during bolt tightening process. A plurality of through holes are formed in the connecting rib plate (3), the plurality of through holes are uniformly distributed along the length direction of the connecting rib plate (3), and the connecting rib plate (3) and the reinforcing mesh (5) between piles are connected by the through holes. The utility model provides a kind of pair of openable C-shaped hoop (2) including installation on cast-in-place pile (1), the inner wall of the C-shaped hoop (2) is arc-shaped and matches the outer arc surface of cast-in-place pile (1), one end of the C-shaped hoop (2) is hinged end (21), the hinged end (21) is used to realize the opening and closing of C-shaped hoop (2), the other end of the C-shaped hoop (2) is locking end (22), the locking end (22) is closed and fixed by bolt assembly (6) that C-shaped hoop (2) realizes on the outer arc surface of cast-in-place pile (1); S1, pile body pretreatment: first determine the support area between adjacent cast-in-place piles (1), then clean the exposed surface of the cast-in-place pile in the area until the fresh concrete base surface is exposed, and finally polish the base surface to control the surface roughness at Ra≤25 μm; S2, hoop installation: open the half-hoop C-shaped hoop (2) from the outside of the foundation pit and set it on the preset position of the outer arc of the cast-in-place pile (1), detect the levelness of the C-shaped hoop (2) to ensure that the horizontal deviation is less than or equal to 3 mm, adjust it in place, then tighten the bolt assembly (6) of the locking end (22) to make the inner wall of the C-shaped hoop (2) tightly fit the outer arc surface of the cast-in-place pile (1), and the limiting flange (23) clamps the surface of the cast-in-place pile (1); S3, welding connection: align the transverse reinforcement of the reinforcing mesh (5) between piles with the connecting rib plate (3) on the outer side of the C-shaped hoop (2) and perform full welding connection, insert the longitudinal reinforcement between piles into the guide slot (4) on the outer side of the C-shaped hoop (2), and weld the longitudinal reinforcement to the slot wall of the guide slot (4) to ensure that the reinforcing mesh (5) and the C-shaped hoop (2) form an integral force frame; S4, spray concrete reinforcement: perform spray concrete operation on the outer side of the installed C-shaped hoop (2) and reinforcing mesh (5), and perform layer-by-layer construction during the spray process, and ensure that the concrete covers the C-shaped hoop (2) and the connecting rib plate (3) during spraying to form a continuous support surface; S5, maintenance and inspection: after the construction of the sprayed concrete, the sprayed concrete is maintained by water spraying to ensure that the strength of the concrete meets the standard; after the maintenance, the thickness of the sprayed layer is detected, the thickness deviation needs to be ≤5mm, the bonding strength of the sprayed layer and the pile body (1) and the hoop (2) is detected, the bonding strength needs to be ≥1.5MPa, and the parts that do not meet the standard are supplemented with sprayed concrete or re-welded and reinforced.

7. The pile reinforcement method according to claim 6, wherein Before the welding operation in step S3, the welding area of the connecting rib plate (3) and the steel bar net (5) is treated by rust removal, the surface oxide is removed by sand blasting rust removal, and the rust removal level reaches Sa2.5 level.

8. The pile reinforcement method according to claim 6, wherein In step S4, the mixing ratio of the sprayed concrete is cement:sand:stone:water=1:2.2:3.5:0.

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9. The pile reinforcement method according to claim 6, wherein In step S4, the strength grade of the sprayed concrete is not less than C25, the maximum particle size of the aggregate is ≤15mm, the spraying pressure is controlled at 0.2~0.4MPa, and the spraying thickness of each layer is 30~50mm.

10. The pile reinforcement method according to claim 6, wherein In step S5, appearance inspection is also included, which needs to observe whether there are cracks, hollowing, and exposed reinforcement defects on the surface of the sprayed concrete layer. If there are cracks with a width of ≥0.2mm, epoxy resin grout is used for repair. If there are hollowing areas with an area of ≥0.1m 2 , the hollowing part is chiseled out and the concrete is sprayed again.

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